Tumor-associated macrophages of mouse mammary tumors. I. Differential cytotoxicity of macrophages from metastatic and nonmetastatic tumors.

Macrophages were isolated from a series of transplanted mouse mammary tumors, originally derived from a single spontaneously arising tumor, to determine whether macrophage content or function correlated with any of a wide range of tumor properties. None of the tumor cell lines differed significantly in susceptibility to killing by MVE-2-activated peritoneal macrophages (cytotoxicity ranged from 40 to 63%). No significant differences were observed in macrophage content among the five tumor lines, nor was there any correlation between macrophage content and tumor weight, time since transplantation, or ability to metastasize. A significant association was observed, however, between a tumor's ability to metastasize to lung spontaneously and the tumoricidal activity of that tumor's infiltrating macrophages. Significant tumoricidal activity was seen when macrophages isolated from every metastatic tumor studied were used, whereas macrophage-mediated tumoricidal activity was observed in only 35% (6 of 17) of nonmetastatic tumors. Macrophage cytotoxicity was associated with spontaneous metastasis and not with lung colony formation per se.