Effector mechanism of human monocyte-mediated cytotoxicity: role of a new tumor cytotoxic factor distinct from interleukin 1 and tumor necrosis factorα

Human blood monocytes activated to the tumoricidal state were previously found to release a factor(s) responsible for tumor cell killing. The activity of the tumor cytotoxic factor(s) (TCF) was determined by release assay of radioactivity from human A375 melanoma cells. On fractionation of the supernatant of activated monocytes by Ultrogel AcA34 and TSK-G3000SW gel chromatographies two major peaks of the material with TCF activity with MWs of 30,000 and 15,000, called TCF-I and TCF-11, respectively were obtained. TCF-II could be neutralized by polyclonal anti-IL-1β antiserum, but anti-IL-1α antiserum did not neutralize either factor. TCF-I was separated by ampholine column electrofocusing into three major fractions with TCF activity at pI 5, 6 and 6.8, named TCF-1α, TCF-1β and TCF-1γ, respectively. The cytotoxic and IL-1 activities of TCF-1α were neutralized by anti-IL-1α serum, whereas those of TCF-1β and TCF-1γ were not completely neutralized by anti-IL-1α or anti-IL-1β antiserum. On DEAE ion-exchange chromatography (TSK DEAE 5PW) TCF-Iβ gave two peaks with TCF activity (TCF-Iβ1 and TCF-Iβ2). TCF-Iβ1 was slightly neutralized by anti-TNFα antibody, but TCF-Iβ2 was not affected by antisera against IL-1α and IL-1β, or anti-TNFα antibody, thus ruling out the possibility that tumor necrosis factor (TNFα) might be involved in tumor cell killing mediated by TCF-Iβ2. These results indicate that human monocyte-mediated cytotoxicity against human A375 melanoma cells is mediated in part by a tumor cytotoxic factor (TCF; MW, 30,000; pI 6), differing from IL-1 and TNFα.