American Journal of Respiratory and Critical Care Medicine vol:183 issue:8 pages:977-986
During T cell receptor (TCR) activation in a particular cytokine environment, naive CD4 T cells may differentiate into lineages defined by their pattern of cytokine production and transcription factors: T helper 1(Th1), Th2, Th17, Th22, follicular helper T cells (Tfh) and inducible regulatory T cells (Treg). Although Th17 cells have only recently been recognized as a distinct lineage of Th cells, associations between interleukin (IL)-17 and human disease have been known somewhat longer. It would be oversimplification to restrict IL-17 to Th17. Indeed IL-17 is also expressed by other cells including gamma-delta (γδ)T-17, Natural Killer (NK)T-17 and lymphoid tissue induced (LTi)-17. IL-17 was cloned in 1995 as a cytokine expressed by T cells, exerting inflammatory effects on epithelial, endothelial and fibroblast cells. IL-17 is a solid link between innate and adaptive immunity and can exert both beneficial as well as deleterious effects. The discovery of IL-17 T cells has provided exciting new insights into host defense, immunoregulation and autoimmunity. Unquestionably, data from mouse models have contributed enormously to our insight into immunologic mechanisms. However, due to numerous differences between murine and human immunology, data obtained in mice are not simply interchangeable. We will review IL-17 T cells exclusively in the human situation and more specifically their potential role in respiratory diseases. The advances in our understanding of IL-17 regulation offers opportunities to dissect the human IL-17 system and to reflect on the clinical presentation of lung diseases. More importantly, the IL-17 system allows us to speculate on new therapeutic opportunities.