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Thivolle A, Mehnert AK, Tihon E, McLaughlin E, Dujeancourt-Henry A, Glover L. DNA double strand break position leads to distinct gene expression changes and regulates VSG switching pathway choice. PLoS Pathog 2021; 17:e1010038. [PMID: 34767618 PMCID: PMC8612549 DOI: 10.1371/journal.ppat.1010038] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 11/24/2021] [Accepted: 10/14/2021] [Indexed: 12/11/2022] Open
Abstract
Antigenic variation is an immune evasion strategy used by Trypanosoma brucei that results in the periodic exchange of the surface protein coat. This process is facilitated by the movement of variant surface glycoprotein genes in or out of a specialized locus known as bloodstream form expression site by homologous recombination, facilitated by blocks of repetitive sequence known as the 70-bp repeats, that provide homology for gene conversion events. DNA double strand breaks are potent drivers of antigenic variation, however where these breaks must fall to elicit a switch is not well understood. To understand how the position of a break influences antigenic variation we established a series of cell lines to study the effect of an I-SceI meganuclease break in the active expression site. We found that a DNA break within repetitive regions is not productive for VSG switching, and show that the break position leads to a distinct gene expression profile and DNA repair response which dictates how antigenic variation proceeds in African trypanosomes. Crucial to triggering antigenic variation is the formation of DNA double strand breaks (DSB). These lesions have been shown to be potent drivers of variant surface glycoprotein (VSG) switching, albeit highly toxic. Trypanosomes immune evasion strategy relies on their ability to rapidly exchange the singly expressed VSG for one that is antigenically distinct. It has been previously shown that the subtelomeric ends, here the locus from which the VSG is expressed, accumulate DSBs. Using the I-SceI meganuclease system we established a series of cell lines to assess how the position of a DSB influences antigenic variation and the cellular response to a break. We show that a DSB in highly repetitive regions are poor triggers for antigenic variation. Contrastingly, a DSB that does lead to VSG switching via recombination results in the upregulation of DNA damage linked genes. Our results provide new insights into how the position of a DSB influences repair pathway choice and the subsequent gene expression changes. We propose that where repair is not dominated by recombination, but rather by an error prone mechanism, silent BES promoters are partially activated to facilitate rapid transcriptional switching should repair be deleterious to the cell.
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Affiliation(s)
- Alix Thivolle
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
| | - Ann-Kathrin Mehnert
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
| | - Eliane Tihon
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
| | - Emilia McLaughlin
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
- Université de Paris, Sorbonne Paris Cité, Paris, France
| | - Annick Dujeancourt-Henry
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
| | - Lucy Glover
- Institut Pasteur, Université de Paris, Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Paris, France
- * E-mail:
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2
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Silva Pereira S, de Almeida Castilho Neto KJG, Duffy CW, Richards P, Noyes H, Ogugo M, Rogério André M, Bengaly Z, Kemp S, Teixeira MMG, Machado RZ, Jackson AP. Variant antigen diversity in Trypanosoma vivax is not driven by recombination. Nat Commun 2020; 11:844. [PMID: 32051413 PMCID: PMC7015903 DOI: 10.1038/s41467-020-14575-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 01/18/2020] [Indexed: 11/09/2022] Open
Abstract
African trypanosomes (Trypanosoma) are vector-borne haemoparasites that survive in the vertebrate bloodstream through antigenic variation of their Variant Surface Glycoprotein (VSG). Recombination, or rather segmented gene conversion, is fundamental in Trypanosoma brucei for both VSG gene switching and for generating antigenic diversity during infections. Trypanosoma vivax is a related, livestock pathogen whose VSG lack structures that facilitate gene conversion in T. brucei and mechanisms underlying its antigenic diversity are poorly understood. Here we show that species-wide VSG repertoire is broadly conserved across diverse T. vivax clinical strains and has limited antigenic repertoire. We use variant antigen profiling, coalescent approaches and experimental infections to show that recombination plays little role in diversifying T. vivax VSG sequences. These results have immediate consequences for both the current mechanistic model of antigenic variation in African trypanosomes and species differences in virulence and transmission, requiring reconsideration of the wider epidemiology of animal African trypanosomiasis.
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Affiliation(s)
- Sara Silva Pereira
- Department of Infection Biology, Institute of Infection and Global Health, University of Liverpool, 146 Brownlow Hill, Liverpool, L3 5RF, UK
| | - Kayo J G de Almeida Castilho Neto
- Department of Veterinary Pathology, Faculty of Agrarian and Veterinary Sciences, São Paulo State University (UNESP), Jaboticabal, SP, Brazil
| | - Craig W Duffy
- Department of Infection Biology, Institute of Infection and Global Health, University of Liverpool, 146 Brownlow Hill, Liverpool, L3 5RF, UK
| | - Peter Richards
- Department of Infection Biology, Institute of Infection and Global Health, University of Liverpool, 146 Brownlow Hill, Liverpool, L3 5RF, UK
| | - Harry Noyes
- Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK
| | - Moses Ogugo
- Livestock Genetic Programme, International Livestock Research Institute, 30709 Naivasha Road, Nairobi, Kenya
| | - Marcos Rogério André
- Department of Veterinary Pathology, Faculty of Agrarian and Veterinary Sciences, São Paulo State University (UNESP), Jaboticabal, SP, Brazil
| | - Zakaria Bengaly
- International Research Centre for Livestock Development in the Sub-humid Zone (CIRDES), No. 559, rue 5-31 angle, Avenue du Gouverneur Louveau, Bobo-Dioulasso, Burkina Faso
| | - Steve Kemp
- Livestock Genetic Programme, International Livestock Research Institute, 30709 Naivasha Road, Nairobi, Kenya
| | - Marta M G Teixeira
- Department of Parasitology, Institute of Biomedical Sciences, University of Sao Paulo, Avenue Professor Lineu Prestes, 1374 Cidade Universitaria, Sao Paulo, SP, 05508-000, Brazil
| | - Rosangela Z Machado
- Department of Veterinary Pathology, Faculty of Agrarian and Veterinary Sciences, São Paulo State University (UNESP), Jaboticabal, SP, Brazil
| | - Andrew P Jackson
- Department of Infection Biology, Institute of Infection and Global Health, University of Liverpool, 146 Brownlow Hill, Liverpool, L3 5RF, UK.
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3
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Faria J, Glover L, Hutchinson S, Boehm C, Field MC, Horn D. Monoallelic expression and epigenetic inheritance sustained by a Trypanosoma brucei variant surface glycoprotein exclusion complex. Nat Commun 2019; 10:3023. [PMID: 31289266 PMCID: PMC6617441 DOI: 10.1038/s41467-019-10823-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 06/04/2019] [Indexed: 02/06/2023] Open
Abstract
The largest gene families in eukaryotes are subject to allelic exclusion, but mechanisms underpinning single allele selection and inheritance remain unclear. Here, we describe a protein complex sustaining variant surface glycoprotein (VSG) allelic exclusion and antigenic variation in Trypanosoma brucei parasites. The VSG-exclusion-1 (VEX1) protein binds both telomeric VSG-associated chromatin and VEX2, an ortholog of nonsense-mediated-decay helicase, UPF1. VEX1 and VEX2 assemble in an RNA polymerase-I transcription-dependent manner and sustain the active, subtelomeric VSG-associated transcription compartment. VSG transcripts and VSG coats become highly heterogeneous when VEX proteins are depleted. Further, the DNA replication-associated chromatin assembly factor, CAF-1, binds to and specifically maintains VEX1 compartmentalisation following DNA replication. Thus, the VEX-complex controls VSG-exclusion, while CAF-1 sustains VEX-complex inheritance in association with the active-VSG. Notably, the VEX2-orthologue and CAF-1 in mammals are also implicated in exclusion and inheritance functions. In trypanosomes, these factors sustain a highly effective and paradigmatic immune evasion strategy.
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Affiliation(s)
- Joana Faria
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
| | - Lucy Glover
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- Trypanosome Molecular Biology, Department of Parasites and Insect Vectors, Institut Pasteur, 25-28 Rue du Docteur Roux, 75015, Paris, France
| | - Sebastian Hutchinson
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- Trypanosome Cell Biology Unit, INSERM U1201, Department of Parasites and Insect Vectors, Institut Pasteur, 25-28 Rue du Docteur Roux, 75015, Paris, France
| | - Cordula Boehm
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
| | - Mark C Field
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
| | - David Horn
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK.
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Jayaraman S, Harris C, Paxton E, Donachie AM, Vaikkinen H, McCulloch R, Hall JPJ, Kenny J, Lenzi L, Hertz-Fowler C, Cobbold C, Reeve R, Michoel T, Morrison LJ. Application of long read sequencing to determine expressed antigen diversity in Trypanosoma brucei infections. PLoS Negl Trop Dis 2019; 13:e0007262. [PMID: 30943202 PMCID: PMC6464242 DOI: 10.1371/journal.pntd.0007262] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Revised: 04/15/2019] [Accepted: 02/25/2019] [Indexed: 12/31/2022] Open
Abstract
Antigenic variation is employed by many pathogens to evade the host immune response, and Trypanosoma brucei has evolved a complex system to achieve this phenotype, involving sequential use of variant surface glycoprotein (VSG) genes encoded from a large repertoire of ~2,000 genes. T. brucei express multiple, sometimes closely related, VSGs in a population at any one time, and the ability to resolve and analyse this diversity has been limited. We applied long read sequencing (PacBio) to VSG amplicons generated from blood extracted from batches of mice sacrificed at time points (days 3, 6, 10 and 12) post-infection with T. brucei TREU927. The data showed that long read sequencing is reliable for resolving variant differences between VSGs, and demonstrated that there is significant expressed diversity (449 VSGs detected across 20 mice) and across the timeframe of study there was a clear semi-reproducible pattern of expressed diversity (median of 27 VSGs per sample at day 3 post infection (p.i.), 82 VSGs at day 6 p.i., 187 VSGs at day 10 p.i. and 132 VSGs by day 12 p.i.). There was also consistent detection of one VSG dominating expression across replicates at days 3 and 6, and emergence of a second dominant VSG across replicates by day 12. The innovative application of ecological diversity analysis to VSG reads enabled characterisation of hierarchical VSG expression in the dataset, and resulted in a novel method for analysing such patterns of variation. Additionally, the long read approach allowed detection of mosaic VSG expression from very few reads–the earliest in infection that such events have been detected. Therefore, our results indicate that long read analysis is a reliable tool for resolving diverse gene expression profiles, and provides novel insights into the complexity and nature of VSG expression in trypanosomes, revealing significantly higher diversity than previously shown and the ability to identify mosaic gene formation early during the infection process. Antigenic variation is a system whereby pathogens switch identity of a protein that is exposed to the host adaptive immune response as a way of remaining one step ahead and avoiding being detected. African trypanosomes have evolved a spectacularly elaborate system of antigenic variation, with variants being used from a library of ~2,000 genes. Our ability to understand how this rich repository is used has been hampered by the resolution of available technologies to discriminate between what can be closely related gene variants. We have applied a long read sequencing technology, which generates sequence information for the whole length of the antigen gene variants, thereby avoiding having to try and piece together antigen sequences from lots of small fragments, the pitfall of standard sequencing. Applying this technology to material taken at specific time points from batches of mice infected with trypanosomes reveals that the diversity of variants is much higher than previously suspected, and that there is a clear semi-predictable pattern in the gene expression. Additionally, using this technology we have been able to detect the presence of ‘mosaic’ genes, which are created by stitching together fragments from several donor genes in the library, much earlier in infection than has been shown previously. Therefore, we shed new light on the complexity of antigenic variation and show that long read sequencing will be a very useful tool in analysing and understanding the expression patterns of closely related genes, and how pathogens use them to cause persistent infections and disease.
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Affiliation(s)
- Siddharth Jayaraman
- Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Claire Harris
- Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Edith Paxton
- Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Anne-Marie Donachie
- Wellcome Centre for Integrative Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Heli Vaikkinen
- Wellcome Centre for Integrative Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Richard McCulloch
- Wellcome Centre for Integrative Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - James P. J. Hall
- Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - John Kenny
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Luca Lenzi
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Christiane Hertz-Fowler
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Christina Cobbold
- Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
- School of Mathematics and Statistics, University of Glasgow, Glasgow, United Kingdom
| | - Richard Reeve
- Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Tom Michoel
- Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Liam J. Morrison
- Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
- * E-mail:
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5
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Briggs E, Crouch K, Lemgruber L, Lapsley C, McCulloch R. Ribonuclease H1-targeted R-loops in surface antigen gene expression sites can direct trypanosome immune evasion. PLoS Genet 2018; 14:e1007729. [PMID: 30543624 PMCID: PMC6292569 DOI: 10.1371/journal.pgen.1007729] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 10/01/2018] [Indexed: 11/19/2022] Open
Abstract
Switching of the Variant Surface Glycoprotein (VSG) in Trypanosoma brucei provides a crucial host immune evasion strategy that is catalysed both by transcription and recombination reactions, each operating within specialised telomeric VSG expression sites (ES). VSG switching is likely triggered by events focused on the single actively transcribed ES, from a repertoire of around 15, but the nature of such events is unclear. Here we show that RNA-DNA hybrids, called R-loops, form preferentially within sequences termed the 70 bp repeats in the actively transcribed ES, but spread throughout the active and inactive ES, in the absence of RNase H1, which degrades R-loops. Loss of RNase H1 also leads to increased levels of VSG coat switching and replication-associated genome damage, some of which accumulates within the active ES. This work indicates VSG ES architecture elicits R-loop formation, and that these RNA-DNA hybrids connect T. brucei immune evasion by transcription and recombination.
