Malaria antigen-specific T-cell responsiveness during infection with Plasmodium falciparum.

Protective immunity against Plasmodium falciparum develops only after several years of repeated exposure to the malarial parasite. We therefore investigated the possibility that acute malaria was associated with malarial antigen-specific immunosuppression. Peripheral lymphocytes of West Africans with and without P. falciparum infections were tested for their in vitro proliferative responses to a preparation of P. falciparum antigen. There was no significant difference between the magnitude of the proliferative response of lymphocytes from infected as compared to normal Africans, although the responses from both African groups were significantly higher than responses from a group of European controls. Furthermore, no soluble inhibitor of antigen-specific proliferation was present in plasma of infected patients. These observations strongly suggest that if the sluggish development of protective immunity in malaria is based upon infection-related immunosuppression, this occurs without affecting the proliferative responsiveness of specific sensitized, circulating T cells. Preliminary observations also indicate that Europeans residing in Africa and taking malaria prophylaxis may acquire sensitized T cells without experiencing clinically apparent infections.