Rabbit and human atherosclerotic lesions contain IgG that recognizes epitopes of oxidized LDL

Ex vivo culture of human atherosclerotic plaques: A model to study immune cells in atherogenesis

BACKGROUND AND AIMS

The mechanisms that drive atherosclerotic plaque progression and destabilization in humans remain largely unknown. Laboratory models are needed to study these mechanisms under controlled conditions. The aim of this study was to establish a new ex vivo model of human atherosclerotic plaques that preserves the main cell types in plaques and the extracellular components in the context of native cytoarchitecture.

METHODS

Atherosclerotic plaques from carotid arteries of 28 patients undergoing carotid endarterectomy were dissected and cultured. At various time-points, samples were collected and analysed histologically. After enzymatic digestion, single cells were analysed with flow cytometry. Moreover, tissue cytokine production was evaluated.

RESULTS

We optimised the plaque dissection protocol by cutting plaques into circular segments that we cultured on collagen rafts at the medium-air interface, thus keeping them well oxygenated. With this technique, the relative presence of T and B lymphocytes did not change significantly during culture, and the sizes of lymphocyte subsets remained stable after day 4 of culture. Macrophages, smooth muscle cells, and fibroblasts with collagen fibres, as well as T and B lymphocyte subsets and CD16 natural killer cells, remained largely preserved for 19 days of culture, with a continuous production of inflammatory cytokines and chemokines.

CONCLUSIONS

Our new model of ex vivo human atherosclerotic plaques, which preserves the main subsets of immune cells in the context of tissue cytoarchitecture, may be used to investigate important aspects of atherogenesis, in particular, the functions of immune cells under controlled laboratory conditions.

Circulating CD4+CXCR5+ T cells contribute to proinflammatory responses in multiple ways in coronary artery disease

Coronary artery disease (CAD) is a common subtype of cardiovascular disease. The major contributing event is atherosclerosis, which is a progressive inflammatory condition resulting in the thickening of the arterial wall and the formation of atheromatous plaques. Recent evidence suggests that circulating CD4⁺CXCR5⁺ T cells can contribute to inflammatory reactions. In this study, the frequency, phenotype, and function of circulating CD4⁺CXCR5⁺ T cells in CAD patients were examined. Data showed that circulating CD4⁺CXCR5⁺ T cells in CAD patients were enriched with a PD-1⁺CCR7^- subset, which was previously identified as the most potent in B cell help. The CD4⁺CXCR5⁺ T cells in CAD patients also secreted significantly higher levels of IFN-γ, IL-17A, and IL-21 than those from healthy controls. Depleting the PD-1⁺ population significantly reduced the cytokine secretion. Interestingly, the CD4⁺CXCR5⁺PD-1^- T cells significantly upregulated PD-1 following anti-CD3/CD28 or SEB stimulation. CD4⁺CXCR5⁺ T cells from CAD patients also demonstrated more potent capacity to stimulate B cell inflammation than those from healthy individuals. The phosphorylation of STAT1 and STAT3 were significantly higher in B cells incubated with CD4⁺CXCR5⁺ T cells from CAD than controls. The IL-6 and IFN-γ expression were also significantly higher in B cells incubated with CD4⁺CXCR5⁺ T cells from CAD. Together, this study demonstrated that CAD patients presented a highly activated CD4⁺CXCR5⁺ T cell subset that could contribute to proinflammatory responses in multiple ways. The possibility of using CD4⁺CXCR5⁺ T cells as a therapeutic target should therefore be examined in CAD patients.

Leukocyte Bim deficiency does not impact atherogenesis in ldlr -/- mice, despite a pronounced induction of autoimmune inflammation

Proapoptotic Bcl-2 family member Bim is particularly relevant for deletion of autoreactive and activated T and B cells, implicating Bim in autoimmunity. As atherosclerosis is a chronic inflammatory process with features of autoimmune disease, we investigated the impact of hematopoietic Bim deficiency on plaque formation and parameters of plaque stability. Bim -/- or wild type bone marrow transplanted ldlr -/- mice were fed a Western type diet (WTD) for 5 or 10 weeks, after which they were immunophenotyped and atherosclerotic lesions were analyzed. Bim -/- transplanted mice displayed splenomegaly and overt lymphocytosis. CD4+ and CD8+ T cells were more activated (increased CD69 and CD71 expression, increased interferon gamma production). B cells were elevated by 147%, with a shift towards the pro-atherogenic IgG-producing B2 cell phenotype, resulting in a doubling of anti-oxLDL IgG1 antibody titers in serum of bim -/- mice. Bim -/- mice displayed massive intraplaque accumulation of Ig complexes and of lesional T cells, although this did not translate in changes in plaque size or stability features (apoptotic cell and macrophage content). The surprising lack in plaque phenotype despite the profound pro-atherogenic immune effects may be attributable to the sharp reduction of serum cholesterol levels in WTD fed bim -/- mice.

Relationship of Autoantibodies to MDA-LDL and ApoB-Immune Complexes to Sex, Ethnicity, Subclinical Atherosclerosis, and Cardiovascular Events

OBJECTIVE

Modifications of lipid constituents within atherosclerotic lesions generate neoepitopes that activate innate and adaptive immune responses. We aimed to define the prevalence, distribution, and relationship of autoantibody titers of oxidized lipoproteins to subclinical atherosclerosis and major adverse cardiovascular events (MACE) in different ethnic groups.

APPROACH AND RESULTS

IgG and IgM autoantibodies to malondialdehyde-modified low-density lipoprotein (MDA-LDL) and apolipoprotein B-100-immune complexes were measured in 3509 individuals (1814 blacks, 1031 whites, 589 Hispanics, and 85 no race identifier) from the Dallas Heart Study with median 10.5-year follow-up. Coronary artery calcium score, abdominal aortic plaque by magnetic resonance imaging, and MACE were quantified. IgG MDA-LDL and IgG and IgM apolipoprotein B-100-immune complexes were significantly different between groups, with blacks having the highest levels of IgG MDA-LDL and IgG apolipoprotein B-100-immune complexes and Hispanics having the highest levels of IgM apolipoprotein B-100-immune complexes (P<0.001 for all). IgGs tended to be higher and IgMs lower with age for all markers. In multivariable-adjusted binary logistic regression analysis, a doubling of IgG MDA-LDL levels was associated with prevalent coronary artery calcium score >10 Agatston units (odds ratio [95% confidence interval], 1.21 [1.07-1.36]; P=0.002). Multivariable-adjusted Cox regression analysis revealed that IgG MDA-LDL was independently associated with time to incident MACE in the entire group (hazard ratio [95% confidence interval], 1.76 [1.16-2.72]; P=0.009 for fourth versus first quartile). This effect was particularly prominent in black subjects (hazard ratio [95% confidence interval], 2.52 [1.39-4.57]; P=0.002).

