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Multiple Plasmodium falciparum Erythrocyte Membrane Protein 1 Variants per Genome Can Bind IgM via Its Fc Fragment Fcμ. Infect Immun 2015. [PMID: 26216422 PMCID: PMC4567627 DOI: 10.1128/iai.00337-15] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) adhesive proteins expressed on the surfaces of infected erythrocytes (IEs) are of key importance in the pathogenesis of P. falciparum malaria. Several structurally and functionally defined PfEMP1 types have been associated with severe clinical manifestations, such as cerebral malaria in children and placental malaria in pregnant women. PfEMP1 that can bind the Fc part of IgM (Fcμ) characterizes one such type, although the functional significance of this IgM binding to PfEMP1 remains unclear. In this study, we report the identification and functional analysis of five IgM-binding PfEMP1 proteins encoded by P. falciparum NF54. In addition to the VAR2CSA-type PFL0030c protein, already known to bind Fcμ and to mediate chondroitin sulfate A (CSA)-specific adhesion of IEs in the placenta, we found four PfEMP1 proteins not previously known to bind IgM this way. Although they all contained Duffy binding-like ε (DBLε) domains similar to those in VAR2CSA-type PfEMP1, they did not mediate IE adhesion to CSA, and IgM binding did not shield IEs from phagocytosis of IgG-opsonized IEs. In this way, these new IgM-binding PfEMP1 proteins resemble the rosette-mediating and IgM-binding PfEMP1 HB3VAR06, but none of them mediated formation of rosettes. We could map the capacity for Fc-specific IgM binding to DBLε domains near the C terminus for three of the four PfEMP1 proteins tested. Our study provides new evidence regarding Fc-dependent binding of IgM to PfEMP1, which appears to be a common and multifunctional phenotype.
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102
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Subudhi AK, Boopathi PA, Pandey I, Kohli R, Karwa R, Middha S, Acharya J, Kochar SK, Kochar DK, Das A. Plasmodium falciparum complicated malaria: Modulation and connectivity between exportome and variant surface antigen gene families. Mol Biochem Parasitol 2015; 201:31-46. [PMID: 26022315 DOI: 10.1016/j.molbiopara.2015.05.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 05/20/2015] [Accepted: 05/21/2015] [Indexed: 12/27/2022]
Abstract
In temperate and sub-tropical regions of Asia and Latin America, complicated malaria manifested as hepatic dysfunction or renal dysfunction is seen in all age groups. There has been a concerted focus on understanding the patho-physiological and molecular basis of complicated malaria in children, much less is known about it in adults. We report here, the analysis of data from a custom, cross strain microarray (Agilent Platform) using material from adult patient samples, showing hepatic dysfunction or renal failure. These are the most common manifestations seen in adults along with cerebral malaria. The data has been analyzed with reference to variant surface antigens, encoded by the var, rifin and stevor gene families. The differential regulation profiles of key genes (comparison between Plasmodium falciparum complicated and uncomplicated isolates) have been observed. The exportome has been analyzed using similar parameters. Gene ontology term based functional enrichment of differentially regulated genes identified, up-regulated genes statistically enriched (P<0.05) to critical biological processes like generation of precursor metabolite and energy, chromosome organization and electron transport chain. Systems network based functional enrichment of overall differentially regulated genes yielded a similar result. We are reporting here, up-regulation of var group B and C genes whose proteins are predicted to interact with CD36 receptor in the host, the up-regulation of domain cassette 13 (DC13) containing var group A, as also the up-regulation of group A rifins and many of the stevors. This is contrary to most other reports from pediatric patients, with cerebral malaria where the up-regulation of mostly var A group genes have been seen. A protein-protein interaction based network has been created and analysis performed. This co-expression and text mining based network has shown overall connectivity between the variant surface antigens (VSA) and the exportome. The up-regulation of var group B and C genes encoding PfEMP1 with different domain architecture would be important for deciding strategies for disease prevention.
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Affiliation(s)
- Amit Kumar Subudhi
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
| | - P A Boopathi
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
| | - Isha Pandey
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
| | - Ramandeep Kohli
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
| | - Rohan Karwa
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
| | - Sheetal Middha
- Department of Medicine, S.P. Medical College, Bikaner, Rajasthan, India.
| | - Jyoti Acharya
- Department of Medicine, S.P. Medical College, Bikaner, Rajasthan, India.
| | - Sanjay K Kochar
- Department of Medicine, S.P. Medical College, Bikaner, Rajasthan, India.
| | - Dhanpat K Kochar
- Rajasthan University of Health Sciences, Jaipur, Rajasthan, India.
| | - Ashis Das
- Department of Biological Sciences, Birla Institute of Technology and Science (BITS), Pilani, Rajasthan, India.
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103
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IgG antibodies to endothelial protein C receptor-binding cysteine-rich interdomain region domains of Plasmodium falciparum erythrocyte membrane protein 1 are acquired early in life in individuals exposed to malaria. Infect Immun 2015; 83:3096-103. [PMID: 26015475 DOI: 10.1128/iai.00271-15] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 05/11/2015] [Indexed: 11/20/2022] Open
Abstract
Severe malaria syndromes are precipitated by Plasmodium falciparum parasites binding to endothelial receptors on the vascular lining. This binding is mediated by members of the highly variant P. falciparum erythrocyte membrane protein 1 (PfEMP1) family. We have previously identified a subset of PfEMP1 proteins associated with severe malaria and found that the receptor for these PfEMP1 variants is endothelial protein C receptor (EPCR). The binding is mediated through the amino-terminal cysteine-rich interdomain region (CIDR) of the subtypes α1.1 and α1.4 to α1.8. In this study, we investigated the acquisition of anti-CIDR antibodies using plasma samples collected in four study villages with different malaria transmission intensities in northeastern Tanzania during a period with a decline in malaria transmission. We show that individuals exposed to high levels of malaria transmission acquire antibodies to EPCR-binding CIDR domains early in life and that these antibodies are acquired more rapidly than antibodies to other CIDR domains. The rate by which antibodies to EPCR-binding CIDR domains are acquired in populations in areas where malaria is endemic is determined by the malaria transmission intensity, and on a population level, the antibodies are rapidly lost if transmission is interrupted. This indicates that sustained exposure is required to maintain the production of the antibodies.
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104
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Ukaegbu UE, Zhang X, Heinberg AR, Wele M, Chen Q, Deitsch KW. A Unique Virulence Gene Occupies a Principal Position in Immune Evasion by the Malaria Parasite Plasmodium falciparum. PLoS Genet 2015; 11:e1005234. [PMID: 25993442 PMCID: PMC4437904 DOI: 10.1371/journal.pgen.1005234] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 04/21/2015] [Indexed: 12/13/2022] Open
Abstract
Mutually exclusive gene expression, whereby only one member of a multi-gene family is selected for activation, is used by the malaria parasite Plasmodium falciparum to escape the human immune system and perpetuate long-term, chronic infections. A family of genes called var encodes the chief antigenic and virulence determinant of P. falciparum malaria. var genes are transcribed in a mutually exclusive manner, with switching between active genes resulting in antigenic variation. While recent work has shed considerable light on the epigenetic basis for var gene activation and silencing, how switching is controlled remains a mystery. In particular, switching seems not to be random, but instead appears to be coordinated to result in timely activation of individual genes leading to sequential waves of antigenically distinct parasite populations. The molecular basis for this apparent coordination is unknown. Here we show that var2csa, an unusual and highly conserved var gene, occupies a unique position within the var gene switching hierarchy. Induction of switching through the destabilization of var specific chromatin using both genetic and chemical methods repeatedly led to the rapid and exclusive activation of var2csa. Additional experiments demonstrated that these represent "true" switching events and not simply de-silencing of the var2csa promoter, and that activation is limited to the unique locus on chromosome 12. Combined with translational repression of var2csa transcripts, frequent "default" switching to this locus and detection of var2csa untranslated transcripts in non-pregnant individuals, these data suggest that var2csa could play a central role in coordinating switching, fulfilling a prediction made by mathematical models derived from population switching patterns. These studies provide the first insights into the mechanisms by which var gene switching is coordinated as well as an example of how a pharmacological agent can disrupt antigenic variation in Plasmodium falciparum.
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Affiliation(s)
- Uchechi E. Ukaegbu
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
| | - Xu Zhang
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
- Key Laboratory of Zoonosis, College of Veterinary Medicine, Jilin University, Xi An Da Lu, Changchun, China
| | - Adina R. Heinberg
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
| | - Mamadou Wele
- University of Sciences Techniques and Technologies of Bamako, Bamako, Mali
| | - Qijun Chen
- Key Laboratory of Zoonosis, College of Veterinary Medicine, Jilin University, Xi An Da Lu, Changchun, China
| | - Kirk W. Deitsch
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
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105
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Hviid L, Jensen ATR. PfEMP1 - A Parasite Protein Family of Key Importance in Plasmodium falciparum Malaria Immunity and Pathogenesis. ADVANCES IN PARASITOLOGY 2015; 88:51-84. [PMID: 25911365 DOI: 10.1016/bs.apar.2015.02.004] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Plasmodium falciparum causes the most severe form of malaria and is responsible for essentially all malaria-related deaths. The accumulation in various tissues of erythrocytes infected by mature P. falciparum parasites can lead to circulatory disturbances and inflammation, and is thought to be a central element in the pathogenesis of the disease. It is mediated by the interaction of parasite ligands on the erythrocyte surface and a range of host receptor molecules in many organs and tissues. Among several proteins and protein families implicated in this process, the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of high-molecular weight and highly variable antigens appears to be the most prominent. In this chapter, we aim to provide a systematic overview of the current knowledge about these proteins, their structure, their function, how they are presented on the erythrocyte surface, and how the var genes encoding them are regulated. The role of PfEMP1 in the pathogenesis of malaria, PfEMP1-specific immune responses, and the prospect of PfEMP1-specific vaccination against malaria are also covered briefly.
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Affiliation(s)
- Lars Hviid
- Centre for Medical Parasitology, University of Copenhagen and Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
| | - Anja T R Jensen
- Centre for Medical Parasitology, University of Copenhagen and Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
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106
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Tessema SK, Monk SL, Schultz MB, Tavul L, Reeder JC, Siba PM, Mueller I, Barry AE. Phylogeography of var gene repertoires reveals fine-scale geospatial clustering of Plasmodium falciparum populations in a highly endemic area. Mol Ecol 2015; 24:484-97. [PMID: 25482097 DOI: 10.1111/mec.13033] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 11/14/2014] [Accepted: 11/17/2014] [Indexed: 11/28/2022]
Abstract
Plasmodium falciparum malaria is a major global health problem that is being targeted for progressive elimination. Knowledge of local disease transmission patterns in endemic countries is critical to these elimination efforts. To investigate fine-scale patterns of malaria transmission, we have compared repertoires of rapidly evolving var genes in a highly endemic area. A total of 3680 high-quality DBLα-sequences were obtained from 68 P. falciparum isolates from ten villages spread over two distinct catchment areas on the north coast of Papua New Guinea (PNG). Modelling of the extent of var gene diversity in the two parasite populations predicts more than twice as many var gene alleles circulating within each catchment (Mugil = 906; Wosera = 1094) than previously recognized in PNG (Amele = 369). In addition, there were limited levels of var gene sharing between populations, consistent with local parasite population structure. Phylogeographic analyses demonstrate that while neutrally evolving microsatellite markers identified population structure only at the catchment level, var gene repertoires reveal further fine-scale geospatial clustering of parasite isolates. The clustering of parasite isolates by village in Mugil, but not in Wosera was consistent with the physical and cultural isolation of the human populations in the two catchments. The study highlights the microheterogeneity of P. falciparum transmission in highly endemic areas and demonstrates the potential of var genes as markers of local patterns of parasite population structure.
