Toll-like receptors (TLRS) control activation of adaptive immune responses by antigen-presenting cells (APCs). However, initiation of adaptive immune responses is also controlled by regulatory T cells (TR cells), which act to prevent activation of autoreactive T cells. Here we describe a second mechanism of immune induction by TLRs, which is independent of effects on costimulation. Microbial induction of the Toll pathway blocked the suppressive effect of CD4+CD25+ TR cells, allowing activation of pathogen-specific adaptive immune responses. This block of suppressor activity was dependent in part on interleukin-6, which was induced by TLRs upon recognition of microbial products.
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