Suppressor T cell Inducing Factor from a Human Macrophage Like Cell Line-U 937

U 987, a human histiocytic lymphoma cell line, spontaneously produces a factor(M-SF) which inhibits blastogenic responses of lymphocytes and Interleukin 2(IL-2) activated killer(IAK) induction from human peripheral blood lymphocytes (PBL). We investigated the mechanism of the suppressor action and the physicochemical character of the M-SF. Suppressive activity of U 937 culture supernatant was absorbed with human peripheral blood T lymphocytes. When the M-SF pretreated T cells were added, the mitogenic response of fresh allogeneic or autologus PBL to phytohaemagglutinin(PHA), Concanavalin A(Con A) and pokeweed mitogen(PWM) were suppressed. In addition, IL-2 activated killer activity was suppressed when the M-SF pretreated T cells were present in the induction phase of IAK. These suppressions were mediated by soluble factors produced by M-SF treated T lymphocytes. These results suggest that the pretreatment of T lymphocytes with M-SF resulted in the induction of suppressor T lymphocytes. M-SF also inhibited the protein kinase activity associated with T cell membrane. The intensity of phosphorylated T cell membrane proteins with the molecular weights of 110, 94, 42, 38 and 34 killodaltons on SDS PAGE were decreased. Dephosphorylation of these proteins may be related to the functional alteration of T lymphocytes. CPG-10 Gel permeation and hydrophobic interaction column chromatographic analysis revealed that the M-SF was an extremely hydrophobic sialoprotein of which approximate molecular weight was 10,000 daltons