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

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-II, respectively were obtained. TCF-II could be neutralized by polyclonal anti-IL-1 beta antiserum, but anti-IL-1 alpha 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-1 alpha, TCF-1 beta and TCF-1 gamma, respectively. The cytotoxic and IL-1 activities of TCF-1 alpha were neutralized by anti-IL-1 alpha serum, whereas those of TCF-1 beta and TCF-1 gamma were not completely neutralized by anti-IL-1 alpha or anti-IL-1 beta antiserum. On DEAE ion-exchange chromatography (TSK DEAE 5PW) TCF-I beta gave two peaks with TCF activity (TCF-I beta 1 and TCF-I beta 2). TCF-I beta 1 was slightly neutralized by anti-TNF alpha antibody, but TCF-I beta 2 was not affected by antisera against IL-1 alpha and IL-1 beta, or anti-TNF alpha antibody, thus ruling out the possibility that tumor necrosis factor (TNF alpha) might be involved in tumor cell killing mediated by TCF-I beta 2. 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 TNF alpha.