B cells and atherosclerosis: A HIV perspective

Atherosclerosis remains a leading cause of cardiovascular disease (CVD) globally, with the complex interplay of inflammation and lipid metabolism at its core. Recent evidence suggests a role of B cells in the pathogenesis of atherosclerosis; however, this relationship remains poorly understood, particularly in the context of HIV. We review the multifaceted functions of B cells in atherosclerosis, with a specific focus on HIV. Unique to atherosclerosis is the pivotal role of natural antibodies, particularly those targeting oxidized epitopes abundant in modified lipoproteins and cellular debris. B cells can exert control over cellular immune responses within atherosclerotic arteries through antigen presentation, chemokine production, cytokine production, and cell-cell interactions, actively participating in local and systemic immune responses. We explore how HIV, characterized by chronic immune activation and dysregulation, influences B cells in the context of atherosclerosis, potentially exacerbating CVD risk in persons with HIV. By examining the proatherogenic and antiatherogenic properties of B cells, we aim to deepen our understanding of how B cells influence atherosclerotic plaque development, especially within the framework of HIV. This research provides a foundation for novel B cell-targeted interventions, with the potential to mitigate inflammation-driven cardiovascular events, offering new perspectives on CVD risk management in PLWH.

Adaptive immunity and atherosclerosis: aging at its crossroads

Adaptive immunity plays a profound role in atherosclerosis pathogenesis by regulating antigen-specific responses, inflammatory signaling and antibody production. However, as we age, our immune system undergoes a gradual functional decline, a phenomenon termed "immunosenescence". This decline is characterized by a reduction in proliferative naïve B- and T cells, decreased B- and T cell receptor repertoire and a pro-inflammatory senescence associated secretory profile. Furthermore, aging affects germinal center responses and deteriorates secondary lymphoid organ function and structure, leading to impaired T-B cell dynamics and increased autoantibody production. In this review, we will dissect the impact of aging on adaptive immunity and the role played by age-associated B- and T cells in atherosclerosis pathogenesis, emphasizing the need for interventions that target age-related immune dysfunction to reduce cardiovascular disease risk.

High immunoglobulin-M levels to oxidation-specific epitopes are associated with lower risk of acute myocardial infarction

Immunoglobulin M (IgM) autoantibodies to oxidation-specific epitopes (OSEs) can be present at birth and protect against atherosclerosis in experimental models. This study sought to determine whether high titers of IgM titers to OSE (IgM OSE) are associated with a lower risk of acute myocardial infarction (AMI) in humans. IgM to malondialdehyde (MDA)-LDL, phosphocholine-modified BSA, IgM apolipoprotein B100-immune complexes, and a peptide mimotope of MDA were measured within 24 h of first AMI in 4,559 patients and 4,617 age- and sex-matched controls in the Pakistan Risk of Myocardial Infarction Study. Multivariate-adjusted logistic regression was used to estimate odds ratio (OR) and 95% confidence interval for AMI. All four IgM OSEs were lower in AMI versus controls (P < 0.001 for all). Males, smokers and individuals with hypertension and diabetes had lower levels of all four IgM OSE than unaffected individuals (P < 0.001 for all). Compared to the lowest quintile, the highest quintiles of IgM MDA-LDL, phosphocholine-modified BSA, IgM apolipoprotein B100-immune complexes, and MDA mimotope P1 had a lower OR of AMI: OR (95% confidence interval) of 0.67 (0.58-0.77), 0.64 (0.56-0.73), 0.70 (0.61-0.80) and 0.72 (0.62-0.82) (P < 0.001 for all), respectively. Upon the addition of IgM OSE to conventional risk factors, the C-statistic improved by 0.0062 (0.0028-0.0095) and net reclassification by 15.5% (11.4-19.6). These findings demonstrate that IgM OSE provides clinically meaningful information and supports the hypothesis that higher levels of IgM OSE may be protective against AMI.

