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Lymphocyte Responses to Plasmodium falciparum Ring-Infected Erythrocyte Surface Antigen (Pf155/RESA) Peptides in Individuals with Naturally Acquired Plasmodium falciparum Malaria
Antibody titers and lymphocyte responses to synthetic peptides corresponding to repeated amino acid sequences of the 3′ and 5′ regions of Pf155/ring-infected erythrocyte surface antigen (RESA) were studied in two groups of Thai subjects, soldiers (Rangers), and villagers who differed in their history of malaria exposure. The frequency of Pf155/RESA seropositivity was similar in the two groups while the frequency of high titer antibody was significantly greater in villagers than in Rangers. Lymphocyte responsiveness in vitro to all Pf155/RESA peptides was infrequent for both groups although half of the subjects studied responded to crude Plasmodium falciparum asexual blood stage malaria antigen (MA). Among responders, Pf155/RESA peptides elicited lymphocyte responses in which proliferation and interferon-gamma (IFN-γ) production were not associated, whereas with MA, the two responses were associated. The MA-stimulated lymphocyte proliferation and IFN-γ production for both groups of volunteers appeared to be independent of antibody titer. In this study, antibody, but not lymphocyte, responses to Pf155/RESA peptides were shown to reflect differences in prior exposure and levels of acquired immunity to falciparum malaria.