T-bet and STAT6 Coordinately Suppress the Development of IL-9-mediated Atopic Dermatitis-like Skin Inflammation in Mice

T-bet and STAT6 are critical factors for helper T cell differentiation in humans and mice. Additionally, polymorphisms in TBX21 (T-bet) and STAT6 are associated with the susceptibility of allergic diseases. However, precise mechanisms of the reciprocal regulation between T-bet and STAT6 in allergy remain unclear. To determine the reciprocal regulation in vivo, we investigated the phenotype of T-bet/STAT6 double-deficient (T-bet-/- STAT6-/-) mice. Unexpectedly, T-bet-/- STAT6-/- mice but not T-bet-/- mice or STAT6-/- mice spontaneously developed severe dermatitis. Not only eosinophils and mast cells but also CD4+ T cells infiltrated into the skin of T-bet-/- STAT6-/- mice. Adoptive transfer of CD4+ T cells of T-bet-/- STAT6-/- mice into SCID mice induced the accumulation of eosinophils and mast cells in the skin, while depletion of CD4+ T cells ameliorated the dermatitis in T-bet-/- STAT6-/- mice. Comprehensive transcriptome analyses revealed that IL-9 expression was enhanced in T-bet-/- STAT6-/- CD4+ T cells. Indeed, IL-9 neutralization ameliorated the dermatitis in T-bet-/- STAT6-/- mice. Importantly, T-bet-/- STAT6-/- CD4+ T cells expressed functional TSLP receptor and produced large amounts of IL-9 upon TSLP stimulation. These results indicate that T-bet and STAT6 suppress atopic dermatitis-like skin inflammation, possibly by inhibiting TSLP-dependent IL-9 production in CD4+ T cells. Total RNA of CD44+ CD4+ T cells in skin-draining LNs was isolated from WT mice, T-bet-/- mice, STAT6-/- mice, or T-bet-/- STAT6-/- mice and subjected to RNA-sequencing analysis.