Development and function of TH17 cells in health and disease

TH17 cells are the newest member of the TH cell family and are characterized by their ability to produce specific cytokines such as IL-17, IL-22, IL-17F, and CCL20. In this review, conditions for the differentiation of TH17 cells are defined in both murine and human systems, with discussion of TH17-specific cytokines and transcription factors. Functionally, TH17 cells contribute to host defense as a new effector TH cell subset with a role in protection against extracellular bacteria through activities on immune and nonimmune cells. Their activities, however, are also pivotal in the development of autoimmune diseases under pathologic conditions. TH17 cells are also beginning to be associated with the development and pathophysiology of allergic diseases, such as allergic contact dermatitis, atopic dermatitis, and asthma. Lymphoid tissue inducer–like cells and natural killer–like cells, termed RORγt+NKp46+ or NK-22 cells, might also play a role in allergic diseases because of their propensity to produce IL-17 and IL-22.