Circumsporozoite proteins of human malaria parasites Plasmodium falciparum and Plasmodium vivax.

Abstract

Monoclonal antibodies were raised against sporozoites of Plasmodium falciparum and P. vivax. The antibodies reacted with polypeptides (circumsporozoite proteins) that are uniformly distributed over the entire surface of sporozoites, as shown by indirect immunofluorescence and by the circumsporozoite precipitin reaction. The epitopes recognized by the monoclonal antibodies were expressed on sporozoites from different geographical isolates of the homologous species but were not detected on sporozoites of heterologous species nor on blood forms of the parasite. The monoclonal antibody to P. falciparum specifically immunoprecipitated 2 polypeptides of apparent MW 67,000 (Pf67) and 58,000 (Pf58) from extracts of [35S]methionine-labeled P. falciparum sporozoites. The anti-P. vivax monoclonal immunoprecipitated 2 proteins of MW 51,000 (Pv51) and 45,000 (Pv45) from extracts of metabolically labeled P. vivax sporozoites. The extracts were reacted with the serum of human volunteers successfully vaccinated with sporozoites of either P. vivax or P. falciparum. The immunoprecipitation patterns were almost identical to those obtained with the corresponding monoclonal antibodies. The circumsporozoite proteins of P. falciparum and P. vivax play a role in immune protection. Incubation of the appropriate monoclonal antibody with viable sporozoites of the homologous species significantly reduced parasite infectivity, as determined by sporozoite neutralization assays carried out in splenectomized chimpanzees.