Interleukin 23 (IL-23) is a heterodimeric cytokine composed of two disulfide-linked subunits, a p19 subunit that is unique to IL-23, and a p40 subunit that is shared with IL-12.IL-23 is secreted by activated macrophages and dendritic cells.Human and mouse p19 share 70 % aa sequence identity. The functional IL-23 receptor complex consists of two receptor subunits, a β1 subunit shared with the IL-12 receptor (IL-12R β1) and a β2-like subunit with STAT4 binding domain, termed the IL-23-specific receptor subunit (IL-23R).IL-23 has been shown to enhance IFN-γ production by memory T cells.Additionally, mouse IL-23 (but not IL-12) can activate mouse memory T cells to produce the potent proinflammatory cytokine IL-17.IL-23 has been shown to be upregulated in certain autoimmune diseases and promote immunity in response to some viral and mycobacterial infections.