CONCLUSIONS

Autoantibodies to oxidized lipoproteins and immune complexes with apoB-100 lipoproteins vary significantly by sex, age, and ethnicity. Higher baseline IgG MDA-LDL titers independently associate with new MACE. These findings may contribute to the understanding of differences in ethnic-specific MACE events.

ATVB Distinguished Scientist Award: How Costimulatory and Coinhibitory Pathways Shape Atherosclerosis

OBJECTIVE

Immune cells play a critical role in atherosclerosis. Costimulatory and coinhibitory molecules of the tumor necrosis factor receptor and CD28 immunoglobulin superfamilies not only shape T-cell and B-cell responses but also have a major effect on antigen-presenting cells and nonimmune cells.

APPROACH AND RESULTS

Pharmacological inhibition or activation of costimulatory and coinhibitory molecules and genetic deletion demonstrated their involvement in atherosclerosis. This review highlights recent advances in understanding how costimulatory and coinhibitory pathways shape the immune response in atherosclerosis.

CONCLUSIONS

Insights gained from costimulatory and coinhibitory molecule function in atherosclerosis may inform future therapeutic approaches.

Postprandial Clearance of Oxidized Low-Density Lipoprotein in Patients with Stroke Due to Atherosclerosis

BACKGROUND

Oxidized low-density lipoprotein (OxLDL) is a contributor to atherosclerosis development. OxLDL formation increases in the postprandial state due to oxidative stress in subjects with coronary artery disease (CAD) and diabetes, but has not been studied in patients with atherosclerotic stroke. We aimed to determine differences in postprandial OxLDL in patients with atherosclerotic stroke compared to stroke from other causes.

METHODS

Patients with ischemic stroke but no history of CAD (n = 42) were enrolled and categorized by stroke subtype as extracranial atherosclerosis (EC), n = 12; intracranial atherosclerosis (IC), n = 16; or other cause, n = 14. After fasting overnight, subjects consumed a standardized fat meal. OxLDL levels were measured at t = 0 and t = 4 hours postprandial using enzyme-linked immunosorbent assay. Comparisons between the mean changes in OxLDL between the groups were performed using the analysis of variance procedure.

RESULTS

The IC group had the highest mean baseline level of OxLDL and the greatest decline during the postprandial period. There was a trend toward a difference in the mean change in OxLDL between the 3 groups (P = .0553). Subjects with atherosclerotic stroke (EC and IC groups) had higher fasting OxLDL and had a significant decline in OxLDL compared to those with stroke from other causes (P = .0164).

CONCLUSIONS

Subjects with stroke due to atherosclerosis, particularly intracranially, demonstrated high fasting OxLDL and a decline in OxLDL during the postprandial period. This decline in OxLDL may indicate an accelerated clearance of OxLDL resulting from meal-induced oxidative stress.

Prevention of oxLDL uptake leads to decreased atherosclerosis in hematopoietic NPC1-deficient Ldlr-/- mice

BACKGROUND AND AIMS

Atherosclerosis is a chronic inflammatory disease of medium and large vessels and is typically characterized by the predominant accumulation of low-density lipoprotein (LDL)-cholesterol inside macrophages that reside in the vessel walls. Previous studies clearly demonstrated an association specifically between the oxidized type of LDL (oxLDL) and atherosclerotic lesion formation. Further observations revealed that these atherosclerotic lesions displayed enlarged, lipid-loaded lysosomes. By increasing natural antibodies against oxLDL, pneumococcal vaccination has been shown to reduce atherosclerosis in LDL receptor knockout (Ldlr^-/-) mice. Relevantly, loss of the lysosomal membrane protein Niemann-Pick Type C1 (NPC1) led to lysosomal accumulation of various lipids and promoted atherosclerosis. Yet, the importance of lysosomal oxLDL accumulation inside macrophages, compared to non-modified LDL, in atherosclerosis has never been established.

METHODS

By transplanting NPC1 bone marrow into lethally irradiated Ldlr^-/- mice, a hematopoietic mouse model for lysosomal cholesterol accumulation was created. Through injections with heat-inactivated pneumococci, we aimed to demonstrate the specific contribution of lysosomal oxLDL accumulation inside macrophages in atherosclerosis development.

RESULTS

While there were no differences in plaque morphology, a reduction in plaque size and plaque inflammation was found in immunized NPC1^mut-transplanted mice, compared to non-immunized NPC1^mut-transplanted mice.

CONCLUSIONS

Lysosomal oxLDL accumulation within macrophages contributes to murine atherosclerosis. Future intervention strategies should focus specifically on preventing oxLDL, unlike non-modified LDL, from being internalized into lysosomes. Such an intervention can have an additive effect to current existing treatments against atherosclerosis.

Heterogeneity of B Cell Functions in Stroke-Related Risk, Prevention, Injury, and Repair

It is well established that post-stroke inflammation contributes to neurovascular injury, blood-brain barrier disruption, and poor functional recovery in both animal and clinical studies. However, recent studies also suggest that several leukocyte subsets, activated during the post-stroke immune response, can exhibit both pro-injury and pro-recovery phenotypes. In accordance with these findings, B lymphocytes, or B cells, play a heterogeneous role in the adaptive immune response to stroke. This review highlights what is currently understood about the various roles of B cells, with an emphasis on stroke risk factors, as well as post-stroke injury and repair. This includes an overview of B cell functions, such as antibody production, cytokine secretion, and contribution to the immune response as antigen presenting cells. Next, evidence for B cell-mediated mechanisms in stroke-related risk factors, including hypertension, diabetes, and atherosclerosis, is outlined, followed by studies that focus on B cells during endogenous protection from stroke. Subsequently, animal studies that investigate the role of B cells in post-stroke injury and repair are summarized, and the final section describes current B cell-related clinical trials for stroke, as well as other central nervous system diseases. This review reveals the complex role of B cells in stroke, with a focus on areas for potential clinical intervention for a disease that affects millions of people globally each year.

Feasibility of diagnosing unstable plaque in patients with acute coronary syndrome using iMap-IVUS

OBJECTIVE

To compare the plaque composition between stable and unstable plaques, characterize unstable plaque by using iMap-intravascular ultrasound (IVUS), and quantify the diagnostic criteria for unstable plaque.

METHODS

Thirty-three acute coronary syndrome (ACS) patients who had undergone coronary angiography and IVUS from February 19, 2014 to December 19, 2014 at Peking University People's Hospital were enrolled in the study. Baseline data were collected. The patients were divided into two groups according to their gray-scale IVUS imaging, stable plaque and unstable plaque. A difference-in-difference evaluation was performed using the baseline data and off-line iMap imaging results between the two groups. A receiver operating characteristic (ROC) curve was constructed to obtain the optimal cut-off value to diagnose unstable plaque.

