Dysfunctionally phosphorylated type 1 insulin receptor substrate in neural-derived blood exosomes of preclinical Alzheimer's disease

Insulin resistance causes diminished glucose uptake in similar regions of the brain in Alzheimer's disease (AD) and type 2 diabetes mellitus (DM2). Brain tissue studies suggested that insulin resistance is caused by low insulin receptor signaling attributable to its abnormal association with more phospho (P)-serine-type 1 insulin receptor substrate (IRS-1) and less P-tyrosine-IRS-1. Plasma exosomes enriched for neural sources by immunoabsorption were obtained once from 26 patients with AD, 20 patients with DM2, 16 patients with frontotemporal dementia (FTD), and matched case control subjects. At 2 time points, they were obtained from 22 others when cognitively normal and 1 to 10 yr later when diagnosed with AD. Mean exosomal levels of extracted P-serine 312-IRS-1 and P-pan-tyrosine-IRS-1 by ELISA and the ratio of P-serine 312-IRS-1 to P-pan-tyrosine-IRS-1 (insulin resistance factor, R) for AD and DM2 and P-serine 312-IRS-1 and R for FTD were significantly different from those for case control subjects. The levels of R for AD were significantly higher than those for DM2 or FTD. Stepwise discriminant modeling showed correct classification of 100% of patients with AD, 97.5% of patients with DM2, and 84% of patients with FTD. In longitudinal studies of 22 patients with AD, exosomal levels of P-serine 312-IRS-1, P-pan-tyrosine-IRS-1, and R were significantly different 1 to 10 yr before and at the time of diagnosis compared with control subjects. Insulin resistance reflected in R values from this blood test is higher for patients with AD, DM2, and FTD than case control subjects; higher for patients with AD than patients with DM2 or FTD; and accurately predicts development of AD up to 10 yr prior to clinical onset.

Identification of preclinical Alzheimer's disease by a profile of pathogenic proteins in neurally derived blood exosomes: A case-control study

BACKGROUND

Proteins pathogenic in Alzheimer's disease (AD) were extracted from neurally derived blood exosomes and quantified to develop biomarkers for the staging of sporadic AD.

METHODS

Blood exosomes obtained at one time-point from patients with AD (n = 57) or frontotemporal dementia (FTD) (n = 16), and at two time-points from others (n = 24) when cognitively normal and 1 to 10 years later when diagnosed with AD were enriched for neural sources by immunoabsorption. AD-pathogenic exosomal proteins were extracted and quantified by enzyme-linked immunosorbent assays.

RESULTS

Mean exosomal levels of total tau, P-T181-tau, P-S396-tau, and amyloid β 1-42 (Aβ1-42) for AD and levels of P-T181-tau and Aβ1-42 for FTD were significantly higher than for case-controls. Step-wise discriminant modeling incorporated P-T181-tau, P-S396-tau, and Aβ1-42 in AD, but only P-T181-tau in FTD. Classification of 96.4% of AD patients and 87.5% of FTD patients was correct. In 24 AD patients, exosomal levels of P-S396-tau, P-T181-tau, and Aβ1-42 were significantly higher than for controls both 1 to 10 years before and when diagnosed with AD.

CONCLUSIONS

Levels of P-S396-tau, P-T181-tau, and Aβ1-42 in extracts of neurally derived blood exosomes predict the development of AD up to 10 years before clinical onset.

Aging enhances release of exosomal cytokine mRNAs by Aβ1-42-stimulated macrophages

Amyloid-β1-42 (Aβ) peptide effects on human models of central nervous system (CNS)-patrolling macrophages (Ms) and CD4 memory T-cells (CD4-Tms) were investigated to examine immune responses to Aβ in Alzheimer's disease. Aβ and lipopolysaccharide (LPS) elicited similar M cytokine and exosomal mRNA (ex-mRNA) responses. Aβ- and LPS-stimulated Ms from 20 ≥65-yr-old subjects generated significantly more IL-1, TNF-α, and IL-6, but not IL-8 or IL-12, and significantly more ex-mRNAs for IL-6, TNF-α, and IL-12, but not for IL-8 or IL-1, than Ms from 20 matched 21- to 45-yr-old subjects. CD4-Tm generation of IL-2, IL-4, and IFN-γ and, for young subjects, IL-10, but not IL-6, evoked by Aβ was significantly lower than with anti-T-cell antigen receptor antibodies (Abs). Abs significantly increased all CD4-Tm ex-mRNAs, but only IL-2 and IL-6 ex-mRNAs were increased by Aβ. There were no significant differences between cytokine and ex-mRNA responses of CD4-Tms from the old compared to the young subjects. M-derived serum exosomes from the old subjects had significantly higher IL-6 and IL-12 ex-mRNA levels than those from the young subjects, whereas there were no differences for CD4-Tm-derived serum exosomes. An Aβ level relevant to neurodegeneration elicited broad M cytokine and ex-mRNA responses that were significantly greater in the old subjects, but only narrow and age-independent CD4-Tm responses.

Distinct energy requirements for human memory CD4 T-cell homeostatic functions

Differentiation and activation of CD4 memory T cells (T(mem) cells) require energy from different sources, but little is known about energy sources for maintenance and surveillance activities of unactivated T(mem) cells. Mitochondrial fatty acid oxidation (FAO) in human unactivated CD4 T(mem) cells was significantly enhanced by inhibition of glycolysis, with respective means of 1.7- and 4.5-fold for subjects <45 yr and >65 yr, and by stimulation of AMP-activated protein kinase, with respective means of 1.3- and 5.2-fold. However, CCL19 and sphingosine 1-phosphate (S1P), which control homeostatic lymphoid trafficking of unactivated T(mem) cells, altered FAO and glycolysis only minimally or not at all. Inhibition of CD4 T(mem)-cell basal FAO, but not basal glycolysis, significantly suppressed CCL19- and S1P-mediated adherence to collagen by >50 and 20%, respectively, and chemotaxis by >20 and 50%. Apoptosis of unactivated T(mem) cells induced by IL-2 deprivation or CCL19 was increased significantly by >150 and 70%, respectively, with inhibition of FAO and by >110 and 30% with inhibition of glycolysis. Anti-TCR antibody activation of T(mem) cells increased their chemotaxis to CCL5, which was dependent predominantly on glycolysis rather than FAO. The sources supplying energy for diverse functions of unactivated T(mem) cells differ from that required for function after immune activation.