Humoral immunity in atherosclerosis and myocardial infarction: from B cells to antibodies

Immune mechanisms are critically involved in the pathogenesis of atherosclerosis and its clinical manifestations. Associations of specific antibody levels and defined B cell subsets with cardiovascular disease activity in humans as well as mounting evidence from preclinical models demonstrate a role of B cells and humoral immunity in atherosclerotic cardiovascular disease. These include all aspects of B cell immunity, the generation of antigen-specific antibodies, antigen presentation and co-stimulation of T cells, as well as production of cytokines. Through their impact on adaptive and innate immune responses and the regulation of many other immune cells, B cells mediate both protective and detrimental effects in cardiovascular disease. Several antigens derived from (oxidised) lipoproteins, the vascular wall and classical autoantigens have been identified. The unique antibody responses they trigger and their relationship with atherosclerotic cardiovascular disease are reviewed. In particular, we focus on the different effector functions of specific IgM, IgG, and IgE antibodies and the cellular responses they trigger and highlight potential strategies to target B cell functions for therapy.

B Cells in Atherosclerosis: Mechanisms and Potential Clinical Applications

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B cells regulate atherosclerotic plaque formation through production of antibodies and cytokines, and effects are subset specific (B1 and B2).

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Putative human atheroprotective B1 cells function similarly to murine B1 in their spontaneous IgM antibody production. However, marker strategies in identifying human and murine B1 are different.

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IgM antibody to oxidation specific epitopes produced by B1 cells associate with human coronary artery disease.

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Neoantigen immunization may be a promising strategy for atherosclerosis vaccine development, but further study to determine relevant antigens still need to be done.

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B-cell–targeted therapies, used in treating autoimmune diseases as well as lymphoid cancers, might have potential applications in treating cardiovascular diseases. Short- and long-term cardiovascular effects of these agents need to be assessed.

Because atherosclerotic cardiovascular disease is a leading cause of death worldwide, understanding inflammatory processes underpinning its pathology is critical. B cells have been implicated as a key immune cell type in regulating atherosclerosis. B-cell effects, mediated by antibodies and cytokines, are subset specific. In this review, we focus on elaborating mechanisms underlying subtype-specific roles of B cells in atherosclerosis and discuss available human data implicating B cells in atherosclerosis. We further discuss potential B cell–linked therapeutic approaches, including immunization and B cell–targeted biologics. Given recent evidence strongly supporting a role for B cells in human atherosclerosis and the expansion of immunomodulatory agents that affect B-cell biology in clinical use and clinical trials for other disorders, it is important that the cardiovascular field be cognizant of potential beneficial or untoward effects of modulating B-cell activity on atherosclerosis.

Autoantibodies Against Methylglyoxal-Modified Apolipoprotein B100 and ApoB100 Peptide Are Associated With Less Coronary Artery Atherosclerosis and Retinopathy in Long-Term Type 1 Diabetes

OBJECTIVE

Methylglyoxal (MGO), a reactive aldehyde forming advanced glycation end products (AGEs), is increased in diabetes and recognized by the immune system, resulting in anti-AGE-specific autoantibodies. The association of these immune responses with macro- and microvascular complications in type 1 diabetes remains unclarified. We investigated associations between MGO-modified apolipoprotein B100 (apoB100) and apoB100 peptide 5 (MGO-p5) autoantibodies and coronary atherosclerosis and retinopathy in type 1 diabetes.

RESEARCH DESIGN AND METHODS

IgM and IgG against MGO-apoB100 and MGO-p5 were measured by ELISA in plasma from 103 subjects with type 1 diabetes and 63 control subjects (Dialong study) and in a replication cohort of 27 subjects with type 1 diabetes (Oslo study). Coronary atherosclerosis was assessed by computed tomography coronary angiography or intravascular ultrasound. Retinopathy was classified by retinal photos.

