Stage-specific proteins and glycoproteins of plasmodium falciparum: identification of antigens unique to schizonts and merozoites.

Establishment of highly synchronized cultures of Plasmodium falciparum enabled identification of stage-specific proteins, glycoproteins, and antigens. Comparison of metabolically labeled constituents of rings, trophozoites, mature schizonts, and merozoites indicated the absence of major proteins or glycorproteins unique to rings or trophozoites. A burst of new synthetic activity occurred during schizogony when several schizont- and merozoite-specific proteins and glycoproteins became apparent. In addition to the knob protein, which was previously shown to be associated with protrusions on the host erythrocyte membrane, a major glycoprotein of parasite origin was identified on the surface membrane of schizonts. Analysis of antigens solubilized from different developmental stages indicated that immune sera, which inhibit growth of parasites in vitro, react mainly with merozoite- and schizont-associated antigens.