IL-20 R alpha is widely expressed and is detected at high levels in multiple tissues including skin, testis, heart, placenta, salivary gland and prostate gland. The expression of IL-20 R alpha, together with that of IL-20 R beta, is upregulated in psoriatic skin lesions on keratinocytes, immune cells, and endothelial cells. IL-20 R alpha heterodimerizes with IL-20 R beta to form the functional receptor that mediates IL-19, IL-20 and IL-24 signals. IL-20 R alpha also heterodimerizes with IL-10 R beta to form the functional receptor complex for IL-26. Binding of these IL-10 family class II cytokines to their functional receptors induces activation of the JAK-STAT signal transduction pathway. At low ligand concentrations, STAT3 has been shown to be the predominant STAT proteins activated through either complexes.