Group 2 innate lymphoid cells utilize the IRF4-IL-9 module to coordinate epithelial cell maintenance of lung homeostasis.

Group 2 innate lymphoid cells (ILC2s) have an important role in acute allergic lung inflammation. Given their distribution and function, lung ILC2s are hypothesized to coordinate epithelial responses to the external environment; however, how barrier surveillance is linked to ILC2 activation remains unclear. Here, we demonstrate that alveolar type II cells are the main source of interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP) generated in response to chitin or migratory helminths. IL-33 and TSLP synergistically induce an interferon regulatory factor 4 (IRF4)-IL-9 program in ILC2s, and autocrine IL-9 promotes rapid IL-5 and IL-13 production required for optimal epithelial responses in the conducting airways. Thus, ILC2s link alveolar function to regulation of airway flow, revealing a key interaction between resident lymphoid and structural cells that might underlie similar organizational hierarchies in other organs.