Cutting edge: regulation of T cell trafficking and primary immune responses by sphingosine 1-phosphate receptor 1

Local Power: The Role of Tissue-Resident Immunity in Human Genital Herpes Simplex Virus Reactivation

From established latency, human herpes virus type 2 (HSV-2) frequently reactivates into the genital tract, resulting in symptomatic ulcers or subclinical shedding. Tissue-resident memory (TRM) CD8+ T cells that accumulate and persist in the genital skin at the local site of recrudescence are the "first responders" to viral reactivation, performing immunosurveillance and containment and aborting the ability of the virus to induce clinical lesions. This review describes the unique spatiotemporal characteristics, transcriptional signatures, and noncatalytic effector functions of TRM CD8+ T cells in the tissue context of human HSV-2 infection. We highlight recent insights into the intricate overlaps between intrinsic resistance, innate defense, and adaptive immunity in the tissue microenvironment and discuss how rapid virus-host dynamics at the skin and mucosal level influence clinical outcomes of genital herpes diseases.

Targeting S1PR1 May Result in Enhanced Migration of Cancer Cells in Bladder Carcinoma

Clinical bladder tumor histological analysis shows that high expression of S1PR1 is associated with poor patient prognosis. However, there are no studies that describe the underlying mechanism. To investigate the relative distribution and actual function of S1PR1 in bladder tumors, we analyzed multiple clinical databases in combination with tumor purity and immune cell infiltration simulations, as well as databases of well-defined histological phenotypes of bladder cancer, and single-cell sequencing of adjacent normal tissues and bladder tumors, and further compared them with bladder cancer cell lines. The results showed that S1PR1 expression was generally higher in normal tissues than in bladder cancer tissues, and its distribution was mainly in endothelial cells or immune cells. The association between high S1PR1 expression and poor prognosis may be due to tumor invasion of adjacent normal tissues, where highly expressed S1PR1 may affect prognostic interpretation. The effect of S1PR1 itself on cancer cells was associated with cell adhesion, and in bladder cancer cells, S1PR1 expression was negatively correlated with cell motility. Moreover, the use of FTY-720 will cause an increased metastatic ability of bladder cancer cells. In conclusion, we suggest that the use of S1PR1-specific inhibition as a synergistic treatment requires more observation and consideration.

miR-155 indicates the fate of CD4+ T cells

MicroRNAs (miRNAs) are a class of short noncoding RNAs that regulate the translation of target messenger RNA (mRNA) and consequently participate in a variety of biological processes at the posttranscriptional level. miR-155, encoded within a region known as the B cell integration cluster (BIC), plays multifunctional roles in shaping lymphocytes ranging from biological development to adaptive immunity. It has been revealed that miR-155 plays a key role in fine-tuning the regulation of lymphocyte subsets, including dendritic cells (DCs), macrophages, B cells, and CD8⁺ and CD4⁺ T cells. Antigen-specific CD4⁺ T lymphocytes are critical for host defense against pathogens and prevention of damage resulting from excessive inflammation. Over the past years, various studies have shown that miR-155 plays a critical role in CD4⁺ T cells function. Therefore, we summarize multiple target genes of miR-155 that regulate aspects of CD4⁺ T cells immunity, particularly CD4⁺ T cells differentiation, in this review. In addition, we also focus on the role of miR-155 in the regulation of immunological diseases, suggesting it as a potential disease biomarker and therapeutic target.

E-protein-regulated expression of CXCR4 adheres preselection thymocytes to the thymic cortex

The E-protein transcription factors E2A and HEB regulate thymocyte expression of the chemokine receptor CXCR4 to retain preselection thymocytes in the thymic cortex. TCR-mediated positive selection signals extinguish CXCR4 expression to allow positively selected thymocytes to migrate from the cortex into the thymic medulla.

Preselection thymocytes are normally retained in the thymic cortex, but the mechanisms responsible remain incompletely understood. We now report that deletion of genes encoding the E-protein transcription factors E2A and HEB disorders chemokine receptor expression on developing thymocytes to allow escape of preselection TCR⁻CD8⁺ thymocytes into the periphery. We document that CXCR4 expression normally anchors preselection thymocytes to the thymic cortex via interaction with its ligand CXCL12 on cortical thymic epithelial cells, and that disruption of CXCR4–CXCL12 engagements release preselection thymocytes from the thymic cortex. We further document that CXCR4 expression must be extinguished by TCR-mediated positive selection signals to allow migration of TCR-signaled thymocytes out of the thymic cortex into the medulla. Thus, E-protein transcription factors regulate the ordered expression pattern of chemokine receptors on developing thymocytes, and the interaction of the chemokine receptor CXCR4 with its ligand adheres TCR-unsignaled preselection thymocytes to the thymic cortex.

Hippo Kinases Mst1 and Mst2 Sense and Amplify IL-2R-STAT5 Signaling in Regulatory T Cells to Establish Stable Regulatory Activity

Interleukin-2 (IL-2) and downstream transcription factor STAT5 are important for maintaining regulatory T (Treg) cell homeostasis and function. Treg cells can respond to low IL-2 levels, but the mechanisms of STAT5 activation during partial IL-2 deficiency remain uncertain. We identified the serine-threonine kinase Mst1 as a signal-dependent amplifier of IL-2-STAT5 activity in Treg cells. High Mst1 and Mst2 (Mst1-Mst2) activity in Treg cells was crucial to prevent tumor resistance and autoimmunity. Mechanistically, Mst1-Mst2 sensed IL-2 signals to promote the STAT5 activation necessary for Treg cell homeostasis and lineage stability and to maintain the highly suppressive phosphorylated-STAT5⁺ Treg cell subpopulation. Unbiased quantitative proteomics revealed association of Mst1 with the cytoskeletal DOCK8-LRCHs module. Mst1 deficiency limited Treg cell migration and access to IL-2 and activity of the small GTPase Rac, which mediated downstream STAT5 activation. Collectively, IL-2-STAT5 signaling depends upon Mst1-Mst2 functions to maintain a stable Treg cell pool and immune tolerance.

Sequestration of T cells in bone marrow in the setting of glioblastoma and other intracranial tumors

T-cell dysfunction contributes to tumor immune escape in patients with cancer and is particularly severe amidst glioblastoma (GBM). Among other defects, T-cell lymphopenia is characteristic, yet often attributed to treatment. We reveal that even treatment-naïve patients and mice with GBM can harbor AIDS-level CD4 counts, as well as contracted, T-cell deficient lymphoid organs. Missing naïve T-cells are instead found sequestered in large numbers in the bone marrow. This phenomenon characterizes not only GBM but a variety of other cancers, although only when tumors are introduced into the intracranial compartment. T-cell sequestration is accompanied by tumor-imposed loss of S1P1 from the T-cell surface and is reversible upon precluding S1P1 internalization. In murine models of GBM, hindering S1P1 internalization and reversing sequestration licenses T-cell-activating therapies that were previously ineffective. Sequestration of T-cells in bone marrow is therefore a tumor-adaptive mode of T-cell dysfunction, whose reversal may constitute a promising immunotherapeutic adjunct.

