Apolipoprotein-mediated pathways of lipid antigen presentation

Myeloid apolipoprotein E controls dendritic cell antigen presentation and T cell activation

Cholesterol homeostasis has a pivotal function in regulating immune cells. Here we show that apolipoprotein E (apoE) deficiency leads to the accumulation of cholesterol in the cell membrane of dendritic cells (DC), resulting in enhanced MHC-II-dependent antigen presentation and CD4⁺ T-cell activation. Results from WT and apoE KO bone marrow chimera suggest that apoE from cells of hematopoietic origin has immunomodulatory functions, regardless of the onset of hypercholesterolemia. Humans expressing apoE4 isoform (ε4/3–ε4/4) have increased circulating levels of activated T cells compared to those expressing WT apoE3 (ε3/3) or apoE2 isoform (ε2/3–ε2/2). This increase is caused by enhanced antigen-presentation by apoE4-expressing DCs, and is reversed when these DCs are incubated with serum containing WT apoE3. In summary, our study identifies myeloid-produced apoE as a key physiological modulator of DC antigen presentation function, paving the way for further explorations of apoE as a tool to improve the management of immune diseases.

Cholesterol homeostasis can modulate immunity via multiple pathways. Here the authors show that apolipoprotein E, an important regulator of cholesterol, produced by myeloid cells can regulate T cell activation by controlling the antigen presentation activity of dendritic cells in both humans and mice.

T Cells in Atherosclerosis in Ldlr-/- and Apoe-/- Mice

Atherosclerosis is the underlying basis for most cardiovascular diseases. It is a chronic inflammation affecting the arterial intima and is promoted by hypercholesterolemia. Cells of both the innate and adaptive immune systems contribute to this inflammation with macrophages and T cells being the most abundant immune cells in the atherosclerotic plaques. In this review, we discuss the studies that examined the role of T cells and T cell subsets in Apoe-/- and Ldlr-/- murine models of atherosclerosis. While there is a general consensus that Th1 cells are pro-atherogenic and regulatory T cells are atheroprotective, the role of other subsets is more ambiguous. In addition, the results in the two models of atherosclerosis do not always yield similar results. Additional studies in the two murine models using cell specific gene manipulations are needed.

The role of apolipoprotein E (rs7412 and rs429358) in age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the most common cause of incurable visual impairment in the developed countries. The main pathological change in AMD is the formation of drusen containing 40% of lipids, dominated by esterified cholesterol (EC) and phosphatidylcholine (PC), and protein. Haplotype ε4 of apolipoprotein E (ApoE) acts as a ligand for the low-density lipoprotein receptor and is involved in the maintenance and repair of neuronal cell membranes.

PURPOSE

This study aimed to evaluate the association of AMD with ApoE gene polymorphism variants (rs7412 and rs429358).

METHODOLOGY

A total of 2133 subjects were enrolled in our research. The study group comprised patients with early AMD (n = 413) and exudative AMD (n = 307), and the control group enrolled randomly selected persons (n = 1413). The genotyping of ApoE (rs7412 and rs429358) was performed using the real-time polymerase chain reaction (PCR) method.

RESULTS

Statistical analysis revealed that ApoE 4/2 genotype was less frequently observed in in older patients with exudative AMD compared to older healthy controls (0.4% vs. 4.0%, p = 0.003).

CONCLUSION

Our data demonstrated that ApoE 4/2 genotype was less frequently observed in old patients (65 years and more) with exudative AMD compared to old healthy controls. It leads to hypothesis on the protective effect of ApoE 4/2 to develop AMD in the elderly.

Preconditioning by Hydrogen Peroxide Enhances Multiple Properties of Human Decidua Basalis Mesenchymal Stem/Multipotent Stromal Cells

Stem cell-based therapies rely on stem cell ability to repair in an oxidative stress environment. Preconditioning of mesenchymal stem cells (MSCs) to a stress environment has beneficial effects on their ability to repair injured tissues. We previously reported that MSCs from the decidua basalis (DBMSCs) of human placenta have many important cellular functions that make them potentially useful for cell-based therapies. Here, we studied the effect of DBMSC preconditioning to a stress environment. DBMSCs were exposed to various concentrations of hydrogen peroxide (H₂O₂), and their functions were then assessed. DBMSC expression of immune molecules after preconditioning was also determined. DBMSC preconditioning with H₂O₂ enhanced their proliferation, colonogenicity, adhesion, and migration. In addition, DBMSCs regardless of H₂O₂ treatment displayed antiangiogenic activity. H₂O₂ preconditioning also increased DBMSC expression of genes that promote cellular functions and decreased the expression of genes, which have opposite effect on their functions. Preconditioning also reduced DBMSC expression of IL-1β, but had no effects on the expression of other immune molecules that promote proliferation, adhesion, and migration. These data show that DBMSCs resist a toxic environment, which adds to their potential as a candidate stem cell type for treating various diseases in hostile environments.

Role of lipid transfer proteins in loading CD1 antigen-presenting molecules

Research to connect lipids with immunology is growing, but details about the specific roles of lipid transfer proteins (LTPs) in antigen presentation remain unclear. A single class of major histocompatibility class-like molecules, called CD1 molecules, can present lipids and glycolipids to the immune system. These molecules all have a common hydrophobic antigen-binding groove. The loading of this groove with various lipids throughout the life of a CD1 molecule defines the immune recognition of lipids by T cells. At each location of residence, CD1 molecules are exposed to particular physicochemical conditions, particular collections of lipids, and unique combinations of LTPs that will define which lipids bind to CD1 and which do not. The lipid transfer machinery that is used by CD1 molecules is entirely hijacked from the normal synthetic and catalytic pathways of lipids. The precise determinants that regulate the presentation of certain lipids over others with respect to chemistry, solubility, and abundance are still poorly defined and require investigation to allow the use of lipids as regular antigenic targets of immunotherapy and vaccine.

A review of the immunologic findings observed in retinitis pigmentosa

Most patients suffering from retinitis pigmentosa (RP) inherit the disorder; however, the immune-pathologic features associated with this disease have yet to be extensively studied. Six reports correlate antiretinal immune activity with vision deterioration in RP patients. Some of these patients have sporadic RP that occurs in excess of expected gene segregation during inheritance. The hypothesis that a primary immune-mediated disease process occurs in this sporadic group is supported by significant associations of RP with autoimmune endocrinopathies and other immune-related conditions or factors; however, no immunologic difference regarding RP family history is reported in the peripheral blood studies of RP patients. Twenty-one percent to 51% of RP patients display antiretinal antibodies, whereas 19-58% have antiretinal lymphocyte reactivity to retinal extract, and 60-85% have activated T cells. Mutations in animal models of RP have been shown to cause endoplasmic reticulum stress that may initiate immunopathology for genetic RP, but oxidative stress also encourages immune cytotoxicity. In addition, necrotic cell death is evident, which promotes inflammatory conditions. We review mechanisms and evidence for an occult inflammation in genetic RP and examine reports of efficacy in retarding RP progression with anti-inflammatory agents in clinical trials.

Cell-specific production, secretion, and function of apolipoprotein E

Apolipoprotein E (apoE) is a 34-kDa glycoprotein that is secreted from many cells throughout the body. ApoE is best known for its role in lipoprotein metabolism. Recent studies underline the association of circulating lipoprotein-associated apoE levels and the development for cardiovascular disease (CVD). Besides its well-established role in pathology of CVD, it is also implicated in neurodegenerative diseases and recent new data on adipose-produced apoE point to a novel metabolic role for apoE in obesity. The regulation of apoE production and secretion is remarkably cell and tissue specific. Here, we summarize recent insights into the differential regulation apoE production and secretion by hepatocytes, monocytes/macrophages, adipocytes, and the central nervous system and relevant variations in apoE biochemistry and function.