RESULTS

MGO-apoB100 IgM and MGO-p5 IgM levels were higher in subjects with diabetes with no coronary artery stenosis compared with subjects with significant stenosis (median [interquartile range]: 96.2 arbitrary units [AU] [71-126.8] vs. 54 AU [36.1-85.4], P = 0.003 for MGO-apoB100; and 77.4 AU [58-106] vs. 36.9 AU [28.9-57.4], P = 0.005 for MGO-p5). MGO-apoB100 IgM and MGO-p5 IgM were associated with less severe coronary stenosis after adjusting for confounders (odds ratio 0.2 [95% CI 0.05-0.6], P = 0.01; and 0.22 [0.06-0.75], P = 0.02). The inverse association of MGO-p5 IgM and coronary stenosis was confirmed in the replication cohort. Subjects with proliferative retinopathy had significantly lower MGO-apoB100 IgM and MGO-p5 IgM than those with background retinopathy.

CONCLUSIONS

Autoantibodies against AGE-modified apoB100 are inversely associated with coronary atherosclerosis and proliferative retinopathy, suggesting vascular protective effects of these autoantibodies in type 1 diabetes.

Circulating antibodies against age-modified proteins in patients with coronary atherosclerosis

Advanced glycation endproducts (AGEs) are formed in a series of non-enzymatic reactions between reducing sugars and the amino groups of proteins and accumulate during aging, diabetes mellitus, chronic kidney disease and other chronic diseases. Accumulation of AGE-modifications alters protein structure and function, transforming these molecules into potential targets of the immune system, presumably triggering the production of autoantibodies against AGEs. In this study, we detected autoantibodies against AGE-modified proteins with ELISA in plasma samples of 91 patients with documented coronary artery disease (CAD), who underwent coronary artery bypass grafting (CABG) surgery. Patients with high levels of autoantibodies had a higher body mass index (BMI 28.6 vs 27.1 kg/m²; p = 0.046), were more likely to suffer from chronic obstructive pulmonary disease (COPD 30% vs 9.8%; p = 0.018), and more likely to need dialysis after the surgery (10% vs 0%; p = 0.037). Our findings show a weak link between the levels of autoantibodies against AGEs and diabetes mellitus (DM 44% vs 24.4%; p = 0.05). In a small subpopulation of patients, antibodies against native bovine serum albumin (BSA) were detected. A growing body of research explores the potential role of antibodies against AGE-modified proteins in pathogenesis of different chronic diseases; our data confirms the presence of AGE-autoantibodies in patients with CAD and that in parallel to the AGEs themselves, they may have a potential role in concomitant clinical conditions in patients undergoing CABG surgery. Further research is necessary to verify the molecular role of these antibodies in different pathological conditions.

Neonatal Exposure to Commensal-Bacteria-Derived Antigens Directs Polysaccharide-Specific B-1 B Cell Repertoire Development

B-1 B cells derive from a developmental program distinct from that of conventional B cells, through B cell receptor (BCR)-dependent positive selection of fetally derived precursors. Here, we used direct labeling of B cells reactive with the N-acetyl-D-glucosamine (GlcNAc)-containing Lancefield group A carbohydrate of Streptococcus pyogenes to study the effects of bacterial antigens on the emergent B-1 B cell clonal repertoire. The number, phenotype, and BCR clonotypes of GlcNAc-reactive B-1 B cells were modulated by neonatal exposure to heat-killed S. pyogenes bacteria. GlcNAc-reactive B-1 clonotypes and serum antibodies were reduced in germ-free mice compared with conventionally raised mice. Colonization of germ-free mice with a conventional microbiota promoted GlcNAc-reactive B-1 B cell development and concomitantly elicited clonally related IgA⁺ plasma cells in the small intestine. Thus, exposure to microbial antigens in early life determines the clonality of the mature B-1 B cell repertoire and ensuing antibody responses, with implications for vaccination approaches and schedules.

