Interferon gamma constrains type 2 lymphocyte niche boundaries during mixed inflammation

Allergic immunity is orchestrated by group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells prominently arrayed at epithelial- and microbial-rich barriers. However, ILC2s and Th2 cells are also present in fibroblast-rich niches within the adventitial layer of larger vessels and similar boundary structures in sterile deep tissues, and it remains unclear whether they undergo dynamic repositioning during immune perturbations. Here, we used thick-section quantitative imaging to show that allergic inflammation drives invasion of lung and liver non-adventitial parenchyma by ILC2s and Th2 cells. However, during concurrent type 1 and type 2 mixed inflammation, IFNγ from broadly distributed type 1 lymphocytes directly blocked both ILC2 parenchymal trafficking and subsequent cell survival. ILC2 and Th2 cell confinement to adventitia limited mortality by the type 1 pathogen Listeria monocytogenes. Our results suggest that the topography of tissue lymphocyte subsets is tightly regulated to promote appropriately timed and balanced immunity.

Keep a Little Fire Burning-The Delicate Balance of Targeting Sphingosine-1-Phosphate in Cancer Immunity

The sphingolipid sphingosine-1-phosphate (S1P) promotes tumor development through a variety of mechanisms including promoting proliferation, survival, and migration of cancer cells. Moreover, S1P emerged as an important regulator of tumor microenvironmental cell function by modulating, among other mechanisms, tumor angiogenesis. Therefore, S1P was proposed as a target for anti-tumor therapy. The clinical success of current cancer immunotherapy suggests that future anti-tumor therapy needs to consider its impact on the tumor-associated immune system. Hereby, S1P may have divergent effects. On the one hand, S1P gradients control leukocyte trafficking throughout the body, which is clinically exploited to suppress auto-immune reactions. On the other hand, S1P promotes pro-tumor activation of a diverse range of immune cells. In this review, we summarize the current literature describing the role of S1P in tumor-associated immunity, and we discuss strategies for how to target S1P for anti-tumor therapy without causing immune paralysis.

Fatty acid chain length drives lysophosphatidylserine-dependent immunological outputs

In humans, lysophosphatidylserines (lyso-PSs) are potent lipid regulators of important immunological processes. Given their structural diversity and commercial paucity, here we report the synthesis of methyl esters of lyso-PS (Me-lyso-PSs) containing medium- to very-long-chain (VLC) lipid tails. We show that Me-lyso-PSs are excellent substrates for the lyso-PS lipase ABHD12, and that these synthetic lipids are acted upon by cellular carboxylesterases to produce lyso-PSs. Next, in macrophages we demonstrate that VLC lyso-PSs orchestrate pro-inflammatory responses and in turn neuroinflammation via a Toll-like receptor 2 (TLR2)-dependent pathway. We also show that long-chain (LC) lyso-PSs robustly induce intracellular cyclic AMP production, cytosolic calcium influx, and phosphorylation of the nodal extracellular signal-regulated kinase to regulate macrophage activation via a TLR2-independent pathway. Finally, we report that LC lyso-PSs potently elicit histamine release during the mast cell degranulation process, and that ABHD12 is the major lyso-PS lipase in these immune cells.

GPR34-mediated sensing of lysophosphatidylserine released by apoptotic neutrophils activates type 3 innate lymphoid cells to mediate tissue repair

Neutrophils migrate rapidly to damaged tissue and play critical roles in host defense and tissue homeostasis. Here we investigated the mechanisms whereby neutrophils participate in tissue repair. In an intestinal epithelia injury model, neutrophil depletion exacerbated colitis and associated with reduced interleukin (IL)-22 and limited activation of type 3 innate lymphoid cells (ILC3s). Co-culture with neutrophils activated ILC3s in a manner dependent on neutrophil apoptosis. Metabolomic analyses revealed that lysophosphatidylserine (LysoPS) from apoptotic neutrophils directly stimulated ILC3 activation. ILC3-specific deletion of Gpr34, encoding the LysoPS receptor GPR34, or inhibition of downstream PI3K-AKT or ERK suppressed IL-22 production in response to apoptotic neutrophils. Gpr34-/- mice exhibited compromised ILC3 activation and tissue repair during colon injury, and neutrophil depletion abrogated these defects. GPR34 deficiency in ILC3s limited IL-22 production and tissue repair in vivo in settings of colon and skin injury. Thus, GPR34 is an ILC3-expressed damage-sensing receptor that triggers tissue repair upon recognition of dying neutrophils.

Lysophosphatidic Acid Is an Inflammatory Lipid Exploited by Cancers for Immune Evasion via Mechanisms Similar and Distinct From CTLA-4 and PD-1

Immunological tolerance has evolved to curtail immune responses against self-antigens and prevent autoimmunity. One mechanism that contributes to immunological tolerance is the expression of inhibitory receptors by lymphocytes that signal to dampen immune responses during the course of an infection and to prevent immune-mediated collateral damage to the host. The understanding that tumors exploit these physiological mechanisms to avoid elimination has led to remarkable, but limited, success in the treatment of cancer through the use of biologics that interfere with the ability of cancers to suppress immune function. This therapy, based on the understanding of how T lymphocytes are normally activated and suppressed, has led to the development of therapeutic blocking antibodies, referred to as immune checkpoint blockade, which either directly or indirectly promote the activation of CD8 T cells to eradicate cancer. Here, we highlight the distinct signaling mechanisms, timing and location of inhibition used by the CTLA-4 and PD-1 inhibitory receptors compared to a novel inhibitory signaling axis comprised of the bioactive lipid, lysophosphatidic acid (LPA), signaling via the LPA5 receptor expressed by CD8 T cells. Importantly, abundant evidence indicates that an LPA-LPA5 signaling axis is also exploited by diverse cancers to suppress T cell activation and function. Clearly, a thorough molecular and biochemical understanding of how diverse T cell inhibitory receptors signal to suppress T cell antigen receptor signaling and function will be important to inform the choice of which complimentary checkpoint blockade modalities might be used for a given cancer.

Neutrophil recruitment mediated by sphingosine 1-phosphate (S1P)/S1P receptors during chronic liver injury

Excessive neutrophils are recruited to damaged tissue and cause collateral injury under chronic inflammatory conditions. Sphingosine 1-phosphate (S1P) modulates kinds of physiological and pathological actions by inducing recruitment of various cell types through S1P receptors (S1PRs). This study aimed to detect the S1P/S1PRs-mediated effects on neutrophil recruitment during chronic liver inflammation. In present study, increased neutrophils originated from bone marrow (BM) were detected in liver tissue of BDL-treated mice. Hepatic sphingosine kinase 1 (SphK, S1P rate-limiting enzyme) or S1P levels positively correlated with neutrophil marker expression in liver of mice and patients. In vitro, expression of S1PR₁, S1PR₂ and S1PR₃ were detected in both mouse BM neutrophils and differentiated human neutrophil-like (dHL60) cells. S1P powerfully boosted the migration and cytoskeletal remodeling of BM neutrophils through S1PR₁ or S1PR₂. Different from BM neutrophils, the migration and cytoskeletal remodeling of dHL60 cells were mediated by S1PR₂ or S1PR₃. S1PR₂ blockade obviously attenuates neutrophil infiltration in bile duct ligation (BDL)-induced mouse liver injury. In conclusion, S1P/S1PRs system plays a pivotal role in neutrophil recruitment.