Lenalidomide enhancement of human T cell functions in human immunodeficiency virus (HIV)-infected and HIV-negative CD4 T lymphocytopenic patients

Suppressed T cell functions in human immunodeficiency virus (HIV) infection were identified and corrected by lenalidomide in middle-aged HIV-infected patients. Chemotaxis of T cells from HIV-infected men (n = 6, mean 43 years) to sphingosine 1-phosphate (S1P) and CCL21 was significantly lower than that of HIV-negative men (n = 6, mean 41 years), and was enhanced significantly up to control levels by 100 and 1000 nM lenalidomide. Generation of interleukin (IL)-2, but not interferon (IFN)-γ, by T cells of middle-aged HIV-infected men was significantly lower than that for controls and was increased significantly by 10-1000 nM lenalidomide up to a maximum of more than 300%. CD4 and CD8 T cells isolated from healthy middle-aged men and reconstituted in vitro at a low CD4 : CD8 ratio typical of HIV infection had depressed chemotaxis to S1P, but not CCL21, and generation of IL-2, but not IFN-γ. Significant enhancement of chemotaxis to S1P and CCL21 was induced by 100-1000 nM lenalidomide only for normal T cells at a low CD4 : CD8 ratio. T cells from HIV-negative middle-aged CD4 T lymphocytopenic patients (n = 3), with a CD4 : CD8 ratio as low as that of HIV-infected patients, had similarly diminished chemotaxis to S1P and CCL21, and depressed generation of IL-2, but not IFN-γ. Lenalidomide at 30-1000 nM significantly enhanced chemotaxis to S1P and IL-2 generation for T cells from HIV-negative CD4 T lymphocytopenic patients as from HIV-infected patients, with less effect on CCL21-elicited chemotaxis and none for IFN-γ generation. Defects in functions of T cells from middle-aged HIV-infected men are partially attributable to CD4 T lymphocytopenia and are corrected by lenalidomide.

Distinctive immunoregulatory effects of adenosine on T cells of older humans

A role for adenosine in immunosenescence was investigated in T cells from older (≥65 yr) and younger (24-45 yr) healthy humans. Adenosine concentrations in cultures of activated T cells were significantly higher (P<0.0001) for older (145±47 nM, mean±sd) than younger (58±5.5 nM) subjects. Expression of the activation coreceptor CD28 was suppressed significantly by 0.1 to 1 μM exogenous adenosine, with greater effects of 1 μM (P<0.01) on T cells of younger (mean suppression of 67 and 65% for CD4 and CD8 T cells, respectively) than older (means of 42 and 46%) subjects. T-cell chemotaxis to CCL21 was suppressed significantly by 0.3 and 1 μM exogenous adenosine, with mean maximum decreases of 39 and 49%, respectively, for younger subjects and 28 and 31% for older subjects. Generation of IL-2 and IFN-γ by T cells of younger and older subjects was suppressed substantially only at adenosine levels of 3 μM or higher. Lower baseline expression of CD28 and chemotaxis to CCL21 and S1P for T cells from older subjects attributable to endogenous adenosine were reversed completely by two different A(2A) adenosine receptor antagonists without affecting T cells of younger subjects. Adenosine is an endogenous T-cell immunosuppressor in older humans, and A(2A) antagonists reverse adenosine-induced T-cell deficiencies of aging.

Defective T cell chemotaxis to sphingosine 1-phosphate and chemokine CCL21 in idiopathic T lymphocytopenia

T cell chemotaxis to sphingosine 1-phosphate (S1P) and the chemokines CCL21 and CCL5 was studied in ten adults with T lymphocytopenia, other immunological abnormalities (nine of ten), and frequent bacterial infections (seven of ten). Mean chemotactic responses to S1P of CD4 T cells from CD4 T lymphocytopenic patients and of CD8 T cells from CD8 T lymphocytopenic patients were significantly lower than those of healthy matched controls. Chemotaxis to CCL21 was lower than that of controls for CD4 T cells of three CD4 T lymphocytopenic patients and for CD8 T cells of three CD8 T lymphocytopenic patients, but none of the T cells of patients had diminished chemotaxis to CCL5. Defective T cell chemotactic responses to S1P and some chemokines may lead to subset-selective abnormal T cell trafficking and chronic T cell lymphocytopenia.

VPAC1 (vasoactive intestinal peptide (VIP) receptor type 1) G protein-coupled receptor mediation of VIP enhancement of murine experimental colitis

Distinct roles of the two T cell G protein-coupled receptors for vasoactive intestinal peptide (VIP), termed VPAC1 and VPAC2, in VIP regulation of autoimmune diseases were investigated in the dextran sodium sulfate (DSS)-induced murine acute colitis model for human inflammatory bowel diseases. In mice lacking VPAC2 (VPAC2-KO), DSS-induced colitis appeared more rapidly with greater weight loss and severe histopathology than in wild-type mice. In contrast, DSS-induced colitis in VPAC1-KO mice was milder than in wild-type mice and VPAC2-KO mice. Tissues affected by colitis showed significantly higher levels of myeloperoxidase, IL-6, IL-1β and MMP-9 in VPAC2-KO mice than wild-type mice, but there were no differences for IL-17, IFN-γ, IL-4, or CCR6. Suppression of VPAC1 signals in VPAC2-KO mice by PKA inhibitors reduced the clinical and histological severity of DSS-induced colitis, as well as tissue levels of IL-6, IL-1β and MMP-9. Thus VIP enhancement of the severity of DSS-induced colitis is mediated solely by VPAC1 receptors.

Preferential enhancement of older human T cell cytokine generation, chemotaxis, proliferation and survival by lenalidomide

Lenalidomide, an analog of thalidomide, modified responses of stimulated T cells from healthy young (ages 21-40 years) and old (≥ age 65 years) subjects. At 0.03 μM to 1 μM, lenalidomide enhanced generation of IL-2 and IFN-γ by T cell receptor-stimulated T cells of young subjects up to respective maximum increases of 17-fold and three-fold, but at 0.3 μM and 1 μM suppressed IL-17 generation. The same concentrations of lenalidomide enhanced IL-2 and IFN-γ generation by stimulated T cells of old subjects more, with greater respective maximal increases of up to 120-fold and six-fold, without suppressing IL-17 generation. Lenalidomide enhanced proliferation and suppressed apoptosis of stimulated T cells from old subjects, by IL-2-dependent mechanisms, and restored diminished T cell chemotactic responses to CCL21 and sphingosine 1-phosphate. The reversal of T cell abnormalities of immunosenescence by low concentrations of lenalidomide suggest a potential for improvement of immunity in the elderly.

