Cytokine rescue from glucocorticoid induced apoptosis in T cells is mediated through inhibition of IkappaBalpha.

We previously reported that dexamethasone (DEX), a synthetic glucocorticoid, causes apoptosis in mature Th cell lines, and that this induction of cell death is prevented by specific cytokines, namely, by IL-2 in Th1 cells and by IL-4 in Th2 cells. We now show that this differential rescue by specific cytokines in Th cells correlates with the level of IkappaBalpha that is regulated by DEX and cytokines. In both cell types the cellular levels of IkappaBalpha mRNA and protein were evaluated by DEX treatment. Interestingly, the DEX-mediated IkappaBalpha induction was completely inhibited by IL-2, but not IL-4, in Th1 cells, while the reverse profile was seen in Th2 cells. In both cell types, the cytokine that inhibits the induction of IkappaBalpha by DEX, also rescues these cells from DEX-induced apoptosis, although the rescue cytokine is different in Th1 and Th2 cells. Our results imply that T cells need to maintain a certain level of NF-kappaB transcriptional activity in order to survive; up- or down-regulation of nuclear NF kappaB through modulation of IkappaBalpha expression by cytokines or DEX may lead to cell survival or cell death, respectively.