Expression of the precursor of the major merozoite surface antigens during the hepatic stage of malaria.

The precursor of major merozoite surface antigens (PMMSA) and its proteolytic products are candidates for an asexual blood stage vaccine. Previous authors have shown that PMMSA epitopes are expressed in the liver or exoerythrocytic (EE) stage of malaria. Using Plasmodium berghei, we show that the molecular weight of the liver stage PMMSA is similar to that of the blood stage and that both EE and blood stage proteins are similarly processed. In the EE stage, it was synthesized toward the end of schizogony and appeared first to localize to the rough endoplasmic reticulum and then, as the cytomeres began to form, to the parasite plasmalemma. The EE and blood stage merozoites expressed similar amounts of this antigen as determined by indirect immunofluorescence.