Inhibition of protein A-induced lymphocyte colony-forming cells by con A-generated suppressor cells or their culture fluid.

Concanavalin A (Con-A)-treated human lymphocytes or their culture fluid suppressed protein A-induced lymphocyte colony formation by more than 40%. The suppressor factor was produced primarily by Con A-stimulated T lymphocytes and maximal production occurred on the 2nd day of culture with 10 microgram Con A, a condition optimal for the induction of suppressor T cells. This suggests that the factors are released by suppressor T cells. We hypothesize that suppressor T cells exert a negative control on clonal proliferation of lymphocytes.