Lipid metabolism and its implication in mycobacteria-host interaction

The complex lipids present in the cell wall of Mycobacterium tuberculosis (Mtb) act as major effector molecules that actively interact with the host, modulating its metabolism and stimulating the immune response, which in turn affects the physiology of both, the host cell and the bacilli. Lipids from the host are also nutrient sources for the pathogen and define the fate of the infection by modulating lipid homeostasis. Although new technologies and experimental models of infection have greatly helped understanding the different aspects of the host-pathogen interactions at the lipid level, the impact of this interaction in the Mtb lipid regulation is still incipient, mainly because of the low background knowledge in this area of research.

Plasma disturbance of phospholipid metabolism in major depressive disorder by integration of proteomics and metabolomics

INTRODUCTION

Major depressive disorder (MDD) is a highly prevalent mental disorder affecting millions of people worldwide. However, a clear causative etiology of MDD remains unknown. In this study, we aimed to identify critical protein alterations in plasma from patients with MDD and integrate our proteomics and previous metabolomics data to reveal significantly perturbed pathways in MDD. An isobaric tag for relative and absolute quantification (iTRAQ)-based quantitative proteomics approach was conducted to compare plasma protein expression between patients with depression and healthy controls (CON).

METHODS

For integrative analysis, Ingenuity Pathway Analysis software was used to analyze proteomics and metabolomics data and identify potential relationships among the differential proteins and metabolites.

RESULTS

A total of 74 proteins were significantly changed in patients with depression compared with those in healthy CON. Bioinformatics analysis of differential proteins revealed significant alterations in lipid transport and metabolic function, including apolipoproteins (APOE, APOC4 and APOA5), and the serine protease inhibitor. According to canonical pathway analysis, the top five statistically significant pathways were related to lipid transport, inflammation and immunity.

CONCLUSION

Causal network analysis by integrating differential proteins and metabolites suggested that the disturbance of phospholipid metabolism might promote the inflammation in the central nervous system.

Integrative Analysis to Identify Common Genetic Markers of Metabolic Syndrome, Dementia, and Diabetes

BACKGROUND Emerging data have established links between systemic metabolic dysfunction, such as diabetes and metabolic syndrome (MetS), with neurocognitive impairment, including dementia. The common gene signature and the associated signaling pathways of MetS, diabetes, and dementia have not been widely studied. MATERIAL AND METHODS We exploited the translational bioinformatics approach to choose the common gene signatures for both dementia and MetS. For this we employed "DisGeNET discovery platform". RESULTS Gene mining analysis revealed that a total of 173 genes (86 genes common to all three diseases) which comprised a proportion of 43% of the total genes associated with dementia. The gene enrichment analysis showed that these genes were involved in dysregulation in the neurological system (23.2%) and the central nervous system (20.8%) phenotype processes. The network analysis revealed APOE, APP, PARK2, CEPBP, PARP1, MT-CO2, CXCR4, IGFIR, CCR5, and PIK3CD as important nodes with significant interacting partners. The meta-regression analysis showed modest association of APOE with dementia and metabolic complications. The directionality of effects of the variants on Alzheimer disease is generally consistent with previous observations and did not differ by race/ethnicity (p>0.05), although our study had low power for this test. CONCLUSIONS Our novel approach showed APOE as a common gene signature with a link to dementia, MetS, and diabetes. Future gene association studies should focus on the association of gene polymorphisms with multiple disease models to identify novel putative drug targets.

Plan B (-cell) in atherosclerosis

Atherosclerosis is a leading cause of death worldwide. It is a complex chronic inflammatory disease involving interactions between vascular, circulating and immune cells. B cells play an important role in chronic inflammation producing antibodies and regulating T and natural killer (NKT) cell activation. The role of B cells in atherosclerosis is complex, with atherogenic and protective roles assigned for distinct B cell subsets. Drugs that deplete B cells or modulate their functions are now used in the treatment of various autoimmune diseases in humans. Here, we briefly review the roles of B cell subsets in atherogenesis, and emphasize the potential impact of B cell targeted therapies on the cardiovascular risk of treated patients. Developing more B cell subset-specific therapies would lead to more effective treatments with enhanced safety profile.

Glycolipid-peptide conjugate vaccines enhance CD8+ T cell responses against human viral proteins

An important goal of vaccination against viruses and virus-driven cancers is to elicit cytotoxic CD8⁺ T cells specific for virus-derived peptides. CD8⁺ T cell responses can be enhanced by engaging help from natural killer T (NKT) cells. We have produced synthetic vaccines that induce strong peptide-specific CD8⁺ T cell responses in vivo by incorporating an NKT cell-activating glycolipid. Here we examine the effect of a glycolipid-peptide conjugate vaccine incorporating an NKT cell-activating glycolipid linked to an MHC class I-restricted peptide from a viral antigen in human peripheral blood mononuclear cells. The vaccine induces CD1d-dependent activation of human NKT cells following enzymatic cleavage, activates human dendritic cells in an NKT-cell dependent manner, and generates a pool of activated antigen-specific CD8⁺ T cells with cytotoxic potential. Compared to unconjugated peptide, the vaccine upregulates expression of genes encoding interferon-γ, CD137 and granzyme B. A similar vaccine incorporating a peptide from the clinically-relevant human papilloma virus (HPV) 16 E7 oncoprotein induces cytotoxicity against peptide-expressing targets in vivo, and elicits a better antitumor response in a model of E7-expressing lung cancer than its unconjugated components. Glycolipid-peptide conjugate vaccines may prove useful for the prevention or treatment of viral infections and tumors that express viral antigens.

The lipid-sensor TREM2 aggravates disease in a model of LCMV-induced hepatitis

Lipid metabolism is increasingly being appreciated to affect immunoregulation, inflammation and pathology. In this study we found that mice infected with lymphocytic choriomeningitis virus (LCMV) exhibit global perturbations of circulating serum lipids. Mice lacking the lipid-sensing surface receptor triggering receptor expressed on myeloid cells 2 (Trem2 ^-/-) were protected from LCMV-induced hepatitis and showed improved virus control despite comparable virus-specific T cell responses. Non-hematopoietic expression of TREM2 was found to be responsible for aggravated hepatitis, indicating a novel role for TREM2 in the non-myeloid compartment. These results suggest a link between virus-perturbed lipids and TREM2 that modulates liver pathogenesis upon viral infection. Targeted interventions of this immunoregulatory axis may ameliorate tissue pathology in hepatitis.

Integration of Metabolomics and Transcriptomics Reveals a Complex Diet of Mycobacterium tuberculosis during Early Macrophage Infection

The nutrients consumed by intracellular pathogens are mostly unknown. This is mainly due to the challenge of disentangling host and pathogen metabolism sharing the majority of metabolic pathways and hence metabolites. Here, we investigated the metabolic changes of Mycobacterium tuberculosis, the causative agent of tuberculosis, and its human host cell during early infection. To this aim, we combined gene expression data of both organisms and metabolite changes during the course of infection through integration into a genome-wide metabolic network. This led to the identification of infection-specific metabolic alterations, which we further exploited to model host-pathogen interactions quantitatively by flux balance analysis. These in silico data suggested that tubercle bacilli consume up to 33 different nutrients during early macrophage infection, which the bacteria utilize to generate energy and biomass to establish intracellular growth. Such multisubstrate fueling strategy renders the pathogen’s metabolism robust toward perturbations, such as innate immune responses or antibiotic treatments.

