Studies on the role of macrophages in regulation of growth and metastasis of murine chemically induced fibrosarcomas.

Murine solid tumors were shown to contain 9-54% medium to large non-malignant cells bearing receptors for immunoglobulin Fc. These cells rapidly adhered to plastic surfaces, were trypsin-resistant, were capable of phagocytosis of latex particles and were sensitive to the lytic effects of anti-macrophage serum and complement. Purified Fc-receptor-positive cells failed to produce tumors, which strongly suggested that they were macrophages. When tumor-cell suspensions, depleted of macrophages by adherence to plastic surfaces, were injected subcutaneously into normal syngeneic mice, the tumors displayed an increased potential for metastasis. By contrast, control animals which received tumor-cell suspensions containing their normal complement of macrophages invariably developed progressive localized tumors. The survival times of mice infected with macrophage-depleted tumor-cell suspensions were significantly shorter (p less than 0.05) than those for animals inoculated with intact tumor-cell suspensions. These studies confirm the existence of a substantial number of macrophages within progressing syngeneic murine solid tumors and strongly suggest a regulatory role for the macrophages in the growth and metastasis of the tumor.