Evidence that rapamycin has differential effects of IL-4 function. Multiple IL-4 signaling pathways and implications...

The immunosuppressive drug rapamycin, which inhibits the response of T cells to growth-promoting lymphokines, has been considered to act as a general inhibitor of cytokine action. Our investigations into the effect of rapamycin on human IL-4, a cytokine controlling B and T cell function, show this not to be the case. Unexpectedly, rapamycin actually synergized with IL-4 in both the upregulation of CD23 expression and the down-regulation of the type II (p75) TNF receptor, while in the same B cell line, rapamycin simultaneously inhibited the IL-4-dependent production of TNF alpha and beta. These results raise the possibility that multiple IL-4 signaling pathways may be responsible for the pleiotropic effects of IL-4, and have important implications for both the experimental and possible clinical in vivo use of rapamycin as a selective immunosuppressant.