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Affiliation(s)
- Sofonias K Tessema
- Division of Infection and Immunity, Walter and Eliza Hall Institute, 3052, Melbourne, Vic., Australia; Department of Medical Biology, University of Melbourne, 3052, Melbourne, Vic., Australia
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107
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Structural conservation despite huge sequence diversity allows EPCR binding by the PfEMP1 family implicated in severe childhood malaria. Cell Host Microbe 2014; 17:118-29. [PMID: 25482433 PMCID: PMC4297295 DOI: 10.1016/j.chom.2014.11.007] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 09/27/2014] [Accepted: 10/30/2014] [Indexed: 11/20/2022]
Abstract
The PfEMP1 family of surface proteins is central for Plasmodium falciparum virulence and must retain the ability to bind to host receptors while also diversifying to aid immune evasion. The interaction between CIDRα1 domains of PfEMP1 and endothelial protein C receptor (EPCR) is associated with severe childhood malaria. We combine crystal structures of CIDRα1:EPCR complexes with analysis of 885 CIDRα1 sequences, showing that the EPCR-binding surfaces of CIDRα1 domains are conserved in shape and bonding potential, despite dramatic sequence diversity. Additionally, these domains mimic features of the natural EPCR ligand and can block this ligand interaction. Using peptides corresponding to the EPCR-binding region, antibodies can be purified from individuals in malaria-endemic regions that block EPCR binding of diverse CIDRα1 variants. This highlights the extent to which such a surface protein family can diversify while maintaining ligand-binding capacity and identifies features that should be mimicked in immunogens to prevent EPCR binding. EPCR binding is retained by PfEMP1 CIDRα1 domains despite huge sequence variation Diverse CIDRα1 domains retain structural and chemical features to bind to EPCR CIDRα1 domains mimic features of a natural ligand of EPCR and block its binding Patient sera contain neutralizing antibodies that prevent parasite binding to EPCR
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108
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Madkhali AM, Alkurbi MO, Szestak T, Bengtsson A, Patil PR, Wu Y, Alharthi S, Jensen ATR, Pleass R, Craig AG. An analysis of the binding characteristics of a panel of recently selected ICAM-1 binding Plasmodium falciparum patient isolates. PLoS One 2014; 9:e111518. [PMID: 25360558 PMCID: PMC4216080 DOI: 10.1371/journal.pone.0111518] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 09/30/2014] [Indexed: 12/21/2022] Open
Abstract
The basis of severe malaria pathogenesis in part includes sequestration of Plasmodium falciparum-infected erythrocytes (IE) from the peripheral circulation. This phenomenon is mediated by the interaction between several endothelial receptors and one of the main parasite-derived variant antigens (PfEMP1) expressed on the surface of the infected erythrocyte membrane. One of the commonly used host receptors is ICAM-1, and it has been suggested that ICAM-1 has a role in cerebral malaria pathology, although the evidence to support this is not conclusive. The current study examined the cytoadherence patterns of lab-adapted patient isolates after selecting on ICAM-1. We investigated the binding phenotypes using variant ICAM-1 proteins including ICAM-1Ref, ICAM-1Kilifi, ICAM-1S22/A, ICAM-1L42/A and ICAM-1L44/A using static assays. The study also examined ICAM-1 blocking by four anti-ICAM-1 monoclonal antibodies (mAb) under static conditions. We also characterised the binding phenotypes using Human Dermal Microvascular Endothelial Cells (HDMEC) under flow conditions. The results show that different isolates have variant-specific binding phenotypes under both static and flow conditions, extending our previous observations that this variation might be due to variable contact residues on ICAM-1 being used by different parasite PfEMP1 variants.
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Affiliation(s)
- Aymen M. Madkhali
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
- Department of Medical Laboratories Technology, College of Applied Medical Sciences, Jazan University, Jazan, Kingdom of Saudi Arabia
| | - Mohammed O. Alkurbi
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
- Department of Laboratory Medicine, College of Applied Medical Sciences, Umm Al-Qura University, Makkah Al-Mukarramah, Kingdom of Saudi Arabia
| | - Tadge Szestak
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Anja Bengtsson
- Centre for Medical Parasitology, Department of International Health, Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Pradeep R. Patil
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Yang Wu
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Saeed Alharthi
- Department of Laboratory Medicine, College of Applied Medical Sciences, Umm Al-Qura University, Makkah Al-Mukarramah, Kingdom of Saudi Arabia
| | - Anja T. R. Jensen
- Centre for Medical Parasitology, Department of International Health, Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Richard Pleass
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Alister G. Craig
- Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
- * E-mail:
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109
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Large, rapidly evolving gene families are at the forefront of host-parasite interactions in Apicomplexa. Parasitology 2014; 142 Suppl 1:S57-70. [PMID: 25257746 PMCID: PMC4413850 DOI: 10.1017/s0031182014001528] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Apicomplexa is a phylum of parasitic protozoa, which includes the malaria parasite Plasmodium, amongst other species that can devastate human and animal health. The past decade has seen the release of genome sequences for many of the most important apicomplexan species, providing an excellent basis for improving our understanding of their biology. One of the key features of each genome is a unique set of large, variant gene families. Although closely related species share the same families, even different types of malaria parasite have distinct families. In some species they tend to be found at the ends of chromosomes, which may facilitate aspects of gene expression regulation and generation of sequence diversity. In others they are scattered apparently randomly across chromosomes. For some families there is evidence they are involved in antigenic variation, immune regulation and immune evasion. For others there are no known functions. Even where function is unknown these families are most often predicted to be exposed to the host, contain much sequence diversity and evolve rapidly. Based on these properties it is clear that they are at the forefront of host–parasite interactions. In this review I compare and contrast the genomic context, gene structure, gene expression, protein localization and function of these families across different species.
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110
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Fratus ASB, Cabral FJ, Fotoran WL, Medeiros MM, Carlos BC, Martha RD, da Silva LHP, Lopes SCP, Costa FTM, Wunderlich G. Antibody recognition of Plasmodium falciparum infected red blood cells by symptomatic and asymptomatic individuals in the Brazilian Amazon. Mem Inst Oswaldo Cruz 2014; 109:598-601. [PMID: 25099336 PMCID: PMC4156453 DOI: 10.1590/0074-0276140027] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 05/12/2014] [Indexed: 12/31/2022] Open
Abstract
In the Amazon Region, there is a virtual absence of severe malaria and few fatal cases of naturally occurring Plasmodium falciparum infections; this presents an intriguing and underexplored area of research. In addition to the rapid access of infected persons to effective treatment, one cause of this phenomenon might be the recognition of cytoadherent variant proteins on the infected red blood cell (IRBC) surface, including the var gene encoded P. falciparum erythrocyte membrane protein 1. In order to establish a link between cytoadherence, IRBC surface antibody recognition and the presence or absence of malaria symptoms, we phenotype-selected four Amazonian P. falciparum isolates and the laboratory strain 3D7 for their cytoadherence to CD36 and ICAM1 expressed on CHO cells. We then mapped the dominantly expressed var transcripts and tested whether antibodies from symptomatic or asymptomatic infections showed a differential recognition of the IRBC surface. As controls, the 3D7 lineages expressing severe disease-associated phenotypes were used. We showed that there was no profound difference between the frequency and intensity of antibody recognition of the IRBC-exposed P. falciparum proteins in symptomatic vs. asymptomatic infections. The 3D7 lineages, which expressed severe malaria-associated phenotypes, were strongly recognised by most, but not all plasmas, meaning that the recognition of these phenotypes is frequent in asymptomatic carriers, but is not necessarily a prerequisite to staying free of symptoms.
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Affiliation(s)
| | - Fernanda Janku Cabral
- Departamento de Parasitologia, Instituto de Ciências Biomédicas,
Universidade de São Paulo, São Paulo, SP, Brasil
| | - Wesley Luzetti Fotoran
- Departamento de Parasitologia, Instituto de Ciências Biomédicas,
Universidade de São Paulo, São Paulo, SP, Brasil
| | - Márcia Melo Medeiros
- Departamento de Parasitologia, Instituto de Ciências Biomédicas,
Universidade de São Paulo, São Paulo, SP, Brasil
| | - Bianca Cechetto Carlos
- Departamento de Parasitologia, Instituto de Ciências Biomédicas,
Universidade de São Paulo, São Paulo, SP, Brasil
| | | | | | - Stefanie Costa Pinto Lopes
- Departamento de Genética, Evolução e Bioagentes, Instituto de Biologia,
Universidade Estadual de Campinas, Campinas, SP, Brasil
| | - Fabio Trindade Maranhão Costa
- Departamento de Genética, Evolução e Bioagentes, Instituto de Biologia,
Universidade Estadual de Campinas, Campinas, SP, Brasil
| | - Gerhard Wunderlich
- Departamento de Parasitologia, Instituto de Ciências Biomédicas,
Universidade de São Paulo, São Paulo, SP, Brasil
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111
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The role of PfEMP1 adhesion domain classification in Plasmodium falciparum pathogenesis research. Mol Biochem Parasitol 2014; 195:82-7. [PMID: 25064606 DOI: 10.1016/j.molbiopara.2014.07.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Revised: 06/14/2014] [Accepted: 07/14/2014] [Indexed: 11/24/2022]
Abstract
The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family has a key role in parasite survival, transmission, and virulence. PfEMP1 are exported to the erythrocyte membrane and mediate binding of infected erythrocytes to the endothelial lining of blood vessels. This process aids parasite survival by avoiding spleen-dependent killing mechanisms, but it is associated with adhesion-based disease complications. Switching between PfEMP1 proteins enables parasites to evade host immunity and modifies parasite tropism for different microvascular beds. The PfEMP1 protein family is one of the most diverse adhesion modules in nature. This review covers PfEMP1 adhesion domain classification and the significant role it is playing in deciphering and deconvoluting P. falciparum cytoadhesion and disease.
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112
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Brancucci NMB, Witmer K, Schmid C, Voss TS. A var gene upstream element controls protein synthesis at the level of translation initiation in Plasmodium falciparum. PLoS One 2014; 9:e100183. [PMID: 24937593 PMCID: PMC4061111 DOI: 10.1371/journal.pone.0100183] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 05/23/2014] [Indexed: 01/14/2023] Open
Abstract
Clonally variant protein expression in the malaria parasite Plasmodium falciparum generates phenotypic variability and allows isogenic populations to adapt to environmental changes encountered during blood stage infection. The underlying regulatory mechanisms are best studied for the major virulence factor P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 is encoded by the multicopy var gene family and only a single variant is expressed in individual parasites, a concept known as mutual exclusion or singular gene choice. var gene activation occurs in situ and is achieved through the escape of one locus from epigenetic silencing. Singular gene choice is controlled at the level of transcription initiation and var 5' upstream (ups) sequences harbour regulatory information essential for mutually exclusive transcription as well as for the trans-generational inheritance of the var activity profile. An additional level of control has recently been identified for the var2csa gene, where an mRNA element in the 5' untranslated region (5' UTR) is involved in the reversible inhibition of translation of var2csa transcripts. Here, we extend the knowledge on post-transcriptional var gene regulation to the common upsC type. We identified a 5' UTR sequence that inhibits translation of upsC-derived mRNAs. Importantly, this 5' UTR element efficiently inhibits translation even in the context of a heterologous upstream region. Further, we found var 5' UTRs to be significantly enriched in uAUGs which are known to impair the efficiency of protein translation in other eukaryotes. Our findings suggest that regulation at the post-transcriptional level is a common feature in the control of PfEMP1 expression in P. falciparum.
