Plasmodium falciparum parasites causing cerebral malaria share variant surface antigens, but are they specific?

BACKGROUND: Variant surface antigens (VSA) expressed on the surface of Plasmodium falciparum-infected red blood cells constitute a key for parasite sequestration and immune evasion. In distinct malaria pathologies, such as placental malaria, specific antibody response against VSA provides protection. This study investigated the antibody response specifically directed against VSA expressed by parasites isolated from individuals presenting a given type of clinical presentation. METHODS: Plasma and isolates were obtained from four groups of Beninese subjects: healthy adults, patients presenting uncomplicated malaria (UM), cerebral malaria (CM), or pregnancy-associated malaria (PAM). The reactivity of plasma samples from each clinical group was measured by flow cytometry against parasites isolated from individuals from each clinical group. RESULTS: Antibody responses against VSA(UM )were predominant in CM, UM and HA plasmas. When analysed according to age in all plasma groups, anti-VSA(CM )and -VSA(UM )antibody levels were similar until six years of age. In older groups (6-18 and >19 years of age), VSA(UM )antibody levels were higher than VSA(CM )antibody levels (P = .01, P = .0008, respectively). Mean MFI values, measured in all plasmas groups except the PAM plasmas, remained low for anti-VSA(PAM )antibodies and did not vary with age. One month after infection the level of anti-VSA antibodies able to recognize heterologous VSA(CM )variants was increased in CM patients. In UM patients, antibody levels directed against heterologous VSA(UM )were similar, both during the infection and one month later. CONCLUSIONS: In conclusion, this study suggests the existence of serologically distinct VSA(CM )and VSA(UM). CM isolates were shown to share common epitopes. Specific antibody response to VSA(UM )was predominant, suggesting a relative low diversity of VSA(UM )in the study area.