Although recent studies have identified regulatory roles for Foxp3+CD8+ T cells, the mechanisms that induce their development and underlie their functions in vivo have not been elucidated. Here, we show that IL-6 positively regulates the Foxp3+CD8+ T-cell development and function. The Foxp31CD81 T cells that differentiated in vitro in the presence of IL-6 suppressed autoimmune colitis and arthritis in vivo. Moreover, Foxp3+CD8+ T cells that developed in vivo in the presence of enhanced IL-6 signaling suppressed the development of a spontaneous Th17 cell-mediated autoimmune arthritis. Thus, we concluded that Foxp31CD81 T cells develop in response to IL-6 and regulate chronic inflammation in Th17 cell-mediated F759 autoimmune arthritis. These results suggested that Foxp3+CD8+ T cells may develop in response to IL-6 under certain inflammatory conditions in vivo and may regulate some other chronic inflammation diseases.
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