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Affiliation(s)
- Nicolas M. B. Brancucci
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Kathrin Witmer
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Christoph Schmid
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Till S. Voss
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
- * E-mail:
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113
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Doritchamou J, Sossou-tchatcha S, Cottrell G, Moussiliou A, Hounton Houngbeme C, Massougbodji A, Deloron P, Ndam NT. Dynamics in the cytoadherence phenotypes of Plasmodium falciparum infected erythrocytes isolated during pregnancy. PLoS One 2014; 9:e98577. [PMID: 24905223 PMCID: PMC4048182 DOI: 10.1371/journal.pone.0098577] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 05/05/2014] [Indexed: 11/19/2022] Open
Abstract
Pregnant women become susceptible to malaria infection despite their acquired immunity to this disease from childhood. The placental sequestration of Plasmodium falciparum infected erythrocytes (IE) is the major feature of malaria during pregnancy, due to ability of these parasites to bind chondroitin sulfate A (CSA) in the placenta through the VAR2CSA protein that parasites express on the surface of IE. We collected parasites at different times of pregnancy and investigated the adhesion pattern of freshly collected isolates on the three well described host receptors (CSPG, CD36 and ICAM-1). Var genes transcription profile and VAR2CSA surface-expression were assessed in these isolates. Although adhesion of IE to CD36 and ICAM-1 was observed in some isolates, CSA-adhesion was the predominant binding feature in all isolates analyzed. Co-existence in the peripheral blood of several adhesion phenotypes in early pregnancy isolates was observed, a diversity that gradually tightens with gestational age in favour of the CSA-adhesion phenotype. Infections occurring in primigravidae were often by parasites that adhered more to CSA than those from multigravidae. Data from this study further emphasize the specificity of CSA adhesion and VAR2CSA expression by parasites responsible for pregnancy malaria, while drawing attention to the phenotypic complexity of infections occurring early in pregnancy as well as in multigravidae.
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Affiliation(s)
- Justin Doritchamou
- PRES Sorbonne Paris Cité, Faculté de Pharmacie, Université Paris Descartes, Paris, France
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France
- Centre d'Etude et de Recherche sur le paludisme associé à la Grossesse et à l'Enfance, Université d'Abomey-Calavi, Cotonou, Benin
| | - Sylvain Sossou-tchatcha
- Centre d'Etude et de Recherche sur le paludisme associé à la Grossesse et à l'Enfance, Université d'Abomey-Calavi, Cotonou, Benin
| | - Gilles Cottrell
- PRES Sorbonne Paris Cité, Faculté de Pharmacie, Université Paris Descartes, Paris, France
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France
| | - Azizath Moussiliou
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France
- ED Physiologie Physiopathologie et thérapeutique Sorbone Université, Université Pierre Marie Curie, Paris, France
| | | | - Achille Massougbodji
- Centre d'Etude et de Recherche sur le paludisme associé à la Grossesse et à l'Enfance, Université d'Abomey-Calavi, Cotonou, Benin
| | - Philippe Deloron
- PRES Sorbonne Paris Cité, Faculté de Pharmacie, Université Paris Descartes, Paris, France
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France
| | - Nicaise Tuikue Ndam
- PRES Sorbonne Paris Cité, Faculté de Pharmacie, Université Paris Descartes, Paris, France
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France
- Centre d'Etude et de Recherche sur le paludisme associé à la Grossesse et à l'Enfance, Université d'Abomey-Calavi, Cotonou, Benin
- * E-mail:
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Zhang Y, Jiang N, Chang Z, Wang H, Lu H, Wahlgren M, Chen Q. The var3 genes of Plasmodium falciparum 3D7 strain are differentially expressed in infected erythrocytes. ACTA ACUST UNITED AC 2014; 21:19. [PMID: 24759654 PMCID: PMC3996964 DOI: 10.1051/parasite/2014019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 04/08/2014] [Indexed: 11/14/2022]
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is an important virulence factor encoded by a family of 59 var genes, including 56 var genes plus 3 small var3 genes. The var genes are among the most diverse sequences in the P. falciparum genome, but the var3 genes are found conserved in most P. falciparum strains. Previous studies have been mainly focused on the typical var genes, while the biological characteristics of the var3 genes remain unknown. In this study, the three var3 genes, PF3D7_0100300, PF3D7_0600400, and PF3D7_0937600, were found to be transcribed in the erythrocytic stages of P. falciparum, with a peak in the transcription level at 16 h post-invasion, but terminated immediately after 16 h post-invasion. The encoded protein of PF3D7_0600400 could be detected in both the late trophozoite stage and schizont stage, while the encoded proteins of PF3D7_0100300 and PF3D7_0937600 could only be detected in the late trophozoite stage and schizont stage, respectively. Thus, the var3 genes of the P. falciparum 3D7 strain were differentially expressed during the erythrocytic development of the parasite.
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Affiliation(s)
- Yana Zhang
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China
| | - Ning Jiang
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China
| | - Zhiguang Chang
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China
| | - Henan Wang
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China
| | - Huijun Lu
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China
| | - Mats Wahlgren
- Department of Microbiology, Tumour- and Cellular Biology, Karolinska Institutet, S-171 71, Stockholm, Sweden
| | - Qijun Chen
- Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun 130062, PR China - Department of Microbiology, Tumour- and Cellular Biology, Karolinska Institutet, S-171 71, Stockholm, Sweden
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115
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Chan JA, Fowkes FJI, Beeson JG. Surface antigens of Plasmodium falciparum-infected erythrocytes as immune targets and malaria vaccine candidates. Cell Mol Life Sci 2014; 71:3633-57. [PMID: 24691798 PMCID: PMC4160571 DOI: 10.1007/s00018-014-1614-3] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 03/04/2014] [Accepted: 03/17/2014] [Indexed: 12/19/2022]
Abstract
Understanding the targets and mechanisms of human immunity to malaria caused by Plasmodium falciparum is crucial for advancing effective vaccines and developing tools for measuring immunity and exposure in populations. Acquired immunity to malaria predominantly targets the blood stage of infection when merozoites of Plasmodium spp. infect erythrocytes and replicate within them. During the intra-erythrocytic development of P. falciparum, numerous parasite-derived antigens are expressed on the surface of infected erythrocytes (IEs). These antigens enable P. falciparum-IEs to adhere in the vasculature and accumulate in multiple organs, which is a key process in the pathogenesis of disease. IE surface antigens, often referred to as variant surface antigens, are important targets of acquired protective immunity and include PfEMP1, RIFIN, STEVOR and SURFIN. These antigens are highly polymorphic and encoded by multigene families, which generate substantial antigenic diversity to mediate immune evasion. The most important immune target appears to be PfEMP1, which is a major ligand for vascular adhesion and sequestration of IEs. Studies are beginning to identify specific variants of PfEMP1 linked to disease pathogenesis that may be suitable for vaccine development, but overcoming antigenic diversity in PfEMP1 remains a major challenge. Much less is known about other surface antigens, or antigens on the surface of gametocyte-IEs, the effector mechanisms that mediate immunity, and how immunity is acquired and maintained over time; these are important topics for future research.
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116
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B-cell responses to pregnancy-restricted and -unrestricted Plasmodium falciparum erythrocyte membrane protein 1 antigens in Ghanaian women naturally exposed to malaria parasites. Infect Immun 2014; 82:1860-71. [PMID: 24566620 DOI: 10.1128/iai.01514-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Protective immunity to Plasmodium falciparum malaria acquired after natural exposure is largely antibody mediated. IgG-specific P. falciparum EMP1 (PfEMP1) proteins on the infected erythrocyte surface are particularly important. The transient antibody responses and the slowly acquired protective immunity probably reflect the clonal antigenic variation and allelic polymorphism of PfEMP1. However, it is likely that other immune-evasive mechanisms are also involved, such as interference with formation and maintenance of immunological memory. We measured PfEMP1-specific antibody levels by enzyme-linked immunosorbent assay (ELISA) and memory B-cell frequencies by enzyme-linked immunosorbent spot (ELISPOT) assay in a cohort of P. falciparum-exposed nonpregnant Ghanaian women. The antigens used were a VAR2CSA-type PfEMP1 (IT4VAR04) with expression restricted to parasites infecting the placenta, as well as two commonly recognized PfEMP1 proteins (HB3VAR06 and IT4VAR60) implicated in rosetting and not pregnancy restricted. This enabled, for the first time, a direct comparison in the same individuals of immune responses specific for a clinically important parasite antigen expressed only during well-defined periods (pregnancy) to responses specific for comparable antigens expressed independent of pregnancy. Our data indicate that PfEMP1-specific B-cell memory is adequately acquired even when antigen exposure is infrequent (e.g., VAR2CSA-type PfEMP1). Furthermore, immunological memory specific for VAR2CSA-type PfEMP1 can be maintained for many years without antigen reexposure and after circulating antigen-specific IgG has disappeared. The study provides evidence that natural exposure to P. falciparum leads to formation of durable B-cell immunity to clinically important PfEMP1 antigens. This has encouraging implications for current efforts to develop PfEMP1-based vaccines.
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117
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Gitau EN, Tuju J, Karanja H, Stevenson L, Requena P, Kimani E, Olotu A, Kimani D, Marsh K, Bull P, Urban BC. CD4+ T cell responses to the Plasmodium falciparum erythrocyte membrane protein 1 in children with mild malaria. THE JOURNAL OF IMMUNOLOGY 2014; 192:1753-61. [PMID: 24453249 PMCID: PMC3918862 DOI: 10.4049/jimmunol.1200547] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The immune response against the variant surface Ag Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against malaria. We have investigated the development and maintenance of CD4+ T cell responses to a small semiconserved area of the Duffy binding–like domain (DBL)α–domain of PfEMP1, the DBLα-tag. Young children were followed up longitudinally, and parasites and PBMCs were isolated from 35 patients presenting with an acute case of uncomplicated malaria. The DBLα-tag from the PfEMP1 dominantly expressed by the homologous parasite isolate was cloned and expressed as recombinant protein. The recombinant DBLα-tag was used to activate PBMCs collected from each acute episode and from an annual cross-sectional survey performed after the acute malaria episode. In this article, we report that CD4+ T cell responses to the homologous DBLα-tag were induced in 75% of the children at the time of the acute episode and in 62% of the children at the following cross-sectional survey on average 235 d later. Furthermore, children who had induced DBLα-tag–specific CD4+IL-4+ T cells at the acute episode remained episode free for longer than children who induced other types of CD4+ T cell responses. These results suggest that a wide range of DBLα-tag–specific CD4+ T cell responses were induced in children with mild malaria and, in the case of CD4+IL-4+ T cell responses, were associated with protection from clinical episodes.
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Affiliation(s)
- Evelyn N Gitau
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, 80108 Kilifi, Kenya
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118
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Sander AF, Lavstsen T, Rask TS, Lisby M, Salanti A, Fordyce SL, Jespersen JS, Carter R, Deitsch KW, Theander TG, Pedersen AG, Arnot DE. DNA secondary structures are associated with recombination in major Plasmodium falciparum variable surface antigen gene families. Nucleic Acids Res 2013; 42:2270-81. [PMID: 24253306 PMCID: PMC3936766 DOI: 10.1093/nar/gkt1174] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many bacterial, viral and parasitic pathogens undergo antigenic variation to counter host immune defense mechanisms. In Plasmodium falciparum, the most lethal of human malaria parasites, switching of var gene expression results in alternating expression of the adhesion proteins of the Plasmodium falciparum-erythrocyte membrane protein 1 class on the infected erythrocyte surface. Recombination clearly generates var diversity, but the nature and control of the genetic exchanges involved remain unclear. By experimental and bioinformatic identification of recombination events and genome-wide recombination hotspots in var genes, we show that during the parasite’s sexual stages, ectopic recombination between isogenous var paralogs occurs near low folding free energy DNA 50-mers and that these sequences are heavily concentrated at the boundaries of regions encoding individual Plasmodium falciparum-erythrocyte membrane protein 1 structural domains. The recombinogenic potential of these 50-mers is not parasite-specific because these sequences also induce recombination when transferred to the yeast Saccharomyces cerevisiae. Genetic cross data suggest that DNA secondary structures (DSS) act as inducers of recombination during DNA replication in P. falciparum sexual stages, and that these DSS-regulated genetic exchanges generate functional and diverse P. falciparum adhesion antigens. DSS-induced recombination may represent a common mechanism for optimizing the evolvability of virulence gene families in pathogens.
