Fig 2: Schematic diagram of IL-12 family.The diagram illustrates the currently known 5 chains (the innermost zone), composite cytokines with their proposed functions (the middle zone), and their receptors (the outermost zone). The five color-coded chains are either α chains (p19, p35, and p28) or β chains (p40 and Ebi3). Each functional cytokine is made of one α and one β chain. IL-12 (p35/p40) is a proinflammatory Th1 activator and stabilizer. Similarly, IL-23 (p19/p40) is a proinflammatory Th1 activator and Th17 stabilizer. On the other hand, IL-27 (p28/Ebi3) is an immunoregulatory cytokine mainly with an anti-inflammatory capacity. IL-35 (p35/Ebi3) is again anti-inflammatory and secreted by Treg cells. Therefore, the four cytokines with their divergent functions can promote a representative model of the immunological spectrum ranging from inflammation to tolerance. The unknown cytokine is a theoretical one and symbolizes the possibility of unraveling other unknown family members in the future. Each chain (p19, p40, p35, Ebi3, p28) binds to its specific receptor (IL23R, IL12RB1, IL12RB2, IL6ST, and IL27RA, respectively) and is coded with the same color of the corresponding chain (receptor names are not shown). Typically, a composite cytokine would require a β chain receptor for high affinity binding and an α chain receptor for signal transduction. For alternative terminology of IL-12 family members refer to Table 1.