The dual nature of T(H)17 cells: shifting the focus to function.

Interleukin 17 (IL-17)-producing helper T cells (T(H)17 cells) have been broadly linked to the pathogenesis of multiple autoimmune diseases. In the few short years since the discovery of T(H)17 cells, new paradigms about their prominence in chronic inflammation and human autoimmunity have emerged. Recent findings that T(H)17 cells might be capable of regulatory functions and that the associated effector molecules IL-17 and IL-22 aid in restricting tissue destruction during inflammatory episodes illuminate the complexities of IL-17 and T(H)17 biology. In this Perspective we highlight critical differences between IL-17 itself and T(H)17 cells and discuss the protective nature of IL-17 and T(H)17 cells.