Interleukin 22 (IL-22) is a member of a group of cytokines called the IL-10 family or IL-10 superfamily (including IL-19, IL-20, IL-24, and IL-26), a class of potent mediators of cellular inflammatory responses. It shares use of IL-10R2 in cell signaling with other members of this family, IL-10, IL-26, IL-28A/B and IL-29. IL-22 is produced by activated DC and T cells and initiates innate immune responses against bacterial pathogens especially in epithelial cells such as respiratory and gut epithelial cells. IL-22 along with IL-17 is rapidly produced by splenic LTi-like cells  and can be also produced by Th17 cells and likely plays a role in the coordinated response of both adaptive and innate immune systems.
Psoriatic patients show strongly elevated IL-22 plasma levels, which correlated with the disease severity. IL-22 plays a protective role in T cell-mediated hepatitis induced by Concanavalin A (Con A), acting as a survival factor for hepatocytes. IL-22 is present in high quantities in the blood of Crohn’s disease patients in contrast to IFN-γ and IL-17.