Pro-inflammatory and angiogenic cytokine that may be involved in epidermal function and psoriasis. Angiogenic and proliferative activities are antagonized by IL10. May act through STAT3. Forms a 1:1:1 heterotrimeric complex with its primary high-affinity heterodimeric receptor IL20RA/IL20RB. Expressed in most tissues and five major cell types: epithelial cells (primarily skin, buccal mucosa, tongue, nasal mucosa, lung, ureter, breast, prostate, fallopian tube, and adrenal gland), myoepithelial cells (mainly prostate), endothelial cells (mainly in small vessels or capillaries), macrophages, and skeletal muscle. Isoform 2 was detected in the lung tissue only. Up-regulated by UV-B irradiation in epithelial keratinocytes. Lung-specific. Belongs to the IL-10 family.