Interleukin 19 (IL-19) is a member of the IL-10 cytokine family and is produced by keratinocytes, B cells, and monocytes (Romer et al.; Wolk et al.). Expression of IL-19 can be induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) or lipopolysaccharide (LPS; Gallagher et al.). IL-19 is considered to be a proinflammatory cytokine, as it upregulates IL-6 and tumor necrosis factor alpha (TNF-α; Liao et al. 2002). IL-19 binds the IL-20 receptor complex (IL-20R) which comprises IL-20R alpha and IL-20R beta to activate the STAT3 pathway (Dumoutier et al.). IL-19 also induces T-helper cell differentiation towards a Th2 response, resulting in the production of IL-10 and additional IL-19 (Liao et al. 2002; Liao et al. 2004). IL-19 has been implicated in aging, vascular disease, Type I diabetes, and rheumatoid arthritis.