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Affiliation(s)
- Adam F Sander
- Centre for Medical Parasitology, Department of International Health, Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Øster Farimagsgade 5, Building 22 & 23, PO Box 2099, 1014 Copenhagen K, Denmark, Centre for Medical Parasitology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen K, Denmark, Department of Systems Biology, Center for Biological Sequence Analysis, Technical University of Denmark, 2800 Lyngby, Denmark, Department of Biology, University of Copenhagen, Ole Maaloees Vej 5, DK-2200 Copenhagen N, Denmark, Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark, Institute of Infection and Immunology Research, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, Scotland, UK and Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10065, USA
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119
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Castillo P, Menéndez C, Mayor A, Carrilho C, Ismail M, Lorenzoni C, Machungo F, Osman N, Quintó L, Romagosa C, Dobaño C, Alonso P, Ordi J. Massive Plasmodium falciparum visceral sequestration: a cause of maternal death in Africa. Clin Microbiol Infect 2013; 19:1035-41. [DOI: 10.1111/1469-0691.12068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 10/04/2012] [Accepted: 10/04/2012] [Indexed: 11/30/2022]
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120
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Abstract
The within-host dynamics of an infection with the malaria parasite Plasmodium falciparum are the result of a complex interplay between the host immune system and parasite. Continual variation of the P. falciparum erythrocyte membrane protein (PfEMP1) antigens displayed on the surface of infected red blood cells enables the parasite to evade the immune system and prolong infection. Despite the importance of antigenic variation in generating the dynamics of infection, our understanding of the mechanisms by which antigenic variation generates long-term chronic infections is still limited. We developed a model to examine the role of cross-reactivity in generating infection dynamics that are comparable to those of experimental infections. The hybrid computational model we developed is attuned to the biology of malaria by mixing discrete replication events, which mimics the synchrony of parasite replication and invasion, with continuous interaction with the immune system. Using simulations, we evaluated the dynamics of a single malaria infection over time. We then examined three major mechanisms by which the dynamics of a malaria infection can be structured: cross-reactivity of the immune response to PfEMP1, differences in parasite clearance rates, and heterogeneity in the rate at which antigens switch. The results of our simulations demonstrate that cross-reactive immune responses play a primary role in generating the dynamics observed in experimentally untreated infections and in lengthening the period of infection. Importantly, we also find that it is the primary response to the initially expressed PfEMP1, or small subset thereof, that structures the cascading cross-immune dynamics and allows for elongation of the infection.
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121
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Larremore DB, Clauset A, Buckee CO. A network approach to analyzing highly recombinant malaria parasite genes. PLoS Comput Biol 2013; 9:e1003268. [PMID: 24130474 PMCID: PMC3794903 DOI: 10.1371/journal.pcbi.1003268] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 08/23/2013] [Indexed: 11/18/2022] Open
Abstract
The var genes of the human malaria parasite Plasmodium falciparum present a challenge to population geneticists due to their extreme diversity, which is generated by high rates of recombination. These genes encode a primary antigen protein called PfEMP1, which is expressed on the surface of infected red blood cells and elicits protective immune responses. Var gene sequences are characterized by pronounced mosaicism, precluding the use of traditional phylogenetic tools that require bifurcating tree-like evolutionary relationships. We present a new method that identifies highly variable regions (HVRs), and then maps each HVR to a complex network in which each sequence is a node and two nodes are linked if they share an exact match of significant length. Here, networks of var genes that recombine freely are expected to have a uniformly random structure, but constraints on recombination will produce network communities that we identify using a stochastic block model. We validate this method on synthetic data, showing that it correctly recovers populations of constrained recombination, before applying it to the Duffy Binding Like-α (DBLα) domain of var genes. We find nine HVRs whose network communities map in distinctive ways to known DBLα classifications and clinical phenotypes. We show that the recombinational constraints of some HVRs are correlated, while others are independent. These findings suggest that this micromodular structuring facilitates independent evolutionary trajectories of neighboring mosaic regions, allowing the parasite to retain protein function while generating enormous sequence diversity. Our approach therefore offers a rigorous method for analyzing evolutionary constraints in var genes, and is also flexible enough to be easily applied more generally to any highly recombinant sequences. The human malaria parasite kills nearly 1 million people each year globally. Frequent genetic exchange between malaria parasites creates enormous genetic diversity that largely explains the lack of an effective vaccine for the disease. Traditional phylogenetic tools cannot accommodate this type of diversity, however, and rigorous analytical tools capable of making sense of gene sequences that recombine frequently are still lacking. Here, we use network techniques that have been developed by the physics and network science communities to analyze malaria parasite gene sequences, allowing us to automatically identify highly variable mosaic regions in sequence data and to derive the network of recombination events. We apply our method to seven fully-sequenced parasite genomes, and show that our method provides new insights into the complex evolutionary patterns of the parasite. Our results suggest that the structure of these sequences allows the parasite to rapidly diversify to evade immune responses while maintaining antigen structure and function.
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Affiliation(s)
- Daniel B. Larremore
- Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America
- Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, Massachusetts, United States of America
- * E-mail:
| | - Aaron Clauset
- Department of Computer Science, University of Colorado, Boulder, Colorado, United States of America
- BioFrontiers Institute, University of Colorado, Boulder, Colorado, United States of America
- Santa Fe Institute, Santa Fe, New Mexico, United States of America
| | - Caroline O. Buckee
- Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America
- Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, Massachusetts, United States of America
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122
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Kirkman LA, Lawrence EA, Deitsch KW. Malaria parasites utilize both homologous recombination and alternative end joining pathways to maintain genome integrity. Nucleic Acids Res 2013; 42:370-9. [PMID: 24089143 PMCID: PMC3874194 DOI: 10.1093/nar/gkt881] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Malaria parasites replicate asexually within their mammalian hosts as haploid cells and are subject to DNA damage from the immune response and chemotherapeutic agents that can significantly disrupt genomic integrity. Examination of the annotated genome of the parasite Plasmodium falciparum identified genes encoding core proteins required for the homologous recombination (HR) pathway for repairing DNA double-strand breaks (DSBs), but surprisingly none of the components of the canonical non-homologous end joining (C-NHEJ) pathway were identified. To better understand how malaria parasites repair DSBs and maintain genome integrity, we modified the yeast I-SceI endonuclease system to generate inducible, site-specific DSBs within the parasite’s genome. Analysis of repaired genomic DNA showed that parasites possess both a typical HR pathway resulting in gene conversion events as well as an end joining (EJ) pathway for repair of DSBs when no homologous sequence is available. The products of EJ were limited in number and identical products were observed in multiple independent experiments. The repair junctions frequently contained short insertions also found in the surrounding sequences, suggesting the possibility of a templated repair process. We propose that an alternative end-joining pathway rather than C-NHEJ, serves as a primary method for repairing DSBs in malaria parasites.
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Affiliation(s)
- Laura A Kirkman
- Department of Internal Medicine, Division of Infectious Diseases and Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10065, USA
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123
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Noble R, Christodoulou Z, Kyes S, Pinches R, Newbold CI, Recker M. The antigenic switching network of Plasmodium falciparum and its implications for the immuno-epidemiology of malaria. eLife 2013; 2:e01074. [PMID: 24062941 PMCID: PMC3778436 DOI: 10.7554/elife.01074] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 08/19/2013] [Indexed: 12/23/2022] Open
Abstract
Antigenic variation in the human malaria parasite Plasmodium falciparum involves sequential and mutually exclusive expression of members of the var multi-gene family and appears to follow a non-random pattern. In this study, using a detailed in vitro gene transcription analysis of the culture-adapted HB3 strain of P. falciparum, we show that antigenic switching is governed by a global activation hierarchy favouring short and highly diverse genes in central chromosomal location. Longer and more conserved genes, which have previously been associated with severe infection in immunologically naive hosts, are rarely activated, however, implying an in vivo fitness advantage possibly through adhesion-dependent survival rates. We further show that a gene’s activation rate is positively associated sequence diversity, which could offer important new insights into the evolution and maintenance of antigenic diversity in P. falciparum malaria. DOI:http://dx.doi.org/10.7554/eLife.01074.001 Our ability to acquire immunity to a disease depends on our immune system learning to recognise foreign molecules—called antigens—that are specific to the disease-causing virus, bacterium or parasite. However, some pathogens, such as the malaria-causing parasite Plasmodium falciparum, get around this defence through a process called antigenic variation. This involves the parasite switching between different antigens over the course of an infection, preventing the host immune system from learning to recognise them and leading to infections that last many weeks or even months. The main antigen in P. falciparum is a protein called PfEMP1, which is encoded by a family of genes called var (‘variable’). Var genes have evolved to be highly diverse, and different parasites have different repertoires of around 50–60 var genes. This ensures that there are a huge number of distinct variants of the PfEMP1 antigen available within the population, allowing the malaria parasite to maintain long-lasting infections and also to infect the same individuals again and again. Previous work has shown that the expression of var genes is not random, but it is not clear what determines which genes are expressed at any given time. Now, Noble et al. have performed a detailed investigation of antigenic switching in P. falciparum. Using clonal parasites, they closely monitored the expression of the entire var gene repertoire during many generations of parasite culture. They observed that although different cultures initially expressed distinct var genes, most of them ended up expressing two particular genes—var27 and var29—at high levels, indicating a hard-wired gene ‘activation hierarchy’. Noble et al. found that whenever the parasites switched antigens, var genes that were centrally located on chromosomes—such as var27 and var29—were more likely to be activated than those at the ends of chromosomes. Moreover, var genes that were highly diverse were more likely to be activated than more conserved genes: this is the first evidence linking var gene evolution with gene activation probabilities. Together, these factors gave rise to the proposed activation hierarchy, which favours genes optimised for immune evasion and aids their continued evolution and diversification. Further work is now needed to identify the molecular mechanisms that control antigenic switching and to determine whether these could represent new therapeutic targets for malaria. DOI:http://dx.doi.org/10.7554/eLife.01074.002
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Affiliation(s)
- Robert Noble
- Department of Zoology , University of Oxford , Oxford , United Kingdom
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124
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Bancells C, Deitsch KW. A molecular switch in the efficiency of translation reinitiation controls expression of var2csa, a gene implicated in pregnancy-associated malaria. Mol Microbiol 2013; 90:472-88. [PMID: 23980802 DOI: 10.1111/mmi.12379] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/24/2013] [Indexed: 12/16/2022]
Abstract
Plasmodium falciparum malaria parasites export the protein PfEMP1 to the surface of infected erythrocytes, enabling them to adhere to receptors in the microvasculature and thereby avoid clearance by the spleen. The gene var2csa encodes the form of PfEMP1 that binds specifically within the placenta, causing pregnancy-associated malaria, and appears to not be expressed in the absence of a placenta. We previously described an upstream open reading frame (uORF) that is responsible for repression of translation of the downstream ORF (dORF) that encodes VAR2CSA, thus keeping the gene silent when parasites infect non-pregnant individuals. To elucidate the molecular mechanism by which this repression is overcome during pregnancy, we stably transformed parasites with reporter gene constructs designed to detect switches in the efficiency of dORF translation. We found that proper regulation of switching relies on two separate components, (i) active translation of the uORF and (ii) sequence-specific characteristics of the surrounding transcript, which together control the ability of the ribosome complex to reinitiate a second round of translation and thus express VAR2CSA. These results provide the first details of a molecular switch that allows parasites take advantage of the unique niche provided by the placenta.