Gender specificity of altered human immune cytokine profiles in aging

Cytokine generation by T cells and monocytes was determined for 50 subjects aged 65 yr or older and concurrently studied young subjects individually matched to each old subject for sex, race, and national origin. Highly significant differences between cytokine levels of old and young subjects all were gender specific. For T cells stimulated with anti-CD3 plus anti-CD28 antibodies, mean ratios of IFN-gamma generation for healthy old to young subjects were 0.22 for men (P<0.001; n=15) and 3.35 for women (P<0.001; n=13), and those of IL-17 were 0.30 for men (P<0.001) and no difference for women. CD8 T cells were the source of high IFN-gamma in healthy old women. For old men with an inflammatory or immune disease (n=10), mean old to young ratios of T-cell-generated IFN-gamma and IL-17 increased with disease severity up to 5.78 and 2.97 (both P<0.01), respectively, without changes for old women with similar diseases (n=12). For differentiated LPS-stimulated monocytes, old to young ratios of TNF-alpha and IL-6 generation were high only in women with immune or inflammatory disease (2.38, P<0.05 and 1.62, P<0.01, respectively), whereas ratios of IFN-gamma-evoked IP-10 chemokine were low in all groups. Alterations in immune cytokine profiles with aging show significant gender specificity.

Human CD4- 8- T cells are a distinctive immunoregulatory subset

Human CD4(-)8(-) T cells are a minor subset quantitatively but potentially important in immunity because they are predominantly distributed at body surfaces, and their number and activities increase in autoimmune diseases and decrease with aging. Distinguishing characteristics of CD4(-)8(-) T cells are found to include a unique profile of cytokines, including Serpin E1, which is not generated by other T cells, MIF, and TGF-beta. At 2-5% of the total in mixtures with CD4 + CD8 T cells, CD4(-)8(-) T cells enhance the generation of IFN-gamma and IL-17 by up to 12- and 5-fold, respectively, without contributing either cytokine or affecting cytokine production by NK/NKT cells. CD4(-)8(-) T cell-derived MIF is their major enhancer and TGFbeta their principal inhibitor of CD4 and CD8 T cell cytokine production. Decreases in CD4(-)8(-) T cell effects may diminish protective immunity in aging, whereas increases may augment the severity of autoimmune diseases.

Increased susceptibility to colitis in the Vasoactive Intestinal Peptide receptor type 2 (VPAC2) mouse : A negative role for VPAC1 receptor in the induction of intestinal inflammation (50.44)

Vasoactive intestinal peptide (VIP) is a prominent neuropeptide with effects on many immune functions which are transduced by VIP G-protein-coupled receptors type 1 (VPAC1) and type 2 (VPAC2) on immune cells. Previous studies have shown that VIP reduces clinical symptoms and inflammation in mouse models of human immune-based diseases such as rheumatoid arthritis, Crohn's Disease, septic shock and multiple sclerosis. We recently demonstrated that VPAC2 knockout (KO) CD4 T cells in the presence of VIP and TGF-b develop into Th17 cells in a cAMP-Protein Kinase A dependent manner. Here we show that increased IL-17 induction in VPAC2-KO CD4 cells is accompanied by a reduced conversion of CD4 T cells into FoxP3+ regulatory T cells. To determine if VPACs play a role in the inflammatory bowel disease (IBD), VPAC2-KO mice were subjected to dextran sulfate sodium (DSS) in drinking water. Compared to wild type (WT), VPAC2-KO mice exhibited rapid and more severe clinical symptoms of colitis and had significantly higher colonic inflammation and increased inflammatory cytokines in colon. Severe colitis in VPAC2-KO mice was ameliorated in the presence of PKA inhibitors. Moreover, VPAC1-KO mice were resistant to the development of DSS-induced colitis. The results demonstrate a new role for VPAC1 which is responsible for increased inflammation in IBD and may provide a new therapeutic target.

Sphingolipid signaling and treatment during remodeling of the uninfarcted ventricular wall after myocardial infarction

The sphingosine kinase (SphK)/sphingosine 1-phosphate (S1P) pathway, known to determine the fate and growth of various cell types, can enhance cardiac myocyte survival in vitro and provide cardioprotection in acute ex vivo heart preparations. However, the relevance of these findings to chronic cardiac pathology has never been demonstrated. We hypothesized that S1P signaling is impaired during chronic remodeling of the uninfarcted ventricle during the evolution of post-myocardial infarction (MI) cardiomyopathy and that a therapeutic enhancement of S1P signaling would ameliorate ventricular dysfunction. SphK expression and activity were measured in the remote, uninfarcted myocardium (RM) of C57Bl/6 mice subjected to coronary artery ligation. The mRNA expression of S1P receptor isoforms was also measured, as was the activation of the downstream S1P receptor mediators. A cardioprotective role for S1P(1) receptor agonism was tested via the administration of the S1P(1)-selective agonist SEW2871 during and after MI. As a result, the expression data suggested that a dramatic reduction in SphK activity in the RM early after MI may reflect a combination of posttranscriptional and posttranslational modulation. SphK activity continued to decline gradually during chronic post-MI remodeling, when S1P(1) receptor mRNA also fell below baseline. The S1P(1)-specific agonism with oral SEW2871 during the first 2-wk after MI reduced apoptosis in the RM and resulted in improved myocardial function, as reflected in the echocardiographic measurement of fractional shortening. In conclusion, these results provide the first documentation of alterations in S1P-mediated signaling during the in situ development of cardiomyopathy and suggest a possible therapeutic role for the pharmacological S1P receptor agonism in the post-MI heart.

Vasoactive intestinal peptide-mediated Th17 differentiation: an expanding spectrum of vasoactive intestinal peptide effects in immunity and autoimmunity

Interactions between neural and immune effector pathways serve a vital role in mammalian defenses against foreign pathogens and toxins. The immune system initiates processes leading to the release of diverse mediators and cytokines that recruit neural and endocrine involvement in immunity. Inversely, transmitters released from nerves innervating immune organs regulate the development and functions of the immune cells. Vasoactive intestinal peptide (VIP) is the quantitatively and functionally most prominent immunoregulatory neuropeptide that participates in local tissue immune responses by potently affecting T cell and macrophage migration, proliferation, and cytokine production. T cells, macrophages, and mast cells express the VIP G protein-coupled receptors (GPCR) VPAC(1) and VPAC(2) that transduce the effects of VIP on immunity. The VIP-VPAC axes also are coupled to abnormal T cell functions in different autoimmune conditions. Recently, it has been shown that VIP also enhances the differentiation of distinctive type of proinflammatory Th17 cells by a VPAC(1)-dependent mechanism. This unique VIP-VPAC(1) signaling in Th17 cell differentiation expands our understanding of VIP immune functions, provides new insights into the immune roles of individual VPAC receptors, and offers meaningful possibilities for improving therapeutic potential of VIP in immune disorders.

