Bidirectional roles of IL-22 in the pathogenesis of allergic airway inflammation.

Asthma is the most prevalent allergic disease of the airway, which is characterized by eosinophilic inflammation, mucus hyperproduction, and airway hyper-responsiveness. Although these pathognomonic features are mainly mediated by antigen-specific Th2 cells and their cytokines, such as IL-4, IL-5, and IL-13, recent studies have revealed that other inflammatory cells, including Th17 cells and innate lymphoid cells (ILCs), also play a critical role in the pathogenesis of asthma. IL-22, one of the cytokines produced by Th17 cells and type 3 ILCs, has distinct functional properties, as IL-22 exclusively acts on non-hematopoietic cells including epithelial cells of mucosal surface and exhibits a broad range of action in regeneration and host protection. In accordance with the fact that lung epithelial cells play a critical role in the pathogenesis of asthma, we and other groups have shown that IL-22 is involved in the regulation of allergic airway inflammation. In this review, we discuss recent advances in the biology of IL-22 and its involvement in the pathogenesis of allergic airway inflammation.