Pruritus secondary to primary biliary cholangitis: a review of the pathophysiology and management with phototherapy

BACKGROUND

Primary biliary cholangitis (PBC) is an autoimmune hepatobiliary disorder characterized by destruction of liver bile ducts leading to intrahepatic cholestasis. It causes intractable pruritus for which ultraviolet (UV)B phototherapy is an experimental treatment when alternative therapies fail. The pathophysiology of cholestatic itch and the mechanism of action of narrowband UVB in this condition remains poorly understood.

OBJECTIVES

To summarize the current literature and propose testable hypotheses for the mechanism of action of phototherapy in attenuating itch.

METHODS

A focused PubMed search for articles relating to the pathogenesis of itch in cholestatic disease was performed. A total of 3855 articles were screened and 50 were found suitable for literature review. Evidence from this literature review was combined with author expertise in the area.

RESULTS

Formulated hypotheses focus on the role of bile salts, autotaxin and specific receptors including G-protein-coupled bile acid receptor, Gpbar1 (also known as TGR5) and the nuclear transcription factor farnesoid X receptor.

CONCLUSIONS

Several testable mechanisms through which phototherapy may exert its effects are discussed in this review. The next steps are to carry out an objective assessment of the efficacy of phototherapy in cholestatic pruritus, gain further knowledge on the underlying pathways, and subsequently trial its use against current licensed therapies. Such studies could lead to increased mechanistic understanding, identification of novel therapeutic targets and the potential to refine phototherapy protocols, leading to improved control of itch and quality of life in patients with PBC. What's already known about this topic? Primary biliary cholangitis (PBC) is frequently associated with intractable pruritus for which current treatment options are often unsuccessful. Phototherapy is used as an experimental treatment for PBC-associated pruritus when alternative better-studied treatments fail. What does this study add? This study reviews the current literature on the pathophysiology and management of cholestatic pruritus, an area which remains poorly understood. We propose testable hypotheses of the mechanisms behind the attenuation of cholestatic pruritus with phototherapy.

Hepatocyte-Derived Lipotoxic Extracellular Vesicle Sphingosine 1-Phosphate Induces Macrophage Chemotaxis

Background: The pathophysiology of non-alcoholic steatohepatitis involves hepatocyte lipotoxicity due to excess saturated free fatty acids and concomitant proinflammatory macrophage effector responses. These include the infiltration of macrophages into hepatic cords in response to incompletely understood stimuli. Stressed hepatocytes release an increased number of extracellular vesicles (EVs), which are known to participate in intercellular signaling and coordination of the behavior of immune cell populations via their cargo. We hypothesized that hepatocyte-derived lipotoxic EVs that are enriched in sphingosine 1-phosphate (S1P) are effectors of macrophage infiltration in the hepatic microenvironment. Methods: Lipotoxic EVs were isolated from palmitate treated immortalized mouse hepatocytes and characterized by nanoparticle tracking analysis. Lipotoxic EV sphingolipids were quantified using tandem mass spectrometry. Wildtype and S1P1 receptor knockout bone marrow-derived macrophages were exposed to lipotoxic EV gradients in a microfluidic gradient generator. Macrophage migration toward EV gradients was captured by time-lapse microscopy and analyzed to determine directional migration. Fluorescence-activated cell sorting along with quantitative PCR and immunohistochemistry were utilized to characterize the cell surface expression of S1P1 receptor on intrahepatic leukocytes and hepatic expression of S1P1 receptor, respectively. Results: Palmitate treatment induced the release of EVs. These EVs were enriched in S1P. Palmitate-induced S1P enriched EVs were chemoattractive to macrophages. EV S1P enrichment depended on the activity of sphingosine kinases 1 and 2, such that, pharmacological inhibition of sphingosine kinases 1 and 2 resulted in a significant reduction in EV S1P cargo without affecting the number of EVs released. When exposed to EVs derived from cells treated with palmitate in the presence of a pharmacologic inhibitor of sphingosine kinases 1 and 2, macrophages displayed diminished chemotactic behavior. To determine receptor-ligand specificity, we tested the migration responses of macrophages genetically deleted in the S1P1 receptor toward lipotoxic EVs. S1P1 receptor knockout macrophages displayed a marked reduction in their chemotactic responses toward lipotoxic palmitate-induced EVs. Conclusions:Palmitate-induced lipotoxic EVs are enriched in S1P through sphingosine kinases 1 and 2. S1P-enriched EVs activate persistent and directional macrophage chemotaxis mediated by the S1P1 receptor, a potential signaling axis for macrophage infiltration during hepatic lipotoxicity, and a potential therapeutic target for non-alcoholic steatohepatitis.

The Sphingosine-1-Phosphate/Sphingosine-1-Phosphate Receptor 2 Axis in Intestinal Epithelial Cells Regulates Intestinal Barrier Function During Intestinal Epithelial Cells-CD4+T-Cell Interactions

BACKGROUND/AIMS

Epithelial cells line the intestinal mucosa and form an important barrier for maintaining host health. This study aimed to explore the mechanism of the Sphingosine-1-phosphate (S1P)/Sphingosine-1-phosphate receptor 2 (S1PR2) pathway in intestinal epithelial cells (IECs) that participate in the intestinal barrier function.

METHODS

In this study, we constructed a knockout of the S1PR2 gene in mice, and Dextra sulfate sodium (DSS) was used to induce colitis. We isolated IECs from wild type (WT) and S1PR2-/- mice, and the endogenous expression of S1PR2 and Zonula occludens 1 (ZO-1) in IEC were detected by Western blot. Next, the major histocompatibility complex II (MHC-II) expression was analyzed by reverse transcription quantitative real-time (RT-qPCR) and flow cytometry. The in vivo and in vitro intestinal permeability were evaluated by serum fluorescein isothiocyanate (FITC) concentration. The tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interferon-γ (IFN-γ) levels in cell suspension were analyzed by enzyme-linked immuno sorbent assay (ELISA). A carboxyfluorescein diacetate succinimidyl ester (CFSE) assay was used to detect the T-cell proliferation in a co-culture system.

