IL-12– and IL-23–induced T helper cell subsets : birds of the same feather flock together

Traditionally, CD4⁺ T cells have been separated into two different subsets named T helper (Th)1 and Th2. A new IL-23–driven subset of Th cells called Th_IL-17 has now been described. The data suggest that IL-23 plays an important role in the differentiation of autoreactive pathogenic T cells. Whether these IL-23–induced Th_IL-17 cells are a unique subset or are related to other Th subsets is discussed.