TRAF4 is crucial for ST2+ memory Th2 cell expansion in IL-33-driven airway inflammation.

Tumor necrosis factor receptor (TNF)-associated factor 4 (TRAF4) is an important regulator of type 2 responses in the airway; however, the underlying cellular and molecular mechanisms remain elusive. Herein, we generated T cell-specific TRAF4-deficient (CD4cre-Traf4fl/fl) mice and investigated the role of TRAF4 in interleukin (IL)-33 receptor (ST2, suppression of tumorigenicity 2)-expressing memory Th2 cells (ST2+ mTh2) in IL-33-mediated type 2 airway inflammation. We found that in vitro polarized TRAF4-deficient (CD4cre-Traf4fl/fl) ST2+ mTh2 cells exhibited decreased IL-33-induced proliferation as compared with TRAF4-sufficient (Traf4fl/fl) cells. Moreover, CD4cre-Traf4fl/fl mice showed less ST2+ mTh2 cell proliferation and eosinophilic infiltration in the lungs than Traf4fl/fl mice in the preclinical models of IL-33-mediated type 2 airway inflammation. Mechanistically, we discovered that TRAF4 was required for the activation of AKT/mTOR and ERK1/2 signaling pathways as well as the expression of transcription factor Myc and nutrient transporters (Slc2a1, Slc7a1, and Slc7a5), signature genes involved in T cell growth and proliferation, in ST2+ mTh2 cells stimulated by IL-33. Taken together, the current study reveals a previously unappreciated role of TRAF4 in ST2+ mTh2 cells in IL-33-mediated type 2 pulmonary inflammation, opening up avenues for the development of new therapeutic strategies.