651
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Saul A. The role of variant surface antigens on malaria-infected red blood cells. PARASITOLOGY TODAY (PERSONAL ED.) 1999; 15:455-7. [PMID: 10511688 DOI: 10.1016/s0169-4758(99)01534-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
It has been proposed that the primary role of variant antigens appearing on the surface of red blood cells infected with malaria parasites is to mediate cytoadherence, and that the antigenic variation they display is an adaptation to avoid immune attack. Here, Allan Saul proposes that their role is the opposite: that their primary purpose is to generate an immune response, which regulates their growth and thereby establishes a chronic infection, and that the role of cytoadherence is to ensure that parasites failing to express this flag to the immune system are destroyed by the spleen.
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Affiliation(s)
- A Saul
- Australian Centre for International and Tropical Health and Nutrition, The Queensland Institute of Medical Research, Brisbane Qld 4029, Australia.
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652
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Buffet PA, Gamain B, Scheidig C, Baruch D, Smith JD, Hernandez-Rivas R, Pouvelle B, Oishi S, Fujii N, Fusai T, Parzy D, Miller LH, Gysin J, Scherf A. Plasmodium falciparum domain mediating adhesion to chondroitin sulfate A: a receptor for human placental infection. Proc Natl Acad Sci U S A 1999; 96:12743-8. [PMID: 10535993 PMCID: PMC23079 DOI: 10.1073/pnas.96.22.12743] [Citation(s) in RCA: 176] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Malaria during the first pregnancy causes a high rate of fetal and neonatal death. The decreasing susceptibility during subsequent pregnancies correlates with acquisition of antibodies that block binding of infected red cells to chondroitin sulfate A (CSA), a receptor for parasites in the placenta. Here we identify a domain within a particular Plasmodium falciparum erythrocyte membrane protein 1 that binds CSA. We cloned a var gene expressed in CSA-binding parasitized red blood cells (PRBCs). The gene had eight receptor-like domains, each of which was expressed on the surface of Chinese hamster ovary cells and was tested for CSA binding. CSA linked to biotin used as a probe demonstrated that two Duffy-binding-like (DBL) domains (DBL3 and DBL7) bound CSA. DBL7, but not DBL3, also bound chondroitin sulfate C (CSC) linked to biotin, a negatively charged sugar that does not support PRBC adhesion. Furthermore, CSA, but not CSC, blocked the interaction with DBL3; both CSA and CSC blocked binding to DBL7. Thus, only the DBL3 domain displays the same binding specificity as PRBCs. Because protective antibodies present after pregnancy block binding to CSA of parasites from different parts of the world, DBL-3, although variant, may induce cross-reactive immunity that will protect pregnant women and their fetuses.
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Affiliation(s)
- P A Buffet
- Unité de Biologie des Interactions Hôte-Parasite, Centre National de la Recherche Scientifique/Unité de Recherche Associée 1960, Institut Pasteur, 75724 Paris, France
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653
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Kaneko O, Soubes SC, Miller LH. Plasmodium falciparum: invasion of Aotus monkey red blood cells and adaptation to Aotus monkeys. Exp Parasitol 1999; 93:116-9. [PMID: 10502476 DOI: 10.1006/expr.1999.4441] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- O Kaneko
- Malaria Cell Biology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Room B1-37, 4 Center Drive, Bethesda, Maryland, 20892-0425, USA
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654
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Kyes SA, Rowe JA, Kriek N, Newbold CI. Rifins: a second family of clonally variant proteins expressed on the surface of red cells infected with Plasmodium falciparum. Proc Natl Acad Sci U S A 1999; 96:9333-8. [PMID: 10430943 PMCID: PMC17783 DOI: 10.1073/pnas.96.16.9333] [Citation(s) in RCA: 250] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many pathogens evade the host immune response or adapt to their environment by expressing surface proteins that undergo rapid switching. In the case of Plasmodium falciparum, products of a multigene family known as var are expressed on the surface of infected red cells, where they undergo clonal antigenic variation and contribute to malaria pathogenesis by mediating adhesion to a variety of host endothelial receptors and to uninfected red blood cells by forming rosettes. Herein we show that a second gene family, rif, which is associated with var at subtelomeric sites in the genome, encodes clonally variant proteins (rifins) that are expressed on the infected red cell surface. Their high copy number, sequence variability, and red cell surface location indicate an important role for rifins in malaria host-parasite interaction.
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Affiliation(s)
- S A Kyes
- Molecular Parasitology Group, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, United Kingdom
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655
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Silamut K, Phu NH, Whitty C, Turner GD, Louwrier K, Mai NT, Simpson JA, Hien TT, White NJ. A quantitative analysis of the microvascular sequestration of malaria parasites in the human brain. THE AMERICAN JOURNAL OF PATHOLOGY 1999; 155:395-410. [PMID: 10433933 PMCID: PMC1866852 DOI: 10.1016/s0002-9440(10)65136-x] [Citation(s) in RCA: 289] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Microvascular sequestration was assessed in the brains of 50 Thai and Vietnamese patients who died from severe malaria (Plasmodium falciparum, 49; P. vivax, 1). Malaria parasites were sequestered in 46 cases; in 3 intravascular malaria pigment but no parasites were evident; and in the P. vivax case there was no sequestration. Cerebrovascular endothelial expression of the putative cytoadherence receptors ICAM-1, VCAM-1, E-selectin, and chondroitin sulfate and also HLA class II was increased. The median (range) ratio of cerebral to peripheral blood parasitemia was 40 (1.8 to 1500). Within the same brain different vessels had discrete but different populations of parasites, indicating that the adhesion characteristics of cerebrovascular endothelium change asynchronously during malaria and also that significant recirculation of parasitized erythrocytes following sequestration is unlikely. The median (range) ratio of schizonts to trophozoites (0.15:1; 0.0 to 11.7) was significantly lower than predicted from the parasite life cycle (P < 0.001). Antimalarial treatment arrests development at the trophozoite stages which remain sequestered in the brain. There were significantly more ring form parasites (age < 26 hours) in the cerebral microvasculature (median range: 19%; 0-90%) than expected from free mixing of these cells in the systemic circulation (median range ring parasitemia: 1.8%; 0-36.2%). All developmental stages of P. falciparum are sequestered in the brain in severe malaria.
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Affiliation(s)
- K Silamut
- Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
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656
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O'Connor RM, Long JA, Allred DR. Cytoadherence of Babesia bovis-infected erythrocytes to bovine brain capillary endothelial cells provides an in vitro model for sequestration. Infect Immun 1999; 67:3921-8. [PMID: 10417157 PMCID: PMC96673 DOI: 10.1128/iai.67.8.3921-3928.1999] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Babesia bovis, an intraerythrocytic parasite of cattle, is sequestered in the host microvasculature, a behavior associated with cerebral and vascular complications of this disease. Despite the importance of this behavior to disease etiology, the underlying mechanisms have not yet been investigated. To study the components involved in sequestration, B. bovis parasites that induce adhesion of the infected erythrocytes (IRBCs) to bovine brain capillary endothelial cells (BBEC) in vitro were isolated. Two clonal lines, CD7(A+I+) and CE11(A+I-), were derived from a cytoadherent, monoclonal antibody 4D9.1G1-reactive parasite population. This antibody recognizes a variant, surface-exposed epitope of the variant erythrocyte surface antigen 1 (VESA1) of B. bovis IRBCs. Both clonal lines were cytoadhesive to BBEC and two other bovine endothelial cell lines but not to COS7 cells, FBK-4 cells, C32 melanoma cells, or bovine brain pericytes. By transmission electron microscopy, IRBCs were observed to bind to BBEC via the knobby protrusions on the IRBC surface, indicating involvement of components associated with these structures. Inhibition of protein export in intact, trypsinized IRBCs ablated both erythrocyte surface reexpression of parasite protein and cytoadhesion. IRBCs allowed to recover surface antigen expression regained the ability to bind endothelial cells, demonstrating that parasite protein export is required for cytoadhesion. We propose the use of this assay as an in vitro model to study the components involved in B. bovis cytoadherence and sequestration.
