Antibodies to the ring-infected erythrocyte surface antigen of Plasmodium falciparum elicited by infection with Plasmodium malariae.

The ring-infected erythrocyte surface antigen (RESA) of Plasmodium falciparum (RESA-P), found in the membrane of erythrocytes infected with young asexual stages of P. falciparum, is a promising vaccine candidate. Antibodies to RESA-P were inducible by infection with another human malaria species, P. malariae. Of 298 serum samples from inhabitants of three isolated localities in Peru where P. vivax and P. malariae were endemic and P. falciparum had never been reported, 26% had anti-RESA-P antibodies as evidenced by a modified immunofluorescent-antibody assay and confirmed by Western blot (immunoblot) analysis. These seroepidemiologic observations were corroborated by the fact that of six chimpanzees infected with P. malariae, three developed anti-RESA-P antibodies after infection. The modified immunofluorescent-antibody-reactive antibodies, purified by adsorption and elution on monolayers of glutaraldehyde-fixed and air-dried P. falciparum-infected erythrocytes, reacted in an immunofluorescent-antibody assay with both parasite structures and erythrocyte membrane in P. falciparum antigen preparations, but only with parasite structures in P. malariae antigen preparations. This serologic cross-reactivity between P. falciparum and P. malariae is of interest in view of the importance of RESA-P as a vaccine candidate and because the two species are coendemic in many areas.