IL-23 induces the differentiation of naive CD4(+) T cells into highly pathogenic helper T cells (Th17/Th(IL-17)) that produce IL-17, IL-17F, IL-6, and TNF-alpha, but not IFN-gamma and IL-4. Two studies in this issue of the JCI demonstrate that blocking IL-23 or its downstream factors IL-17 and IL-6, but not the IL-12/IFN-gamma pathways, can significantly suppress disease development in animal m...

Interleukin (IL)-23 is a heterodimeric cytokine closely related to IL-12. Yet, despite a strong structural relationship that includes a shared p40 subunit, this does not translate into functional similarity. In fact, the opposite is true, in that these two cytokines appear to have profoundly different roles in regulating host immune responses. It is now clear that IL-23 has key roles in autoimm...

T helper (Th) cells are known to differentiate into several distinct subsets depending on their environment. The Interleukin 17 (IL-17)-producing subset Th17, which was reported and named in 2005, has been extensively analyzed because a strong association with inflammatory disorders has been suggested. The condition in which Th17 cells are differentiated, critical transcription factors, and sim...