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The effect of reinoculation with trypomastigotes on the level of protective antibodies in mice chronically infected with T. cruzi.

1. The levels of specific antibodies were determined in sera from mice chronically infected with T. cruzi using indirect immunofluorescence, complement-mediated lysis, and neutralization of bloodstream trypomastigote (Try) infectivity upon their incubation with the test sera in vitro and passive transfer of immune sera. 2. The sera were obtained at different times after T. cruzi inoculation performed one to five times using live Y or CL bloodstream Try, two polar strains of T. cruzi. 3. High levels of protective and nonprotective antibodies were detected from week 4, the first interval studied, onward, regardless of number of inoculations and time of infection. 4. Sera from CL-infected mice had lower antibody titers at week 4 and the ability of whole sera or semipurified IgG to neutralize the infectivity of bloodstream Try was lower at this time. 5. All other sera obtained during the chronic phase were strongly effective in decreasing parasite infectivity as measured by lower parasitemia and mortality of mice inoculated with the serum-treated Y strain bloodstream Try.