IL-23 is a covalently linked heterodimeric cytokine, which is closely related to IL-12. Macrophages and dendritic cells 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 and the 19 kDa protein p19 that is unique to IL-23. Its effects are mediated by a receptor composed of IL-12 receptor subunit β1 and an IL-23 specific subunit. IL-12 and IL-23 show different functions although both contain the p40 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 CD4
+ 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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