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Affiliation(s)
- R M O'Connor
- Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA
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657
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Beeson JG, Brown GV, Molyneux ME, Mhango C, Dzinjalamala F, Rogerson SJ. Plasmodium falciparum isolates from infected pregnant women and children are associated with distinct adhesive and antigenic properties. J Infect Dis 1999; 180:464-72. [PMID: 10395863 PMCID: PMC2613477 DOI: 10.1086/314899] [Citation(s) in RCA: 198] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Plasmodium falciparum malaria during pregnancy is an important cause of maternal and infant morbidity and mortality. Accumulation of large numbers of P. falciparum-infected erythrocytes in the maternal blood spaces of the placenta may be mediated by adhesion of infected erythrocytes to molecules presented on the syncytiotrophoblast surface. In this study, isolates from placentas and peripheral blood of infected pregnant women and from children were tested for binding to purified receptors and for agglutination with adult sera. Results suggest that adhesion to chondroitin sulfate A may be involved in placental parasite sequestration in most cases, but other factors are also likely to be important. Agglutination assay results suggest that parasites infecting pregnant women are antigenically distinct from those common in childhood disease. The prevalence of agglutinating antibodies to pregnancy isolates was generally low, but it was highest in multigravidae who are likely to have had the greatest exposure.
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Affiliation(s)
- J G Beeson
- The Walter and Eliza Hall Institute of Medical Research, Post Office, Royal Melbourne Hospital, Victoria, Australia.
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658
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Giha HA, Staalsoe T, Dodoo D, Elhassan IM, Roper C, Satti GM, Arnot DE, Theander TG, Hviid L. Nine-year longitudinal study of antibodies to variant antigens on the surface of Plasmodium falciparum-infected erythrocytes. Infect Immun 1999; 67:4092-8. [PMID: 10417178 PMCID: PMC96708 DOI: 10.1128/iai.67.8.4092-4098.1999] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PfEMP1 is an antigenically variable molecule which mediates the adhesion of parasitized erythrocytes to a variety of cell types and which is believed to constitute an important target for naturally acquired protective immune responses in malaria. For 9 years we have monitored individuals living in an area of low-intensity, seasonal, and unstable malaria transmission in eastern Sudan, and we have used this database to study the acquisition, specificity, and duration of the antibody response to variant parasitized erythrocyte surface antigens. Both the levels and the spectrum of reactivity of these antibodies varied considerably among individuals, ranging from low levels of antibodies recognizing only few parasitized erythrocyte surface antigens to high levels of broad-specificity antibodies. In general, episodes of clinical malaria were associated with increases in the levels of parasitized erythrocyte surface-specific antibodies that subsided within months of the attack. This response was often, but not always, specific for the antigenic variants expressed by the parasite isolate causing disease. Our study provides evidence that Palciparum falciparum malaria is associated with a short-lived, variant-specific antibody response to PfEMP1-like antigens exposed on the surface of parasitized erythrocytes. Furthermore, our data suggest that the antigenic repertoires of variant antigens expressed by different parasite isolates show considerable overlapping, at least under Sahelian conditions of low-intensity, seasonal, and unstable malaria transmission. Finally, we demonstrate the existence of persistent differences among individuals in the capacity to mount antibody responses to variant surface antigens.
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Affiliation(s)
- H A Giha
- Centre for Medical Parasitology, Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), and Institute for Medical Microbiology and Immunology, University of Copenhagen, Copenhagen, Denmark
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659
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Abstract
In the past year, the major advances in malaria antigenic variation have been concerned with the transcription and switching of variant antigen genes, and the functional expression of regions of the major variant antigen. Also, new variant gene families have been discovered as a result of the Malaria Genome Project.
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Affiliation(s)
- C I Newbold
- Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, OX3 9DS, UK.
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660
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Ward CP, Clottey GT, Dorris M, Ji DD, Arnot DE. Analysis of Plasmodium falciparum PfEMP-1/var genes suggests that recombination rearranges constrained sequences. Mol Biochem Parasitol 1999; 102:167-77. [PMID: 10477185 DOI: 10.1016/s0166-6851(99)00106-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The var genes of Plasmodium falciparum encode a family of parasite erythrocyte surface antigens, the PfEMP-1 proteins, which function as adhesion ligands for host endothelial and erythrocyte receptors. PfEMP-1 is extremely polymorphic although the extent of this variation in naturally transmitted parasite populations is unclear. We have identified 56 different sequences from the Duffy binding-like (DBL-1) domain of var genes amplified from six different P. falciparum clones isolated from patient infections in a Sudanese village in October-November 1989. These clones have been compared with 25 PfEMP-1 sequences expressed from different var gene loci by the 3D7A clone and 48 PfEMP-1 sequences from different isolates in endemic areas such as Kenya, Brazil, Gambia, Vietnam and Vanuatu to analyse diversity in clonal, local and 'global' P. falciparum populations. Evidence that certain conserved sequences recur in clones from one Sudanese village and in isolates from all over the world suggests that var gene diversity is the result of recombinational reshuffling of a subset of conserved, presumably ancestral sequences. Recurrence of particular var sequence blocks thus leads to 'overlaps' in the PfEMP-1 sequence repertoire of different P. falciparum clones.
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Affiliation(s)
- C P Ward
- Institute of Cell, Animal and Population Biology, Division of Biology, University of Edinburgh, Scotland, UK
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661
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Albano FR, Berman A, La Greca N, Hibbs AR, Wickham M, Foley M, Tilley L. A homologue of Sar1p localises to a novel trafficking pathway in malaria-infected erythrocytes. Eur J Cell Biol 1999; 78:453-62. [PMID: 10472798 DOI: 10.1016/s0171-9335(99)80072-7] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
We have identified a homologue of the GTP-binding protein, Sar1p, in Plasmodium falciparum. Sar1p is a small GTPase that is thought to play a crucial role in trafficking of proteins between the endoplasmic reticulum and the Golgi. The P.falciparum SAR1 gene is located on chromosome 4 and comprises two exons separated by a 508 bp intron. The deduced amino acid sequence of PfSar1p (GenBank accession number AF104306) shows 71% similarity (58% identity) to Sar1p from Saccharomyces cerevisiae. Expression of PfSar1p in erythrocytic stages of P. falciparum was confirmed by sequencing of a tryptic peptide derived from a polypeptide excised from an SDS-polyacrylamide gel. A recombinant protein corresponding to approximately 70% of the PfSar1p sequence was used to raise antibodies. The affinity-purified antiserum recognised a protein with an apparent molecular weight of 23 K in Western blots of malaria-infected erythrocytes but not in uninfected erythrocytes. PfSar1p was shown to be largely insoluble in non-ionic detergent and a low ionic strength buffer. Confocal immunofluorescence microscopy of malaria-infected erythrocytes was used to show that PfSar1p is located near the periphery of the parasite in discrete compartments, which appear to be distinct from the parasite endoplasmic reticulum. In addition, PfSar1p appears to be exported to structures outside the parasite in the erythrocyte cytoplasm. The export of PfSar1p to the erythrocyte cytosol is inhibited by treatment with brefeldin A. This provides the first evidence that the malaria parasite is capable of elaborating components of the classical vesicle-mediated trafficking machinery outside the boundaries of its own plasma membrane.
