Identification and biochemical characterization of antigens of tachyzoites and bradyzoites of Toxoplasma gondii with cross-reactive epitopes.

The aim of the present work was the identification and biochemical characterization of antigens from the tachyzoite and bradyzoite stages of Toxoplasma gondii that share cross-reactive epitopes. Our previous work has demonstrated the induction by tachyzoite excreted-secreted antigens of both a humoral and a cell-mediated protective response. We investigated the question as to whether some bradyzoite and tachyzoite (excreted-secreted, soluble or membrane) antigens share cross-reactive epitopes. Using immunoprecipitation techniques, we identified four tachyzoite antigens with molecular weights of 63, 43, 39, and 28.5 kDa, which were recognized both by sera raised against tachyzoite antigens and by chronic-phase human sera with residual IgG antibodies. In an attempt to define the biochemical nature of these antigens, we show that the 43- and 28.5-kDa antigens seem to be glycosylated since they bind to concanavalin A, as does a 37-kDa tachyzoite antigen.