Nutrient acquisition from the host environment is crucial for the survival of intracellular pathogens, but conceptual and technical challenges limit our knowledge of pathogen diets. To overcome some of these technical roadblocks, we exploited an experimentally accessible model for early infection of human macrophages by Mycobacterium tuberculosis, the etiological agent of tuberculosis, to study host-pathogen interactions with a multi-omics approach. We collected metabolomics and complete transcriptome RNA sequencing (dual RNA-seq) data of the infected macrophages, integrated them in a genome-wide reaction pair network, and identified metabolic subnetworks in host cells and M. tuberculosis that are modularly regulated during infection. Up- and downregulation of these metabolic subnetworks suggested that the pathogen utilizes a wide range of host-derived compounds, concomitant with the measured metabolic and transcriptional changes in both bacteria and host. To quantify metabolic interactions between the host and intracellular pathogen, we used a combined genome-scale model of macrophage and M. tuberculosis metabolism constrained by the dual RNA-seq data. Metabolic flux balance analysis predicted coutilization of a total of 33 different carbon sources and enabled us to distinguish between the pathogen’s substrates directly used as biomass precursors and the ones further metabolized to gain energy or to synthesize building blocks. This multiple-substrate fueling confers high robustness to interventions with the pathogen’s metabolism. The presented approach combining multi-omics data as a starting point to simulate system-wide host-pathogen metabolic interactions is a useful tool to better understand the intracellular lifestyle of pathogens and their metabolic robustness and resistance to metabolic interventions.

IMPORTANCE The nutrients consumed by intracellular pathogens are mostly unknown. This is mainly due to the challenge of disentangling host and pathogen metabolism sharing the majority of metabolic pathways and hence metabolites. Here, we investigated the metabolic changes of Mycobacterium tuberculosis, the causative agent of tuberculosis, and its human host cell during early infection. To this aim, we combined gene expression data of both organisms and metabolite changes during the course of infection through integration into a genome-wide metabolic network. This led to the identification of infection-specific metabolic alterations, which we further exploited to model host-pathogen interactions quantitatively by flux balance analysis. These in silico data suggested that tubercle bacilli consume up to 33 different nutrients during early macrophage infection, which the bacteria utilize to generate energy and biomass to establish intracellular growth. Such multisubstrate fueling strategy renders the pathogen’s metabolism robust toward perturbations, such as innate immune responses or antibiotic treatments.

Efficient Targeting and Activation of Antigen-Presenting Cells In Vivo after Modified mRNA Vaccine Administration in Rhesus Macaques

mRNA vaccines are rapidly emerging as a powerful platform for infectious diseases because they are well tolerated, immunogenic, and scalable and are built on precise but adaptable antigen design. We show that two immunizations of modified non-replicating mRNA encoding influenza H10 hemagglutinin (HA) and encapsulated in lipid nanoparticles (LNP) induce protective HA inhibition titers and H10-specific CD4⁺ T cell responses after intramuscular or intradermal delivery in rhesus macaques. Administration of LNP/mRNA induced rapid and local infiltration of neutrophils, monocytes, and dendritic cells (DCs) to the site of administration and the draining lymph nodes (LNs). While these cells efficiently internalized LNP, mainly monocytes and DCs translated the mRNA and upregulated key co-stimulatory receptors (CD80 and CD86). This coincided with upregulation of type I IFN-inducible genes, including MX1 and CXCL10. The innate immune activation was transient and resulted in priming of H10-specific CD4⁺ T cells exclusively in the vaccine-draining LNs. Collectively, this demonstrates that mRNA-based vaccines induce type-I IFN-polarized innate immunity and, when combined with antigen production by antigen-presenting cells, lead to generation of potent vaccine-specific responses.

Four pathways of CD1 antigen presentation to T cells

CD1a, CD1b, CD1c and CD1d proteins migrate through distinct subcellular compartments of antigen presenting cells and so can be considered to take four separate pathways leading to display of lipid antigens to T cell receptors. This review discusses the intersection of CD1 trafficking and lipid antigen loading mechanisms in cells, highlighting key controversies relating to CD1 gene expression, size mismatches between antigens and CD1 binding clefts and unexpected mechanisms of T cell receptor-based recognition.

The processing and presentation of lipids and glycolipids to the immune system

The recognition of CD1-lipid complexes by T cells was discovered 20 years ago and has since been an emerging and expanding field of investigation. Unlike protein antigens, which are presented on MHC class I and II molecules, lipids can only be presented by CD1 molecules, a unique family of MHC-like proteins whose singularity is a hydrophobic antigen-binding groove. The processing and loading of lipid antigens inside this groove of CD1 molecules require localization to endosomal and lysosomal subcellular compartments and their acidic pHs. This particular environment provides the necessary glycolytic enzymes and lipases that process lipid and glycolipid antigens, as well as a set of lipid transfer proteins that load the final version of the antigen inside the groove of CD1. The overall sequence of events needed for efficient presentation of lipid antigens is now understood and presented in this review. However, a large number of important details have been elusive. This elusiveness is linked to the inherent technical difficulties of studying lipids and the lipid-protein interface in vitro and in vivo. Here, we will expose some of those limitations and describe new approaches to address them during the characterization of lipids and glycolipids antigen presentation.

Emerging Roles of Apolipoprotein E and Apolipoprotein A-I in the Pathogenesis and Treatment of Lung Disease

Emerging roles are being recognized increasingly for apolipoproteins in the pathogenesis and treatment of lung diseases on the basis of their ability to suppress inflammation, oxidative stress, and tissue remodeling, and to promote adaptive immunity and host defense. Apolipoproteins, such as apolipoprotein E (apoE) and apolipoprotein A-I (apoA-I), are important components of lipoprotein particles that facilitate the transport of cholesterol, triglycerides, and phospholipids between plasma and cells. ApoE-containing lipoprotein particles are internalized into cells by low-density lipoprotein receptors (LDLRs), whereas apoA-I can interact with the ATP-binding cassette subfamily A member 1 (ABCA1) transporter to efflux cholesterol and phospholipids out of cells. ApoE and apoA-I also mediate receptor-independent effects, such as binding to and neutralizing LPS. Both apoE and apoA-I are expressed by lung cells, which allows apoE/LDLR- and apoA-I/ABCA1-dependent pathways to modulate normal lung health and the pathogenesis of respiratory diseases, including asthma, acute lung injury, cancer, emphysema, pulmonary fibrosis, and pulmonary hypertension. Data from human studies and research using experimental murine model systems have shown that both apoE and apoA-I pathways play primarily protective roles in lung biology and respiratory disease. Furthermore, apolipoprotein mimetic peptides, corresponding to the LDLR-binding domain of apoE or the class A amphipathic α-helical structure of apoA-I, have antiinflammatory and antioxidant effects that attenuate the severity of lung disease in murine models. Thus, the development of inhaled apolipoprotein mimetic peptides as a novel treatment paradigm could represent a significant advance for patients with respiratory disease who do not respond to current therapies.

Expression profiles of cholesterol metabolism-related genes are altered during development of experimental autoimmune encephalomyelitis in the rat spinal cord

Increased evidence suggests that dysregulation of cholesterol metabolism may be a key event contributing to progression of multiple sclerosis (MS). Using an experimental autoimmune encephalomyelitis (EAE) model of MS we revealed specific changes in the mRNA and protein expression of key molecules involved in the maintaining of cholesterol homeostasis in the rat spinal cord: 3-hydroxy-3-methylglutaryl-coenzyme-A reductase (HMGCR), apolipoprotein E (ApoE) and cholesterol 24-hydroxylase (CYP46A1) during the course of disease. The presence of myelin lipid debris was seen only at the peak of EAE in demyelination loci being efficiently removed during the recovery period. Since CYP46A1 is responsible for removal of cholesterol excess, we performed a detailed profiling of CYP46A1 expression and revealed regional and temporal specificities in its distribution. Double immunofluorescence staining demonstrated CYP46A1 localization with neurons, infiltrated macrophages, microglia and astrocytes in the areas of demyelination, suggesting that these cells play a role in cholesterol turnover in EAE. We propose that alterations in the regulation of cholesterol metabolism at the onset and peak of EAE may add to the progression of disease, while during the recovery period may have beneficial effects contributing to the regeneration of myelin sheath and restoration of neuronal function.