2019 Russell Ross Memorial Lecture in Vascular Biology: B Lymphocyte-Mediated Protective Immunity in Atherosclerosis

Atherosclerosis-the major underlying pathology of cardiovascular disease-is characterized by accumulation and subsequent oxidative modification of lipoproteins within the artery wall, leading to inflammatory cell infiltration and lesion formation that can over time result in arterial stenosis, ischemia, and downstream adverse events. The contribution of innate and adaptive immunity to atherosclerosis development is well established, and B cells have emerged as important modulators of both pro- and anti-inflammatory effects in atherosclerosis. Murine B cells can broadly be divided into 2 subsets: (1) B-2 cells, which are bone marrow derived and include conventional follicular and marginal zone B cells, and (2) B-1 cells, which are largely fetal liver derived and persist in adults through self-renewal. B-cell subsets are developmentally, functionally, and phenotypically distinct with unique subset-specific contributions to atherosclerosis development. Mechanisms whereby B cells regulate vascular inflammation and atherosclerosis will be discussed with a particular emphasis on B-1 cells. B-1 cells have a protective role in atherosclerosis that is mediated in large part by IgM antibody production. Accumulating evidence over the last several years has pointed to a previously underappreciated heterogeneity in B-1 cell populations, which may have important implications for understanding atherosclerosis development and potential targeted therapeutic approaches. This heterogeneity within atheroprotective innate B-cell subsets will be highlighted.

Glycan Reactive Natural Antibodies and Viral Immunity

Adaptive antibody responses provide a crucial means of host defense against viral infections by mediating the neutralization and killing infectious pathogens. At the forefront of humoral defense against viruses lie a subset of innate-like serum antibodies known as natural antibodies (NAbs). NAbs serve multifaceted functions in host defense and play an essential role in early immune responses against viruses. However, there remain many unanswered questions with regard to both the breadth of viral antigens recognized by NAbs, and how B cell ontology and individual antigenic histories intersect to control the development and function of antiviral human NAbs. In the following article we briefly review the current understanding of the functions and source of NAbs in the immune repertoire, their role during antiviral immune responses, the factors influencing the maturation of the NAb repertoire, and finally, the gaps and future research needed to advance our understanding of innate-like B cell biology for the purpose of harnessing NAbs for host defense against viral infections.

Reproductive immunomodulatory functions of B cells in pregnancy

Pregnancy, a challenging physiological state, requires shuffling of conventional immune work-sets. Strategies to tolerate the semi-allogenic fetus in normal human pregnancy are multivariate with perfect modulation of the immune cells. Pregnancy is marked by B cell lymphocytopenia accompanied by reduced responsiveness to infectious agents. Besides this old age concept, plenty of research confirms that B cells have other crucial roles in pregnancy and undergo a wide range of modifications in terms of its proliferation, switching between its subtypes, variation in antibody productions, shifting the tides of cytokines as well as regulating other immune cells. B cells establish tolerant environment in pregnancy by producing protective antibodies to encounter the foreign paternal antigens. Regulatory B cells (Bregs) have adopted anti-inflammatory characteristics to sustain normal pregnancy. Moreover, the colossal physiological alterations during human pregnancy also include synchronized changes in the cross-talks between the pregnancy hormones and B cells. These aspects of pregnancy from the view point of B cell functions have so far appeared individually in discrete reports. This review finds its novelty in concisely presenting every facet of association of B cell with human pregnancy.

Human B-1 Cells and B-1 Cell Antibodies Change With Advancing Age

Age-related deficits in the immune system have been associated with an increased incidence of infections, autoimmune diseases, and cancer. Human B cell populations change quantitatively and qualitatively in the elderly. However, the function of human B-1 cells, which play critical anti-microbial and housekeeping roles, have not been studied in the older age population. In the present work, we analyzed how the frequency, function and repertoire of human peripheral blood B-1 cells (CD19+CD20+CD27+CD38^low/intCD43+) change with age. Our results show that not only the percentage of B-1 cells but also their ability to spontaneously secrete IgM decreased with age. Further, expression levels of the transcription factors XBP-1 and Blimp-1 were significantly lower, while PAX-5, characteristic of non-secreting B cells, was significantly higher, in healthy donors over 65 years (old) as compared to healthy donors between 20 and 45 years (young). To further characterize the B-1 cell population in older individuals, we performed single cell sequencing analysis of IgM heavy chains from healthy young and old donors. We found reduced repertoire diversity of IgM antibodies in B-1 cells from older donors as well as differences in usage of certain VH and DH specific genes, as compared to younger. Overall, our results show impairment of the human B-1 cell population with advancing age, which might impact the quality of life and onset of disease within the elderly population.