RESULTS

The intestinal mucosal barrier damage in S1PR2-/- mice was more severe than in the WT mice, and there were more CD4+T-cells in the colon tissue of DSS-treated S1PR2-/- mice. Either the mouse colon carcinoma cell line (CT26. WT) or the IECs upregulated MHC-II expression, which then promoted CD4+T-cell proliferation. The S1P/S1PR2 pathway controlled MHC-II expression to regulate CD4+T-cell proliferation via the extracellular signal-regulated kinase (ERK) pathway. In addition, the IFN-γ that was secreted by CD4+T-cells increased DSS-induced damage of intestinal epithelial cell barrier function. ZO-1 expression was increased by S1P in CT26.WT cells, while S1PR2 antagonist JTE-013 expression was downregulated. However, in CT26.WTsi-S1PR2 cells, S1P had no effect on ZO-1 expression.

CONCLUSIONS

The S1P/S1PR2 axis in IECs mediated CD4+T-cell activation via the ERK pathway and MHC-II expression to regulate intestinal barrier function.

Sphingosine 1-Phosphate Signaling and Its Pharmacological Modulation in Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic haemopoietic stem cell transplantation (HSCT) is increasingly used to treat haematological malignant diseases via the graft-versus-leukaemia (GvL) or graft-versus-tumour effects. Although improvements in infectious disease prophylaxis, immunosuppressive treatments, supportive care, and molecular based tissue typing have contributed to enhanced outcomes, acute graft-versus-host disease and other transplant related complications still contribute to high mortality and significantly limit the more widespread use of HSCT. Sphingosine 1-phosphate (S1P) is a zwitterionic lysophospholipid that has been implicated as a crucial signaling regulator in many physiological and pathophysiological processes including multiple cell types such as macrophages, dendritic cells, T cells, T regulatory cells and endothelial cells. Recent data suggested important roles for S1P signaling in engraftment, graft-versus-host disease (GvHD), GvL and other processes that occur during and after HSCT. Based on such data, pharmacological intervention via S1P modulation may have the potential to improve patient outcome by regulating GvHD and enhancing engraftment while permitting effective GvL.

During Hepatitis C Virus (HCV) Infection and HCV-HIV Coinfection, an Elevated Plasma Level of Autotaxin Is Associated With Lysophosphatidic Acid and Markers of Immune Activation That Normalize During Interferon-Free HCV Therapy

BACKGROUND

 Immune activation predicts morbidity during hepatitis C virus (HCV) infection and human immunodeficiency virus (HIV) infection, although mechanisms underlying immune activation are unclear. Plasma levels of autotaxin and its enzymatic product, lysophosphatidic acid (LPA), are elevated during HCV infection, and LPA activates immunocytes, but whether this contributes to immune activation is unknown.

METHODS

 We evaluated plasma levels of autotaxin, interleukin 6 (IL-6), soluble CD14 (sCD14), soluble CD163 (sCD163), and Mac2 binding protein (Mac2BP) during HCV infection, HIV infection, and HCV-HIV coinfection, as well as in uninfected controls, before and after HIV antiretroviral therapy (ART) initiation and during interferon-free HCV therapy.

RESULTS

 We observed greater plasma autotaxin levels in HCV-infected and HCV-HIV-coinfected participants, compared with uninfected participants, primarily those with a higher ratio of aspartate aminotransferase level to platelet count. Autotaxin levels correlated with IL-6, sCD14, sCD163, Mac2BP, and LPA levels in HCV-infected participants and with Mac2BP levels in HCV-HIV-coinfected participants, while in HIV-infected individuals, sCD14 levels correlated with Mac2BP levels. Autotaxin, LPA, and sCD14 levels normalized, while sCD163 and Mac2BP levels partially normalized within 6 months of starting interferon-free HCV therapy. sCD163 and IL-6 levels normalized within 6 months of starting ART for HIV infection. In vitro, LPA activated monocytes.

CONCLUSIONS

 These data indicate that elevated levels of autotaxin and soluble markers of immune activation during HCV infection are partially reversible within 6 months of initiating interferon-free HCV treatment and that autotaxin may be causally linked to immune activation during HCV infection and HCV-HIV coinfection.

The Sphingosine-1-Phosphate Lyase (LegS2) Contributes to the Restriction of Legionella pneumophila in Murine Macrophages

L. pneumophila is the causative agent of Legionnaires’ disease, a human illness characterized by severe pneumonia. In contrast to those derived from humans, macrophages derived from most mouse strains restrict L. pneumophila replication. The restriction of L. pneumophila replication has been shown to require bacterial flagellin, a component of the type IV secretion system as well as the cytosolic NOD-like receptor (NLR) Nlrc4/ Ipaf. These events lead to caspase-1 activation which, in turn, activates caspase-7. Following caspase-7 activation, the phagosome-containing L. pneumophila fuses with the lysosome, resulting in the restriction of L. pneumophila growth. The LegS2 effector is injected by the type IV secretion system and functions as a sphingosine 1-phosphate lyase. It is homologous to the eukaryotic sphingosine lyase (SPL), an enzyme required in the terminal steps of sphingolipid metabolism. Herein, we show that mice Bone Marrow-Derived Macrophages (BMDMs) and human Monocyte-Derived Macrophages (hMDMs) are more permissive to L. pneumophila legS2 mutants than wild-type (WT) strains. This permissiveness to L. pneumophila legS2 is neither attributed to abolished caspase-1, caspase-7 or caspase-3 activation, nor due to the impairment of phagosome-lysosome fusion. Instead, an infection with the legS2 mutant resulted in the reduction of some inflammatory cytokines and their corresponding mRNA; this effect is mediated by the inhibition of the nuclear transcription factor kappa-B (NF-κB). Moreover, BMDMs infected with L. pneumophila legS2 mutant showed elongated mitochondria that resembles mitochondrial fusion. Therefore, the absence of LegS2 effector is associated with reduced NF-κB activation and atypical morphology of mitochondria.

Mast cell plasticity and sphingosine-1-phosphate in immunity, inflammation and cancer

Mast cells (MC) are found in all vascularized tissues at homeostasis and, until recently, were viewed only as effector cells of allergic reactions via degranulation, the canonical process through which MC release mediators, including histamine and pre-formed proteases and cytokines such as TNF. Cross-linking of IgE bound to surface high affinity receptors for IgE (FcɛRI) by a specific antigen (Ag) triggers signaling events leading to degranulation. We and others have reported the concomitant production and export of an influential multifaceted sphingolipid mediator, sphingosine-1-phosphate (S1P) transported outside of MC by ATP-binding cassettes (ABC) transporters, i.e., independently of degranulation. Indeed, the MC horizon expanded by the discovery of their unique ability to selectively release mediators depending upon the stimulus and receptors involved. Aside from degranulation and transporter usage, MC are also endowed with piecemeal degranulation, a slower process during which mediator release occurs with minor morphological changes. The broad spectrum of pro- and anti-inflammatory bioactive substances MC produce and release, their amounts and delivery pace render these cells bona fide fine-tuners of the immune response. In this viewpoint article, MC developmental, phenotypic and functional plasticity, its modulation by microRNAs and its relevance to immunity, inflammation and cancer will be discussed.