Reciprocal Crosstalk between Dendritic Cells and Natural Killer T Cells: Mechanisms and Therapeutic Potential

Natural killer T cells carrying a highly conserved, semi-invariant T cell receptor (TCR) [invariant natural killer T (iNKT) cells] are a subset of unconventional T lymphocytes that recognize glycolipids presented by CD1d molecules. Although CD1d is expressed on a variety of hematopoietic and non-hematopoietic cells, dendritic cells (DCs) are key presenters of glycolipid antigen in vivo. When stimulated through their TCR, iNKT cells rapidly secrete copious amounts of cytokines and induce maturation of DCs, thereby facilitating coordinated stimulation of innate and adaptive immune responses. The bidirectional crosstalk between DCs and iNKT cells determines the functional outcome of iNKT cell-targeted responses and iNKT cell agonists are used and currently being evaluated as adjuvants to enhance the efficacy of antitumor immunotherapy. This review illustrates mechanistic underpinnings of reciprocal DCs and iNKT cell interactions and discusses how those can be harnessed for cancer therapy.

Autoreactivity to Sulfatide by Human Invariant NKT Cells

Invariant NKT (iNKT) cells are innate-like lymphocytes that recognize lipid Ags presented by CD1d. The prototypical Ag, α-galactosylceramide, strongly activates human and mouse iNKT cells, leading to the assumption that iNKT cell physiology in human and mouse is similar. In this article, we report the surprising finding that human, but not mouse, iNKT cells directly recognize myelin-derived sulfatide presented by CD1d. We propose that sulfatide is recognized only by human iNKT cells because of the unique positioning of the 3-O-sulfated β-galactose headgroup. Surface plasmon resonance shows that the affinity of human CD1d-sulfatide for the iNKT cell receptor is relatively low compared with CD1d-α-galactosylceramide (K_D of 19-26 μM versus 1 μM). Apolipoprotein E isolated from human cerebrospinal fluid carries sulfatide that can be captured by APCs and presented by CD1d to iNKT cells. APCs from patients with metachromatic leukodystrophy, who accumulate sulfatides due to a deficiency in arylsulfatase-A, directly activate iNKT cells. Thus, we have identified sulfatide as a self-lipid recognized by human iNKT cells and propose that sulfatide recognition by innate T cells may be an important pathologic feature of neuroinflammatory disease and that sulfatide in APCs may contribute to the endogenous pathway of iNKT cell activation.

Inhibition of endocytic lipid antigen presentation by common lipophilic environmental pollutants

Environmental pollutants as non-heritable factors are now recognized as triggers for multiple human inflammatory diseases involving T cells. We postulated that lipid antigen presentation mediated by cluster of differentiation 1 (CD1) proteins for T cell activation is susceptible to lipophilic environmental pollutants. To test this notion, we determined whether the common lipophilic pollutants benzo[a]pyrene and diesel exhaust particles impact on the activation of lipid-specific T cells. Our results demonstrated that the expression of CD1a and CD1d proteins, and the activation of CD1a- and CD1d-restricted T cells were sensitively inhibited by benzo[a]pyrene even at the low concentrations detectable in exposed human populations. Similarly, diesel exhaust particles showed a marginal inhibitory effect. Using transcriptomic profiling, we discovered that the gene expression for regulating endocytic and lipid metabolic pathways was perturbed by benzo[a]pyrene. Imaging flow cytometry also showed that CD1a and CD1d proteins were retained in early and late endosomal compartments, respectively, supporting an impaired endocytic lipid antigen presentation for T cell activation upon benzo[a]pyrene exposure. This work conceptually demonstrates that lipid antigen presentation for T cell activation is inhibited by lipophilic pollutants through profound interference with gene expression and endocytic function, likely further disrupting regulatory cytokine secretion and ultimately exacerbating inflammatory diseases.

CD1b-autoreactive T cells contribute to hyperlipidemia-induced skin inflammation in mice

A large proportion of human T cells are autoreactive to group 1 CD1 proteins, which include CD1a, CD1b, and CD1c. However, the physiological role of the CD1 proteins remains poorly defined. Here, we have generated a double-transgenic mouse model that expresses human CD1b and CD1c molecules (hCD1Tg) as well as a CD1b-autoreactive TCR (HJ1Tg) in the ApoE-deficient background (hCD1Tg HJ1Tg Apoe-/- mice) to determine the role of CD1-autoreactive T cells in hyperlipidemia-associated inflammatory diseases. We found that hCD1Tg HJ1Tg Apoe-/- mice spontaneously developed psoriasiform skin inflammation characterized by T cell and neutrophil infiltration and a Th17-biased cytokine response. Anti-IL-17A treatment ameliorated skin inflammation in vivo. Additionally, phospholipids and cholesterol preferentially accumulated in diseased skin and these autoantigens directly activated CD1b-autoreactive HJ1 T cells. Furthermore, hyperlipidemic serum enhanced IL-6 secretion by CD1b+ DCs and increased IL-17A production by HJ1 T cells. In psoriatic patients, the frequency of CD1b-autoreactive T cells was increased compared with that in healthy controls. Thus, this study has demonstrated the pathogenic role of CD1b-autoreactive T cells under hyperlipidemic conditions in a mouse model of spontaneous skin inflammation. As a large proportion of psoriatic patients are dyslipidemic, this finding is of clinical significance and indicates that self-lipid-reactive T cells might serve as a possible link between hyperlipidemia and psoriasis.

The autophagy machinery restrains iNKT cell activation through CD1D1 internalization

Invariant natural killer T (iNKT) cells are innate T cells with powerful immune regulatory functions that recognize glycolipid antigens presented by the CD1D protein. While iNKT cell-activating glycolipids are currently being explored for their efficacy to improve immunotherapy against infectious diseases and cancer, little is known about the mechanisms that control CD1D antigen presentation and iNKT cell activation in vivo. CD1D molecules survey endocytic pathways to bind lipid antigens in MHC class II-containing compartments (MIICs) before recycling to the plasma membrane. Autophagosomes intersect with MIICs and autophagy-related proteins are known to support antigen loading for increased CD4⁺ T cell immunity. Here, we report that mice with dendritic cell (DC)-specific deletion of the essential autophagy gene Atg5 showed better CD1D1-restricted glycolipid presentation in vivo. These effects led to enhanced iNKT cell cytokine production upon antigen recognition and lower bacterial loads during Sphingomonas paucimobilis infection. Enhanced iNKT cell activation was independent of receptor-mediated glycolipid uptake or costimulatory signals. Instead, loss of Atg5 in DCs impaired clathrin-dependent internalization of CD1D1 molecules via the adaptor protein complex 2 (AP2) and, thus, increased surface expression of stimulatory CD1D1-glycolipid complexes. These findings indicate that the autophagic machinery assists in the recruitment of AP2 to CD1D1 molecules resulting in attenuated iNKT cell activation, in contrast to the supporting role of macroautophagy in CD4⁺ T cell stimulation.

