Biological and immunological studies on a low virulence isolate of the Tulahuén strain of Trypanosoma cruzi.

Reduced virulence for mice was characterized in an isolate (LV1) of a clone of the Tulahuén strain of Trypanosoma cruzi. LV1 caused long term chronic parasitemias which were measured for 140 days in both C3H/He and BALB/c mice inoculated with 1 x 10(5) trypanosomes/mouse. In contrast to the acute and rapidly lethal Tulahuén strain infections in both strains of mice, all of the animals survived the LV1 infections. Sera of C3H/He mice infected with the Tulahuén strain or LV1 isolate displayed similar titers in an enzyme-linked immunosorbent assay (ELISA) when reacted against homologous or heterologous extracts of epimastigote stages of the trypanosomes. Western blot reactions of the Tulahuén, Raccoon V, LV1 isolates, and the closely related European bat parasite, Trypanosoma dionisii defined shared antigens between the strains and species, while some appeared to be strain- and species-specific. The studies indicate a mutational event(s) resulted in reduced virulence and suggest that survival of the mice infected with T. cruzi is not correlated with high ELISA antibody titers. Since lower antibody titers are exhibited by mice infected with LV1 than mice infected with the Tulahuén strain, survival may be dependent on the specificities of the antibodies synthesized during the infections, cell mediated immune responses, and/or biochemical factors of the LV1 isolate which control virulence and differ from those of the original Tulahuén strain.