A sting in the tale of TH2 immunity

Allergies are widely considered misguided Th2 cell responses. In this issue, Palm et al. (2013) and Marichal et al. (2013) show that mice mount anti-venom Th2 cell responses that share components of the "allergic" response but confer protection.

The role of sphingosine 1-phosphate in inflammation and cancer

The enzymes that catalyze formation of the bioactive sphingolipid, sphingosine 1-phosphate, sphingosine kinase 1 and 2, are predictive markers in inflammatory diseases and cancer as evidenced by data from patients, knockout mice and the use of available molecular and chemical inhibitors. Thus, there is a compelling case for therapeutic targeting of sphingosine kinase. In addition, there are several examples of functional interaction between sphingosine 1-phosphate receptors and sphingosine kinase 1 that can drive malicious amplification loops that promote cancer cell growth. These novel aspects of sphingosine 1-phosphate pathobiology are reviewed herein.

Phospholipids: "greasing the wheels" of humoral immunity

Phospholipids are major structural components of all cellular membranes. In addition, certain phospholipids execute regulatory activities that affect cell behavior, function and fate in critically important physiological settings. The influence of phospholipids is especially obvious in the adaptive immune system, where these macromolecules mediate both intrinsic and extrinsic effects on B and T lymphocytes. This review article highlights the action of lysophospholipid sphingosine-1-phosphate as a lymphocyte chemoattractant, the function of phosphatidylinositol phosphates as signaling conduits in lymphocytes and the role of phospholipids as raw materials for membrane assembly and organelle biogenesis in activated B lymphocytes. Special emphasis is placed on the means by which these three processes push humoral immune responses forward. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

An emerging link in stem cell mobilization between activation of the complement cascade and the chemotactic gradient of sphingosine-1-phosphate

Under steady-state conditions, hematopoietic stem/progenitor cells (HSPCs) egress from bone marrow (BM) and enter peripheral blood (PB) where they circulate at low levels. Their number in PB, however, increases significantly in several stress situations related to infection, organ/tissue damage, or strenuous exercise. Pharmacologically mediated enforced egress of HSPCs from the BM microenvironment into PB is called "mobilization", and this phenomenon has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present the accumulated evidence that innate immunity, including the complement cascade and the granulocyte/monocyte lineage, and the PB plasma level of the bioactive lipid sphingosine-1-phosphate (S1P) together orchestrate this evolutionarily conserved mechanism that directs trafficking of HSPCs.

Immunological function of sphingosine 1-phosphate in the intestine

It has been shown that dietary materials are involved in immune regulation in the intestine. Lipids mediate immune regulation through a complex metabolic network that produces many kinds of lipid mediators. Sphingosine-1-phosphate (S1P) is a lipid mediator that controls cell trafficking and activation. In this review, we focus on the immunological functions of S1P in the regulation of intestinal immune responses such as immunoglobulin A production and unique T cell trafficking, and its role in the development of intestinal immune diseases such as food allergies and intestinal inflammation, and also discuss the relationship between dietary materials and S1P metabolism.

G-protein-coupled receptors in control of natural killer cell migration

Natural killer (NK) cells are highly motile cells that patrol lymphoid and non-lymphoid organs, and are poised to react to infectious or other inflammatory situations. Several NK cell subsets equipped with different sets of chemotactic G-protein-coupled receptors, and which display distinct distribution across lymphoid and non-lymphoid organs, have been described. These receptors detect various guidance cues including sphingosine-1-phosphate and chemokines that orchestrate NK cell trafficking. Here, we highlight recent advances regarding the receptors involved in NK cell migration, with a focus on bone marrow egress, entry into activated lymph nodes, extravasation into inflamed tissues, and motility within lymph nodes or tumors. Understanding NK cell migration could provide a rational basis for the design of novel therapies in various clinical conditions.

Lysophosphatidic acid and autotaxin: emerging roles in innate and adaptive immunity

Lysophosphatidic acid (LPA) can affect the growth, migration, and activation of many different cell types. Research in this field has recently accelerated due to the molecular cloning of LPA receptors as well as advances in our understanding of LPA metabolism. A major pathway for LPA generation is the hydrolysis of lysophosphatidylcholine by the enzyme autotaxin (ATX). Although most research to-date has been conducted in other disciplines (e.g., neurobiology and cardiovascular diseases), emerging data point to an important role for LPA and ATX in regulating immune responses. Here we review current understanding of LPA and ATX in immunity with an emphasis on migration and activation of lymphocytes and dendritic cells. New gene-targeted and transgenic mice, receptor-specific antibodies, and pathway antagonists should rapidly enhance our understanding of this versatile lysolipid in immune responses in the near future.

[Regulation of immunity by sphingosine 1-phosphate and its G protein-coupled receptors--review]

Sphingosine 1-phosphate (S1P) is an important biologically active lysophospholipid that transmits signals through a family of G-protein-coupled receptors (GPCRs) to regulate the vital functions of several types of immune cells. The S1P GPCRs suppress both generation of specialized functional cytokines, such as IFN-gamma and IL-4, and proliferation of T-cells. Although S1P is chemotactic to T cells, B cells, dendritic cells, and natural killer cells, the major effect of S1P on the immune system is the regulation of lymphocyte recirculation and tissue distribution by S1P and S1P1. Chemotactic response of CD4+CD25+ regulatory T cells to S1P is reduced, but its optimal suppressive activities require S1P. FTY720, a new class of immunomodulator, is rapidly phosphorylated by sphingosine kinase 2 in vivo to form the biologically active phosphorylated-FTY720 (FTY720-P), which closely resembles S1P. The FTY720-P is a true agonist for S1P1, S1P3, S1P4, and S1P5, it affects the tissue distribution and functional activity of T cells, B cells, dendritic cells and regulatory T cells. FTY720 were demonstrated to be a hypotoxic, great effective and reversible immunosuppressive efficacy to prevent allograft rejection and treat some autoimmune diseases. In this article, the synthesis and metabolism of S1P, the expression of S1P GPCRs in immune cells, the effect of S1P on immune cells, the drugs targeted to S1P GPCRs and their clinical implications are reviewed.

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).

