1B). Splenic Treg cells from mice with EAE produced IL-17 at a similar frequency, indicating that there was no systemic perturbation in the capacity of Treg cells to produce IL-17 during EAE. However, the frequency of IL-17+ cells was markedly lower in the Treg-cell population sampled from the inflamed CNS of those same mice with EAE (Fig. 1B and C) and was reflected in the level of IL-17 detected in these cultures (Fig. 1D). As Th1-associated effector cytokines act as negative regulators of

Th17 differentiation, we tested whether CNS-Treg cells produced IFN-γ, but found no evidence for this under any conditions tested, including exposure to IL-12 (Supporting Information Fig. 1). Bisulphite sequence analysis of CpG motifs Ipatasertib supplier within the Treg-specific demethylation region (TSDR) revealed complete demethylation in both splenic and EGFR inhibitor CNS-Treg cells (Fig. 1E), a pattern associated with natural Treg cells rather than the incomplete demethylation seen among in vitro generated iTreg cells [[4]]. Therefore, epigenetic differences at

the TSDR did not account for the inability of CNS-Treg cells to produce IL-17. Previous studies have shown that the increased proportion of Foxp3+ T cells in the CNS during EAE is not due to the peripheral conversion of Foxp3− T cells to Foxp3+ adaptive Treg cells [[5]]. Our analysis of the TSDR supports this view. IL-6 can drive IL-17 production by naïve T cells and by Treg cells [[2, 6]]. The IL-6 receptor is composed of an IL-6-specific α chain (CD126) coupled with the signaling chain gp130, which is shared with other cytokine receptors (reviewed in [[7]]). Cells lacking surface expression of the PIK3C2G IL-6R can also respond to IL-6 bound to the soluble form of the IL-6Rα, which then binds gp130 at the cell surface to provide IL-6 trans-signaling [[8]]. Peripheral Foxp3− and Foxp3+ T cells from naïve mice responded rapidly to either IL-6 or hyper DS s-IL-6R (HDS), an IL-6-sIL-6R fusion protein that triggers trans-signaling [[9]], as measured by the appearance of pSTAT1 and pSTAT3 (Supporting Information Fig. 2). However, unlike their

splenic counterparts, CNS CD4+ cells from mice with EAE showed no expression of pSTAT1 or pSTAT3 after incubation with either IL-6 or HDS (Fig. 2A). Notably, this insensitivity was evident on all CNS CD4+ cells and was not restricted to the Treg-cell population. The relative resistance of induced Treg cells to the induction of IL-17 production has been correlated with their loss of IL-6 receptor expression [[10, 11]]. Reduced CD126 expression on CNS CD4+ cells would account for their insensitivity to IL-6, but they would be predicted to maintain responsiveness to IL-6 trans-signaling if they still expressed gp130. We found that both GFP+ and GFP− CD4+ cells from the CNS showed markedly reduced levels of both CD126 and gp130 in comparison with their splenic counterparts from the same mice (Fig. 2B and C).