IAI Accepts, published online ahead of print on 9 November 2009

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Infect. Immun. doi:10.1128/IAI.00929-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Precarious balance: Th17 cells in host defense

Ariana Peck and Elizabeth D. Mellins^*

Department of Pediatrics, Division of Immunology and Transplantation Biology, Stanford University School of Medicine, Stanford, California 94305, USA

^* To whom correspondence should be addressed. Email: mellins{at}stanford.edu.

Lineage-specific responses from the effector T cell repertoire form a critical component of adaptive immunity. The recent identification of Th17 cells—a third, distinct lineage of helper T cells—collapses the long-accepted paradigm in which Th1 and Th2 cells distinctly mediate cellular and humoral immunity, respectively. In this minireview, we discuss the involvement of the Th17 lineage during infection by extracellular bacteria, intracellular bacteria and fungi. Emerging trends suggest that the Th17 population bridges innate and adaptive immunity to produce a robust antimicrobial, inflammatory response. However, because Th17 cells mediate both host defense and pathological inflammation, elucidating mechanisms that attenuate but do not completely abolish the Th17 response may have powerful implications for therapy.