Spontaneous tumor cell killing by human blood monocytes and human peritoneal macrophages: lack of alteration by endotoxin or quenchers of reactive oxygen species.

Human mononuclear phagocytes (monocytes and macrophages) act as effectors in the destruction of tumor cells. Peritoneal macrophages from normal or infertile women killed a variety of tumor cells in vitro more efficiently than did blood monocytes from the same subjects. Lysis depended on the effector-to-target cell ratio and was neither reproduced by supernatants from nor lysates of the mononuclear phagocytes. Normal fibroblasts were not lysed. Lipopolysaccharide (10(1)-10(4) ng/ml) did not alter the monocyte- or macrophage-mediated tumor cell killing. The monocytes and macrophages had equivalent basal and phorbol 12,13-myristate acetate-stimulated H2O2 and O-2 production, and the reactive oxygen species scavengers or quenchers catalase, superoxide dismutase, mannitol, and L-histidine did not diminish the killing. These observations suggest that the spontaneous tumor cell killing by human mononuclear phagocytes was not mediated by reactive oxygen species.