Estrogen-mediated regulation of Th1, Th2 and Treg effector functions are well documented but, surprisingly, it is still not known whether estrogen modulates IL-17, a powerful proinflammatory cytokine that plays a pivotal role in several inflammatory and autoimmune diseases. Therefore in the present study, we determined whether estrogen regulates the expression levels of IL-17 in wildtype C57BL/6 mice. By ELISA, ELISPOT and/or flow cytometric analyses, we found that estrogen upregulated the levels of not only IL-17, but also the IL-17-specific transcription factor retinoic acid-related orphan receptor gamma t (RORγt), in activated splenocytes. IL-17 levels were further enhanced by exposure of activated splenocytes to IL-23, particularly in cells from estrogen-treated mice. Exposure of splenocytes to IL-27 or IFN-γ at the time of activation markedly inhibited the levels of IL-17 and RORγt. Interestingly, a delay of 24 hours in exposure of activated splenocytes to IL-27 or IFN-γ decreased IL-17 levels (albeit less profoundly) but not RORγt. These findings imply that the suppressive effects of IL-27 and IFN-γ are more effective prior to the differentiation and commitment of IL-17-secreting cells. Furthermore, inhibition of JAK-2 by AG490 suppressed IL-17 but not RORγt expression suggesting that other transcription factors are also critical in estrogen-mediated upregulation of IL-17.
Keywords: IL-17, estrogen, IL-27, IFN-γ, lupus, RORγt