Interleukin 31 (IL-31), a four-helix bundle inflammatory cytokine, belongs to the IL-6 cytokine family which includes IL-6, oncostatin M, leukemia inhibitory factor (LIF), and cardiotrophin-1 ( Dillon et al.). IL-31 signals through a heterodimer composed of IL-31RA (also known as gp130-like receptor or GPL) and the oncostatin-M receptor (OSMR), both of which are expressed on monocytes (Diveu et al.; Ghilardi et al.), epithelial cells (Ip et al.), and keratinocytes (Kato et al.). Signaling through the GPL/OSMR complex activates the JAK/STAT, RAS/ERK, and PI3K/AKT signaling pathways, resulting in the downstream activation of STAT1, STAT3, and STAT5 transcription factors (Cornelissen et al.; Dambacher et al.; Dillon et al.; Ip et al.). IL-31 responses have been associated with allergic responses and inflammatory skin diseases including atopic dermatitis (Cornelissen et al.; Gangemi et al.).