Human Interleukin-20 (IL-20) is encoded by the IL20 gene located on the chromosome 1 and belongs to the IL-10 family that including IL-10, IL-19, IL-22, IL-24, and IL-26. It is secreted by activated keratinocytes and monocytes, and signals through two distinct cell-surface receptor complexes on keratinocytes and other epithelial cells. IL-20 has functions of regulating proliferation and differentiation of keratinocytes during inflammation, and causing cell expansion of multipotential hematopoietic progenitor cells.