Fig. 1.

Regulation of Th-cell differentiation by activating and inhibitory members of the IL-12 family. IL-12, IL-23 and IL-27 are involved in differentiation and activation of Th1 cells at different stages of Th1 development. Homodimeric p40 can act both in Th1 activation as well as in Th1 inhibition. EBI3x is able to directly drive Th2 responses by supporting the growth and activation of invariant NKT cells, which produce IL-4 [51]. This expands the IL-12 family members beyond exclusively Th1 regulating factors. Additonal mechanisms beyond Th1/Th2 regulation (such as IL-23-induced IL-17 production by memory T cells) are operative [38]. Abbreviations: EBI3, Epstein–Barr virus (EBV)-induced gene 3; IL-12, interleukin-12; NK, natural killer; x, as yet uncharacterized binding partner of EBI3.