Purity >95% as determined by SDS-PAGE. Interleukin 31 (IL-31) is an immunoregulatory cytokine that is expressed by activated type 2 T helper (Th2) cells. IL-31 signals through a heterodimer receptor consisting of the IL-31 Receptor A (IL-31RA) and the oncostatin M receptor (OSMR), which are expressed on monocytes, epithelial cells, and keratinocytes. IL-31 promotes allergic reactions and inflammatory skin diseases.