Inhibition of blastogenic factor by alloantigen-activated human lymphocytes

Human suppressor cells generated in mixed lymphocyte cultures (MLC) appear to inhibit both cellular proliferation and the mitogenic effects of blastogenic factor (BF). The results presented here indicate that the inhibition of BF by alloantigen-activated lymphocytes is not due to decreased lymphocyte proliferation as such, since BF normally produced by non-proliferating cultures was also suppressed. Moreover, the inhibition was not caused by direct suppression of the BF-producing lymphocytes, since incubation of BF with alloantigen-activated lymphocytes neutralized the mitogenic effects of BF. We therefore conclude that activated lymphocytes generated in human MLC directly inhibit or utilize BF. Our experiments also indicate that the activated lymphocytes do not have to proliferate to inhibit BF activity.