Interleukin-12 and interleukin-23 (shared p40 subunit) (IL-12/23)

Interleukin-12 (IL-12) and interleukin-23 (IL-23) are related heterodimeric cytokines that play distinct but overlapping roles in immune regulation[1][2][6]. Both cytokines share a common **p40 subunit** (encoded by the IL-12B gene) but have distinct second subunits: p35 (IL-12A) for IL-12 and p19 (IL-23A) for IL-23. They signal through receptor complexes that both include the **IL-12Rβ1** receptor protein but diverge in their second receptor chain (IL-12Rβ2 for IL-12, IL-23R for IL-23)[1][2][4][6]. IL-12 principally drives T helper 1 (Th1) cell differentiation and promotes IFN-γ production, while IL-23 is crucial for the maintenance and expansion of Th17 cells, which produce IL-17 and contribute to inflammation, autoimmunity, and defense against certain pathogens[2][5][6]. Therapeutic blockade of the p40 subunit inhibits both IL-12 and IL-23 pathways and is effective in treating several autoimmune and inflammatory disorders, most notably **psoriasis** and **inflammatory bowel diseases**, by dampening pathogenic T-cell responses[6]. Because IL-12/23 blockade broadly suppresses immune activation, it carries the risk of increased infection and possible malignancy with chronic use.

Other names

IL12/23IL-12 p40shared IL-12 family cytokinesp40 cytokinesIL-12B

Blockade of the p40 subunit shared by IL-12 and IL-23, thus inhibiting both cytokines' signaling[6]; Downregulation of Th1 and Th17 responses