RESULTS

Percentages of fibrotic and necrotic tissues, absolute values of lipidic, necrotic, and calcified tissues, and plaque burden were independent predictors for unstable plaque. Absolute necrotic area was the best predictor and exhibited the highest diagnostic value for plaque vulnerability (area under the curve (AUC)=0.806, P=0.000, 95% CI (0.718, 0.894)). The cut-off score for predicting unstable plaque was 4.0 mm(2).

CONCLUSIONS

This study attempted to propose a cut-off value based on absolute necrotic area using iMap-IVUS to predict plaque vulnerability in patients with ACS. This score might provide a valuable reference for diagnosing unstable plaque.

Allium sativum Compared to Cilostazol as an Inhibitor of Myointimal Hyperplasia

Objective

Intimal hyperplasia is associated with graft failure and vascular sutures in the first year after surgery and in postangioplasty restenosis. Allium sativum (common garlic) lowers cholesterol and has antioxidant effects; it also has antiplatelet and antitumor properties and, therefore, has great potential to reduce or inhibit intimal hyperplasia of the arteries. Our objective is to determine if the garlic has an efficacy to inhibit myointimal hyperplasia compared to cilostazol.

Methods

Female New Zealand rabbits were divided into the following groups (n=10 each) according to treatment: group A, garlic, 800 µg×kg-1×day-1, orally; group C, cilostazol, 50 mg.day-1, orally; group PS, 10 ml of 0.9% physiological saline solution, orally. Our primary is the difference of the mean of myointimal hyperplasia. Statistical analysis was performed by using ANOVA and Tukey tests, as well as the Chi-square test. We calculated the 95% confidence interval for each point estimate, and the P value was set as < 0.05.

Results

Group PS had a mean hyperplasia rate of 35.74% (95% CI, 31.76-39.71%); group C, 16.21% (95% CI, 13.36-19.05%); and group A, 21.12% (95% CI, 17.26-25.01%); P < 0.0001.

Conclusion

We conclude that Allium sativum had the same efficacy in inhibiting myointimal hyperplasia when compared to the positive control, cilostazol.

Smooth Muscle Cell Foam Cell Formation, Apolipoproteins, and ABCA1 in Intracranial Aneurysms: Implications for Lipid Accumulation as a Promoter of Aneurysm Wall Rupture

Saccular intracranial aneurysm (sIA) aneurysm causes intracranial hemorrhages that are associated with high mortality. Lipid accumulation and chronic inflammation occur in the sIA wall. A major mechanism for lipid clearance from arteries is adenosine triphosphate-binding cassette A1 (ABCA1)-mediated lipid efflux from foam cells to apolipoprotein A-I (apoA-I). We investigated the association of wall degeneration, inflammation, and lipid-related parameters in tissue samples of 16 unruptured and 20 ruptured sIAs using histology and immunohistochemistry. Intracellular lipid accumulation was associated with wall remodeling (p = 0.005) and rupture (p = 0.020). Foam cell formation was observed in smooth muscle cells, in addition to CD68- and CD163-positive macrophages. Macrophage infiltration correlated with intracellular lipid accumulation and apolipoproteins, including apoA-I. ApoA-I correlated with markers of lipid accumulation and wall degeneration (p = 0.01). ApoA-I-positive staining colocalized with ABCA1-positive cells particularly in sIAs with high number of smooth muscle cells (p = 0.003); absence of such colocalization was associated with wall degeneration (p = 0.017). Known clinical risk factors for sIA rupture correlated inversely with apoA-I. We conclude that lipid accumulation associates with sIA wall degeneration and risk of rupture, possibly via formation of foam cells and subsequent loss of mural cells. Reduced removal of lipids from the sIA wall via ABCA1-apoA-I pathway may contribute to this process.

Atherosclerosis: the interplay between lipids and immune cells

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of mortality worldwide. The underlying cause of the majority of cardiovascular disease is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. However, today's picture of the pathogenesis of atherosclerosis is much more complex, with a key role for immune cells and inflammation in conjunction with hyperlipidemia, especially elevated (modified) LDL levels. Knowledge on immune cells and immune responses in atherosclerosis has progressed tremendously over the past decades, and the same is true for the role of lipid metabolism and the different lipid components. However, it is largely unknown how lipids and the immune system interact. In this review, we will describe the effect of lipids on immune cell development and function, and the effects of immune cells on lipid metabolism.

RECENT FINDINGS

Recently, novel data have emerged that show that immune cells are affected, and behave differently in a hyperlipidemic environment. Moreover, immune cells have reported to be able to affect lipid metabolism.

SUMMARY

In this review, we will summarize the latest findings on the interactions between lipids and the immune system, and we will discuss the potential consequences of these novel insights for future therapies for atherosclerosis.

Immune-inflammatory responses in atherosclerosis: Role of an adaptive immunity mainly driven by T and B cells

Adaptive immune response plays an important role in atherogenesis. In atherosclerosis, the proinflammatory immune response driven by Th1 is predominant but the anti-inflammatory response mediated mainly by regulatory T cells is also present. The role of Th2 and Th17 cells in atherogenesis is still debated. In the plaque, other T helper cells can be observed such as Th9 and Th22 but is little is known about their impact in atherosclerosis. Heterogeneity of CD4(+) T cell subsets presented in the plaque may suggest for plasticity of T cell that can switch the phenotype dependening on the local microenvironment and activating/blocking stimuli. Effector T cells are able to recognize self-antigens released by necrotic and apoptotic vascular cells and induce a humoral immune reaction. Tth cells resided in the germinal centers help B cells to switch the antibody class to the production of high-affinity antibodies. Humoral immunity is mediated by B cells that release antigen-specific antibodies. A variety of B cell subsets were found in human and murine atherosclerotic plaques. In mice, B1 cells could spontaneously produce atheroprotective natural IgM antibodies. Conventional B2 lymphocytes secrete either proatherogenic IgG, IgA, and IgE or atheroprotective IgG and IgM antibodies reactive with oxidation-specific epitopes on atherosclerosis-associated antigens. A small population of innate response activator (IRA) B cells, which is phenotypically intermediate between B1 and B2 cells, produces IgM but possesses proatherosclerotic properties. Finally, there is a minor subset of splenic regulatory B cells (Bregs) that protect against atherosclerotic inflammation through support of generation of Tregs and production of anti-inflammatory cytokines IL-10 and TGF-β and proapoptotic molecules.

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.

Antihypertensive therapy increases natural immunity response in hypertensive patients

AIMS

The aim of this work was to evaluate the effects of treatment of hypertension on the autoantibodies to apolipoprotein B-derived peptides (anti-ApoB-D peptide Abs) response, inflammation markers and vascular function.

MAIN METHODS

Eighty-eight patients with hypertension (stage 1 or 2) were recruited and advised to receive perindopril (4mg), hydrochlorothiazide (25mg), or indapamide (1.5mg) for 12weeks in a blinded fashion. Office and 24-h ambulatory blood pressure monitoring (24h ABPM), flow-mediated dilatation (FMD), nitrate-induced dilatation (NID), titers of IgG and IgM anti-ApoB-D peptide Abs, hsCRP, and interleukins (IL-8 and IL-10) were evaluated at baseline and 12weeks after therapies.

