Natural macrophage cytotoxicity against Trichomonas vaginalis is mediated by soluble lytic factors

Mechanisms of lysis of the extracellular protozoan Trichomonas vaginalis by uninduced resident macrophages were analyzed. Supernatants obtained by culturing such macrophages with T. vaginalis were cytotoxic for the protozoa in a dose-dependent manner. Supernatants from macrophages cultured alone were cytotoxic at lower levels, whereas those obtained from T. vaginalis alone and from macrophages cultured with unrelated cells (B77) were not cytotoxic. Cytotoxic activity appeared after 4 h of contact between effectors and target cells and reached a plateau at 18 to 24 h. Microtubule disrupting agents (colchicine and vinblastine) enhanced protozoan lysis, whereas cytochalasin B, an inhibitor of microfilaments, completely blocked T. vaginalis lysis. Treatment of macrophages with protein synthesis inhibitors (cycloheximide and puromycin) impaired effector cytotoxicity. Lytic activity remained after dialysis of supernatants, treatment with 10% bovine fetal serum, and treatment at 56 degrees C for 1 h, but it was completely prevented by treatment at 90 degrees C for 10 min. In conclusion, our data show that natural cytotoxicity against T. vaginalis is performed by normal resident macrophages through the release of at least two heterogeneous soluble factors.