Apolipoprotein B100 autoimmunity and atherosclerosis - disease mechanisms and therapeutic potential

A bibliometric analysis of immunotherapy for atherosclerosis: trends and hotspots prediction

Introduction

An increasing number of studies have demonstrated that immunotherapy may play a significant role in treating Atherosclerosis and has emerged as a promising therapy in this field. The aim of this study is to provide a comprehensive perspective through bibliometric analysis and investigate the existing hotspots and frontiers.

Methods

This study searched records from Web of Science, PubMed, and Scopus from January 1, 1999, to May 27, 2023. By using bibliometric software CiteSpace (6.3.R1) and VOSviewer (1.6.19), co-occurrence analysis was used to count the frequency of co-occurrence of certain elements (e.g., countries, regions, institutions, etc.), cluster analysis was used to classify keywords, and burst analysis was used to identify research trends and hotspots.

Results

The results showed that the number of annual publications has grown in a fluctuating manner; the USA, China, and the Netherlands have the highest numbers of publications, and the top three institutions are located in the Netherlands, Sweden, and the USA. In addition, Nilsson J published the highest number of papers; Ridker PM and his article "Anti-inflammatory Therapy with Canakinumab for Atherosclerotic Disease" have played prominent roles. The top four Journals with the highest numbers of publications are "Arteriosclerosis Thrombosis and Vascular Biology", "Frontiers in Cardiovascular Medicine", "Circulation" and "Vaccine". In addition, keyword analysis indicates that inflammation, nanoparticles, adverse events associated with immune checkpoint inhibitors, T cells and tumor necrosis factor will be future research hotspots.

Discussion

This study provides a comprehensive bibliometric analysis of immunotherapy in atherosclerosis, offering insights that advance scientific understanding. It not only assists researchers in grasping the current hotspots in this field but also reveals potential directions for future investigation. Moreover, future studies can optimize immunotherapy strategies based on hotspot predictions to decelerate the progression of atherosclerosis.

The Impact of Metabolic and Bariatric Surgery on Apo B100 Levels in Individuals with high BMI: A Multi-Centric Prospective Cohort Study

BACKGROUND

Metabolic and Bariatric surgery (MBS) leads to significant weight loss and improvements in obesity-related comorbidities. However, the impact of MBS on Apolipoprotein B100 (Apo-B100) regulation is unclear. Apo-B100 is essential for the assembly and secretion of serum lipoprotein particles. Elevated levels of these factors can accelerate the development of atherosclerotic plaques in blood vessels. This study aimed to evaluate changes in Apo-B100 levels following MBS.

METHODS

121 participants from the Iranian National Obesity and Metabolic Surgery Database (INOSD) underwent Laparoscopic Sleeve Gastrectomy (LSG) (n = 43), One-Anastomosis Gastric Bypass (OAGB) (n = 70) or Roux-en-Y Gastric Bypass (RYGB) (n = 8). Serum Apo-B100, lipid profiles, liver enzymes, and fasting glucose were measured preoperatively and six months postoperatively.

RESULTS

Apo-B100 levels significantly decreased from 94.63 ± 14.35 mg/dL preoperatively to 62.97 ± 19.97 mg/dL after six months (p < 0.01), alongside reductions in total cholesterol, triglycerides, LDL, VLDL, AST, and ALT (p < 0.05). Greater Apo-B100 reductions occurred in non-diabetics versus people with diabetes (p = 0.012) and strongly correlated with baseline Apo-B100 (r = 0.455, p < 0.01) and LDL levels (r = 0.413, p < 0.01). However, surgery type did not impact Apo-B100 changes in multivariate analysis (p > 0.05).

CONCLUSION

Bariatric surgery leads to a significant reduction in Apo-B100 levels and improvements in lipid profiles and liver enzymes, indicating a positive impact on dyslipidemia and cardiovascular risk in individuals with high BMI.

Immunodominant MHC-II (Major Histocompatibility Complex II) Restricted Epitopes in Human Apolipoprotein B

BACKGROUND

CD (cluster of differentiation) 4+ T-cell responses to APOB (apolipoprotein B) are well characterized in atherosclerotic mice and detectable in humans. CD4+ T cells recognize antigenic peptides displayed on highly polymorphic HLA (human leukocyte antigen)-II. Immunogenicity of individual APOB peptides is largely unknown in humans. Only 1 HLA-II-restricted epitope was validated using the DRB1*07:01-APOB3036-3050 tetramer. We hypothesized that human APOB may contain discrete immunodominant CD4+ T-cell epitopes that trigger atherosclerosis-related autoimmune responses in donors with diverse HLA alleles.

METHODS

We selected 20 APOB-derived peptides (APOB20) from an in silico screen and experimentally validated binding to the most commonly occurring human HLA-II alleles. We optimized a restimulation-based workflow to evaluate antigenicity of multiple candidate peptides in HLA-typed donors. This included activation-induced marker assay, intracellular cytokine staining, IFNγ (interferon gamma) enzyme-linked immunospot and cytometric bead array. High-throughput sequencing revealed TCR (T-cell receptor) clonalities of APOB-reactive CD4+ T cells.

RESULTS

Using stringent positive, negative, and crossover stimulation controls, we confirmed specificity of expansion-based protocols to detect CD4+ T cytokine responses to the APOB20 pool. Ex vivo assessment of AIM+CD4+ T cells revealed a statistically significant autoimmune response to APOB20 but not to a ubiquitously expressed negative control protein, actin. Resolution of CD4+ T responses to the level of individual peptides using IFNγ enzyme-linked immunospot led to the discovery of 6 immunodominant epitopes (APOB6) that triggered robust CD4+ T activation in most donors. APOB6-specific responding CD4+ T cells were enriched in unique expanded TCR clonotypes and preferentially expressed memory markers. Cytometric bead array analysis detected APOB6-induced secretion of both proinflammatory and regulatory cytokines. In clinical samples from patients with angiographically verified coronary artery disease, APOB6 stimulation induced higher activation and memory phenotypes and augmented secretion of proinflammatory cytokines TNF (tumor necrosis factor) and IFNγ, compared with patients with low coronary artery disease.

