Abstract
The view of CD4 T-cell-mediated immunity as a balance between distinct lineages of Th1 and Th2 cells has changed dramatically. Identification of the IL-17 family of cytokines and of the fact that IL-23 mediates the expansion of IL-17-producing T cells uncovered a new subset of Th cells designated Th17 cells, which have emerged as a third independent T-cell subset that may play an essential role in protection against certain extracellular pathogens. Moreover, Th17 cells have been extensively analyzed because of their strong association with inflammatory disorders and autoimmune diseases. Also, they appear to be critical for controlling these disorders. Similar to Th1 and Th2 cells, Th17 cells require specific cytokines and transcription factors for their differentiation. Th17 cells have been characterized as one of the major pathogenic Th cell populations underlying the development of many autoimmune diseases, and they are enhanced and stabilized by IL-23. The characteristics of Th17 cells, cytokines, and their sources, as well as their role in infectious and autoimmune diseases, are discussed in this review.
Highlights
CD4+ T cells play an important role in the initiation of immune responses by providing help to other cells and taking on a variety of effector functions during immune reactions
Phosphorylation of STAT3 is essential for the development of IL-17-producing T-helper (Th17) cells, whereas STAT4 is important for increasing IFNγ production and the subsequent differentiation of Th1 cells [42]
While Th17 cells have been involved in the promotion of autoimmunity and Treg cells have been involved in the control of Th17 cells, the balance Th17/Treg has been judged important in the control of immunity mediated by Th17 cells [4]
Summary
CD4+ T cells play an important role in the initiation of immune responses by providing help to other cells and taking on a variety of effector functions during immune reactions. Naıve CD4+ T cells activate, expand, and differentiate into different effector subsets called T helpers—(Th) Th1, Th2, Th9, Th17, and Th22—that are characterized by the production of distinct cytokines and effector functions [1]. The Tcell subsets have been expanded, and Th17 cells have been described as a novel subset of the specialized Th cells lineage that produces IL-17 but not IFN-γ or IL-4 [6]. These cells are potent inducers of tissue inflammation and require TGFβ in International Journal of Inflammation combination with other cytokines such as IL-6 and IL-23 for their differentiation [7]
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