The novel sphingosine-1-phosphate receptors antagonist AD2900 affects lymphocyte activation and inhibits T-cell entry into the lymph nodes

Sphingolipid derivatives play key roles in immune cell migration and function. Synthetic sphingolipid analogues are used as therapeutics to intervene various inflammatory and malignant conditions. We hypothesize that different analogs have different effects on immune cells and therefore can be used as treatment for specific diseases. This study examines the properties of the novel synthetic sphingolipid analog, AD2900, and its effects on immune cell activation and lymphocyte localization in homeostasis. AD2900 is an antagonist for all sphingosine-1-phosphate (S1P) receptors. It demonstrates a significant inhibitory effect on the proliferation of activated human peripheral blood mononuclear cells, which is dependent on cAMP reduction and calcium signal transduction but not on phospholipase C activation. AD2900 causes a significant but reversible downregulation of S1P1 expression on the cell surface. AD2900 administration to C57BL/6J mice leads to the accumulation of T cells in the blood and spleen and in turn reduces T-cell number in the lymph nodes. Moreover, AD2900 treatment shows significant effects on the localization of T-cell subpopulations. These results demonstrate the key roles of S1P in T-cell trafficking in a steady state and suggest a potential clinical application for AD2900. Notably, this sphingolipid analog does not cause a severe lymphopenia. The clinical effect of AD2900 in hemato-oncologic diseases and immune-related diseases needs further investigation.

Effects of sphingosine-1-phosphate receptor 1 phosphorylation in response to FTY720 during neuroinflammation

Fingolimod (FTY720, Gilenya), a sphingosine-1-phosphate receptor (S1PR) modulator, is one of the first-line immunomodulatory therapies for treatment of relapsing-remitting multiple sclerosis (MS). Human S1PR1 variants have been reported to have functional heterogeneity in vitro, suggesting that S1PR1 function may influence FTY720 efficacy. In this study, we examined the influence of S1PR1 phosphorylation on response to FTY720 in neuroinflammation. We found that mice carrying a phosphorylation-defective S1pr1 gene [S1PR1(S5A) mice] were refractory to FTY720 treatment in MOG_35-55-immunized and Th17-mediated experimental autoimmune encephalomyelitis (EAE) models. Long-term treatment with FTY720 induced significant lymphopenia and suppressed Th17 response in the peripheral immune system via downregulating STAT3 phosphorylation in both WT and S1PR1(S5A) mice. However, FTY720 did not effectively prevent neuroinflammation in the S1PR1(S5A) EAE mice as a result of encephalitogenic cells expressing C-C chemokine receptor 6 (CCR6). Combined treatment with FTY720 and anti-CCR6 delayed disease progression in S1PR1(S5A) EAE mice, suggesting that CCR6-mediated cell trafficking can overcome the effects of FTY720. This work may have translational relevance regarding FTY720 efficacy in MS patients and suggests that cell type-specific therapies may enhance therapeutic efficacy in MS.

Histone H3 Lysine 27 demethylases Jmjd3 and Utx are required for T-cell differentiation

Although histone H3 lysine 27 trimethylation (H3K27Me3) is associated with gene silencing, whether H3K27Me3 demethylation affects transcription and cell differentiation in vivo has remained elusive. To investigate this, we conditionally inactivated the two H3K27Me3 demethylases, Jmjd3 and Utx, in non-dividing intrathymic CD4(+) T-cell precursors. Here we show that both enzymes redundantly promote H3K27Me3 removal at, and expression of, a specific subset of genes involved in terminal thymocyte differentiation, especially S1pr1, encoding a sphingosine-phosphate receptor required for thymocyte egress. Thymocyte expression of S1pr1 was not rescued in Jmjd3- and Utx-deficient male mice, which carry the catalytically inactive Utx homolog Uty, supporting the conclusion that it requires H3K27Me3 demethylase activity. These findings demonstrate that Jmjd3 and Utx are required for T-cell development, and point to a requirement for their H3K27Me3 demethylase activity in cell differentiation.

Sphingosine-1-phosphate receptor 1 agonist SEW2871 prolongs heterotopic heart allograft survival in mice

Sphingosine-1-phosphate (S1P) is a biologically active metabolite of plasma-membrane sphingolipids that is essential for immune cell trafficking. Recent studies have revealed immunomodulatory functions of S1P and its receptors (S1PR1-S1PR5) in many inflammatory conditions, such as asthma and autoimmunity. Here, we explore the efficacy of SEW2871, a selective S1PR1 agonist, in the prevention of acute allograft rejection in a murine cardiac transplantation model. Treatment of recipient mice with SEW2871 significantly prolongs cardiac allograft survival as compared to those recipients treated with control vehicle. The enhanced graft survival is associated with reduced circulating lymphocytes and allograft inflammatory cell infiltration. The cytokine analysis showed decreased allograft expression of TNF-α, IFN-γ and IL-2 in the SEW2871-treated mice. Moreover, administration of SEW2871 increases the percentage of CD4(+) T regulatory cells and FoxP3 expression in spleen of allograft recipients. Therefore, SEW2871 plays a critical role in regulation of lymphocyte trafficking and development, which directly contributes to prolongation of the allograft survival.

mTOR and metabolic regulation of conventional and regulatory T cells

mTOR signaling links bioenergetic and biosynthetic metabolism to immune responses. mTOR is activated by diverse upstream stimuli, including immune signals, growth factors, and nutrients. Recent studies highlight crucial roles of mTOR signaling in immune functions mediated by conventional T cells and T_regs In this review, we discuss the regulation of mTOR signaling in T cells and the functional impacts of mTOR and metabolic pathways on T cell-mediated immune responses, with a particular focus on the differentiation and function of T_regs.

mTOR Links Environmental Signals to T Cell Fate Decisions

T cell fate decisions play an integral role in maintaining the health of organisms under homeostatic and inflammatory conditions. The localized microenvironment in which developing and mature T cells reside provides signals that serve essential functions in shaping these fate decisions. These signals are derived from the immune compartment, including antigens, co-stimulation, and cytokines, and other factors, including growth factors and nutrients. The mechanistic target of rapamycin (mTOR), a vital sensor of signals within the immune microenvironment, is a central regulator of T cell biology. In this review, we discuss how various environmental cues tune mTOR activity in T cells, and summarize how mTOR integrates these signals to influence multiple aspects of T cell biology.

