Relative resistance of Brazil strain trypomastigote forms of Trypanosoma cruzi to in vitro antibody-dependent complement-mediated lysis.

Various assay conditions were employed in experiments examining the susceptibility of trypomastigote forms of the Brazil strain of Trypanosoma cruzi to antibody-dependent complement-mediated lysis. To identify optimal assay conditions, both guinea pig serum and normal human serum were used as complement sources, and fibroblast-derived or blood-form trypomastigotes were either coincubated with immune sera and complement together, or the parasites were first precoated with antibodies and then were incubated in complement. Under conditions promoting maximal lysis by antibodies and complement, 60-90% of the trypomastigote forms were not lysed. These results indicate that trypomastigotes of certain isolates of T. cruzi, such as the Brazil strain, may possess an escape mechanism by which they evade complement-mediated lysis.