Regulatory T cells (Treg) are critically involved in maintaining immunological tolerance, but this potent suppression must be quenched to allow the generation of adaptive immune responses. Here we report that type 1 sphingosine-1-phosphate (S1P) receptor (S1P1) delivers an intrinsic negative signal to restrain thymic generation, peripheral maintenance and suppressive activity of Treg cells. Combining loss- and gain-of-function genetic approaches, we found that S1P1 blocked the differentiation of thymic Treg precursors and function of mature Treg cells, and affected Treg-mediated immune tolerance. S1P1 induced the selective activation of the Akt-mTOR pathway to impede Treg development and function. Dynamic regulation of S1P1 contributed to lymphocyte priming and immune homeostasis. Thus, by antagonizing Treg-mediated immune suppression, the lipid-activated S1P1-Akt-mTOR pathway orchestrates adaptive immune responses.

Naïve CD4+ T cells differentiate into diverse effector and regulatory lineages to orchestrate immunity and tolerance. The differentiation of pro-inflammatory TH1 and anti-inflammatory Foxp3+ regulatory T cells (Treg) was reciprocally regulated by S1P1, a receptor for the bioactive lipid sphingosine-1-phosphate. S1P1 inhibited extrathymic and natural Treg generation while driving TH1 cell development in a reciprocal manner and disrupted immune homeostasis. S1P1 signaled through mTOR and antagonized TGF-β function mainly by attenuating sustained Smad3 activity. S1P1 function was dependent upon endogenous sphingosine kinase activity. Remarkably, two seemingly unrelated immunosuppressants FTY720 and rapamycin targeted the same S1P1 and mTOR pathway to regulate the dichotomy between TH1 and Treg cells. Our studies establish an S1P1-mTOR axis that controls T cell lineage specification.

As a phenotypically plastic cellular population, macrophages change their physiology in response to environmental signals. Emerging evidence suggests that macrophages are capable of tightly coordinating their metabolic programs to adjust their immunological and bioenergetic functional properties, as needed. Upon mitogenic stimulation, quiescent macrophages enter the cell cycle, increasing their bioenergetic and biosynthetic activity to meet the demands of cell growth. Proinflammatory stimulation, however, suppresses cell proliferation, while maintaining a heightened metabolic activity imposed by the production of bactericidal factors. Here, we report that the mitogenic stimulus, colony-stimulating factor 1 (CSF-1), engages a myelocytomatosis viral oncogen (Myc)-dependent transcriptional program that is responsible for cell cycle entry and the up-regulation of glucose and glutamine catabolism in bone marrow-derived macrophages (BMDMs). However, the proinflammatory stimulus, lipopolysaccharide (LPS), suppresses Myc expression and cell proliferation and engages a hypoxia-inducible factor alpha (HIF1α)-dependent transcriptional program that is responsible for heightened glycolysis. The acute deletion of Myc or HIF1α selectively impaired the CSF-1-or LPS-driven metabolic activities in BMDM, respectively. Finally, inhibition of glycolysis by 2-deoxyglucose (2-DG) or genetic deletion of HIF1α suppressed LPS-induced inflammation in vivo. Our studies indicate that a switch from a Myc-dependent to a HIF1α-dependent transcriptional program may regulate the robust bioenergetic support for an inflammatory response, while sparing Myc-dependent proliferation.T he cells of the immune system are constantly exposed to environmental challenges and are capable of tailoring their metabolic programs to meet distinct physiological needs. Macrophages, like other immune cells, rapidly change their physiology in response to various environmental cues. Macrophages undergo proliferation in response to mitogenic stimuli, such as colony-stimulating factor 1 (CSF-1) [also known as macrophage CSF (M-CSF)], and this cellular turnover is essential for macrophage homeostasis and may occur in mature macrophages, bypassing the need for self-renewing progenitors (1, 2). Proliferating macrophages consume considerable amounts of energy and require de novo synthesis of macromolecules to support their growth and proliferation (3-6). Therefore, macrophages must coordinately regulate metabolic programs to meet their bioenergetic and biosynthetic demand during proliferation. Despite the emerging view that extracellular signaling events dictate cell growth, proliferation, and death, in part by modulating metabolic activities in cancer cells and T lymphocytes, the precise mechanisms and crucial players of reprogramming metabolism during macrophage proliferation are incompletely understood.Upon encountering an invading microorganism, the bioenergetic potential in macrophages quickly shifts away from fulfilling the needs of cell proliferation to mount a robust...

Distinct metabolic programs support the differentiation of CD4(+) T cells into separate functional subsets. In this study, we investigated metabolic mechanisms underlying the differentiation of IL-9-producing CD4(+) T cells (Th9) in allergic airway inflammation and cancerous tumors. We found that histone deacetylase SIRT1 negatively regulated Th9 cell differentiation. A deficiency of SIRT1 induced by either conditional deletion in mouse CD4(+) T cells or the use of small interfering RNA (siRNA) in mouse or human T cells increased IL-9 production, whereas ectopic SIRT1 expression inhibited it. Notably, SIRT1 inhibited Th9 cell differentiation that regulated anti-tumor immunity and allergic pulmonary inflammation. Glycolytic activation through the mTOR-hypoxia-inducible factor-1α (HIF1α) was required for the differentiation of Th9 cells that conferred protection against tumors and is involved in allergic airway inflammation. Our results define the essential features of SIRT1-mTOR-HIF1α signaling-coupled glycolytic pathway in inducing Th9 cell differentiation, with implications for metabolic reprogramming as an immunotherapeutic approach.

