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      Metabolic coordination of T cell quiescence and activation

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      Nature Reviews Immunology

      Springer Science and Business Media LLC

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          Abstract

          Naive T cells are actively maintained in a quiescent state that promotes their survival and persistence. On antigen stimulation, T cells exit quiescence to initiate clonal expansion and effector differentiation. Initial studies focused on the immune receptors and transcriptional regulators involved in T cell quiescence and activation, but recent findings highlight cell metabolism as a crucial regulator of these processes. Here we summarize these intrinsic metabolic programmes and also describe how cell-extrinsic factors, such as nutrients and regulatory T cells, directly and indirectly balance quiescence and activation programmes in conventional T cells. We propose that immunological cues and nutrients license and tune metabolic programmes and signalling networks that communicate in a bidirectional manner to promote quiescence exit. Understanding the programmes that regulate T cell quiescence will be key for developing novel approaches to modulate protective and pathological T cell responses in human diseases.

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          Most cited references 112

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          GCN2 kinase in T cells mediates proliferative arrest and anergy induction in response to indoleamine 2,3-dioxygenase.

          Indoleamine 2,3 dioxygenase (IDO) catabolizes the amino acid tryptophan. IDO-expressing immunoregulatory dendritic cells (DCs) have been implicated in settings including tumors, autoimmunity, and transplant tolerance. However, the downstream molecular mechanisms by which IDO functions to regulate T cell responses remain unknown. We now show that IDO-expressing plasmacytoid DCs activate the GCN2 kinase pathway in responding T cells. GCN2 is a stress-response kinase that is activated by elevations in uncharged tRNA. T cells with a targeted disruption of GCN2 were not susceptible to IDO-mediated suppression of proliferation in vitro. In vivo, proliferation of GCN2-knockout T cells was not inhibited by IDO-expressing DCs from tumor-draining lymph nodes. IDO induced profound anergy in responding wild-type T cells, but GCN2-knockout cells were refractory to IDO-induced anergy. We hypothesize that GCN2 acts as a molecular sensor in T cells, allowing them to detect and respond to conditions created by IDO.
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            The glucose transporter Glut1 is selectively essential for CD4 T cell activation and effector function.

            CD4 T cell activation leads to proliferation and differentiation into effector (Teff) or regulatory (Treg) cells that mediate or control immunity. While each subset prefers distinct glycolytic or oxidative metabolic programs in vitro, requirements and mechanisms that control T cell glucose uptake and metabolism in vivo are uncertain. Despite expression of multiple glucose transporters, Glut1 deficiency selectively impaired metabolism and function of thymocytes and Teff. Resting T cells were normal until activated, when Glut1 deficiency prevented increased glucose uptake and glycolysis, growth, proliferation, and decreased Teff survival and differentiation. Importantly, Glut1 deficiency decreased Teff expansion and the ability to induce inflammatory disease in vivo. Treg cells, in contrast, were enriched in vivo and appeared functionally unaffected and able to suppress Teff, irrespective of Glut1 expression. These data show a selective in vivo requirement for Glut1 in metabolic reprogramming of CD4 T cell activation and Teff expansion and survival. Copyright © 2014 Elsevier Inc. All rights reserved.
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              Homeostatic maintenance of natural Foxp3+ CD25+ CD4+ regulatory T cells by interleukin (IL)-2 and induction of autoimmune disease by IL-2 neutralization

              Interleukin (IL)-2 plays a crucial role in the maintenance of natural immunologic self-tolerance. Neutralization of circulating IL-2 by anti–IL-2 monoclonal antibody for a limited period elicits autoimmune gastritis in BALB/c mice. Similar treatment of diabetes-prone nonobese diabetic mice triggers early onset of diabetes and produces a wide spectrum of T cell–mediated autoimmune diseases, including gastritis, thyroiditis, sialadenitis, and notably, severe neuropathy. Such treatment selectively reduces the number of Foxp3-expressing CD25+ CD4+ T cells, but not CD25− CD4+ T cells, in the thymus and periphery of normal and thymectomized mice. IL-2 neutralization inhibits physiological proliferation of peripheral CD25+ CD4+ T cells that are presumably responding to normal self-antigens, whereas it is unable to inhibit their lymphopenia-induced homeostatic expansion in a T cell–deficient environment. In normal naive mice, CD25low CD4+ nonregulatory T cells actively transcribe the IL-2 gene and secrete IL-2 protein in the physiological state. IL-2 is thus indispensable for the peripheral maintenance of natural CD25+ CD4+ regulatory T cells (T reg cells). The principal physiological source of IL-2 for the maintenance of T reg cells appears to be other T cells, especially CD25low CD4+ activated T cells, which include self-reactive T cells. Furthermore, impairment of this negative feedback loop via IL-2 can be a cause and a predisposing factor for autoimmune disease.
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                Author and article information

                Journal
                Nature Reviews Immunology
                Nat Rev Immunol
                Springer Science and Business Media LLC
                1474-1733
                1474-1741
                August 12 2019
                Article
                10.1038/s41577-019-0203-y
                31406325
                © 2019

                http://www.springer.com/tdm

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