Transcriptomics identified a critical role for Th2 cell-intrinsic miR-155 in mediating allergy and antihelminth immunity

Allergic diseases, orchestrated by hyperactive CD4(+) Th2 cells, are some of the most common global chronic diseases. Therapeutic intervention relies upon broad-scale corticosteroids with indiscriminate impact. To identify targets in pathogenic Th2 cells, we took a comprehensive approach to identify the microRNA (miRNA) and mRNA transcriptome of highly purified cytokine-expressing Th1, Th2, Th9, Th17, and Treg cells both generated in vitro and isolated ex vivo from allergy, infection, and autoimmune disease models. We report here that distinct regulatory miRNA networks operate to regulate Th2 cells in house dust mite-allergic or helminth-infected animals and in vitro Th2 cells, which are distinguishable from other T cells. We validated several miRNA (miR) candidates (miR-15a, miR-20b, miR-146a, miR-155, and miR-200c), which targeted a suite of dynamically regulated genes in Th2 cells. Through in-depth studies using miR-155(-/-) or miR-146a(-/-) T cells, we identified that T-cell-intrinsic miR-155 was required for type-2 immunity, in part through regulation of S1pr1, whereas T-cell-intrinsic miR-146a was required to prevent overt Th1/Th17 skewing. These data identify miR-155, but not miR-146a, as a potential therapeutic target to alleviate Th2-medited inflammation and allergy.

Proinflammatory cytokines differentially regulate adipocyte mitochondrial metabolism, oxidative stress, and dynamics

Proinflammatory cytokines differentially regulate adipocyte mitochondrial metabolism, oxidative stress, and dynamics. Macrophage infiltration of adipose tissue and the chronic low-grade production of inflammatory cytokines have been mechanistically linked to the development of insulin resistance, the forerunner of type 2 diabetes mellitus. In this study, we evaluated the chronic effects of TNFα, IL-6, and IL-1β on adipocyte mitochondrial metabolism and morphology using the 3T3-L1 model cell system. TNFα treatment of cultured adipocytes led to significant changes in mitochondrial bioenergetics, including increased proton leak, decreased ΔΨm, increased basal respiration, and decreased ATP turnover. In contrast, although IL-6 and IL-1β decreased maximal respiratory capacity, they had no effect on ΔΨm and varied effects on ATP turnover, proton leak, or basal respiration. Only TNFα treatment of 3T3-L1 cells led to an increase in oxidative stress (as measured by superoxide anion production and protein carbonylation) and C16 ceramide synthesis. Treatment of 3T3-L1 adipocytes with cytokines led to decreased mRNA expression of key transcription factors and control proteins implicated in mitochondrial biogenesis, including PGC-1α and eNOS as well as deceased expression of COX IV and Cyt C. Whereas each cytokine led to effects on expression of mitochondrial markers, TNFα exclusively led to mitochondrial fragmentation and decreased the total level of OPA1 while increasing OPA1 cleavage, without expression of levels of mitofusin 2, DRP-1, or mitofilin being affected. In summary, these results indicate that inflammatory cytokines have unique and specialized effects on adipocyte metabolism, but each leads to decreased mitochondrial function and a reprogramming of fat cell biology.

Defective sphingosine 1-phosphate receptor 1 (S1P1) phosphorylation exacerbates TH17-mediated autoimmune neuroinflammation

Sphingosine-1-phosphate (S1P) signaling regulates lymphocyte egress from lymphoid organs into systemic circulation. Sphingosine phosphate receptor 1 (S1P₁) agonist, FTY-720 (Gilenya™) arrests immune trafficking and prevents multiple sclerosis (MS) relapses. However, alternative mechanisms of S1P-S1P₁ signaling have been reported. Phosphoproteomic analysis of MS brain lesions revealed S1P₁ phosphorylation on S351, a residue crucial for receptor internalization. Mutant mice harboring a S1pr1 gene encoding phosphorylation-deficient receptors [S1P₁(S5A)] developed severe experimental autoimmune encephalomyelitis (EAE) due to T helper (T_H) 17-mediated autoimmunity in the peripheral immune and nervous system. S1P₁ directly activated Janus-like kinase–signal transducer and activator of transcription 3 (JAK-STAT3) pathway via interleukin 6 (IL-6). Impaired S1P₁ phosphorylation enhances T_H17 polarization and exacerbates autoimmune neuroinflammation. These mechanisms may be pathogenic in MS.

Immune surveillance by CD8αα+ skin-resident T cells in human herpes virus infection

Most herpes simplex virus 2 (HSV-2) reactivations in humans are subclinical and associated with rapid expansion and containment of virus. Previous studies have shown CD8⁺ T cells persist in genital skin and mucosa at the dermal-epidermal junction (DEJ), the portal of neuronal release of reactivating virus, for prolonged time periods after lesions are cleared^1,2. The phenotype and function of this persistent CD8⁺ T-cell population remain unknown. Here, using cell type-specific laser capture microdissection, transcriptional profiling and T-cell receptor beta (TCRβ) genotyping on sequential genital skin biopsies, we show CD8αα⁺ T cells are the dominant resident population of DEJ CD8⁺ T cells that persist at the site of prior HSV-2 reactivation. CD8αα⁺ T cells located at the DEJ lack chemokine receptor expression required for lymphocyte egress and recirculation, express gene signatures of T-cell activation and antiviral activity, and produce cytolytic granules during clinical and virological quiescent time periods. Sequencing of the TCRβ chain repertoire revealed that the DEJ CD8αα⁺ T cells are oligoclonal with diverse usage of TCR VB genes, which differ from those commonly described for MAIT and NKT cells. Dominant clonotypes overlapped among multiple recurrence episodes over a period of two and a half years. Episodes of rapid asymptomatic HSV-2 containment were also associated with a high CD8 effector-to-target ratio and focal enrichment of CD8αα⁺ T cells. These studies indicate DEJ CD8αα⁺ T cells are tissue resident cells that appear to play a fundamental role in immune surveillance and in initial containment of HSV-2 reactivation in human peripheral tissue. Elicitation of CD8αα⁺ T cells might be a critical component for developing effective vaccines against skin and mucosal infections.