CONCLUSIONS

Using 3 cohorts, each with ≈20 donors, we discovered and validated 6 immunodominant, HLA-II-restricted APOB epitopes. The immune response to these APOB epitopes correlated with coronary artery disease severity.

Does a myocardial infarction boost your (B cell) memory?

Graphical abstract Establishment of an autoreactive B cell memory after myocardial infarction: a working hypothesis. The demise of cardiac cells leads to the release of cryptoantigens that induce a humoral immune response that leads to accumulation of immunoglobulins in plaques and eventually amplifies atherogenesis at remote sites.

Escherichia coli lipopolysaccharide may affect the endothelial barrier and IL-10 expression of apolipoprotein B100-pulsed dendritic cells

Atherogenesis is associated with chronic gut infections; however, the mechanisms are not clear. The aim of the study was to determine whether lipopolysaccharide of E. coli (E. coli LPS) may affect endothelial barrier and modify IL-10 expression in dendritic cells (DCs). Human umbilical vein endothelial cells (HUVECs) and monocyte-derived DCs were treated with E. coli LPS, apolipoprotein B100 (ApoB100) and 7-ketocholesterol (7-kCH) - harmful oxidized form of cholesterol. The effect of E. coli LPS, 7-kCH and ApoB100 on the barrier functions of HUVECs in real-time cell electric impedance sensing system (RTCA-DP) was assessed. Furthermore, the effect of 7-kCH and ApoB100 on barrier functions of HUVECs co-cultured with DCs previously treated with LPS was analyzed. Both E. coli LPS and 7-kCH decreased barrier functions of HUVECs and reduced tight junction protein mRNA expression, whereas ApoB100 increased endothelial barrier. In DCs, ApoB100 and E. coli LPS decreased IL-10 mRNA expression. In HUVECs co-cultured with DCs treated with LPS and subsequently pulsed with ApoB100 or 7-kCH, IL-10 mRNA expression was lower. E. coli LPS-exposed DCs diminished the protective effect of ApoB100 on endothelial integrity and led to the decrease in occludin mRNA expression. LPS potentially derived from gut microflora may destabilize endothelial barrier together with oxidized cholesterol and intensify the immunogenicity of ApoB100.

Role of alternative splicing of VEGF-A in the development of atherosclerosis

Vascular endothelial cell growth factor A (VEGF-A) signaling promotes the endothelial cell proliferation, macrophage infiltration and foam cell formation, which play pivotal roles in the pathogenesis of atherosclerosis (AS). However, the role of alternative splicing of VEGF here is not known. Here, ApoE (-/-) mice supplied high-fat diet (HFD mice) were used to generate AS, while ApoE (-/-) mice supplied with normal diet (NOR mice) were used as a control. Aortic endothelial cells (AECs) and infiltrated macrophages were purified and quantified by flow cytometry. Alternative splicing of VEGF and the regulator of VEGF splicing, SRPK1, were assessed by RT-qPCR and immunoblotting in both AECs and aortic macrophages. We found that HFD mice developed AS in 12 weeks, while the NOR did not. Compared to NOR mice, HFD mice possessed significantly more AECs and AEC proliferation, and had significantly more aortic infiltrated macrophages and more apoptosis of them. Significant shift of VEGF-A splicing to pro-angiogenic VEGF₁₆₅ was detected in both AECs and macrophages from HFD mice, seemingly through upregulation of SRPK1. In vitro, SRPK1 overexpression significantly increased EC proliferation and macrophage apoptosis. Thus, our data suggest that alternative splicing of VEGF-A to pro-angiogenic VEGF₁₆₅ may contribute to the development of AS.

Antibody to oxidized low-density lipoprotein inhibits THP1 cells from apoptosis by suppressing NF-κB pathway activation

Background

This study aimed to investigate whether the oxidized low-density lipoprotein (Ox-LDL) antibody is able to inhibit THP1 cell apoptosis by suppressing NF-κB pathway.

Methods

THP1 cells were induced to macrophages with phorbol 12-myristate 13-acetate (PMA). Macrophages were divided into control group, Ox-LDL group and antibody group, cells in which were treated with phosphate buffered saline (PBS), Ox-LDL (50 mg/mL), Ox-LDL (50 µg/mL) plus Ox-LDL antibody (100 mg/L), respectively, for 24 h. The apoptosis rate was determined by inverted microscopy and flow cytometry. The protein and mRNA expression of NF-κB (P65), caspase-3 and BCL2 was detected by Western blotting and reverse transcription polymerase chain reaction (RT-PCR), respectively.

Results

The apoptosis rate reduced significantly in antibody group as compared to Ox-LDL and control groups (P<0.05). The protein and mRNA expression of NF-κB pathway was markedly lowered in antibody group than in Ox-LDL and control groups (P<0.05), which reduced the Ox-LDL induced inflammation.

Conclusions

Ox-LDL antibody may be used to attenuate Ox-LDL induced inflammation and apoptosis, preventing atherosclerosis patients from acute coronary syndrome (ACS).

Exploratory proteomic analysis implicates the alternative complement cascade in primary CNS vasculitis

OBJECTIVE

To identify molecular correlates of primary angiitis of the CNS (PACNS) through proteomic analysis of CSF from a biopsy-proven patient cohort.

METHODS

Using mass spectrometry, we quantitatively compared the CSF proteome of patients with biopsy-proven PACNS (n = 8) to CSF from individuals with noninflammatory conditions (n = 11). Significantly enriched molecular pathways were identified with a gene ontology workflow, and high confidence hits within enriched pathways (fold change >1.5 and concordant Benjamini-Hochberg-adjusted p < 0.05 on DeSeq and t test) were identified as differentially regulated proteins.