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Affiliation(s)
- Emma Briggs
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Glasgow, United Kingdom
| | - Kathryn Crouch
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Glasgow, United Kingdom
| | - Leandro Lemgruber
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Glasgow, United Kingdom
| | - Craig Lapsley
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Glasgow, United Kingdom
| | - Richard McCulloch
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, College of Medical, Veterinary and Life Sciences, Institute of Infection, Immunity and Inflammation, Glasgow, United Kingdom
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da Silva MS, Hovel-Miner GA, Briggs EM, Elias MC, McCulloch R. Evaluation of mechanisms that may generate DNA lesions triggering antigenic variation in African trypanosomes. PLoS Pathog 2018; 14:e1007321. [PMID: 30440029 PMCID: PMC6237402 DOI: 10.1371/journal.ppat.1007321] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Antigenic variation by variant surface glycoprotein (VSG) coat switching in African trypanosomes is one of the most elaborate immune evasion strategies found among pathogens. Changes in the identity of the transcribed VSG gene, which is always flanked by 70-bp and telomeric repeats, can be achieved either by transcriptional or DNA recombination mechanisms. The major route of VSG switching is DNA recombination, which occurs in the bloodstream VSG expression site (ES), a multigenic site transcribed by RNA polymerase I. Recombinogenic VSG switching is frequently catalyzed by homologous recombination (HR), a reaction normally triggered by DNA breaks. However, a clear understanding of how such breaks arise-including whether there is a dedicated and ES-focused mechanism-is lacking. Here, we synthesize data emerging from recent studies that have proposed a range of mechanisms that could generate these breaks: action of a nuclease or nucleases; repetitive DNA, most notably the 70-bp repeats, providing an intra-ES source of instability; DNA breaks derived from the VSG-adjacent telomere; DNA breaks arising from high transcription levels at the active ES; and DNA lesions arising from replication-transcription conflicts in the ES. We discuss the evidence that underpins these switch-initiation models and consider what features and mechanisms might be shared or might allow the models to be tested further. Evaluation of all these models highlights that we still have much to learn about the earliest acting step in VSG switching, which may have the greatest potential for therapeutic intervention in order to undermine the key reaction used by trypanosomes for their survival and propagation in the mammalian host.
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Affiliation(s)
- Marcelo Santos da Silva
- Laboratório Especial de Ciclo Celular, Center of Toxins, Immune Response and Cell Signaling (CeTICS), Instituto Butantan, São Paulo, Brazil
- The Wellcome Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Galadriel A. Hovel-Miner
- The George Washington University, Department of Microbiology Immunology, and Tropical Medicine, Washington, DC, United States of America
| | - Emma M. Briggs
- The Wellcome Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
| | - Maria Carolina Elias
- Laboratório Especial de Ciclo Celular, Center of Toxins, Immune Response and Cell Signaling (CeTICS), Instituto Butantan, São Paulo, Brazil
| | - Richard McCulloch
- The Wellcome Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
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Mizushima D, Amgalanbaatar T, Davaasuren B, Molefe NI, Battur B, Battsetseg B, Inoue N, Yokoyama N, Suganuma K. The utility of an rTeGM6-4r-based immunochromatographic test for the serological diagnosis of non-tsetse-transmitted equine trypanosomosis in rural areas of Mongolia. Parasitol Res 2018; 117:2913-2919. [PMID: 29943319 DOI: 10.1007/s00436-018-5982-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 06/19/2018] [Indexed: 11/26/2022]
Abstract
Our previous studies report epidemics of non-tsetse-transmitted equine trypanosomosis in Mongolia. However, the current status of non-tsetse-transmitted equine trypanosomosis endemicity remains to be clarified in some parts of Mongolia. We previously reported the potential application of rTeGM6-4r-based diagnostic tools, an rTeGM6-4r-based immunochromatographic test (ICT) and an enzyme-linked immunosorbent assay (ELISA), in the serological surveillance of equine trypanosomosis in Mongolia. In the present study, the utility of the rTeGM6-4r-based ICT was validated. The rTeGM6-4r-based ICT accurately diagnosed positive reference sera that had been prepared from dourine horses in Mongolia, similarly to the rTeGM6-4r-based ELISA. The diagnostic performance of the rTeGM6-4r-based ICT was maintained when the strips were preserved for at least 2 months under dry conditions. The ICT detected 42 positive serum samples from a total of 1701 equine sera that had been collected from all 21 provinces of Mongolia. The κ-value, sensitivity and specificity of rTeGM6-4r-based ICT were 0.58, 50.0% (95% CI, 37.7-62.3%) and 99.3% (95% CI, 98.7-99.6%), respectively, in comparison to the rTeGM6-4r-based ELISA. Our field-friendly rTeGM6-4r-based ICT was found to be useful for the serological diagnosis of non-tsetse-transmitted equine trypanosomosis in rural areas of Mongolia.
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Affiliation(s)
- Daiki Mizushima
- National Research Center for Protozoan Diseases, OIE Reference Laboratory for Surra, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan
| | - Tovuu Amgalanbaatar
- Institute of Veterinary Medicine, Laboratory of Molecular Genetics, Mongolian University of Life Sciences, Zaisan, Ulaanbaatar, 17024, Mongolia
| | - Batdorj Davaasuren
- National Research Center for Protozoan Diseases, OIE Reference Laboratory for Surra, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan
- Institute of Veterinary Medicine, Laboratory of Molecular Genetics, Mongolian University of Life Sciences, Zaisan, Ulaanbaatar, 17024, Mongolia
| | - Nthatisi Innocentia Molefe
- National Research Center for Protozoan Diseases, OIE Reference Laboratory for Surra, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan
| | - Banzragch Battur
- Institute of Veterinary Medicine, Laboratory of Molecular Genetics, Mongolian University of Life Sciences, Zaisan, Ulaanbaatar, 17024, Mongolia
| | - Badgar Battsetseg
- Institute of Veterinary Medicine, Laboratory of Molecular Genetics, Mongolian University of Life Sciences, Zaisan, Ulaanbaatar, 17024, Mongolia
| | - Noboru Inoue
- Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan
| | - Naoaki Yokoyama
- National Research Center for Protozoan Diseases, OIE Reference Laboratory for Surra, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan
| | - Keisuke Suganuma
- National Research Center for Protozoan Diseases, OIE Reference Laboratory for Surra, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan.
- Research Center for Global Agromedicine, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido, 080-8555, Japan.
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8
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Pinger J, Chowdhury S, Papavasiliou FN. Variant surface glycoprotein density defines an immune evasion threshold for African trypanosomes undergoing antigenic variation. Nat Commun 2017; 8:828. [PMID: 29018220 PMCID: PMC5635023 DOI: 10.1038/s41467-017-00959-w] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2017] [Accepted: 08/02/2017] [Indexed: 11/15/2022] Open
Abstract
Trypanosoma brucei is a protozoan parasite that evades its host's adaptive immune response by repeatedly replacing its dense variant surface glycoprotein (VSG) coat from its large genomic VSG repertoire. While the mechanisms regulating VSG gene expression and diversification have been examined extensively, the dynamics of VSG coat replacement at the protein level, and the impact of this process on successful immune evasion, remain unclear. Here we evaluate the rate of VSG replacement at the trypanosome surface following a genetic VSG switch, and show that full coat replacement requires several days to complete. Using in vivo infection assays, we demonstrate that parasites undergoing coat replacement are only vulnerable to clearance via early IgM antibodies for a limited time. Finally, we show that IgM loses its ability to mediate trypanosome clearance at unexpectedly early stages of coat replacement based on a critical density threshold of its cognate VSGs on the parasite surface. Trypanosoma brucei evades the host immune system through replacement of a variant surface glycoprotein (VSG) coat. Here, the authors show that VSG replacement takes several days to complete, and the parasite is vulnerable to the host immune system for a short period of time during the process.
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Affiliation(s)
- Jason Pinger
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA.
- The David Rockefeller Graduate School, 1230 York Avenue, New York, NY, 10065, USA.
| | - Shanin Chowdhury
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA
| | - F Nina Papavasiliou
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA.
- Division of Immune Diversity, German Cancer Research Center, Im Neuenheimer Feld 280, Heidelberg, 69120, Germany.
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Zimmermann H, Subota I, Batram C, Kramer S, Janzen CJ, Jones NG, Engstler M. A quorum sensing-independent path to stumpy development in Trypanosoma brucei. PLoS Pathog 2017; 13:e1006324. [PMID: 28394929 PMCID: PMC5398725 DOI: 10.1371/journal.ppat.1006324] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 04/20/2017] [Accepted: 03/29/2017] [Indexed: 11/19/2022] Open
Abstract
For persistent infections of the mammalian host, African trypanosomes limit their population size by quorum sensing of the parasite-excreted stumpy induction factor (SIF), which induces development to the tsetse-infective stumpy stage. We found that besides this cell density-dependent mechanism, there exists a second path to the stumpy stage that is linked to antigenic variation, the main instrument of parasite virulence. The expression of a second variant surface glycoprotein (VSG) leads to transcriptional attenuation of the VSG expression site (ES) and immediate development to tsetse fly infective stumpy parasites. This path is independent of SIF and solely controlled by the transcriptional status of the ES. In pleomorphic trypanosomes varying degrees of ES-attenuation result in phenotypic plasticity. While full ES-attenuation causes irreversible stumpy development, milder attenuation may open a time window for rescuing an unsuccessful antigenic switch, a scenario that so far has not been considered as important for parasite survival.
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Affiliation(s)
- Henriette Zimmermann
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Ines Subota
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Christopher Batram
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Susanne Kramer
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Christian J. Janzen
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Nicola G. Jones
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Markus Engstler
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
- * E-mail:
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Cheung JLY, Wand NV, Ooi CP, Ridewood S, Wheeler RJ, Rudenko G. Blocking Synthesis of the Variant Surface Glycoprotein Coat in Trypanosoma brucei Leads to an Increase in Macrophage Phagocytosis Due to Reduced Clearance of Surface Coat Antibodies. PLoS Pathog 2016; 12:e1006023. [PMID: 27893860 PMCID: PMC5125712 DOI: 10.1371/journal.ppat.1006023] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 10/25/2016] [Indexed: 11/19/2022] Open
Abstract
The extracellular bloodstream form parasite Trypanosoma brucei is supremely adapted to escape the host innate and adaptive immune system. Evasion is mediated through an antigenically variable Variant Surface Glycoprotein (VSG) coat, which is recycled at extraordinarily high rates. Blocking VSG synthesis triggers a precytokinesis arrest where stalled cells persist for days in vitro with superficially intact VSG coats, but are rapidly cleared within hours in mice. We therefore investigated the role of VSG synthesis in trypanosome phagocytosis by activated mouse macrophages. T. brucei normally effectively evades macrophages, and induction of VSG RNAi resulted in little change in phagocytosis of the arrested cells. Halting VSG synthesis resulted in stalled cells which swam directionally rather than tumbling, with a significant increase in swim velocity. This is possibly a consequence of increased rigidity of the cells due to a restricted surface coat in the absence of VSG synthesis. However if VSG RNAi was induced in the presence of anti-VSG221 antibodies, phagocytosis increased significantly. Blocking VSG synthesis resulted in reduced clearance of anti-VSG antibodies from the trypanosome surface, possibly as a consequence of the changed motility. This was particularly marked in cells in the G2/ M cell cycle stage, where the half-life of anti-VSG antibody increased from 39.3 ± 4.2 seconds to 99.2 ± 15.9 seconds after induction of VSG RNAi. The rates of internalisation of bulk surface VSG, or endocytic markers like transferrin, tomato lectin or dextran were not significantly affected by the VSG synthesis block. Efficient elimination of anti-VSG-antibody complexes from the trypanosome cell surface is therefore essential for trypanosome evasion of macrophages. These experiments highlight the essentiality of high rates of VSG recycling for the rapid removal of host opsonins from the parasite surface, and identify this process as a key parasite virulence factor during a chronic infection.
