Macrophages activated in vitro with lymphocyte mediators kill neoplastic but not normal cells.

Normal guinea pig macrophages incubated for 3 days in vitro with mediator-rich lymphocyte supernatants become cytotoxic for the syngeneic tumors, line 1 hepatoma and MCA-25 fibrosarcoma. Under identical experimental conditions the survival of two normal syngeneic cell types, fibroblasts and kidney cells, was not affected. The activating supernatants were prepared by stimulating sensitized lymphocyte cultures with an antigen unrelated to the target cells. Therefore, this type of macrophage-mediated cytotoxicity appears to be nonspecific but restricted to cells with malignant growth capacities.