Transformation of Trypanosoma cruzi trypomastigote bloodstream forms by immune IgM and its Fab mu fragment into activators of the alternative complement pathway.

1. We report that purified immune IgM obtained from Chagasic patients during the chronic stage of the disease and also immune IgM and its Fab mu fragments obtained from chronically T. cruzi-infected mice are capable of preparing trypomastigote forms of T. cruzi to be lysed by complement. 2. Mouse strains susceptible, moderately susceptible and resistant to T. cruzi infection are equally capable of producing antibodies with lytic activity as well as antibodies detectable by immunofluorescence and by immunoenzymatic assay. 3. The epitopes recognized by polyclonal lytic antibodies are present on the surface of trypomastigotes from many different strains and stocks of T. cruzi.