Immunosuppressive human anti-lymphocyte autoantibodies specific for the type 1 sphingosine 1-phosphate receptor

Anti-lymphocyte antibodies (Abs) that suppress T-cell chemotactic and other responses to sphingosine 1-phosphate (S1P), but not to chemokines, were found in a lymphopenic patient with recurrent infections. Lymphocyte type 1 S1P receptor (S1P(1)) that transduces S1P chemotactic stimulation was recognized by patient Abs in Western blots of T cells, S1P(1) transfectants, and S1P(1)-hemagglutinin purified by monoclonal anti-hemagglutinin Ab absorption. The amino terminus of S1P(1), but not any extracellular loop, prevented anti-S1P(1) Ab suppression of S1P(1) signaling and T-cell chemotaxis to S1P. Human purified anti-S1P(1) Abs decreased mouse blood lymphocyte levels by a mean of 72%, suppressed mouse T-cell chemotaxis to S1P in vivo, and significantly reduced the severity of dextran sodium sulfate-induced colitis in mice. Human Abs to the amino terminus of S1P(1) suppress T-cell trafficking sufficiently to impair host defense and provide therapeutic immunosuppression.

Cutting edge: vasoactive intestinal peptide (VIP) induces differentiation of Th17 cells with a distinctive cytokine profile

Immune cellular effects of vasoactive intestinal peptide (VIP) are transduced by VIP G protein-coupled receptors type 1 (VPAC1) and type 2 (VPAC2). We now show that VIP with TGFbeta stimulates the transformation of CD4 T cells to a distinctive type of Th17 cell that generates IL-17 but not IL-6 or IL-21. VIP induction of Th17 cells was higher in VPAC2 knockout mice than wild-type mice, suggesting that VPAC1 is the principal transducer. Compared with Th17 cells elicited by IL-6, those evoked by VIP were similar in the secretion of IL-17 and IL-22, but lacked IL-21 secretion. Suppression of VIP induction of Th17 cells by protein kinase A inhibitors and enhancement by pharmacologically increased cAMP supports a role for this signal. The ability of VIP-VPAC1 axis signals to evoke development of a novel type of Th17 cells demonstrates the unique specificity of neuroregulatory mechanisms in the immunological environment.

Changing paradigms in the immunological science of allergy: 2008

Our evolving knowledge of the universe of immune cytokines has permitted more precise definition of the extensive involvement of many cell-derived protein factors in the mediation of allergic diseases and asthma. Several newly recognized cytokines, which are derived from epithelial cells of the respiratory system, skin, and gastrointestinal tract or intraepithelial T cells in the context of interactions with nonimmune parenchymal cells, have potent stimulatory or inhibitory effects on the differentiation and/or activities of T helper (Th) 2-type CD4 T cells. Their properties and effects are reviewed from the perspective of novel targets for antiallergic therapy.

Regulation of the roles of sphingosine 1-phosphate and its type 1 G protein-coupled receptor in T cell immunity and autoimmunity

The lipid mediator sphingosine 1-phosphate (S1P) and its type 1 G protein-coupled receptor (S1P1) affect mammalian immunity through alterations in thymocyte emigration, differentiation of T cell subsets, lymphocyte trafficking in lymphoid organs and other tissues, T cell-dendritic cell and T cell-B cell interactions, and cytokine generation. Recent attention to effects of the S1P-S1P1 axis on non-migration functions of lymphocytes includes delineation of a role in terminal differentiation and survival of Th17 effector cells and adaptive Treg cells of the CD4 T cell constellation, and a greater understanding of interactions of the S1P-S1P1 axis with immune cytokines in lymphocyte survival and activities. This breadth of involvement of the S1P-S1P1 axis in immune responses that often are altered in immunological diseases has provided many opportunities for novel therapeutic interventions. A spectrum of pharmacological and immunochemical agents is available that alter immunity by affecting either tissue and fluid concentrations of S1P or levels of expression and signaling activities of S1P1. Such agents have so far been beneficial in the settings of autoimmunity and rejection of transplanted organs, and are likely to become valuable constituents of combined drug programs.

Nuclear factor-kappaB-dependent reversal of aging-induced alterations in T cell cytokines

Immunosenescence is characterized by decreases in protective immune responses and increases in inflammation and autoimmunity. The T helper (Th)17 subset of cluster-of-differentiation (CD)4 T cells, which is identified by its generation of interleukin (IL) -17, is implicated in autoimmune pathogenesis. To elucidate immunosenescent changes in Th17 cell cytokines, splenic CD4 T cells from 22- to 24-month-old (old) mice and 6- to 10-wk-old (young) mice were incubated on anti-CD3 plus anti-CD28 (anti-T cell antigen receptor) antibodies. After 96 h, T cells of old C57BL/6 and CBA mice generated up to 20-fold more IL-17 and up to 3-fold more IL-6 than those of young mice; T cells of young mice generated up to 5-fold more IL-21 than those of old mice; and no difference was found for IFN-gamma. At 24 h, cytokine mRNA levels paralleled 96 h cytokine concentrations. Naive CD4 T cells from old mice incubated on anti-T cell antigen receptor antibodies with transforming growth factor-beta, IL-1, IL-6, and IL-23 to induce de novo differentiation of Th17 cells had more IL-17 mRNA and produced more IL-17 than those of young mice. BAY11-7082 and the phytochemicals triptolide and butein suppressed nuclear concentrations of nuclear factor-kappaB and secreted levels of IL-17, IL-21, and IFN-gamma in parallel, with greater potency in Th17 cells from young than old mice. Pharmacological correction of altered generation of Th17 cell cytokines in immunosenescence represents a novel therapeutic approach to aging-induced inflammatory diseases.

Signals from type 1 sphingosine 1-phosphate receptors enhance adult mouse cardiac myocyte survival during hypoxia

Sphingosine 1-phosphate (S1P) is a biologically active lysophospholipid that serves as a key regulator of cellular differentiation and survival. Immune stimuli increase S1P synthesis and secretion by mast cells and platelets, implicating this molecule in tissue responses to injury and inflammation. Binding of S1P to G(i) protein-coupled receptors activates phosphatidylinositol 3-kinase and Akt in a variety of tissues. To elucidate the mechanisms by which S1P enhances adult cardiac myocyte survival during hypoxia, we used a mouse cell culture system in which S1P(1) receptors were observed to transduce signals from exogenous S1P, an S1P(1) receptor antibody with agonist properties, and the pharmacological agents FTY720 and SEW2871. S1P(1) receptor mRNA and protein were abundantly expressed by adult mouse cardiac myocytes. S1P-S1P(1) receptor axis enhancement of myocyte survival during hypoxia was abolished by phosphatidylinositol 3-kinase inhibition. S1P(1) receptor function was closely associated with activation of Akt, inactivation of GSK-3beta, and reduction of cytochrome c release from heart mitochondria. These observations highlight the importance of S1P(1) receptors on ventricular myocytes as mediators of inducible resistance against cellular injury during severe hypoxic stress.

