IL-19, a member of the IL-10 cytokine family, is expressed in epithelial cells, endothelial cells, and macrophages. It can bind the interleukin-20 receptor complex IL-20R1/IL-20R2 and lead to the activation of the signal transducer and activator of transcription 3 (STAT3). IL-19 induces IL-6 and TNF-α
production in monocytes. It also induces cell apoptosis and reactive oxygen species production in monocytes, which suggests a role of this cytokine in inflammatory responses. It is up-regulated in monocytes following stimulation with lipopolysaccharide (LPS), and granulocyte-macrophage colony-stimulating factor (GM-CSF). IL-19 alters the balance of Th1 and Th2 cells in favor of Th2 cells. IL-19 contributes to a range of diseases and disorders, such as breast cancer, squamous cell carcinoma of the skin, asthma, endotoxic shock, uremia, psoriasis, rheumatoid arthritis, and periodontal and vascular disease.