Toxoplasma gondii: antigenic differences between endozoites and cystozoites defined by monoclonal antibodies.

The antigenic differences between endozoites and cystozoites of Toxoplasma gondii were analyzed by indirect immunofluorescent assay and Western blotting using monoclonal antibodies. An antigenic determinant of an antigen of 20 kDa mol. wt. that appeared to be localized in the cytoplasm was observed to be specific to cystozoites alone. The 20-kDa antigen was diffused throughout the parasite and was observed in cystozoites produced both in vivo and in vitro.