Evidence for diversity of Plasmodium falciparum sporozoite surface antigens derived from analysis of antibodies elicited in humans.

We have compared the reactivities of antibodies developed by individuals frequently exposed to Plasmodium falciparum infections with the epitopes contained within the repeats of the circumsporozoite (CS) protein and their reactivities with the epitopes of a native molecule(s) accessible on the sporozoite surface. Results of direct-binding assays and competition assays between artificial and native molecules or between human antibodies and anti-CS monoclonal antibodies suggest that humans respond preferentially to epitopes not contained within the repeats of the CS protein and probably not contained in the whole CS protein. Human monoclonal antibodies reactive with P. falciparum sporozoite surface antigens were produced by Epstein-Barr virus transformation of human lymphocytes. Their pattern of reactivity with sporozoites from a number of different isolates indicates the existence of several distinct epitopes on the parasite surface. Differences between isolates and between sporozoites within a given sample were observed. No single human monoclonal antibody capable of detecting an epitope expressed in all the parasites studied was found.