The sphingosine-1-phosphate analogue FTY720 impairs mucosal immunity and clearance of the enteric pathogen Citrobacter rodentium

The sphingosine-1-phosphate (S1P) analogue FTY720 is therapeutically efficacious in multiple sclerosis and in the prevention of transplant rejection. It prevents the migration of lymphocytes to sites of pathology by trapping them within the peripheral lymph nodes, mesenteric lymph nodes (MLNs), and Peyer's patches. However, evidence suggests that its clinical use may increase the risk of mucosal infections. We investigated the impact of FTY720 treatment on susceptibility to gastrointestinal infection with the mouse enteric pathogen Citrobacter rodentium. This attaching and effacing bacterium induces a transient bacterial colitis in immunocompetent mice that resembles human infection with pathogenic Escherichia coli. FTY720 treatment induced peripheral blood lymphopenia, trapped lymphocytes in the MLNs, and prevented the clearance of bacteria when mice were infected with luciferase-tagged C. rodentium. FTY720-treated C. rodentium-infected mice had enhanced colonic inflammation, with significantly higher colon mass, colon histopathology, and neutrophil infiltration than vehicle-infected animals. In addition, FTY720-treated infected mice had significantly lower numbers of colonic dendritic cells, macrophages, and T cells. Gene expression analysis demonstrated that FTY720-treated infected mice had an impaired innate immune response and a blunted mucosal adaptive immune response, including Th1 cytokines. The data demonstrate that the S1P analogue FTY720 adversely affects the immune response to and clearance of C. rodentium.

Naive, effector and memory CD8 T-cell trafficking: parallels and distinctions

Trafficking of CD8 T cells, in both the steady-state and during episodes of infection or inflammation, is a highly dynamic process and involves a variety of receptor-ligand interactions. A thorough, mechanistic understanding of how this process is regulated could potentially lead to disease prevention strategies, through either enhancing (for infectious diseases or tumors) or limiting (for autoimmunity) recruitment of antigen-specific CD8 T cells to areas of tissue inflammation. As CD8 T cells transition from naive to effector to memory cells, changes in gene expression will ultimately dictate anatomical localization of these cells in vivo. In this article, we discuss recent advances in understanding how antigenic stimulation influences expression of various trafficking receptors and ligands, and how this determines the tissue localization of CD8 T cells.

Sphingosine kinase inhibition exerts both pro- and anti-atherogenic effects in low-density lipoprotein receptor-deficient (LDL-R(-/-)) mice

Sphingosine 1-phosphate (S1P), a lysosphingolipid associated with high-density lipoprotein (HDL), contributes to the anti-atherogenic potential attributed to this lipoprotein. This study examined whether a reduction of S1P plasma levels affects atherosclerosis in a murine model of disease. LDL-R(-/-)mice on Western diet were given ABC294640, an inhibitor of sphingosine kinase (SphK) for 16 weeks. ABC294640 decreased plasma S1P by approximately 30%. However, ABC294640 failed to affect atherosclerotic lesion formation. Plasma triglycerides were reduced whereas total and HDL-cholesterol remained unchanged in course of ABC294640 treatment. ABC294640 increased plasma interleukin (IL)-12p70 and RANTES concentration as well as IL-12p70, RANTES and interferon (IFN)-γ production by peritoneal cells and this was paralleled by enhanced activity of peritoneal and spleen dendritic cells as evidenced by up-regulation of CD86 and MHC-II on CD11c(+) cells. As a consequence, increased T-cell activation was noted in ABC294640-treated mice as indicated by enhanced CD4(+) splenocyte proliferation, IFN-γ and IL-2 production, and CD69 expression. Concomitantly, however, ABC294640 treatment redistributed CD4(+) and CD8(+) cells from blood to lymphatic organs and reduced T-cell number within atherosclerotic lesions. In addition, plasma sVCAM-1, sICAM-1, and MCP-1 levels as well as in vivo leukocyte adhesion and CCL19-induced T-cell penetration into peritoneum were lower in ABC294640-treated animals. In vitro experiments demonstrated reduced VCAM-1 and ICAM-1 expression and lymphocyte adhesion to endothelial cells exposed to ABC294640. In conclusion, treatment with SphK inhibitor leads to both pro- and anti-atherogenic effects in LDL-R(-/-) mice. As a consequence, SphK inhibition fails to affect atherosclerosis despite significant S1P reduction in plasma.

Effects of lysophospholipids on tumor microenvironment

The effects of lysophospholipids (LPLs) on cancer microenvironment is a vast and growing field. These lipids are secreted physiologically by various cell types. They play highly important roles in the development, activation and regulation of the immune system. They are also secreted by cancerous cells and there is a strong association between LPLs and cancer. It is clear that these lipids and in particular sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) play major roles in regulating the growth of tumor cells, and in manipulating the immune system. These activities can be divided into two parts; the first involves the ability of S1P and LPA to either directly or through some of the enzymes that generate them such as sphingosine kinases or phospholipases, induce the motility and invasiveness of tumor cells. The second mechanism involves the recently discovered effects of these lipids on the anti-tumor effector natural killer (NK) cells. Whereas S1P and LPA induce the recruitment of these effector cells, they also inhibit their cytolysis of tumor cells. This may support the environment of cancer and the ability of cancer cells to grow, spread and metastasize. Consequently, LPLs or their receptors may be attractive targets for developing drugs in the treatment of cancer where LPLs or their receptors are up-regulated.

HIF1alpha-dependent glycolytic pathway orchestrates a metabolic checkpoint for the differentiation of TH17 and Treg cells

HIF1α induction by mTOR represents a metabolic checkpoint for the differentiation of T_H17 and T_reg cells.

Upon antigen stimulation, the bioenergetic demands of T cells increase dramatically over the resting state. Although a role for the metabolic switch to glycolysis has been suggested to support increased anabolic activities and facilitate T cell growth and proliferation, whether cellular metabolism controls T cell lineage choices remains poorly understood. We report that the glycolytic pathway is actively regulated during the differentiation of inflammatory T_H17 and Foxp3-expressing regulatory T cells (T_reg cells) and controls cell fate determination. T_H17 but not T_reg cell–inducing conditions resulted in strong up-regulation of the glycolytic activity and induction of glycolytic enzymes. Blocking glycolysis inhibited T_H17 development while promoting T_reg cell generation. Moreover, the transcription factor hypoxia-inducible factor 1α (HIF1α) was selectively expressed in T_H17 cells and its induction required signaling through mTOR, a central regulator of cellular metabolism. HIF1α–dependent transcriptional program was important for mediating glycolytic activity, thereby contributing to the lineage choices between T_H17 and T_reg cells. Lack of HIF1α resulted in diminished T_H17 development but enhanced T_reg cell differentiation and protected mice from autoimmune neuroinflammation. Our studies demonstrate that HIF1α–dependent glycolytic pathway orchestrates a metabolic checkpoint for the differentiation of T_H17 and T_reg cells.

