Mechanisms of resistance against experimental Trypanosoma cruzi infection. Requirements for cellular destruction of circulating forms of T. cruzi in human and murine in vitro systems.

The sensitivity of host (circulating) forms of T. cruzi to cell-mediated immunological destruction and requirements for the reaction were examined. Both human and mouse leucocytes were found to kill significant numbers of parasites in the presence of specific antibodies against the flagellates. Antibody involvement was confirmed by the marked ihhibitory effects on cytotoxicity that resulted from the addition to reaction mixtures of either aggregated normal IgG or purified protein A. Similar inhibition was observed when antiserum to T. cruzi was pre-absorbed with an insoluble protein A preparation. In addition, immunoglobulins present in normal mouse serum failed to support cytotoxicity by cells with demonstrated effector capacity in parallel antibody-containing reactions. In this system, human peripheral blood lymphocytes, neutrophils and eosinophils but not adherent mononuclear cells were able to kill T. cruzi. Also active were mouse lymphoid cells, neutrophils and adherent mononuclear cells. Minimal effector:target cell ratios resulting in detectable trypanosome killing were 0 x 2 and 0 x 6 for human and mouse lymphoid cells, respectively. The present results are relevant to the understanding of the possible mechanisms underlying the protective effects of the immune response against T. cruzi infection.