KEY FINDINGS

All treatments reduced office BP, and improved FMD (P<0.05 vs. baseline). The NID was improved only in the perindopril arm (P<0.05 vs. baseline). The 24h-ABPM was reduced with perindopril and hydrochlorothiazide therapies (P<0.05 vs. baseline), but not with indapamide, and this effect was followed by increase in titers of IgM Anti-ApoB-D peptide Abs (P<0.05 vs. baseline), without modifications in titers IgG Anti-ApoB-D peptide Abs and interleukins. Multivariable regression analysis has shown that change in the titers of IgM anti-ApoB-D peptide was associated with the changes in FMD (β -0.347; P<0.05).

SIGNIFICANCE

These findings shed light to a possible modulator effect of the antihypertensive therapy on the natural immunity responses and vascular function.

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.

Beyond vascular inflammation--recent advances in understanding atherosclerosis

Atherosclerosis is the most life-threatening pathology worldwide. Its major clinical complications, stroke, myocardial infarction, and heart failure, are on the rise in many regions of the world--despite considerable progress in understanding cause, progression, and consequences of atherosclerosis. Originally perceived as a lipid-storage disease of the arterial wall (Die cellularpathologie in ihrer begründung auf physiologische und pathologische gewebelehre. August Hirschwald Verlag Berlin, [1871]), atherosclerosis was recognized as a chronic inflammatory disease in 1986 (New Engl J Med 314:488-500, 1986). The presence of lymphocytes in atherosclerotic lesions suggested autoimmune processes in the vessel wall (Clin Exp Immunol 64:261-268, 1986). Since the advent of suitable mouse models of atherosclerosis (Science 258:468-471, 1992; Cell 71:343-353, 1992; J Clin Invest 92:883-893, 1993) and the development of flow cytometry to define the cellular infiltrate in atherosclerotic lesions (J Exp Med 203:1273-1282, 2006), the origin, lineage, phenotype, and function of distinct inflammatory cells that trigger or inhibit the inflammatory response in the atherosclerotic plaque have been studied. Multiphoton microscopy recently enabled direct visualization of antigen-specific interactions between T cells and antigen-presenting cells in the vessel wall (J Clin Invest 122:3114-3126, 2012). Vascular immunology is now emerging as a new field, providing evidence for protective as well as damaging autoimmune responses (Int Immunol 25:615-622, 2013). Manipulating inflammation and autoimmunity both hold promise for new therapeutic strategies in cardiovascular disease. Ongoing work (J Clin Invest 123:27-36, 2013; Front Immunol 2013; Semin Immunol 31:95-101, 2009) suggests that it may be possible to develop antigen-specific immunomodulatory prevention and therapy-a vaccine against atherosclerosis.

Reduced Atherosclerosis in apoE-inhibitory FcγRIIb-Deficient Mice Is Associated With Increased Anti-Inflammatory Responses by T Cells and Macrophages

OBJECTIVE

Fcγ receptors (FcγRs) are classified as activating (FcγRI, III, and IV) and inhibitory (FcγRII) receptors. We have reported that deletion of activating FcγRs in apolipoprotein E (apoE) single knockout mice attenuated atherosclerosis. In this report, we investigated the hypothesis that deficiency of inhibitory FcγRIIb exacerbates atherosclerosis.

APPROACH AND RESULTS

ApoE-FcγRIIb double knockout mice, congenic to the C57BL/6 (apoE-FcγRIIbB6 (-/-)), were generated and atherosclerotic lesions were assessed. In contrary to our hypothesis, when compared with apoE single knockout mice, arterial lesions were significantly decreased in apoE-FcγRIIbB6 (-/-) male and female mice fed chow or high-fat diets. Chimeric mice generated by transplanting apoE-FcγRIIbB6 (-/-) marrow into apoE single knockout mice also developed reduced lesions. CD4(+) T cells from apoE-FcγRIIbB6 (-/-) mice produced higher levels of interleukin-10 and transforming growth factor-β than their apoE single knockout counterparts. As our findings conflict with a previous report using apoE-FcγRIIb129/B6 (-/-) mice on a mixed genetic background, we investigated whether strain differences contributed to the anti-inflammatory response. Macrophages from FcγRIIb129/B6 (-/-) mice on a mixed genetic background produced more interleukin-1β and MCP-1 (monocyte chemoattractant protein-1) in response to immune complexes, whereas congenic FcγRIIbB6 (-/-) mice generated more interleukin-10 and significantly less interleukin-1β. Interestingly, the expression of lupus-associated slam genes, located in proximity to fcgr2b in mouse chromosome 1, is upregulated only in mixed FcγRIIb129/B6 (-/-) mice.

CONCLUSIONS

Our findings demonstrate a detrimental role for FcγRIIb signaling in atherosclerosis and the contribution of anti-inflammatory cytokine responses in the attenuated lesions observed in apoE-FcγRIIbB6 (-/-) mice. As 129/sv genome-derived lupus-associated genes have been implicated in lupus phenotype in FcγRIIb129/B6 (-/-) mice, our findings suggest possible epistatic mechanism contributing to the decreased lesions.

Sterile inflammation in the spleen during atherosclerosis provides oxidation-specific epitopes that induce a protective B-cell response

The B-cell response in atherosclerosis is directed toward oxidation-specific epitopes such as phosphorylcholine (PC) that arise during disease-driven oxidation of self-antigens. PC-bearing antigens have been used to induce atheroprotective antibodies against modified low-density lipoproteins (oxLDL), leading to plaque reduction. Previous studies have found that B-cell transfer from aged atherosclerotic mice confers protection to young mice, but the mechanism is unknown. Here, we dissected the atheroprotective response in the spleen and found an ongoing germinal center reaction, accumulation of antibody-forming cells, and inflammasome activation in apolipoprotein E-deficient mice (Apoe(-/-)). Specific B-cell clone expansion involved the heavy chain variable region (Vh) 5 and Vh7 B-cell receptor families that harbor anti-PC reactivity. oxLDL also accumulated in the spleen. To investigate whether protection could be induced by self-antigens alone, we injected apoptotic cells that carry the same oxidation-specific epitopes as oxLDL. This treatment reduced serum cholesterol and inhibited the development of atherosclerosis in a B-cell-dependent manner. Thus, we conclude that the spleen harbors a protective B-cell response that is initiated in atherosclerosis through sterile inflammation. These data highlight the importance of the spleen in atherosclerosis-associated immunity.

Targeting the adaptive immune system: new strategies in the treatment of atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatments that target the inflammatory nature of atherosclerosis are still under development. Discovery of novel targets involved in the inflammation of the arterial wall creates opportunities to design new therapeutics that successfully modulate atherosclerosis. Here, we review drug targets that have proven to play pivotal roles in the adaptive immune system in atherosclerosis, and we discuss their potential as novel therapeutics.

