Cytokinetic studies of the effects of activated macrophages on tumor target cells.

The kinetics of the in vitro interaction between activated mouse macrophages and tumor target cells were studied in Swiss-Webster female mice with the use of the inhibition of uptake of tritiated thymidine by target cells as a quantitative measure of macrophage-effected cytostasis. Unlike the normal macrophage, the individual activated macrophage had an enhanced capacity to inhibit DNA synthesis in tumor target cells. Such cytostasis appeared to result from direct contact between activated macrophages and target cells. Culture conditions discouraging direct contact caused little or no cytostasis, regardless of the ratio of macrophages to target cells. When culture conditions favored direct contact between effector cells and target cells, cytostasis was markedly increased if the ratio of macrophages to target cells was raised.