A role for BATF3 in T9 differentiation and T-cell-driven mucosal pathologies.

T helper 9 (T9) cells are important for the development of inflammatory and allergic diseases. The T9 transcriptional network converges signals from cytokines and antigen presentation but is incompletely understood. Here, we identified TL1A, a member of the TNF superfamily, as a strong inducer of mouse and human T9 differentiation. Mechanistically, TL1A induced the expression of the transcription factors BATF and BATF3 and facilitated their binding to the Il9 promoter leading to enhanced secretion of IL-9. BATF- and BATF3-deficiencies impaired IL-9 secretion under T9 and T9-TL1A-polarizing conditions. In vivo, using a T-cell transfer model, we demonstrated that TL1A promoted IL-9-dependent, T9 cell-induced intestinal and lung inflammation. Neutralizing IL-9 antibodies attenuated TL1A-driven mucosal inflammation. Batf3 T9-TL1A cells induced reduced inflammation and cytokine expression in vivo compared to WT cells. Our results demonstrate that TL1A promotes T9 cell differentiation and function and define a role for BATF3 in T-cell-driven mucosal inflammation.