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A longitudinal study was undertaken in Burkina Faso among 293 children aged 6 months to 9 years in order to determine the correlation between an antibody response to several individual malarial antigens and malarial infection. It was found that the presence of a positive antibody response at the beginning of the rainy season to three long synthetic peptides corresponding to Plasmodium falciparum Exp-1 101-162, MSP-3 154-249 and GLURP 801-920 but not to CSP 274-375 correlated with a statistically significant decrease in malarial infection during the ongoing transmission season. The simultaneous presence of an antibody response to more than one antigen is indicative of a lower frequency of malarial infection. This gives scientific credibility to the notion that a successful malaria vaccine should contain multiple antigens.

Summary The present work describes the recognition of three synthetic polypeptides encompassing the N- and C-terminal regions of the transmembrane Exp-1 protein of the parasite Plasmodium falciparum by plasma and peripheral blood mononuclear cells from naturally exposed individuals living in African endemic areas. The three polypeptides comprise the sequences 23–105, 73–162 and 101–162, and overlap at the transmembrane domain (73–105). Thus, they permitted characterization of the immune response specific to the N- and C-terminal domains in an independent fashion. Two different populations were evaluated, one in the village of Safo in Mali and the other in the villages of Somnaway, Kabortenga and Toussouktenga in Burkina Faso. Antibodies to the sequence 73–162 of Pf Exp-1 were found in 70% of adult Mali donors and in all of the donors tested from Burkina Faso. Strikingly, the N-terminal fragment Pf Exp-1 23–105 was only weakly recognized by a few donors. Evaluation of the T-cell response indicated that the peptide Pf Exp-1 23–105 was more potent than Pf Exp-1 73–162 in inducing a proliferative response. A correlation between peptide-specific interferon-γ and interleukin-6 production and proliferation to peptide Pf Exp-1 23–105 was observed. Further studies are needed to evaluate this molecule as a vaccine candidate.