Activation by Retinoic Acid Potentiation of Mitogen-induced Human T-Lymphocyte

The capacity of retinole acid to modulate human T-lymphocyte and B-lymphocyte activation by mitogens was examined. Tlymphocyte proliferation stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) or phytohemagglutinin was enhanced by 5 nw to 5 U.Mretinoic acid in a dose-dependent manner with a 65 ± 35% (SD) increase (n = 6, P < 0.01) in TPA-stimulated proliferation induced by 5 U.Mretinoic acid. Retinoic acid en hanced T-lymphocyte proliferation over a wide range of back ground proliferation induced by different TPA concentrations. Retinoic acid alone did not stimulate T-lymphocyte proliferation. In contrast retinoic acid inhibited B-lymphocyte proliferation stim ulated by TPA or phytohemagglutinin with 26.7 ±23.4% inhibi tion of TPA-stimulated proliferation induced by 5 UMretinoic acid (P < 0.02). Retinoic acid had intermediate effects on the prolif eration of different mixtures of Tand B-lymphocytes stimulated by TPA or phytohemagglutinin. The recognition that retinoic acid has opposing effects on human Tand B-lymphocyte activation by mitogens may account for the conflicting reports of the effects of retinoids on the immune response of unpurified human lym phocyte preparations.