IL-31 mRNA encodes a 164-aa precursor and a predicted 141-aa mature polypeptide, displaying an apparent molecular mass of 24 kDa in its glycosylated form. IL31 is a newly discovered four-helix bundle cytokine and expressed by several types of cells under both normal and disease state, such as activated CD4+T cells, mast cells, monocytes, macrophages, immature and mature monocyte-derived dendritic cells and so on. IL-31 signals through a heterodimeric receptor complex consisting of the IL31 receptor alpha (IL31Rα) and the oncostatin M receptor (OSMR). IL-31 plays a predominant function in the mediation of inflammatory and lymphoma-associated itch. Increased IL-31 expression has been detected in inflamed tissues from patients with atopic dermatitis, bowel diseases, allergic asthma and rhinitis.