Glycyrrhizin as a promoter of the late signal transduction for interleukin-2

　　Cellular and molecular mechanisms of the immunomodulatory action of glycyrrhizin （GL） were studied. We demonstrated that GL displays a unique action to prolong the duration of the T-cell receptor-mediated in vitro splenic T-lymphocyte growth response to anti-CD3 monoclonal antibody （mAb） or concanavalin A （Con A） through enhancement of interleukin-2 （IL-2） secretion and IL-2 receptor （IL-2R） expression. The augmentation by GL of IL-2 production was also found in spleen cells stimulated with A23187 plus phorbol 12-myristate 13-acetate （PMA）， suggesting that GL primarily affects some post-receptor stage of the signal transduction. We also found that the time of GL action for promoting IL-2 production and growth response was 2 hr or more after receptor activation. Correspondingly， GL did not augment the anti-CD3 mAb or Con A-mediated protein tyrosine phosphorylation and c-fos transcription. We concluded from these results that GL acts as a promoter of the late signal transduction of T lymphocytes for IL-2 production.