Th17 augmentation in OTII TCR plus T cell-selective type 1 sphingosine 1-phosphate receptor double transgenic mice

Sphingosine 1-phosphate (S1P) in blood and lymph controls lymphoid traffic and tissue migration of T cells through signals from the type 1 S1PR (S1P(1)), but less is known of effects of the S1P-S1P(1) axis on nonmigration functions of T cells. CD4 T cells from a double transgenic (DTG) mouse express OTII TCRs specific for OVA peptide 323-339 (OVA) and a high level of transgenic S1P(1), resistant to suppression by T cell activation. OVA-activated DTG CD4 T cells respond as expected to S1P by chemotactic migration and reduction in secretion of IFN-gamma. In addition, DTG CD4 T cells stimulated by OVA secrete a mean of 2.5-fold more IL-17 than those from OTII single transgenic mice with concomitantly higher levels of mRNA encoding IL-17 by real-time PCR and of CD4 T cells with intracellular IL-17 detected by ELISPOT assays. OVA challenge of s.c. air pockets elicited influx of more OTII TCR-positive T cells producing a higher level of IL-17 in DTG mice than OTII control mice. Augmentation of the number and activity of Th17 cells by the S1P-S1P(1) axis may thus enhance host defense against microbes and in other settings increase host susceptibility to autoimmune diseases.

Cutting edge: Alternative signaling of Th17 cell development by sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) in blood and lymph controls T cell traffic and proliferation through type 1 S1P receptor (S1P(1)) signals, but suppression of IFN-gamma generation has been the only consistently observed effect on T cell cytokines. The fact that S1P enhances the development of Th17 cells from Ag-challenged transgenic S1P(1)-overexpressing CD4 T cells suggested that the S1P-S1P(1) axis may promote the expansion of Th17 cells in wild-type mice. In a model of Th17 cell development from CD4 T cells stimulated by anti-CD3 plus anti-CD28 Abs and a mixture of TGF-beta1, IL-1, and IL-6, S1P enhanced their number and IL-17-generating activity the same as IL-23. As for IL-23 enhancement of Th17 cell development, that by S1P was prevented by IL-4 plus IFN-gamma and by IL-27. The prevention of S1P augmentation of Th17 cell development by the S1P receptor agonist and down-regulator FTY720 implies that FTY720 immunosuppression is attributable partially to inhibition of Th17-mediated inflammation.

Changing paradigms in the immunological science of allergy

The nonallergic roles of mast cells in infections and immune tolerance recently have been elucidated more fully at mechanistic levels. Mast cells that have been activated by contact with microbial surfaces secrete chemotactic mediators capable of attracting leukocytes through blood vessels permeabilized by other mediators. In the setting of allograft transplantation, regulatory CD4 T cells promote tolerance both by direct immunosuppressive effects and by releasing interleukin (IL)-9 that attracts and stimulates differentiation of mast cells with the capacity to induce local tolerance. For the first time in over 20 years, two new subclasses of CD4 T cells have been identified that have major immune functions. The first are T-helper interleukin-17 (T(H)17) cells, which mediate acute and chronic inflammation in recurring exacerbations of autoimmune diseases, and the second are sets of adaptive regulatory T cells, which control CD4 effector T cells and other immune effector cells by secreting transforming growth factor-beta or IL-10.

Type 1 sphingosine 1-phosphate G protein-coupled receptor (S1P1) mediation of enhanced IL-4 generation by CD4 T cells from S1P1 transgenic mice

Sphingosine 1-phosphate (S1P) is a natural lipid mediator that regulates immune cell traffic, Ab production, and T cell cytokine generation by mechanisms that enhance Th2 activities. Responses to S1P are controlled principally by the diverse expression patterns of its receptors in different cells. In T cells, the type 1 (S1P(1)) and type 4 (S1P(4)) G protein-coupled receptors are predominant. S1P(1) mainly transduces effects on T cell migration and trafficking, whereas S1P(4) transduces immunosuppression via its effects on T cell proliferation and cytokine production. Using T cell-specific S1P(1) transgenic (TG) mice, we investigated the regulatory effects of the S1P-S1P(1) axis on T cell cytokine production. The production of IL-4, but not IL-2 or IFN-gamma, was significantly up-regulated >10-fold in activated CD4 T cells from S1P(1) TG mice compared with those from wild-type mice. Quantitative real-time PCR analysis revealed that IL-4 up-regulation was initiated at the mRNA level as early as 4 h after T cell activation. The up-regulation of IL-4 mRNA was mediated by c-Maf, Jun B, and Gata3 as demonstrated by increases in their protein expression and DNA-binding activities. In contrast, the expression and DNA-binding activities of T-bet, FosB, C-Fos, Jun D, Fra-1, Fra-2, and c-Jun all were identical in wild-type and TG CD4 T cells. Immunological assays showed that increased IL-4 levels induced greater production of IgE. Thus, the S1P-S1P(1) axis specifically up-regulates c-Maf, Jun B, and Gata3, which consequently enhance IL-4 production that may lead to a Th2 phenotype.

Vasoactive intestinal peptide (VIP) up-regulates IL-17 generation by mouse CD4 T cells (100.1)

VIP produced by cholinergic and sensory nerves and by T cells affects T cell functions through the constitutively-expressed VPAC1 and inducible VPAC2 G protein-coupled receptors. Transgenic mice overexpressing VPAC2 (TG) selectively on CD4 T cells exhibit increased hypersensitivity and immunoinflammatory responses. Present studies were designed to examine the capacity of the VIP-VPAC2 axis to recruit the Th17 inflammatory subset of CD4 T cells. Splenic CD4 T cells isolated from TG and wild-type (WT) mice were incubated with adherent anti-CD3 and anti-CD28 antibodies and cytokines that initiate Th17 development, without and with IL-23 or VIP. IL-17 generation quantified by ELISA was enhanced significantly by 1μM VIP with the same time-course as for IL-23 over five days. IL-17 generation by CD4 T cells of TG mice was significantly greater than by those of WT mice with and without added VIP. Augmentation of IL-17 generation by both VIP and IL-23 was suppressed similarly by IL-27. Thus VIP may be a neuroalternative endogenous stimulus for Th17 development and recruit Th17 cells independently of IL-23 in inflammatory and autoimmune processes. (NIH grant AI029912)