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Affiliation(s)
- Jackie L. Y. Cheung
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Nadina V. Wand
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Cher-Pheng Ooi
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Sophie Ridewood
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Richard J. Wheeler
- Department of Pathology, Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Gloria Rudenko
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
- * E-mail:
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Affiliation(s)
- Monica R. Mugnier
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
| | - C. Erec Stebbins
- The Rockefeller University, Laboratory of Structural Microbiology, New York, New York, United States of America
| | - F. Nina Papavasiliou
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
- * E-mail:
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12
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Clemente TM, Cortez C, Novaes ADS, Yoshida N. Surface Molecules Released by Trypanosoma cruzi Metacyclic Forms Downregulate Host Cell Invasion. PLoS Negl Trop Dis 2016; 10:e0004883. [PMID: 27483135 PMCID: PMC4970754 DOI: 10.1371/journal.pntd.0004883] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 07/07/2016] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The question whether metacylic trypomastigote (MT) forms of different T. cruzi strains differentially release surface molecules, and how they affect host cell invasion, remains to be fully clarified. We addressed that question using T. cruzi strains that differ widely in the ability to invade cells. METHODOLOGY/PRINCIPAL FINDINGS Metacyclic forms were incubated at 37°C for 1 h in complete D10 medium or in nutrient-deprived PBS containing Ca2+ and Mg2+ (PBS++). The conditioned medium (CM), collected after parasite centrifugation, was used for cell invasion assays and Western blot analysis, using monoclonal antibodies directed to gp82 and gp90, the MT surface molecules that promote and negatively regulate invasion, respectively. CM of poorly invasive G strain (G-CM) contained high amounts of gp90 and gp82, either in vesicles or as soluble molecules. CM of highly invasive CL strain (CL-CM) contained gp90 and gp82 at very low levels. HeLa cells were incubated for 1 h with CL strain MT in D10, in absence or in the presence of G-CM or CL-CM. Parasite invasion was significantly inhibited by G-CM, but not by CL-CM. As G strain MT invasion rate in D10 is very low, assays with this strain were performed in PBS++, which induces invasion-promoting lysosome-spreading. G-CM, but not CL-CM, significantly inhibited G strain internalization, effect that was counteracted by preincubating G-CM with an anti-gp90 monoclonal antibody or anti-gp82 polyclonal antibody that do not recognize live MT. G strain CM generated in PBS++ contained much lower amounts of gp90 and gp82 as compared to CM produced in D10, and exhibited lower inhibitory effect on host cell invasion. CONCLUSION/SIGNIFICANCE Our data suggest that the surface molecules spontaneously released by MT impair parasite-host cell interaction, gp82 presumably competing with the molecule expressed on MT surface for the host cell receptor, and gp90 further contributing to down modulate invasion.
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Affiliation(s)
- Tatiana Mordente Clemente
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, Brasil
| | - Cristian Cortez
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, Brasil
| | | | - Nobuko Yoshida
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, Brasil
- * E-mail:
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13
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Hovel-Miner G, Mugnier MR, Goldwater B, Cross GAM, Papavasiliou FN. A Conserved DNA Repeat Promotes Selection of a Diverse Repertoire of Trypanosoma brucei Surface Antigens from the Genomic Archive. PLoS Genet 2016; 12:e1005994. [PMID: 27149665 PMCID: PMC4858185 DOI: 10.1371/journal.pgen.1005994] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 03/28/2016] [Indexed: 12/02/2022] Open
Abstract
African trypanosomes are mammalian pathogens that must regularly change their protein coat to survive in the host bloodstream. Chronic trypanosome infections are potentiated by their ability to access a deep genomic repertoire of Variant Surface Glycoprotein (VSG) genes and switch from the expression of one VSG to another. Switching VSG expression is largely based in DNA recombination events that result in chromosome translocations between an acceptor site, which houses the actively transcribed VSG, and a donor gene, drawn from an archive of more than 2,000 silent VSGs. One element implicated in these duplicative gene conversion events is a DNA repeat of approximately 70 bp that is found in long regions within each BES and short iterations proximal to VSGs within the silent archive. Early observations showing that 70-bp repeats can be recombination boundaries during VSG switching led to the prediction that VSG-proximal 70-bp repeats provide recombinatorial homology. Yet, this long held assumption had not been tested and no specific function for the conserved 70-bp repeats had been demonstrated. In the present study, the 70-bp repeats were genetically manipulated under conditions that induce gene conversion. In this manner, we demonstrated that 70-bp repeats promote access to archival VSGs. Synthetic repeat DNA sequences were then employed to identify the length, sequence, and directionality of repeat regions required for this activity. In addition, manipulation of the 70-bp repeats allowed us to observe a link between VSG switching and the cell cycle that had not been appreciated. Together these data provide definitive support for the long-standing hypothesis that 70-bp repeats provide recombinatorial homology during switching. Yet, the fact that silent archival VSGs are selected under these conditions suggests the 70-bp repeats also direct DNA pairing and recombination machinery away from the closest homologs (silent BESs) and toward the rest of the archive. Chromosomal translocations can fuel genetic change or cause catastrophic genomic damage. African trypanosomes, exemplified by Trypanosoma brucei sub-species, are unicellular parasites that can chronically infect their human and livestock hosts by using a strategy of antigenic variation by which they repeatedly change their protein coats. Switching the surface coat requires the accurate selection and translocation of a single silent coat gene, from a large genomic archive, into an actively transcribed site. How the coat genes from within this deep archive are selected and activated was unproven. Here we show that a specific repetitive DNA sequence is required to access coat genes from diverse sites within the genome. The likely outcome of restricting this process of coat gene selection in natural infections would be a reduction in the chronic nature of African trypanosomiasis.
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Affiliation(s)
- Galadriel Hovel-Miner
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
- The George Washington University, Department of Microbiology Immunology, and Tropical Medicine, Washington, DC, United States of America
- * E-mail:
| | - Monica R. Mugnier
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
| | - Benjamin Goldwater
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
| | - George A. M. Cross
- The Rockefeller University, Laboratory of Molecular Parasitology, New York, New York, United States of America
| | - F. Nina Papavasiliou
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
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14
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Abstract
Variations on the statement “the variant surface glycoprotein (VSG) coat that covers the external face of the mammalian bloodstream form of Trypanosoma brucei acts a physical barrier” appear regularly in research articles and reviews. The concept of the impenetrable VSG coat is an attractive one, as it provides a clear model for understanding how a trypanosome population persists; each successive VSG protects the plasma membrane and is immunologically distinct from previous VSGs. What is the evidence that the VSG coat is an impenetrable barrier, and how do antibodies and other extracellular proteins interact with it? In this review, the nature of the extracellular surface of the bloodstream form trypanosome is described, and past experiments that investigated binding of antibodies and lectins to trypanosomes are analysed using knowledge of VSG sequence and structure that was unavailable when the experiments were performed. Epitopes for some VSG monoclonal antibodies are mapped as far as possible from previous experimental data, onto models of VSG structures. The binding of lectins to some, but not to other, VSGs is revisited with more recent knowledge of the location and nature of N-linked oligosaccharides. The conclusions are: (i) Much of the variation observed in earlier experiments can be explained by the identity of the individual VSGs. (ii) Much of an individual VSG is accessible to antibodies, and the barrier that prevents access to the cell surface is probably at the base of the VSG N-terminal domain, approximately 5 nm from the plasma membrane. This second conclusion highlights a gap in our understanding of how the VSG coat works, as several plasma membrane proteins with large extracellular domains are very unlikely to be hidden from host antibodies by VSG. African trypanosomes have evolved two key strategies to prevent killing by the host immune response and, thus, maintain a long-term infection in a mammal. Both are based on a densely packed coat of a single protein, the variant surface glycoprotein (VSG), which covers the entire extracellular surface of the cell. The first strategy is antigenic variation, through which individual cells switch the identity of the expressed VSG at a low frequency and are selected by the host immune response. If the VSG is novel, the trypanosome proliferates, maintaining the infection; if it doesn't switch, or if the new VSG is not novel, it will be killed. In the second strategy, the VSG acts as a protective barrier, shielding the cell from innate and adaptive immune factors until there is an overwhelming titre of antibodies recognising the expressed VSG. In this review, the VSG coat is modelled, and past experiments that investigated how it protected the trypanosome are revisited using current knowledge of VSG sequence and structure. The conclusions are: (i) the identity of the individual VSGs explains early experimental variation; (ii) most of the VSG molecule is accessible to antibodies. This second conclusion highlights a gap in our understanding of how the VSG coat works, as several plasma membrane proteins with large extracellular domains are very unlikely to be hidden from host antibodies by VSG.
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Affiliation(s)
- Angela Schwede
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | | | - Paula MacGregor
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
- * E-mail:
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15
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Hovel-Miner G, Mugnier M, Papavasiliou FN, Pinger J, Schulz D. A Host-Pathogen Interaction Reduced to First Principles: Antigenic Variation in T. brucei. Results Probl Cell Differ 2015; 57:23-46. [PMID: 26537376 DOI: 10.1007/978-3-319-20819-0_2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Antigenic variation is a common microbial survival strategy, powered by diversity in expressed surface antigens across the pathogen population over the course of infection. Even so, among pathogens, African trypanosomes have the most comprehensive system of antigenic variation described. African trypanosomes (Trypanosoma brucei spp.) are unicellular parasites native to sub-Saharan Africa, and the causative agents of sleeping sickness in humans and of n'agana in livestock. They cycle between two habitats: a specific species of fly (Glossina spp. or, colloquially, the tsetse) and the bloodstream of their mammalian hosts, by assuming a succession of proliferative and quiescent developmental forms, which vary widely in cell architecture and function. Key to each of the developmental forms that arise during these transitions is the composition of the surface coat that covers the plasma membrane. The trypanosome surface coat is extremely dense, covered by millions of repeats of developmentally specified proteins: procyclin gene products cover the organism while it resides in the tsetse and metacyclic gene products cover it while in the fly salivary glands, ready to make the transition to the mammalian bloodstream. But by far the most interesting coat is the Variant Surface Glycoprotein (VSG) coat that covers the organism in its infectious form (during which it must survive free living in the mammalian bloodstream). This coat is highly antigenic and elicits robust VSG-specific antibodies that mediate efficient opsonization and complement mediated lysis of the parasites carrying the coat against which the response was made. Meanwhile, a small proportion of the parasite population switches coats, which stimulates a new antibody response to the prevalent (new) VSG species and this process repeats until immune system failure. The disease is fatal unless treated, and treatment at the later stages is extremely toxic. Because the organism is free living in the blood, the VSG:antibody surface represents the interface between pathogen and host, and defines the interaction of the parasite with the immune response. This interaction (cycles of VSG switching, antibody generation, and parasite deletion) results in stereotypical peaks and troughs of parasitemia that were first recognized more than 100 years ago. Essentially, the mechanism of antigenic variation in T. brucei results from a need, at the population level, to maintain an extensive repertoire, to evade the antibody response. In this chapter, we will examine what is currently known about the VSG repertoire, its depth, and the mechanisms that diversify it both at the molecular (DNA) and at the phenotypic (surface displayed) level, as well as how it could interact with antibodies raised specifically against it in the host.
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Affiliation(s)
- Galadriel Hovel-Miner
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - Monica Mugnier
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - F Nina Papavasiliou
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA.
| | - Jason Pinger
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - Danae Schulz
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
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Camargo R, Izquier A, Uzcanga GL, Perrone T, Acosta-Serrano A, Carrasquel L, Arias LP, Escalona JL, Cardozo V, Bubis J. Variant surface glycoproteins from Venezuelan trypanosome isolates are recognized by sera from animals infected with either Trypanosoma evansi or Trypanosoma vivax. Vet Parasitol 2014; 207:17-33. [PMID: 25468674 PMCID: PMC4303646 DOI: 10.1016/j.vetpar.2014.11.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 10/27/2014] [Accepted: 11/06/2014] [Indexed: 12/24/2022]
Abstract
Soluble forms of VSGs from seven Venezuelan animal trypanosomes were purified and characterized. All purified soluble VSGs exhibited cross-reactivity with Trypanosoma vivax. Anti-VSG antibodies behaved as markers of infection for non-tsetse transmitted trypanosomes. All purified soluble VSGs can be used as diagnostic reagents for bovine trypanosomosis.
