Investigation of the human macrophage. II. The in vitro cytotoxicity of macrophages.

Macrophage-mediated cytotoxicity in vitro was studied by a tritiated thymidine incorporation inhibition assay as well as by microscopic examination and optical transmitance determination. It was found that macrophages from patients with malignant diseases showed cytotoxic effects on two malignant human cell lines. The cytotoxic activity was more marked in patients who were clinically tumor-free. Some patients with benign diseases and normal subjects also exhibited cytotoxic macrophages. Macrophage-mediated cytotoxicity (MMC) was thus nonspecific in nature. Cell-free exudate from cancer patients did not influence MMC appreciably. The experimental methods and the possible significance of MMC are discussed.