Quantification of T cells reactive to Pf155/RESA peptides in Plasmodium falciparum-exposed individuals

This study was designed to estimate, among T lymphocytes circulating in the peripheral blood of donors exposed to malaria parasites, the frequencies of those responding to Plasmodium falciparum antigens, and more specifically to Pf155/RESA peptides. The values of peptide-reactive T-cell frequencies were dispersed and rather low, ranging from 1:24,000 to undetectable (superior to 1:300,000). Subjects presented with different past exposure to parasites: either they had been repetitively exposed to malaria parasite infestation or they were recovering from a recent treated malaria attack. However, they had similar frequencies of T cells reactive to Pf155/RESA peptides. With cells from a minority of patients, "saw-tooth curves" were obtained, suggesting the existence of suppressor mechanisms operating in vitro in our limiting dilution assay.