T-bet and STAT6 Coordinately Suppress the Development of IL-9-Mediated Atopic Dermatitis-Like Skin Inflammation in Mice.

T-bet and signal transducer and activator of transcription (STAT) 6 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 severe combined immunodeficient mice induced the accumulation of eosinophils and mast cells in the skin, whereas 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. T-bet STAT6 CD4 T cells expressed functional thymic stromal lymphopoietin receptors and produced large amounts of IL-9 on thymic stromal lymphopoietin stimulation. These results indicate that T-bet and STAT6 coordinately suppress atopic dermatitis-like skin inflammation, possibly by inhibiting thymic stromal lymphopoietin-dependent IL-9 production in CD4 T cells.