CD19+ B-Cells, a New Biomarker of Mortality in Hemodialysis Patients

Background and objectives

Mortality of patients on hemodialysis (HD) remains very high despite recent improvements in HD techniques. Cardiovascular (CV) complications and infections are the main causes of death. Some studies suggest that disturbances in the immune system could play a role in this disproportionate mortality, through the links of immunity with inflammation and propensity to infections. However, few studies have addressed the role of lymphocyte populations and the global and CV mortality of HD patients.

Aim

To analyze the relationship of peripheral blood lymphocyte populations (PBLP) and all-cause and CV mortality of HD patients.

Design, setting, participants, and measurements

We design a prospective observational single center study in a cohort of HD prevalent patients. PBLP were analyzed at baseline and after 1 year and patients were followed for a 5-year period. Main outcomes were all-cause and CV mortality.

Results

One hundred and four patients (51% male, mean age 64.8 ± 15 years) were included. Follow-up was 18 (7–47) months. Fifty-five patients (52.8%) died, main causes of death being CVD (40%) and infections (29.1%). Low total lymphocyte counts were found in 47 patients (45.2%), and the most frequency lymphopenias were CD19⁺ B-cell (57.7%), CD3⁺ (40.4%), and CD4⁺ (36.5%). After 1 year, all determinations were lower except CD56⁺CD16⁺CD3⁻ natural killer. Patient survival was significantly lower in patients with a CD19⁺ B-cell count < 100 cells/μL at baseline as compared to patients with CD19⁺ B-cell ≥ 100 cells/μL counts at the end of follow-up (16.5 vs 54%, p = 0.003). By multivariable analysis, age, history of CV disease, Charlson index, a KT/V < 1.2, and a CD19⁺ B-cell count < 100 cells/μL at baseline and after 1-year were factors associated with of all-cause mortality. A CD19⁺ B-cell count < 100 cells/μL at baseline was associated with CV mortality.

Conclusion

CD19⁺ B-cell lymphopenia is very common among HD patients, and it could be an independent predictor of all-cause and CV mortality. More studies are needed to confirm these findings.

Innate and adaptive immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disorder of the large and medium-size arteries characterized by the subendothelial accumulation of cholesterol, immune cells, and extracellular matrix. At the early onset of atherogenesis, endothelial dysfunction takes place. Atherogenesis is further triggered by the accumulation of cholesterol-carrying low-density lipoproteins, which acquire properties of damage-associated molecular patterns and thereby trigger an inflammatory response. Following activation of the innate immune response, mainly governed by monocytes and macrophages, the adaptive immune response is started which further promotes atherosclerotic plaque formation. In this review, an overview is given describing the role of damage-associated molecular patterns, NLRP3 inflammasome activation, and innate and adaptive immune cells in the atherogenesis process.

A novel monoclonal antibody targeting carboxymethyllysine, an advanced glycation end product in atherosclerosis and pancreatic cancer

Advanced glycation end products are formed by non-enzymatic reactions between proteins and carbohydrates, causing irreversible lysine and arginine alterations that severely affect protein structure and function. The resulting modifications induce inflammation by binding to scavenger receptors. An increase in advanced glycation end products is observed in a number of diseases e.g. atherosclerosis and cancer. Since advanced glycation end products also are present in healthy individuals, their detection and quantification are of great importance for usage as potential biomarkers. Current methods for advanced glycation end product detection are though limited and solely measure total glycation. This study describes a new epitope-mapped single chain variable fragment, D1-B2, against carboxymethyllysine, produced from a phage library that was constructed from mouse immunizations. The phage library was selected against advanced glycation end product targets using a phage display platform. Characterization of its binding pattern was performed using large synthetic glycated peptide and protein libraries displayed on microarray slides. D1-B2 showed a preference for an aspartic acid, three positions N-terminally from a carboxymethyllysine residue and also bound to a broad collection of glycated proteins. Positive immunohistochemical staining of mouse atherosclerotic plaques and of a tissue microarray of human pancreatic tumors confirmed the usability of the new scFv for advanced glycation end product detection in tissues. This study demonstrates a promising methodology for high-throughput generation of epitope-mapped monoclonal antibodies against AGE.