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Affiliation(s)
- F R Albano
- Department of Biochemistry, La Trobe University, Melbourne, Australia
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662
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Urban BC, Ferguson DJ, Pain A, Willcox N, Plebanski M, Austyn JM, Roberts DJ. Plasmodium falciparum-infected erythrocytes modulate the maturation of dendritic cells. Nature 1999; 400:73-7. [PMID: 10403251 DOI: 10.1038/21900] [Citation(s) in RCA: 447] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The malaria parasite Plasmodium falciparum is one of the most successful human pathogens. Specific virulence factors remain poorly defined, although the adhesion of infected erythrocytes to the venular endothelium has been associated with some of the syndromes of severe disease. Immune responses cannot prevent the development of symptomatic infections throughout life, and clinical immunity to the disease develops only slowly during childhood. An understanding of the obstacles to the development of protective immunity is crucial for developing rational approaches to prevent the disease. Here we show that intact malaria-infected erythrocytes adhere to dendritic cells, inhibit the maturation of dendritic cells and subsequently reduce their capacity to stimulate T cells. These data demonstrate both a novel mechanism by which malaria parasites induce immune dysregulation and a functional role beyond endothelial adhesion for the adhesive phenotypes expressed at the surface of infected erythrocytes.
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Affiliation(s)
- B C Urban
- Institute of Molecular Medicine, Oxford Centre, John Radcliffe Hospital, Headington, UK
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663
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Soubes SC, Liu X, Miller LH. Representational difference analysis of cDNA between two Dd2 clones of Plasmodium falciparum. Mol Biochem Parasitol 1999; 101:217-21. [PMID: 10413056 DOI: 10.1016/s0166-6851(99)00034-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- S C Soubes
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892-0425, USA
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664
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Deitsch KW, del Pinal A, Wellems TE. Intra-cluster recombination and var transcription switches in the antigenic variation of Plasmodium falciparum. Mol Biochem Parasitol 1999; 101:107-16. [PMID: 10413047 DOI: 10.1016/s0166-6851(99)00062-6] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Antigenic variation and immune evasion by Plasmodium falciparum parasitized erythrocytes are mediated by expression switches among members of the multicopy var gene family. Here we describe a cluster of var genes on chromosome 12 that showed spontaneous recombination and switches in the transcription of individual genes. The transcription switches were not associated with sequence changes in promoter regions. Transfected episomes containing a luciferase reporter under control of a var promoter were expressed regardless of the transcriptional status of the endogenous promoter. The results suggest epigenetic regulation of P. falciparum var gene transcription that depends upon the local structure of chromatin and its associated proteins.
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Affiliation(s)
- K W Deitsch
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-0425, USA
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665
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Newbold C, Craig A, Kyes S, Rowe A, Fernandez-Reyes D, Fagan T. Cytoadherence, pathogenesis and the infected red cell surface in Plasmodium falciparum. Int J Parasitol 1999; 29:927-37. [PMID: 10480730 DOI: 10.1016/s0020-7519(99)00049-1] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The particular virulence of Plasmodium falciparum compared with the other malaria species which naturally infect humans is thought to be due to the way in which the parasite modifies the surface of the infected red cell. Approximately 16 hours into the asexual cycle, parasite encoded proteins appear on the red cell surface which mediate adherence to a variety of host tissues. Binding of infected red cells to vascular endothelium, a process which occurs in all infections, is thought to be an important factor in the pathogenesis of severe disease where concentration of organisms in particular organs such as the brain occurs. Binding to uninfected red cells to form erythrocyte rosettes, a property of some isolates, is linked to disease severity. Here we summarise the data on the molecular basis of these interactions on both the host and parasite surfaces and review the evidence for the involvement of particular receptors in specific disease syndromes. Finally we discuss the relevance of these data to the development of new treatments for malaria.
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Affiliation(s)
- C Newbold
- Molecular Parasitology Group, Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, UK.
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666
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Holt DC, Gardiner DL, Thomas EA, Mayo M, Bourke PF, Sutherland CJ, Carter R, Myers G, Kemp DJ, Trenholme KR. The cytoadherence linked asexual gene family of Plasmodium falciparum: are there roles other than cytoadherence? Int J Parasitol 1999; 29:939-44. [PMID: 10480731 DOI: 10.1016/s0020-7519(99)00046-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The binding of erythrocytes infected with Plasmodium falciparum to the endothelium lining the small blood vessels of the brain and other organs can mediate severe pathology. A region at the right end of chromosome 9 has been implicated in the binding of parasitised erythrocytes to the endothelial receptor CD36. A gene expressed in asexual erythrocytic stage parasites has been identified in this region and termed the cytoadherence linked asexual gene (clag). Antisense RNA production and targeted gene disruption of clag resulted in greatly reduced binding to CD36. Hybridisation to 3D7 chromosomes showed clag to be a part of a gene family of at least nine members. All members analysed so far have a conserved gene structure of at least nine exons, as well as putative transmembrane domains. The possible functions of the gene family are discussed.
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Affiliation(s)
- D C Holt
- The Menzies School of Health Research, Casuarina, NT, Australia
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667
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Reeder JC, Cowman AF, Davern KM, Beeson JG, Thompson JK, Rogerson SJ, Brown GV. The adhesion of Plasmodium falciparum-infected erythrocytes to chondroitin sulfate A is mediated by P. falciparum erythrocyte membrane protein 1. Proc Natl Acad Sci U S A 1999; 96:5198-202. [PMID: 10220443 PMCID: PMC21841 DOI: 10.1073/pnas.96.9.5198] [Citation(s) in RCA: 166] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chondroitin sulfate A (CSA) is an important receptor for the sequestration of Plasmodium falciparum in the placenta, but the parasite ligand involved in adhesion has not previously been identified. Here we report the identification of a var gene transcribed in association with binding to CSA and present evidence that the P. falciparum erythrocyte membrane protein 1 product of the gene is the parasite ligand mediating CSA binding. Description of this gene and the implication of P. falciparum erythrocyte membrane protein 1 as the parasite ligand paves the way to a more detailed understanding of the pathogenesis of placental infection and potential therapeutic strategies targeting the interaction.
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Affiliation(s)
- J C Reeder
- The Walter and Eliza Hall Institute of Medical Research, Post Office Royal Melbourne Hospital, Victoria 3050, Australia.
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668
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Preiser PR, Jarra W, Capiod T, Snounou G. A rhoptry-protein-associated mechanism of clonal phenotypic variation in rodent malaria. Nature 1999; 398:618-22. [PMID: 10217144 DOI: 10.1038/19309] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The recognition and invasion of host cells are mediated by components of the apical complex of the ookinete, sporozoite and merozoite stages of Plasmodium parasites. The paired rhoptries (organelles involved in host-cell recognition) in the apical complex contain many proteins of as-yet unknown function. In the rodent malaria agent P. yoelii yoelii, a multigene family codes for merozoite rhoptry proteins of relative molecular mass 235,000 (p235 proteins); these proteins are thought to determine the subset of erythrocytes that the parasites invade. Further support for this idea came from the identification of a region in p235 with weak but significant homology to reticulocyte-binding protein-2 of P. vivax and the demonstration that at least one p235 member binds to the erythrocyte surface membrane. Here, using single, micromanipulated P.y.yoelii parasites, we describe a new mechanism of gene expression by which the merozoites originating from a single schizont each express a distinct member of this multigene family. We propose that this new type of clonal phenotypic variation provides the parasite with a survival strategy in the mammalian host; this strategy contributes to the observed chronicity of malarial infections. This phenomenon is genetically and functionally distinct from classical antigenic variation, which is mediated by the var multigene family of P. falciparum.
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Affiliation(s)
- P R Preiser
- Division of Parasitology, National Institute for Medical Research, London, UK.
