IL20/Interleukin-20 belongs to the IL-10 family. It is a cytokine structurally related to interleukin 10. IL20/Interleukin-20 can be detected in skin, trachea, and other tissues. It is produced by activated keratinocytes and monocytes and transmits an intracellular signal through two distinct cell-surface receptor complexes on keratinocytes and other epithelial cells. It has been shown that interleukin-20 transduces its signal through signal transducer and activator of transcription 3 (STAT3) in keratinocytes. It may be involved in epidermal function and psoriasis. It also regulates the proliferation and differentiation of keratinocytes during inflammation, particularly inflammation associated with the skin. Also, IL20/Interleukin-20 also causes cell expansion of multipotential hematopoietic progenitor cells. A specific receptor for this cytokine is found to be expressed in skin and upregulated dramatically in psoriatic skin, suggesting a role for this protein in epidermal function and psoriasis.