CpG array analysis of histone H3 lysine 4 trimethylation in peripheral blood mononuclear cells of uremia patients

Studies of the epigenome have attracted little interest in nephrology, especially in uremia. Several lines of evidence have suggested that there are links between genomic DNA hypomethylation and cardiovascular complications in uremia patients. However, to date, our knowledge about the alterations in histone methylation in uremia is unknown. H3K4me3 variations were analyzed in peripheral blood mononuclear cells from 20 uremia patients and 20 healthy subjects, using chromatin immunoprecipitation microarray (ChIP-chip) approach. ChIP-real-time polymerase chain reaction (PCR) was used to validate the microarray results. mRNA expression and DNA methylation status can be further analyzed by quantitative (q) reverse transcription (RT)-PCR and methyl-DNA immunoprecipitation (MeDIP)-qPCR, respectively. Seven hundred twenty-six increased and 218 decreased H3K4me3 genes displaying significant H3K4me3 differences were found in uremia patients compared with healthy subjects. The results of ChIP-real-time PCR coincided well with microarray results. Expression analysis by qRT-PCR revealed positive correlations between mRNA and H3K4me3 levels. Aberrant DNA methylation can also be found on selected positive genes (CNOT1 PLTP EDG1 TCF3 KIR3DL2). In addition, we even found that there is an inverse relationship between H3K4me3 and promoter DNA methylation in uremia patients. Our studies indicate that there are significant alterations of H3K4me3 in uremia patients; these significant H3K4me3 candidates may help to explain the immunological disturbance and high cardiovascular complications in uremia patients. Such novel findings show the significance of H3K4me3 as a potential biomarker or promising target for epigenetic-based uremia therapies.

Dissecting the role of the S1P/S1PR axis in health and disease

Sphingosine-1-phosphate (S1P) is a pleiotropic sphingophospholipid generated from the phosphorylation of sphingosine by sphingosine kinases (SPHKs). S1P has been experimentally demonstrated to modulate an array of cellular processes such as cell proliferation, cell survival, cell invasion, vascular maturation, and angiogenesis by binding with any of the five known G-protein-coupled sphingosine 1 phosphate receptors (S1P1-5) on the cell surface in an autocrine as well as a paracrine manner. Recent studies have shown that the S1P receptors (S1PRs) and SPHKs are the key targets for modulating the pathophysiological consequences of various debilitating diseases, such as cancer, sepsis, rheumatoid arthritis, ulcerative colitis, and other related illnesses. In this article, we recapitulate these novel discoveries relative to the S1P/S1PR axis, necessary for the proper maintenance of health, as well as the induction of tumorigenic, angiogenic, and inflammatory stimuli that are vital for the development of various diseases, and the novel therapeutic tools to modulate these responses in oral biology and medicine.

ECM1 controls T(H)2 cell egress from lymph nodes through re-expression of S1P(1)

Type 2 helper T cells (T(H)2) are critically involved in allergies and asthma. Here we demonstrate that extracellular matrix protein-1 (ECM1) is highly and selectively expressed in T(H)2 cells. ECM1 deficiency caused impaired T(H)2 responses and reduced allergic airway inflammation in vivo. Functional analysis demonstrated that although the T(H)2 polarization of ECM1-deficient cells was unimpaired, these cells had a defect in migration and were retained in peripheral lymphoid organs. This was associated with reduced expression of KLF2 and S1P(1). We also found that ECM1 could directly bind the interleukin-2 (IL-2) receptor to inhibit IL-2 signaling and activate S1P(1) expression. Our data identify a previously unknown function of ECM1 in regulating T(H)2 cell migration through control of KLF2 and S1P(1) expression.

Sphingosine-1-phosphate and immune regulation: trafficking and beyond

Sphingosine-1-phosphate (S1P) is a bioactive lipid with important functions in the immune system. S1P levels are regulated by the balance between its synthesis through sphingosine kinases and its degradation by S1P lyase. S1P signals through plasma membrane G-protein-coupled receptors (S1PR1-S1PR5) or acts directly on intracellular targets. Although it has long been known that the S1P-S1PR1 axis mediates T cell egress from lymphoid organs, recent studies have revealed intrinsic functions of S1P and its receptors in both innate and adaptive immune systems that are independent of immune cell trafficking. Here I summarize recent advances in understanding of the roles of S1P and S1P receptors in inflammatory and allergic responses and lymphocyte differentiation, which directly contribute to the regulation of inflammatory and autoimmune diseases. I also describe strategies to target S1P and S1P receptors for immune-mediated diseases, particularly the immunosuppressant FTY720 (fingolimod), which has recently become the first oral therapy for relapsing multiple sclerosis.

Inhibition of sphingosine 1-phosphate lyase for the treatment of rheumatoid arthritis: discovery of (E)-1-(4-((1R,2S,3R)-1,2,3,4-tetrahydroxybutyl)-1H-imidazol-2-yl)ethanone oxime (LX2931) and (1R,2S,3R)-1-(2-(isoxazol-3-yl)-1H-imidazol-4-yl)butane-1,2,3,4-tetraol (LX2932)

Sphingosine 1-phosphate lyase (S1PL) has been characterized as a novel target for the treatment of autoimmune disorders using genetic and pharmacological methods. Medicinal chemistry efforts targeting S1PL by direct in vivo evaluation of synthetic analogues of 2-acetyl-4(5)-(1(R),2(S),3(R),4-tetrahydroxybutyl)-imidazole (THI, 1) led to the discovery of 2 (LX2931) and 4 (LX2932). The immunological phenotypes observed in S1PL deficient mice were recapitulated by oral administration of 2 or 4. Oral dosing of 2 or 4 yielded a dose-dependent decrease in circulating lymphocyte numbers in multiple species and showed a therapeutic effect in rodent models of rheumatoid arthritis (RA). Phase I clinical trials indicated that 2, the first clinically studied inhibitor of S1PL, produced a dose-dependent and reversible reduction of circulating lymphocytes and was well tolerated at dose levels of up to 180 mg daily. Phase II evaluation of 2 in patients with active rheumatoid arthritis is currently underway.

The S1P(1)-mTOR axis directs the reciprocal differentiation of T(H)1 and T(reg) cells

Naïve CD4⁺ T cells differentiate into diverse effector and regulatory lineages to orchestrate immunity and tolerance. The differentiation of pro-inflammatory T_H1 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 T_H1 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 T_H1 and Treg cells. Our studies establish an S1P₁-mTOR axis that controls T cell lineage specification.

