Modulation of the expression of Tac antigen (T-cell growth factor response) on human thymocytes.

This study shows that anti-Tac antibody does not bind to human thymocytes unless they are activated. Human thymocytes could be induced to express Tac antigen (TCGF receptor) on their cell surface by Concanavalin A. B lymphoblastoid cells or 12-O-tetradecanoylphorbol 13-acetate alone did not induce TCGF receptors, but they did exert a very marked synergistic effect with Concanavalin A. This observation is consistent with our earlier finding that B lymphoblastoid cells secrete a factor which exerts a synergistic effect on the induction of lymphokine secretion by thymocytes and T-cells. The early expression of Tac antigen was independent of thymocyte proliferation. Anti-Tac antibody (10(-3)) inhibited the expression of TCGF receptors and late proliferation of thymocytes. TCGF did not reverse this inhibition nor did it prevent the binding of Tac antibody, but it enhanced the expression of Tac antigen.