Salivarian trypanosomes sequentially express only one variant surface glycoprotein (VSG) on their cell surface from a large repertoire of VSG genes. Seven cryopreserved animal trypanosome isolates known as TeAp-ElFrio01, TEVA1 (or TeAp-N/D1), TeGu-N/D1, TeAp-Mantecal01, TeGu-TerecayTrino, TeGu-Terecay03 and TeGu-Terecay323, which had been isolated from different hosts identified in several geographical areas of Venezuela were expanded using adult albino rats. Soluble forms of predominant VSGs expressed during the early infection stages were purified and corresponded to concanavalin A-binding proteins with molecular masses of 48–67 kDa by sodium dodecyl sulfate-polyacrylamide gel electropohoresis, and pI values between 6.1 and 7.5. The biochemical characterization of all purified soluble VSGs revealed that they were dimers in their native form and represented different gene products. Sequencing of some of these proteins yielded peptides homologous to VSGs from Trypanosoma (Trypanozoon) brucei and Trypanosoma (Trypanozoon) evansi and established that they most likely are mosaics generated by homologous recombination. Western blot analysis showed that all purified VSGs were cross-reacting antigens that were recognized by sera from animals infected with either T. evansi or Trypanosoma (Dutonella) vivax. The VSG glycosyl-phosphatidylinositol cross-reacting determinant epitope was only partially responsible for the cross-reactivity of the purified proteins, and antibodies appeared to recognize cross-reacting conformational epitopes from the various soluble VSGs. ELISA experiments were performed using infected bovine sera collected from cattle in a Venezuelan trypanosome-endemic area. In particular, soluble VSGs from two trypanosome isolates, TeGu-N/D1 and TeGu-TeracayTrino, were recognized by 93.38% and 73.55% of naturally T. vivax-infected bovine sera, respectively. However, approximately 70% of the sera samples did not recognize all seven purified proteins. Hence, the use of a combination of various VSGs for the diagnosis of animal trypanosomosis is recommended.
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Affiliation(s)
- Rocío Camargo
- Fundación Instituto de Estudios Avanzados IDEA, Caracas, Venezuela; Universidad Simón Bolívar, Departamento de Biología Celular, Caracas, Venezuela
| | - Adriana Izquier
- Universidad Simón Bolívar, Departamento de Biología Celular, Caracas, Venezuela; Universidad Central de Venezuela, Instituto de Ciencia y Tecnología de Alimentos, Caracas, Venezuela
| | | | - Trina Perrone
- Instituto Venezolano de Investigaciones Científicas IVIC, Centro de Biofísica y Bioquímica, Caracas, Venezuela
| | | | - Liomary Carrasquel
- Universidad Simón Bolívar, Departamento de Biología Celular, Caracas, Venezuela
| | - Laura P Arias
- Universidad Simón Bolívar, Departamento de Química, Caracas, Venezuela
| | - José L Escalona
- Universidad Simón Bolívar, Departamento de Química, Caracas, Venezuela
| | - Vanessa Cardozo
- Universidad Simón Bolívar, Departamento de Biología Celular, Caracas, Venezuela
| | - José Bubis
- Universidad Simón Bolívar, Departamento de Biología Celular, Caracas, Venezuela.
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Farrow AL, Rachakonda G, Gu L, Krendelchtchikova V, Nde PN, Pratap S, Lima MF, Villalta F, Matthews QL. Immunization with Hexon modified adenoviral vectors integrated with gp83 epitope provides protection against Trypanosoma cruzi infection. PLoS Negl Trop Dis 2014; 8:e3089. [PMID: 25144771 PMCID: PMC4140675 DOI: 10.1371/journal.pntd.0003089] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 06/30/2014] [Indexed: 11/23/2022] Open
Abstract
BACKGROUND Trypanosoma cruzi is the causative agent of Chagas disease. Chagas disease is an endemic infection that affects over 8 million people throughout Latin America and now has become a global challenge. The current pharmacological treatment of patients is unsuccessful in most cases, highly toxic, and no vaccines are available. The results of inadequate treatment could lead to heart failure resulting in death. Therefore, a vaccine that elicits neutralizing antibodies mediated by cell-mediated immune responses and protection against Chagas disease is necessary. METHODOLOGY/PRINCIPAL FINDINGS The "antigen capsid-incorporation" strategy is based upon the display of the T. cruzi epitope as an integral component of the adenovirus' capsid rather than an encoded transgene. This strategy is predicted to induce a robust humoral immune response to the presented antigen, similar to the response provoked by native Ad capsid proteins. The antigen chosen was T. cruzi gp83, a ligand that is used by T. cruzi to attach to host cells to initiate infection. The gp83 epitope, recognized by the neutralizing MAb 4A4, along with His6 were incorporated into the Ad serotype 5 (Ad5) vector to generate the vector Ad5-HVR1-gp83-18 (Ad5-gp83). This vector was evaluated by molecular and immunological analyses. Vectors were injected to elicit immune responses against gp83 in mouse models. Our findings indicate that mice immunized with the vector Ad5-gp83 and challenged with a lethal dose of T. cruzi trypomastigotes confer strong immunoprotection with significant reduction in parasitemia levels, increased survival rate and induction of neutralizing antibodies. CONCLUSIONS/SIGNIFICANCE This data demonstrates that immunization with adenovirus containing capsid-incorporated T. cruzi antigen elicits a significant anti-gp83-specific response in two different mouse models, and protection against T. cruzi infection by eliciting neutralizing antibodies mediated by cell-mediated immune responses, as evidenced by the production of several Ig isotypes. Taken together, these novel results show that the recombinant Ad5 presenting T. cruzi gp83 antigen is a useful candidate for the development of a vaccine against Chagas disease.
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Affiliation(s)
- Anitra L. Farrow
- Department of Medicine, Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Girish Rachakonda
- Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, United States of America
| | - Linlin Gu
- Department of Medicine, Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Valentina Krendelchtchikova
- Department of Medicine, Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Pius N. Nde
- Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, United States of America
| | - Siddharth Pratap
- Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, United States of America
| | - Maria F. Lima
- Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, United States of America
| | - Fernando Villalta
- Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, United States of America
| | - Qiana L. Matthews
- Department of Medicine, Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
- Center for AIDS Research, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
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Sullivan L, Fleming J, Sastry L, Mehlert A, Wall SJ, Ferguson MAJ. Identification of sVSG117 as an immunodiagnostic antigen and evaluation of a dual-antigen lateral flow test for the diagnosis of human African trypanosomiasis. PLoS Negl Trop Dis 2014; 8:e2976. [PMID: 25033401 PMCID: PMC4102454 DOI: 10.1371/journal.pntd.0002976] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2014] [Accepted: 05/12/2014] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The diagnosis of human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense relies mainly on the Card Agglutination Test for Trypanosomiasis (CATT). There is no immunodiagnostic for HAT caused by T. b. rhodesiense. Our principle aim was to develop a prototype lateral flow test that might be an improvement on CATT. METHODOLOGY/PRINCIPLE FINDINGS Pools of infection and control sera were screened against four different soluble form variant surface glycoproteins (sVSGs) by ELISA and one, sVSG117, showed particularly strong immunoreactivity to pooled infection sera. Using individual sera, sVSG117 was shown to be able to discriminate between T. b. gambiense infection and control sera by both ELISA and lateral flow test. The sVSG117 antigen was subsequently used with a previously described recombinant diagnostic antigen, rISG65, to create a dual-antigen lateral flow test prototype. The latter was used blind in a virtual field trial of 431 randomized infection and control sera from the WHO HAT Specimen Biobank. CONCLUSION/SIGNIFICANCE In the virtual field trial, using two positive antigen bands as the criterion for infection, the sVSG117 and rISG65 dual-antigen lateral flow test prototype showed a sensitivity of 97.3% (95% CI: 93.3 to 99.2) and a specificity of 83.3% (95% CI: 76.4 to 88.9) for the detection of T. b. gambiense infections. The device was not as good for detecting T. b. rhodesiense infections using two positive antigen bands as the criterion for infection, with a sensitivity of 58.9% (95% CI: 44.9 to 71.9) and specificity of 97.3% (95% CI: 90.7 to 99.7). However, using one or both positive antigen band(s) as the criterion for T. b. rhodesiense infection improved the sensitivity to 83.9% (95% CI: 71.7 to 92.4) with a specificity of 85.3% (95% CI: 75.3 to 92.4). These results encourage further development of the dual-antigen device for clinical use.
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Affiliation(s)
- Lauren Sullivan
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Jennifer Fleming
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Lalitha Sastry
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Angela Mehlert
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | | | - Michael A. J. Ferguson
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, United Kingdom
- * E-mail:
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19
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Bhattacharyya T, Falconar AK, Luquetti AO, Costales JA, Grijalva MJ, Lewis MD, Messenger LA, Tran TT, Ramirez JD, Guhl F, Carrasco HJ, Diosque P, Garcia L, Litvinov SV, Miles MA. Development of peptide-based lineage-specific serology for chronic Chagas disease: geographical and clinical distribution of epitope recognition. PLoS Negl Trop Dis 2014; 8:e2892. [PMID: 24852444 PMCID: PMC4031129 DOI: 10.1371/journal.pntd.0002892] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Accepted: 04/09/2014] [Indexed: 11/18/2022] Open
Abstract
Background Chagas disease, caused by infection with the protozoan Trypanosoma cruzi, remains a serious public health issue in Latin America. Genetically diverse, the species is sub-divided into six lineages, known as TcI–TcVI, which have disparate geographical and ecological distributions. TcII, TcV, and TcVI are associated with severe human disease in the Southern Cone countries, whereas TcI is associated with cardiomyopathy north of the Amazon. T. cruzi persists as a chronic infection, with cardiac and/or gastrointestinal symptoms developing years or decades after initial infection. Identifying an individual's history of T. cruzi lineage infection directly by genotyping of the parasite is complicated by the low parasitaemia and sequestration in the host tissues. Methodology/Principal Findings We have applied here serology against lineage-specific epitopes of the T. cruzi surface antigen TSSA, as an indirect approach to allow identification of infecting lineage. Chagasic sera from chronic patients from a range of endemic countries were tested by ELISA against synthetic peptides representing lineage-specific TSSA epitopes bound to avidin-coated ELISA plates via a biotin labelled polyethylene glycol-glycine spacer to increase rotation and ensure each amino acid side chain could freely interact with their antibodies. 79/113 (70%) of samples from Brazil, Bolivia, and Argentina recognised the TSSA epitope common to lineages TcII/TcV/TcVI. Comparison with clinical information showed that a higher proportion of Brazilian TSSApep-II/V/VI responders had ECG abnormalities than non-responders (38% vs 17%; p<0.0001). Among northern chagasic sera 4/20 (20%) from Ecuador reacted with this peptide; 1/12 Venezuelan and 1/34 Colombian samples reacted with TSSApep-IV. In addition, a proposed TcI-specific epitope, described elsewhere, was demonstrated here to be highly conserved across lineages and therefore not applicable to lineage-specific serology. Conclusions/Significance These results demonstrate the considerable potential for synthetic peptide serology to investigate the infection history of individuals, geographical and clinical associations of T. cruzi lineages. Chagas disease remains a significant public health issue in Latin America. Caused by the single-celled parasite Trypanosoma cruzi, the main route of infection is via contact with contaminated faeces from blood-sucking triatomine bugs, but following successful insecticide spraying campaigns, congenital, food-borne, and transfusion/transplantation routes of infection have become more relevant. In the absence of successful chemotherapy, T. cruzi usually persists in the body for life, and in symptomatic cases may lead to death or debilitation by heart failure and/or gastrointestinal megasyndromes. As a species, T. cruzi displays great genetic diversity, and is subdivided into lineages called TcI - TcVI. Associating T. cruzi lineage with clinical symptoms is a key goal of Chagas disease research. Direct isolation and typing of T. cruzi from chronically infected patients is hampered by the sequestration of the parasite in host tissues. Identifying lineage-specific antibodies in serum provides an alternative approach to determining an individual's history of infection. Here, we performed lineage-specific serology using samples from a range of South American countries. We show that lineage-specific seropositivity is associated with geographical distributions and clinical outcome. These findings have wide implications for further diagnostics development and improved understanding of the epidemiology of Chagas disease.
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Affiliation(s)
- Tapan Bhattacharyya
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
- * E-mail:
| | | | - Alejandro O. Luquetti
- Laboratorio de Chagas, Hospital das Clinicas, Universidade Federal de Goiás, Goiânia, Goias, Brazil
| | - Jaime A. Costales
- Centro de Investigación en Enfermedades Infecciosas, Escuela de Biología, Pontificia Universidad Católica del Ecuador, Quito, Ecuador
| | - Mario J. Grijalva
- Centro de Investigación en Enfermedades Infecciosas, Escuela de Biología, Pontificia Universidad Católica del Ecuador, Quito, Ecuador
- Tropical Disease Institute, Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio, United States of America
| | - Michael D. Lewis
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Louisa A. Messenger
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Trang T. Tran
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Juan-David Ramirez
- Facultad de Ciencias Naturales y Matemáticas, Universidad del Rosario, Bogotá, Colombia
| | - Felipe Guhl
- Centro de Investigaciones en Microbiología y Parasitología Tropical, Universidad de los Andes, Bogotá, Colombia
| | - Hernan J. Carrasco
- Universidad Central de Venezuela Instituto de Medicina Tropical, Caracas, Venezuela
| | - Patricio Diosque
- Unidad de Epidemiología Molecular, Instituto de Patología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Salta, Salta, Argentina
| | - Lineth Garcia
- Facultad de Medicina, Universidad Mayor de San Simón, Cochabamba, Bolivia
| | | | - Michael A. Miles
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
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Abstract
Studies on Variant Surface Glycoproteins (VSGs) and antigenic variation in the African trypanosome, Trypanosoma brucei, have yielded a remarkable range of novel and important insights. The features first identified in T. brucei extend from unique to conserved-among-trypanosomatids to conserved-among-eukaryotes. Consequently, much of what we now know about trypanosomatid biology and much of the technology available has its origin in studies related to VSGs. T. brucei is now probably the most advanced early branched eukaryote in terms of experimental tractability and can be approached as a pathogen, as a model for studies on fundamental processes, as a model for studies on eukaryotic evolution or often all of the above. In terms of antigenic variation itself, substantial progress has been made in understanding the expression and switching of the VSG coat, while outstanding questions continue to stimulate innovative new approaches. There are large numbers of VSG genes in the genome but only one is expressed at a time, always immediately adjacent to a telomere. DNA repair processes allow a new VSG to be copied into the single transcribed locus. A coordinated transcriptional switch can also allow a new VSG gene to be activated without any detectable change in the DNA sequence, thereby maintaining singular expression, also known as allelic exclusion. I review the story behind VSGs; the genes, their expression and switching, their central role in T. brucei virulence, the discoveries that emerged along the way and the persistent questions relating to allelic exclusion in particular.