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Affiliation(s)
- Cristina Bancells
- Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY, 10065, USA
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125
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Berger SS, Turner L, Wang CW, Petersen JEV, Kraft M, Lusingu JPA, Mmbando B, Marquard AM, Bengtsson DBAC, Hviid L, Nielsen MA, Theander TG, Lavstsen T. Plasmodium falciparum expressing domain cassette 5 type PfEMP1 (DC5-PfEMP1) bind PECAM1. PLoS One 2013; 8:e69117. [PMID: 23874884 PMCID: PMC3706608 DOI: 10.1371/journal.pone.0069117] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Accepted: 06/07/2013] [Indexed: 11/18/2022] Open
Abstract
Members of the Plasmodium falciparum Erythrocyte Membrane protein 1 (PfEMP1) family expressed on the surface of malaria-infected erythrocytes mediate binding of the parasite to different receptors on the vascular lining. This process drives pathologies, and severe childhood malaria has been associated with the expression of particular subsets of PfEMP1 molecules. PfEMP1 are grouped into subtypes based on upstream sequences and the presence of semi-conserved PfEMP1 domain compositions named domain cassettes (DCs). Earlier studies have indicated that DC5-containing PfEMP1 (DC5-PfEMP1) are more likely to be expressed in children with severe malaria disease than in children with uncomplicated malaria, but these PfEMP1 subtypes only dominate in a relatively small proportion of the children with severe disease. In this study, we have characterised the genomic sequence characteristic for DC5, and show that two genetically different parasite lines expressing DC5-PfEMP1 bind PECAM1, and that anti-DC5-specific antibodies inhibit binding of DC5-PfEMP1-expressing parasites to transformed human bone marrow endothelial cells (TrHBMEC). We also show that antibodies against each of the four domains characteristic for DC5 react with native PfEMP1 expressed on the surface of infected erythrocytes, and that some of these antibodies are cross-reactive between the two DC5-containing PfEMP1 molecules tested. Finally, we confirm that anti-DC5 antibodies are acquired early in life by individuals living in malaria endemic areas, that individuals having high levels of these antibodies are less likely to develop febrile malaria episodes and that the antibody levels correlate positively with hemoglobin levels.
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Affiliation(s)
- Sanne S. Berger
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
- * E-mail: (SB); (TL)
| | - Louise Turner
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Christian W. Wang
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Jens E. V. Petersen
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Maria Kraft
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - John P. A. Lusingu
- National Institute for Medical Research (NIMR), Tanga Medical Research Centre, Tanga, Tanzania
| | - Bruno Mmbando
- National Institute for Medical Research (NIMR), Tanga Medical Research Centre, Tanga, Tanzania
| | - Andrea M. Marquard
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Dominique B. A. C. Bengtsson
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Lars Hviid
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Morten A. Nielsen
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Thor G. Theander
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
| | - Thomas Lavstsen
- Centre for Medical Parasitology at Department of International Health, Immunology and Microbiology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), University of Copenhagen, Copenhagen, Denmark
- * E-mail: (SB); (TL)
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Avril M, Brazier AJ, Melcher M, Sampath S, Smith JD. DC8 and DC13 var genes associated with severe malaria bind avidly to diverse endothelial cells. PLoS Pathog 2013; 9:e1003430. [PMID: 23825944 PMCID: PMC3694856 DOI: 10.1371/journal.ppat.1003430] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 04/30/2013] [Indexed: 11/25/2022] Open
Abstract
During blood stage infection, Plasmodium falciparum infected erythrocytes (IE) bind to host blood vessels. This virulence determinant enables parasites to evade spleen-dependent killing mechanisms, but paradoxically in some cases may reduce parasite fitness by killing the host. Adhesion of infected erythrocytes is mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1), a family of polymorphic adhesion proteins encoded by var genes. Whereas cerebral binding and severe malaria are associated with parasites expressing DC8 and DC13 var genes, relatively little is known about the non-brain endothelial selection on severe malaria adhesive types. In this study, we selected P. falciparum-IEs on diverse endothelial cell types and demonstrate that DC8 and DC13 var genes were consistently among the major var transcripts selected on non-brain endothelial cells (lung, heart, bone marrow). To investigate the molecular basis for this avid endothelial binding activity, recombinant proteins were expressed from the predominant upregulated DC8 transcript, IT4var19. In-depth binding comparisons revealed that multiple extracellular domains from this protein bound brain and non-brain endothelial cells, and individual domains largely did not discriminate between different endothelial cell types. Additionally, we found that recombinant DC8 and DC13 CIDR1 domains exhibited a widespread endothelial binding activity and could compete for DC8-IE binding to brain endothelial cells, suggesting they may bind the same host receptor. Our findings provide new insights into the interaction of severe malaria adhesive types and host blood vessels and support the hypothesis that parasites causing severe malaria express PfEMP1 variants with a superior ability to adhere to diverse endothelial cell types, and may therefore endow these parasites with a growth and transmission advantage.
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Affiliation(s)
- Marion Avril
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Andrew J. Brazier
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Martin Melcher
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Sowmya Sampath
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Joseph D. Smith
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
- Department of Global Health, University of Washington, Seattle, Washington, United States of America
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127
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Zilversmit MM, Chase EK, Chen DS, Awadalla P, Day KP, McVean G. Hypervariable antigen genes in malaria have ancient roots. BMC Evol Biol 2013; 13:110. [PMID: 23725540 PMCID: PMC3680017 DOI: 10.1186/1471-2148-13-110] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 05/06/2013] [Indexed: 01/07/2023] Open
Abstract
Background The var genes of the human malaria parasite Plasmodium falciparum are highly polymorphic loci coding for the erythrocyte membrane proteins 1 (PfEMP1), which are responsible for the cytoaherence of P. falciparum infected red blood cells to the human vasculature. Cytoadhesion, coupled with differential expression of var genes, contributes to virulence and allows the parasite to establish chronic infections by evading detection from the host’s immune system. Although studying genetic diversity is a major focus of recent work on the var genes, little is known about the gene family's origin and evolutionary history. Results Using a novel hidden Markov model-based approach and var sequences assembled from additional isolates and species, we are able to reveal elements of both the early evolution of the var genes as well as recent diversifying events. We compare sequences of the var gene DBLα domains from divergent isolates of P. falciparum (3D7 and HB3), and a closely-related species, Plasmodium reichenowi. We find that the gene family is equally large in P. reichenowi and P. falciparum -- with a minimum of 51 var genes in the P. reichenowi genome (compared to 61 in 3D7 and a minimum of 48 in HB3). In addition, we are able to define large, continuous blocks of homologous sequence among P. falciparum and P. reichenowi var gene DBLα domains. These results reveal that the contemporary structure of the var gene family was present before the divergence of P. falciparum and P. reichenowi, estimated to be between 2.5 to 6 million years ago. We also reveal that recombination has played an important and traceable role in both the establishment, and the maintenance, of diversity in the sequences. Conclusions Despite the remarkable diversity and rapid evolution found in these loci within and among P. falciparum populations, the basic structure of these domains and the gene family is surprisingly old and stable. Revealing a common structure as well as conserved sequence among two species also has implications for developing new primate-parasite models for studying the pathology and immunology of falciparum malaria, and for studying the population genetics of var genes and associated virulence phenotypes.
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Affiliation(s)
- Martine M Zilversmit
- National Institute of Allergy of Infectious Disease, National Institutes of Health, 12735 Twinbrook Parkway, Rockville, MD 20852, USA.
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128
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Sulistyaningsih E, Fitri LE, Löscher T, Berens-Riha N. Diversity of the var gene family of Indonesian Plasmodium falciparum isolates. Malar J 2013; 12:80. [PMID: 23446319 PMCID: PMC3614516 DOI: 10.1186/1475-2875-12-80] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2012] [Accepted: 02/19/2013] [Indexed: 11/30/2022] Open
Abstract
Background The large polymorphic protein PfEMP1 is encoded by the var gene family. PfEMP1 has been shown to play an important role as cytoadherence ligand on the surface of infected erythrocytes and thereby contributes to the distinct pathogenesis of malaria. The study explored the diversity of the DBL1α and DBL2β-C2 domains of the protein from Indonesian Plasmodium falciparum field isolates. Methods Samples of patients with severe and uncomplicated malaria from two different malaria-endemic areas in Indonesia were collected and DNA directly extracted. Dried blood on filter paper was prepared for RNA extraction. PCR amplicons were either cloned and subsequently sequenced or directly sequenced for analysis on nucleotide and amino acid level. Recently published as well as self-designed primers were used for amplification. Results Blood from eight patients was finally used for analysis. Seventy-one different sequences out of over 500 DBL1α sequenced clones were observed, resulting in an average of 8.9 different DBL1α sequences per isolate. The average DBL1α sequence similarity within isolates was similar to between isolates. Phylogenetic analysis demonstrated no clustering of sequences regarding strain or geographical origin. The DBL1α sequences were analysed by distribution of semi-conserved features (cysteine/PoLV1-4 grouping) and classified into six sequence groups. The DBL1α cys2 type was observed in all expressed sequences in vivo. Expression of certain DBL sequences implied potential involvement in the pathogenesis. As expected, the DBL2β-C2 domains showed high to moderate homology among each other. Conclusion The DBL1α domains of PfEMP1 from clinical Indonesian isolates showed high divergence among same isolates and some similarities with other Asia-Pacific strains. Further investigations of important var gene domains with a larger sample size are required to confirm with statistical significance observed associations with severe malaria in Indonesian samples.
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Affiliation(s)
- Erma Sulistyaningsih
- Department of Tropical Medicine and Infectious Diseases, University of Munich, Munich 80802, Germany.
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129
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Mitotic evolution of Plasmodium falciparum shows a stable core genome but recombination in antigen families. PLoS Genet 2013; 9:e1003293. [PMID: 23408914 PMCID: PMC3567157 DOI: 10.1371/journal.pgen.1003293] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Accepted: 12/17/2012] [Indexed: 12/30/2022] Open
Abstract
Malaria parasites elude eradication attempts both within the human host and across nations. At the individual level, parasites evade the host immune responses through antigenic variation. At the global level, parasites escape drug pressure through single nucleotide variants and gene copy amplification events conferring drug resistance. Despite their importance to global health, the rates at which these genomic alterations emerge have not been determined. We studied the complete genomes of different Plasmodium falciparum clones that had been propagated asexually over one year in the presence and absence of drug pressure. A combination of whole-genome microarray analysis and next-generation deep resequencing (totaling 14 terabases) revealed a stable core genome with only 38 novel single nucleotide variants appearing in seventeen evolved clones (avg. 5.4 per clone). In clones exposed to atovaquone, we found cytochrome b mutations as well as an amplification event encompassing the P. falciparum multidrug resistance associated protein (mrp1) on chromosome 1. We observed 18 large-scale (>1 kb on average) deletions of telomere-proximal regions encoding multigene families, involved in immune evasion (9.5×10−6 structural variants per base pair per generation). Six of these deletions were associated with chromosomal crossovers generated during mitosis. We found only minor differences in rates between genetically distinct strains and between parasites cultured in the presence or absence of drug. Using these derived mutation rates for P. falciparum (1.0–9.7×10−9 mutations per base pair per generation), we can now model the frequency at which drug or immune resistance alleles will emerge under a well-defined set of assumptions. Further, the detection of mitotic recombination events in var gene families illustrates how multigene families can arise and change over time in P. falciparum. These results will help improve our understanding of how P. falciparum evolves to evade control efforts within both the individual hosts and large populations. Malaria is one of the six diseases that together are responsible for 90% of all infectious disease deaths throughout the world. The five species of Plasmodium that cause human malaria take over 655,000 lives each year. Parasites evade the immune response through antigenic variation and develop resistance to anti-malarial drugs through genetic changes in either the drug target or genes conferring resistance. We used whole-genome sequencing and microarray techniques to study evolution in P. falciparum parasites propagated in vitro for up to 180 generations. We determined the mutation rate and found that the core genome of a single clone is stable, while the subtelomeric regions are prone to acquire structural variants. These changes occur mainly in multigene families involved in immune evasion. Our findings indicate that the parasite specifically increases the sequence variability in multigene families through mitotic recombination. This high plasticity of the parasite genome suggests that multiple haplotypes will be present in a natural infection initiated by a single parasite.