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669
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Hayward RE, Tiwari B, Piper KP, Baruch DI, Day KP. Virulence and transmission success of the malarial parasite Plasmodium falciparum. Proc Natl Acad Sci U S A 1999; 96:4563-8. [PMID: 10200302 PMCID: PMC16372 DOI: 10.1073/pnas.96.8.4563] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Virulence of Plasmodium falciparum is associated with the expression of variant surface antigens designated PfEMP1 (P. falciparum erythrocyte membrane protein 1) that are encoded by a family of var genes. Data presented show that the transmission stages of P. falciparum also express PfEMP1 variants. Virulence in this host-parasite system can be considered a variable outcome of optimizing the production of sexual transmission stages from the population of disease-inducing asexual stages. Immunity to PfEMP1 will contribute to the regulation of this trade-off by controlling the parasite population with potential to produce mature transmission stages.
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Affiliation(s)
- R E Hayward
- Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS United Kingdom
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670
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Mackinnon MJ, Read AF. Selection for high and low virulence in the malaria parasite Plasmodium chabaudi. Proc Biol Sci 1999; 266:741-8. [PMID: 10331293 PMCID: PMC1689830 DOI: 10.1098/rspb.1999.0699] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
What stops parasites becoming ever more virulent? Conventional wisdom and most parasite-centred models of the evolution of virulence suppose that risk of host (and, hence, parasite) death imposes selection against more virulent strains. Here we selected for high and low virulence within each of two clones of the rodent malaria parasite Plasmodium chabaudi on the basis of between-host differences in a surrogate measure of virulence--loss of live weight post-infection. Despite imposing strong selection for low virulence which mimicked 50-75% host mortality, the low virulence lines increased in virulence as much as the high virulence lines. Thus, artificial selection on between-host differences in virulence was unable to counteract natural selection for increased virulence caused by within-host selection processes. The parasite's asexual replication rate and number of sexual transmission forms also increased in all lines, consistent with evolutionary models explaining high virulence. An upper bound to virulence, though not the asexual replication rate, was apparent, but this bound was not imposed by host mortality. Thus, we found evidence of the factors assumed to drive evolution of increased virulence, but not those thought to counter this selection.
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Affiliation(s)
- M J Mackinnon
- Institute of Cell, Animal and Population Biology, University of Edinburgh, UK.
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671
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Staalsoe T, Giha HA, Dodoo D, Theander TG, Hviid L. Detection of antibodies to variant antigens onPlasmodium falciparum-infected erythrocytes by flow cytometry. ACTA ACUST UNITED AC 1999. [DOI: 10.1002/(sici)1097-0320(19990401)35:4<329::aid-cyto5>3.0.co;2-y] [Citation(s) in RCA: 137] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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672
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Horrocks P, Lanzer M. Differences in nucleosome organization over episomally located plasmids coincides with aberrant promoter activity in P. falciparum. Parasitol Int 1999; 48:55-61. [PMID: 11269326 DOI: 10.1016/s1383-5769(99)00002-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Here we investigated whether the Plasmodium falciparum GBP130 promoter maintains its developmental activity during the intraerythrocytic cycle when located on an episomal plasmid introduced using transient transfection. Comparing its activity with that of the endogenous chromosomally located GBP130 promoter indicates that the episomally located GBP130 promoter looses its developmental restriction, being rendered constitutively active. Loss of developmental restriction coincides with the absence of phased nucleosomal arrays over the episome. These data suggest that epigenetic factors may play a role in developmentally regulated gene expression in P. falciparum.
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Affiliation(s)
- P Horrocks
- Zentrum für Infektionsforschung der Universität Würzburg, Germany
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673
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674
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Piper KP, Roberts DJ, Day KP. Plasmodium falciparum: analysis of the antibody specificity to the surface of the trophozoite-infected erythrocyte. Exp Parasitol 1999; 91:161-9. [PMID: 9990344 DOI: 10.1006/expr.1998.4368] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Current opinion supports the view that immunity to the surface of the trophozoite-infected erythrocyte (IE) is to Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1). Here we provide further evidence using the mutant cell line 1776/C10 which no longer expresses PfEMP-1 at the IE surface, due to a subtelomeric deletion in chromosome 9. We have measured antibody reactivity to this mutant in comparison to it's intact isogenic parent line 1776, which does express PfEMP-1, using the sensitive technique of flow cytometry. IgG-specific antibodies (subclass IgG1) in the plasma of hyperimmune adults, reacted to 1776 but never to the 1776/C10 mutant. Antibody subclasses were also measured in individual plasma samples to the surface of trophozoite-IE. Predominantly IgG1 antibodies were detected, with a few individual plasma having additional IgG3 antibodies. Previous studies have used the agglutination assay to measure sero-conversion to PfEMP-1. Here we show that both agglutination and flow cytometric methods are comparable, suggesting that agglutination of trophozoite-IE is mediated by IgG antibodies. Comparison of the isogenic cell lines 1776 and 1776/C10 differing in expression of PfEMP-1 provides further evidence that IgG antibodies, in particular of the cytophilic subclasses, mediate recognition of PfEMP-1.
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Affiliation(s)
- K P Piper
- Wellcome Trust Centre for the Epidemiology of Infectious Diseases, Department of Zoology, University of Oxford, U.K.
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675
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Bull PC, Lowe BS, Kortok M, Marsh K. Antibody recognition of Plasmodium falciparum erythrocyte surface antigens in Kenya: evidence for rare and prevalent variants. Infect Immun 1999; 67:733-9. [PMID: 9916084 PMCID: PMC96380 DOI: 10.1128/iai.67.2.733-739.1999] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is the name given to a family of parasite proteins that are inserted into the infected erythrocyte surface. Studies using agglutination assays have shown previously that PfEMP1 epitopes are extremely diverse. In a study in Kenya, 21 parasite isolates, including nine from children with severe malaria, were tested for agglutination by 33 pairs of plasma, 21 of which were from the corresponding children. Each plasma pair consisted of a sample taken at the time of disease (acute) and one taken 3 weeks later (convalescent). In agreement with previous studies, infection was generally followed by the induction of antibodies specific to the homologous parasite isolate. In addition however, the results show that (i) some isolates were agglutinated very frequently by heterologous plasma; (ii) unexpectedly, these frequently agglutinated isolates tended to be from individuals with severe malaria; (iii) an inverse relationship existed between the agglutination frequency of each parasite isolate in heterologous plasma and the agglutinating antibody repertoire of the homologous child at the time of disease; and (iv) A 3-month-old child apparently still carrying maternal antibodies was infected by a rarely agglutinated isolate. This child's plasma agglutinated all isolates at the time of disease, apart from the homologous isolate. These results support the idea that preexisting anti-PfEMP1 antibodies can select the variants that are expressed during a new infection and may suggest the existence of a dominant subset of PfEMP1 variants.
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Affiliation(s)
- P C Bull
- Kenya Medical Research Institute CGMRC, Kilifi Unit, Kilifi, Kenya.
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676
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al-Khedery B, Barnwell JW, Galinski MR. Antigenic variation in malaria: a 3' genomic alteration associated with the expression of a P. knowlesi variant antigen. Mol Cell 1999; 3:131-41. [PMID: 10078196 DOI: 10.1016/s1097-2765(00)80304-4] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Antigenic variation of malaria parasites was discovered in P. knowlesi, using a schizont-infected cell agglutination (SICA) assay to detect variant antigens expressed at the surface of infected erythrocytes. Later studies utilizing stable clones, Pk1(A+) and its direct derivative, Pk1(B+)1+, showed that SICA[+] clones express distinct parasite-encoded antigens of approximately 200 kDa. Here we identify a P. knowlesi variant antigen gene and cDNA and demonstrate that it encodes the 205 kDa variant antigen expressed by B+ parasites. This gene belongs to a multigene family, which we term SICAvar. Its ten-exon structure with seven cysteine-rich coding modules is unique compared to P. falciparum var genes. Further, we highlight a 3' genomic alteration that we predict is related to SICAvar gene switching.
