Eos promotes TH2 differentiation by propagating the IL-2/STAT5 signaling pathway.

The Ikaros zinc finger transcription factor Eos has been commonly implicated in regulatory T cells to promote their immunosuppressive functions. Paradoxically, a new role is emerging for Eos in promoting pro-inflammatory responses of conventional CD4+ T cells in the dysregulated setting of autoimmunity. Even so, the precise role of Eos in regulating the differentiation and function of healthy effector CD4+ T cell subsets remains unclear. Here, we find that Eos is a positive regulator of CD4+ T helper 2 (TH2) cells--effector T cells implicated in the induction of allergic asthma. Using murine in vitro TH2 cells and an in vivo house dust mite asthma model, we found that Eos-deficient T cells had reduced expression of key TH2 transcription factors, effector cytokines, and differentiation receptors. Mechanistically, among various TH2-polarizing pathways, the IL-2/STAT5 axis and its downstream TH2 gene targets emerged as one of the most significantly downregulated networks in Eos deficiency. Using in vitro TH2 cells and overexpression of Eos zinc-finger-domain mutants, we discovered that Eos forms a novel complex with and supports the tyrosine-phosphorylated signaling activity of STAT5. Overall, these data define a novel regulatory mechanism whereby Eos promotes IL-2/STAT5 activity to facilitate TH2 differentiation.