Bidirectional control by glycyrrhizin of the growth response of lymphocytes stimulated through a receptor-bypassed pathway.

This study demonstrates a unique action of glycyrrhizin (GL) in bidirectionally controlling the growth response of lymphocytes stimulated through a receptor-bypassed pathway by calcium ionophore A23187 and phorbol 12-myristate 13-acetate (PMA). GL up-regulated the response of lymphocytes in vitro to lower concentrations of A23187 and PMA, and down-regulated the response to higher concentrations. We also provide evidence that GL controls the response of lymphocytes of different cell types or maturation stages in different ways, probably because these lymphocytes require different levels of signals as optimum. Finally, the GL-mediated bidirectional controls of the lymphocyte growth response were shown to be adherent cell-independent. The bidirectional controls demonstrated may be significant in normalizing the lymphocyte responses to very weak or very high stimuli.