RESULTS

Compared to noninflammatory controls, 283 proteins were differentially expressed in the CSF of patients with PACNS, with significant enrichment of the complement cascade pathway (C4-binding protein, CD55, CD59, properdin, complement C5, complement C8, and complement C9) and neural cell adhesion molecules. A subset of clinically relevant findings were validated by Western blot and commercial ELISA.

CONCLUSIONS

In this exploratory study, we found evidence of deregulation of the alternative complement cascade in CSF from biopsy-proven PACNS compared to noninflammatory controls. More specifically, several regulators of the C3 and C5 convertases and components of the terminal cascade were significantly altered. These preliminary findings shed light on a previously unappreciated similarity between PACNS and systemic vasculitides, especially anti-neutrophil cytoplasmic antibody-associated vasculitis. The therapeutic implications of this common biology and the diagnostic and therapeutic utility of individual proteomic findings warrant validation in larger cohorts.

2016 Jeffrey M. Hoeg Award Lecture

Innate and adaptive immune effector mechanisms, in conjunction with hyperlipidemia, are important drivers of atherosclerosis. The interaction between the different immune cells and the secretion of cytokines and chemokines determine the progression of atherosclerosis. The activation or dampening of the immune response is tightly controlled by immune checkpoints. Costimulatory and coinhibitory immune checkpoints represent potential targets for immune modulatory therapies for atherosclerosis. This review will discuss the current knowledge on immune checkpoints in atherosclerosis and the clinical potential of immune checkpoint targeted therapy for atherosclerosis.

The cathelicidin protein CRAMP is a potential atherosclerosis self-antigen in ApoE(-/-) mice

Auto-immunity is believed to contribute to inflammation in atherosclerosis. The antimicrobial peptide LL-37, a fragment of the cathelicidin protein precursor hCAP18, was previously identified as an autoantigen in psoriasis. Given the reported link between psoriasis and coronary artery disease, the biological relevance of the autoantigen to atherosclerosis was tested in vitro using a truncated (t) form of the mouse homolog of hCAP18, CRAMP, on splenocytes from athero-prone ApoE(-/-) mice. Stimulation with tCRAMP resulted in increased CD8+ T cells with Central Memory and Effector Memory phenotypes in ApoE(-/-) mice, differentially activated by feeding with normal chow or high fat diet. Immunization of ApoE(-/-) with different doses of the shortened peptide (Cramp) resulted in differential outcomes with a lower dose reducing atherosclerosis whereas a higher dose exacerbating the disease with increased neutrophil infiltration of the atherosclerotic plaques. Low dose Cramp immunization also resulted in increased splenic CD8+ T cell degranulation and reduced CD11b+CD11c+ conventional dendritic cells (cDCs), whereas high dose increased CD11b+CD11c+ cDCs. Our results identified CRAMP, the mouse homolog of hCAP-18, as a potential self-antigen involved in the immune response to atherosclerosis in the ApoE(-/-) mouse model.

Hepatitis C virus and atherosclerosis: A legacy after virologic cure?

Hepatitis C virus (HCV) is a major pathogen with approximately 3% of the world's population (over 170 million) infected. Epidemiological studies have shown HCV is associated with an increased risk of cardiovascular and cerebrovascular mortality as well as peripheral arterial disease. This is despite HCV inducing an ostensibly favourable lipid profile with accompanying low classical risk score for atherosclerosis (AS). We discuss possible factors involved in the aetiopathogenesis of atherosclerosis in chronic HCV and hypothesise that an important mechanism underlying the development of AS is the presence of circulating low-density immune complexes that induce an inflammatory response. We suggest that HCV particles may be inducing an antibody response to lipoproteins present in the lipoviral particles and sub-viral particles - a concept similar to the more general 'autoantibody' response to modified LDL. After virologic cure some AS risk factors will recede but an increase in serum cholesterol could result in progression of early atherosclerotic lesions, leaving a legacy from persistent HCV infection that has clinical and therapeutic implications.

The Ratio of Regulatory (FOXP3+) to Total (CD3+) T Cells Determined by Epigenetic Cell Counting and Cardiovascular Disease Risk: A Prospective Case-cohort Study in Non-diabetics

Background

Experimental and clinical evidence indicate that inflammatory processes in atherogenesis and the development of cardiovascular complications are promoted by a loss of regulatory T cell (Treg)-mediated immunological tolerance to plaque antigens. Yet, the association between alterations of systemic Treg frequency and cardiovascular disease incidence remains uncertain.

Methods

A nested case-cohort study was conducted within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Heidelberg, comprising a random subcohort (n = 778) and primary cases of myocardial infarction (MI, n = 276) and ischemic stroke (n = 151). Pre-diagnostic FOXP3 + Treg and total CD3 + T-lymphocyte (tTL) frequencies in blood were measured by epigenetic-based, quantitative real-time PCR-assisted cell counting.

Results

Multivariate, Prentice-weighted Cox regression analyses revealed that lower Treg/tTL ratios were not associated with the risk of either MI (lowest vs. highest sex-specific quartile; hazard ratio: 0.72, 95% confidence interval: 0.46 to 1.13; P_trend = 0.51) or stroke (HR: 0.90, 95% CI: 0.51 to 1.60; P_trend = 0.78). There were no correlations of Treg/tTL ratios with C-reactive protein, HbA1c, and various lipid parameters.

Conclusions

Among middle-aged adults from the general population, imbalances in the relative frequency of Tregs within the total T cell compartment do not confer an increased risk of MI or stroke.

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We studied if peripheral immune tolerance, as reflected by regulatory (FOXP3+) to total (CD3+) T cells, relates to CVD risk.

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Epigenetic-based, qPCR assisted cell counting was used to quantify T cell subsets in long-term stored buffy coat samples.

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Lower Treg-mediated immune tolerance does not confer an increased risk of major CVD events.

