IL-20 receptor beta (IL-20 R beta ), also known as IL-20 R2, is a transmembrane glycoprotein in the class II cytokine receptor family. These receptors are characterized by tandem fibronectin type III domains in their extracellular region and the lack of a WSXWS motif (1). Class II cytokine receptors form heterodimeric signaling receptor complexes that mediate class II cytokine signals. Subunits of the different receptor complexes are shared and serve multiple functions (1). Human IL-20 R beta consists of a 204 aa extracellular domain (ECD) with two fibronectin type III domains, a 21 aa transmembrane segment, and a 57 aa cytoplasmic domain (2). Within the ECD, human IL-20 R beta shares 81% aa sequence identity with mouse IL-20 R beta. It shares 15%-28% aa sequence identity with the human class II cytokine receptors IFN‑ alpha  R1, IFN-alpha R2, IFN-gamma R1, IFN-gamma R2, IL-10 R alpha, IL-10 R beta, IL-20 R alpha, IL-22BP, IL-22 R alpha, IL-28 R, and tissue factor. Strong IL-20 R beta expression is normally restricted to skin and testis (3). IL-20 R beta is also expressed in psoriatic skin, rheumatoid arthritis synovial membranes, and hepatocytes of LPS-treated mice, and it contributes to the local inflammatory reaction (3-6). IL-20 R beta heterodimerizes with IL-20 R alpha to form the receptor complex that mediates IL-19, IL-20 and IL-24 signals (3, 7-10). It also heterodimerizes with IL-22 R to form the functional receptor complex for IL-20 and IL-24 (7-9). Binding of these IL-10 family class II cytokines to their receptors induces activation of the JAK-STAT signal transduction pathway.