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Affiliation(s)
- B al-Khedery
- Department of Medical and Molecular Parasitology, New York University School of Medicine, New York 10010, USA
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677
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Miller LH, Good MF, Kaslow DC. Vaccines against the blood stages of falciparum malaria. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 452:193-205. [PMID: 9889974 DOI: 10.1007/978-1-4615-5355-7_22] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- L H Miller
- Laboratory of Parasitic Diseases, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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678
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Le Scanf C, Fandeur T, Bonnefoy S, Guillotte M, Mercereau-Puijalon O. Novel target antigens of the variant-specific immune response to Plasmodium falciparum identified by differential screening of an expression library. Infect Immun 1999; 67:64-73. [PMID: 9864197 PMCID: PMC96278 DOI: 10.1128/iai.67.1.64-73.1999] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A primary infection by the Plasmodium falciparum Palo Alto O and R antigenic variants induces a variant-specific immunity in the Saimiri sciureus monkey. We have shown that these variants express distinct PfEMP1 antigens and differ in their levels of expression of additional antigens, including two conserved erythrocyte membrane-associated proteins, HRP1 and PfEMP3. To identify the antigens eliciting a variant-specific response, we conducted a differential screening of a lambdagt11 library with variant-specific sera. We report here the analysis of the 46 anti-R-specific clones. Two specific targets of the anti-R response were identified: (i) PfEMP3, suggesting that immunogenicity of this antigen is modulated by its relative abundance in different variants, and (ii) Asn-rich motifs. Most anti-R-specific clones, derived from so-far-undescribed genes, were detected by a cross-reaction on poly(Asn) stretches, as indicated by elimination of the signal after absorption on Asn-rich sequences. Reverse transcription-PCR (RT-PCR) showed that expression of the gene defined by clone 13 was R specific. Pepscan analysis of clone 13 identified three Asn-rich polypeptides and one unique peptide reacting specifically with antibodies eluted from the R-infected erythrocyte surface. Antisera raised to the unique peptide reacted with an R-specific protein. Attempts to demonstrate that clone 13 was derived from a var gene by using PCRs combining clone 13 and var-derived primers were unsuccessful. The var genes expressed by O and R parasites were identified not by this strategy but by RT-PCR with var-specific primers. This work has provided novel insights into immunity to antigenic variants and has identified a novel gene switched on during antigenic variation.
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Affiliation(s)
- C Le Scanf
- Laboratoire de Parasitologie Moléculaire, Institut Pasteur de Guyane, French Guiana.
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679
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Cheng Q, Cloonan N, Fischer K, Thompson J, Waine G, Lanzer M, Saul A. stevor and rif are Plasmodium falciparum multicopy gene families which potentially encode variant antigens. Mol Biochem Parasitol 1998; 97:161-76. [PMID: 9879895 DOI: 10.1016/s0166-6851(98)00144-3] [Citation(s) in RCA: 201] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Several multicopy gene families have been described in Plasmodium falciparum, including the var genes that code for the variant surface antigen PfEMP1, the stevor family of subtelomeric open reading frames and the rif interspersed repetitive elements. This report documents the chromosomal location of stevor genes, their transcription and characteristics of the deduced protein. On 14 chromosomes, 34 stevor copies were identified from the Dd2 parasite line. Most are in subtelomeric regions within 50 kb of the telomere. stevor genes are located close to var genes and rij. All stevor genes sequenced had two exons: a short exon 1 encoding a start codon and a transmembrane domain; exon 2 encoding for the remainder of the approximately 30 kDa protein and including two more transmembrane segments. A similar structure was found for copies of rif and its predicted protein. In both STEVOR and RIF proteins, a highly polymorphic region is predicted to be a loop on the outer side of the membrane. We propose that stevor and rif are members of a larger superfamily. The number of copies of stevor and rif, their location close to the var genes, their extreme polymorphism and the predicted structure of the proteins suggest that stevor and rif code for variant surface antigens.
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Affiliation(s)
- Q Cheng
- The Queensland Institute of Medical Research, Royal Brisbane Hospital, Australia
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680
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Smith JD, Kyes S, Craig AG, Fagan T, Hudson-Taylor D, Miller LH, Baruch DI, Newbold CI. Analysis of adhesive domains from the A4VAR Plasmodium falciparum erythrocyte membrane protein-1 identifies a CD36 binding domain. Mol Biochem Parasitol 1998; 97:133-48. [PMID: 9879893 DOI: 10.1016/s0166-6851(98)00145-5] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The A4VAR is a variant antigen expressed by a clonal line that binds CD36 and intercellular adhesion molecule-1, ICAM-1. We have cloned and sequenced the extracellular domain coded by the A4var gene. To probe the relationship between A4var expression and parasite adhesion to ICAM-1, var mRNA and protein expression were analyzed in an enriched population of A4 parasites that displayed higher ICAM-1 binding. By Northern analyses, A4var was the predominant var message and antisera raised against a recombinant A4VAR protein reacted with the majority of infected erythrocytes, reinforcing previous conclusions that A4VAR binds ICAM-1. A4VAR contains five Duffy-binding like (DBL) domains, and two cysteine-rich interdomain regions (CIDR) domains. DBL and CIDR domains from A4VAR were expressed in mammalian cells to determine which regions mediate binding to CD36 and ICAM-1. Using several different binding assays, the A4VAR CIDR1 was the only domain found to bind CD36. In contrast, the same assays were unable to identify the ICAM-1 binding domain in A4VAR. This is the first time that each of the DBL and CIDR domains from a Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) have been systematically expressed and tested for binding. These results confirm that CIDR1 is sufficient to bind CD36 without any apparent contribution from other domains.
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Affiliation(s)
- J D Smith
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA
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681
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682
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Abstract
The malaria parasite invades the human erythrocyte and converts this simple "sack of haemoglobin" back into a functional eukaryotic cell. Parasite-encoded proteins are trafficked to the red blood cell membrane where they modify its properties to meet the needs of the intracellular parasite. Trafficking of proteins within the parasite probably occurs via a "classical" vesicle-mediated secretory pathway; however, the transit of proteins from the parasite plasma membrane to the erythrocyte membrane appears to involve both a novel vesicle-mediated pathway and a direct protein-translocation system. The polypeptide signals that direct parasite proteins into these novel export pathways may include an unusual "internal" hydrophobic sequence, as well as a series of basic motifs.
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Affiliation(s)
- M Foley
- Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia
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683
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Barragan A, Kremsner PG, Weiss W, Wahlgren M, Carlson J. Age-related buildup of humoral immunity against epitopes for rosette formation and agglutination in African areas of malaria endemicity. Infect Immun 1998; 66:4783-7. [PMID: 9746579 PMCID: PMC108590 DOI: 10.1128/iai.66.10.4783-4787.1998] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this report, we show an age-related buildup of agglutinating activity as well as serum activity against rosette formation in children living in areas of Kenya and Gabon where malaria is endemic. Sera from Kenyans in general exhibited a stronger and wider immune response toward the epitopes, probably reflecting a difference in transmission patterns between the two areas. Thus, our results indicate that repeated malaria attacks in areas of endemicity, and consequently exposure to different isolate-specific antigens, will elicit an antibody-mediated response eventually enabling recognition of the majority of rosetting and agglutinating antigens. The correlation between antirosetting and agglutinating capacity was poor in individual cases, indicating that the rosetting epitopes are only a minor part of the highly diverse surface-exposed antigens (mainly PfEMP1) on the surface of parasitized erythrocytes toward which antibodies may react. These data together with our previous findings that the protection against cerebral malaria correlates with presence of antirosetting antibodies shed new light on our understanding of the gradual acquisition of immunity toward severe complications of malarial infection which children reared in areas of endemicity attain.