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130
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Tegar M, Purnomo H. Tea Leaves Extracted as Anti-Malaria based on Molecular Docking PLANTS. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/j.proenv.2013.02.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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131
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Bengtsson A, Joergensen L, Rask TS, Olsen RW, Andersen MA, Turner L, Theander TG, Hviid L, Higgins MK, Craig A, Brown A, Jensen ATR. A novel domain cassette identifies Plasmodium falciparum PfEMP1 proteins binding ICAM-1 and is a target of cross-reactive, adhesion-inhibitory antibodies. THE JOURNAL OF IMMUNOLOGY 2012; 190:240-9. [PMID: 23209327 DOI: 10.4049/jimmunol.1202578] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cerebral Plasmodium falciparum malaria is characterized by adhesion of infected erythrocytes (IEs) to the cerebral microvasculature. This has been linked to parasites expressing the structurally related group A subset of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of IE adhesion ligands and to IEs with affinity for ICAM-1. However, recent evidence has cast doubt on both these associations, tempering hopes of the feasibility of developing a vaccine based on ICAM-1-binding PfEMP1. In this study, we report the identification of a domain cassette (DC) present in group A var genes from six genetically distinct P. falciparum parasites. The three domains in the cassette, which we call DC4, had a high level of sequence identity and cluster together phylogenetically. Erythrocytes infected by these parasites and selected in vitro for expression of DC4 adhered specifically to ICAM-1. The ICAM-1-binding capacity of DC4 was mapped to the C-terminal third of its Duffy-binding-like β3 domain. DC4 was the target of broadly cross-reactive and adhesion-inhibitory IgG Abs, and levels of DC4-specific and adhesion-inhibitory IgG increased with age among P. falciparum-exposed children. Our study challenges earlier conclusions that group A PfEMP1 proteins are not central to ICAM-1-specific IE adhesion and support the feasibility of developing a vaccine preventing cerebral malaria by inhibiting cerebral IE sequestration.
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Affiliation(s)
- Anja Bengtsson
- Centre for Medical Parasitology, Department of International Health, Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen 1014, Denmark
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132
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Insulator-like pairing elements regulate silencing and mutually exclusive expression in the malaria parasite Plasmodium falciparum. Proc Natl Acad Sci U S A 2012. [PMID: 23197831 DOI: 10.1073/pnas.1214572109] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Plasmodium falciparum causes the deadliest form of human malaria. Its virulence is attributed to its ability to modify the infected RBC and to evade human immune attack through antigenic variation. Antigenic variation is achieved through tight regulation of antigenic switches between variable surface antigens named "P. falciparum erythrocyte membrane protein-1" encoded by the var multicopy gene family. Individual parasites express only a single var gene at a time, maintaining the remaining var genes in a transcriptionally silent state. Strict pairing between var gene promoters and a second promoter within an intron found in each var gene is required for silencing and counting of var genes by the mechanism that controls mutually exclusive expression. We have identified and characterized insulator-like DNA elements that are required for pairing var promoters and introns and thus are essential for regulating silencing and mutually exclusive expression. These elements, found in the regulatory regions of each var gene, are bound by distinct nuclear protein complexes. Any alteration in the specific, paired structure of these elements by either deletion or insertion of additional elements results in an unregulated var gene. We propose a model by which silencing and mutually exclusive expression of var genes is regulated by the precise arrangement of insulator-like DNA pairing elements.
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133
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Abstract
The goal of this case-series was to increase our understanding of some complex within and between-host infection dynamics through the creation of mathematical and computational models that are able to capture the existing host and/or parasite heterogeneity. This goal was reached through a series of research projects (regarding experimental autoimmune encephalomyelitis (EAE) in mice, Mycobacterium avium subspecies paratuberculosis infection in cattle, Eimeria acervulina infection in chicken and human malaria) that gradually build up in complexity of both the system modelled and the modelling techniques used. In this case-series, the vast majority of model components have a direct link with reality. The results have shown some detailed examples of the valuable contribution that models have in understanding infection processes. The most satisfying achievements have come from those models that were able to, in hindsight, make complicated experimental results seem obvious and logical, and where the process of building the model was as insightful as the final results. The models created in these projects help to explain a wide range of sometimes contradictory experimental results and are used to predict the effect of control measures. In addition, they generate ideas for the development of new methods of control.
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Affiliation(s)
- Maite Severins
- Department of Theoretical Epidemiology, University of Utrecht, The Netherlands.
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134
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Li B. Telomere components as potential therapeutic targets for treating microbial pathogen infections. Front Oncol 2012; 2:156. [PMID: 23125966 PMCID: PMC3485576 DOI: 10.3389/fonc.2012.00156] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Accepted: 10/16/2012] [Indexed: 01/12/2023] Open
Abstract
In a number of microbial pathogens that undergoes antigenic variation to evade the host's immune attack, genes encoding surface antigens are located at subtelomeric loci, and recent studies have revealed that telomere components play important roles in regulation of surface antigen expression in several of these pathogens, indicating that telomeres play critical roles in microbial pathogen virulence regulation. Importantly, although telomere protein components and their functions are largely conserved from protozoa to mammals, telomere protein homologs in microbial pathogens and humans have low sequence homology. Therefore, pathogen telomere components are potential drug targets for therapeutic approaches because first, most telomere proteins are essential for pathogens' survival, and second, disruption of pathogens' antigenic variation mechanism would facilitate host's immune system to clear the infection.
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Affiliation(s)
- Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University Cleveland, OH, USA
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135
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Brancucci NMB, Witmer K, Schmid CD, Flueck C, Voss TS. Identification of a cis-acting DNA-protein interaction implicated in singular var gene choice in Plasmodium falciparum. Cell Microbiol 2012; 14:1836-48. [PMID: 22891919 PMCID: PMC3549481 DOI: 10.1111/cmi.12004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 08/06/2012] [Accepted: 08/08/2012] [Indexed: 01/23/2023]
Abstract
Plasmodium falciparum is responsible for the most severe form of malaria in humans. Antigenic variation of P. falciparum erythrocyte membrane protein 1 leads to immune evasion and occurs through switches in mutually exclusive var gene transcription. The recent progress in Plasmodium epigenetics notwithstanding, the mechanisms by which singularity of var activation is achieved are unknown. Here, we employed a functional approach to dissect the role of var gene upstream regions in mutually exclusive activation. Besides identifying sequence elements involved in activation and initiation of transcription, we mapped a region downstream of the transcriptional start site that is required to maintain singular var gene choice. Activation of promoters lacking this sequence occurs no longer in competition with endogenous var genes. Within this region we pinpointed a sequence-specific DNA–protein interaction involving a cis-acting sequence motif that is conserved in the majority of var loci. These results suggest an important role for this interaction in mutually exclusive locus recognition. Our findings are furthermore consistent with a novel mechanism for the control of singular gene choice in eukaryotes. In addition to their importance in P. falciparum antigenic variation, our results may also help to explain similar processes in other systems.
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Affiliation(s)
- Nicolas M B Brancucci
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, 4051 Basel, Switzerland
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136
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Mugasa J, Qi W, Rusch S, Rottmann M, Beck HP. Genetic diversity of expressed Plasmodium falciparum var genes from Tanzanian children with severe malaria. Malar J 2012; 11:230. [PMID: 22799500 PMCID: PMC3488018 DOI: 10.1186/1475-2875-11-230] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 07/02/2012] [Indexed: 11/17/2022] Open
Abstract
Background Severe malaria has been attributed to the expression of a restricted subset of the var multi-gene family, which encodes for Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 mediates cytoadherence and sequestration of infected erythrocytes into the post-capillary venules of vital organs such as the brain, lung or placenta. var genes are highly diverse and can be classified in three major groups (ups A, B and C) and two intermediate groups (B/A and B/C) based on the genomic location, gene orientation and upstream sequences. The genetic diversity of expressed var genes in relation to severity of disease in Tanzanian children was analysed. Methods Children with defined severe (SM) and asymptomatic malaria (AM) were recruited. Full-length var mRNA was isolated and reversed transcribed into var cDNA. Subsequently, the DBL and N-terminal domains, and up-stream sequences were PCR amplified, cloned and sequenced. Sequences derived from SM and AM isolates were compared and analysed. Results The analysis confirmed that the var family is highly diverse in natural Plasmodium falciparum populations. Sequence diversity of amplified var DBL-1α and upstream regions showed minimal overlap among isolates, implying that the var gene repertoire is vast and most probably indefinite in endemic areas. var DBL-1α sequences from AM isolates were more diverse with more singletons found (p<0.05) than those from SM infections. Furthermore, few var DBL-1α sequences from SM patients were rare and restricted suggesting that certain PfEMP1 variants might induce severe disease. Conclusions The genetic sequence diversity of var genes of P. falciparum isolates from Tanzanian children is large and its relationship to disease severity has been studied. Observed differences suggest that different var genes might have fundamentally different roles in the host-parasite interaction. Further research is required to examine clear disease-associations of var gene subsets in different geographical settings. The importance of very strict clinical definitions and appropriate large control groups needs to be emphasized for future studies on disease associations of PfEMP1.
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Structural basis for the ABO blood-group dependence of Plasmodium falciparum rosetting. PLoS Pathog 2012; 8:e1002781. [PMID: 22807674 PMCID: PMC3395597 DOI: 10.1371/journal.ppat.1002781] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 05/15/2012] [Indexed: 11/29/2022] Open
Abstract
The ABO blood group influences susceptibility to severe Plasmodium falciparum malaria. Recent evidence indicates that the protective effect of group O operates by virtue of reduced rosetting of infected red blood cells (iRBCs) with uninfected RBCs. Rosetting is mediated by a subgroup of PfEMP1 adhesins, with RBC binding being assigned to the N-terminal DBL1α1 domain. Here, we identify the ABO blood group as the main receptor for VarO rosetting, with a marked preference for group A over group B, which in turn is preferred to group O RBCs. We show that recombinant NTS-DBL1α1 and NTS-DBL1α1-CIDR1γ reproduce the VarO-iRBC blood group preference and document direct binding to blood group trisaccharides by surface plasmon resonance. More detailed RBC subgroup analysis showed preferred binding to group A1, weaker binding to groups A2 and B, and least binding to groups Ax and O. The 2.8 Å resolution crystal structure of the PfEMP1-VarO Head region, NTS-DBL1α1-CIDR1γ, reveals extensive contacts between the DBL1α1 and CIDR1γ and shows that the NTS-DBL1α1 hinge region is essential for RBC binding. Computer docking of the blood group trisaccharides and subsequent site-directed mutagenesis localized the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBLα1. RBC binding involves residues that are conserved between rosette-forming PfEMP1 adhesins, opening novel opportunities for intervention against severe malaria. By deciphering the structural basis of blood group preferences in rosetting, we provide a link between ABO blood grouppolymorphisms and rosette-forming adhesins, consistent with the selective role of falciparum malaria on human genetic makeup. Rosetting, the capacity of infected red blood cells (RBCs) to bind uninfected RBCs, is a Plasmodium falciparum virulence factor. Rosetting is influenced by the ABO blood group, being less efficient with O RBCs. Although this preference may account for protection against severe malaria afforded by the O blood group, its understanding is fragmentary. We identify the ABO blood group as the main receptor for the rosetting Palo Alto VarO parasites, which display a marked preference for blood group A. Rosetting is caused by a sub-group of PfEMP1 adhesins. PfEMP1-VarO shares with other rosetting lines a specific NTS-DBL1α1-CIDR1γ Head region. We show that the Head region binds RBCs more efficiently than NTS-DBL1α1 and that ABO blood group polymorphisms influence binding of both domains. The 2.8 Å resolution crystal structure of the Head region reveals extensive contacts between the DBL1α1 and CIDR1γ domains, and shows structural features of the NTS-DBL1α1 hinge region essential for RBC binding. We localize the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBL1α1 and document direct binding of the Head region to A and B trisaccharides These findings provide novel insights into the interactions established by malaria parasites with a prominent human blood group.
