Bacillus Calmette-Guérin-activated murine macrophages kill syngeneic melanoma cells under strict anaerobic conditions.

Abstract

The spontaneous killing of B559 melanoma cells by BCG-elicited macrophages was studied under strictly anaerobic conditions to investigate the role of O2 in macrophage-mediated cytotoxicity. The number of melanoma cells capable of forming colonies after aerobic or anaerobic incubation with BCG-macrophages was used as the index of cytotoxicity. The BCG-macrophages killed melanoma cells regardless of the amount of O2 present. The killing observed was proportional to the ratio of effector cells added; a ratio of 25:1 effector to target cells was required to achieve nearly 90% cytotoxicity both aerobically and anaerobically. This cytotoxicity was not dependent on a diffusible macrophage product nor on alteration of the medium by macrophages, since tumor cells incubated in the same culture medium, but not in contact with a mixed population of tumor cells and macrophages, were not killed. Macrophage-mediated cytotoxicity was evidently dependent on macrophage-tumor cell contact. The mechanism responsible for the O2-independent cytotoxicity is unknown at present.