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The Stability and Complexity of Antibody Responses to the Major Surface Antigen of Plasmodium falciparum Are Associated with Age in a Malaria Endemic Area

2011; Elsevier BV; Volume: 10; Issue: 11 Linguagem: Inglês

10.1074/mcp.m111.008326

1535-9484

Alyssa E. Barry, Angela Trieu, Freya J. I. Fowkes, Jozelyn Pablo, Mina Kalantari-Dehaghi, Algis Jasinskas, Xiaolin Tan, Matthew A. Kayala, Livingstone Tavul, Peter M. Siba, Karen P. Day, Pierre Baldi, Philip L. Felgner, Denise L. Doolan,

HIV Research and Treatment

Individuals that are exposed to malaria eventually develop immunity to the disease with one possible mechanism being the gradual acquisition of antibodies to the range of parasite variant surface antigens in their local area. Major antibody targets include the large and highly polymorphic Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) family of proteins. Here, we use a protein microarray containing 123 recombinant PfEMP1-DBLα domains (VAR) from Papua New Guinea to seroprofile 38 nonimmune children (<4 years) and 29 hyperimmune adults (≥15 years) from the same local area. The overall magnitude, prevalence and breadth of antibody response to VAR was limited at 20) with age, consistent with the breadth of response stabilizing with age. In addition, the antibody response was limited in uninfected children compared with infected children but was similar in adults irrespective of infection status. Analysis of the variant-specific response confirmed that the antibody signature expands with age and infection. This also revealed that the antibody signatures of the youngest children overlapped substantially, suggesting that they are exposed to the same subset of PfEMP1 variants. VAR proteins were either seroprevalent from early in life, (<3 years), from later in childhood (≥3 years) or rarely recognized. Group 2 VAR proteins (Cys2/MFK-REY+) were serodominant in infants (<1-year-old) and all other sequence subgroups became more seroprevalent with age. The results confirm that the anti-PfEMP1-DBLα antibody responses increase in magnitude and prevalence with age and further demonstrate that they increase in stability and complexity. The protein microarray approach provides a unique platform to rapidly profile variant-specific antibodies to malaria and suggests novel insights into the acquisition of immunity to malaria. Individuals that are exposed to malaria eventually develop immunity to the disease with one possible mechanism being the gradual acquisition of antibodies to the range of parasite variant surface antigens in their local area. Major antibody targets include the large and highly polymorphic Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) family of proteins. Here, we use a protein microarray containing 123 recombinant PfEMP1-DBLα domains (VAR) from Papua New Guinea to seroprofile 38 nonimmune children (<4 years) and 29 hyperimmune adults (≥15 years) from the same local area. The overall magnitude, prevalence and breadth of antibody response to VAR was limited at 20) with age, consistent with the breadth of response stabilizing with age. In addition, the antibody response was limited in uninfected children compared with infected children but was similar in adults irrespective of infection status. Analysis of the variant-specific response confirmed that the antibody signature expands with age and infection. This also revealed that the antibody signatures of the youngest children overlapped substantially, suggesting that they are exposed to the same subset of PfEMP1 variants. VAR proteins were either seroprevalent from early in life, (<3 years), from later in childhood (≥3 years) or rarely recognized. Group 2 VAR proteins (Cys2/MFK-REY+) were serodominant in infants (<1-year-old) and all other sequence subgroups became more seroprevalent with age. The results confirm that the anti-PfEMP1-DBLα antibody responses increase in magnitude and prevalence with age and further demonstrate that they increase in stability and complexity. The protein microarray approach provides a unique platform to rapidly profile variant-specific antibodies to malaria and suggests novel insights into the acquisition of immunity to malaria. Malaria caused by infection with Plasmodium falciparum is responsible for over 500 million clinical cases and at least 1 million deaths each year, predominantly in children under five years of age (1Snow R.W. Guerra C.A. Noor A.M. Myint H.Y. Hay S.I. The global distribution of clinical episodes of Plasmodium falciparum malaria.Nature. 2005; 434: 214-217Crossref PubMed Scopus (2151) Google Scholar). After repeated exposure, individuals living in endemic areas develop naturally acquired immunity to malaria, which manifests as an age-associated decline in the prevalence of severe, then mild clinical episodes (reviewed in (2Doolan D.L. Dobaño C. Baird J.K. Acquired immunity to malaria.Clin Microbiol. Rev. 2009; 22 (Table of Contents): 13-36Crossref PubMed Scopus (784) Google Scholar, 3Marsh K. Kinyanjui S. Immune effector mechanisms in malaria.Parasite Immunol. 2006; 28: 51-60Crossref PubMed Scopus (304) Google Scholar)). 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Plasmodium falciparum variant surface antigen expression varies between isolates causing severe and nonsevere malaria and is modified by acquired immunity.J. Immunol. 2002; 168: 3444-3450Crossref PubMed Scopus (169) Google Scholar, 21Bull P.C. Berriman M. Kyes S. Quail M.A. Hall N. Kortok M.M. Marsh K. Newbold C.I. Plasmodium falciparum Variant Surface Antigen Expression Patterns during Malaria.PLoS Pathog. 