MAPPING OF SPECIFIC AND PROMISCUOUS HLA-DR-RESTRICTED T-CELL EPITOPESON THE PLASMODIUM-FALCIPARUM 27-KILODALTON SEXUAL STAGE-SPECIFIC ANTIGEN

We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual stage-specific antigen, of the human malaria parasite Plasmodium falciparum in subjects with a history of malaria. Pfg27, expressed early in the sexual stages, is recognized by monoclo nal antibodies capable of reducing the infectivity of gametocytes in m osquitoes. By using 16 Pfg27-specific CD4(+)-T-cell clones derived fro m three donors, seven different T-cell epitopes were identified. Among them, P11 (amino acids 191 to 210 of the Pfg27 sequence, IDVVDSYIIKPI PALPVTPD) was found to contain a previously described binding motif fo r multiple HLA-DR allotypes, Indeed, P11 was found to be promiscuous i n that it could be recognized by T cells in the context of at least fi ve different HLA-DR molecules. The cytokine profile of the clones was mixed. Seven of nine T-cell clones exhibited a Th0-like cytokine profi le, producing high levels of gamma interferon (IFN-gamma) and interleu kin-4 (IL-4) upon stimulation with specific peptides and mitogens. The other two clones had a Th1-like cytokine profile with high expression of IFN-gamma and no IL-4. Identification of a promiscuous epitope in Pfg27 could play a significant role in the design of a subunit vaccine for suppressing malaria transmission.