IL-20 receptor alpha (IL-20 R alpha ), also named IL-20 R1, CRF2-8, and ZCYTOR7, belongs to the class II cytokine receptor family, which includes 12 members. These receptors are characterized by the patterns of conserved amino acid (aa) residues in their extracellular domains, which are composed of tandem fibronectin type III domains (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