Anti-bis(monoacylglycero)phosphate antibody accumulates acetylated LDL-derived cholesterol in cultured macrophages

Bis(monoacylglycero)phosphate (BMP), also called lysobisphosphatidic acid, is a phospholipid highly enriched in the internal membranes of multivesicular late endosomes, in which it forms specialized lipid domains. It has been suggested that BMP-rich membranes regulate cholesterol transport. Here, we examine the effects of an anti-BMP antibody on cholesterol metabolism and transport in two macrophage cell lines, RAW 264.7 and THP-1, during loading with acetylated low density lipoprotein (AcLDL). Anti-BMP antibody was internalized and accumulated in both macrophage cell types. Cholesterol staining with filipin and mass measurements indicate that AcLDL-stimulated accumulation of free cholesterol (FC) was enhanced in macrophages that had accumulated the antibody. Unlike the hydrophobic amine U18666A (3-beta-[2-(diethylamino)ethoxy]androst-5-en-17-one), esterification of AcLDL-derived cholesterol by ACAT was not modified after anti-BMP treatment. AcLDL loading led to an increase of FC in the plasma membrane. This increase was further enhanced in anti-BMP-treated macrophages. However, cholesterol efflux to HDL was reduced in antibody-treated cells. These results suggest that the accumulation of anti-BMP antibody alters cholesterol homeostasis in AcLDL-loaded macrophages.

Targeting sphingosine-1-phosphate for cancer therapy

This review summarises some important new findings that implicate sphingosine-1-phosphate (S1P) as a potent tumorigenic and angiogenic agent released from cancerous tumours into the tumour microenvironment. Also explored is the novel concept that bioactive lipid signalling molecules, like S1P, can themselves be targets for rational drug design, thereby opening up an entire class of lipidomic-based therapeutics for oncology and other human diseases.

The role of the lysophospholipid sphingosine 1-phosphate in immune cell biology

Sphingosine 1-phosphate (S1P) has been shown to be a bioactive lipid mediator intimately involved in mediating a variety of immunological processes. In particular, S1P regulates lymphocyte cell trafficking between the lymphatic system and the blood. The lysophospholipid signals mainly through five related G protein-coupled receptor subtypes, termed S1P(1) to S1P(5). S1P(1) seems to play an essential role in cell trafficking, as this receptor subtype promotes the egress of T and B cells from secondary lymphatic organs. This S1P(1)-mediated migratory response is a consequence of different S1P levels in the serum and lymphatic organs. In addition to its direct effects on lymphocyte motility, S1P strengthens cell barrier integrity in sinus-lining endothelial cells, thereby reducing lymphocyte egress out of lymph nodes. Furthermore, S1P modulates cytokine profiles in T and dendritic cells, resulting in an elevated differentiation of T helper-2 cells during the T cell activation process. It is of interest that the mode of molecular action of the novel immunomodulator FTY720 interferes with the signaling of S1P. After phosphorylation, FTY720 shares structural similarity with S1P, but in contrast to the natural ligand, phosphorylated FTY720 induces a prolonged internalization of S1P(1), resulting in an impaired S1P-mediated migration of lymphocytes.

Sphingosine kinase and sphingosine-1-phosphate regulate migration, endocytosis and apoptosis of dendritic cells

Dendritic cells (DC) are inducers of primary immune responses and represent an attractive vector for cancer immunotherapy. Sphingosine kinase (SphK) and its product sphingosine-1-phosphate (S1P) play an important role in the regulation of immune cells and cancer, affecting processes such as differentiation, growth or migration. We studied the role of SphK and S1P on migration of DC. RT-PCR showed mRNA expression of SphK in DC, declining from immature (iDC) to mature DC (mDC) to antigen-loaded mDC. Expression of S1P receptors was S1P(1) > S1P(2) = S1P(3), unrelated to maturation or antigen uptake. In transwell assays, iDC migrated towards SDF-1, MIP-1alpha, MCP and S1P, whereby S1P combined with a chemokine had a synergistic effect. mDC migrated towards 6Ckine and MIP-3beta, but not towards S1P. The SphK-inhibitor dihydro-sphingosine (DHS) reduced migration of iDC but not of mDC. In addition S1P(3)-inhibitor suramin inhibited DC migration in response to S1P. DHS had a reverse effect on endocytosis, enhancing the uptake of FITC dextran. We also observed an anti-apoptotic effect of S1P on mDC for the first time. This indicates that SphK/S1P may play a role in accumulation of peripheral iDC at the location of antigen and subsequent antigen-uptake. These findings may help to optimise DC-based cancer immunotherapy by modulation of SphK/S1P.

Comprehensive analysis of monoclonal antibodies against detergent-insoluble membrane/lipid rafts of HL60 cells

Glycosphingolipids and cholesterol are principal components of plasmamembrane microdomains, i.e. lipid rafts. Recent studies revealed the possible presence of a variety of microdomains that distinctly differ in terms of their molecular composition and functions. To understand their precise structures and functions, we produced monoclonal antibodies (MAbs) by immunizing mice to the microdomains prepared from a fraction of detergent-insoluble membrane (DIM) of HL60 cells. Biochemical characterization of the antigen epitopes led to classification of the MAbs into two groups. One group consists of MAbs that react with lipids such as phosphatidylglucoside, lysophosphatidylinositol, and gangliosides (GM1a and GD1b), and the other consists of MAbs that react with proteins such as annexin I, aminopeptidase N and acrogranin. Immunofluorescence staining of HL60 cells with the MAbs, except for the MAbs that recognize lysophosphatidylinositol or annexin I, resulted in patchy-like images of the cell membranes. Interestingly, MAbs belonging to the former group had the potential to induce cell proliferation/differentiation in vitro. Our MAbs against the DIM fraction of HL60 cells can be valuable tools for the study of membrane microdomains.

Validation of an anti-sphingosine-1-phosphate antibody as a potential therapeutic in reducing growth, invasion, and angiogenesis in multiple tumor lineages

S1P has been proposed to contribute to cancer progression by regulating tumor proliferation, invasion, and angiogenesis. We developed a biospecific monoclonal antibody to S1P to investigate its role in tumorigenesis. The anti-S1P mAb substantially reduced tumor progression and in some cases eliminated measurable tumors in murine xenograft and allograft models. Tumor growth inhibition was attributed to antiangiogenic and antitumorigenic effects of the antibody. The anti-S1P mAb blocked EC migration and resulting capillary formation, inhibited blood vessel formation induced by VEGF and bFGF, and arrested tumor-associated angiogenesis. The anti-S1P mAb also neutralized S1P-induced proliferation, release of proangiogenic cytokines, and the ability of S1P to protect tumor cells from apoptosis in several tumor cell lines, validating S1P as a target for therapy.