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Avril M, Tripathi AK, Brazier AJ, Andisi C, Janes JH, Soma VL, Sullivan DJ, Bull PC, Stins MF, Smith JD. A restricted subset of var genes mediates adherence of Plasmodium falciparum-infected erythrocytes to brain endothelial cells. Proc Natl Acad Sci U S A 2012; 109:E1782-90. [PMID: 22619321 PMCID: PMC3387091 DOI: 10.1073/pnas.1120534109] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Cerebral malaria (CM) is a deadly complication of Plasmodium falciparum infection, but specific interactions involved in cerebral homing of infected erythrocytes (IEs) are poorly understood. In this study, P. falciparum-IEs were characterized for binding to primary human brain microvascular endothelial cells (HBMECs). Before selection, CD36 or ICAM-1-binding parasites exhibited punctate binding to a subpopulation of HBMECs and binding was CD36 dependent. Panning of IEs on HBMECs led to a more dispersed binding phenotype and the selection of three var genes, including two that encode the tandem domain cassette 8 (DC8) and were non-CD36 binders. Multiple domains in the DC8 cassette bound to brain endothelium and the cysteine-rich interdomain region 1 inhibited binding of P. falciparum-IEs by 50%, highlighting a key role for the DC8 cassette in cerebral binding. It is mysterious how deadly binding variants are maintained in the parasite population. Clonal parasite lines expressing the two brain-adherent DC8-var genes did not bind to any of the known microvascular receptors, indicating unique receptors are involved in cerebral binding. They could also adhere to brain, lung, dermis, and heart endothelial cells, suggesting cerebral binding variants may have alternative sequestration sites. Furthermore, young African children with CM or nonsevere control cases had antibodies to HBMEC-selected parasites, indicating they had been exposed to related variants during childhood infections. This analysis shows that specific P. falciparum erythrocyte membrane protein 1 types are linked to cerebral binding and suggests a potential mechanism by which individuals may build up immunity to severe disease, in the absence of CM.
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Affiliation(s)
- Marion Avril
- Seattle Biomedical Research Institute, Seattle, WA 98109-5219
| | - Abhai K. Tripathi
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | | | - Cheryl Andisi
- Kenya Medical Research Institute–Wellcome Trust Research Programme, 80108, Kilifi, Kenya
| | - Joel H. Janes
- Seattle Biomedical Research Institute, Seattle, WA 98109-5219
- Department of Global Health, University of Washington, Seattle, WA 98109
| | - Vijaya L. Soma
- Seattle Biomedical Research Institute, Seattle, WA 98109-5219
| | - David J. Sullivan
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Peter C. Bull
- Kenya Medical Research Institute–Wellcome Trust Research Programme, 80108, Kilifi, Kenya
- Nuffield Department of Clinical Medicine, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, United Kingdom; and
| | - Monique F. Stins
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD 21287
| | - Joseph D. Smith
- Seattle Biomedical Research Institute, Seattle, WA 98109-5219
- Department of Global Health, University of Washington, Seattle, WA 98109
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140
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Plasmodium falciparum erythrocyte membrane protein 1 domain cassettes 8 and 13 are associated with severe malaria in children. Proc Natl Acad Sci U S A 2012; 109:E1791-800. [PMID: 22619319 DOI: 10.1073/pnas.1120455109] [Citation(s) in RCA: 202] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The clinical outcome of Plasmodium falciparum infections ranges from asymptomatic parasitemia to severe malaria syndromes associated with high mortality. The virulence of P. falciparum infections is associated with the type of P. falciparum erythrocyte membrane protein 1 (PfEMP1) expressed on the surface of infected erythrocytes to anchor these to the vascular lining. Although var2csa, the var gene encoding the PfEMP1 associated with placental malaria, was discovered in 2003, the identification of the var/PfEMP1 variants associated with severe malaria in children has remained elusive. To identify var/PfEMP1 variants associated with severe disease outcome, we compared var transcript levels in parasites from 88 children with severe malaria and 40 children admitted to the hospital with uncomplicated malaria. Transcript analysis was performed by RT-quantitative PCR using a set of 42 primer pairs amplifying var subtype-specific loci covering most var/PfEMP1 subtypes. In addition, we characterized the near-full-length sequence of the most prominently expressed var genes in three patients diagnosed with severe anemia and/or cerebral malaria. The combined analysis showed that severe malaria syndromes, including severe anemia and cerebral malaria, are associated with high transcript levels of PfEMP1 domain cassette 8-encoding var genes. Transcript levels of group A var genes, including genes encoding domain cassette 13, were also significantly higher in patients with severe syndromes compared with those with uncomplicated malaria. This study specifies the var/PfEMP1 types expressed in severe malaria in children, and thereby provides unique targets for future efforts to prevent and treat severe malaria infections.
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Wang CW, Lavstsen T, Bengtsson DC, Magistrado PA, Berger SS, Marquard AM, Alifrangis M, Lusingu JP, Theander TG, Turner L. Evidence for in vitro and in vivo expression of the conserved VAR3 (type 3) plasmodium falciparum erythrocyte membrane protein 1. Malar J 2012; 11:129. [PMID: 22533832 PMCID: PMC3407477 DOI: 10.1186/1475-2875-11-129] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2012] [Accepted: 04/25/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Members of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion antigen family are major contributors to the pathogenesis of P. falciparum malaria infections. The PfEMP1-encoding var genes are among the most diverse sequences in nature, but three genes, var1, var2csa and var3 are found conserved in most parasite genomes. The most severe forms of malaria disease are caused by parasites expressing a subset of antigenically conserved PfEMP1 variants. Thus the ubiquitous and conserved VAR3 PfEMP1 is of particular interest to the research field. Evidence of VAR3 expression on the infected erythrocyte surface has never been presented, and var3 genes have been proposed to be transcribed and expressed differently from the rest of the var gene family members. METHODS In this study, parasites expressing VAR3 PfEMP1 were generated using anti-VAR3 antibodies and the var transcript and PfEMP1 expression profiles of the generated parasites were investigated. The IgG reactivity by plasma from children living in malaria-endemic Tanzania was tested to parasites and recombinant VAR3 protein. Parasites from hospitalized children were isolated and the transcript level of var3 was investigated. RESULTS Var3 is transcribed and its protein product expressed on the surface of infected erythrocytes. The VAR3-expressing parasites were better recognized by children´s IgG than a parasite line expressing a Group B var gene. Two in 130 children showed increased recognition of parasites expressing VAR3 and to the recombinant VAR3 protein after a malaria episode and the isolated parasites showed high levels of var3 transcripts. CONCLUSIONS Collectively, the presented data suggest that var3 is transcribed and its protein product expressed on the surface of infected erythrocytes in the same manner as seen for other var genes both in vitro and in vivo. Only very few children exhibit seroconversion to VAR3 following a malaria episode requiring hospitalization, supporting the previous conclusion drawn from var3 transcript analysis of parasites collected from children hospitalized with malaria, that VAR3 is not associated with severe anaemia or cerebral malaria syndromes in children.
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Affiliation(s)
- Christian W Wang
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Thomas Lavstsen
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Dominique C Bengtsson
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Pamela A Magistrado
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Sanne S Berger
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Andrea M Marquard
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Michael Alifrangis
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - John P Lusingu
- National Institute for Medical Research (NIMR), Tanga Medical Research Centre, Tanga, Tanzania
| | - Thor G Theander
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
| | - Louise Turner
- Centre for Medical Parasitology at Department of International Health, Immunology, and Microbiology, University of Copenhagen and at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), 1014, Copenhagen, Denmark
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142
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Antigenic variation and the generation of diversity in malaria parasites. Curr Opin Microbiol 2012; 15:456-62. [PMID: 22503815 DOI: 10.1016/j.mib.2012.03.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Accepted: 03/08/2012] [Indexed: 11/27/2022]
Abstract
Investigations into the genetic basis underlying antigenic variation in malaria parasites have primarily described transcriptional regulation of the large, multi-copy gene families that encode red cell surface antigens. In particular, extensive alterations to chromatin structure and subnuclear localization have been shown to play key roles in mutually exclusive expression, gene silencing and activation, and epigenetic memory. However the mechanisms responsible for the generation of sequence diversity within these gene families, a characteristic that is equally important for a parasite's ability to avoid the host's immune response, remains poorly understood in malaria. Recent work in model organisms suggests that the mechanisms controlling gene activation and silencing might also contribute to preferential recombination between antigen encoding genes, thus linking these two key processes.
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143
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Buckee CO, Recker M. Evolution of the multi-domain structures of virulence genes in the human malaria parasite, Plasmodium falciparum. PLoS Comput Biol 2012; 8:e1002451. [PMID: 22511852 PMCID: PMC3325180 DOI: 10.1371/journal.pcbi.1002451] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Accepted: 02/10/2012] [Indexed: 11/30/2022] Open
Abstract
The var gene family of Plasmodium falciparum encodes the immunodominant variant surface antigens PfEMP1. These highly polymorphic proteins are important virulence factors that mediate cytoadhesion to a variety of host tissues, causing sequestration of parasitized red blood cells in vital organs, including the brain or placenta. Acquisition of variant-specific antibodies correlates with protection against severe malarial infections; however, understanding the relationship between gene expression and infection outcome is complicated by the modular genetic architectures of var genes that encode varying numbers of antigenic domains with differential binding specificities. By analyzing the domain architectures of fully sequenced var gene repertoires we reveal a significant, non-random association between the number of domains comprising a var gene and their sequence conservation. As such, var genes can be grouped into those that are short and diverse and genes that are long and conserved, suggesting gene length as an important characteristic in the classification of var genes. We then use an evolutionary framework to demonstrate how the same evolutionary forces acting on the level of an individual gene may have also shaped the parasite's gene repertoire. The observed associations between sequence conservation, gene architecture and repertoire structure can thus be explained by a trade-off between optimizing within-host fitness and minimizing between-host immune selection pressure. Our results demonstrate how simple evolutionary mechanisms can explain var gene structuring on multiple levels and have important implications for understanding the multifaceted epidemiology of P. falciparum malaria. Plasmodium falciparum, the most severe of the human malarias, contains within its genome a family of ∼60 var genes which play an important role in disease pathology and maintenance of chronic infections. Var genes have a modular genetic architecture and encode varying numbers of binding domains with specific preferences to a range of host tissues. Given the availability of host receptors for binding and the immunogenic properties of each domain it is not clear why genes encode multiple domains at once and how these are structured within each parasite's antigenic repertoire. Here we investigate the domain architecture of these important virulence genes and highlight an evolutionary trade-off between maintaining within-host fitness and optimizing between-host transmission success as an important driver in structuring var genes and var gene repertoires alike.
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Affiliation(s)
- Caroline O. Buckee
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Mario Recker
- Department of Zoology, University of Oxford, Oxford, United Kingdom
- * E-mail:
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144
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Warimwe GM, Fegan G, Musyoki JN, Newton CR, Opiyo M, Githinji G, Andisi C, Menza F, Kitsao B, Marsh K, Bull PC. Prognostic indicators of life-threatening malaria are associated with distinct parasite variant antigen profiles. Sci Transl Med 2012; 4:129ra45. [PMID: 22496547 PMCID: PMC3491874 DOI: 10.1126/scitranslmed.3003247] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
PfEMP1 is a family of cytoadhesive surface antigens expressed on erythrocytes infected with Plasmodium falciparum, the parasite that causes the most severe form of malaria. These surface antigens play a role in immune evasion and are thought to contribute to the pathogenesis of the malaria parasite. Previous studies have suggested a role for a specific subset of PfEMP1 called "group A" in severe malaria. To explore the role of group A PfEMP1 in disease, we measured the expression of the var genes that encode them in parasites from clinical isolates collected from children suffering from malaria. We also looked at the ability of these clinical isolates to induce rosetting of erythrocytes, which indicates a cytoadhesion phenotype that is thought to be important in pathogenesis. These two sets of data were correlated with the presence of two life-threatening manifestations of severe malaria in the children: impaired consciousness and respiratory distress. Using regression analysis, we show that marked rosetting was associated with respiratory distress, whereas elevated expression of group A-like var genes without elevated rosetting was associated with impaired consciousness. The results suggest that manifestations of malarial disease may reflect the distribution of cytoadhesion phenotypes expressed by the infecting parasite population.
