Co-operation between macrophages and a factor from lymphocytes in tumor lysis in vitro

Peritoneal cells from C3H/He mice immunized against syngeneic MM46 ascites tumor cells specifically lysed these tumor cells in vitro, while spleen cells or lymph node cells from immunized hosts were completely ineffective. The effector cells differed from lymphocytes in their morphological characteristics, property of adherence, phagocytic activity, and sensitivity to anti-theta serum. The cytolytic action of the peritoneal cells was not due to cytotoxic lymphocytes, but to macrophages. These macrophages lysed tumor cells in co-operation with a factor derived from immunoglobulin-bearing lymphocytes. Neither macrophages from immunized hosts nor the factor from lymphocytes alone had a cytolytic action on the target cells. Normal macrophages showed some cytolytic activity in the presence of the factor from lymphocytes.