Inhibition of sphingosine-1-phosphate lyase for the treatment of autoimmune disorders

During nearly a decade of research dedicated to the study of sphingosine signaling pathways, we identified sphingosine-1-phosphate lyase (S1PL) as a drug target for the treatment of autoimmune disorders. S1PL catalyzes the irreversible decomposition of sphingosine-1-phosphate (S1P) by a retro-aldol fragmentation that yields hexadecanaldehyde and phosphoethanolamine. Genetic models demonstrated that mice expressing reduced S1PL activity had decreased numbers of circulating lymphocytes due to altered lymphocyte trafficking, which prevented disease development in multiple models of autoimmune disease. Mechanistic studies of lymphoid tissue following oral administration of 2-acetyl-4(5)-(1(R),2(S),3(R),4-tetrahydroxybutyl)-imidazole (THI) 3 showed a clear relationship between reduced lyase activity, elevated S1P levels, and lower levels of circulating lymphocytes. Our internal medicinal chemistry efforts discovered potent analogues of 3 bearing heterocycles as chemical equivalents of the pendant carbonyl present in the parent structure. Reduction of S1PL activity by oral administration of these analogues recapitulated the phenotype of mice with genetically reduced S1PL expression.

The receptor S1P1 overrides regulatory T cell-mediated immune suppression through Akt-mTOR

Regulatory T cells (T_reg) 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 T_reg cells. Combining loss- and gain-of-function genetic approaches, we found that S1P₁ blocked the differentiation of thymic T_reg precursors and function of mature Treg cells, and affected T_reg-mediated immune tolerance. S1P₁ induced the selective activation of the Akt-mTOR pathway to impede T_reg development and function. Dynamic regulation of S1P₁ contributed to lymphocyte priming and immune homeostasis. Thus, by antagonizing T_reg-mediated immune suppression, the lipid-activated S1P₁-Akt-mTOR pathway orchestrates adaptive immune responses.

Lysophospholipid receptors in vertebrate development, physiology, and pathology

Lysophospholipid (LP) research has experienced a period of renaissance with the discovery of the lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) receptors in the late 1990s. Vertebrate LP receptors regulate embryogenesis, vascular development, neurogenesis, uterine development, oocyte survival, immune cell trafficking and inflammatory reactions. LP signaling is important in cancer, autoimmunity and inflammatory diseases. Research on LP biology has contributed to the development of a first-generation S1P receptor modulator that has entered phase III clinical trials for the treatment of multiple sclerosis. Further basic research on LP signaling is anticipated to lead to novel therapeutic tools to combat various human diseases.

The vascular S1P gradient-cellular sources and biological significance

Sphingosine 1-phosphate (S1P), a product of sphingomyelin metabolism, is enriched in the circulatory system whereas it is estimated to be much lower in interstitial fluids of tissues. This concentration gradient, termed the vascular S1P gradient appears to form as a result of substrate availability and the action of metabolic enzymes. S1P levels in blood and lymph are estimated to be in the muM range. In the immune system, the S1P gradient is needed as a spatial cue for lymphocyte and hematopoietic cell trafficking. During inflammatory reactions in which enhanced vascular permeability occurs, a burst of S1P becomes available to its receptors in the extravascular compartment, which likely contributes to the tissue reactions. Thus, the presence of the vascular S1P gradient is thought to contribute to physiological and pathological conditions. From an evolutionary perspective, S1P receptors may have co-evolved with the advent of a closed vascular system and the trafficking paradigms for hematopoietic cells to navigate in and out of the vascular system.

p21 Ras/impedes mitogenic signal propagation regulates cytokine production and migration in CD4 T cells

The propensity of T cells to generate coordinated cytokine responses is critical for the host to develop resistance to pathogens while maintaining the state of immunotolerance to self-antigens. The exact mechanisms responsible for preventing the overproduction of proinflammatory cytokines including interferon (IFN)-gamma are not fully understood, however. In this study, we examined the role of a recently described Ras GTPase effector and repressor of the Raf/MEK/ERK cascade called impedes mitogenic signal propagation (Imp) in limiting the induction of T-cell cytokines. We found that stimulation of the T cell receptor complex leads to the rapid development of a physical association between Ras and Imp. Consistent with the hypothesis that Imp inhibits signal transduction, we also found that disengagement of this molecule by the Ras(V12G37) effector loop mutant or RNA interference markedly enhances the activation of the NFAT transcription factor and IFN-gamma secretion. A strong output of IFN-gamma is responsible for the distinct lymphocyte traffic pattern observed in vivo because the transgenic or retroviral expression of Ras(V12G37) caused T cells to accumulate preferentially in the lymph nodes and delayed their escape from the lymphoid tissue, respectively. Together, our results describe a hitherto unrecognized negative regulatory role for Imp in the production of IFN-gamma in T cells and point to Ras-Imp binding as an attractive target for therapeutic interventions in conditions involving the production of this inflammatory cytokine.

Finding a way out: lymphocyte egress from lymphoid organs

The egress of lymphocytes from the thymus and secondary lymphoid organs into circulatory fluids is essential for normal immune function. The discovery that a small-molecule inhibitor of lymphocyte exit, FTY720, is a ligand for sphingosine 1-phosphate (S1P) receptors led to studies demonstrating that S1P receptor type 1 (S1P1) is needed in T cells and B cells for their egress from lymphoid organs. S1P exists in higher concentrations in blood and lymph than in lymphoid organs, and this differential is also required for lymphocyte exit. Transcriptional and post-translational mechanisms regulate S1P1 and thus the egress of lymphocytes. In this review we discuss the body of evidence supporting a model in which lymphocyte egress is promoted by encounter with S1P at exit sites. We relate this model to work examining the effects of S1P receptor agonists on endothelium.

Silencing S1P1 receptors regulates collagen-V reactive lymphocyte-mediated immunobiology in the transplanted lung

Type V collagen (col[V])-reactive lymphocytes contribute to lung transplant rejection, but the mechanisms for emigration into the graft are unknown. Sphingosine-1-phosphate-1 receptors (S1P(1R)) are believed to be required for lymphocyte emigration in other studies, but their role in col(V)-reactive lymphocyte rejection responses is not known. Utilizing small interfering RNA (siRNA) to reduce S1P(1R) expression on col(V)-reactive lymphocytes, we examined the role of S1P(1R) in the rejection response. Quantitative polymerase chain reaction (PCR) revealed strong expression of S1P(1R) messenger RNA (mRNA)on col(V)-reactive lymphocytes isolated from immunized rats. S1P(1R)-specific siRNA (S1P(1R) siRNA) reduced expression of S1P(1R) mRNA and protein, whereas scramble siRNA (SC siRNA) had no effect. Adoptive transfer of lymphocytes treated with S1P(1R) siRNA to rat Wistar Kyoto (WKY) lung isograft recipients resulted in retention of cells within the liver with fewer cells in mediastinal lymph nodes when compared to cells exposed to SC siRNA. S1P(1R)-deficient cells proliferated in response to alloantigens, but not in response to col(V), and produced less interferon (IFN)-gamma in response to col(V) compared to controls. Downregulating S1P(1R) did not affect production of interleukin (IL)-10and tumor necrosis factor (TNF)-alpha, or expression of adhesion molecules critical for migration, but prevented rejection pathology and lowered local levels of IFN-gamma post adoptive transfer. These data demonstrate novel roles of S1P(1R,) which include regulating emigration and modulating lymphocyte activation.