Fcγ receptors and ligands and cardiovascular disease

Fcγ receptors (FcγRs) classically modulate intracellular signaling on binding of the Fc region of IgG in immune response cells. How FcγR and their ligands affect cardiovascular health and disease has been interrogated recently in both preclinical and clinical studies. The stimulation of activating FcγR in endothelial cells, vascular smooth muscle cells, and monocytes/macrophages causes a variety of cellular responses that may contribute to vascular disease pathogenesis. Stimulation of the lone inhibitory FγcR, FcγRIIB, also has adverse consequences in endothelial cells, antagonizing NO production and reparative mechanisms. In preclinical disease models, activating FcγRs promote atherosclerosis, whereas FcγRIIB is protective, and activating FcγRs also enhance thrombotic and nonthrombotic vascular occlusion. The FcγR ligand C-reactive protein (CRP) has undergone intense study. Although in rodents CRP does not affect atherosclerosis, it causes hypertension and insulin resistance and worsens myocardial infarction. Massive data have accumulated indicating an association between increases in circulating CRP and coronary heart disease in humans. However, Mendelian randomization studies reveal that CRP is not likely a disease mediator. CRP genetics and hypertension warrant further investigation. To date, studies of genetic variants of activating FcγRs are insufficient to implicate the receptors in coronary heart disease pathogenesis in humans. However, a link between FcγRIIB and human hypertension may be emerging. Further knowledge of the vascular biology of FcγR and their ligands will potentially enhance our understanding of cardiovascular disorders, particularly in patients whose greater predisposition for disease is not explained by traditional risk factors, such as individuals with autoimmune disorders.

Circulating autoantibodies against the apolipoprotein B-100 peptides p45 and p210 in relation to the occurrence of carotid plaques in 64-year-old women

Objectives

Immune responses against oxidized low density lipoprotein (LDL) play a key role in atherosclerosis. Previous studies have indicated inverse associations between autoantibodies to epitopes in oxidized LDL and cardiovascular disease. In this study we investigated the associations between autoantibodies against the apolipoprotein B-100 (apoB-100) peptides p45 and p210 and occurrence of carotid plaques.

Design

The study cohort consisted of a population-based sample of 64-year-old women with varying degrees of glucose tolerance (n=594). To identify and record the occurrence of carotid atherosclerotic plaques ultrasonography was used. Measurements of plasma IgM and IgG autoantibodies against the native and malondialdehyde (MDA)-modified apoB-100 peptides p45 and p210 were performed by ELISA.

Results

Women with carotid plaques were found to have lower levels of IgM MDA-p210 autoantibodies compared to plaque-free women. The number of carotid plaques in each subject and the total carotid plaque area correlated inversely with IgM MDA-p210 levels (r=-0.11, P=0.009 and r=-0.11, P=0.013, respectively). Furthermore, levels of IgM MDA-p210 above the lowest tertile were associated with an odds ratio of 0.55 (95% CI 0.38-0.79, P=0.001) for occurrence of carotid plaques, independently of other risk markers and statin treatment. Associations between apo-B100 peptide autoantibodies and cardiovascular risk factors were generally weak but subjects with impaired glucose tolerance had higher levels of IgM against MDA-p210.

Conclusion

The present study demonstrates that high levels of IgM against MDA-p210 are associated with less severe carotid disease in women. These findings provide additional support for a role of immune responses against oxidized LDL in cardiovascular disease.

Modulation of autoimmunity and atherosclerosis - common targets and promising translational approaches against disease

Atherosclerosis is a chronic inflammatory disease of the arterial wall that is influenced by several risk factors, including hyperlipidemia and hypertension. Autoimmune diseases substantially increase the risk for cardiovascular disease (CVD). Although atherosclerotic CVD, such as myocardial and stroke, is much more prevalent than classical autoimmune conditions such as rheumatoid arthritis, psoriasis, and systemic lupus erythematosus, these types of pathology have many similarities, raising the possibility that therapies against autoimmune disease can have beneficial effects on CVD. Substantial clinical and experimental data support the potential for immunomodulatory approaches to combating both autoimmune and cardiovascular diseases, including classical immunosuppressants, anticytokine therapy, the targeting of T and B cells and their responses, and vaccination. In this review, we discuss experimental and clinical studies that have used immunomodulatory approaches to mitigate autoimmune reactions and examine their potential to prevent and treat atherosclerotic CVD.

Vaccination to modulate atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the artery wall. Adaptive immunity plays a key role in the pathogenesis of atherosclerosis. Recently, modulation of the immune response against atherosclerotic plaque antigen(s) has attracted attention as a potentially preventive and therapeutic approach. Here, we review a series of studies on immunization with various antigens targeting treatment and prevention of atherosclerosis. Atherosclerosis-related antigens include oxidized low-density lipoprotein (LDL), apolipoprotein B-100 (ApoB-100) and heat shock protein (HSP) 60/65. Accumulating evidence supports the idea that immunization with these antigenic proteins or peptides may reduce atherosclerosis. In this review, we discuss the current status of immunization studies and possible associated mechanisms of atheroprotection.

Influence of persistent organic pollutants on oxidative stress in population-based samples

Persistent organic pollutants (POPs) are a large group of chemicals widely used and produced in various industrial applications. Many cell culture/animal studies have shown that POPs can induce oxidative stress. Since such data is lacking in humans, we conducted a large population-based study to analyze associations between POPs and oxidative stress markers. We measured following POPs; 16 polychlorinated biphenyls (PCBs), 5 organochlorine (OC) pesticides, octachlorinated dibenzo-p-dioxin, and polybrominated diphenyl ether 47, and oxidative stress markers; homocysteine, reduced [GSH] and oxidized glutathione [GSSG], glutathione ratio [GSSG/GSH], total glutathione, oxidized low-density lipoprotein [ox-LDL], ox-LDL antibodies, conjugated dienes, baseline conjugated dienes of LDL, and total anti-oxidative capacity in plasma samples collected from 992 70-year old individuals (50% women) from the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) cohort. Linear regression analyses were performed to study the associations between oxidative stress markers and summary measures of POPs including the total toxic equivalence (TEQ), sums of PCBs and OC pesticides (main exposures) while adjusting for potential confounders. In multivariable-adjusted analyses, sum of PCBs showed strong associations with ox-LDL (β=0.94; P=2.9*10(-6)). Further, sum of PCBs showed association with glutathione-related markers (GSSG: β=-0.01; P=6.0*10(-7); GSSG/GSH: β=-0.002; P=9.7*10(-10)), although in reverse direction. Other summary measures did not show any significant association with these markers. In our study of elderly individuals from the general population, we show that plasma levels of POPs are associated with markers of increased oxidative stress thereby suggesting that even low dose background exposure to POPs may be involved in oxidative stress.

