A comparison of sporozoite and cyst merozoite surface proteins of Sarcocystis.

Surface labeling of Sarcocystis muris and S. suicanis sporozoites with N-hydroxysuccinimide biotin led to the detection of major membrane proteins with relative molecular weights of 29 and 30 kDa, respectively. Immunoblots of Sarcocystis sporozoite proteins probed with sera from infected hosts or with polyclonal monospecific antibodies generated against membrane antigens of cyst merozoites (noncorresponding stages) showed cross-reactivity between the two developmental stages (cyst merozoites and sporozoites) as well as between the species S. muris and S. suicanis. Two-dimensional gel electrophoresis resulted in the identification of isoforms of the sporozoite membrane antigens, with isoelectric points ranging from pH 4.7 to pH 6.4 for S. muris and from pH 4.7 to pH 5.2 for S. suicanis. The molecular masses, the charge heterogeneity, and the immunological reactivity of the surface proteins of Sarcocystis sporozoites were similar to those of cyst merozoites of both species.