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Affiliation(s)
- A Barragan
- Microbiology and Tumor Biology Center, Karolinska Institutet, Swedish Institute for Infectious Disease Control, Stockholm Sweden; Department of Parasitology, Institute of Tropical Medicine, University of Tübingen, Tübingen, Germany
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684
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Cooke BM, Nicoll CL, Baruch DI, Coppel RL. A recombinant peptide based on PfEMP-1 blocks and reverses adhesion of malaria-infected red blood cells to CD36 under flow. Mol Microbiol 1998; 30:83-90. [PMID: 9786187 DOI: 10.1046/j.1365-2958.1998.01040.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
During falciparum malaria infection, severe complications ensue because parasitized red blood cells (PRBCs) adhere to endothelial cells and accumulate in the microvasculature. At the molecular level, adhesion is mediated by interaction of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1) on the PRBC surface with receptors on the surface of endothelial cells, including CD36. We have shown that a recombinant 179-residue subfragment of PfEMP-1 (rC1-2[1-179]), which encompasses the CD36-binding region, inhibits and reverses adhesion of PRBCs to CD36 under physiologically relevant flow conditions. rC1-2[1-179] inhibited adhesion in a concentration-dependent manner over the range 100 pM to 2 microM, with up to 99% of adhesion blocked at the highest concentration tested. The antiadhesive activity of rC1-2[1-179] was not strain specific and almost totally ablated adhesion of four different parasite lines. Furthermore, rC1-2[1-179] showed remarkable ability to progressively reverse adhesion when flowed over adherent PRBCs for 2h. The effect of rC1-2[1-179] was, however, specific for CD36-mediated adhesion and had no effect on adhesion mediated by CSA. Interference with binding of PRBCs to the vascular endothelium using rC1-2[1-179] or smaller organic mimetics may be a useful therapeutic approach to ameliorate severe complications of falciparum malaria.
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Affiliation(s)
- B M Cooke
- Department of Microbiology, Monash University, Clayton, Victoria, Australia.
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685
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Scherf A, Hernandez-Rivas R, Buffet P, Bottius E, Benatar C, Pouvelle B, Gysin J, Lanzer M. Antigenic variation in malaria: in situ switching, relaxed and mutually exclusive transcription of var genes during intra-erythrocytic development in Plasmodium falciparum. EMBO J 1998; 17:5418-26. [PMID: 9736619 PMCID: PMC1170867 DOI: 10.1093/emboj/17.18.5418] [Citation(s) in RCA: 405] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Members of the Plasmodium falciparum var gene family encode clonally variant adhesins, which play an important role in the pathogenicity of tropical malaria. Here we employ a selective panning protocol to generate isogenic P.falciparum populations with defined adhesive phenotypes for CD36, ICAM-1 and CSA, expressing single and distinct var gene variants. This technique has established the framework for examining var gene expression, its regulation and switching. It was found that var gene switching occurs in situ. Ubiquitous transcription of all var gene variants appears to occur in early ring stages. However, var gene expression is tightly regulated in trophozoites and is exerted through a silencing mechanism. Transcriptional control is mutually exclusive in parasites that express defined adhesive phenotypes. In situ var gene switching is apparently mediated at the level of transcriptional initiation, as demonstrated by nuclear run-on analyses. Our results suggest that an epigenetic mechanism(s) is involved in var gene regulation.
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Affiliation(s)
- A Scherf
- Unité de Biologie des Interactions Hôte-Parasite, CNRS URA 1960, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France.
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686
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Amani V, Boubou MI, Pied S, Marussig M, Walliker D, Mazier D, Rénia L. Cloned lines of Plasmodium berghei ANKA differ in their abilities to induce experimental cerebral malaria. Infect Immun 1998; 66:4093-9. [PMID: 9712753 PMCID: PMC108491 DOI: 10.1128/iai.66.9.4093-4099.1998] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Infection with Plasmodium berghei ANKA is usually lethal. The parasite causes in some mouse strains a neurovascular syndrome, experimental cerebral malaria (ECM), involving immunopathological reactions. The effects on the development of ECM of the mouse genetic background have been clearly demonstrated, but nothing is known about the effects of the clonal diversity of the parasite. We showed that various cloned lines derived from a polyclonal line of P. berghei ANKA caused ECM but that the extent of ECM induction was dependent on the amount of inoculum. Subtle differences in ECM characteristics (survival time and hypothermia) were also observed. We also confirmed, using the 1.49L cloned line, that the mouse genetic background strongly affects ECM.
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Affiliation(s)
- V Amani
- INSERM U313 and Department of Parasitology, Groupe Hospitalier Pitié-Salpêtrière, 75013 Paris, France
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687
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Mota MM, Brown KN, Holder AA, Jarra W. Acute Plasmodium chabaudi chabaudi malaria infection induces antibodies which bind to the surfaces of parasitized erythrocytes and promote their phagocytosis by macrophages in vitro. Infect Immun 1998; 66:4080-6. [PMID: 9712751 PMCID: PMC108489 DOI: 10.1128/iai.66.9.4080-4086.1998] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CBA/Ca mice infected with 5 x 10(4) Plasmodium chabaudi chabaudi AS-parasitized erythrocytes experience acute but self-limiting infections of relatively short duration. Parasitemia peaks ( approximately 40% infected erythrocytes) on day 10 or 11 and is then partially resolved over the ensuing 5 to 6 days, a period referred to as crisis. How humoral and cellular immune mechanisms contribute to parasite killing and/or clearance during crisis is controversial. Humoral immunity might be parasite variant, line, or species specific, while cellular immune responses would be relatively less specific. For P. c. chabaudi AS, parasite clearance is largely species and line specific during this time, which suggests a primary role for antibody activity. Accordingly, acute-phase plasma (APP; taken from P. c. chabaudi AS-infected mice at day 11 or 12 postinfection) was examined for the presence of parasite-specific antibody activity by enzyme-linked immunosorbent assay. Antibody binding to the surface of intact, live parasitized erythrocytes, particularly those containing mature (trophozoite and schizont) parasites, was demonstrated by immunofluorescence in APP and the immunoglobulin G (IgG)-containing fraction thereof. Unfractionated APP (from P. c. chabaudi AS-infected mice), as well as its IgG fraction, specifically mediated the opsonization and internalization of P. c. chabaudi AS-parasitized erythrocytes by macrophages in vitro. APP from another parasite line (P. c. chabaudi CB) did not mediate the same effect against P. c. chabaudi AS-parasitized erythrocytes. These results, which may represent one mechanism of parasite removal during crisis, are discussed in relation to the parasite variant, line, and species specificity of parasite clearance during this time.
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Affiliation(s)
- M M Mota
- Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
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688
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Abstract
The most important function of any parasite is to secure transmission to new hosts. The gametocyte, the stage which has become developmentally committed to the sexual cycle, provides a critical link in the transmission of Plasmodium falciparum from the human host to the anopheline mosquito vector. It is therefore imperative that our determination to understand the biology of the gametocyte is greater than the technical obstacles which have resulted in the gametocyte being left very much out of the limelight by the intensive investigation of the asexual bloodstream parasite. Here we explore the areas of gametocyte biology which by nature of their relevance to control and pathology as well as basic biology, are the subjects of investigation in our laboratory. We also point out areas in need of particular attention.
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Affiliation(s)
- K P Day
- Wellcome Centre for Epidemiology of Infectious Disease, Department of Zoology, University of Oxford, UK
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689
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Abstract
The past few years have witnessed considerable progress in molecular and biochemical studies of intracellular trafficking in malaria-infected red cells. Highlights include the identification of solute channels in the vacuolar membrane and the red blood cell membrane, a tubovesicular membrane network that delivers exogenous nutrients and drugs to the parasite, and parasite gene families that mediate adherence to endothelial cells and red cells.