ABCG1 is required for pulmonary B-1 B cell and natural antibody homeostasis

Many metabolic diseases, including atherosclerosis, type 2 diabetes, pulmonary alveolar proteinosis, and obesity, have a chronic inflammatory component involving both innate and adaptive immunity. Mice lacking the ATP-binding cassette transporter G1 (ABCG1) develop chronic inflammation in the lungs, which is associated with the lipid accumulation (cholesterol, cholesterol ester, and phospholipid) and cholesterol crystal deposition that are characteristic of atherosclerotic lesions and pulmonary alveolar proteinosis. In this article, we demonstrate that specific lipids, likely oxidized phospholipids and/or sterols, elicit a lung-specific immune response in Abcg1(-/-) mice. Loss of ABCG1 results in increased levels of specific oxysterols, phosphatidylcholines, and oxidized phospholipids, including 1-palmitoyl-2-(5'-oxovaleroyl)-sn-glycero-3-phosphocholine, in the lungs. Further, we identify a niche-specific increase in natural Ab (NAb)-secreting B-1 B cells in response to this lipid accumulation that is paralleled by increased titers of IgM, IgA, and IgG against oxidation-specific epitopes, such as those on oxidized low-density lipoprotein and malondialdehyde-modified low-density lipoprotein. Finally, we identify a cytokine/chemokine signature that is reflective of increased B cell activation, Ab secretion, and homing. Collectively, these data demonstrate that the accumulation of lipids in Abcg1(-/-) mice induces the specific expansion and localization of B-1 B cells, which secrete NAbs that may help to protect against the development of atherosclerosis. Indeed, despite chronic lipid accumulation and inflammation, hyperlipidemic mice lacking ABCG1 develop smaller atherosclerotic lesions compared with controls. These data also suggest that Abcg1(-/-) mice may represent a new model in which to study the protective functions of B-1 B cells/NAbs and suggest novel targets for pharmacologic intervention and treatment of disease.

Lymphocyte migration into atherosclerotic plaque

Adaptive immunity is involved in the pathogenesis of atherosclerosis, but the recruitment of T and B lymphocytes to atherosclerotic lesions is not as well studied as that of monocytes. In this review, we summarize the current understanding of the role of lymphocyte subsets in the pathogenesis of atherosclerosis and discuss chemokines and chemokine receptors involved in lymphocyte homing to atherosclerotic lesions. We review evidence for involvement of the chemokines CCL5, CCL19, CCL21, CXCL10, and CXCL16 and macrophage migration inhibitory factor in lymphocyte homing in atherosclerosis. Also, we review the role of their receptors CCR5, CCR6, CCR7, CXCR3, CXCR6, and CXCR2/CXCR4 and the role of the L-selectin in mouse models of atherosclerosis.

Imaging of oxidation-specific epitopes with targeted nanoparticles to detect high-risk atherosclerotic lesions: progress and future directions

Oxidation-specific epitopes (OSE) within developing atherosclerotic lesions are key antigens that drive innate and adaptive immune responses in atherosclerosis, leading to chronic inflammation. Oxidized phospholipids and malondialdehyde-lysine epitopes are well-characterized OSE present in human atherosclerotic lesions, particularly in pathologically defined vulnerable plaques. Using murine and human OSE-specific antibodies as targeting agents, we have developed radionuclide and magnetic resonance based nanoparticles, containing gadolinium, manganese or lipid-coated ultrasmall superparamagnetic iron oxide, to non-invasively image OSE within experimental atherosclerotic lesions. These methods quantitate plaque burden, allow detection of lesion progression and regression, plaque stabilization, and accumulation of OSE within macrophage-rich areas of the artery wall, suggesting they detect the most active lesions. Future studies will focus on using "natural" antibodies, lipopeptides, and mimotopes for imaging applications. These approaches should enhance the clinical translation of this technique to image, monitor, evaluate efficacy of novel therapeutic agents, and guide optimal therapy of high-risk atherosclerotic lesions.

B cells and humoral immunity in atherosclerosis

Insights into the important contribution of inflammation and immune functions in the development and progression of atherosclerosis have greatly improved our understanding of this disease. Although the role of T cells has been extensively studied for decades, only recently has the role of B cells gained more attention. Recent studies have identified differential effects of different B-cell subsets and helped to clarify the still poorly understood mechanisms by which these act. B1 cells have been shown to prevent lesion formation, whereas B2 cells have been suggested to promote it. Natural IgM antibodies, mainly derived from B1 cells, have been shown to mediate atheroprotective effects, but the functional role of other immunoglobulin classes, particularly IgG, still remains elusive. In this review, we will focus on recent insights on the role of B cells and various immunoglobulin classes and how these may mediate their effects in atherosclerotic lesion formation. Moreover, we will highlight potential therapeutic approaches focusing on B-cell depletion that could be used to translate experimental evidence to human disease.

Circulating immunoglobulins are not associated with intraplaque mast cell number and other vulnerable plaque characteristics in patients with carotid artery stenosis

Background

Recently, we have shown that intraplaque mast cell numbers are associated with atherosclerotic plaque vulnerability and with future cardiovascular events, which renders inhibition of mast cell activation of interest for future therapeutic interventions. However, the endogenous triggers that activate mast cells during the progression and destabilization of atherosclerotic lesions remain unidentified. Mast cells can be activated by immunoglobulins and in the present study, we aimed to establish whether specific immunoglobulins in plasma of patients scheduled for carotid endarterectomy were related to (activated) intraplaque mast cell numbers and plasma tryptase levels. In addition, the levels were related to other vulnerable plaque characteristics and baseline clinical data.

Methods and Results

OxLDL-IgG, total IgG and total IgE levels were measured in 135 patients who underwent carotid endarterectomy. No associations were observed between the tested plasma immunoglobulin levels and total mast cell numbers in atherosclerotic plaques. Furthermore, no associations were found between IgG levels and the following plaque characteristics: lipid core size, degree of calcification, number of macrophages or smooth muscle cells, amount of collagen and number of microvessels. Interestingly, statin use was negatively associated with plasma IgE and oxLDL-IgG levels.

Conclusions

In patients suffering from carotid artery disease, total IgE, total IgG and oxLDL-IgG levels do not associate with plaque mast cell numbers or other vulnerable plaque histopathological characteristics. This study thus does not provide evidence that the immunoglobulins tested in our cohort play a role in intraplaque mast cell activation or grade of atherosclerosis.