Inflammation in the arterial intima plays a central role in atherosclerotic cardiovascular disease and may develop owing to autoimmune-like responses targeted against plaque antigens. While the ratio between regulatory T cells (Tregs) and effector T cells is thought to control such immune response outcomes and tolerance within the T cell compartment, we found no association with incidence of major CVD events. These findings imply that reduced systemic Treg frequencies observed in CVD patients follow rather than precede disease manifestation and that Treg variation within a physiological range may not – as previously reported - constitute a pre-disposing risk factor for CVD.

The Proteomic Landscape of Human Ex Vivo Regulatory and Conventional T Cells Reveals Specific Metabolic Requirements

Human CD4⁺CD25^hiFoxp3⁺CD127⁻ Treg and CD4⁺CD25⁻Foxp3⁻ Tconv cell functions are governed by their metabolic requirements. Here we report a comprehensive comparative analysis between ex vivo human Treg and Tconv cells that comprises analyses of the proteomic networks in subcellular compartments. We identified a dominant proteomic signature at the metabolic level that primarily impacted the highly-tuned balance between glucose and fatty-acid oxidation in the two cell types. Ex vivo Treg cells were highly glycolytic while Tconv cells used predominantly fatty-acid oxidation (FAO). When cultured in vitro, Treg cells engaged both glycolysis and FAO to proliferate, while Tconv cell proliferation mainly relied on glucose metabolism. Our unbiased proteomic analysis provides a molecular picture of the impact of metabolism on ex vivo human Treg versus Tconv cell functions that might be relevant for therapeutic manipulations of these cells.

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Ex vivo human Treg cells are highly glycolytic and proliferating

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Ex vivo human Tconv cells use fatty-acid oxidation (FAO) and are non-proliferating

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In vitro proliferation of human Treg cells requires both glycolysis and FAO

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In vitro proliferation of human Tconv cells relies mainly on glycolysis

Spontaneous Coronary Artery Dissection: Report of 3 Cases and Literature Review Hormonal, Autoimmune, Morphological Factors

The number of cases with spontaneous coronary artery dissection (SCAD) is considered to be being underestimated because of a large amount of SCAD leading to sudden death without previous diagnosis. Besides, not only in clinics but also in autopsy practice, correct diagnosis of SCAD is important to prevent forensic malpractice.The article is intended to discuss the pathological findings through the forensic point of view for improving the malpractice expertise in scope of clinicians' timely antemortem diagnosis according to risk factors and in scope of forensic pathologists' the cause of death determination ability according to macroscopical and microscopical findings of the autopsy.In 3 cases reported, the main characteristics were the female sex, pregnancy history and a sudden death without any trauma. However, although there are many women giving birth or using oral contraceptives, only some of them are facing with SCAD. This suggests the possibility of some hereditary factors, whereas hereditary characteristics may be understood in many different ways like hormone-releasing regulating mechanisms as well as immunity, morphology, or any other mechanism. For instance, autoimmunity has been also a hereditary underlying factor for vessel injury considered in presented cases.

Low Levels of Apolipoprotein B-100 Autoantibodies Are Associated With Increased Risk of Coronary Events

OBJECTIVE

Previous smaller studies have indicated inverse associations between autoantibodies to oxidized low-density lipoprotein epitopes, and cardiovascular disease. The present study investigated associations between autoantibodies against the apolipoprotein B-100 peptides p45 and p210, respectively, and risk of incident cardiovascular disease in a large population-based cohort.

APPROACH AND RESULTS

Apolipoprotein B-100 autoantibodies were analyzed by ELISA in a prospective study, including 5393 individuals (aged 46-68 years) belonging to the cardiovascular arm of the Malmö Diet and Cancer study with a follow-up time of >15 years. Subjects that suffered an acute coronary event during follow-up (n=382) had lower levels at baseline of IgM autoantibodies recognizing the native and malondialdehyde-modified apolipoprotein B-100 peptides p45 and p210 and also lower IgG levels recognizing native p210, whereas no association was found with risk for stroke (n=317). Subjects in the highest compared with lowest tertile of IgM-p45MDA (hazard ratio [95% confidence interval]: 0.72 [0.55, 0.94]; P=0.017) and IgG-p210native (hazard ratio [95% confidence interval]: 0.73 [0.56, 0.97]; P=0.029) had lower risk for incident coronary events after adjustment for cardiovascular risk factors in Cox proportional hazard regression models. Moreover, subjects with high levels of IgG-p210native were less likely to have carotid plaques as assessed by ultrasonography at baseline (odds ratio=0.81, 95% confidence interval 0.70-0.95, P=0.008 after adjustment for risk factors).

CONCLUSIONS

This large prospective study demonstrates that subjects with high levels of apolipoprotein B-100 autoantibodies have a lower risk of coronary events supporting a protective role of these autoantibodies in cardiovascular disease.

Apolipoprotein B-100 Antibody Interaction With Atherosclerotic Plaque Inflammation and Repair Processes

BACKGROUND AND PURPOSE

Treatment with IgG against the malondialdehyde (MDA)-modified apolipoprotein B-100 epitope p45 reduces atherosclerosis in experimental models. This study investigated the association between p45 IgG autoantibodies and plaque inflammation in subjects with advanced cardiovascular disease.

METHODS

Native and MDA-p45 IgG levels were analyzed by ELISA in 349 carotid endarterectomy patients. In a subcohort of 195 subjects, endarterectomy samples were analyzed by immunohistochemistry and ELISA to determine plaque constituents and inflammation. Peripheral blood mononuclear cells were isolated from healthy donors.

RESULTS

Patients with preoperative events of neurological ischemia had lower levels of native p45 IgG. Low levels of MDA-p45 IgG were associated with increased risk of postoperative cardiovascular death during a mean follow-up of 54 months. High plasma levels of native p45 IgG were associated with increased plaque content of collagen and smooth muscle cell growth factors, as well as with lower levels of proinflammatory cytokines. Exposure of peripheral blood mononuclear cells from healthy donors to recombinant MDA-p45 IgG in presence of oxidized low-density lipoprotein reduced the expression of tumor necrosis factor-α and stimulated release of smooth muscle cell growth factors.

