Effects on in vitro tumor growth of murine macrophages isolated from sarcoma lines differing in immunogenicity and metastasizing capacity

Macrophages were isolated from the strongly immunogenic, non-metastasizing FS6 sarcoma transplanted in syngeneic C57BL/6 mice and from a weakly immunogenic, spontaneously metastasizing line (mFS6) of the same tumor. Macrophages isolated from the FS6 sarcoma non-specifically inhibited growth and DNA synthesis of tumor cells in vitro. After culture FS6 macrophages rapidly lost their cytotoxic activity and became capable of non-specifically stimulating tumor growth in vitro. Macrophages obtained from the mFS6 tumor non-specifically enhanced the proliferative activity of tumor target cells and this capacity was maintained when the macrophages were cultured.