Antibody-dependent macrophage-mediated cytolysis in a murine syngeneic tumor system.

Peritoneal immune macrophages from C3H mice immunized against syngeneic MM46 ascites tumor cells specifically lysed these tumor cells in the presence of immune sera in vitro. An active factor(s) essential for macrophage-mediated cytolysis was purified nonspecifically by gel filtration and then three types of ion-exchange column chromatography. One factor was a specific antibody belonging to the IgG2 a subclass. Neither immune macrophages nor the syngeneic antitumor antibody alone had a cytolytic action on the target cells. Thus, we named the reaction antibody-dependent immune macrophage-mediated cytolysis. The immune macrophages apparently destroyed the sensitized tumor cells in vitro by a nonphagocytic form of cell-contact and this type of cytolysis was independent of a complement. No evidence was obtained for a soluble cytotoxic factor released on interaction of immune macrophages with sensitized tumor cells. Living immune macrophages were essential for the cytolytic action and their activity depended on contractile microfilaments and protein synthesis as revealed by studies with specific inhibitors.