Biochemical and immunological characterization of major surface antigens of Sarcocystis muris and S. suicanis cyst merozoites

Surface proteins of Sarcocystis cyst merozoites were labeled by biotinylation or radioiodination and identified on Western blots after sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE). The major labeled proteins of S. muris and S. suicanis have relative molecular masses of 31 and 33 kDa, respectively. Immunoblots performed with the 31-kDa protein and sera of experimentally infected mice or with monoclonal antibodies to S. muris revealed that this protein is immunogenic. Indirect fluorescent antibody tests (IFAT) executed using Sarcocystis cyst merozoites and polyclonal monospecific antibodies obtained from rabbits immunized with homogeneous major surface antigens gave additional evidence for the localization of the identified antigens in the pellicle. Analysis of S. muris and S. suicanis proteins by two-dimensional gel electrophoresis revealed multiple isoelectric forms.