Interleukin-22 receptor subunit alpha-2 (IL-22RA2), also known as interleukin-22-binding protein (IL-22BP), is a subunit of the receptor for interleukin 22. IL-22BP belongs to the type I I cytokine receptor family and contains 3 fibronectin type-III domains. IL-22BP/IL-22RA2 is expressed in a range of tissues, including those in the digestive, female reproductive, and immune systems. It is expressed in placenta, spleen, breast, skin and lung. It is also detected in intestinal tract, testis, brain, heart and thymus. The dominant cell types expressing IL-22BP/IL-22RA2 were mononuclear cells and epithelium. IL-22BP/IL-22RA2 may play an important role as an IL-22 antagonist in the regulation of inflammatory responses. Interleukin-22 (IL-22) is a member of IL-1 family. It is produced by T cells and induces the production of acute-phase reactants. IL-22 plays important roles in immune response through activation of the STAT 3 signal transduction pathway. Two types of IL-22-binding receptor have been discovered, a membrane-bound receptor and a soluble receptor.