Interleukin 22 (IL-22), also known as IL-10–related T cell–derived inducible factor (IL-TIF), is a member of the IL-10 family which consists of potent mediators of cellular inflammatory response. IL-22 is expressed by innate and adaptive immune cells, including NK cells, lymphoid tissue inducer-like cells, TH
17 cells, and TH
22 cells. IL-22 acts directly on non-hematopoietic cells. It induces its signals through a two-component receptor comprised of IL-22R1 and IL10Rβ, belonging to the class II cytokine receptor family. The receptor is expressed only on the surface of epithelial cells and some fibroblasts in organs like gut, lung, skin, and liver. IL-22 has been shown to act cooperatively with IL-17A and IL-17F to enhance expression of acute-phase proteins. Members of the IL-10 family show partial homology in their amino acid sequences, but show distinct biological functions. Human and mouse IL-22 proteins share 81% amino acid identity.