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Affiliation(s)
- K Haldar
- Department of Microbiology, Stanford University School of Medicine, Stanford, CA 94305 USA
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690
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Abstract
Malaria infection of the host cells requires host-parasite recognition events mediated by adhesion and signaling molecules. Recent development of systems for stable transformation and targeted integration of exogenous DNA in malaria parasites provides a powerful tool to study the structure and function of Plasmodium attachment motifs, and their role in infection and disease.
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Affiliation(s)
- R L Coppel
- Department of Microbiology, Monash University, Clayton, Victoria 3168, Australia
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691
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Chen Q, Fernandez V, Sundström A, Schlichtherle M, Datta S, Hagblom P, Wahlgren M. Developmental selection of var gene expression in Plasmodium falciparum. Nature 1998; 394:392-5. [PMID: 9690477 DOI: 10.1038/28660] [Citation(s) in RCA: 370] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The protozoan Plasmodium falciparum causes lethal malaria. Adhesion of erythrocytes infected with P. falciparum to vascular endothelium and to uninfected red blood cells (rosetting) may be involved in the pathogenesis of severe malaria. The binding is mediated by the antigenically variant erythrocyte-membrane-protein-1 (PfEMP-1), which is encoded by members of the P. falciparum var gene family. The control of expression and switching of var genes seems to lack resemblance to mechanisms operating in variant gene families of other microbial pathogens. Here we show that multiple, distinct var gene transcripts (about 24 or more) can be detected by reverse transcription and polymerase chain reaction in bulk cultures of the rosetting parasite FCR3S1.2, despite the adhesive homogeneity of the cultures. We also detected several var transcripts in single erythrocytes infected with a ring-stage parasite of FCR3S1.2, and found that different var genes are transcribed simultaneously from several chromosomes in the same cell. In contrast, we detected only one var transcript, FCR3S1.2 var-1, which encodes the rosetting PfEMP-1 protein, in individual rosette-adhesive trophozoite-infected cells, and we found only one PfEMP-1 type at the erythrocyte surface by labelling with 125iodine and immunoprecipitation. We conclude that a single P. falciparum parasite simultaneously transcribes multiple var genes but, through a developmentally regulated process, selects only one PfEMP-1 to reach the surface of the host cell.
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Affiliation(s)
- Q Chen
- Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden
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692
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Horrocks P, Lanzer M. Transfection of Plasmodium: A new chapter in the molecular analysis of malaria. Parasitol Int 1998. [DOI: 10.1016/s1383-5769(98)00007-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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693
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Day KP, Hayward RE, Smith D, Culvenor JG. CD36-dependent adhesion and knob expression of the transmission stages of Plasmodium falciparum is stage specific. Mol Biochem Parasitol 1998; 93:167-77. [PMID: 9662702 DOI: 10.1016/s0166-6851(98)00040-1] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Plasmodium falciparum trophozoites sequester from the peripheral circulation by adherence to host endothelium. Gametocytes, also sequester during maturation. Analysis of the adhesion phenotype of stage I to V gametocytes of several isolates/clones was assessed by binding of infected cells to C32 melanoma cells (C32MC) and the purified adhesion proteins, leucocyte differentiation antigen (CD36) and intercellular adhesion molecule-1 (ICAM-1). These cells and proteins, have previously been shown to be receptors for adherence of trophozoites. Early gametocytes (stages I-IIA) were found to bind to C32MC as well as the purified receptor CD36 but not to ICAM-1. Early gametocytes bound to C32MC via CD36 and the parasite ligand involved in this binding was trypsin sensitive. Stage IIB to V gametocytes did not adhere to C32MC, CD36 nor ICAM-1. Electron-dense protruberances known as knobs and histidine rich protein 1 (HRP 1) expression have been associated with trophozite adhesion to CD36. Knobs were present at the surface of early but not late gametocyte infected cells. Stage-specific patterns of HRP 1 expression, consistent with a role for this molecule in CD36 adhesion of early gametocytes, were also observed. The adhesion phenotype of these young gametocytes was indistinguishable from that of the trophozoites by all criteria examined. These data support the hypothesis that other host receptors mediate the binding of late gametocytes.
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Affiliation(s)
- K P Day
- Wellcome Trust Centre for Epidemiology of Infectious Disease, Department of Zoology, University of Oxford.
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694
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Fernandez V, Treutiger CJ, Nash GB, Wahlgren M. Multiple adhesive phenotypes linked to rosetting binding of erythrocytes in Plasmodium falciparum malaria. Infect Immun 1998; 66:2969-75. [PMID: 9596774 PMCID: PMC108296 DOI: 10.1128/iai.66.6.2969-2975.1998] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The cerebral form of severe malaria is associated with excessive intravascular sequestration of Plasmodium falciparum-infected erythrocytes (PRBC). Retention and accumulation of PRBC may lead to occlusion of brain microvessels and direct the triggering of acute pathologic changes. Here we report that by selection, cloning, and subcloning, we have identified rare P. falciparum parasites expressing a pan-adhesive phenotype linked to erythrocyte rosetting, a previously identified correlate of cerebral malaria. Rosetting PRBC not only bound uninfected erythrocytes but also formed autoagglutinates, adhered to endothelial cells, and bound to CD36, immunoglobulins, and the blood group A antigen. The linkage of rosetting, autoagglutination, and cytoadherence involved the coexpression on a single PRBC of ligands with multiple specificities and the binding to two or more receptors on erythrocytes and to at least two other cell adhesion molecules, including a new endothelial cell receptor for P. falciparum-infected erythrocytes. Limited proteolysis that differentially cleaved the rosetting ligand PfEMP1 from the PRBC surface abrogated all the binding phenotypes of these parasites, implicating the variant antigen PfEMP1 as a carrier of multiple ligand specificities. The results encourage the further study of pan-adhesion as a potentially important parasite phenotype in the pathogenesis of severe P. falciparum malaria.
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Affiliation(s)
- V Fernandez
- Microbiology and Tumor Biology Center, Karolinska Institutet, and Swedish Institute for Infectious Disease Control, S-171 77 Stockholm, Sweden
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695
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Abstract
In the past 10 years, our knowledge of the malaria parasite has increased enormously: identification and analysis of parasite antigens, demonstration of protection of monkeys and mice following immunization with these antigens, and better understanding of the mechanisms of immunity to malaria and the pathogenesis of disease in malaria. Powerful new adjuvants have been developed, some of which--it is hoped--will be suitable for human use. Recently, a successful human trial of a vaccine aimed at sporozoites (the stage inoculated by mosquitoes) was completed. However, it is the red blood cell stage of the parasite that causes disease, and it is against this stage--in which the parasite grows at an exponential rate--that it has proven very difficult to induce a protective immune response by vaccination. This review focuses on recent exciting developments toward a blood-stage vaccine. We analyze the major obstacles to vaccine development and outline a strategy involving public- and industry-funded research that should result in development of a vaccine.