CONCLUSIONS

This study confirms previous experimental findings of anti-inflammatory properties of apolipoprotein B-100 p45 antibodies and provides the first clinical evidence of associations between p45 IgG autoantibody levels and atherosclerotic plaque inflammation, plaque repair as well as prevalent and incident cardiovascular events in carotid endarterectomy patients. These findings suggest the possibility that treatment with anti-p45 antibodies may have beneficial effects in advanced cardiovascular disease.

2015 Russell Ross Memorial Lecture in Vascular Biology: Protective Autoimmunity in Atherosclerosis

Atherosclerosis is an inflammatory disease of the arterial wall. It is accompanied by an autoimmune response against apolipoprotein B-100, the core protein of low-density lipoprotein, which manifests as CD4 T cell and antibody responses. To assess the role of the autoimmune response in atherosclerosis, the nature of the CD4 T cell response against apolipoprotein B-100 was studied with and without vaccination with major histocompatibility complex-II-restricted apolipoprotein B-100 peptides. The immunologic basis of autoimmunity in atherosclerosis is discussed in the framework of theories of adaptive immunity. Older vaccination approaches are also discussed. Vaccinating Apoe(-/-) mice with major histocompatibility complex-II-restricted apolipoprotein B-100 peptides reduces atheroma burden in the aorta by ≈40%. The protective mechanism likely includes secretion of interleukin-10. Protective autoimmunity limits atherosclerosis in mice and suggests potential for developing preventative and therapeutic vaccines for humans.

Regulatory T cells in atherosclerosis: critical immune regulatory function and therapeutic potential

Atherosclerosis is a chronic inflammatory disease that is mediated by innate and adaptive immune responses. The disease is characterized by sub-endothelial accumulation and modification of lipids in the artery wall triggering an inflammatory reaction which promotes lesion progression and eventual plaque rupture, thrombus formation, and the respective clinical sequelae such as myocardial infarction or stroke. During the past decade, T-cell-mediated immune responses, especially control of pro-inflammatory signals by regulatory T cells (Tregs), have increasingly attracted the interest of experimental and clinical researchers. By suppression of T cell proliferation and secretion of anti-inflammatory cytokines, such as interleukin-10 (IL-10) and transforming growth factor-β, Tregs exert their atheroprotective properties. Atherosclerosis-prone, hyperlipidemic mice harbor systemically less Tregs compared to wild-type mice, suggesting an imbalance of immune cells which affects local and systemic inflammatory and potentially metabolic processes leading to atherogenesis. Restoring or increasing Treg frequency and enhancing their suppressive capacity by various modulations may pose a promising approach for treating inflammatory conditions such as cardiovascular diseases. In this review, we briefly summarize the immunological basics of atherosclerosis and introduce the role and contribution of different subsets of T cells. We then discuss experimental data and current knowledge pertaining to Tregs in atherosclerosis and perspectives on manipulating the adaptive immune system to alleviate atherosclerosis and cardiovascular disease.

Simvastatin Efficiently Lowers Small LDL-IgG Immune Complex Levels: A Therapeutic Quality beyond the Lipid-Lowering Effect

We investigated a polyethylene glycol non-precipitable low-density lipoprotein (LDL) subfraction targeted by IgG and the influence of statin therapy on plasma levels of these small LDL-IgG-immune complexes (LDL-IgG-IC). LDL-subfractions were isolated from 6 atherosclerotic subjects and 3 healthy individuals utilizing iodixanol density gradient ultracentrifugation. Cholesterol, apoB and malondialdehyde (MDA) levels were determined in each fraction by enzymatic testing, dissociation-enhanced lanthanide fluorescence immunoassay and high-performance liquid chromatography, respectively. The levels of LDL-IgG-IC were quantified densitometrically following lipid electrophoresis, particle size distribution was assessed with dynamic light scattering and size exclusion chromatography. The influence of simvastatin (40 mg/day for three months) on small LDL-IgG-IC levels and their distribution among LDL-subfractions (salt gradient separation) were investigated in 11 patients with confirmed coronary artery disease (CAD). We demonstrate that the investigated LDL-IgG-IC are small particles present in atherosclerotic patients and healthy subjects. In vitro assembly of LDL-IgG-IC resulted in particle density shifts indicating a composition of one single molecule of IgG per LDL particle. Normalization on cholesterol levels revealed MDA values twice as high for LDL-subfractions rich in small LDL-IgG-IC if compared to dominant LDL-subfractions. Reactivity of affinity purified small LDL-IgG-IC to monoclonal antibody OB/04 indicates a high degree of modified apoB and oxidative modification. Simvastatin therapy studied in the CAD patients significantly lowered LDL levels and to an even higher extent, small LDL-IgG-IC levels without affecting their distribution. In conclusion simvastatin lowers levels of small LDL-IgG-IC more effectively than LDL-cholesterol and LDL-apoB levels in atherosclerotic patients. This antiatherogenic effect may additionally contribute to the known beneficial effects of this drug in the treatment of atherosclerosis.

Atheroprotective immunity and cardiovascular disease: therapeutic opportunities and challenges

Emerging knowledge of the role of atheroprotective immune responses in modulating inflammation and tissue repair in atherosclerotic lesions has provided promising opportunities to develop novel therapies directly targeting the disease process in the artery wall. Regulatory T (Treg) cells have a protective role through release of anti-inflammatory cytokines and suppression of autoreactive effector T cells. Studies in experimental animals have shown that blocking the generation or action of Treg cells is associated with more aggressive development of atherosclerosis. Conversely, cell transfer and other approaches to expand Treg cell populations in vivo result in reduced atherosclerosis. There have been relatively few clinical studies of Treg cells and cardiovascular disease, but the available evidence also supports a protective function. These observations have raised hope that it may be possible to develop therapies that act by enforcing the suppressive activities of Treg cells in atherosclerotic lesions. One approach to achieve this goal has been through development of vaccines that stimulate immunological tolerance for plaque antigens. Several pilot vaccines based on LDL-derived antigens have demonstrated promising results in preclinical testing. If such therapies can be shown to be effective also in clinical trials, this could have an important impact on cardiovascular prevention and treatment. Here, we review the current knowledge of the mode of action of atheroprotective immunity and of the ways to stimulate such pathways in experimental settings. The challenges in translating this knowledge into the clinical setting are also discussed within the perspective of the experience of introducing immune-based therapies for other chronic noninfectious diseases.