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Affiliation(s)
- David Horn
- Division of Biological Chemistry & Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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21
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Cestari I, Evans-Osses I, Schlapbach LJ, de Messias-Reason I, Ramirez MI. Mechanisms of complement lectin pathway activation and resistance by trypanosomatid parasites. Mol Immunol 2013; 53:328-34. [PMID: 23063472 DOI: 10.1016/j.molimm.2012.08.015] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Accepted: 08/15/2012] [Indexed: 11/28/2022]
Abstract
Studies in the past decade have demonstrated a crucial role for the complement lectin pathway in host defence against protozoan microbes. Recognition of pathogen surface molecules by mannan-binding lectin and ficolins revealed new mechanisms of innate immune defence and a diversity of parasite strategies of immune evasion. In the present review, we will discuss the current knowledge of: (1) the molecular mechanism of lectin pathway activation by trypanosomes; (2) the mechanisms of complement evasion by trypanosomes; and (3) host genetic deficiencies of complement lectin pathway factors that contribute to infection susceptibility and disease progression. This review will focus on trypanosomatids, the parasites that cause Chagas disease, leishmaniasis and sleeping sickness (African trypanosomiasis).
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Affiliation(s)
- Igor Cestari
- Seattle Biomedical Research Institute, Seattle, WA 98109, USA
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22
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Povelones ML, Gluenz E, Dembek M, Gull K, Rudenko G. Histone H1 plays a role in heterochromatin formation and VSG expression site silencing in Trypanosoma brucei. PLoS Pathog 2012; 8:e1003010. [PMID: 23133390 PMCID: PMC3486875 DOI: 10.1371/journal.ppat.1003010] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 09/20/2012] [Indexed: 11/30/2022] Open
Abstract
The African sleeping sickness parasite Trypanosoma brucei evades the host immune system through antigenic variation of its variant surface glycoprotein (VSG) coat. Although the T. brucei genome contains ∼1500 VSGs, only one VSG is expressed at a time from one of about 15 subtelomeric VSG expression sites (ESs). For antigenic variation to work, not only must the vast VSG repertoire be kept silent in a genome that is mainly constitutively transcribed, but the frequency of VSG switching must be strictly controlled. Recently it has become clear that chromatin plays a key role in silencing inactive ESs, thereby ensuring monoallelic expression of VSG. We investigated the role of the linker histone H1 in chromatin organization and ES regulation in T. brucei. T. brucei histone H1 proteins have a different domain structure to H1 proteins in higher eukaryotes. However, we show that they play a key role in the maintenance of higher order chromatin structure in bloodstream form T. brucei as visualised by electron microscopy. In addition, depletion of histone H1 results in chromatin becoming generally more accessible to endonucleases in bloodstream but not in insect form T. brucei. The effect on chromatin following H1 knock-down in bloodstream form T. brucei is particularly evident at transcriptionally silent ES promoters, leading to 6–8 fold derepression of these promoters. T. brucei histone H1 therefore appears to be important for the maintenance of repressed chromatin in bloodstream form T. brucei. In particular H1 plays a role in downregulating silent ESs, arguing that H1-mediated chromatin functions in antigenic variation in T. brucei. Trypanosoma brucei causes African sleeping sickness, endemic to sub-Saharan Africa. Bloodstream form T. brucei is covered with a dense coat of variant surface glycoprotein (VSG). Only one VSG is expressed at a time out of a vast repertoire of ∼1500 VSGs. The active VSG is transcribed in a telomeric VSG expression site (ES), and VSG switching allows immune evasion. Exactly how monoallelic exclusion of VSG ESs operates, and how switching between ESs is mediated remains mysterious, although epigenetics and chromatin structure clearly play a major role. The linker histone H1 is thought to orchestrate higher order chromatin structure in eukaryotes, but its exact function is unclear. We investigated the role of histone H1 in the regulation of antigenic variation in T. brucei. We show that histone H1 is associated with chromatin and is required for higher order chromatin structure. Depletion of histone H1 results in derepression of silent VSG ES promoters, indicating that H1-mediated chromatin functions in antigenic variation in T. brucei.
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Affiliation(s)
- Megan L. Povelones
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
| | - Eva Gluenz
- The Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Marcin Dembek
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
| | - Keith Gull
- The Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Gloria Rudenko
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
- * E-mail:
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23
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Van Nieuwenhove L, Büscher P, Balharbi F, Humbert M, Dieltjens T, Guisez Y, Lejon V. Identification of mimotopes with diagnostic potential for Trypanosoma brucei gambiense variant surface glycoproteins using human antibody fractions. PLoS Negl Trop Dis 2012; 6:e1682. [PMID: 22720103 PMCID: PMC3373652 DOI: 10.1371/journal.pntd.0001682] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Accepted: 04/27/2012] [Indexed: 11/18/2022] Open
Abstract
Background At present, screening of the population at risk for gambiense human African trypanosomiasis (HAT) is based on detection of antibodies against native variant surface glycoproteins (VSGs) of Trypanosoma brucei (T.b.) gambiense. Drawbacks of these native VSGs include culture of infective T.b. gambiense trypanosomes in laboratory rodents, necessary for production, and the exposure of non-specific epitopes that may cause cross-reactions. We therefore aimed at identifying peptides that mimic epitopes, hence called “mimotopes,” specific to T.b. gambiense VSGs and that may replace the native proteins in antibody detection tests. Methodology/Principal Findings A Ph.D.-12 peptide phage display library was screened with polyclonal antibodies from patient sera, previously affinity purified on VSG LiTat 1.3 or LiTat 1.5. The peptide sequences were derived from the DNA sequence of the selected phages and synthesised as biotinylated peptides. Respectively, eighteen and twenty different mimotopes were identified for VSG LiTat 1.3 and LiTat 1.5, of which six and five were retained for assessment of their diagnostic performance. Based on alignment of the peptide sequences on the original protein sequence of VSG LiTat 1.3 and 1.5, three additional peptides were synthesised. We evaluated the diagnostic performance of the synthetic peptides in indirect ELISA with 102 sera from HAT patients and 102 endemic negative controls. All mimotopes had areas under the curve (AUCs) of ≥0.85, indicating their diagnostic potential. One peptide corresponding to the VSG LiTat 1.3 protein sequence also had an AUC of ≥0.85, while the peptide based on the sequence of VSG LiTat 1.5 had an AUC of only 0.79. Conclusions/Significance We delivered the proof of principle that mimotopes for T.b. gambiense VSGs, with diagnostic potential, can be selected by phage display using polyclonal human antibodies. Control of the chronic form of sleeping sickness or gambiense human African trypanosomiasis (HAT) consists of accurate diagnosis followed by treatment. We aim to replace the native variant surface glycoprotein (VSG) parasite antigens that are presently used in most antibody detection tests with peptides that can be synthesised in vitro. Antibodies recognising VSG were purified from HAT patient sera and were used to select phage-expressed peptides that mimic VSG epitopes from a Ph.D.-12 phage display library. The diagnostic potential of the corresponding synthetic peptides was demonstrated in indirect ELISA with sera from HAT patients and endemic negative controls. We proved that diagnostic mimotopes for T.b. gambiense VSGs can be selected by phage display technology, using polyclonal human antibodies.
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Affiliation(s)
| | - Philippe Büscher
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
- * E-mail:
| | - Fatima Balharbi
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Michael Humbert
- Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America
- Harvard Medical School, Boston, Massachusetts, United States of America
| | - Tessa Dieltjens
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Yves Guisez
- Department of Biology, University of Antwerp, Antwerp, Belgium
| | - Veerle Lejon
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
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Gadelha C, Holden JM, Allison HC, Field MC. Specializations in a successful parasite: what makes the bloodstream-form African trypanosome so deadly? Mol Biochem Parasitol 2011; 179:51-8. [PMID: 21763356 DOI: 10.1016/j.molbiopara.2011.06.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2011] [Revised: 06/14/2011] [Accepted: 06/15/2011] [Indexed: 12/24/2022]
Abstract
Most trypanosomatid parasites have both arthropod and mammalian or plant hosts, and the ability to survive and complete a developmental program in each of these very different environments is essential for life cycle progression and hence being a successful pathogen. For African trypanosomes, where the mammalian stage is exclusively extracellular, this presents specific challenges and requires evasion of both the acquired and innate immune systems, together with adaptation to a specific nutritional environment and resistance to mechanical and biochemical stresses. Here we consider the basis for these adaptations, the specific features of the mammalian infective trypanosome that are required to meet these challenges, and how these processes both inform on basic parasite biology and present potential therapeutic targets.
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25
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Bockstal V, Guirnalda P, Caljon G, Goenka R, Telfer JC, Frenkel D, Radwanska M, Magez S, Black SJ. T. brucei infection reduces B lymphopoiesis in bone marrow and truncates compensatory splenic lymphopoiesis through transitional B-cell apoptosis. PLoS Pathog 2011; 7:e1002089. [PMID: 21738467 PMCID: PMC3128123 DOI: 10.1371/journal.ppat.1002089] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Accepted: 04/12/2011] [Indexed: 12/31/2022] Open
Abstract
African trypanosomes of the Trypanosoma brucei species are extracellular protozoan parasites that cause the deadly disease African trypanosomiasis in humans and contribute to the animal counterpart, Nagana. Trypanosome clearance from the bloodstream is mediated by antibodies specific for their Variant Surface Glycoprotein (VSG) coat antigens. However, T. brucei infection induces polyclonal B cell activation, B cell clonal exhaustion, sustained depletion of mature splenic Marginal Zone B (MZB) and Follicular B (FoB) cells, and destruction of the B-cell memory compartment. To determine how trypanosome infection compromises the humoral immune defense system we used a C57BL/6 T. brucei AnTat 1.1 mouse model and multicolor flow cytometry to document B cell development and maturation during infection. Our results show a more than 95% reduction in B cell precursor numbers from the CLP, pre-pro-B, pro-B, pre-B and immature B cell stages in the bone marrow. In the spleen, T. brucei induces extramedullary B lymphopoiesis as evidenced by significant increases in HSC-LMPP, CLP, pre-pro-B, pro-B and pre-B cell populations. However, final B cell maturation is abrogated by infection-induced apoptosis of transitional B cells of both the T1 and T2 populations which is not uniquely dependent on TNF-, Fas-, or prostaglandin-dependent death pathways. Results obtained from ex vivo co-cultures of living bloodstream form trypanosomes and splenocytes demonstrate that trypanosome surface coat-dependent contact with T1/2 B cells triggers their deletion. We conclude that infection-induced and possibly parasite-contact dependent deletion of transitional B cells prevents replenishment of mature B cell compartments during infection thus contributing to a loss of the host's capacity to sustain antibody responses against recurring parasitemic waves. African trypanosomiasis caused by Trypanosoma brucei species is fatal in both humans and animals and cannot be combated by vaccination because of extensive parasite antigenic variation. Effective trypanosome control and clearance from the bloodstream involves the action of antibodies specific for the parasite's highly diverse variable surface glycoprotein antigens. However, experimental infections in mice have shown that trypanosomiasis elicits a rapid process of B cell exhaustion and loss of protective antibody responses. Indeed, both marginal zone B cells, the first line of defense against blood-borne pathogens like T. brucei parasites, and follicular B cells, which are the major source for developing high-affinity antibody-producing plasma cells and memory B cells, become depleted during infection. In addition, existing B-cell memory, both against parasite antigens and non related pathogens, is destroyed early on in infection. Here, we demonstrate that during infection, B cell development is decreased in the bone marrow and early B cell development is taken over by the spleen. However, full maturation of developing B cells is abrogated by the occurrence of transitional B cell apoptosis. This impairs the replenishment of the mature marginal zone and follicular B cell pools and prevents the buildup of protective immunity against successive parasitemic waves.
