Article

T cell receptor signal strength in Treg and iNKT cell development demonstrated by a novel fluorescent reporter mouse

Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55414, USA.
Journal of Experimental Medicine (Impact Factor: 13.91). 06/2011; 208(6):1279-89. DOI: 10.1084/jem.20110308
Source: PubMed

ABSTRACT The ability of antigen receptors to engage self-ligands with varying affinity is crucial for lymphocyte development. To further explore this concept, we generated transgenic mice expressing GFP from the immediate early gene Nr4a1 (Nur77) locus. GFP was up-regulated in lymphocytes by antigen receptor stimulation but not by inflammatory stimuli. In T cells, GFP was induced during positive selection, required major histocompatibility complex for maintenance, and directly correlated with the strength of T cell receptor (TCR) stimulus. Thus, our results define a novel tool for studying antigen receptor activation in vivo. Using this model, we show that regulatory T cells (T(reg) cells) and invariant NKT cells (iNKT cells) perceived stronger TCR signals than conventional T cells during development. However, although T(reg) cells continued to perceive strong TCR signals in the periphery, iNKT cells did not. Finally, we show that T(reg) cell progenitors compete for recognition of rare stimulatory TCR self-ligands.

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    • "Retinoids induce both Nur77-dependent transcription and the appearance of Bcl-2/BH3 domain in the DP thymocytes Previous studies have shown that retinoids induce apoptosis primarily in double positive (DP) thymocytes [12], but the basal expression of Nur77 shows a differentiation-dependence [49]. While in DP thymocytes the expression of Nur77 is low, both positive and negative selection induces the expression of Nur77, the expression correlating with the strength of the TCR signal. "
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    ABSTRACT: Nur77 is a transcription factor, which plays a determinant role in mediating T cell receptor-induced cell death of thymocytes. In addition to regulation of transcription, Nur77 contributes to apoptosis induction by targeting mitochondria, where it can convert Bcl-2, an anti-apoptotic protein into a proapoptotic molecule. Previous studies have demonstrated that retinoids are actively produced in the mouse thymus and can induce a transcription-dependent apoptosis in mouse thymocytes. Here we show that retinoic acids induce the expression of Nur77, and retinoid-induced apoptosis is completely dependent on Nur77, as retinoids were unable to induce apoptosis in Nur77 null thymocytes. In wild-type thymocytes retinoids induced enhanced expression of the apoptosis-related genes FasL, TRAIL, NDG-1, Gpr65 and Bid, all of them in a Nur77-dependent manner. The combined action of these proteins led to Caspase 8-dependent Bid cleavage in the mitochondria. In addition, we could demonstrate the Nur77-dependent induction of STAT1 leading to enhanced Bim expression, and the mitochondrial translocation of Nur77 leading to the exposure of the Bcl-2/BH3 domain. The retinoid-induced apoptosis was dependent on both Caspase 8 and STAT1. Our data together indicate that retinoids induce a Nur77-dependent cell death program in thymocytes activating the mitochondrial pathway of apoptosis. Copyright © 2014. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 01/2015; 1853(3). DOI:10.1016/j.bbamcr.2014.12.035 · 5.30 Impact Factor
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    • "As retinoids are known to contribute to TGF-␤-induced pTreg formation (Benoist and Mathis 2011), it is interesting to speculate whether they could also contribute to the formation of thymusderived Treg cells. Partly because RAs are known to enhance the activation of the Foxp3+ locus (Benson et al. 2007) and partly because by antagonizing the biological activity of Nur77 by RAR␣ in DP thymocytes (see below) they might promote the survival of those CD4 + thymocytes that have TCR specificities with intermediate affinity for self-antigens and express only immediate levels of Nur77 (Moran et al. 2011). "
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    ABSTRACT: The thymus provides the microenvironment in which thymocytes develop into mature T-cells, and interactions with thymic stromal cells are thought to provide the necessary signals for thymocyte maturation. Recognition of self-MHC by T-cells is a basic requirement for mature T-cell functions, and those thymocytes that do not recognize or respond too strongly to the peptide-loaded self-MHC molecules found in the thymus undergo apoptosis. As a result, 95% of the thymocytes produced will die and be subsequently cleared by macrophages. This review describes a complex crosstalk between developing thymocytes and engulfing macrophages which is mediated by retinoids produced by engulfing macrophages. The interaction results in the harmonization of the rate of cell death of dying double positive cells with their clearance and replacement, and in promotion of the differentiation of the selected cells in the thymus.
    Immunobiology 07/2013; DOI:10.1016/j.imbio.2013.06.009 · 3.18 Impact Factor
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    • "Most importantly, the Nur77-GFP system is sensitive enough that it reports even very weak TCR signals. Nur77-GFP OT-I T cells that are primed with LM-V4 (SIIVFEKL), an antigen that is about 700-fold less potent than SIINFEKL (Zehn et al., 2009), still express high levels of GFP (Moran et al., 2011). We thus believe that the Nur77- GFP reporter mouse is ideal to address the role of TCR signals in BA-CTL generation. "
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    ABSTRACT: During an infection the antigen-nonspecific memory CD8 T cell compartment is not simply an inert pool of cells, but becomes activated and cytotoxic. It is unknown how these cells contribute to the clearance of an infection. We measured the strength of T cell receptor (TCR) signals that bystander-activated, cytotoxic CD8 T cells (BA-CTLs) receive in vivo and found evidence of limited TCR signaling. Given this marginal contribution of the TCR, we asked how BA-CTLs identify infected target cells. We show that target cells express NKG2D ligands following bacterial infection and demonstrate that BA-CTLs directly eliminate these target cells in an innate-like, NKG2D-dependent manner. Selective inhibition of BA-CTL-mediated killing led to a significant defect in pathogen clearance. Together, these data suggest an innate role for memory CD8 T cells in the early immune response before the onset of a de novo generated, antigen-specific CD8 T cell response.
    Cell Reports 03/2013; 3(3). DOI:10.1016/j.celrep.2013.02.020 · 7.21 Impact Factor
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