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

Interleukin 17 (IL-17)-producing helper T cells (TH17 cells) have been broadly linked to the pathogenesis of multiple autoimmune diseases. In the few short years since the discovery of TH17 cells, new paradigms about their prominence in chronic inflammation and human autoimmunity have emerged. Recent findings that TH17 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 TH17 biology. In this Perspective we highlight critical differences between IL-17 itself and TH17 cells and discuss the protective nature of IL-17 and TH17 cells.