A human T cell-derived soluble factor able to suppress pokeweed mitogen-induced immunoglobulin production

Human peripheral blood T cells or Fc gamma receptor-positive T cells activated with the mitogen concanavalin A produce a soluble suppressor factor that inhibits polyclonal B cell immunoglobulin production. The factor suppresses pokeweed mitogen- (PWM) induced plaque-forming cells (PFC) by a noncytotoxic effect. It does not significantly affect lymphocyte proliferation, and exerts its effect independently of the presence of T cells. It is active in suppressing PFC when added from day 0 to day 3 of PWM cultures. Suppression is blocked by the addition of the monosaccharide L-rhamnose. The factor is stable at pH 2.0 and stable at 56 degrees C, but is inactivated by 2-mercaptoethanol. The approximate m.w. by gel filtration is 20,000 to 25,000. The above characteristics distinguish this suppressor factor from soluble immune suppressor supernatant, lymphotoxin, and gamma-interferon. They do not distinguish the suppressor factor from migration inhibition factor, which is also present in the supernatants.