Functions of sphingolipid metabolism in mammals--lessons from genetic defects

Much is known about the pathways that control the biosynthesis, transport and degradation of sphingolipids. During the last two decades, considerable progress has been made regarding the roles this complex group of lipids play in maintaining membrane integrity and modulating responses to numerous signals. Further novel insights have been provided by the analysis of newly discovered genetic diseases in humans as well as in animal models harboring mutations in the genes whose products control sphingolipid metabolism and action. Through the description of the phenotypic consequences of genetic defects resulting in the loss of activity of the many proteins that synthesize, transport, bind, or degrade sphingolipids, this review summarizes the (patho)physiological functions of these lipids.

Sphingosylphosphorylcholine activates dendritic cells, stimulating the production of interleukin-12

Compared with other lysophospholipid mediators such as sphingosine-1-phosphate and lysophosphatidic acid, little is known about the physiological significance of the related bioactive lysosphingolipid sphingosylphosphorylcholine (SPC), which is present in high-density lipoprotein particles. The present study was undertaken to evaluate the effect of SPC on human immature dendritic cells (DCs). Reverse transcription-polymerase chain reaction and flow cytometry assays revealed that DCs express two putative receptors for SPC, ovarian cancer G-protein-coupled receptor 1 and G-protein-coupled receptor 4. Exposure to SPC induced a rapid and transient increase in intracellular free calcium concentrations but did not stimulate endocytosis or chemotaxis of DCs. SPC increased the expression of HLA-DR, CD86 and CD83 and improved the T-cell priming ability of DCs, as well as the ability of DCs to stimulate the production of interferon-gamma by allogeneic peripheral blood mononuclear cells during the mixed lymphocyte reaction. Consistent with these results, we also observed that SPC stimulated the production of interleukin (IL)-12 and IL-18 by DCs. Taken together, our results support the notion that the accumulation of SPC in peripheral tissues during the course of inflammatory processes may favour the development of T helper type 1 immunity.

Sphingosine 1-phosphate receptors in health and disease: mechanistic insights from gene deletion studies and reverse pharmacology

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that is critically involved in the embryonic development of the cardiovascular and central nervous systems. In the adult, S1P can produce cytoskeletal re-arrangements in many cell types to regulate immune cell trafficking, vascular homeostasis and cell communication in the central nervous system. S1P is contained in body fluids and tissues at different concentrations, and excessive production of the pleiotropic mediator at inflammatory sites may participate in various pathological conditions. Gene deletion studies and reverse pharmacology (techniques aiming to identify both ligands and function of receptors) provided evidence that many effects of S1P are mediated via five G-protein-coupled S1P receptor subtypes, and novel therapeutic strategies based on interaction with these receptors are being initiated. The prototype S1P receptor modulator, FTY720 (fingolimod), targets four of the five S1P receptor subtypes and may act at several levels to modulate lymphocyte trafficking via lymphocytic and endothelial S1P1 and, perhaps, other inflammatory processes through additional S1P receptor subtypes. A recently completed Phase II clinical trial suggested that the drug may provide an effective treatment of relapsing-remitting multiple sclerosis. FTY720 is currently being evaluated in larger-scale, longer-term, Phase III studies. This review provides an overview on S1P activities and S1P receptor function in health and disease, and summarizes the clinical experience with FTY720 in transplantation and multiple sclerosis.

Migration of CD4 T cells and dendritic cells toward sphingosine 1-phosphate (S1P) is mediated by different receptor subtypes: S1P regulates the functions of murine mature dendritic cells via S1P receptor type 3

Dendritic cells (DCs) and lymphocytes are known to show a migratory response to the phospholipid mediator, sphingosine 1-phosphate (S1P). However, it is unclear whether the same S1P receptor subtype mediates the migration of lymphocytes and DCs toward S1P. In this study, we investigated the involvement of S1P receptor subtypes in S1P-induced migration of CD4 T cells and bone marrow-derived DCs in mice. A potent S1P receptor agonist, the (S)-enantiomer of FTY720-phosphate [(S)-FTY720-P], at 0.1 nM or higher and a selective S1P receptor type 1 (S1P(1)) agonist, SEW2871, at 0.1 muM or higher induced a dose-dependent down-regulation of S1P(1). The pretreatment with these compounds resulted in a significant inhibition of mouse CD4 T cell migration toward S1P. Thus, it is revealed that CD4 T cell migration toward S1P is highly dependent on S1P(1). Mature DCs, when compared with CD4 T cells or immature DCs, expressed a relatively higher level of S1P(3) mRNA. S1P at 10-1000 nM induced a marked migration and significantly enhanced the endocytosis of FITC-dextran in mature but not immature DCs. Pretreatment with (S)-FTY720-P at 0.1 microM or higher resulted in a significant inhibition of S1P-induced migration and endocytosis in mature DCs, whereas SEW2871 up to 100 microM did not show any clear effect. Moreover, we found that S1P-induced migration and endocytosis were at an extremely low level in mature DCs prepared from S1P(3)-knockout mice. These results indicate that S1P regulates migration and endocytosis of murine mature DCs via S1P(3) but not S1P(1).

Sphingosine-1-phosphate lyase in immunity and cancer: silencing the siren

Sphingosine-1-phosphate (S1P) is a bioactive lipid that promotes cell survival, proliferation and migration, platelet aggregation, mediates ischemic preconditioning, and is essential for angiogenesis and lymphocyte trafficking. Sphingosine-1-phosphate lyase (SPL) is the enzyme responsible for the irreversible degradation of S1P and is, thus, in a strategic position to regulate these same processes by removing available S1P signaling pools, that is, silencing the siren. In fact, recent studies have implicated SPL in the regulation of immunity, cancer surveillance and other physiological processes. Here, we summarize the current understanding of SPL function and regulation, and discuss how SPL might facilitate cancer chemoprevention and serve as a target for modulation of immune responses in transplantation settings and in the treatment of autoimmune disease.