Analysis of apolipoprotein genes and their involvement in disease response of channel catfish after bacterial infection

Apolipoproteins are protein component of plasma lipoproteins. They exert crucial roles in lipoprotein metabolism and serve as enzyme cofactors, receptor ligands, and lipid transfer carriers in mammals. In teleosts, apolipoproteins are also involved in diverse processes including embryonic and ontogenic development, liver and digestive system organogenesis, and innate immunity. In this study, we identified a set of 19 apolipoprotein genes in channel catfish (Ictalurus punctatus). Phylogenetic analysis and syntenic analysis were conducted to determine their identities and evolutionary relationships. The expression signatures of apolipoproteins in channel catfish were determined in healthy tissues and after infections with two major bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. In healthy channel catfish, most apolipoprotein genes exhibited tissue-specific expression patterns in channel catfish. After ESC and columnaris infections, 5 and 7 apolipoprotein genes were differentially expressed respectively, which presented a pathogen-specific and time-dependent pattern of regulation. After ESC infection, three exchangeable apolipoproteins (apoA-IB, apoC-I, and apoE-B) were suppressed in catfish intestine, while two nonexchangeable apolipoproteins (apoB-A and apoB-B) were slightly up-regulated. After columnaris infection, apoB-B, apoD-B, and apoE-A were significantly down-regulated in catfish gill, while apoF, apoL-IV, apoO-like, and apo-14 kDa showed significantly up-regulation. Taken together, these results suggested that apolipoprotein genes may play significant roles in innate immune responses to bacterial pathogens in channel catfish.

oxLDL and eLDL Induced Membrane Microdomains in Human Macrophages

Background

Extravasation of macrophages and formation of lipid-laden foam cells are key events in the development and progression of atherosclerosis. The degradation of atherogenic lipoproteins subsequently leads to alterations in cellular lipid metabolism that influence inflammatory signaling. Especially sphingolipids and ceramides are known to be involved in these processes. We therefore analyzed monocyte derived macrophages during differentiation and after loading with enzymatically (eLDL) and oxidatively (oxLDL) modified low-density lipoproteins (LDL).

Methods

Primary human monocytes were isolated from healthy, normolipidemic blood donors using leukapheresis and counterflow elutriation. On the fourth day of MCSF-induced differentiation eLDL (40 μg/ml) or oxLDL (80 μg/ml) were added for 48h. Lipid species were analyzed by quantitative tandem mass spectrometry. Taqman qPCR was performed to investigate transcriptional changes in enzymes involved in sphingolipid metabolism. Furthermore, membrane lipids were studied using flow cytometry and confocal microscopy.

Results

MCSF dependent phagocytic differentiation of blood monocytes had only minor effects on the sphingolipid composition. Levels of total sphingomyelin and total ceramide remained unchanged, while lactosylceramides, cholesterylesters and free cholesterol decreased. At the species level most ceramide species showed a reduction upon phagocytic differentiation. Loading with eLDL preferentially increased cellular cholesterol while loading with oxLDL increased cellular ceramide content. Activation of the salvage pathway with a higher mRNA expression of acid and neutral sphingomyelinase, neutral sphingomyelinase activation associated factor and glucosylceramidase as well as increased surface expression of SMPD1 were identified as potentially underlying mechanisms. Moreover, flow-cytometric analysis revealed a higher cell-surface-expression of ceramide, lactosylceramide (CDw17), globotriaosylceramide (CD77), dodecasaccharide-ceramide (CD65s) and GM1 ganglioside upon oxLDL loading. ApoE in contrast to apoA-I preferentially bound to the ceramide enriched surfaces of oxLDL loaded cells. Confocal microscopy showed a co-localization of acid sphingomyelinase with ceramide rich membrane microdomains.

Conclusion

eLDL leads to the formation of lipid droplets and preferentially induces cholesterol/sphingomyelin rich membrane microdomains while oxLDL promotes the development of cholesterol/ceramide rich microdomains via activation of the salvage pathway.

Cellular endocytic compartment localization of expressed canine CD1 molecules

CD1 molecules are glycoproteins present primarily on dendritic cells (DCs), which recognize and present a variety of foreign- and self-lipid antigens to T-cells. Humans have five different CD1 isoforms that survey distinct cellular compartments allowing for recognition of a large repertoire of lipids. The canine CD1 family consists of seven functional CD1 molecules (canine CD1a2, CD1a6, CD1a8, CD1a9, CD1b, CD1c and CD1e) and one presumed non-functional isoform (canine CD1d) due to a disrupted gene structure. The aim of this study was to describe in vitro steady-state localization ptterns of canine CD1 isoforms and their correlation with endocytic organelles. GFP-fused canine CD1 293T cell transfectants were stained with markers for early endocytic compartments (EEA-1) and late endocytic/lysosomal compartments (LAMP-1), respectively, and analyzed by confocal microscopy. Canine CD1a molecules localized to the plasma membrane and partially to the early endocytic compartment, but not to late endosomes or lysosomes. In contrast, canine CD1b was highly associated with late endosomal/lysosomal compartments and showed a predominant intracellular expression pattern. Canine CD1c protein expression localized more promiscuously to both the early endosomal compartments and the late endosomal/lysosomal compartments. The canine CD1e molecule showed a strictly intracellular expression with a partial overlap with late endosomal/lysosomal compartments. Lastly, canine CD1d was expressed abnormally showing only a diminished GFP expression. In conclusion, canine CD1 transfectants show distinct localization patterns that are similar to human CD1 proteins with the exception of the canine CD1d isoform, which most likely is non-functional. These findings imply that canine CD1 localization overall resembles human CD1 trafficking patterns. This knowledge is important for the understanding of lipid antigen-receptor immunity in the dog.

Donor-unrestricted T cells in the human CD1 system

The CD1 and MHC systems are specialized for lipid and peptide display, respectively. Here, we review evidence showing how cellular CD1a, CD1b, CD1c, and CD1d proteins capture and display many cellular lipids to T cell receptors (TCRs). Increasing evidence shows that CD1-reactive T cells operate outside two classical immunogenetic concepts derived from the MHC paradigm. First, because CD1 proteins are non-polymorphic in human populations, T cell responses are not restricted to the donor's genetic background. Second, the simplified population genetics of CD1 antigen-presenting molecules can lead to simplified patterns of TCR usage. As contrasted with donor-restricted patterns of MHC-TCR interaction, the donor-unrestricted nature of CD1-TCR interactions raises the prospect that lipid agonists and antagonists of T cells could be developed.

Activation strategies for invariant natural killer T cells

Invariant natural killer T (iNKT) cells are a specialized T cell subset that plays an important role in host defense, orchestrating both innate and adaptive immune effector responses against a variety of microbes. Specific microbial lipids and mammalian self lipids displayed by the antigen-presenting molecule CD1d can activate iNKT cells through their semi-invariant αβ T cell receptors (TCRs). iNKT cells also constitutively express receptors for inflammatory cytokines typically secreted by antigen-presenting cells (APCs) after recognition of pathogen-associated molecular patterns (PAMPs), and they can be activated through these cytokine receptors either in combination with TCR signals, or in some cases even in the absence of TCR signaling. During infection, experimental evidence suggests that both TCR-driven and cytokine-driven mechanisms contribute to iNKT cell activation. While the relative contributions of these two signaling mechanisms can vary widely depending on the infectious context, both lipid antigens and PAMPs mediate reciprocal activation of iNKT cells and APCs, leading to downstream activation of multiple other immune cell types to promote pathogen clearance. In this review, we discuss the mechanisms involved in iNKT cell activation during infection, focusing on the central contributions of both lipid antigens and PAMP-induced inflammatory cytokines, and highlight in vivo examples of activation during bacterial, viral, and fungal infections.

Are human iNKT cells keeping tabs on lipidome perturbations triggered by oxidative stress in the blood?

The central paradigm of conventional MHC-restricted T cells is that they respond specifically to foreign peptides, while displaying tolerance to self-antigens. In contrast, it is now becoming clear that a number of innate-like T cell subsets-CD1-restricted T cells, Vγ9Vδ2 T cells, and MAIT cells-may operate by different rules: rather than focusing on the recognition of specific foreign antigens, these T cells all appear to respond to alterations to lipid-related pathways. By monitoring perturbations to the "lipidome," these T cells may be able to spring into action to deal with physiological situations that are of self as well as microbial origin. iNKT cells are a prime example of this type of lipidome-reactive T cell. As a result of their activation by self lyso-phospholipid species that are generated downstream of blood lipid oxidation, human iNKT cells in the vasculature may respond sensitively to a variety of oxidative stresses. Some of the cytokines produced by activated iNKT cells have angiogenic effects (e.g., GM-CSF, IL-8), whereas others (e.g., IFN-γ) are pro-inflammatory factors that can propagate vascular pathology by influencing the functions of macrophages and dendritic cells. Consistent with this, evidence is accumulating that iNKT cells contribute to atherosclerosis, which is one of the most common inflammatory pathologies, and one that is integrally related to characteristics of the lipidome.