Detection of circulating IgG antibodies to apolipoprotein B100 in acute myocardial infarction

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Anti-ApoB IgG is involved in the development of acute myocardial infarction (AMI).

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We looked for biomarkers for the prediction of acute myocardial infarction.

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An ELISA antibody test was developed to detect anti-ApoB IgG.

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The test was used in clinical screening for anti-ApoB IgG in patients with AMI.

A number of studies have reported an association between increased levels of antibodies against oxidized low-density lipoprotein (oxLDL) and cardiovascular disease, but the anti-oxLDL antibody has not been confirmed to serve as an effective biomarker for prediction of acute myocardial infarction (AMI). Apolipoprotein B₁₀₀ (ApoB₁₀₀)-derived peptide fragments generated by proteolytic degradation and aldehyde modification are the major antigens in oxLDL, and so the present work was undertaken to detect circulating IgG for Apo-B₁₀₀-derived peptide antigens. An in-house enzyme-linked immunosorbent assay (ELISA) was developed with eight ApoB₁₀₀-derived peptide antigens (Ag1–Ag8) to detect circulating anti-ApoB₁₀₀ IgG levels in 267 patients with AMI and 201 control subjects. Binary logistic regression analysis revealed that circulating IgG for Ag1 was significantly higher in the patient group than the control group (P < 0.001) after adjustment for age, gender, smoking, hypertension, diabetes and circulating levels of cholesterol, HDL, LDL, ApoA and ApoB₁₀₀. None of the other seven antigens detected an increase in IgG levels in AMI patients compared with control subjects. Spearman correlation analysis showed no correlation between IgG antibody for Ag1 and clinical characteristics. In conclusion, the linear peptide antigens derived from ApoB₁₀₀ may be suitable for the development of an ELISA antibody test for prediction of AMI, although further confirmation is still needed in large-scale clinical studies.

A study of IgG antibodies to the ApoB protein in non-ST segment elevation acute coronary syndrome

OBJECTIVES

It has long been noted that there is an association of antibodies against oxidized low-density lipoprotein (oxLDL) with cardiovascular disease, but the anti-oxLDL antibody has not been confirmed as a biomarker for prediction of acute coronary syndrome (ACS). Apolipoprotein B (ApoB) may carry the epitopes for the immune response to oxLDL. The present work was thus undertaken to detect circulating antibodies to ApoB in non-ST segment elevation ACS (NSTE-ACS).

DESIGN

A total of 130 patients with NSTE-ACS and 201 control subjects were recruited. Six ApoB-derived peptipe antigens (Ag1-Ag6) were used to develop an in-house enzyme-linked immunosorbent assay to examine circulating anti-ApoB IgG levels.

RESULTS

The anti-Ag1 IgG level was significantly higher in the patient group than the control group (P < 0.001) and the non-ST segment elevation myocardial infarction appeared to be the main form of NSTE-ACS contributing to the increased levels of anti-Ag1 IgG (P < 0.001); there was no significant alteration in the levels of IgG to the other 5 antigens in NSTE-ACS.

CONCLUSIONS

Circulating anti-ApoB IgG test may be useful for prediction of NSTE-ACS although further confirmation is needed in large-scale clinical studies.

Use of Mouse Models in Atherosclerosis Research

Cardiovascular disease is the major cause of death in most developed nations and the social and economic burden of this disease is quite high. Atherosclerosis is a major underlying basis for most cardiovascular diseases including myocardial infarction and stroke. Genetically modified mouse models, particularly mice deficient in apoprotein E or the LDL receptor, have been widely used in preclinical atherosclerosis studies to gain insight into the mechanisms underlying this pathology. This chapter reviews several mouse models of atherosclerosis progression and regression as well as the role of immune cells in disease progression and the genetics of murine atherogenesis.

Apolipoprotein B, the villain in the drama?

Low-density lipoprotein (LDL) is the major atherogenic lipoprotein and the primary target of lipid-lowering therapy for treating ischemic cardiovascular disease. Apolipoprotein B (apoB), an important structural component of LDL, plays a key role in cholesterol transport and removal in vascular wall. On the other hand, under pathological process, apoB interacts with the arterial wall to initiate the cascade of events that leads to atherosclerosis. However, interactions between apoB and vascular wall remain to be determined. Here, we address a pathological role of apoB per se and whole LDL particle in dysfunction of vascular endothelium and smooth muscle cells i.e. decreased endothelium-dependent vasodilation and increased receptor-mediated vasoconstriction. We intend to discuss: i) how apoB is responsible for the deleterious effects of LDL in the development of ischemic cardiovascular disease; ii) why vaccine based on peptides derived from apoB-100 is a promising therapy for treating ischemic cardiovascular disease, and iii) direct inhibition of apoB production should be a better therapeutic option than simple LDL-cholesterol lowering therapy in the patients with severe hypercholesterolemia at high cardiovascular risk with statin intolerance. In conclusion, apoB, but not cholesterol, plays a major role in LDL-induced dysfunction of endothelium, suggesting that direct apoB-targeting agents might be a promising therapy for the treatment of ischemic cardiovascular disease.