FTY720, a Synthetic Sphingosine 1 Phosphate Analogue, Inhibits Development of Atherosclerosis in Low-Density Lipoprotein Receptor–Deficient Mice

BACKGROUND

Numerous in vitro studies suggest that sphingosine 1-phosphate (S1P), a bioactive lysosphingolipid associated with high-density lipoproteins, accounts at least partly for the potent antiinflammatory properties of high-density lipoprotein and, thereby, contributes to the antiatherogenic potential attributed to high-density lipoproteins. The present study was undertaken to investigate whether modulation of S1P signaling would affect atherosclerosis in a murine model of disease.

METHODS AND RESULTS

Low-density lipoprotein receptor-deficient mice on a cholesterol-rich diet were given FTY720, a synthetic S1P analogue, at low (0.04 mg/kg per day) or high (0.4 mg/kg per day) doses for 16 weeks. FTY720 dose-dependently reduced atherosclerotic lesion formation, both in the aortic root and brachiocephalic artery, and almost completely blunted necrotic core formation. Plasma lipids remained unchanged during the course of FTY720 treatment. However, FTY720 lowered blood lymphocyte count (at a high dose) and significantly interfered with lymphocyte function, as evidenced by reduced splenocyte proliferation and interferon-gamma levels in plasma. Plasma concentrations of proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-6, IL-12, and regulated on activation normal T cell expressed and secreted were reduced by FTY720 administration. Moreover, lipopolysaccharide-elicited generation of nitrite/nitrate and IL-6--two markers of classical (M1) macrophage activation--was inhibited, whereas IL-4-induced production of IL-1-receptor antagonist, a marker of alternative (M2) macrophage activation, was augmented in peritoneal macrophages from FTY720-treated low-density lipoprotein receptor-deficient mice.

CONCLUSIONS

The present results demonstrate that an S1P analogue inhibits atherosclerosis by modulating lymphocyte and macrophage function, and these results are consistent with the notion that S1P contributes to the antiatherogenic potential of high-density lipoprotein.

Memory T cells in allograft rejection

T cell repertoire of many humans contains high frequencies of memory T cells specific for alloantigens. The increasing evidence implicates these cells as a barrier to allograft survival and to the induction of transplantation tolerance. This review discusses several aspects of memory T cell immunobiology pertinent to their role in transplantation.

Sphingosine-1 phosphate prevents monocyte/endothelial interactions in type 1 diabetic NOD mice through activation of the S1P1 receptor

Monocyte recruitment and adhesion to vascular endothelium are key early events in atherosclerosis. We examined the role of sphingosine-1-phosphate (S1P) on modulating monocyte/endothelial interactions in the NOD/LtJ (NOD) mouse model of type 1 diabetes. Aortas from nondiabetic and diabetic NOD mice were incubated in the absence or presence of 100 nmol/L S1P. Fluorescently labeled monocytes were incubated with the aortas. Aortas from NOD diabetic mice bound 7-fold more monocytes than nondiabetic littermates (10+/-1 monocytes bound/field for nondiabetic mice vs 74+/-12 monocytes bound/field for diabetic mice, P<0.0001). Incubation of diabetic aortas with 100 nmol/L S1P reduced monocyte adhesion to endothelium by 90%. We found expression of S1P1, S1P2, and S1P3 receptors on NOD aortic endothelial cells. The S1P1 receptor-specific agonist SEW2871 inhibited monocyte adhesion to diabetic aortas. Studies in diabetic S1P3-deficient mice revealed that the S1P3 receptor did not play a pivotal role in this process. S1P reduced endothelial VCAM-1 induction in type 1 diabetic NOD mice, most likely through inhibition of nuclear factor kappaB translocation to the nucleus. Thus, S1P activation of the S1P1 receptor functions in an antiinflammatory manner in type 1 diabetic vascular endothelium to prevent monocyte/endothelial interactions. S1P may play an important role in the prevention of vascular complications of type 1 diabetes.

T lymphocytes on the move: chemokines, PI 3-kinase and beyond

The ordered, directional migration of T lymphocytes is a key process in development, immune surveillance and the immune response. Chemokines have an important role in the guidance of T lymphocytes and activate several members of the phosphoinositide 3-kinase (PI 3-kinase) family, which contribute to various aspects of the migratory machinery in many cell systems. However, the role of PI 3-kinase in T-cell movement is unclear, and its importance has been largely dismissed. Over the past two years, there has been exciting progress in our appreciation not only of the finer details of PI 3-kinase involvement in T-cell migration, but also of other signalling events that probably influence T-cell migration in response to recognized chemoattractants. These aspects of T-cell migration are the subject of this review.

CD69 down-modulation and inhibition of thymic egress by short- and long-term selective chemical agonism of sphingosine 1-phosphate receptors

Thymic development requires proliferation, selection, maturation and release of mature single-positive CD4 and CD8 T cells into the periphery. In mice, non-selective sphingosine-1 phosphate (S1P) receptor agonists, active on four of the five known S1P receptors, alter thymocyte phenotype and egress. Here, we show that down-modulation of CD69 occurs acutely and transiently at a discrete and late stage of medullary development after a single-dose administration of S1P(1) receptor-selective agonist, which induces long-term tonic receptor activation in the absence of receptor degradation. In addition, agonist acutely inhibited egress of mature thymocytes into peripheral lymphoid organs, suggesting that both the phenotype and migration of medullary thymocytes are regulated simultaneously and coordinately by agonism of S1P(1) alone. Long-term dosing shifted the early/late medullary thymocyte ratio with an expansion of the late medullary compartment, as mature CD69(-) thymocytes were retained within the thymus. Therefore, chemical agonism of S1P(1) accelerates medullary phenotypic maturation and inhibits egress, leading to the expansion and accumulation of the recent thymocyte emigrant population in the medulla. However, chemical agonism fails to replicate the S1P(1)-null CD69(hi) late medullary phenotype, suggesting that agonism and gene deletion operate by distinct mechanisms, and that functional receptor antagonism may not be required for lymphocyte sequestration.

Sphingosine 1-phosphate and its receptors: an autocrine and paracrine network

Sphingosine 1-phosphate (S1P) is a biologically active lysophospholipid that transmits signals through a family of G-protein-coupled receptors to control cellular differentiation and survival, as well as the vital functions of several types of immune cell. In this Review article, we discuss recent results that indicate that S1P and its receptors are required for the emigration of thymocytes from the thymus, the trafficking of lymphocytes in secondary lymphoid organs and the migration of B cells into splenic follicles. In an autocrine manner, through interactions with different G-protein-coupled receptors, S1P also enhances optimal mast-cell migration and release of pro-inflammatory mediators in allergic reactions. S1P-S1P-receptor regulatory systems might therefore be novel targets for the therapy of diverse immunological diseases.