Interleukin 19 (IL-19) is an immunosuppressive protein that belongs to the IL-10 cytokine subfamily.The IL-19 protein is composed of 159 amino acids and has a quaternary structure with alpha helix motifs and loops. IL-19 is preferentially expressed in monocytes, macrophages, and T and B lymphocytes, but interacts with immune cells (macrophages, T cells, B cells) and non-immune cells (endothelial cells and brain resident glial cells, etc). IL-19 is associated with broad functions across inflammation, cell development, viral responses, and lipid metabolism. As an immunosuppressive cytokine, IL-19 promotes the Th2 (regulatory) T-cell response which supports an anti-inflammatory lymphocyte phenotype, dampens the Th1 T-cell response and inflammatory cytokine secretion (IFNγ), increases IL-10 (anti-inflammatory) expression in peripheral blood mononuclear cells (PBMC), and inhibits the production of immunoglobulin G (IgG) from B cells.