Interleukin 23 (IL-23) is a heterodimeric cytokine composed of the IL-12p40 subunit and the IL-23p19 subunit, where the p40 subunit is shared by IL-23 and IL-12.The functional receptor for IL-23 has been identified and consists of IL-12Rβ1 and IL-23R.IL-23 plays a role in the immune type 1 polarized T cell response. Although IL-12 potently activates naïve T cells, initial reports suggested that IL-23 preferentially acts on memory T cells to promote their secretion of IFN-γ and proliferation, suggesting an important role in the control of bacterial infections.IL-23 was further described as a key cytokine in the control of inflammation in peripheral tissues.Overexpression of p19 has been associated with multiple organ and inflammation in epithelial tissues including the skin.IL-23 is involved in inflammation in the central nervous system and autoimmune diseases.