Mechanisms to Suppress ILC2-induced Airway Inflammation.

Epithelial cell-derived cytokines such as IL-33 and IL-25 activate group 2 innate lymphoid cells (ILC2s), which are known to be important sources of type 2 cytokines such as IL-5 and IL-13 in a variety of asthma mouse models. Recently, human studies have also reported the involvement of ILC2s in asthma, as ILC2s are increased in peripheral blood and bronchoalveolar lavage fluid in patients with asthma. Compared with positive regulators such as IL-25 and IL-33, the mechanisms to suppress the ILC2s-induced inflammation remain unclear. Because ILC2s express various cytokine receptors, the function of ILC2s would likely be influenced by cytokines present around ILC2s in the lungs. We reported that IL-2, IL-7, and thymic stromal lymphopoietin (TSLP) induced phosphorylation of signal transducer and activator of transcription 5 (STAT5) and promoted the proliferation of ILC2s and type 2 cytokine production when combined with IL-33. TSLP enhanced the expression of Bcl-xL, an antiapoptotic molecule, and caused corticosteroid-resistant airway inflammation via ILC2s in mice. Furthermore, pimozide, a STAT5 inhibitor, counteracted the TSLP-induced corticosteroid resistance and suppressed airway inflammation. As a negative regulator, we have found that IFN-γ and IL-27 suppressed the proliferation and type 2 cytokine production of ILC2s in vitro and in vivo. Interestingly, ILC2s-induced eosinophilic inflammation was more severe in IFN-γ receptor-deficient mice than in control mice. These findings suggest the importance of environmental cytokines for the regulation of ILC2s, and this would lead to a new approach to control airway inflammation in asthma.