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Affiliation(s)
- M F Good
- Cooperative Research Center for Vaccine Technology, Queensland Institute of Medical Research, Brisbane, Australia
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696
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Di Noia JM, D'Orso I, Aslund L, Sánchez DO, Frasch AC. The Trypanosoma cruzi mucin family is transcribed from hundreds of genes having hypervariable regions. J Biol Chem 1998; 273:10843-50. [PMID: 9556557 DOI: 10.1074/jbc.273.18.10843] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In previous works we have identified genes in the protozoan parasite Trypanosoma cruzi whose structure resemble those of mammalian mucin genes. Indirect evidence suggested that these genes might encode the core protein of parasite mucins, glycoproteins that were proposed to be involved in the interaction with, and invasion of, mammalian host cells. We now show that the mucin gene family from T. cruzi is much larger and diverse than expected. A minimal number of 484 mucin genes per haploid genome is calculated for a parasite clone. Most, if not all, genes are transcribed, as deduced from cDNA analysis. Comparison of the cDNA sequences showed evidences of a high mutation rate in localized regions of the genes. Sequence conservation among members of the family is much higher in the untranslated (UTR) regions than in the sequences encoding the mature mucin core protein. Transcription units can be classified into two main subfamilies according to the sequence homologies in the 5'-UTR, whereas the 3'-UTR is highly conserved in all clones analyzed. The common origin of members of this gene family as well as their relationships can be defined by sequence comparison of different domains in the transcription units. The regions encoding the N and C termini, supposed to correspond to the leader peptide and membrane-anchoring signal, respectively, (Di Noia, J. M., Sánchez, D. O., and Frasch, A. C. C. (1995) J. Biol. Chem. 270, 24146-24149) are highly conserved. Conversely, the central regions are highly variable. These regions encode the target sites for O-glycosylation and are made of a variable number of repetitive units rich in Thr and Pro residues or are nonrepetitive but still rich in Thr/Ser and Pro residues. The region putatively coding for the N-terminal domain of the mature core protein is hypervariable, being different in most of the transcripts sequenced. Nonrepetitive central domains are unique to each gene. Gene-specific probes show that the relative abundance of different mRNAs varies greatly within the same parasite clone.
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Affiliation(s)
- J M Di Noia
- Instituto de Investigaciones Biotecnológicas, Universidad Nacional de General San Martín, Casilla de Correo 30, 1650, Provincia de Buenos Aires, Argentina
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697
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Bull PC, Lowe BS, Kortok M, Molyneux CS, Newbold CI, Marsh K. Parasite antigens on the infected red cell surface are targets for naturally acquired immunity to malaria. Nat Med 1998; 4:358-60. [PMID: 9500614 PMCID: PMC3836255 DOI: 10.1038/nm0398-358] [Citation(s) in RCA: 473] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The feasibility of a malaria vaccine is supported by the fact that children in endemic areas develop naturally acquired immunity to disease. Development of disease immunity is characterized by a decrease in the frequency and severity of disease episodes over several years despite almost continuous infection, suggesting that immunity may develop through the acquisition of a repertoire of specific, protective antibodies directed against polymorphic target antigens. Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a potentially important family of target antigens, because these proteins are inserted into the red cell surface and are prominently exposed and because they are highly polymorphic and undergo clonal antigenic variation, a mechanism of immune evasion maintained by a large family of var genes. In a large prospective study of Kenyan children, we have used the fact that anti-PfEMP1 antibodies agglutinate infected erythrocytes in a variant-specific manner, to show that the PfEMP1 variants expressed during episodes of clinical malaria were less likely to be recognized by the corresponding child's own preexisting antibody response than by that of children of the same age from the same community. In contrast, a heterologous parasite isolate was just as likely to be recognized. The apparent selective pressure exerted by established anti-PfEMP1 antibodies on infecting parasites supports the idea that such responses provide variant-specific protection against disease.
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Affiliation(s)
- P C Bull
- Kenya Medical Research Institute CRC, Kilifi Unit.
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698
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Abstract
Malaria remains the most prevalent and devastating parasitic disease worldwide. Vaccination is considered to be an approach that will complement other strategies for prevention and control of the disease in the future. In the last 10 years, intense studies aimed at the development of a malaria vaccine have provided important knowledge of the nature of the host immunological mechanisms of protection and their respective target antigens. It became well established that protective immune responses can be generated against the distinct stages of Plasmodium. However, in general, protective immune responses are directed at stage-specific antigens. The elucidation of the primary structure of these antigens made possible the generation of synthetic and recombinant proteins that are being extensively used in experimental immunizations against the infection. Today, several epitopes of limited polymorphism have been described and protective immunity can be generated by immunization with them. These epitopes are being tested as primary candidates for a subunit vaccine against malaria. Here we critically review the major roadblocks for the development of a malaria vaccine and provide some insight on how these problems are being solved.
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Affiliation(s)
- I S Soares
- Departamento de Patologia, Universidade Federal do Pará, Belém, Brasil
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699
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Ramasamy R. Molecular basis for evasion of host immunity and pathogenesis in malaria. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1406:10-27. [PMID: 9545516 DOI: 10.1016/s0925-4439(97)00078-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The article relates the ability of the malaria parasite Plasmodium falciparum to avoid a protective immune response, and to induce pathological changes, to the properties of specific parasite molecules. Cytoadherence and rosetting are important features of cerebral malaria and involve proteins located on the surface of the infected red blood cell. Proinflammatory cytokines, particularly tumour necrosis factor (TNF), play a role in protective immunity and in inducing pathology. Glycophosphatidyl inositol membrane anchors of parasite proteins possess insulin like activity and induce TNF synthesis. People subject to repeated infections in malaria endemic areas rarely develop complete or sterile immunity to malaria. They frequently carry small numbers of parasites in the blood, with little symptoms of the disease, illustrating a phenomenon termed semi-immunity. The basis for semi-immunity is incompletely understood. Malaria parasites are susceptible to several immunological effector mechanisms. The presence of extensive repetitive regions is a feature of many P. falciparum proteins. Available evidence suggests that the structural characteristics of the repeats and their location on the surface of parasite proteins promote immunogenicity. The repeats may help the parasite evade host immunity by (i) exhibiting sequence polymorphism, (ii) preventing the normal affinity and isotype maturation of an immune response, (iii) functioning possibly as B cell superantigens, (iv) generating predominantly thymus independent antibody responses, and (v) acting as a sink for binding protective antibodies. Sequence diversity in non-repetitive regions and antigenic variation in parasite molecules located on the surface of infected red blood cells also play a role in immune evasion. Some sequence homologies between parasite and human proteins may be due to molecular mimicry. Homologies in other instances can cause autoimmune responses. The immune evasion mechanisms of the parasite need to be considered in developing vaccines. Protective immunity and pathology may be delicately balanced in malaria.
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Affiliation(s)
- R Ramasamy
- Molecular Biology Laboratory, Institute of Fundamental Studies, Kandy, Sri Lanka.
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700
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Chen Q, Barragan A, Fernandez V, Sundström A, Schlichtherle M, Sahlén A, Carlson J, Datta S, Wahlgren M. Identification of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) as the rosetting ligand of the malaria parasite P. falciparum. J Exp Med 1998; 187:15-23. [PMID: 9419207 PMCID: PMC2199182 DOI: 10.1084/jem.187.1.15] [Citation(s) in RCA: 221] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Severe Plasmodium falciparum malaria is characterized by excessive sequestration of infected and uninfected erythrocytes in the microvasculature of the affected organ. Rosetting, the adhesion of P. falciparum-infected erythrocytes to uninfected erythrocytes is a virulent parasite phenotype associated with the occurrence of severe malaria. Here we report on the identification by single-cell reverse transcriptase PCR and cDNA cloning of the adhesive ligand P. falciparum erythrocyte membrane protein 1 (PfEMP1). Rosetting PfEMP1 contains clusters of glycosaminoglycan-binding motifs. A recombinant fusion protein (Duffy binding-like 1-glutathione S transferase; Duffy binding-like-1-GST) was found to adhere directly to normal erythrocytes, disrupt naturally formed rosettes, block rosette reformation, and bind to a heparin-Sepharose matrix. The adhesive interactions could be inhibited with heparan sulfate or enzymes that remove heparan sulfate from the cell surface whereas other enzymes or similar glycosaminoglycans of a like negative charge did not affect the binding. PfEMP1 is suggested to be the rosetting ligand and heparan sulfate, or a heparan sulfate-like molecule, the receptor both for PfEMP1 binding and naturally formed erythrocyte rosettes.
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Affiliation(s)
- Q Chen
- Microbiology and Tumor Biology Center, Karolinska Institutet, the Swedish Institute for Infectious Disease Control, S-171 77 Stockholm, Sweden
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