IL-22, a cytokine structurally related to IL10, was originally identified in the mouse as a gene induced by IL9 in T cells and mast cells (1). IL-22 was initially designated as ILTIF (IL10-related T cell-derived inducible factor). Mouse IL-TIF consists of 179 amino acids, including four cysteins, and has a predicted molecular weight of 20 KD. IL-22 shows 22% sequence identity with mouse IL-10 and belongs to a family of cytokines with limited homology to IL-10, namely IL-10, IL-19, IL-20, IL-24, IL-26, IL-28A, IL-28B, and IL-29 (the latter 3 also known as IFN-λ) (3). IL-22 biological activity is initiated by binding to a cell-surface complex composed of IL-22R1 and IL-10R2 receptor chains and further regulated by interactions with a soluble binding protein, IL-22BP, which shares sequence similarity with an extracellular region of IL-22R1 (sIL-22R1) (3). Both chains of the IL-22R complex belong to the class II CRF. Two types of IL-22-binding receptor have been discovered, a membrane-bound receptor and a soluble receptor, both encoded by different genes (4). IL-22 is produced by immune cells and acts on nonimmune cells to regulate local tissue inflammation. As a product of the recently identified T helper 17 lineage of CD4(+) effector lymphocytes, IL-22 plays a critical role in mucosal immunity as well as in dysregulated inflammation observed in autoimmune diseases (5).