Atheroprotective immunization with malondialdehyde-modified LDL is hapten specific and dependent on advanced MDA adducts: implications for development of an atheroprotective vaccine

Immunization with homologous malondialdehyde (MDA)-modified LDL (MDA-LDL) leads to atheroprotection in experimental models supporting the concept that a vaccine to oxidation-specific epitopes (OSEs) of oxidized LDL could limit atherogenesis. However, modification of human LDL with OSE to use as an immunogen would be impractical for generalized use. Furthermore, when MDA is used to modify LDL, a wide variety of related MDA adducts are formed, both simple and more complex. To define the relevant epitopes that would reproduce the atheroprotective effects of immunization with MDA-LDL, we sought to determine the responsible immunodominant and atheroprotective adducts. We now demonstrate that fluorescent adducts of MDA involving the condensation of two or more MDA molecules with lysine to form malondialdehyde-acetaldehyde (MAA)-type adducts generate immunodominant epitopes that lead to atheroprotective responses. We further demonstrate that a T helper (Th) 2-biased hapten-specific humoral and cellular response is sufficient, and thus, MAA-modified homologous albumin is an equally effective immunogen. We further show that such Th2-biased humoral responses per se are not atheroprotective if they do not target relevant antigens. These data demonstrate the feasibility of development of a small-molecule immunogen that could stimulate MAA-specific immune responses, which could be used to develop a vaccine approach to retard or prevent atherogenesis.

Anti-inflammatory therapies for cardiovascular disease

Atherothrombosis is no longer considered solely a disorder of lipoprotein accumulation in the arterial wall. Rather, the initiation and progression of atherosclerotic lesions is currently understood to have major inflammatory influences that encompass components of both the innate and acquired immune systems. Promising clinical data for 'upstream' biomarkers of inflammation such as interleukin-6 (IL-6) as well as 'downstream' biomarkers such as C-reactive protein, observations regarding cholesterol crystals as an activator of the IL-1β generating inflammasome, and recent Mendelian randomization data for the IL-6 receptor support the hypothesis that inflammatory mediators of atherosclerosis may converge on the central IL-1, tumour necrosis factor (TNF-α), IL-6 signalling pathway. On this basis, emerging anti-inflammatory approaches to vascular protection can be categorized into two broad groups, those that target the central IL-6 inflammatory signalling pathway and those that do not. Large-scale Phase III trials are now underway with agents that lead to marked reductions in IL-6 and C-reactive protein (such as canakinumab and methotrexate) as well as with agents that impact on diverse non-IL-6-dependent pathways (such as varespladib and darapladib). Both approaches have the potential to benefit patients and reduce vascular events. However, care should be taken when interpreting these trials as outcomes for agents that target IL-6 signalling are unlikely to be informative for therapies that target alternative pathways, and vice versa. As the inflammatory system is redundant, compensatory, and crucial for survival, evaluation of risks as well as benefits must drive the development of agents in this class.

Apolipoprotein B100 danger-associated signal 1 (ApoBDS-1) triggers platelet activation and boosts platelet-leukocyte proinflammatory responses

Low-density lipoproteins (LDL), occurring in vivo in both their native and oxidative form, modulate platelet function and thereby contribute to atherothrombosis. We recently identified and demonstrated that 'ApoB100 danger-associated signal 1' (ApoBDS-1), a native peptide derived from Apolipoprotein B-100 (ApoB100) of LDL, induces inflammatory responses in innate immune cells. Platelets are critically involved in the development as well as in the lethal consequences of atherothrombotic diseases, but whether ApoBDS-1 has also an impact on platelet function is unknown. In this study we examined the effect of ApoBDS-1 on human platelet function and platelet-leukocyte interactions in vitro. Stimulation with ApoBDS-1 induced platelet activation, degranulation, adhesion and release of proinflammatory cytokines. ApoBDS-1-stimulated platelets triggered innate immune responses by augmenting leukocyte activation, adhesion and transmigration to/through activated HUVEC monolayers, under flow conditions. These platelet-activating effects were sequence-specific, and stimulation of platelets with ApoBDS-1 activated intracellular signalling pathways, including Ca2+, PI3K/Akt, PLC, and p38- and ERK-MAPK. Moreover, our data indicates that ApoBDS-1-induced platelet activation is partially dependent of positive feedback from ADP on P2Y1 and P2Y12, and TxA2. In conclusion, we demonstrate that ApoBDS-1 is an effective platelet agonist, boosting platelet-leukocyte's proinflammatory responses, and potentially contributing to the multifaceted inflammatory-promoting effects of LDL in the pathogenesis of atherothrombosis.

Circulating CD40+ and CD86+ B cell subsets demonstrate opposing associations with risk of stroke

OBJECTIVE

Accumulating evidence shows that immune cells play an important role in atherosclerosis. Most attention has focused on the role of different T cell subsets, whereas the possible involvement of B cells has been less studied. In this study, we assessed the association of 2 different B cell subsets, CD19(+)CD40(+) and CD19(+)CD86(+) B cells, with risk for development of acute cardiovascular events.

APPROACH AND RESULTS

The prospective study included 700 subjects randomly selected from the cardiovascular cohort of the Malmö Diet and Cancer study. Mononuclear leukocytes, stored at -140(○)C at the baseline investigation in 1991-1994, were thawed and B cell subsets analyzed by flow cytometry. Cytokine release from CD3/CD28-stimulated mononuclear leukocytes was measured with multiplex ELISA. Baseline carotid intima-media thickness and stenosis were assessed by ultrasonography, and clinical events were monitored through validated national registers during a median/mean follow-up time of 15 years. The subjects in the highest tertile of CD19(+)CD40(+) B cells had a significantly lower risk of incident stroke after adjustment for other risk factors. In contrast, CD19(+)CD86(+) B cells were associated with higher risk for development of a stroke event and increased release of proinflammatory cytokines from mononuclear leukocytes.

CONCLUSIONS

These observations provide evidence for an involvement of B cells in the incidence of stroke and suggest that both pathogenic and protective B cell subsets exist.

