Critical role of IL-7/IL-7R signaling in survival and expansion of
differentiated Th17 cells. Th17 cell development is a dichotomous process
that is regulated through a complex cytokine network. The differentiation of
Th17 cells is mainly mediated by STAT3 signaling through cytokines such as
IL-6, IL-21 and IL-23. There is dynamic expression of IL-7R on Th17 cells in
the course of T-cell activation/differentiation. In the latter phase, where
IL-7R is re-expressed, IL-7 is critically required to sustain survival and
expansion of differentiated Th17 cells through STAT5 signaling. IL-7R
antagonism renders differentiated Th17 cells susceptible to apoptosis
through altered expression of the proapoptotic protein Bax and the
antiapoptotic molecule Bcl-2. APC, antigen-presenting cell; IL-7R, IL-7
receptor; MHC–TCR, major histocompatibility complex–T-cell
receptor; TGF, transforming growth factor; Th, T helper.