Objective and design: The goal of this review is to examine the effector functions of Th17 cells in host defense and autoimmunity. Material: Published literature on Th17 cells was reviewed with a focus on the secreted products that mediate effector activities of these cells. Results: Th17 cells secrete an array of cytokines that contribute to host defense and that bridge the innate and adaptive arms of the immune response. When this subset of T cells is dysregulated, autoimmune phenomena develop that contribute to the manifestations of many autoimmune diseases. Conclusions: Th17 cells are positioned at a crossroads between innate and adaptive immunity and provide mediators that are essential for host defense. Current interest in harnessing this system for treatment of autoimmune disease will be challenged by the need to avoid abrogating these many protective functions.
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