Autoantibodies against aldehyde-modified collagen type IV are associated with risk of development of myocardial infarction

BACKGROUND

Oxidation of LDL particles entrapped in the extracellular matrix of the arterial wall is a key factor in the development of atherosclerosis. Lipid oxidation products, such as malondialdehyde (MDA), react with surrounding extracellular matrix proteins and cause modifications that are recognized by the immune system. MDA modification of collagen type IV is increased in carotid lesions from symptomatic patients and correlates with autoantibodies against MDA-modified collagen type IV in plasma.

OBJECTIVE

The aim of this study was to determine whether autoantibodies against MDA-modified collagen type IV predict risk of development of myocardial infarction (MI).

METHODS

Plasma levels of MDA-modified collagen type IV IgM and IgG antibodies were analysed by enzyme-linked immunosorbent assay in 385 subjects with incident MI during 13 years of follow-up and 410 age- and sex-matched controls in the Malmö Diet and Cancer study.

RESULTS

MDA-modified collagen type IV IgG levels were higher in cases with incident MI than in controls. Subjects in the highest tertile of MDA-modified collagen type IV IgG had an increased risk of MI (hazard ratio 1.56, 95% confidence interval 1.22-2.00, P for trend 0.0004). This association remained significant after adjusting for factors included in the Framingham risk score and diabetes. High levels of MDA-collagen type IV IgG were associated with increased carotid intima-media thickness and elevated plasma levels of matrix metalloproteinase 10 and 12.

CONCLUSIONS

Immune responses against MDA-modified collagen type IV are associated with more severe carotid disease and increased risk of MI. These immune responses may reflect LDL oxidation in the artery wall, but could also affect the atherosclerotic disease process.

The endothelial border to health: Mechanistic evidence of the hyperglycemic culprit of inflammatory disease acceleration

The endothelial cell (EC) layer constitutes a barrier that controls movements of fluid, solutes and cells between blood and tissue. Further, the endothelial layer regulates vascular tone and directs local humoral and cellular inflammatory processes. The strategic position makes it an important player for maintenance of health and for development of a number of diseases. Endothelial dysfunction is known to be an important component of type 2 diabetes, but is also assumed to be involved in many other diseases, for example, rheumatoid arthritis, inflammatory bowel disease, asthma, and cardiovascular diseases. We here suggest that the EC plays a pivotal role in disease pathophysiology through initiation, potentiation, and maintenance of several inflammatory mechanisms. Our contention is based on the observation that hyperglycemia-intermittent or sustained, local or systemic-is a major culprit for several endothelial dysfunctions. There is also mounting epidemiological evidence that dietary intake of refined sugars is important for the development of a number of diseases beyond obesity and type 2 diabetes. Various diseases involving inflammatory and immunological components are accelerated by hyperglycemic events because the endothelium transduces "high glucose" signaling into significant pathophysiological phenomena leading to reduced endothelial barrier function, compromised vascular tone regulation and inflammation (e.g., cytokine secretion and RAGE activation). In addition, endothelial extracellular proteins form epitopes for potential specific antibody formation upon interactions with reducing sugars. This paper reviews the endothelial metabolism, biology, inflammatory processes, physical barrier functions, and summarizes evidence that although stochastic in nature, endothelial responses to hyperglycemia are major contributors to disease pathophysiology. We present molecular and mechanistic evidence that both biological and physical barriers, protein function, specific immunity, and inflammatory processes are compromised by hyperglycemic events and thus, hyperglycemic events alone should be considered risk factors for numerous human diseases. © 2017 IUBMB Life, 69(3):148-161, 2017.

B cells and atherosclerosis

B cells have emerged as important immune cells in cardiovascular disease. Initial studies have suggested that B cells protect against atherosclerosis development. However, subsequent studies demonstrating aggravation of atherosclerosis by B-2 cells have shed light on the subset-dependent effects of B cells. Here, we review the literature that has led to our current understanding of B cell regulation of atherosclerosis, touching on the importance of subsets, local regulation, human translation, and therapeutic potential.