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Affiliation(s)
- Viki Bockstal
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
- Laboratory for Cellular and Molecular Immunology, Vrije Universiteit Brussel, Brussels, Belgium
- Department of Molecular and Cellular Interactions, VIB, Brussels, Belgium
| | - Patrick Guirnalda
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
| | - Guy Caljon
- Laboratory for Cellular and Molecular Immunology, Vrije Universiteit Brussel, Brussels, Belgium
- Department of Molecular and Cellular Interactions, VIB, Brussels, Belgium
- Unit of Veterinary Protozoology, Institute of Tropical Medicine, Antwerp, Belgium
| | - Radhika Goenka
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
| | - Janice C. Telfer
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
| | - Deborah Frenkel
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
| | | | - Stefan Magez
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
- Laboratory for Cellular and Molecular Immunology, Vrije Universiteit Brussel, Brussels, Belgium
- Department of Molecular and Cellular Interactions, VIB, Brussels, Belgium
- * E-mail: (SJB); (SM)
| | - Samuel J. Black
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts, United States of America
- * E-mail: (SJB); (SM)
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26
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Stijlemans B, Caljon G, Natesan SKA, Saerens D, Conrath K, Pérez-Morga D, Skepper JN, Nikolaou A, Brys L, Pays E, Magez S, Field MC, De Baetselier P, Muyldermans S. High affinity nanobodies against the Trypanosome brucei VSG are potent trypanolytic agents that block endocytosis. PLoS Pathog 2011; 7:e1002072. [PMID: 21698216 PMCID: PMC3116811 DOI: 10.1371/journal.ppat.1002072] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Accepted: 04/04/2011] [Indexed: 11/19/2022] Open
Abstract
The African trypanosome Trypanosoma brucei, which persists within the bloodstream of the mammalian host, has evolved potent mechanisms for immune evasion. Specifically, antigenic variation of the variant-specific surface glycoprotein (VSG) and a highly active endocytosis and recycling of the surface coat efficiently delay killing mediated by anti-VSG antibodies. Consequently, conventional VSG-specific intact immunoglobulins are non-trypanocidal in the absence of complement. In sharp contrast, monovalent antigen-binding fragments, including 15 kDa nanobodies (Nb) derived from camelid heavy-chain antibodies (HCAbs) recognizing variant-specific VSG epitopes, efficiently lyse trypanosomes both in vitro and in vivo. This Nb-mediated lysis is preceded by very rapid immobilisation of the parasites, massive enlargement of the flagellar pocket and major blockade of endocytosis. This is accompanied by severe metabolic perturbations reflected by reduced intracellular ATP-levels and loss of mitochondrial membrane potential, culminating in cell death. Modification of anti-VSG Nbs through site-directed mutagenesis and by reconstitution into HCAbs, combined with unveiling of trypanolytic activity from intact immunoglobulins by papain proteolysis, demonstrates that the trypanolytic activity of Nbs and Fabs requires low molecular weight, monovalency and high affinity. We propose that the generation of low molecular weight VSG-specific trypanolytic nanobodies that impede endocytosis offers a new opportunity for developing novel trypanosomiasis therapeutics. In addition, these data suggest that the antigen-binding domain of an anti-microbial antibody harbours biological functionality that is latent in the intact immunoglobulin and is revealed only upon release of the antigen-binding fragment. Haemoparasites, such as African trypanosomes, have developed potent immune evasion mechanisms to avoid antibody-mediated elimination. Consequently, trypanosome surface antigen-specific immunoglobulins in the absence of complement are non-trypanocidal. In contrast, certain monovalent nanobodies (Nb), monomeric antigen-binding domains derived from camelid Heavy-Chain Antibodies (HCAb) and which have a much lower molecular weight (15 kDa) than classical antibodies (150 kDa), efficiently lyse trypanosomes both in vitro and in vivo. This is surprising as classically immunoglobulin effector functions are mediated via the Fc-domain, which is absent from the Nb. We demonstrate that the Nb-mediated trypanolysis depends on the low molecular weight, monovalency and high affinity and is associated with loss of motility, a major block to endocytosis, energy depletion and cell death. Overall, targeting the parasite surface with low molecular weight, high affinity Nbs is sufficient to exert a direct therapeutic action. Therefore, the exploitation of Nbs against African trypanosomiasis represents a novel therapeutic strategy. Furthermore, demonstration that a high affinity antigen-binding Nb or Fab fragment lacking an effector domain (i.e., Fc-domain or an attached toxin) can exert a direct biological function, suggests that intact antibodies likely harbour latent functionality which only become revealed upon removal of the Fc-domain.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antibodies, Protozoan/immunology
- Antibodies, Protozoan/pharmacology
- Antibodies, Protozoan/therapeutic use
- Antibody Affinity
- Cells, Cultured
- Down-Regulation/drug effects
- Endocytosis/drug effects
- Humans
- Mice
- Mice, Inbred C57BL
- Models, Biological
- Models, Molecular
- Molecular Sequence Data
- Nanoparticles
- Trypanocidal Agents/pharmacology
- Trypanocidal Agents/therapeutic use
- Trypanosoma brucei brucei/immunology
- Trypanosoma brucei brucei/metabolism
- Trypanosoma brucei brucei/physiology
- Trypanosoma brucei brucei/ultrastructure
- Trypanosomiasis, African/immunology
- Trypanosomiasis, African/metabolism
- Trypanosomiasis, African/therapy
- Variant Surface Glycoproteins, Trypanosoma/immunology
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Affiliation(s)
- Benoît Stijlemans
- Laboratory of Cellular and Molecular Immunology, Vrije Universiteit Brussels, Brussels, Belgium.
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Van Nieuwenhove LC, Rogé S, Balharbi F, Dieltjens T, Laurent T, Guisez Y, Büscher P, Lejon V. Identification of peptide mimotopes of Trypanosoma brucei gambiense variant surface glycoproteins. PLoS Negl Trop Dis 2011; 5:e1189. [PMID: 21695105 PMCID: PMC3114753 DOI: 10.1371/journal.pntd.0001189] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Accepted: 04/15/2011] [Indexed: 01/28/2023] Open
Abstract
Background The current antibody detection tests for the diagnosis of gambiense human African trypanosomiasis (HAT) are based on native variant surface glycoproteins (VSGs) of Trypanosoma brucei (T.b.) gambiense. These native VSGs are difficult to produce, and contain non-specific epitopes that may cause cross-reactions. We aimed to identify mimotopic peptides for epitopes of T.b. gambiense VSGs that, when produced synthetically, can replace the native proteins in antibody detection tests. Methodology/Principal Findings PhD.-12 and PhD.-C7C phage display peptide libraries were screened with mouse monoclonal antibodies against the predominant VSGs LiTat 1.3 and LiTat 1.5 of T.b. gambiense. Thirty seven different peptide sequences corresponding to a linear LiTat 1.5 VSG epitope and 17 sequences corresponding to a discontinuous LiTat 1.3 VSG epitope were identified. Seventeen of 22 synthetic peptides inhibited the binding of their homologous monoclonal to VSG LiTat 1.5 or LiTat 1.3. Binding of these monoclonal antibodies to respectively six and three synthetic mimotopic peptides of LiTat 1.5 and LiTat 1.3 was significantly inhibited by HAT sera (p<0.05). Conclusions/Significance We successfully identified peptides that mimic epitopes on the native trypanosomal VSGs LiTat 1.5 and LiTat 1.3. These mimotopes might have potential for the diagnosis of human African trypanosomiasis but require further evaluation and testing with a large panel of HAT positive and negative sera. The control of human African trypanosomiasis or sleeping sickness, a deadly disease in sub-Saharan Africa, mainly depends on a correct diagnosis and treatment. The aim of our study was to identify mimotopic peptides (mimotopes) that may replace the native proteins in antibody detection tests for sleeping sickness and hereby improve the diagnostic sensitivity and specificity. We selected peptide expressing phages from the PhD.-12 and PhD.-C7C phage display libraries with mouse monoclonal antibodies specific to variant surface glycoprotein (VSG) LiTat 1.3 or LiTat 1.5 of Trypanosoma brucei gambiense. The peptide coding genes of the selected phages were sequenced and the corresponding peptides were synthesised. Several of the synthetic peptides were confirmed as mimotopes for VSG LiTat 1.3 or LiTat 1.5 since they were able to inhibit the binding of their homologous monoclonal to the corresponding VSG. These peptides were biotinylated and their diagnostic potential was assessed with human sera. We successfully demonstrated that human sleeping sickness sera recognise some of the mimotopes of VSG LiTat 1.3 and LiTat 1.5, indicating the diagnostic potential of such peptides.
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Abstract
Human African trypanosomiasis (sleeping sickness) occurs in sub-Saharan Africa. It is caused by the protozoan parasite Trypanosoma brucei, transmitted by tsetse flies. Almost all cases are due to Trypanosoma brucei gambiense, which is indigenous to west and central Africa. Prevalence is strongly dependent on control measures, which are often neglected during periods of political instability, thus leading to resurgence. With fewer than 12 000 cases of this disabling and fatal disease reported per year, trypanosomiasis belongs to the most neglected tropical diseases. The clinical presentation is complex, and diagnosis and treatment difficult. The available drugs are old, complicated to administer, and can cause severe adverse reactions. New diagnostic methods and safe and effective drugs are urgently needed. Vector control, to reduce the number of flies in existing foci, needs to be organised on a pan-African basis. WHO has stated that if national control programmes, international organisations, research institutes, and philanthropic partners engage in concerted action, elimination of this disease might even be possible.
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Affiliation(s)
- Reto Brun
- Swiss Tropical Institute, Basel, Switzerland.
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29
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Abstract
Antigenic variation allows Trypanosoma brucei to evade the host immune response by switching the expression of 1 out of approximately 15 telomeric variant surface glycoprotein (VSG) expression sites (ESs). VSG ES transcription is mediated by RNA polymerase I in a discrete nuclear site named the ES body (ESB). However, nothing is known about how the monoallelic VSG ES transcriptional state is maintained over generations. In this study, we show that during S and G2 phases and early mitosis, the active VSG ES locus remains associated with the single ESB and exhibits a delay in the separation of sister chromatids relative to control loci. This delay is dependent on the cohesin complex, as partial knockdown of cohesin subunits resulted in premature separation of sister chromatids of the active VSG ES. Cohesin depletion also prompted transcriptional switching from the active to previously inactive VSG ESs. Thus, in addition to maintaining sister chromatid cohesion during mitosis, the cohesin complex plays an essential role in the correct epigenetic inheritance of the active transcriptional VSG ES state.
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Affiliation(s)
- David Landeira
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Cientificas, 18100 Granada, Spain
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30
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Dagenais TR, Demick KP, Bangs JD, Forest KT, Paulnock DM, Mansfield JM. T-cell responses to the trypanosome variant surface glycoprotein are not limited to hypervariable subregions. Infect Immun 2009; 77:141-51. [PMID: 18936180 PMCID: PMC2612290 DOI: 10.1128/iai.00729-08] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Revised: 07/13/2008] [Accepted: 10/13/2008] [Indexed: 11/20/2022] Open
Abstract
Variable subregions within the variant surface glycoprotein (VSG) coat displayed by African trypanosomes are predicted sites for T- and B-cell recognition. Hypervariable subregion 1 (HV-1) is localized to an internal amphipathic alpha helix in VSG monomers and may have evolved due to selective pressure by host T-cell responses to epitopes within this subregion. The prediction of T-cell receptor-reactive sites and major histocompatibility complex class II binding motifs within the HV-1 subregion, coupled with the conservation of amino acid residues in other regions of the molecule sufficient to maintain secondary and tertiary VSG structure, prompted us to test the hypothesis that Th cells may preferentially recognize HV-1 subregion peptides. Thus, we examined the fine specificity of VSG-specific T-cell lines, T-cell hybridomas, and Th cells activated during infection. Our results demonstrate that T-cell epitopes are distributed throughout the N-terminal domain of VSG but are not clustered exclusively within HV-1 or other hypervariable subregions. In contrast, T-cell-reactive sites were not detected within the relatively conserved C-terminal domain of VSG. Overall, this study is the first to dissect the fine specificity of T-cell responses to the trypanosome VSG and suggests that evolution of a conserved HV-1 region may be unrelated to selective pressures exerted by host T-cell responses. This study also demonstrates that T cells do not recognize the relatively invariant C-terminal region of the VSG molecule during infection, suggesting that it could serve as a potential subunit vaccine to provide variant cross-specific immunity for African trypanosomiasis.
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Affiliation(s)
- Taylor R Dagenais
- Department of Bacteriology, Microbial Sciences Building, 1550 Linden Drive, University of Wisconsin-Madison, Madison, WI 53706, USA
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31
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Abstract
The survival ofTrypanosoma brucei relies on the sucessive expression of a single surface protein gene from a family of around 1,000 genes. This switching appears to be partly dictated by epigenetic changes in chromatin.
