Macrophage-mediated cytotoxicity: role of a soluble macrophage cytotoxic factor similar to lymphotoxin and tumor necrosis factor.

Abstract

Guinea pig peritoneal macrophages, when activated for cytotoxicity by the calcium ionophore A23187 or lipopolysaccharide, produce a cytotoxic factor [macrophage cytotoxic factor (M.vphi.-CF)] that is not blocked by catalase or protease inhibitors. Fractionation of culture supernates containing M.vphi.-CF by gel filtration revealed 1 peak of cytotoxic activity of Mr .apprxeq. 45,000, the same as guinea pig lymphotoxin (LT). Antiserum prepared against purified guinea pig LT completely neutralized the cytotoxic activity of M.vphi.-CF. In addition, the cytotoxic factor in guinea pig tumor necrosis serum was found to have a Mr of 45,000 and was neutralized by anti-LT. Thus, M.vphi.-CF is physicochemically and immunochemically similar to LT and tumor necrosis factor if not identical. To investigate the role of M.vphi.-CF in macrophage-mediated cytotoxicity, anti-LT was added to A23187- or lipopolysaccharide-activated macrophages before addition of L-929 target cells. In 10 of 16 experiments, the inhibition of macrophage-mediated cytotoxicity was 100%. In the others, cytotoxicity was blocked partially, the lowest inhibition being 49%. The effectiveness of inhibition appeared to be inversely related to the intensity of macrophage activation. M.vphi.-CF plays a significant role in macrophage-mediated cytotoxicity but involvement of another mechanism cannot be excluded.