Investigation of serum oxidized low-density lipoprotein IgG levels in patients with angiographically defined coronary artery disease

It has been suggested that antioxidized low-density lipoprotein (anti-oxLDL) antibodies play a role in the pathogenesis of atherosclerosis. The aim of this study was to measure serum ox-LDL IgG levels in 31 patients with angiographically defined coronary artery disease (CAD) (≥50% stenosis in at least one major coronary artery; CAD⁺ group) and compare these levels with those of 32 subjects with <50% coronary stenosis (CAD⁻ group) and 24 healthy age- and sex-matched controls using ELISA. We did not find any significant difference between CAD⁺, CAD⁻, and control groups in regard to oxLDL IgG levels (P = 0.83). Serum oxLDL IgG levels did not differ between 1VD (one vessel disease), 2VD (2 vessels disease), and 3VD (3 vessels disease) subgroups of CAD⁺ patients (P = 0.20). Serum anti-oxLDL titers were only significantly correlated with LDL-C in the CAD⁺ group (P < 0.05) and waist and hip circumference (P < 0.05 and P < 0.01, resp.) in the CAD⁻ group. In stepwise regression analysis, none of the conventional cardiovascular risk factors was associated with serum ox-LDL IgG levels. The present results suggest that serum levels of ox-LDL IgG are neither associated with the presence and severity of CAD nor with the conventional cardiovascular risk factors.

Innate immune system cells in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall characterized by innate and adaptive immune system involvement. A key component of atherosclerotic plaque inflammation is the persistence of different innate immune cell types including mast cells, neutrophils, natural killer cells, monocytes, macrophages and dendritic cells. Several endogenous signals such as oxidized low-density lipoproteins, and exogenous signals such as lipopolysaccharides, trigger the activation of these cells. In particular, these signals orchestrate the early and late inflammatory responses through the secretion of pro-inflammatory cytokines and contribute to plaque evolution through the formation of foam cells, among other events. In this review we discuss how innate immune system cells affect atherosclerosis pathogenesis.

Understanding the role of B cells in atherosclerosis: potential clinical implications

Atherosclerosis is a progressive inflammatory disease of the medium to large arteries that is the largest contributor to cardiovascular disease. B-cell subsets have been shown in animal models of atherosclerosis to have both atherogenic and atheroprotective properties. In this review, we highlight the research that developed our understanding of the role of B cells in atherosclerosis both in humans and mice. From this we discuss the potential clinical impact B cells could have both as diagnostic biomarkers and as targets for immunotherapy. Finally, we recognize the inherent difficulty in translating findings from animal models into humans given the differences in both cardiovascular disease and the immune system between mice and humans, making the case for greater efforts at addressing the role of B cells in human atherosclerosis.

Relationship between oxidized LDL, IgM, and IgG autoantibodies to ox-LDL levels with recurrent cardiovascular events in Swedish patients with previous myocardial infarction

We determined whether plasma levels of circulating oxidized low-density lipoprotein (LDL; E06), immunoglobulin (Ig) G, and IgM autoantibodies binding to malonyldialdehyde-modified LDL (MDA-LDL) may predict cardiovascular events (CVEs). Patients (n=123) with a previous myocardial infarction (MI) were included. The primary end point was defined as any of the following: cardiovascular death from any cause, nonfatal reinfarction or stroke, percutaneous coronary intervention, coronary artery bypass grafting, and hospitalization due to angina pectoris. There were 43 CVEs during the follow-up period of 8.4±3.5 years. There was no significant difference in the levels of E06 and MDA-LDL IgG between the CVE and the event-free group. However, MDA-LDL IgM levels were significantly lower in patients in the CVE group (9524±6326 relative light unit [RLU]) compared with the event-free (10,975±5398 RLU) group (P=.04). In conclusion, levels of MDA-LDL IgM were associated with an increased risk of CVE in patients with a previous MI.

Heat shock proteins 60 and 70 specific proinflammatory and cytotoxic response of CD4+CD28null cells in chronic kidney disease

Background. CD4⁺CD28^null T cells are expanded in peripheral blood of patients with chronic kidney disease and associated with subclinical atherosclerosis. However, triggers for the oligoclonal expansion and activation of these cells are not clear. Methods. We investigated twenty-five stage V-IV chronic kidney disease (CKD) patients and eight healthy subjects (HC). Peripheral mononuclear cells were isolated and incubated with heat shock protein- (HSP) 60 and 70. CD4⁺CD28^null and CD4⁺CD28⁺ cells were sorted by flowcytometry and antigen specific response was assessed by the mRNA and protein expression of interferon (IFN)-γ, perforin, and granzyme B using qRT-PCR and Elispot. Results. The basal mRNA expression of IFN-γ, perforin, and granzyme B in CD4⁺CD28^null cells was higher in subjects with CKD compared to that in HC (P < 0.0001). Subjects with CKD also showed expression of IFN-γ, perforin, and granzyme B in the CD4⁺CD28⁺ subset, but this was much weaker than that seen in the CD4⁺CD28^null population (P < 0.0001). We did not note the expression of these molecules at mRNA or protein level in either subset of CD4 cells in HC. After incubation with HSP60 and HSP70, CD4⁺CD28^null cells showed increased expression at mRNA (P < 0.001) and protein level (P < 0.001). CD4⁺CD28⁺ cells also showed a weak increase in expression. No antigen-specific response was noted in HC. Conclusion. These data show that CD4⁺CD28^null cells in subjects with CKD react with HSP60 and HSP70 by upregulating the expression of IFN-γ, perforin and granzyme B. Increased circulating level of HSP60 and HSP70 might play a role in initiation and/or progression of atherosclerosis in CKD subjects through perturbation of CD4⁺CD28^null cells.

Lipid accumulation, lipid oxidation, and low plasma levels of acquired antibodies against oxidized lipids associate with degeneration and rupture of the intracranial aneurysm wall

Background

Rupture of a saccular intracranial aneurysm (sIA) causes an often fatal subarachnoid hemorrhage (SAH). Why some sIAs rupture remains unknown. Since sIA walls bear some histological similarities with early atherosclerotic lesions, we hypothesized that accumulation and oxidation of lipids might occur in the sIA wall and might associate with sIA wall degeneration. Tissue samples from sIA fundi (n = 54) were studied with histochemistry and a panel of previously characterized antibodies for epitopes of oxidized LDL (OxLDL). Plasma samples from sIA carriers (n = 125) were studied with ELISA and EIA for IgG and IgM -antibodies against a panel of OxLDL epitopes.

Results

Lipid accumulation, foam cells, and oxidized lipids were found both in unruptured and ruptured sIA walls. Lipid accumulation associated with wall degeneration (P < 0.001), as did the expression of adipophilin, a marker of lipid ingestion by cells. Lipid accumulation associated also with loss of mural cells (P < 0.001), as did the accumulation of OxLDL (P < 0.001). Plasma IgG antibody titers against OxLDL or malondialdehyde modified LDL were higher in patients with unruptured sIAs than in patients with aneurysmal SAH (P ≤ 0.001). A trend but not statistically significant differences were found in plasma IgM antibodies against oxidized lipids.

Conclusions

Accumulation of lipids and their oxidation in the sIA wall associates with the degeneration of the sIA wall. Acquired immunity against oxidized lipid epitopes may be protective of lipid associated sIA wall degeneration, but warrants further studies.

