IRAK1 drives intestinal inflammation by promoting the generation of effector Th cells with optimal gut homing capacity

Interleukin-1 receptor associated kinase 1 (IRAK1) is an important component of the IL-1R and TLR signaling pathways, which influence Th cell differentiation. Here, we show that IRAK1 promotes Th17 development by mediating IL-1 induced upregulation of IL-23R and subsequent STAT3 phosphorylation, thus enabling sustained IL-17 production. Moreover, we show that IRAK1 signaling fosters Th1 differentiation by mediating T-bet induction and counteracts Treg generation. Cotransfer experiments revealed that Irak1-deficient CD4+ T cells have a cell-intrinsic defect in generating Th1 and Th17 cells under inflammatory conditions in spleen, mesenteric lymph nodes and colon tissue. Furthermore, IRAK1 expression in T cells was shown to be essential for T cell accumulation in the inflamed intestine and mLNs. Transcriptome analysis ex vivo revealed that IRAK1 promotes T cell activation and induction of gut-homing molecules in a cell-intrinsic manner. Accordingly, Irak1-deficient T cells failed to upregulate surface expression of 47 integrin after transfer into Rag1-/- mice and their ability to induce colitis was greatly impaired. Lack of IRAK1 in recipient mice provided additional protection from colitis. Therefore, IRAK1 plays an important role in intestinal inflammation by mediating T cell activation, differentiation and their accumulation in the gut. Thus, IRAK1 is a promising novel target for therapy of inflammatory bowel diseases.

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Heiseke AF, Jeuk BH, Markota A, Straub T, Lehr HA, Reindl W, Krug AB