Comparative studies of antigens of erythrocytic and exoerythrocytic merozoites of Plasmodium lophurae: characterization of a surface glycoprotein from exoerythrocytic merozoites.

Rabbits were immunized with merozoite-enriched preparations of erythrocytic and exoerythrocytic Plasmodium lophurae. The antisera were used to compare antigens of the two types of merozoites. The indirect immunofluorescent antibody test showed the presence of common antigens. The growth of exoerythrocytic parasites was inhibited by the homologous antiserum and to a lesser extent by the antiserum prepared against erythrocytic forms. Cultures of exoerythrocytic parasites as well as their normal host cells were labeled metabolically with 35S-methionine, tritiated proline and glucosamine. Nonidet P-40 extracts of labeled merozoite-enriched preparations, infected cells, and normal cells were immunoprecipitated with the two types of antisera and the immunoprecipitates were analyzed on polyacrylamide gels. The results showed that erythrocytic and exoerythrocytic merozoites have several common proteins. A major difference was a glycoprotein with an approximate molecular weight of 110,000 daltons. This glycoprotein was associated with the surface of exoerythrocytic merozoites and was not recognized by antibodies prepared against erythrocytic forms.