Inflammation and immune system interactions in atherosclerosis

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, accounting for 16.7 million deaths each year. The underlying cause of the majority of CVD is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. Today's picture is far more complex. Atherosclerosis is considered a chronic inflammatory disease that results in the formation of plaques in large and mid-sized arteries. Both cells of the innate and the adaptive immune system play a crucial role in its pathogenesis. By transforming immune cells into pro- and anti-inflammatory chemokine- and cytokine-producing units, and by guiding the interactions between the different immune cells, the immune system decisively influences the propensity of a given plaque to rupture and cause clinical symptoms like myocardial infarction and stroke. In this review, we give an overview on the newest insights in the role of different immune cells and subtypes in atherosclerosis.

Vaccines against atherosclerosis

Atherosclerosis is the primary cause of acute myocardial infarction and stroke. It is well established that arterial inflammation in response to accumulation and oxidation of lipoproteins in the vascular wall is the major factor responsible for the development of atherosclerosis. During recent years, it has become apparent that this vascular inflammation is modulated by a complex array of autoimmune responses against modified self-antigens in the atherosclerotic plaque and that both protective and pathogenic immune responses become activated as part of the disease process. Studies of hypercholesterolemia-induced immune activation in mouse models of atherosclerosis have demonstrated that Th1 cells contribute to disease progression while regulatory T cells are protective. It has been suggested that antigen presentation of modified self-antigens in the inflammatory environment of atherosclerotic plaques favors generation of antigen-specific Th1 cells over that of regulatory T cells, resulting in a local loss of tolerance. This concept has stimulated the development of plaque-antigen tolerogenic vaccines to dampen plaque inflammation and disease progression. A first generation of atherosclerosis vaccines based on peptides derived from apoB100 and heat shock proteins have demonstrated promising results in animal studies and are now approaching clinical testing.

Beijing ambient particle exposure accelerates atherosclerosis in ApoE knockout mice

BACKGROUND

Air pollution is associated with significant adverse health effects including increased cardiovascular morbidity and mortality. However research on the cardiovascular effect of "real-world" exposure to ambient particulate matter (PM) in susceptible animal model is very limited. In this study, we aimed to investigate the association between Beijing ambient particle exposure and the atherosclerosis development in the apolipoprotein E knockout mice (ApoE(-/-) mice).

METHODS

Two parallel exposure chambers were used for whole body exposure among ApoE knockout mice. One of the chambers was supplied with untreated ambient air (PM group) and the other chamber was treated with ambient air filtered by high-efficiency particulate air (HEPA) filter (FA group). Twenty mice were divided into two groups and exposed to ambient PM (n=10 for PM group) or filtered air (n=10 for FA group) for two months from January 18th to March 18th, 2010. During the exposure, the mass concentrations of PM2.5 and PM10 in the two chambers were continuously monitored. Additionally, a receptor source apportionment model of chemical mass balance using 19 organic tracers was applied to determine the contributions of sources on the PM2.5 in terms of natural gas, diesel vehicle, gasoline vehicle, coal burning, vegetable debris, biomass burning and cooking. At the end of the two-month exposure, biomarkers of oxidative stress, inflammation and lipid metabolism in bronchoalveolar lavage fluid (BAL) and blood samples were determined and the plaque area on the aortic endothelium was quantified.

RESULTS

In the experiment, the concentrations of PM10 and PM2.5 in PM chamber were 99.45μg/m(3) and 61.0μg/m(3) respectively, while PM2.5 in FA chamber was 17.6μg/m(3). Source apportionment analysis by organic tracers showed that gasoline vehicle (39.9%) and coal burning (24.3%) emission were the two major sources contributing to the mass concentration of PM2.5 in Beijing. Among the ApoE knockout mice, the PM group were significantly higher than the FA group in terms of serum total cholesterol, low-density lipoprotein, tumor necrosis factor-alpha (TNF-alpha) and C-reactive protein as well as TNF-alpha and interleukin-6 in BAL. Also the total antioxidant capacity and oxidized low-density lipoprotein were significantly different between the two groups. In addition, pathological analysis of aortic arch reveals that the plaques area in the PM group increased significantly compared to the FA group.

CONCLUSIONS

Our results demonstrated that ambient PM exposure could induce considerable oxidative stress and systemic inflammation in ApoE knockout mice and contribute to the progression of atherosclerosis.

Pathogenic role of modified LDL antibodies and immune complexes in atherosclerosis

There is strong evidence supporting a key role of the adaptive immune response in atherosclerosis, given that both activated Th cells producing predominantly interferon-γ and oxidized LDL (oxLDL) and the corresponding antibodies have been isolated from atheromatous plaques. Studies carried out using immune complexes (IC) prepared with human LDL and rabbit antibodies have demonstrated proatherogenic and pro-inflammatory properties, mostly dependent on the engagement of Fcγ receptors Ⅰ and Ⅱ in macrophages and macrophage-like cell lines. Following the development of a methodology for isolating modified LDL (mLDL) antibodies from serum and isolated IC, it was confirmed that antibodies reacting with oxLDL and advanced glycation end product-modified LDL are predominantly IgG of subtypes 1 and 3 and that mLDL IC prepared with human reagents possesses pro-inflammatory and proatherogenic properties. In previous studies, LDL separated from isolated IC has been analyzed for its modifications, and the reactivity of antibodies isolated from the same IC with different LDL modifications has been tested. Recently, we obtained strong evidence suggesting that the effects of mLDL IC on phagocytic cells are modulated by the composition of the mLDL. Clinical studies have shown that the level of mLDL in circulating IC is a strong predictor of cardiovascular disease (CVD) and, in diabetic patients, other significant complications, such as nephropathy and retinopathy. In conclusion, there is convincing ex vivo and clinical data supporting the hypothesis that, in humans, the humoral immune response to mLDL is pathogenic rather than protective.

Evidence on the pathogenic role of auto-antibodies in acute cardiovascular diseases

Atherothrombosis is the major determinant of acute ischaemic cardiovascular events, such as myocardial infarction and stroke. Inflammatory processes have been linked to all phases of atherogenesis In particular, the identification of autoimmunity mediators in the complex microenvironment of chronic inflammation has become the focus of attention in both early and advanced atherogenic processes. Auto-antibodies against self-molecules or new epitopes generated by oxidative processes infiltrate atherosclerotic plaques and were shown to modulate the activity of immune cells by binding various types of receptors. However, despite mounting evidence for a pathophysiological role of autoantibodies in atherothrombosis, the clinical relevance for circulating autoantibodies in cardiovascular outcomes is still debated. This review aims at illustrating the mechanisms by which different types of autoantibodies might either promote or repress atherothrombosis and to discuss the clinical studies assessing the role of auto-antibodies as prognostic biomarkers of plaque vulnerability.