IL-20 is a soluble protein belonging to the IL-10 cytokine family. Secreted by activated keratinocytes and monocytes, the two receptors expressed on the surface of other endothelial cells transmit signals to the cells. In inflammatory conditions, especially skin inflammation, IL-20 can regulate the proliferation and differentiation of keratin; it can also induce the expansion of pluripotent hematopoietic progenitor cells.