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Abstract
To evade the host immune system, several pathogens periodically change their cell-surface epitopes. In the African trypanosomes, antigenic variation is achieved by tightly regulating the expression of a multigene family encoding a large repertoire of variant surface glycoproteins (VSGs). Immune evasion relies on two important features: exposing a single type of VSG at the cell surface and periodically and very rapidly switching the expressed VSG. Transcriptional switching between resident telomeric VSG genes does not involve DNA rearrangements, and regulation is probably epigenetic. The histone methyltransferase DOT1B is a nonessential protein that trimethylates lysine 76 of histone H3 in Trypanosoma brucei. Here we report that transcriptionally silent telomeric VSGs become partially derepressed when DOT1B is deleted, whereas nontelomeric loci are unaffected. DOT1B also is involved in the kinetics of VSG switching: in ΔDOT1B cells, the transcriptional switch is so slow that cells expressing two VSGs persist for several weeks, indicating that monoallelic transcription is compromised. We conclude that DOT1B is required to maintain strict VSG silencing and to ensure rapid transcriptional VSG switching, demonstrating that epigenetics plays an important role in regulating antigenic variation in T. brucei. The surface of Trypanosoma brucei, a unicellular parasite that lives in the bloodstream of its mammalian host, is coated with glycoprotein (VSG) molecules. To evade elimination by the immune system, this parasite replaces its coat with one tailored from another glycoprotein variant. Even though there are hundreds of VSG genes in the genome, this process, called antigenic variation, works because all are silenced except for the one that encodes the current coat. In this work, we show that the chromatin-modifying enzyme DOT1B helps to epigenetically regulate the number of VSGs each parasite can have at a time at the surface and how fast each parasite can switch from one coat to another. In parasites lacking DOT1B, silent VSG genes become partially active and the switch from one VSG to another slows down, allowing two different VSGs to appear on the surface of an individual parasite at the same time. Our studies reveal the importance of epigenetics in regulating VSG genes and provide new insights toward the understanding of this unique survival device. Antigenic variation in Trypanosoma brucei relies on monoallelic expression of a multigene family. New evidence shows that a chromatin-modifying enzyme prevents simultaneous expression of different proteins at the parasite's surface.
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Affiliation(s)
- Luisa M Figueiredo
- Laboratory of Molecular Parasitology, the Rockefeller University, New York, New York, United States of America
| | | | - George A.M Cross
- Laboratory of Molecular Parasitology, the Rockefeller University, New York, New York, United States of America
- * To whom correspondence should be addressed. E-mail:
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MacGregor P, Matthews KR. Modelling trypanosome chronicity: VSG dynasties and parasite density. Trends Parasitol 2007; 24:1-4. [PMID: 18024198 DOI: 10.1016/j.pt.2007.09.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 09/21/2007] [Accepted: 09/21/2007] [Indexed: 02/05/2023]
Abstract
A new mathematical model developed by Lythgoe et al. shows that the semi-predictable order of trypanosome antigenic variation can be generated by two parasite-intrinsic factors. The first is the different probabilities of antigen-gene activation that result from the different molecular mechanisms by which the genes become expressed. The second is the density-dependent differentiation of slender to stumpy cells. The study has important implications for understanding the dynamics of antigenic variation and for modelling the consequences of therapeutic strategies directed against trypanosomes.
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Affiliation(s)
- Paula MacGregor
- Institute of Immunology and Infection Research, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK
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34
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Abstract
African trypanosomes evade humoral immunity through antigenic variation whereby, they switch expression of the variant surface glycoprotein (VSG) gene encoding their glycoprotein surface coat. Switching proceeds by duplication from an archive of silent VSG genes into a transcriptionally active locus, and precedent suggests silent genes can contribute, combinatorially to formation of expressed, functional genes through segmental gene conversion. The genome project has revealed that most of the silent archive consists of hundreds of VSG genes in subtelomeric tandem arrays, and that most of these are not functional genes. The aim of this review is to explore links between the uncovered trypanosome genotype and the phenotype of antigenic variation, stretching from the broad phenotype-transmission in the field and the overcoming of herd immunity-to events within single infections. Highlighting in particular the possible impact of phenotype selection on the evolution of the VSG archive and the mechanisms for its expression leads to a theoretical framework to further our understanding of this complex immune evasion strategy.
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Affiliation(s)
- Lucio Marcello
- Wellcome Centre for Molecular Parasitology, University of Glasgow, Glasgow Biomedical Research Centre, 120 University Place, Glasgow G12 8TA, UK
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35
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Abstract
Trypanosoma brucei thwarts the host immune response by replacing its variant surface glycoprotein (VSG). The actively transcribed VSG is located in one of approximately 20 telomeric expression sites (ES). Antigenic variation can occur by transcriptional switching, reciprocal translocations, or duplicative gene conversion events among ES or with the large repertoire of telomeric and non-telomeric VSG. In recently isolated strains, duplicative gene conversion occurs at a high frequency and predominates, but the switching frequency decreases dramatically upon laboratory-adaptation. Uniquely, T. brucei telomeres grow--apparently indefinitely--at a steady rate of 6-12 base pairs (bp) per population doubling (PD), but the telomere adjacent to an active ES undergoes frequent truncations. Using two-dimensional gel electrophoresis, we demonstrate that all of the chromosome classes of fast-switching and minimally propagated T. brucei have shorter telomeres than extensively propagated Lister 427 clones, suggesting a link between laboratory adaptation, telomere growth, and VSG switching rates.
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Affiliation(s)
| | - George A. M. Cross
- * Corresponding author. Tel.: +1 212-327-7571; fax: +1 212-327-7845. E-mail address:
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36
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Navarro M, Peñate X, Landeira D. Nuclear architecture underlying gene expression in Trypanosoma brucei. Trends Microbiol 2007; 15:263-70. [PMID: 17481901 DOI: 10.1016/j.tim.2007.04.004] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 03/26/2007] [Accepted: 04/16/2007] [Indexed: 11/24/2022]
Abstract
The influence of nuclear architecture on the regulation of developmental gene expression has recently become evident in many organisms ranging from yeast to humans. During interphase, chromosomes and nuclear structures are in constant motion; therefore, correct temporal association is needed to meet the requirements of gene expression. Trypanosoma brucei is an excellent model system in which to analyze nuclear spatial implications in the regulation of gene expression because the two main surface-protein genes (procyclin and VSG) are transcribed by the highly compartmentalized RNA polymerase I and undergo distinct transcriptional activation or downregulation during developmental differentiation. Furthermore, the infective bloodstream form of the parasite undergoes antigenic variation, displaying sequentially different types of VSG by allelic exclusion. Here, we discuss recent advances in understanding the role of chromosomal nuclear positioning in the regulation of gene expression in T. brucei.
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Affiliation(s)
- Miguel Navarro
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas (Spanish National Research Council), Avda. del Conocimiento s/n, 18100 Granada, Spain.
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37
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Alsford S, Horn D. RNA polymerase I transcription stimulates homologous recombination in Trypanosoma brucei. Mol Biochem Parasitol 2007; 153:77-9. [PMID: 17316839 PMCID: PMC3827967 DOI: 10.1016/j.molbiopara.2007.01.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Revised: 01/15/2007] [Accepted: 01/16/2007] [Indexed: 10/23/2022]
Affiliation(s)
| | - David Horn
- Corresponding author: London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT. UK. Phone: (020) 7927 2352, Fax: (020) 7636 8739,
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Abstract
Telomeres are specialized DNA-protein complexes that stabilize chromosome ends, protecting them from nucleolytic degradation and illegitimate recombination. Telomeres form a heterochromatic structure that can suppress the transcription of adjacent genes. These structures might have additional roles in Trypanosoma brucei, as the major surface antigens of this parasite are expressed during its infectious stages from subtelomeric loci. We propose that the telomere protein complexes of trypanosomes and vertebrates are conserved and offer the hypothesis that growth and breakage of telomeric repeats has an important role in regulating parasite antigenic variation in trypanosomes.
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Affiliation(s)
- Oliver Dreesen
- The Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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39
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Abstract
Major modifications of immune system have been observed in African trypanosomiasis. These immune reactions do not lead to protection and are also involved in immunopathology disorders. The major surface component (variable surface glycoprotein,VSG) is associated with escape to immune reactions, cytokine network dysfunctions and autoantibody production. Most of our knowledge result from experimental trypanosomiasis. Innate resistance elements have been characterised. In infected mice, VSG preferentially stimulates a Th 1-cell subset. A response of <FONT FACE=Symbol>gd</FONT> and CD8 T cells to trypanosome antigens was observed in trypanotolerant cattle. An increase in CD5 B cells, responsible for most serum IgM and production of autoantibodies has been noted in infected cattle. Macrophages play important roles in trypanosomiasis, in synergy with antibodies (phagocytosis) and by secreting various molecules (radicals, cytokines, prostaglandins,...). Trypanosomes are highly sensitive to TNF-alpha, reactive oxygen and nitrogen intermediates. TNF-alpha is also involved in cachexia. IFN-gamma acts as a parasite growth factor. These various elements contribute to immunosuppression. Trypanosomes have learnt to use immune mechanisms to its own profit. Recent data show the importance of alternative macrophage activation, including arginase induction. L-ornithine produced by host arginase is essential to parasite growth. All these data reflect the deep insight into the immune system realised by trypanosomes and might suggest interference therapeutic approaches.
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Abstract
The African trypanosome Trypanosoma brucei is best known for its extraordinarily sophisticated antigenic variation of a protective variant surface glycoprotein (VSG) coat. T. brucei has >1000 VSG genes and pseudogenes, of which one is transcribed at a time from one of multiple telomeric VSG expression sites. Switching the active VSG gene can involve DNA rearrangements replacing the old VSG with a new one, or alternatively transcriptional control. The astonishing revelation from the T. brucei genome sequence is that <7% of the sequenced VSGs seem to have fully functional coding regions. This preponderance of pseudogenes in the VSG gene repertoire will necessitate a rethink of how antigenic variation in African trypanosomes operates.
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Affiliation(s)
- Jesse E Taylor
- Peter Medawar Building for Pathogen Research, University of Oxford, South Parks Road, Oxford OX1 3SY, UK
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41
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Dreesen O, Cross GAM. Consequences of telomere shortening at an active VSG expression site in telomerase-deficient Trypanosoma brucei. Eukaryot Cell 2006; 5:2114-9. [PMID: 17071826 PMCID: PMC1694812 DOI: 10.1128/ec.00059-06] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Trypanosoma brucei evades the host immune response by sequential expression of a large family of variant surface glycoproteins (VSG) from one of approximately 20 subtelomeric expression sites (ES). VSG transcription is monoallelic, and little is known about the regulation of antigenic switching. To explore whether telomere length could affect antigenic switching, we created a telomerase-deficient cell line, in which telomeres shortened at a rate of 3 to 6 bp at each cell division. Upon reaching a critical length, short silent ES telomeres were stabilized by a telomerase-independent mechanism. The active ES telomere progressively shortened and frequently broke. Upon reaching a critical length, the short active ES telomere stabilized, but the transcribed VSG was gradually lost from the population and replaced by a new VSG through duplicative gene conversion. We propose a model in which subtelomeric-break-induced replication-mediated repair at a short ES telomere leads to duplicative gene conversion and expression of a new VSG.
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Affiliation(s)
- Oliver Dreesen
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6307, USA
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42
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Semballa S, Okomo-Assoumou MC, Holzmuller P, Büscher P, Magez S, Lemesre JL, Daulouede S, Courtois P, Geffard M, Vincendeau P. Identification of a tryptophan-like epitope borne by the variable surface glycoprotein (VSG) of African trypanosomes. Exp Parasitol 2006; 115:173-80. [PMID: 17014849 DOI: 10.1016/j.exppara.2006.08.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2006] [Revised: 07/28/2006] [Accepted: 08/02/2006] [Indexed: 10/24/2022]
Abstract
Antibodies (Ab) directed against a tryptophan-like epitope (WE) were previously detected in patients with human African trypanosomiasis (HAT). We investigated whether or not these Ab resulted from immunization against trypanosome antigen(s) expressing a WE. By Western blotting, we identified an antigen having an apparent molecular weight ranging from 60 to 65 kDa, recognized by purified rabbit anti-WE Ab. This antigen, present in trypomastigote forms, was absent in procyclic forms and Trypanosoma cruzi trypomastigotes. Using purified variable surface glycoproteins (VSG) from various trypanosomes, we showed that VSG was the parasite antigen recognized by these rabbit Ab. Anti-WE and anti-VSG Ab were purified from HAT sera by affinity chromatography. Immunoreactivity of purified antibodies eluted from affinity columns and of depleted fractions showed that WE was one of the epitopes borne by VSG. These data underline the existence of an invariant WE in the structure of VSG from several species of African trypanosomes.
