Roles of IL-22 in allergic airway inflammation. Upon antigen inhalation, CD4+ T cells and LTi-like cells in the lung produce IL-22. IL-22 inhibits the expression of lung epithelial cell-derived cytokines and chemokines, including IL-25, IL-33, and CCL17, and attenuates the development of allergic airway inflammation. In addition, IL-22 may enhance barrier function of airway epithelial cells, which may contribute to the protective function of IL-22 in asthma. On the other hand, IL-22 may cause the proliferation of airway smooth muscle cells in humans, which may lead to airway remodeling in asthma.