Glycolipid activators of invariant NKT cells as vaccine adjuvants

Natural Killer T cells (NKT cells) are a subpopulation of T lymphocytes with unique phenotypic properties and a remarkably broad range of immune effector and regulatory functions. One subset of these cells, known as invariant NKT cells (iNKT cells), has become a significant focus in the search for new and better ways to enhance immunotherapies and vaccination. These unconventional T cells are characterized by their ability to be specifically activated by a range of foreign and self-derived glycolipid antigens presented by CD1d, an MHC class I-related antigen presenting molecule that has evolved to bind and present lipid antigens. The development of synthetic α-galactosylceramides as a family of powerful glycolipid agonists for iNKT cells has led to approaches for augmenting a wide variety of immune responses, including those involved in vaccination against infections and cancers. Here we review the basic background biology of iNKT cells that is relevant to their potential for improving immune responses, and summarize recent work supporting the further development of glycolipid activators of iNKT cells as a new class of vaccine adjuvants.

The CD1 family: serving lipid antigens to T cells since the Mesozoic era

Class I-like CD1 molecules are in a family of antigen-presenting molecules that bind lipids and lipopeptides, rather than peptides for immune surveillance by T cells. Since CD1 lacks the high degree of polymorphism found in their major histocompatibility complex (MHC) class I molecules, different species express different numbers of CD1 isotypes, likely to be able to present structurally diverse classes of lipid antigens. In this review, we will present a historical overview of the structures of the different human CD1 isotypes and also discuss species-specific adaptations of the lipid-binding groove. We will discuss how single amino acid changes alter the shape and volume of the CD1 binding groove, how these minor changes can give rise to different numbers of binding pockets, and how these pockets affect the lipid repertoire that can be presented by any given CD1 protein. We will compare the structures of various lipid antigens and finally, we will discuss recognition of CD1-presented lipid antigens by antigen receptors on T cells (TCRs).

Transcriptomic Approaches in the Zebrafish Model for Tuberculosis-Insights Into Host- and Pathogen-specific Determinants of the Innate Immune Response

Mycobacterium marinum infection in zebrafish has become a well-established model of tuberculosis. Both embryonic and adult zebrafish infection studies have contributed to our knowledge of the development and function of tuberculous granulomas, which are typical of mycobacterial pathogenesis. In this review we discuss how transcriptome profiling studies have helped to characterize this infection process. We illustrate this using new RNA sequencing (RNA-Seq) data that reveals three main phases in the host response to M. marinum during the early stages of granuloma development in zebrafish embryos and larvae. The early phase shows induction of complement and transcription factors, followed by a relatively minor induction of pro-inflammatory cytokines within hours following phagocytosis of M. marinum. A minimal response is observed in the mid-phase, between 6 hours and 1day post infection, when the tissue dissemination of M. marinum begins. During subsequent larval development the granulomas expand and a late-phase response is apparent, which is characterized by progressively increasing induction of complement, transcription factors, pro-inflammatory cytokines, matrix metalloproteinases, and other defense and inflammation-related gene groups. This late-phase response shares common components with the strong and acute host transcriptome response that has previously been reported for Salmonella typhimurium infection in zebrafish embryos. In contrast, the early/mid-phase response to M. marinum infection, characterized by suppressed pro-inflammatory signaling, is strikingly different from the acute response to S. typhimurium infection. Furthermore, M. marinum infection shows a collective and strongly fluctuating regulation of lipoproteins, while S. typhimurium infection has pronounced effects on amino acid metabolism and glycolysis.

The Rationale for Insulin Therapy in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia, with a prevalence that increases with age. By 2050, the worldwide number of patients with AD is projected to reach more than 140 million. The prominent signs of AD are progressive memory loss, accompanied by a gradual decline in cognitive function and premature death. AD is the clinical manifestation of altered proteostasis. The initiating step of altered proteostasis in most AD patients is not known. The progression of AD is accelerated by several chronic disorders, among which the contribution of diabetes to AD is well understood at the cell biology level. The pathological mechanisms of AD and diabetes interact and tend to reinforce each other, thus accelerating cognitive impairment. At present, only symptomatic interventions are available for treating AD. To optimise symptomatic treatment, a personalised therapy approach has been suggested. Intranasal insulin administration seems to open the possibility for a safe, and at least in the short term, effective symptomatic intervention that delays loss of cognition in AD patients. This review summarizes the interactions of AD and diabetes from the cell biology to the patient level and the clinical results of intranasal insulin treatment of cognitive decline in AD.

Interactive effects of C-reactive protein levels on the association between APOE variants and triglyceride levels in a Taiwanese population

Background

Apolipoprotein E (APOE) plays a major role in lipid metabolism and inflammation. However, the association between APOE gene polymorphisms and serum triglyceride levels remains controversial. We tested the effects of APOE variants on triglyceride levels and their interactions with the inflammatory marker C-reactive protein (CRP) in a Taiwanese population.

Methods

Two APOE single nucleotide polymorphisms (SNPs) rs429358 and rs7412 were genotyped by TaqMan Assay using real time PCR in 595 healthy subjects attending the clinic for routine visits.

Results

After adjustment for clinical covariates, subjects carrying the rs429358-TT genotype and non-ε4 alleles were found to have higher CRP levels, whereas those with rs7412-CC genotype and non-ε2 alleles had significantly higher total and low-density lipoprotein cholesterol levels (all P < 0.01). Using subgroup and interaction analyses, we observed significantly lower triglyceride levels in subjects carrying the rs429358-TT genotype and non-ε4 alleles in the low CRP group (P = 2.71× 10⁻⁴ and P = 4.32 × 10⁻⁴, respectively), but not in those in the high CRP group (interaction P = 0.013 and 0.045, respectively). In addition, multivariate stepwise linear regression analysis showed that subjects carrying the rs429358-TT genotype and non-ε4 alleles with low CRP levels had significantly lower triglyceride levels (P < 0.001 and P < 0.001, respectively). In addition, when combined with the risk alleles of GCKR, APOA5 and LPL gene variants, we observed that triglyceride levels increased significantly with the number of risk alleles (P = 2.9 × 10⁻¹²).

Conclusions

The combination of SNPs and ε alleles at the APOE locus is involved in managing lipid and CRP levels in the Taiwanese population. APOE polymorphisms interact with CRP to regulate triglyceride levels, thus triglyceride concentration is influenced by both the genetic background of the APOE locus and the inflammatory status of a subject.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-016-0262-z) contains supplementary material, which is available to authorized users.

A new cryptic cationic antimicrobial peptide from human apolipoprotein E with antibacterial activity and immunomodulatory effects on human cells

Cationic antimicrobial peptides (AMPs) possess fast and broad-spectrum activity against both Gram-negative and Gram-positive bacteria, as well as fungi. It has become increasingly evident that many AMPs, including those that derive from fragments of host proteins, are multifunctional and able to mediate various immunomodulatory functions and angiogenesis. Among these, synthetic apolipoprotein-derived peptides are safe and well tolerated in humans and have emerged as promising candidates in the treatment of various inflammatory conditions. Here, we report the characterization of a new AMP corresponding to residues 133-150 of human apolipoprotein E. Our results show that this peptide, produced either by chemical synthesis or by recombinant techniques in Escherichia coli, possesses a broad-spectrum antibacterial activity. As shown for several other AMPs, ApoE (133-150) is structured in the presence of TFE and of membrane-mimicking agents, like SDS, or bacterial surface lipopolysaccharide (LPS), and an anionic polysaccharide, alginate, which mimics anionic capsular exo-polysaccharides of several pathogenic microorganisms. Noteworthy, ApoE (133-150) is not toxic toward several human cell lines and triggers a significant innate immune response, assessed either as decreased expression levels of proinflammatory cytokines in differentiated THP-1 monocytic cells or by the induction of chemokines released from PBMCs. This novel bioactive AMP also showed a significant anti-inflammatory effect on human keratinocytes, suggesting its potential use as a model for designing new immunomodulatory therapeutics.