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Affiliation(s)
- S Semballa
- EA 3677 Laboratoire de Parasitologie, Université de Bordeaux II, France
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43
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Homann M, Lorger M, Engstler M, Zacharias M, Göringer HU. Serum-stable RNA aptamers to an invariant surface domain of live African trypanosomes. Comb Chem High Throughput Screen 2006; 9:491-9. [PMID: 16925510 DOI: 10.2174/138620706777935324] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
African trypanosomes are extracellular blood parasites that cause sleeping sickness in humans and Nagana in cattle. The therapeutics used to control and treat these diseases are very ineffective and thus, the development of new drugs is urgently needed. We have previously suggested to use trypanosome-specific RNA aptamers as tools for the development of novel trypanocidal compounds. Here, we report the selection of a 2'-NH(2)-modified RNA aptamer that binds to live trypanosomes with an affinity of 70 +/- 15 nM. The aptamer adopts a stable G-quartet structure and has a half-life in human serum of > 30 h. RNA binding is restricted to the flagellar attachment zone, located between the cell body and the flagellum of the parasite. We demonstrate that antigen-tagged preparations of the aptamer can bind to live trypanosomes and that they can be used to re-direct immunoglobulins to the parasite surface.
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Affiliation(s)
- Matthias Homann
- Institute of Microbiology and Genetics, Darmstadt University of Technology, Schnittspahnstrasse 10, D-64287 Darmstadt, Germany.
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Baral TN, Magez S, Stijlemans B, Conrath K, Vanhollebeke B, Pays E, Muyldermans S, De Baetselier P. Experimental therapy of African trypanosomiasis with a nanobody-conjugated human trypanolytic factor. Nat Med 2006; 12:580-4. [PMID: 16604085 DOI: 10.1038/nm1395] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Accepted: 03/10/2006] [Indexed: 11/08/2022]
Abstract
High systemic drug toxicity and increasing prevalence of drug resistance hampers efficient treatment of human African trypanosomiasis (HAT). Hence, development of new highly specific trypanocidal drugs is necessary. Normal human serum (NHS) contains apolipoprotein L-I (apoL-I), which lyses African trypanosomes except resistant forms such as Trypanosoma brucei rhodesiense. T. b. rhodesiense expresses the apoL-I-neutralizing serum resistance-associated (SRA) protein, endowing this parasite with the ability to infect humans and cause HAT. A truncated apoL-I (Tr-apoL-I) has been engineered by deleting its SRA-interacting domain, which makes it lytic for T. b. rhodesiense. Here, we conjugated Tr-apoL-I with a single-domain antibody (nanobody) that efficiently targets conserved cryptic epitopes of the variant surface glycoprotein (VSG) of trypanosomes to generate a new manmade type of immunotoxin with potential for trypanosomiasis therapy. Treatment with this engineered conjugate resulted in clear curative and alleviating effects on acute and chronic infections of mice with both NHS-resistant and NHS-sensitive trypanosomes.
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Affiliation(s)
- Toya Nath Baral
- Department of Cellular and Molecular Interactions, Vlaams Interuniversitair Instituut voor Biotechnologie, Laboratorium voor Cellulaire en Moleculaire Immunologie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium.
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Pan W, Ogunremi O, Wei G, Shi M, Tabel H. CR3 (CD11b/CD18) is the major macrophage receptor for IgM antibody-mediated phagocytosis of African trypanosomes: Diverse effect on subsequent synthesis of tumor necrosis factor α and nitric oxide. Microbes Infect 2006; 8:1209-18. [PMID: 16616573 DOI: 10.1016/j.micinf.2005.11.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Revised: 11/19/2005] [Accepted: 11/23/2005] [Indexed: 10/25/2022]
Abstract
Immunoglobulin M (IgM) antibodies to the variant surface glycoproteins (VSG) of African trypanosomes are the first and predominant class of anti-trypanosomal antibodies in the infected host. They are a major factor in controlling waves of parasitemia, but not in long-term survival. The macrophage receptor(s) that enables phagocytosis of IgM anti-VSG-coated African trypanosomes is unknown. We assessed whether complement receptor CR3 (CD11b/CD18) might be involved in mediating phagocytosis of Trypanosoma congolense. We show that murine complement C3 fragments are deposited onto T. congolense when the trypanosomes are incubated with IgM anti-VSG and fresh mouse serum. In the presence of fresh mouse serum, there is significantly and markedly less phagocytosis of IgM-opsonized T. congolense by CD11b-deficient macrophages compared to phagocytosis by wild-type macrophages (78% fewer T. congolense are ingested per macrophage). Significantly less tumor necrosis factor (TNF)-alpha (38% less), but significantly more nitric oxide (NO) (63% more) are released by CD11b-deficient macrophages that have engulfed trypanosomes than by equally treated wild-type macrophages. We conclude that CR3 is the major, but not the only, receptor involved in IgM anti-VSG-mediated phagocytosis of T. congolense by macrophages. We further conclude that IgM anti-VSG-mediated phagocytosis of T. congolense enhances synthesis of disease-producing TNF-alpha and inhibits synthesis of parasite-controlling NO. We suggest that signaling of inhibition of NO synthesis is mediated via CR3.
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Affiliation(s)
- Wanling Pan
- Department of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada
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46
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Abstract
African trypanosomes are well known for their ability to avoid immune elimination by switching the immunodominant variant surface glycoprotein (VSG) coat during infection. However, antigenic variation is only one of several means by which trypanosomes manipulate the immune system of their hosts. In this article, the role of parasite factors such as GPI anchor residues of the shed VSG molecule and the release of CpG DNA, in addition to host factors such as IFN-gamma, in regulating key aspects of innate and acquired immunity during infection is examined. The biological relevance of these immunoregulatory events is discussed in the context of host and parasite survival.
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Affiliation(s)
- J M Mansfield
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA.
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47
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Hall BS, Smith E, Langer W, Jacobs LA, Goulding D, Field MC. Developmental variation in Rab11-dependent trafficking in Trypanosoma brucei. Eukaryot Cell 2005; 4:971-80. [PMID: 15879531 PMCID: PMC1140102 DOI: 10.1128/ec.4.5.971-980.2005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
In Trypanosoma brucei, endocytosis is developmentally regulated and is substantially more active in the mammalian infective stage, where it likely plays a role in immune evasion. The small GTPase TbRAB11 is highly expressed in the mammalian stage and mediates recycling of glycosylphosphatidylinositol-anchored proteins, including the variant surface glycoprotein (VSG) and the transferrin receptor, plus trafficking of internalized anti-VSG antibody and transferrin. No function has been assigned to TbRAB11 in the procyclic (insect) stage trypanosome. The importance of TbRAB11 to both bloodstream and procyclic form viability was assessed by RNA interference (RNAi). Suppression of TbRAB11 in the bloodstream form was rapidly lethal and led to cells with round morphology and an enlarged flagellar pocket. TbRAB11 RNAi was also lethal in procyclic forms, which also became rounded, but progression to cell death was significantly slower and the flagellar pocket remained normal. In bloodstream forms, silencing of TbRAB11 had no effect on exocytosis of newly synthesized VSG, fluid-phase endocytosis, or transferrin uptake, but export of internalized transferrin was inhibited. Lectin endocytosis assays revealed a block to postendosomal transport mediated by suppressing TbRAB11. By contrast, in procyclic forms, depletion of TbRAB11 blocks both fluid-phase endocytosis and internalization of surface proteins. In normal bloodstream forms, most VSG is recycled, but in procyclics, internalized surface proteins accumulated in the lysosome. These data demonstrate that TbRAB11 controls recycling and is essential in both life stages of T. brucei but that its primary role is subject to developmental variation.
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Affiliation(s)
- Belinda S Hall
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, United Kingdom.
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48
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Abstract
Telomeres and subtelomeres are important to the virulence of a number of pathogens, as they harbour large diverse gene families associated with the maintenance of infection. Evasion of immunity by African trypanosomes involves the differential expression of variant surface glycoproteins (VSGs), which are encoded by a family of >1500 genes and pseudogenes. This silent archive is located subtelomerically and is activated by gene conversion into specialized transcription units, which themselves are subject to silencing by allelic exclusion. Current research addresses the role of telomeres in the conversion and silencing mechanisms and in the diversification of the VSG archive.
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Affiliation(s)
- David Horn
- London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
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49
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Drennan MB, Stijlemans B, Van den Abbeele J, Quesniaux VJ, Barkhuizen M, Brombacher F, De Baetselier P, Ryffel B, Magez S. The Induction of a Type 1 Immune Response following aTrypanosoma bruceiInfection Is MyD88 Dependent. J Immunol 2005; 175:2501-9. [PMID: 16081822 DOI: 10.4049/jimmunol.175.4.2501] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The initial host response toward the extracellular parasite Trypanosoma brucei is characterized by the early release of inflammatory mediators associated with a type 1 immune response. In this study, we show that this inflammatory response is dependent on activation of the innate immune system mediated by the adaptor molecule MyD88. In the present study, MyD88-deficient macrophages are nonresponsive toward both soluble variant-specific surface glycoprotein (VSG), as well as membrane-bound VSG purified from T. brucei. Infection of MyD88-deficient mice with either clonal or nonclonal stocks of T. brucei resulted in elevated levels of parasitemia. This was accompanied by reduced plasma IFN-gamma and TNF levels during the initial stage of infection, followed by moderately lower VSG-specific IgG2a Ab titers during the chronic stages of infection. Analysis of several TLR-deficient mice revealed a partial requirement for TLR9 in the production of IFN-gamma and VSG-specific IgG2a Ab levels during T. brucei infections. These results implicate the mammalian TLR family and MyD88 signaling in the innate immune recognition of T. brucei.
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MESH Headings
- Adaptor Proteins, Signal Transducing/deficiency
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/physiology
- Animals
- Antigens, Differentiation/genetics
- Antigens, Differentiation/physiology
- Cell Membrane/immunology
- Cell Membrane/parasitology
- Cells, Cultured
- DNA, Protozoan/physiology
- Immunity, Innate/genetics
- Macrophage Activation/genetics
- Macrophage Activation/immunology
- Macrophages/immunology
- Macrophages/metabolism
- Macrophages/parasitology
- Mice
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Mice, Knockout
- Myeloid Differentiation Factor 88
- Parasitemia/genetics
- Parasitemia/immunology
- Parasitemia/prevention & control
- Receptors, Immunologic/deficiency
- Receptors, Immunologic/genetics
- Receptors, Immunologic/physiology
- Signal Transduction/genetics
- Signal Transduction/immunology
- Solubility
- Toll-Like Receptor 9/deficiency
- Toll-Like Receptor 9/genetics
- Toll-Like Receptor 9/physiology
- Trypanosoma brucei brucei/genetics
- Trypanosoma brucei brucei/immunology
- Trypanosomiasis, African/genetics
- Trypanosomiasis, African/immunology
- Trypanosomiasis, African/parasitology
- Trypanosomiasis, African/prevention & control
- Variant Surface Glycoproteins, Trypanosoma/immunology
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Affiliation(s)
- Michael B Drennan
- Immunology of Infectious Disease Medical Research Council/University of Cape Town Unit, Institute of Infectious Disease and Molecular Medicine, Health Science Faculty, University of Cape Town, Cape Town, South Africa.
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50
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Abstract
Host resistance to African trypanosomiasis is partially dependent on an early and strong T-independent B-cell response against the variant surface glycoprotein (VSG) coat expressed by trypanosomes. The repetitive array of surface epitopes displayed by a monotypic surface coat, in which identical VSG molecules are closely packed together in a uniform architectural display, cross-links cognate B-cell receptors and initiates T-independent B-cell activation events. However, this repetitive array of identical VSG epitopes is altered during the process of antigenic variation, when former and nascent VSG proteins are transiently expressed together in a mosaic surface coat. Thus, T-independent B-cell recognition of the trypanosome surface coat may be disrupted by the introduction of heterologous VSG molecules into the coat structure. To address this hypothesis, we transformed Trypanosoma brucei rhodesiense LouTat 1 with the 117 VSG gene from Trypanosoma brucei brucei MiTat 1.4 in order to produce VSG double expressers; coexpression of the exogenous 117 gene along with the endogenous LouTat 1 VSG gene resulted in the display of a mosaic VSG coat. Results presented here demonstrate that the host's ability to produce VSG-specific antibodies and activate B cells during early infection with VSG double expressers is compromised relative to that during infection with the parental strain, which displays a monotypic coat. These findings suggest a previously unrecognized mechanism of immune response evasion in which coat-switching trypanosomes fail to directly activate B cells until coat VSG homogeneity is achieved. This process affords an immunological advantage to trypanosomes during the process of antigenic variation.
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Affiliation(s)
- Melissa E Dubois
- Department of Bacteriology, University of Wisconsin-Madison, 1925 Willow Drive, Madison, WI 53706, USA
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