2005; 1: e26Crossref PubMed Scopus (132) Google Scholar, 22Normark J. Nilsson D. Ribacke U. Winter G. Moll K. Wheelock C.E. Bayarugaba J. Kironde F. Egwang T.G. Chen Q. Andersson B. Wahlgren M. PfEMP1-DBL1alpha amino acid motifs in severe disease states of Plasmodium falciparum malaria.Proc. Natl. Acad. Sci. U.S.A. 2007; 104: 15835-15840Crossref PubMed Scopus (71) Google Scholar, 28Kaestli M. Cockburn I.A. Cortés A. Baea K. Rowe J.A. Beck H.P. Virulence of malaria is associated with differential expression of Plasmodium falciparum var gene subgroups in a case-control study.J. 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Recent evidence shows that this hierarchy of var gene expression is imprinted in the host antibody response, with antibodies against recombinant PfEMP1 domains from the P. falciparum reference strain, 3D7, showing a marked bias toward group A var genes in very young children (<1-year-old) compared with broader recognition of all subgroups by older children and adults (36Cham G.K. Turner L. Kurtis J.D. Mutabingwa T. Fried M. Jensen A.T. Lavstsen T. Hviid L. Duffy P.E. Theander T.G. Hierarchical, domain type-specific acquisition of antibodies to Plasmodium falciparum erythrocyte membrane protein 1 in Tanzanian children.Infect. Immun. 2010; 78: 4653-4659Crossref PubMed Scopus (52) Google Scholar, 37Cham G.K. Turner L. Lusingu J. Vestergaard L. Mmbando B.P. Kurtis J.D. Jensen A.T. Salanti A. Lavstsen T. Theander T.G. Sequential, ordered acquisition of antibodies to Plasmodium falciparum erythrocyte membrane protein 1 domains.J. 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A prospective analysis of the Ab response to Plasmodium falciparum before and after a malaria season by protein microarray.Proc. Natl. Acad. Sci. U.S.A. 2010; 107: 6958-6963Crossref PubMed Scopus (329) Google Scholar, 46Trieu A. Kayala M.A. Burk C. Molina D.M. Freilich D.A. Richie T.L. Baldi P. Felgner P.L. Doolan D.L. Sterile protective immunity to malaria is associated with a panel of novel P. falciparum antigens.Mol. Cell. Proteomics. 2011; 10 (M111.007948)Abstract Full Text Full Text PDF Scopus (117) Google Scholar). Here, we describe the analysis of antibodies to PfEMP1 in Papua New Guinean (PNG) children and adults who are exposed to malaria, using a protein microarray fabricated with 123 recombinant PfEMP1-DBLα domains sampled from parasites infecting the same human population (20Barry A.E. Leliwa-Sytek A. Tavul L. Imrie H. Migot-Nabias F. Brown S.M. McVean G.A. Day K.P. Population genomics of the immune evasion (var) genes of Plasmodium falciparum.PLoS Pathog. 2007; 3: e34Crossref PubMed Scopus (120) Google Scholar). By investigating antibody responses to large numbers of naturally circulating PfEMP1 variants in parallel, this study provides new and important insights into acquisition of immunity to malaria. Samples archived in a biobank at the PNG Institute of Medical Research were used in the study. The informed consent procedure for the initial study consisted of (1) the provision of general information about the aims of the study to the community through holding a village meeting known as a "tok save," (2) information sessions on the study with parents of eligible children in their own household or hamlet, (3) formal meetings with village leaders to obtain their consent for their community to participate in the study. Except for the general information session (step (1)), where there was a complete translation from Melanesian pidgin into local language, all discussions, meetings and forms were held or written in pidgin with village reporters who could translate into the local language when necessary. The aims of the study were conveyed to the individuals in layman's terms. Informed consent was given verbally on the basis of this explanation during enrolment for the survey, as this was the ethical expectation at the time (c.1999). All consenting members of selected populations were eligible for enrolment into the community surveys. People with concurrent or chronic illness that might impede their participation in the surveys were excluded. Enrolment in the study, possible only if consent was given, was recorded in a database. The use of these archived samples for the current study was approved by the PNG Institute of Medical Research Institutional Review Board (IRB) and the Medical Research Advisory Committee of PNG; the Alfred Research and Ethics Unit, Melbourne, Australia, and the University of California Irvine IRB, USA. The study was conducted in the local region of Amele, Madang Province on the north coast of PNG and included eight villages distributed over a 10 km2 area. In this region, intense transmission of P. falciparum malaria occurs year round (47Cattani J.A. Tulloch J.L. Vrbova H. Jolley D. Gibson F.D. Moir J.S. Heywood P.F. Alpers M.P. Stevenson A. Clancy R. The epidemiology of malaria in a population surrounding Madang, Papua New Guinea.Am. J. Trop. Med. Hyg. 1986; 35: 3-15Crossref PubMed Scopus (180) Google Scholar) with inoculation rates ranging from 68–526 infective bites per person per year (48Burkot T.R. Graves P.M. Paru R. Wirtz R.A. Heywood P.F. Human malaria transmission studies in the Anopheles punctulatus complex in Papua New Guinea: sporozoite rates, inoculation rates, and sporozoite densities.Am. J. Trop. Med. Hyg. 1988; 39: 135-144Crossref PubMed Scopus (86) Google Scholar). Blood samples were obtained from asymptomatic volunteers of all ages in November to December of 1999, and separated into plasma (stored at −80°C), buffy coat, and erythrocyte fractions by centrifugation (both stored in