Targeting sphingosine-1-phosphate: a novel avenue for cancer therapeutics

Sphingosine-1-phosphate (S1P) is a pleiotropic lipid mediator that has been shown to regulate cell growth, cell survival, cell invasion, vascular maturation, and angiogenesis, processes that are important for cancer progression. In this issue of Cancer Cell, Visentin et al. demonstrate that a monoclonal antibody that binds S1P with extremely high affinity and specificity significantly slows tumor progression and associated angiogenesis in several animal models of human cancer. Their results suggest that S1P not only affects tumor cells themselves, but also is permissive or required for the actions of angiogenic factors, and thus may be a bona fide cancer target.

Anti-lysobisphosphatidic acid antibodies in patients with antiphospholipid syndrome and systemic lupus erythematosus

Lyso(bis)phosphatidic acid (LBPA) is a novel antigenic target in anti-phospholipid syndrome (APS) and antibodies directed against LBPA (aLBPA) have been detected in sera from APS patients. In this study we first evaluated aLBPA in comparison with the most widely used methods (i.e. anticardiolipin [(aCL)-enzyme-linked immunosorbent assay (ELISA)] and antibeta-2-glycoprotein-I antibodies (abeta(2)-GPI-ELISA) utilized to detect antiphospholipid antibodies in patients with primary or secondary APS, systemic lupus erythematosus, chronic HCV infection and healthy subjects. We then assessed the relationship between aLBPA, lupus anticoagulant (LAC) and the main clinical manifestations of APS. Finally, we evaluated the presence of 'pure' (i.e. beta(2)-GPI-independent) aLBPA in patients with APS and controls. The results indicate that aLBPA as well as abeta(2)-GPI display higher specificity but lower sensitivity for APS compared to aCL. Moreover, serum aLBPA correlate closely with aCL and abeta(2)-GPI in APS patients and are strictly associated with LAC positivity. We demonstrate that beta(2)-GPI binds to LBPA with affinity similar to CL, and antibodies able to react with phosholipid-protein complex exist; however, 'pure' aLBPA can also be detected in sera of APS patients. Altogether these data confirm that LBPA may be an antigenic target in APS and that aLBPA are serological markers of APS with similar sensitivity and specificity compared to abeta(2)-GPI. However, the clinical utility of aLBPA detection alone or in combination with aCL and/or abeta(2)-GPI remains to be elucidated in larger and longitudinal studies.

The S1P-analog FTY720 differentially modulates T-cell homing via HEV: T-cell-expressed S1P1 amplifies integrin activation in peripheral lymph nodes but not in Peyer patches

Sphingosine-1-phosphate (S1P) and its receptor S1P1 control T-cell egress from thymus and secondary lymphoid organs (SLOs). To further define the role of S1P1 in lymphocyte trafficking, we performed adoptive transfer experiments and intravital microscopy (IVM) using both S1P1-/- lymphocytes and recipient wild-type (WT) mice treated with FTY720, an immunosuppressant that downmodulates S1P receptors. S1P1 deficiency and FTY720 caused rapid disappearance of T cells from blood, prolonged retention in SLOs, and accumulation in bone marrow, but did not alter interstitial T-cell motility in peripheral lymph nodes (PLNs) as assessed by multiphoton IVM. However, S1P1-/- lymphocytes displayed reduced short-term homing to PLNs due to attenuated integrin-mediated firm arrest in high endothelial venules (HEVs). By contrast, S1P1-/- T cells homed normally to Peyer patches (PPs), whereas S1P1-/- B cells had a marked defect in homing to PPs and arrested poorly in PP HEVs. Therefore, S1P1 not only controls lymphocyte egress from SLOs, but also facilitates in a tissue- and subset-specific fashion integrin activation during homing. Interestingly, FTY720 treatment enhanced accumulation of both S1P1 sufficient and S1P1-/- T cells in PPs by enhancing integrin-mediated arrest in HEVs. Thus, FTY720 exerts unique effects on T-cell traffic in PPs that are independent of T-cell-expressed S1P1.

Modulation of adaptive immune responses by sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) has long been recognized as a mediator of a variety of cell functions. A growing body of evidence has accumulated demonstrating its role in cell migration and as a mediator of growth factor-induced events. In recent years, it has become apparent that S1P also mediates many cytokine and chemokine functions. Cells of the immune system function and migrate in response to a complex network of cytokines and chemokines, and the outcome is determined by the interplay of the effects of these molecules on the target cell. S1P may be a bona fide component of these networks and influence the responses of cells to these immune modulators.

Serum lysophosphatidic acid concentrations measured by dot immunogold filtration assay in patients with acute myocardial infarction

In this study the relation between lysophosphatidic acid (LPA) and myocardial infarction was investigated, the typical and simplified methods for measuring serum LPA concentration by dot immunogold filtration assay (DIFA) based on a polyclonal antibody to LPA were developed, and serum LPA concentrations were measured in 31 patients with acute myocardial infarction (AMI) and 12 controls (blood donors) by DIFA. Serum LPA levels were raised more than twofold 8 h after the onset of AMI. Maximal elevation (10.43 mg/L) was found at 48-72 h following onset and remained higher than the control concentration (1.66 mg/L) 7 days after AMI. The rise in serum LPA concentration in AMI patients suggests that LPA might be involved in AMI-related pathophysiology in the cardiovascular system. The simplified DIFA developed in the present study for measuring serum LPA concentration is convenient and highly sensitive.

Sphingosine 1-phosphate induces antimicrobial activity both in vitro and in vivo

Sphingosine 1-phosphate (S1P), a polar sphingolipid metabolite, is involved in a wide spectrum of biological processes, including Ca(++) mobilization, cell growth, differentiation, motility, and cytoskeleton organization. Here, we show a novel role of S1P in the induction of antimicrobial activity in human macrophages that leads to the intracellular killing of nonpathogenic Mycobacterium smegmatis and pathogenic M. tuberculosis. Such activity is mediated by host phospholipase D, which favors the acidification of mycobacteria-containing phagosomes. Moreover, when it was intravenously injected in mycobacteria-infected mice, S1P reduced mycobacterial growth and pulmonary tissue damage. These results identify S1P as a novel regulator of the host antimicrobial effector pathways.

Sphingosine 1-phosphate and its type 1 G protein-coupled receptor: trophic support and functional regulation of T lymphocytes

The lysophospholipid (LPL) growth factors sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are generated by macrophages, dendritic cells, mast cells, and platelets, which leads to lymph and plasma concentrations of 0.1-1 microM. Distinctive profiles of G protein-coupled receptors (GPCRs) for S1P and LPA are expressed by each type of immune cell and are regulated by cellular activation. At 1-100 nM, S1P signals T cells through their principal S1P(1) GPCRs with consequent protection from apoptosis, enhancement of chemotaxis, and facilitation of optimal regulatory activity of CD4(+)25(+) T cells. At 0.3-3 microM, S1P inhibits T cell chemotaxis and to a lesser extent other functions. These S1P-S1P(1) GPCR signals suppress 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 decrease in lymphoid tissue traffic of T cells in transgenic mice, which overexpress lymphocyte S1P(1) GPCRs. The immunotherapeutic activity of S1P(1) GPCR antagonists, which limits T cell access to organ grafts and autoimmune antigens, does not reduce other functional capabilities of T cells. LPLs and their GPCRs thus constitute an immunoregulatory system of sufficient prominence for pharmacological targeting in transplantation, autoimmunity, and immunodeficiency.