Sphingosine 1 phosphate (S1P) -Type 1 Sphingosine 1-Phosphate G Protein-Coupled Receptor (S1P1) axis promotes peripheral generation of CD4+CD25+ regulatory T cells (131.5)

Regulatory T cells (Tregs) are a CD4+CD25+ subset of T cells that control normal immunity and autoimmunity by suppressing diverse functions of other immune cells. S1P regulates many immune functions via S1P1 and occasionally through another of its five receptors. The generation of Tregs from CD4+CD25− T cells in non-thymic lymphoid organs may be evoked by T cell activation and the actions of certain immune regulators, such as TGF-beta and IL-4. Using flow cytometry, we found there were1.4–1.8 fold more Tregs in CD4+ T cells of spleen, lymph node, and blood from S1P1 TG mice than in wild-type (WT) mice. In contrast, the numbers of Tregs in the CD4+ T cells from thymus of WT and S1P1 TG mice were the same. Cell proliferation assays using CD4+CD25− effector T cells as targets indicated that overexpressed Tregs in S1P1 TG mice had similar suppressive effects per T cell as Tregs in WT mice. In vitro assays showed around 5% of isolated CD4+CD25− T cells from S1P1 TG mice were converted to CD4+CD25+ Tregs by TCR stimulation or antigen activation in the presence of 10−7 M S1P. Real time PCR and flow cytometry assay showed the induction of FoxP3 mRNA and protein expression in these peripherally generated Tregs. Increased peripheral generation of Tregs by the S1P-S1P1 axis may alter the level of immune and autoimmune reactions sufficiently to make this system a therapeutic target for immunomodulatory drugs.

TH17 Augmentation in OTII TCR plus T Cell-Selective Type 1 Sphingosine 1-Phosphate Receptor Double Transgenic Mice (95.9)

Sphingosine 1-phosphate (S1P) in blood and lymph controls lymphoid traffic and tissue migration of T cells through signals from the type 1 S1P receptor (S1P1), but less is known of effects of the S1P-S1P1 axis on non-migration functions of T cells. CD4 T cells from a double transgenic (DTG) mouse express OTII TCRs specific for ovalbumin peptide 323–339 (OVA) and a high level of TG S1P1, resistant to suppression by T cell activation. Activated DTG CD4 T cells respond as expected to S1P by chemotactic migration and reduction of OVA-evoked secretion of IFN-gamma. In addition, DTG CD4 T cells stimulated by OVA secrete a mean of 2.5-fold more IL-17 than those from OTII single TG mice with concomitantly higher levels of mRNA encoding IL-17 by real-time PCR and intracellular IL-17 detected by ELISpot assays. OVA challenge of subcutaneous air-pockets elicited influx of more OTII-TCR-positive T cells producing a higher level of IL-17 in DTG mice than OTII control mice. Augmentation of the number and activity of Th17 cells by the S1P-S1P1 axis may enhance host defense against microbes and in other settings increase host susceptibility to autoimmune diseases.

(supported by NIH HL31809)

Alternative Signaling of TH17 Cell Development by Sphingosine 1-Phosphate (S1P) (90.2)

S1P from diverse blood and lymphoid cells signals T cell migration and other functions through its type 1 G protein-coupled receptor (S1P1). Our recent observation of increased levels of Th17 cells in mice with T cell-selective overexpression of transgenic S1P1 prompted studies of mechanisms of stimulation of Th17 cell development by the S1P- S1P1 axis. Incubation of C57BL\6 mouse splenic CD4 T cells on adherent anti-CD3 + anti-CD28 antibodies with IL-1beta, IL-6, and TGF-beta1 led to development of 26+/−9% Th17 cells (mean+/-SD, n=4), quantified by an ELISpot assay, that increased to 59+/−5% with 10-6 M S1P and 61+/−4% with IL-23 after 5 days. On day 5, secretion of IL-17 quantified by ELISA increased from 52+/−30 to 261+/−117, 470+/−98, and 438+/−61 pg/ml/24 hr/106 T cells with S1P, IL-23, and the S1P1–selective agonist SEW2871, respectively. CD4 T cell secretion of IL-4 and IFN-gamma were decreased significantly as IL-17 increased, and addition of recombinant IL-4 + IFN-gamma blunted IL-17 responses significantly. S1P-S1P1 enhancement of Th17 development was suppressed as well by IL-27 and NF-kappaB inhibition. The importance of stimulation of Th17 development and activity by the S1P- S1P1 axis is supported by the similarity of magnitude of effect and susceptibility to immunoregulation to that of IL-23.

Sphingosine 1-phosphate as an intracellular messenger and extracellular mediator in immunity

The omnific mediator system composed of sphingosine 1-phosphate (S1P) and its five G-protein-coupled receptors, designated S1P(1)-S1P(5), affects diverse cellular functions in the nervous, endocrine, cardiovascular and immune systems. The many activities of the S1P-S1P(1) axis, which predominates in the cardiovascular and immune systems, have previously been classified according to their relationship with the distinct functional roles of each type of cell or according to their most frequently used signalling pathways. In the immune system, cell surface S1P(1) receptors transduce the rapid, transient effects of extracellular S1P on T- and B-lymphocyte trafficking in the lymphoid system, lymphocyte migration in non-immune tissues and cytokine generation. After immune stimulation of T- and B-lymphocytes, S1P(1) receptors translocate from the cell surface to endosomal and nuclear compartments. The present hypothesis is that nuclear S1P(1) receptors represent distinct signalling complexes that, through a series of transcriptional events, transduce the sustained effects of intracellular S1P on survival and proliferation of T-lymphocytes. It is postulated that similar types of sustained signalling from nuclear S1P receptors in other types of cells affect proliferation, survival and specific effector functional activities. Effective pharmacological approaches to intracellular, as well as cell surface, S1P-S1P receptor axes will thus require the bioaccessibility of agonists and antagonists to the nuclear domain of relevant target cells.

CONCLUSION

Most investigations of the effects of the S1P-S1P(1) axis in immunity have focused primarily on rapid, transient alterations in lymphocyte migration and trafficking, and on mast cell migration and secretion of chemical mediators. The discovery of functional S1P(1)-G protein signalling complexes in the nuclear membranes of activated lymphocytes, that are coupled to the transduction of prolonged inhibition of proliferative responses by intracellular S1P, adds a new dimension to the role of the S1P-S1P(1) axis in immunity. Recruitment of this novel, potentially immunosuppressive, function of S1P(1) may be beneficial in some autoimmune diseases and will require application of cell membrane-permeant S1P(1)-specific drugs.

