Trypanosoma cruzi: recognition of trypomastigote surface antigens by lytic antisera from mice resistant to acute infection.

The complement-dependent lytic activity of various mouse antisera to Trypanosoma cruzi was tested, using purified culture metacyclic trypomastigotes as targets, in an attempt to verify the correlation between resistance to T. cruzi and lytic antibodies, Sera of mice immunized with killed trypomastigotes, which resisted acute infection by insect-derived metacyclics of T. cruzi, consistently lysed over 95% of trypomastigotes in vitro. In contrast, fewer than 50% of parasites were lysed by sera of mice immunized with killed epimastigotes, which, upon challenge with metacyclic forms, developed high parasitemias comparable to those of non-immunized controls. All immune sera with high lytic activity, namely sera of mice immunized with killed trypomastigotes and sera of chronically infected mice, reacted with a set of 131I-labeled trypomastigote surface proteins with apparent molecular weights of 77,000, 82,000, and 88,000, which failed to be recognized by sera of mice immunized with epimastigotes, Absorption of lytic sera with trypomastigotes, but not with epimastigotes, greatly reduced the ability to lyse trypomastigotes and to precipitate the surface polypeptides.