REVIEW

Cell Research (2009): 399-411
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More stories on Th17 cells

Alexandre S Bass¹, Hilde Cheroutre² and Daniel Mucida²

Correspondence: Daniel Mucida, Tel: +1-858-752-6771; Fax: +1-858-752-6992 E-mail: mucida@liai.org

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For more than two decades, immunologists have been using the so-called Th1/Th2 paradigm to explain most of the phenomena related to adaptive immunity. The Th1/Th2 paradigm implied the existence of two different, mutually regulated, CD4⁺ T helper subsets: Th1 cells, driving cell-mediated immune responses involved in tissue damage and fighting infection against intracellular parasites; and Th2 cells that mediate IgE production and are particularly involved in eosinophilic inflammation, allergy and clearance of helminthic infections. A third member of the T helper set, IL-17-producing CD4⁺ T cells, now called Th17 cells, was recently described as a distinct lineage that does not share developmental pathways with either Th1 or Th2 cells. The Th17 subset has been linked to autoimmune disorders, being able to produce IL-17, IL-17F and IL-21 among other inflammatory cytokines. Interestingly, it has been reported that there is not only a cross-regulation among Th1, Th2 and Th17 effector cells but there is also a dichotomy in the generation of Th17 and T regulatory cells. Therefore, Treg and Th17 effector cells arise in a mutually exclusive fashion, depending on whether they are activated in the presence of TGF-β or TGF-β plus inflammatory cytokines such as IL-6. This review will address the discovery of the Th17 cells, and recent progress on their development and regulation.

Cell Research (2009) 19:399–411. doi: 10.1038/cr.2009.26; published online 3 March 2009

Keywords: adaptive immunity, tolerance, IFN-γ, IL-4, IL-23, TGF-β