Interleukin 31 (IL-31) is 141 amino acid cytokine (molecular weight 15.8 kDa). It is produced primarily by CD4+ TH2 cells and serves to promote an inflammatory response and is involved in triggering the cellular in response to various pathogens. IL-31 binds to a heterodimeric receptor comprised of IL-31RA (IL-13 Receptor A) and OSMR (Oncostatin M Receptor) expressed on T cells, dendritic cells, and macrophages. It has been clinically shown that IL-31 plays a key role in the chronic inflammatory disease atopic dermatitis.