STRUCTURE AND FUNCTION OF PROTECTIVE ANTIBODIES FROM MEMORY B CELLS AGAINST MALARIA

Malaria remains a significant contributor to the global burden of disease. In endemic regions, malaria mostlyaffects children. Older individuals are protected from disease by an immune response against the parasite?sblood stage. Eliciting a protective immune response in children by vaccination would significantly reducemalaria morbidity and mortality. Antibodies are a critical component of such protection. A strong correlationexists between antibodies against merozoite antigens and a reduction in malaria incidence. Unfortunately,vaccines based on these antigens have thus far not been effective, suggesting that our understanding ofprotective immunity is far from complete. This proposal stems from the observation that persistent malariaexposure eventually gives rise to antibodies reactive against heterologous parasite strains. The long period oftime necessary for the development of protective anti-malaria immunity is suggestive of a long evolutionarypathway towards the generation of such cross-strain reactive antibodies. In addition, protection against diseasehas been shown to correlate with selected antibody effector functions. We hypothesize that the memory B cellpool of malaria-exposed individuals will contain cells that make cross-strain reactive IgGs that aredirected against merozoite antigens, are highly somatically mutated and are of selected IgGsubclasses. To test this hypothesis, we will compare structural and functional features of antibodies directedagainst two merozoite antigens, MSP1 and AMA1, among immune adults, semi-immune children, and childrenwho have been exposed but are still susceptible to malaria. In Specific Aim 1, we will isolate MSP1- andAMA1-specific memory B cells from these individuals and express their monoclonal antibodies using linearexpression cassettes to confirm antigen specificity and determine cross-strain reactivity. In Specific Aim 2, theheavy and light chain variable region sequences and IgG subclasses will be determined for a comparativeanalysis of antibody structures among the three groups of individuals. In addition, antibodies with diversestructural features will be cloned and expressed in their original IgG subclass, and their inhibitory capacityagainst four different strains of P. falciparum will be analyzed in functional assays. This project will usevaluable material from naturally exposed individuals in combination with advanced methodologies to dissectprotective anti-malaria immunity. The comparison of structural and functional antibody features betweensusceptible and protected individuals will provide a wealth of data about the types of antibodies that a bloodstage vaccine should ideally elicit, with respect to features of both the ?head? and the ?tail? of these antibodies.In a follow-up study, identification of the conserved epitopes recognized by these antibodies will reveal noveltargets for immunization.