IDENTIFICATION OF HUMAN T-CELL HYBRIDOMA-DERIVED MACROPHAGE ACTIVATING FACTOR AS INTERLEUKIN-2

Macrophages are activated by a two-step mechanism involving at least two kinds of factors, a priming and a triggering factor, to become cytotoxic to various tumor cells. In the present study, we purified macrophage-activating factor for cytotoxicity I (MAF-C 1), defined as a priming macrophage activating factor (MAF), by about 1,600-fold from the culture supernatant of a human T cell hybridoma, H3-E9-6, by a series of chromatographic procedures. We identified MAF-CI activity released from H3-E9-6 cells as interleukin-2 (IL-2) from the following findings. (i) The physicochemical properties of MAF-CI and IL-2 were almost identical. (ii) Purified MAF-CI active fraction also showed T cell proliferating activity. (iii) MAF-CI activity in the purified fraction was completely neutralized by anti-IL-2 antibodies. (iv) Human recombinant IL-2 (rIL-2), at a suboptimal dose, and lipopolysaccharide (LPS) synergistically induced monocyte-mediated cytotoxicity.