High-Density Lipoproteins: Nature's Multifunctional Nanoparticles

High-density lipoproteins (HDL) are endogenous nanoparticles involved in the transport and metabolism of cholesterol, phospholipids, and triglycerides. HDL is well-known as the "good" cholesterol because it not only removes excess cholesterol from atherosclerotic plaques but also has anti-inflammatory and antioxidative properties, which protect the cardiovascular system. Circulating HDL also transports endogenous proteins, vitamins, hormones, and microRNA to various organs. Compared with other synthetic nanocarriers, such as liposomes, micelles, and inorganic and polymeric nanoparticles, HDL has unique features that allow them to deliver cargo to specific targets more efficiently. These attributes include their ultrasmall size (8-12 nm in diameter), high tolerability in humans (up to 8 g of protein per infusion), long circulating half-life (12-24 h), and intrinsic targeting properties to different recipient cells. Various recombinant ApoA proteins and ApoA mimetic peptides have been recently developed for the preparation of reconstituted HDL that exhibits properties similar to those of endogenous HDL and has a potential for industrial scale-up. In this review, we will summarize (a) clinical pharmacokinetics and safety of reconstituted HDL products, (b) comparison of HDL with inorganic and other organic nanoparticles,

Effects of different isoforms of apoE on aggregation of the α-synuclein protein implicated in Parkinson's disease

Parkinson's disease is a progressive brain disorder due to the degeneration of dopaminergic neurons in the substantia nigra. The accumulation of aggregated forms of α-synuclein protein into Lewy bodies is one of the characteristic features of this disease although the pathological role of any such protein deposits in causing neurodegeneration remains elusive. Here, the effects of different apolipoprotein E isoforms (apoE2, apoE3, apoE4) on the aggregation of α-synuclein in vitro were examined using thioflavin T assays and also an immunoassay to detect the formation of multimeric forms. Our results revealed that the aggregation of α-synuclein is influenced by apoE concentration. At low concentrations of apoE (<15nM), all of the isoforms were able to increase the aggregation of α-synuclein (50μM), with apoE4 showing the greatest stimulatory effect. This is in contrast to a higher concentration (>15nM) of these isoforms, where a decrease in the aggregation of α-synuclein was noted. The data show that exceptionally low levels of apoE may seed α-syn aggregation, which could potentially lead to the pathogenesis of α-synuclein-induced neurodegeneration. On the other hand, higher levels of apoE could potentially lower the degree of α-synuclein aggregation and confer protection. The differential effects noted with apoE4 could explain why this particular isoform results in an earlier age of onset for Parkinson's disease.

Evasion of Innate and Adaptive Immunity by Mycobacterium tuberculosis

Through thousands of years of reciprocal coevolution, Mycobacterium tuberculosis has become one of humanity's most successful pathogens, acquiring the ability to establish latent or progressive infection and persist even in the presence of a fully functioning immune system. The ability of M. tuberculosis to avoid immune-mediated clearance is likely to reflect a highly evolved and coordinated program of immune evasion strategies that interfere with both innate and adaptive immunity. These include the manipulation of their phagosomal environment within host macrophages, the selective avoidance or engagement of pattern recognition receptors, modulation of host cytokine production, and the manipulation of antigen presentation to prevent or alter the quality of T-cell responses. In this article we review an extensive array of published studies that have begun to unravel the sophisticated program of specific mechanisms that enable M. tuberculosis and other pathogenic mycobacteria to persist and replicate in the face of considerable immunological pressure from their hosts. Unraveling the mechanisms by which M. tuberculosis evades or modulates host immune function is likely to be of major importance for the development of more effective new vaccines and targeted immunotherapy against tuberculosis.

Association between APOE polymorphism and metabolic syndrome in Uyghur ethnic men

OBJECTIVES

This study aimed to examine the association between apolipoprotein E (APOE) polymorphism and metabolic syndrome (MetS) among Uyghur ethnic men in Xinjiang, China.

PARTICIPANTS

A total of 482 patients with MetS and 510 healthy sex-matched and age-matched controls were recruited from the Xinjiang Uyghur Autonomous Region of China. The participants were subjected to routine physical and blood biochemical tests, and APOE genotyping was performed.

RESULTS

The APOE ε3/3 was the predominant type, with a frequency of 71.8%, while ε2/2 was less common than ε4/4 in Uyghur males. The frequencies of the APOE2, E3 and E4 alleles in Uyghur males were 8.5%, 80.0% and 11.5%, respectively. However, the distribution of APOE genotypes was significantly different between the MetS and control groups (p<0.001). In the MetS group, the frequencies of the ε2 and ε4 alleles and the frequencies of the ε2/2, ε2/3 and ε2/4 genotypes were significantly lower than those of the control group. Those individuals without the ε2 and ε4 alleles had higher MetS prevalence than the other gene carriers, and the ORs of these individuals developing MetS were 1.5 and 1.27 compared to the gene carriers. Triglyceride, serum total cholesterol and low-density lipoprotein cholesterol levels were lower and serum high-density lipoprotein was higher in the ε2 carriers than the ε3 carriers, and the prevalence of MetS, central obesity, high blood pressure, hypercholesterolaemia and hypertriglyceridaemia was lower in the APOE2 group than in the APOE4 group. The risks of these individuals with ε4 allele carriers getting these changes were 1.327, 1.780, 1.888, 1.428 and 2.571 times greater than those of ε2 allele carriers.

CONCLUSIONS

APOE4 is associated with many individual components of MetS, whereas APOE2 was associated with a reduced risk of MetS at the univariate level in Uyghur ethnic men.

Remodeling of plasma lipoproteins in patients with rheumatoid arthritis: Interleukin-6 receptor-alpha inhibition with tocilizumab

PURPOSE

Rheumatoid arthritis (RA) is associated with increased cardiovascular risk, mediated in part by elevated circulating interleukin-6 levels and proinflammatory changes in plasma lipoproteins. We hypothesized that RA patients acquire inflammation-induced modifications to the protein cargo of circulating lipoproteins that may be reversed by tocilizumab, an interleukin-6 receptor-alpha inhibitor.

EXPERIMENTAL DESIGN

Size-exclusion chromatography and reverse-phase protein arrays using 29 antibodies against 26 proteins were applied at baseline and after tocilizumab treatment to analyze the distributions of apolipoproteins, enzymes, lipid transfer proteins, and other associated proteins in plasma lipoprotein fractions from 20 women with RA.

RESULTS

A 30% reduction in high-density lipoprotein (HDL)-associated serum amyloid A4 and complement C4 occurred with tocilizumab. Levels of C-reactive protein, associated or comigrating with HDL and low-density lipoprotein (LDL) peaks, were reduced on treatment by approximately 80% and 24%, respectively. Reductions in lipoprotein-associated phospholipase A2, lipoprotein (a), and cholesteryl ester transfer protein in the LDL fraction suggest reductions in LDL-associated proatherogenic factors. Elevations in very low-density lipoprotein (VLDL) enriched with apolipoprotein E were equally observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Tocilizumab treatment led to reductions in proinflammatory components and proatherogenic proteins associated with HDL. Whether changes in the proteome of VLDL, LDL, and HDL induced by anti-inflammatory tocilizumab treatment in RA patients modify cardiovascular disease risk requires further investigation.

