This information is current as T Cells within the Thymus Leads to the Generation of Stable Regulatory Locus Foxp 3 Active Demethylation of the Huehn

Stable expression of Foxp3 in regulatory T cells (Tregs) depends on DNA demethylation at the Treg-specific demethylated region (TSDR), a conserved, CpG-rich region within the Foxp3 locus. The TSDR is selectively demethylated in ex vivo Tregs purified from secondary lymphoid organs, but it is unclear at which stage of Treg development demethylation takes place. In this study, we show that commitment to a stable lineage occurred during early stages of murine thymic Treg development by engraving of lineage-specific epigenetic marks in parallel with establishment of a Treg-specific gene expression profile. TSDR demethylation was achieved through an active mechanism and involved enzymes of the ten-eleven-translocation family and hydroxylation of methylated cytosines, a modification that is implicated as an initiating step of mitosis-independent DNA demethylation pathways and has not yet been observed at specific loci during immune cell differentiation. Together, our results demonstrate that initiating TSDR demethylation during early stages of thymic Treg development commences stabilization of Foxp3 expression and guarantees full functionality and long-term lineage stability of Tregs. C D4 + regulatory T cells (Tregs) play an essential role in maintaining immune homeostasis and preventing autoim-mune reactivity of potentially self-reactive lymphocytes that have escaped central tolerance mechanisms (1). For proper development and function, Tregs crucially depend on the forkhead box transcription factor Foxp3, and loss of Foxp3 function in humans and rodents results in devastating autoimmunity (2–7). The vast majority of Foxp3 + Tregs is generated during T cell development in the thymus (8). Development of thymic Tregs mainly takes place in medullary regions at the CD4 single-positive (CD4SP; i.e., CD4 + CD8 2) stage (9, 10). Thymic Treg development requires that CD4SP thymocytes encounter cognate Ag presented by thymic APCs in the context of MHC class II (11–14), and CD4SP thymocytes appear to be predisposed to upregulate Foxp3 expression (15). According to the two-step model of thymic Treg development, this TCR signaling event induces upregulation of IL-2R a-chain (CD25), rendering these thymocytes receptive to subsequent cytokine signals that foster their development into fully functional Foxp3 + Tregs (16, 17). IL-2 plays a predominant role in this second step of thymic Treg development. However, its loss can be compensated by other cytokines that signal through receptors containing the common g subunit, such as IL-7 and IL-15 (16, 18, 19). Stability of Foxp3 expression correlates to DNA demethylation at a conserved intronic CpG-rich region within the Foxp3 gene locus, designated Treg-specific demethylated …