CD4 + CD25 + regulatory T cells (Treg cells) are important in maintenance of peripheral tolerance. The direct effect of CD4 + CD25 + Treg cells on macrophages was studied using a mouse model in which syngeneic CD4 + CD25 + Treg cells were adoptively transferred into the peritoneal cavity of SCID mice. Peritoneal macrophages in mice transferred with CD4 + CD25 + Treg cells expressed significantly higher levels of CD23, CD47 and CD206 and less CD80 and major histocompatibility complex class II molecules as compared with those mice that received either CD4 + CD25 À T cells or no cells. Macrophages of mice injected with CD4 + CD25 + Treg cells displayed a remarkably enhanced phagocytosis of chicken red blood cells, and arginase activity together with an increased interleukin-10 (IL-10) production, whereas they showed a decreased antigen-presenting ability and nitric oxide production. Keywords: alternatively activated macrophages; classically activated macrophages; immune tolerance; mouse; arginase Mononuclear phagocytes, an important part of innate immunity, have pivotal roles in pathogen and tissue debris clearance, antigen capture and presentation as well as in shaping the development of adaptive immune response. Macrophages are a highly heterogeneous cell population that adapt and respond to a large variety of microenvironmental signals. 1 Distinct macrophage subsets expressing different patterns of chemokines, surface markers and metabolic enzymes and showing diversity of functions can be induced in inflammatory and noninflammatory settings. 2-4 M1 (classically activated) macrophages, after induction by proinflammatory mediators, such as lipopolysaccharide (LPS), interleukin-1b (IL-1b) and interferon-g (IFN-g), produce significant amounts of proinflammatory cytokines (TNF-a, IFN-g, IL-6 and IL-12) and generate reactive oxygen species such as nitric oxide (NO) by activation of inducible nitric oxide synthase (Nos2). [2][3][4] In contrast, M2 (alternatively activated) macrophages, which are induced by exposure to IL-4, IL-13, IL-10, transforming growth factor-b (TGF-b) and glucocorticoids, produce less proinflammatory cytokines and instead, simultaneously also show more production of anti-inflammatory cytokines IL-10, TGF-b and IL-1 receptor antagonist as well as enzyme arginase. 2,5,6 Furthermore, M2 macrophages express high levels of CD206 and CD163. Overall, M2 macrophages are believed to participate in the blockade of inflammatory responses and promotion of tissue repair and type II immunity. 7,8 Importantly, recent studies have shown that M2 macrophages, which are different from M1 macrophages, have been implicated in controlling CD4 + T-cell hyporesponsiveness by inducing CD4 + CD25 + Treg cells or inhibiting IL-17-producing CD4 + T cells (Th17) in autoimmunity, transplant immunity or pathogenic infections. 9-11 These studies indicate that different macrophage subsets have distinguished roles in modulating immune response or tolerance.It is now known that CD4 + CD25 + regulatory T cells (Treg cells), which e...

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Myeloid-derived suppressor cells (MDSC) display an immature phenotype that may assume a classically activated (M1) or alternatively activated phenotype (M2) in tumors. In this study, we investigated metabolic mechanisms underlying the differentiation of MDSCs into M1 or M2 myeloid lineage and their effect on cancer pathophysiology. We found that SIRT1 deficiency in MDSCs directs a specific switch to M1 lineage when cells enter the periphery from bone marrow, decreasing the suppressive function in favor of a proinflammatory M1 phenotype associated with tumor cell attack. Glycolytic activation through the mTOR-hypoxia-inducible factor1a (HIF-1a) pathway was required for differentiation to the M1 phenotype, which conferred protection against tumors. Our results define the essential nature of a SIRT1-mTOR/HIF-1a glycolytic pathway in determining MDSC differentiation, with implications for metabolic reprogramming as a cancer therapeutic approach. Cancer Res; 74(3); 727-37. Ó2013 AACR.

A progressive decline in the integrity of the immune system is one of the physiologic changes during aging. The frequency of autoimmune diseases or immune disorders increases in the aging population, but the state of regulatory T (Treg) cells in aged individuals has not been well determined. In the present study, we investigated the levels, phenotypes, and function of CD4(+)CD25(+) Treg cells in Balb/c mice, which were older than 20 months. Significantly enhanced percentages of CD4(+)CD25(+) Treg cells in the periphery (blood, spleen, and lymph nodes) of the aged mice were observed. These Treg cells showed modified Vbeta family distribution, reduced levels of CD45 receptor B and CD62 ligand molecules, as well as normal levels of forkhead box p3. However, when the inhibiting function of Treg cells was assayed in the in vitro assays and in a delayed-type hypersensitivity (DTH) model, CD4(+)CD25(+) Treg cells of aged mice displayed significantly lower inhibiting ability on alloantigen-induced DTH reaction or cytokine productions (IL-2 and IFN-gamma) but not cell proliferation of effector T cells, as compared with CD4(+)CD25(+) Treg cells of young mice. In addition, the percentages of CD4(+)CD8(-)CD25(+) Treg cells in the thymi of aged mice increased significantly, but their total cell numbers decreased markedly in these mice. Our present studies indicated collectively that the percentages, phenotypes, the size of TCR repertoire, and function of CD4(+)CD25(+) Treg cells were altered significantly with aging in mice. The functional defects of CD4(+)CD25(+) Treg cells may shed light on the role of CD4(+)CD25(+) Treg cells in the increased sensitivity to autoimmune diseases of aged populations.