TSLP and IL‐33 reciprocally promote each other's lung protein expression and ILC2 receptor expression to enhance innate type‐2 airway inflammation

Background The epithelial cell‐derived danger signal mediators thymic stromal lymphopoietin (TSLP) and IL‐33 are consistently associated with adaptive Th2 immune responses in asthma. In addition, TSLP and IL‐33 synergistically promoted group 2 innate lymphoid cell (ILC2) activation to induce innate allergic inflammation. However, the mechanism of this synergistic ILC2 activation is unknown. Methods BALB/c WT and TSLP receptor‐deficient (TSLPR−/−) mice were challenged intranasally with Alternaria extract (Alt‐Ext) or PBS for 4 consecutive days to evaluate innate airway allergic inflammation. WT mice pre‐administered with rTSLP or vehicle, TSLPR−/− mice, and IL‐33 receptor‐deficient (ST2−/−) mice were challenged intranasally with Alt‐Ext or vehicle once or twice to evaluate IL‐33 release and TSLP expression in the lung. TSLPR and ST2 expression on lung ILC2 were measured by flow cytometry after treatment of rTSLP, rIL‐33, rTSLP + rIL‐33, or vehicle. Results Thymic stromal lymphopoietin receptor deficient mice had significantly decreased the number of lung ILC2 expressing IL‐5 and IL‐13 following Alt‐Ext‐challenge compared to WT mice. Further, eosinophilia, protein level of lung IL‐4, IL‐5, and IL‐13, and airway mucus score were also significantly decreased in TSLPR−/− mice compared to WT mice. Endogenous and exogenous TSLP increased Alt‐Ext‐induced IL‐33 release into BALF, and ST2 deficiency decreased Alt‐Ext‐induced TSLP expression in the lung. Further, rTSLP and rIL‐33 treatment reciprocally increased each other's receptor expression on lung ILC2 in vivo and in vitro. Conclusion Thymic stromal lymphopoietin and IL‐33 signaling reciprocally enhanced each other's protein release and expression in the lung following Alt‐Ext‐challenge and each other's receptor expression on lung ILC2 to enhance ILC2 activation. We found that TSLPR deficiency significantly decrease the number of lung ILC2, airway eosinophils, and mucus production in mouse challenged with Alternaria extract. TSLP‐TSLPR and IL‐33‐ST2 signaling augments each other's protein release and expression in the lung epithelial cells after aeroallergen challenge. TSLP and IL‐33 signaling increases each other's receptor expression on lung ILC2, and the IL‐33‐augmented TSLPR expression enhances pSTAT5 in the ILC2.