Diverse pathways for nuclear signaling by G protein‐coupled receptors and their ligands

Recent realization that plasma membrane G protein-coupled receptors (GPCRs) may translocate and establish ligand-responsive signaling complexes in other cellular structures has motivated studies of site-specific differences in transductional pathways. GPCRs and their ligands may signal transcription and other nuclear events by two basic mechanisms. The first consists of GPCR-complex activation of messengers that enter the nucleus and there initiate cell-modifying processes without the GPCR leaving the plasma membrane. The second encompasses entry into the nuclear membranes or matrix of either GPCR ligands, which bind to non-GPCR nuclear signaling proteins, proteolytic fragments of GPCRs capable of ligand-independent signaling, or intact GPCRs with transduction-competent factors that directly initiate or regulate transcriptional events. With the second mechanism, often concurrent down-regulation of plasma membrane GPCRs terminates signaling from the cell-surface and moves it into the nuclear domain. Site-dependent differences in signals from the same GPCR provide potentials for unique cellular abnormalities attributable to defective intracellular movement and distribution of a GPCR, site-specific alterations in ligand concentration, and limited intracellular bioavailability of pharmacological agents that can interact specifically with both nuclear and plasma membrane forms of a GPCR.

Distinctive T cell-suppressive signals from nuclearized type 1 sphingosine 1-phosphate G protein-coupled receptors

Sphingosine 1-phosphate (S1P) generated by cells of innate immunity and the type 1 S1P G protein-coupled receptor (S1P(1)) on mobile T cells constitute a major system for control of lymphoid organ traffic and tissue migration of T cells. Now we show that T cell activation mediated by the T cell antigen receptor translocates plasma membrane S1P(1) to nuclear envelope membranes for association there with G(i/o), Erk (1/2), and other proteins that plasma membrane S1P(1) uses to signal T cell proliferation. However, nuclear S1P(1) and plasma membrane S1P(1) transduce opposite effects of S1P on T cell proliferation and relevant signaling as exemplified by respective decreases and increases in T cell nuclear concentrations of both phospho-Erk and active (phosphorylated) c-Jun. T cell antigen receptor-mediated activation of T cells therefore both eliminates migration responses to S1P by down-regulation of plasma membrane S1P(1) and translocates the S1P-S1P(1) axis into the nuclear domain where signals are directed to transcriptional control of immune functions other than migration.

Differential signaling of T cell generation of IL-4 by wild-type and short-deletion variant of type 2 G protein-coupled receptor for vasoactive intestinal peptide (VPAC2)

Vasoactive intestinal peptide (VIP) released from some neurons and T cells affects T cell migration, cytokine generation, and other functions by binding to constitutively expressed type 1 G protein-coupled receptor (VPAC1) or activation-induced type 2 G protein-coupled receptor (VPAC2). Recently, a short-deletion (SD) splice variant of mouse VPAC2 that lacks 14 amino acids at the end of the last transmembrane domain has been identified in T cells and shown to resemble wild-type (WT) VPAC2 in affinity of VIP binding but to differ by lack of signaling of T cell adenylyl cyclase, migration, and IL-2 secretion. As Th2 cells are the principal source of immune VIP and have the greatest functional responses to VIP, the differences in signals transduced by WT and SD VPAC2 were studied in VPAC2-low D10G4.1 model Th2 cell transfectants individually expressing the respective types of VPAC2 equally. WT and SD VPAC2 Th2 cell transfectants secreted equal amounts of VIP. WT VPAC2 transfectants generated more IL-4 than did SD VPAC2 transfectants, and this increment was dependent on endogenous VIP. Exogenous VIP further increased IL-4 production by WT VPAC2 transfectants but decreased IL-4 production by SD VPAC2 transfectants. Cotransfection of the two constructs diminished VIP enhancement of IL-4 production seen with WT VPAC2 alone by preventing increases in nuclear levels of the requisite transcription factors c-Maf and Jun B. Thus the ratio of two forms of T cell VPAC2 determines the net effect of VIP on IL-4 generation by activated Th2 cells.

Nitric oxide signaling via nuclearized endothelial nitric-oxide synthase modulates expression of the immediate early genes iNOS and mPGES-1

Stimulation of freshly isolated rat hepatocytes with lysophosphatidic acid (LPA) resulted in LPA1 receptor-mediated and nitricoxide-dependent up-regulation of the immediate early genes iNOS (inducible nitric-oxide synthase (NOS)) and mPGES-1 (microsomal prostaglandin E synthase-1). Because LPA is a ligand for both cell surface and intracellular receptor sites and a potent endothelial NOS (eNOS) activator, we hypothesized that NO derived from activated nuclearized eNOS might participate in gene regulation. Herein we show, by confocal microscopy performed on porcine cerebral endothelial cells expressing native LPA1-receptor and eNOS and on HTC4 rat hepatoma cells co-transfected with recombinant human LPA1-receptor and fused eNOS-GFP cDNA, a dynamic eNOS translocation from peripheral to nuclear regions upon stimulation with LPA. Nuclear localization of eNOS and its downstream effector, soluble guanylate cyclase, were demonstrated in situ in rat liver specimens by immunogold labeling using specific antibodies. Stimulation of this nuclear fraction with LPA and the NO donor sodium nitroprusside resulted, respectively, in increased production of nitrite (and eNOS phosphorylation) and cGMP; these separate responses were also correspondingly blocked by NOS inhibitor L-NAME and soluble guanylate cyclase inhibitor ODQ. In addition, sodium nitroprusside evoked a sequential increase in nuclear Ca2+ transients, activation of p42 MAPK, NF-kappaB binding to DNA consensus sequence, and dependent iNOS RNA. This study describes a hitherto unrecognized molecular mechanism by which nuclear eNOS through ensuing NO modulates nuclear calcium homeostasis involved in gene transcription-associated events. Moreover, our findings strongly support the concept of the nucleus as an autonomous signaling compartment.

Type 1 sphingosine 1-phosphate G protein-coupled receptor signaling of lymphocyte functions requires sulfation of its extracellular amino-terminal tyrosines

The type 1 sphingosine 1-phosphate (S1P) G protein-coupled receptor (S1P1) transduces signals from S1P that mediate thymocyte emigration, T cell transmigration of lymph nodes, and T cell chemotaxis in tissues. Alterations in expression of functional S1P1 receptors by lymphocytes are the major mechanisms controlling their responses to S1P and were thought to be solely a consequence of the balance between surface down-regulation and insertion. However, results now show that lack of sulfation of tyrosines 19 and 22 of the extracellular N terminus of S1P1 diminishes high-affinity S1P binding and decreases S1P signaling of T cell migration and other functions. Non-sulfatable mutant (Y19,22F)S1P1 endows T cells with lower-affinity binding of [32P]S1P than wild-type S1P1 and transduces lesser effects of S1P on chemotaxis, chemokine-elicited chemotaxis, and T cell receptor-mediated proliferation and cytokine generation. Inhibition of S1P1 tyrosine sulfation or sulfatase removal of S1P1 sulfate in mouse CD4 T cells suppresses immune functional effects of S1P. Tyrosine sulfation of S1P1 may be a major controller of S1P effects on T cell traffic.

