The interleukin (IL)-12 superfamily. This cytokine superfamily contains at least four members: IL-12, IL-23, IL-27, and IL-35. They share peptides as indicated; note that EIB3 shares significant homology with p40. The key effects on T-cell subsets are depicted, showing IL-12 driving Th1 cells, IL-23 expanding Th17 cells, and IL-35 modulating regulatory T (Treg) function. It is unclear at this time whether IL-35 is exclusively Treg-derived or whether it can emanate from adjacent cell lineages to promote Treg function. IL-27 has bimodal function in T-cell regulation dependent upon the maturity and differentiation status of the T cell.