Interleukin 23 (IL-23) is a covalently linked heterodimeric cytokine, which is closely related to IL-12. Macrophages and dendritic cells (DCs) are the major sources of both IL-12 and IL-23, which act on receptors primarily expressed by T cells, NK cells, and NKT cells. IL-23 consists of the p40 subunit shared with IL-12 (IL-12B, IL-12 p40, IL-23 p40) and the 19 kDa protein p19 (IL-23 p19, IL-23A). Its effects are mediated by a receptor composed of IL-12 receptor subunit B1 and an IL-23 specific subunit. While IL-12 drives the development of T
H 1 cells, IL-23 mediates the full differentiation and maintenance of T
H 17 cells. IL-23 stimulates memory CD4
+ rather than naive T cells and promotes the production of pro-inflammatory cytokines. As a key cytokine in the survival and proliferation of T
H 17 cells, IL-23 has central roles in autoimmune diseases and promotes chronic inflammation. It has been shown that single chain fusion proteins of naturally heterodimeric cytokines such as IL-12 or IL-23 are bioactive
in vitro and
in vivo .
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