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Affiliation(s)
- George M. Warimwe
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Gregory Fegan
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
- Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Oxford, OX3 9DU, UK
| | - Jennifer N. Musyoki
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Charles R.J.C. Newton
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Michael Opiyo
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - George Githinji
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Cheryl Andisi
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Francis Menza
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Barnes Kitsao
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
| | - Kevin Marsh
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
- Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Oxford, OX3 9DU, UK
| | - Peter C. Bull
- Kenya Medical Research Institute-Wellcome Trust Research Programme, P.O. Box 230-80108 Kilifi, Kenya
- Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Oxford, OX3 9DU, UK
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145
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Lawton J, Brugat T, Yan YX, Reid AJ, Böhme U, Otto TD, Pain A, Jackson A, Berriman M, Cunningham D, Preiser P, Langhorne J. Characterization and gene expression analysis of the cir multi-gene family of Plasmodium chabaudi chabaudi (AS). BMC Genomics 2012; 13:125. [PMID: 22458863 PMCID: PMC3384456 DOI: 10.1186/1471-2164-13-125] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Accepted: 03/29/2012] [Indexed: 11/13/2022] Open
Abstract
Background The pir genes comprise the largest multi-gene family in Plasmodium, with members found in P. vivax, P. knowlesi and the rodent malaria species. Despite comprising up to 5% of the genome, little is known about the functions of the proteins encoded by pir genes. P. chabaudi causes chronic infection in mice, which may be due to antigenic variation. In this model, pir genes are called cirs and may be involved in this mechanism, allowing evasion of host immune responses. In order to fully understand the role(s) of CIR proteins during P. chabaudi infection, a detailed characterization of the cir gene family was required. Results The cir repertoire was annotated and a detailed bioinformatic characterization of the encoded CIR proteins was performed. Two major sub-families were identified, which have been named A and B. Members of each sub-family displayed different amino acid motifs, and were thus predicted to have undergone functional divergence. In addition, the expression of the entire cir repertoire was analyzed via RNA sequencing and microarray. Up to 40% of the cir gene repertoire was expressed in the parasite population during infection, and dominant cir transcripts could be identified. In addition, some differences were observed in the pattern of expression between the cir subgroups at the peak of P. chabaudi infection. Finally, specific cir genes were expressed at different time points during asexual blood stages. Conclusions In conclusion, the large number of cir genes and their expression throughout the intraerythrocytic cycle of development indicates that CIR proteins are likely to be important for parasite survival. In particular, the detection of dominant cir transcripts at the peak of P. chabaudi infection supports the idea that CIR proteins are expressed, and could perform important functions in the biology of this parasite. Further application of the methodologies described here may allow the elucidation of CIR sub-family A and B protein functions, including their contribution to antigenic variation and immune evasion.
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Affiliation(s)
- Jennifer Lawton
- Division of Parasitology, MRC National Institute for Medical Research, London, UK
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146
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Fastman Y, Noble R, Recker M, Dzikowski R. Erasing the epigenetic memory and beginning to switch--the onset of antigenic switching of var genes in Plasmodium falciparum. PLoS One 2012; 7:e34168. [PMID: 22461905 PMCID: PMC3312910 DOI: 10.1371/journal.pone.0034168] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Accepted: 02/23/2012] [Indexed: 11/19/2022] Open
Abstract
Antigenic variation in Plasmodium falciparum is regulated by transcriptional switches among members of the var gene family, each expressed in a mutually exclusive manner and encoding a different variant of the surface antigens collectively named PfEMP1. Antigenic switching starts when the first merozoites egress from the liver and begin their asexual proliferation within red blood cells. By erasing the epigenetic memory we created parasites with no var background, similar to merozoites that egress from the liver where no var gene is expressed. Creating a null-var background enabled us to investigate the onset of antigenic switches at the early phase of infection. At the onset of switching, var transcription pattern is heterogeneous with numerous genes transcribed at low levels including upsA vars, a subtype that was implicated in severe malaria, which are rarely activated in growing cultures. Analysis of subsequent in vitro switches shows that the probability of a gene to turn on or off is not associated with its chromosomal position or promoter type per se but on intrinsic properties of each gene. We concluded that var switching is determined by gene specific associated switch rates rather than general promoter type or locus associated switch rates. In addition, we show that fine tuned reduction in var transcription increases their switch rate, indicating that transcriptional perturbation can alter antigenic switching.
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Affiliation(s)
- Yair Fastman
- Department of Microbiology & Molecular Genetics, The Kuvin Center for the Study of Infectious and Tropical Diseases, IMRIC, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Robert Noble
- Department of Zoology, University of Oxford, Oxford, United Kingdom
| | - Mario Recker
- Department of Zoology, University of Oxford, Oxford, United Kingdom
| | - Ron Dzikowski
- Department of Microbiology & Molecular Genetics, The Kuvin Center for the Study of Infectious and Tropical Diseases, IMRIC, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
- * E-mail:
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147
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Merrick CJ, Huttenhower C, Buckee C, Amambua-Ngwa A, Gomez-Escobar N, Walther M, Conway DJ, Duraisingh MT. Epigenetic dysregulation of virulence gene expression in severe Plasmodium falciparum malaria. J Infect Dis 2012; 205:1593-600. [PMID: 22448008 DOI: 10.1093/infdis/jis239] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Chronic infections with the human malaria parasite Plasmodium falciparum depend on antigenic variation. P. falciparum erythrocyte membrane protein 1 (PfEMP1), the major erythrocyte surface antigen mediating parasite sequestration in the microvasculature, is encoded in parasites by a highly diverse family of var genes. Antigenic switching is mediated by clonal variation in var expression, and recent in vitro studies have demonstrated a role for epigenetic processes in var regulation. Expression of particular PfEMP1 variants may result in parasite enrichment in different tissues, a factor in the development of severe disease. Here, we study in vivo human infections and provide evidence that infection-induced stress responses in the host can modify PfEMP1 expression via the perturbation of epigenetic mechanisms. Our work suggests that severe disease may not be the direct result of an adaptive virulence strategy to maximize parasite survival but that it may indicate a loss of control of the carefully regulated process of antigenic switching that maintains chronic infections.
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148
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Witmer K, Schmid CD, Brancucci NMB, Luah YH, Preiser PR, Bozdech Z, Voss TS. Analysis of subtelomeric virulence gene families in Plasmodium falciparum by comparative transcriptional profiling. Mol Microbiol 2012; 84:243-59. [PMID: 22435676 PMCID: PMC3491689 DOI: 10.1111/j.1365-2958.2012.08019.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The Plasmodium falciparum genome is equipped with several subtelomeric gene families that are implicated in parasite virulence and immune evasion. Members of these families are uniformly positioned within heterochromatic domains and are thus subject to variegated expression. The best-studied example is that of the var family encoding the major parasite virulence factor P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 undergoes antigenic variation through switches in mutually exclusive var gene transcription. var promoters function as crucial regulatory elements in the underlying epigenetic control strategy. Here, we analysed promoters of upsA, upsB and upsC var, rifA1-type rif, stevor, phist and pfmc-2tm genes and investigated their role in endogenous gene transcription by comparative genome-wide expression profiling of transgenic parasite lines. We find that the three major var promoter types are functionally equal and play an essential role in singular gene choice. Unlike var promoters, promoters of non-var families are not silenced by default, and transcription of non-var families is not subject to the same mode of mutually exclusive transcription as has been observed for var genes. Our findings identified a differential logic in the regulation of var and other subtelomeric virulence gene families, which will have important implications for our understanding and future analyses of phenotypic variation in malaria parasites.
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Affiliation(s)
- Kathrin Witmer
- Swiss Tropical and Public Health Institute, 4051 Basel, Switzerland
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149
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Oleinikov AV, Voronkova VV, Frye IT, Amos E, Morrison R, Fried M, Duffy PE. A plasma survey using 38 PfEMP1 domains reveals frequent recognition of the Plasmodium falciparum antigen VAR2CSA among young Tanzanian children. PLoS One 2012; 7:e31011. [PMID: 22295123 PMCID: PMC3266279 DOI: 10.1371/journal.pone.0031011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2011] [Accepted: 12/30/2011] [Indexed: 11/29/2022] Open
Abstract
PfEMP1 proteins comprise a family of variant antigens that appear on the surface of P. falciparum-infected erythrocytes and bind to multiple host receptors. Using a mammalian expression system and BioPlex technology, we developed an array of 24 protein constructs representing 38 PfEMP1 domains for high throughput analyses of receptor binding as well as total and functional antibody responses. We analyzed the reactivity of 561 plasma samples from 378 young Tanzanian children followed up to maximum 192 weeks of life in a longitudinal birth cohort. Surprisingly, reactivity to the DBL5 domain of VAR2CSA, a pregnancy malaria vaccine candidate, was most common, and the prevalence of reactivity was stable throughout early childhood. Reactivity to all other PfEMP1 constructs increased with age. Antibodies to the DBL2βC2PF11_0521 domain, measured as plasma reactivity or plasma inhibition of ICAM1 binding, predicted reduced risk of hospitalization for severe or moderately severe malaria. These data suggest a role for VAR2CSA in childhood malaria and implicate DBL2βC2PF11_0521 in protective immunity.
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Affiliation(s)
- Andrew V Oleinikov
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America.
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150
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Gitau EN, Tuju J, Stevenson L, Kimani E, Karanja H, Marsh K, Bull PC, Urban BC. T-cell responses to the DBLα-tag, a short semi-conserved region of the Plasmodium falciparum membrane erythrocyte protein 1. PLoS One 2012; 7:e30095. [PMID: 22272280 PMCID: PMC3260199 DOI: 10.1371/journal.pone.0030095] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Accepted: 12/09/2011] [Indexed: 11/25/2022] Open
Abstract
The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a variant surface antigen expressed on mature forms of infected erythrocytes. It is considered an important target of naturally acquired immunity. Despite its extreme sequence heterogeneity, variants of PfEMP1 can be stratified into distinct groups. Group A PfEMP1 have been independently associated with low host immunity and severe disease in several studies and are now of potential interest as vaccine candidates. Although antigen-specific antibodies are considered the main effector mechanism in immunity to malaria, the induction of efficient and long-lasting antibody responses requires CD4+ T-cell help. To date, very little is known about CD4+ T-cell responses to PfEMP1 expressed on clinical isolates. The DBLα-tag is a small region from the DBLα-domain of PfEMP1 that can be amplified with universal primers and is accessible in clinical parasite isolates. We identified the dominant expressed PfEMP1 in 41 individual clinical parasite isolates and expressed the corresponding DBLα-tag as recombinant antigen. Individual DBLα-tags were then used to activate CD4+ T-cells from acute and convalescent blood samples in children who were infected with the respective clinical parasite isolate. Here we show that CD4+ T-cell responses to the homologous DBLα-tag were induced in almost all children during acute malaria and maintained in some for 4 months. Children infected with parasites that dominantly expressed group A-like PfEMP1 were more likely to maintain antigen-specific IFNγ-producing CD4+ T-cells than children infected with parasites dominantly expressing other PfEMP1. These results suggest that group A-like PfEMP1 may induce long-lasting effector memory T-cells that might be able to provide rapid help to variant-specific B cells. Furthermore, a number of children induced CD4+ T-cell responses to heterologous DBLα-tags, suggesting that CD4+ T-cells may recognise shared epitopes between several DBLα-tags.
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Affiliation(s)
- Evelyn N. Gitau
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
- Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - James Tuju
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
| | - Liz Stevenson
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
| | - Eva Kimani
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
| | - Henry Karanja
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
| | - Kevin Marsh
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
- Centre for Tropical Medicine, Nuffield Department of Internal Medicine, Oxford University, Oxford, United Kingdom
| | - Peter C. Bull
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
- Centre for Tropical Medicine, Nuffield Department of Internal Medicine, Oxford University, Oxford, United Kingdom
| | - Britta C. Urban
- KEMRI-Wellcome Trust Collaborative Programme, Centre for Geographic Medicine Coast, Kilifi, Kenya
- Liverpool School of Tropical Medicine, Liverpool, United Kingdom
- * E-mail:
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