Although the binding activity of Ezh2 at the Il17a promoter was higher than at the Ifng promoter, we recognized some binding activity of Ezh2 at the Ifng and Tbx21 promoters. Therefore, a dual activity of Ezh2 as transcriptional activator of Il17a and repressor of the alternative cytokine genes, is feasible,

albeit we have not observed derepression of the opposing cytokine genes Ifng and Il4 following Selleck PARP inhibitor the knockdown of Ezh2. It is possible that a more severe silencing of PcG expression is necessary to reveal their repressive activities. With regard to Tbx21, in some experiments we did find upregulation of its expression following Ezh2 knockdown, but this finding was not consistent, and currently we cannot draw any conclusions in that aspect. Published results using reporter mouse PS 341 strain mapping the fate of cells that have activated IL-17A demonstrated that IL-17A expressing Th cells have distinct extent of plasticity in different inflammatory setting in vivo: they can either acquire the Th1 effector functions instead or in addition to their Th17 phenotype 41. However, the Th17 cells can also shut off their Th17 transcriptional profile without turning on other lineage-specific programs 41. Probably, the mode of the reprogramming process is affected by the external cytokine milieu. Intrinsic factors, which can be modulated during differentiation, may also influence the stability

of the Th17 phenotype, and can underlie some conflicting estimations as to the extent of the plasticity of the Th17 lineage in vivo 36, 40, 41, 45. In our in vitro experiments, we found that the differentiation of Th17 cells in the presence of TGF-β and IL-6 but in the absence of IL-23 resulted in a more stable expression pattern of Rorc mRNA 18 h following cytokine-free restimulation (data not shown); namely, the expression of Rorc mRNA was not reduced 18 h following Ribonucleotide reductase restimulation in the absence of TGF-β, if the cells were differentiated with TGF-β and IL-6 but in the absence of IL-23 (although the expression of Rora and

of both Il17a and Il17f mRNAs did decrease). These results suggest that even though the changes in the expression of Rorc in cells differentiated with or without IL-23 are initially invisible, the presence of IL-23 during differentiation may potentiate a subsequent more flexible Rorc repression pattern. Indeed the involvement of IL-23 in promoting Th17 plasticity is starting to emerge. In vivo models of genetic ablation of Il23 revealed that IL-23 drives the Th1-IFN-γ inflammatory axis 77, and in its absence the differentiation of T cells into both Th1 and Th17 cells is severely impaired 78. Moreover, the IL17A+IFN-γ+ double positive CD4+ T-cell population was significantly reduced in Il23r−/− mice 18, and experiments in IL-17A fate mapping mouse strain confirmed that IL-23 enhance the emergence of this double positive population 41.