Plasmodium falciparum:Altered Expression of Erythrocyte Membrane-Associated Antigens during Antigenic Variation

The O and R antigenic variants of thePlasmodium falciparumPalo Alto strain present differences in the morphology of the infected red blood cell membrane, in their adhesion properties, surface immunofluorescence, and agglutination specificities and importantly, induce a variant-specific protection after a primary infection inSaimiri sciureusmonkeys. To identify potential targets of variant-specific immunity, we have compared the antigenic makeup of both variants by immunoblot. O-specific monkey sera generated similar profiles on both parasite types, while R-specific sera showed a consistent difference on a high-molecular-mass undefined antigen. Distinct antibody specificities were eluted from the surface of O- or R-infected erythrocytes, generating variant-specific agglutination, surface immunofluorescence, and immuno-blot profiles. An antiserum raised to Pf60.1, predicted to cross-react with the cytoplasmic domain of PfEMP1, reacted with specific, SDS-soluble antigens in both variants. Antigens associated with the membrane of the infected red blood cells were further investigated using several specific antisera. The 85-kDaHRP1gene product was more abundant in O than in R parasites, while the reverse was observed for the PfEMP3 protein. These data indicate that O and R parasites differ in the expression of several antigens associated with the membrane of the infected red blood cell.