Trypanosoma cruzi infects many mammalian cell types in vitro, including fibroblasts and macrophages. We have analyzed and compared the infection of mouse 3T3 fibroblasts and J774 macrophage-like tumor cells by cloned Y-A1.2 T. cruzi trypomastigotes. The effects of T. cruzi-specific antibodies and of interferon (IFN) on infection were considered. Specific antibodies protected 3T3 fibroblasts from infection by T. cruzi, but increased the relative infectivity for J774 cells due to binding of the opsonized parasite to J774 Fc receptors. It was also apparent that IFN-alpha, beta (produced by fibroblasts) and IFN-gamma (produced by T lymphocytes) activated trypanocidal activities in both 3T3 and J774 cells, although IFN-gamma was 100 to 2000 times more effective than IFN-alpha, beta on the basis of IFN antiviral units added per culture. When anti-T. cruzi antibodies and IFN-alpha, beta or IFN-gamma were used jointly, a synergistic protective effect was observed with both 3T3 fibroblasts and J774 cells. These results suggest that B and T lymphocytes might collaborate in vivo in the protection against T. cruzi infections by the production of anti-trypomastigote antibodies and IFN-gamma, respectively.

The surface membrane antigens of infectious Trypanosoma cruzi trypomastigotes were studied at the levels of the strain and of individual trypomastigote clones. Blood trypomastigotes from three T. cruzi strains, Y, CL and Tehuantepec ("Teh"), were grown in vitro by weekly infection of J774 mouse macrophage tumor cells. Each T. cruzi strain was subsequently cloned by infection of J774 cells at limited trypomastigote dilution, and antisera were produced in mice against a selection of trypomastigote clones. Criss-cross panel analyses indicated the existence of a large degree of polymorphism among trypomastigote surface antigens. Various trypomastigote surface antigens were cross-reactive, appeared to be highly conserved, and were common to the three strains considered and to all the clones derived from each strain. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that numerous trypomastigote antigenic proteins were precipitated by mouse antisera generated against cloned trypomastigotes. Some of these proteins were commonly distributed, while others were polymorphic. Finally, a state of cross-reactive immunity could be induced in C3H/He mice by infection with a cloned T. cruzi trypomastigote population. Immune mice resisted subsequent infections with lethal doses of wild-type bloodstream trypomastigotes from any one of the three T. cruzi strains.

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