Inflammation and coagulation in atherosclerosis

Cardiovascular diseases remain to be the leading cause of death in Western societies. Despite major findings in vascular biology that lead to a better understanding of the pathomechanisms involved in atherosclerosis, treatment of the disease has only changed slightly within the last years. A big body of evidence suggests that atherosclerosis is a chronic inflammatory disease of the vessel wall. Accumulation and peroxidation of LDL-particles within the vessel wall trigger a strong inflammatory response, causing macrophage and T-cell accumulation within the vessel wall. Additionally, B-cells and specific antibodies against LDL-particles, as well as the complement system are implicated in atherogenesis. Besides data from clinical trials and autopsy studies it was the implementation of mouse models of atherosclerosis and the emerging field of direct gen-modification that lead to a thorough description of the pathophysiological mechanisms involved in the disease and created overwhelming evidence for a participation of the immune system. Recently, the cross-talk between coagulation and inflammation in atherogenesis has gained attention. Serious limitations and disparities in the pathophysiology of atherosclerosis in mice and men complicated the translation of experimental data into clinical practice. Despite these limitations, new anti-inflammatory medical therapies in cardiovascular disease are currently being tested in clinical trials.

The influence of innate and adaptive immune responses on atherosclerosis

Both the chronic development of atherosclerotic lesions and the acute changes in lesion phenotype that lead to clinical cardiovascular events are significantly influenced by the innate and adaptive immune responses to lipoprotein deposition and oxidation in the arterial wall. The rapid pace of discovery of mechanisms of immunologic recognition, effector functions, and regulation has significantly influenced the study of atherosclerosis, and our new knowledge is beginning to affect how we treat this ubiquitous disease. In this review, we discuss recent advances in our understanding of how innate and adaptive immunity contribute to atherosclerosis, as well as therapeutic opportunities that arise from this knowledge.

Oxidation-specific epitopes and immunological responses: Translational biotheranostic implications for atherosclerosis

Oxidation-specific epitopes (OSE), present on oxidized LDL (OxLDL), apoptotic cells, cell debris and modified proteins in the vessel wall, accumulate in response to hypercholesterolemia, and generate potent pro-inflammatory, disease-specific antigens. They represent an important class of 'danger associated molecular patterns' (DAMPs), against which a concerted innate immune response is directed. OSE are recognized by innate 'pattern recognition receptors', such as scavenger receptors present on dendritic cells and monocyte/macrophages, as well as by innate proteins, such as IgM natural antibodies and soluble proteins, such as C-reactive protein and complement factor H. These innate immune responses provide a first line of defense against atherosclerosis-specific DAMPs, and engage adaptive immune responses, provided by T and B-2 cells, which provide a more specific and definitive response. Such immune responses are ordinarily directed to remove foreign pathogens, such as those found on microbial pathogens, but when persistent or maladaptive, lead to host damage. In this context, atherosclerosis can be considered as a systemic chronic inflammatory disease initiated by the accumulation of OSE type DAMPs and perpetuated by maladaptive response of the innate and adaptive immune system. Understanding this paradigm leads to new approaches to defining cardiovascular risk and suggests new modes of therapy. Therefore, OSE have become potential targets of diagnostic and therapeutic agents. Human and murine OSE-targeting antibodies have been developed and are now being used as biomarkers in human studies and experimentally in translational applications of non-invasive molecular imaging of oxidation-rich plaques and immunotherapeutics.

Mucosal tolerance to a combination of ApoB and HSP60 peptides controls plaque progression and stabilizes vulnerable plaque in Apob(tm2Sgy)Ldlr(tm1Her)/J mice

Oral tolerance to auto antigens reduces the development of atherosclerosis in mouse models. However, the effect of immune tolerance to multiple self antigenic peptides in plaque progression and stabilization is not known. We studied the protective effect of mucosal tolerance to peptides from apolipoprotein B (ApoB; 661–680) and heat shock protein 60 (HSP60; 153–163), in combination with diet, in the prevention of atherosclerotic lesion progression and plaque stabilization in ApoB^tm25gyLDLr^tm1Her mice. We found that oral administration of five doses of a combination of ApoB and HSP60 peptides (20 µg/mice/dose) induced tolerance to both the peptides and reduced early plaque development by 39.9% better than the individual peptides (ApoB = 28.7%;HSP60 = 26.8%)(P<0.001). Oral tolerance to combination of peptides along with diet modification arrested plaque progression by 37.6% which was associated with increases in T-regulatory cell and transforming growth factor-β expression in the plaque and peripheral circulation. Reduced macrophage infiltration and tumor necrosis factor-α expression in the plaque was also observed. Tolerance with continued hypercholesterolemia resulted in 60.8% reduction in necrotic core area suggesting plaque stabilization, which was supported by reduction in apoptosis and increased efferocytosis demonstrated by greater expression of receptor tyrosine kinase Mer (MerTK) in the plaque. Tolerance to the two peptides also reduced the expression of matrix metalloproteinase 9, tissue factor, calprotectin, and increased its collagen content. Our study suggests that oral tolerance to ApoB and HSP60 peptide combination induces CD4⁺ CTLA4⁺ Tregs and CD4⁺CD25⁺Foxp3⁺ Tregs secreting TGF-β, which inhibit pathogenic T cell response to both peptides thus reducing the development and progression of atherosclerosis and provides evidence for plaque stabilization in ApoB^tm25gyLDLr^tm1Her mice.

Adaptive immunity in atherogenesis: new insights and therapeutic approaches

Many remarkable advances have improved our understanding of the cellular and molecular events in the pathogenesis of atherosclerosis. Chief among these is the accumulating knowledge of how the immune system contributes to all phases of atherogenesis, including well-known inflammatory reactions consequent to intimal trapping and oxidation of LDL. Advances in our understanding of the innate and adaptive responses to these events have helped to clarify the role of inflammation in atherogenesis and suggested new diagnostic modalities and novel therapeutic targets. Here we focus on recent advances in understanding how adaptive immunity affects atherogenesis.