Tissue-Specific Distribution of iNKT Cells Impacts Their Cytokine Response

Three subsets of invariant natural killer T (iNKT) cells have been identified, NKT1, NKT2, and NKT17, which produce distinct cytokines when stimulated, but little is known about their localization. Here, we have defined the anatomic localization and systemic distribution of these subsets and measured their cytokine production. Thymic NKT2 cells that produced interleukin-4 (IL-4) at steady state were located in the medulla and conditioned medullary thymocytes. NKT2 cells were abundant in the mesenteric lymph node (LN) of BALB/c mice and produced IL-4 in the T cell zone that conditioned other lymphocytes. Intravenous injection of α-galactosylceramide activated NKT1 cells with vascular access, but not LN or thymic NKT cells, resulting in systemic interferon-γ and IL-4 production, while oral α-galactosylceramide activated NKT2 cells in the mesenteric LN, resulting in local IL-4 release. These findings indicate that the localization of iNKT cells governs their cytokine response both at steady state and upon activation.

Differences in the Genetic Susceptibility to Age-Related Macular Degeneration Clinical Subtypes

PURPOSE

We compared across age-related macular degeneration (AMD) subtypes the effect of AMD risk variants, their predictive power, and heritability.

METHODS

The prevalence of AMD was estimated among active non-Hispanic white Kaiser Permanente Northern California members who were at least 65 years of age as of June 2013. The genetic analysis included 5,170 overall AMD cases ascertained from electronic health records (EHR), including 1,239 choroidal neovascularization (CNV) cases and 1,060 nonexudative AMD cases without CNV, and 23,130 controls of non-Hispanic white ancestry from the Kaiser Permanente Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort. Imputation was based on the 1000 Genomes Project reference panel.

RESULTS

The narrow-sense heritability due to common autosomal single nucleotide polymorphisms (SNPs) was 0.37 for overall AMD, 0.19 for AMD unspecified, 0.20 for nonexudative AMD, and 0.60 for CNV. For the 19 previously reported AMD risk loci, the area under the receiver operating characteristic (ROC) curve was 0.675 for overall AMD, 0.640 for AMD unspecified, 0.678 for nonexudative AMD, and 0.766 for CNV. The individual effects on the risk of AMD for 18 of the 19 SNPs were in a consistent direction with those previously reported, including a protective effect of the APOE ε4 allele. Conversely, the risk of AMD was significantly increased in carriers of the ε2 allele.

CONCLUSIONS

These findings provide an independent confirmation of many of the previously identified AMD risk loci, and support a potentially greater role of genetic factors in the development of CNV. The replication of established associations validates the use of EHR in genetic studies of ophthalmologic traits.

Recognition of Microbial Glycolipids by Natural Killer T Cells

T cells can recognize microbial antigens when presented by dedicated antigen-presenting molecules. While peptides are presented by classical members of the major histocompatibility complex (MHC) family (MHC I and II), lipids, glycolipids, and lipopeptides can be presented by the non-classical MHC member, CD1. The best studied subset of lipid-reactive T cells are type I natural killer T (iNKT) cells that recognize a variety of different antigens when presented by the non-classical MHCI homolog CD1d. iNKT cells have been shown to be important for the protection against various microbial pathogens, including B. burgdorferi, the causative agents of Lyme disease, and S. pneumoniae, which causes pneumococcal meningitis and community-acquired pneumonia. Both pathogens carry microbial glycolipids that can trigger the T cell antigen receptor (TCR), leading to iNKT cell activation. iNKT cells have an evolutionary conserved TCR alpha chain, yet retain the ability to recognize structurally diverse glycolipids. They do so using a conserved recognition mode, in which the TCR enforces a conserved binding orientation on CD1d. TCR binding is accompanied by structural changes within the TCR binding site of CD1d, as well as the glycolipid antigen itself. In addition to direct recognition of microbial antigens, iNKT cells can also be activated by a combination of cytokines (IL-12/IL-18) and TCR stimulation. Many microbes carry TLR antigens, and microbial infections can lead to TLR activation. The subsequent cytokine response in turn lower the threshold of TCR-mediated iNKT cell activation, especially when weak microbial or even self-antigens are presented during the cause of the infection. In summary, iNKT cells can be directly activated through TCR triggering of strong antigens, while cytokines produced by the innate immune response may be necessary for TCR triggering and iNKT cell activation in the presence of weak antigens. Here, we will review the molecular basis of iNKT cell recognition of glycolipids, with an emphasis on microbial glycolipids.

Interferon gamma response to Mycobacterium avium subsp. paratuberculosis specific lipopentapeptide antigen L5P in cattle

After Mycobacterium avium subsp. paratuberculosis (Map) infection the cell-mediated immune (CMI) response indicative of early Th1 activation may be detected using interferon-gamma release assay (IGRA). Currently, the purified protein derivatives (PPDs), i.e., the total extract of mycobacteria antigens are used to recall CMI responses against Map. This study aimed to assess the ability of the chemically synthesized Map specific cell wall lipopentapeptide L5P to induce CMI response in cows infected by Map compared to PPD. L5P and PPD elicited an IFN-γ response in 12 and 35 animals from two Map infected herds respectively, but IFN-γ was not detected in the 13 cows recruited from a non-infected herd. Levels of IFN-γ detected were higher with PPD than with L5P. There was no correlation between the IFN-γ response and the humoral response to Map or faecal culture.

Regulation of Lipid Specific and Vitamin Specific Non-MHC Restricted T Cells by Antigen Presenting Cells and Their Therapeutic Potentials

Since initial reports, more than 25 years ago, that T cells recognize lipids in the context on non-polymorphic CD1 molecules, our understanding of antigen presentation to non-peptide-specific T cell populations has deepened. It is now clear that αβ T cells bearing semi-invariant T cell receptor, as well as subsets of γδ T cells, recognize a variety of self and non-self lipids and contribute to shaping immune responses via cross talk with dendritic cells and B cells. Furthermore, it has been demonstrated that small molecules derived from the microbial riboflavin biosynthetic pathway (vitamin B2) bind monomorphic MR1 molecules and activate mucosal-associated invariant T cells, another population of semi-invariant T cells. Novel insights in the biological relevance of non-peptide-specific T cells have emerged with the development of tetrameric CD1 and MR1 molecules, which has allowed accurate enumeration and functional analysis of CD1- and MR1-restricted T cells in humans and discovery of novel populations of semi-invariant T cells. The phenotype and function of non-peptide-specific T cells will be discussed in the context of the known distribution of CD1 and MR1 molecules by different subsets of antigen-presenting cells at steady state and following infection. Concurrent modulation of CD1 transcription and lipid biosynthetic pathways upon TLR stimulation, coupled with efficient lipid antigen processing, result in the increased cell surface expression of antigenic CD1-lipid complexes. Similarly, MR1 expression is almost undetectable in resting APC and it is upregulated following bacterial infection, likely due to stabilization of MR1 molecules by microbial antigens. The tight regulation of CD1 and MR1 expression at steady state and during infection may represent an important mechanism to limit autoreactivity, while promoting T cell responses to foreign antigens.

The paradoxical role of IL-17 in atherosclerosis

Atherosclerosis is a chronic inflammatory disease mediated by innate and adaptive immune responses. In recent years, CD4(+) T cells (Th1, Th2, Treg, and Th17) have been increasingly studied for their role in atherosclerosis pathophysiology, atheroma stability, plaque rupture, and life-threatening acute coronary syndrome. IL-17, a marker cytokine of Th17 cells, has been reported to be involved in the pathogenesis of rheumatoid arthritis, inflammatory bowel disease, and asthma. However, its role in atherosclerosis has been poorly characterized. This article provides a comprehensive overview of the role of IL-17 in the development of atherosclerosis and human coronary artery diseases.