T cell tolerance and immunity to commensal bacteria

► Tolerance is required to commensal bacteria and depends on regulatory T cells. ► Regulatory T cells specific to commensal bacteria are generated from naïve T cells in the periphery. ► Bacterial products can facilitate Treg cell function via the induction of IL-10, an immunosuppressive cytokine. ► Specific commensal bacterial species induce inflammatory or tolerogenic T cell responses in the gut.