Signaling and biological actions of sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) is a product of sphingomyelin (SM) metabolism. It is present in most eukaryotic organisms; however, in higher vertebrates (bony fishes to mammals), it is utilized as a regulator of cell function by binding to extracellular receptors. Its role as a second messenger function was originally proposed; however, the unequivocal role of S1P as a second messenger in higher eukaryotes is lacking at present. As an extracellular mediator, S1P binds to a family of G-protein-coupled receptors named S1P(1-5), originally referred to as (EDG-1, 3, 5, 6 and 8). These receptors couple to multiple G-proteins and regulate intracellular signaling pathways. Most tissues express one or more S1P receptor subtypes; therefore, S1P is known as a multifunctional physiologic mediator. Its precise physiologic roles in multiple organ systems are just beginning to be elucidated; however, at present, regulation of cardiogenesis, vascular system formation, oocyte survival and immune cell trafficking has been recently reported. Currently, a S1P receptor agonist, is undergoing clinical trials as an agent to fight organ transplant rejection. Since S1P is a fundamental multifunctional mediator, better understanding of the biology of S1P holds great promise to develop novel tools to control various diseases.

Lysophospholipids and their G protein-coupled receptors in inflammation and immunity

Among the family of lipid-derived mediators, the group of lysophospholipids including lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) have growth-related and -unrelated effects on diverse cell types including lymphocytes, macrophages, smooth muscle cells, endothelial cells, and neuronal cells. This review summarizes the known effects of lysophospholipids and their G protein-coupled receptors (GPCRs) in inflammation and immunity. Lysophospholipids have the capacity to evoke and modulate immune responses by attracting and activating T-cells, B-cells and macrophages directly and influencing their interactions with other cell types. Immune cells express multiple subsets of lysophospholipid receptors, which are critical for specific cellular responses such as proliferation and migration that are fundamental to immunity. Investigation of the expression pattern of EDG-receptors on human T-cells revealed a dynamic transcriptional regulation influenced by both developmental stages and activation states. Other lipid mediators like psychosine and other GPCRs for lipid mediators like G2A also may be involved in the development of normal immune and inflammatory reactions and diseases. These observations suggest that agonists and antagonists for lysophospholipid receptors may influence immune responses.

Lysophospholipid mediators of immunity and neoplasia

Lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P) and some other structurally related lysophospholipids are active growth factors and stimuli for diverse cellular functions. LPA and S1P promote early T cell migration to tissue sites of immune responses and regulate T cell proliferation and secretion of numerous cytokines. Edg-4 (LPA2) LPA receptors, which are constitutively expressed by helper T cells, and Edg-2 (LPA1) LPA receptors, which are expressed only by activated helper T cells, transduce opposite effects of LPA on some T cell responses. A similar mechanism is observed for fine regulation of Edg R-mediated effects of LPA on ovarian cancer cells. Edg-4 (LPA2) R transduces proliferative responses, recruitment of autocrine protein growth factors, and migration of ovarian cancer cells, whereas Edg-2 (LPA1) R transduces inhibition of Edg-4 (LPA2) R-mediated responses and concurrently elicits apoptosis and anoikis of ovarian cancer cells. Edg-4 (LPA2) R is a distinctive functional marker for ovarian carcinoma, and is expressed both as the wild-type and a carboxyl-terminally extended gain-of-function mutant. Newly discovered non-lipid agonists and antagonists for individual Edg receptors will permit more sophisticated analyses of their respective contributions in human biology and pathophysiology, and may represent novel therapeutic modalities in immune disorders and cancer.

Evidence for anticoagulant activity and beta2-GPI accumulation in late endosomes of endothelial cells induced by anti-LBPA antibodies

This investigation was undertaken to test whether anti-LBPA antibodies and IgG from patients with APS interfere with intracellular beta2GPI distribution in EAhy926 endothelial cells and with the coagulation system. Cell incubation with anti-LBPA MoAb or with patients' IgG resulted in antibody binding to late endosomes and caused beta2GPI redistribution and accumulation within perinuclear vesicular structures reminiscent of late endosomes. This finding suggests that aPI may contribute to the pathogenic mechanisms of APS by modifying the intracellular traffic of proteins, by interactions between aPl and LBPA, beta2GPI and/or LBPA-beta2GPI complexes. The anticoagulant activity of anti-LBPA MoAb was analyzed in a sensitized activated partial thromboplastin time (aPTT) system and in a dilute Russell's viper venom time (dRVVT). A significant, concentration-dependent effect of the antibody on both aPTT and dRVVT prolongation was found. These observations suggest that LBPA is an important lipid target for aPl with potential functional implications for the immunopathogenesis of APS.

Localization of lysobisphosphatidic acid-rich membrane domains in late endosomes

Late endosomes accumulate internal membranes within the lumen of the organelle. These internal membranes are enriched in the late endosome specific phospholipid, lysobisphosphatidic acid (LBPA). The organization of LBPA-rich membrane domains is not well characterized. Using an LBPA-specific monoclonal antibody (6C4), we show that these membrane domains are not accessible from the cytoplasm. Using fluorescence correlation spectroscopy, we also show that 6C4 only binds sonicated, but not intact, late endosomes, presumably reflecting the release of internal membranes upon endosome rupture.

Production and application of LPA polyclonal antibody

By using colloidal gold as a hapten carrier, a kind of antibody against lysophosphatidic acid (LPA) was developed and used to successfully detect 500 ng/mL LPA in dot immunogold filtration assay. Such application of the LPA antibody could offer us a way to diagnose ovarian cancer at its early stage.

Cutting edge: differential constitutive expression of functional receptors for lysophosphatidic acid by human blood lymphocytes

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) from platelets and macrophages mediate T cell functions. Endothelial differentiation gene-encoded G protein-coupled receptors (Edg Rs) are specific for S1P (Edg-1, -3, -5, and -8 Rs) and LPA (Edg-2, -4, and -7 Rs). Human T cell tumors express many Edg Rs for both LPA and S1P. In contrast, human blood CD4+ T cells express predominantly Edg-4, and CD8+ T cells show only traces of Edg-2 and -5, by quantification of mRNA and Edg R Ags. LPA at 10-10-10-6 M suppressed significantly the secretion of IL-2 from anti-CD3 plus anti-CD28 Ab-challenged CD4+ T cells, but not CD8+ T cells. Monoclonal anti-Edg-4 R Ab, like LPA, suppressed stimulated IL-2 secretion from CD4+ T cells, but not CD8+ T cells. Constitutive expression of Edg-4 by CD4+, but not CD8+, human T cells accounts for differential functional responsiveness of the T cell subsets to LPA.