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.

Type 4 sphingosine 1-phosphate G protein-coupled receptor (S1P4) transduces S1P effects on T cell proliferation and cytokine secretion without signaling migration

Sphingosine 1-phosphate (S1P) has diverse effects on T cells that are mediated by the predominant S1P1 and S1P4 G protein-coupled receptors (GPCRs). S1P4 is expressed principally by leukocytes, but little is known of its T cell effects in immunity. Two approaches were used to investigate S1P4 signals in T cells. First, S1P4 was introduced into D10G4.1 mouse Th2 cells and EL4.IL-2 mouse T cells lacking endogenous S1P GPCRs. Second, mouse splenic CD4 T cells were treated with FTY720 to suppress S1P1 and leave S1P4 GPCRs as the only functionally relevant S1P receptor. Unlike S1P1, S1P4 failed to transduce chemotactic responses of any of the S1P4-only T cells to S1P or the phyto-S1P ligand selective for S1P4, or to suppress their chemotactic responses to chemokines. The S1P-S1P4 axis significantly inhibited T cell proliferation in each of the S1P4-only T cells activated by anti-CD3 and anti-CD28 MoAbs. Secretion of IL-4 by S1P4-D10G4.1 cells, IL-2 by S1P4-EL4.IL-2, and IFN-gamma by FTY720-treated CD4 T cells were significantly inhibited by S1P. In contrast, S1P enhanced secretion of IL-10 by stimulated S1P4-D10G4.1 T cells. Thus, S1P4 mediates immunosuppressive effects of S1P by inhibiting proliferation and secretion of effector cytokines, while enhancing secretion of the suppressive cytokine IL-10.

Immunological effects of transgenic constitutive expression of the type 1 sphingosine 1-phosphate receptor by mouse lymphocytes

The type 1 sphingosine 1-phosphate (S1P) G protein-coupled receptor (S1P1) normally transduces S1P effects on lymph node (LN) egress and tissue migration of naive lymphocytes. We now show that persistent expression of S1P1 by lymphocytes of S1P1-transgenic (Tg) mice suppresses delayed-type hypersensitivity and results in production of significantly more IgE Ab and less IgG2 Ab than in wild-type (wt) mice. wt host LN homing of 51Cr-labeled T cells from S1P1-Tg mice was only 30-40% of that for wt T cells. Adoptive-transfer of dye-labeled activated T cells from S1P1-Tg mice into wt mice resulted in 2.2-fold more in blood and 60% less in LNs than for activated wt T cells after 1 day. Proliferative responses of stimulated T cells from S1P1-Tg mice were only 10-34% of those for wt T cells. Disordered cellular and humoral immunity of S1P1-Tg mice thus may be attributable to both altered T cell traffic and depressed T cell functions, suggesting that S1P1-specific agonists may represent a novel therapeutic approach to autoimmunity and transplant rejection.

Sphingosine 1-phosphate and its G protein-coupled receptors constitute a multifunctional immunoregulatory system

The lysophospholipid growth factors sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are generated by many cells involved in immunity, including macrophages, dendritic cells, mast cells, and platelets, with resultant lymph and plasma concentrations of 0.1-1 microM. All immune cells express distinctive profiles of G protein-coupled receptors (GPCRs) for S1P and LPA, which are regulated developmentally and by cellular activation. For T-cells, constitutive S1P signaling through their principal S1P(1) GPCR inhibits chemotactic responses to chemokines, with lesser suppression of proliferation and cytokine production. These S1P-S1P(1) GPCR signals tonically reduce T-cell chemotactic sensitivity to chemokines and thereby limit homing of blood and spleen T-cells to secondary lymphoid tissues. S1P(1) GPCR antagonists evoke lymphopenia by permitting blood T-cells to enter lymph nodes and blocking S1P(1) GPCR-dependent T-cell efflux from lymph nodes. Inversely, there is a longer than normal persistance in blood and a decrease in lymphoid transit time for T-cells overexpressing transgenic S1P(1) GPCRs. The immunotherapeutic potential of S1P(1) GPCR antagonists derives from their capacity to limit T-cell access to organ grafts and autoimmune antigens without reducing their other intrinsic functional capabilities. Lysophospholipids and their GPCRs thus constitute an immunoregulatory system of sufficient prominence for pharmacological targeting in transplantation, autoimmunity and immunodeficiency.

Regulation of immunity by lysosphingolipids and their G protein-coupled receptors

T and B lymphocytes, as well as endothelial cells, express distinctive profiles of G protein-coupled receptors for sphingosine 1-phosphate, which is a major regulator of T cell development, B and T cell recirculation, tissue homing patterns, and chemotactic responses to chemokines. The capacity of drugs that act on type 1 sphingosine 1-phosphate receptors to suppress organ graft rejection in humans and autoimmunity in animal models without apparent impairment of host defenses against infections suggests that this system is a promising target for new forms of immunotherapy.

An IgM-kappa rat monoclonal antibody specific for the type 1 sphingosine 1-phosphate G protein-coupled receptor with antagonist and agonist activities

Sphingosine 1-phosphate (S1P) type 1G protein-coupled receptors (S1P1 GPCRs) are specific high-affinity transducers for this lipid growth factor and cellular mediator. S1P1 GPCRs are widely-expressed and physiologically critical in the cardiovascular and immune systems. Functional rat monoclonal antibodies (MoAbs) have been generated against human S1P1 GPCRs expressed in rat null-cell transductants to provide bioavailable agents capable of stimulating or suppressing the S1P-S1P1 GPCR axis. The rat IgM-kappa anti-S1P1 GPCR MoAb designated 4B5.2 binds specifically to native human or mouse S1P1 GPCRs in cell membranes, but not to solubilized and denatured S1P1 GPCRs. Specific binding of 32P-S1P to cellular S1P1 GPCRs is not blocked by 4B5.2. T cell chemotactic responses to S1P and S1P suppression of T cell chemotaxis to chemokines both are inhibited selectively by 4B5.2. In contrast, generation of gamma-interferon by stimulated T cells is diminished by 4B5.2 as by S1P. T cell S1P1 GPCR-selective antagonist and agonist effects of 4B5.2 in vivo may alter immune responses as distinctively as the available poly-S1P GPCR-directed pharmacological agents, without the undesirable side-effects attributable to actions of these agents on other S1P GPCRs.