Control of carcinogenesis: a possible role for the activated macrophage

Cytotoxic activity of activated mouse macrophages against mouse embryo fibroblasts was tested before and after spontaneous transformation of the fibroblasts in vitro. Activated macrophages caused little or no destruction of untransformed fibroblasts but were markedly cytotoxic to the same fibroblasts after spontaneous transformation. The efferent limb of this cytotoxic reaction appears to be nonimmunologic and to be related to abnormal growth properties rather than to the antigenic composition of target cells.