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1.  Transcription factors RUNX1 and RUNX3 in the induction and suppressive function of Foxp3+ inducible regulatory T cells 
The Journal of Experimental Medicine  2009;206(12):2701-2715.
Forkhead box P3 (FOXP3)+CD4+CD25+ inducible regulatory T (iT reg) cells play an important role in immune tolerance and homeostasis. In this study, we show that the transforming growth factor-β (TGF-β) induces the expression of the Runt-related transcription factors RUNX1 and RUNX3 in CD4+ T cells. This induction seems to be a prerequisite for the binding of RUNX1 and RUNX3 to three putative RUNX binding sites in the FOXP3 promoter. Inactivation of the gene encoding RUNX cofactor core-binding factor-β (CBFβ) in mice and small interfering RNA (siRNA)-mediated suppression of RUNX1 and RUNX3 in human T cells resulted in reduced expression of Foxp3. The in vivo conversion of naive CD4+ T cells into Foxp3+ iT reg cells was significantly decreased in adoptively transferred CbfbF/F CD4-cre naive T cells into Rag2−/− mice. Both RUNX1 and RUNX3 siRNA silenced human T reg cells and CbfbF/F CD4-cre mouse T reg cells showed diminished suppressive function in vitro. Circulating human CD4+ CD25high CD127− T reg cells significantly expressed higher levels of RUNX3, FOXP3, and TGF-β mRNA compared with CD4+CD25− cells. Furthermore, FOXP3 and RUNX3 were colocalized in human tonsil T reg cells. These data demonstrate Runx transcription factors as a molecular link in TGF-β–induced Foxp3 expression in iT reg cell differentiation and function.
PMCID: PMC2806624  PMID: 19917773
2.  In vivo switch to IL-10–secreting T regulatory cells in high dose allergen exposure 
The Journal of Experimental Medicine  2008;205(12):2887-2898.
High dose bee venom exposure in beekeepers by natural bee stings represents a model to understand mechanisms of T cell tolerance to allergens in healthy individuals. Continuous exposure of nonallergic beekeepers to high doses of bee venom antigens induces diminished T cell–related cutaneous late-phase swelling to bee stings in parallel with suppressed allergen-specific T cell proliferation and T helper type 1 (Th1) and Th2 cytokine secretion. After multiple bee stings, venom antigen–specific Th1 and Th2 cells show a switch toward interleukin (IL) 10–secreting type 1 T regulatory (Tr1) cells. T cell regulation continues as long as antigen exposure persists and returns to initial levels within 2 to 3 mo after bee stings. Histamine receptor 2 up-regulated on specific Th2 cells displays a dual effect by directly suppressing allergen-stimulated T cells and increasing IL-10 production. In addition, cytotoxic T lymphocyte–associated antigen 4 and programmed death 1 play roles in allergen-specific T cell suppression. In contrast to its role in mucosal allergen tolerance, transforming growth factor β does not seem to be an essential player in skin-related allergen tolerance. Thus, rapid switch and expansion of IL-10–producing Tr1 cells and the use of multiple suppressive factors represent essential mechanisms in immune tolerance to a high dose of allergens in nonallergic individuals.
PMCID: PMC2585856  PMID: 19001136
3.  GATA3-Driven Th2 Responses Inhibit TGF-β1–Induced FOXP3 Expression and the Formation of Regulatory T Cells 
PLoS Biology  2007;5(12):e329.
Transcription factors act in concert to induce lineage commitment towards Th1, Th2, or T regulatory (Treg) cells, and their counter-regulatory mechanisms were shown to be critical for polarization between Th1 and Th2 phenotypes. FOXP3 is an essential transcription factor for natural, thymus-derived (nTreg) and inducible Treg (iTreg) commitment; however, the mechanisms regulating its expression are as yet unknown. We describe a mechanism controlling iTreg polarization, which is overruled by the Th2 differentiation pathway. We demonstrated that interleukin 4 (IL-4) present at the time of T cell priming inhibits FOXP3. This inhibitory mechanism was also confirmed in Th2 cells and in T cells of transgenic mice overexpressing GATA-3 in T cells, which are shown to be deficient in transforming growth factor (TGF)-β–mediated FOXP3 induction. This inhibition is mediated by direct binding of GATA3 to the FOXP3 promoter, which represses its transactivation process. Therefore, this study provides a new understanding of tolerance development, controlled by a type 2 immune response. IL-4 treatment in mice reduces iTreg cell frequency, highlighting that therapeutic approaches that target IL-4 or GATA3 might provide new preventive strategies facilitating tolerance induction particularly in Th2-mediated diseases, such as allergy.
Author Summary
Specific immune responses against foreign or autologous antigens are driven by specialized epitope-specific T cells, whose numbers expand upon recognition of antigen found on professional antigen-presenting cells. The subsequent maturation process involves the differentiation of certain T cell phenotypes such as pro-inflammatory cells (Th1, Th2, Th17) or regulatory T (Treg) cells, which serve to keep the immune response in check. The current study focuses on the role of two key transcription factors—FOXP3 and GATA3—in controlling the commitment of these cells. We demonstrate that the Th2 cytokine IL-4 inhibits the induction of FOXP3 and thus inhibits the generation of inducible Treg cells. We show that IL-4–induced GATA3 mediates FOXP3 inhibition by directly binding to a GATA element in the FOXP3 promoter. We hypothesize that therapeutic agents aimed at neutralizing IL-4 could be a novel strategy to facilitate inducible Treg cell generation and thus promotion of tolerance in allergies and other Th2-dominated diseases.
It is shown that Th2 responses prevent the generation of inducible Tregs. This is mediated by IL-4 induction of GATA3, which binds directly to and represses the FOXP3 promoter. This mechanism is likely to be relevant in the induction of immunotolerance, particularly in allergic diseases.
PMCID: PMC2222968  PMID: 18162042

Results 1-3 (3)