IL-17–producing T cells in lung immunity and inflammation

TH17 cells are a recently described effector CD4 T-cell subset characterized by the production of IL-17A, IL-17F, and IL-22, which have been implicated in the pathogenesis of several autoimmune diseases. TH17 and other IL-17A–producing T cells, including a population of γδ T cells and natural killer T cells, have also been associated with the development of skin, intestinal, and lung inflammatory diseases, such as asthma, granulomatous disease, chronic obstructive pulmonary disease, and cystic fibrosis. On the other hand, IL-17–producing T cells play important roles in protective immunity against some bacterial infections, mainly through the recruitment and activation of neutrophils. Thus, their regulation appears to be critical, and excess or deficient IL-17 elaboration leads either to deficient responses or disease. This review will summarize TH17 cell differentiation and discuss the host beneficial and detrimental function of IL-17A and related cytokines produced by different subpopulations of T cells.