Interleukin-22(IL-22) is a member of a group of the IL-10 family, a class of potent mediators of cellular inflammatory responses. IL-22 is produced by activated DC and T cells. IL-22 and IL-10 receptor chains play a role in cellular targeting and signal transduction. It can initiate and regulate innate immune responses against bacterial pathogens especially in epithelial cells such as respiratory and gut epithelial cells. IL-22 along with IL-17 likely plays a role in the coordinated response of both adaptive and innate immune systems. IL-22 also promotes hepatocyte survival in the liver and epithelial cells in the lung and gut similar to IL-10. Biological activity of IL-22 is initiated by binding to a cell-surface complex consisting of IL-22R1 and IL-10R2 receptor chains. IL-22 biological activity is further regulated by interactions with a soluble binding protein, IL-22BP. IL-22BP and an extracellular region of IL-22R1 share sequence similarity. In some cases, the pro-inflammatory versus tissue-protective functions of IL-22 are regulated by cytokine IL-17A.