Sera from children with type 1 diabetes mellitus react against a new group of antigens composed of lysophospholipids

Several autoantibodies related to Type 1 diabetes mellitus and their corresponding autoantigens have been previously identified. While peptide antigens are more widely recognized, lipid antigens like sulfatides and gangliosides are also known epitopes for the diabetic humoral immune response. Islet cell antibodies (ICA) in Type 1 diabetes are heterogeneous immunoglobulins directed against selected antigens in the islets of Langerhans. Moreover, ICA may be the best predictive marker of disease in family members of patients with Type 1 diabetes. The aims of this study were: (1) to purify lipids from porcine pancreas that contain ICA epitopes; (2) to characterize these lipid antigens, and (3) to use the purified lipids in an assay to detect antibodies in patients with Type 1 diabetes. A unique family of 4 lysophospholipids, 1 fully characterized as lysophosphatidylmyoinositol, partially inhibited ICA staining, and therefore, were considered to be candidate antigens for an ICA immunoassay. Using a dot blot immunoassay, we detected antibodies directed against these phospholipids in 28 out of 46 (61%) diabetic sera, while detecting only 1 false positive out of 28 nondiabetic sera (3.6%; p < 0.0001 comparing diabetic vs. nondiabetic serum). Therefore, lysophospholipid immunoassay positivity is present in sera of Type 1 diabetic patients. Furthermore, we detected 15 out of 23 ICA-negative diabetic sera (65.2%), showing that our phospholipid immunoassay does not correlate with ICA positivity.

Interaction of anti-phospholipid antibodies with late endosomes of human endothelial cells

Anti-phospholipid antibodies (APLAs) are associated with thrombosis and/or recurrent pregnancy loss. APLAs bind to anionic phospholipids directly or indirectly via a cofactor such as beta(2)-glycoprotein 1 (beta(2)GPI). The lipid target of APLA is not yet established. Recently, we observed that APLAs in vitro can bind lysobisphosphatidic acid (LBPA). The internal membranes of late endosomes are enriched in this phospholipid. The current study was undertaken to determine to what extent binding of APLA to LBPA is correlated with binding to cardiolipin and to beta(2)GPI and to determine whether patient antibodies interact with late endosomes of human umbilical vein endothelial cells (HUVECs) and thus modify the intracellular trafficking of proteins. Binding of patient immunoglobulin G (n=37) to LBPA was correlated significantly with binding to cardiolipin. Although LBPA binding was correlated to a lesser extent with beta(2)GPI binding, we observed that beta(2)GPI binds with high affinity to LBPA. Immunofluorescence studies showed that late endosomes of HUVECs contain LBPA. Patient but not control antibodies recognized late endosomes, but not cardiolipin-rich mitochondria, even when we used antibodies that were immunopurified on cardiolipin. Incubation of HUVECs with patient plasma samples immunoreactive toward LBPA resulted in an accumulation of the antibodies in late endosomes and led to a redistribution of the insulinlike growth factor 2/mannose-6-phosphate receptor from the Golgi apparatus to late endosomes. Our results suggest that LBPA is an important lipid target of APLA in HUVECs. These antibodies are internalized by the cells and accumulate in late endosomes. By modifying the intracellular trafficking of proteins, APLA could contribute to several of the proposed pathogenic mechanisms leading to the antiphospholipid syndrome.

Cooperation of fibronectin with lysophosphatidic acid induces motility and transcellular migration of rat ascites hepatoma cells

We have previously shown that the transcellular migration of rat ascites hepatoma (AH130-MM1) cells through a cultured mesothelial cell monolayer (MCL) is triggered with lysophosphatidic acid (LPA) that stimulates actin polymerization and myosin light chain phosphorylation through the activation of Rho-ROCK (Rho-kinase) cascade. When, however, the motility of MM1 cells on a glass surface was tested by phagokinetic track motility assay, LPA failed to induce the motility. Nevertheless, when the glass had been coated with fibronectin (FN), LPA could induce phagokinetic motility which was accompanied by transformation of MM1 cells to fusiform-shape and assembly of focal adhesion. beta1 integrin, the counter receptor of FN, was expressed on MM1 cells. Anti-FN antibody, anti-beta1 integrin antibody and cyclo-GRGDSPA remarkably suppressed LPA-induced phagokinetic motility. These antibodies suppressed LPA-induced transcellular migration through MCL, as well. These results indicate that actin polymerization and phosphorylation of myosin light chain through Rho activation are insufficient for inducing motility but the cooperative FN/beta1 integrin-mediated adhesion is necessary for both the phagokinetic motility and transcellular migration of MM1 cells.

A lipid associated with the antiphospholipid syndrome regulates endosome structure and function

Little is known about the structure and function of membrane domains in the vacuolar apparatus of animal cells. A unique feature of late endosomes, which are part of the pathway that leads to lysosomes, is that they contain a complex system of poorly characterized internal membranes in their lumen. These endosomes are therefore known as multivesicular or multilamellar organelles. Some proteins distribute preferentially within these internal membranes, whereas others are exclusively localized to the organelle's limiting membrane. The composition and function of this membrane system are poorly understood. Here we show that these internal membranes contain large amounts of a unique lipid, and thus form specialized domains within endosomes. These specialized domains are involved in sorting the multifunctional receptor for insulin-like growth factor 2 and ligands bearing mannose-6-phosphate, in particular lysosomal enzymes. We also show that this unique lipid is a specific antigen for human antibodies associated with the antiphospholipid syndrome. These antibodies may act intracellularly by altering the protein-sorting functions of endosomes.

Lysophosphatidylethanolamine is the antigen to which apparent antibody to phosphatidylethanolamine binds

Because binding of antiphospholipid antibody (aPL) to phosphatidylethanolamine (PE) is central to the definition of the antigenic epitope targeted by aPLs, we examined the binding of aPL-positive SLE sera to PE under various conditions. No serum bound to PE uncontaminated with lysophosphatidylethanolamine (1PE), but many aPL-positive sera bound to 1PE-contaminated PE and to 1PE coated onto an ELISA plate. Absorption studies indicated partial cross-reactivity between PE containing 1PE and cardiolipin. We conclude that clinical aPLs do not bind to PE. Prior reports to the contrary most likely represent binding of aPL to PE's degradation product, 1PE.