Glycyrrhizin as a promoter of the late signal transduction for interleukin-2 production by splenic lymphocytes.

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.