Manipulation of the glycan-specific natural antibody repertoire for immunotherapy

Natural immunoglobulin derived from innate-like B lymphocytes plays important roles in the suppression of inflammatory responses and represents a promising therapeutic target in a growing number of allergic and autoimmune diseases. These antibodies are commonly autoreactive and incorporate evolutionarily conserved specificities, including certain glycan-specific antibodies. Despite this conservation, exposure to bacterial polysaccharides during innate-like B lymphocyte development, through either natural exposure or immunization, induces significant changes in clonal representation within the glycan-reactive B cell pool. Glycan-reactive natural antibodies (NAbs) have been reported to play protective and pathogenic roles in autoimmune and inflammatory diseases. An understanding of the composition and functions of a healthy glycan-reactive NAb repertoire is therefore paramount. A more thorough understanding of NAb repertoire development holds promise for the design of both biological diagnostics and therapies. In this article, we review the development and functions of NAbs and examine three glycan specificities, represented in the innate-like B cell pool, to illustrate the complex roles environmental antigens play in NAb repertoire development. We also discuss the implications of increased clonal plasticity of the innate-like B cell repertoire during neonatal and perinatal periods, and the prospect of targeting B cell development with interventional therapies and correct defects in this important arm of the adaptive immune system.

Human B-1 and B-2 B Cells Develop from Lin-CD34+CD38lo Stem Cells

The B-1 B cell population is an important bridge between innate and adaptive immunity primarily because B-1 cells produce natural Ab. Murine B-1 and B-2 cells arise from distinct progenitors; however, in humans, in part because it has been difficult to discriminate between them phenotypically, efforts to pinpoint the developmental origins of human B-1 and B-2 cells have lagged. To characterize progenitors of human B-1 and B-2 cells, we separated cord blood and bone marrow Lin^-CD34⁺ hematopoietic stem cells into Lin^-CD34⁺CD38^lo and Lin^-CD34⁺CD38^hi populations. We found that transplanted Lin^-CD34⁺CD38^lo cells, but not Lin^-CD34⁺CD38^hi cells, generated a CD19⁺ B cell population after transfer into immunodeficient NOD.Cg-Prkdc^scid Il2rg^tm1wjl/SxJ neonates. The emergent CD19⁺ B cell population was found in spleen, bone marrow, and peritoneal cavity of humanized mice and included distinct populations displaying the B-1 or the B-2 cell phenotype. Engrafted splenic B-1 cells exhibited a mature phenotype, as evidenced by low-to-intermediate expression levels of CD24 and CD38. The engrafted B-1 cell population expressed a VH-DH-JH composition similar to cord blood B-1 cells, including frequent use of VH4-34 (8 versus 10%, respectively). Among patients with hematologic malignancies who underwent hematopoietic stem cell transplantation, B-1 cells were found in the circulation as early as 8 wk posttransplantation. Altogether, our data demonstrate that human B-1 and B-2 cells develop from a Lin^-CD34⁺CD38^lo stem cell population, and engrafted B-1 cells in humanized mice exhibit an Ig-usage pattern comparable to B-1 cells in cord blood.

Cellular mechanisms and consequences of glycation in atherosclerosis and obesity

Post-translational modification of proteins imparts diversity to protein functions. The process of glycation represents a complex set of pathways that mediates advanced glycation endproduct (AGE) formation, detoxification, intracellular disposition, extracellular release, and induction of signal transduction. These processes modulate the response to hyperglycemia, obesity, aging, inflammation, and renal failure, in which AGE formation and accumulation is facilitated. It has been shown that endogenous anti-AGE protective mechanisms are thwarted in chronic disease, thereby amplifying accumulation and detrimental cellular actions of these species. Atop these considerations, receptor for advanced glycation endproducts (RAGE)-mediated pathways downregulate expression and activity of the key anti-AGE detoxification enzyme, glyoxalase-1 (GLO1), thereby setting in motion an interminable feed-forward loop in which AGE-mediated cellular perturbation is not readily extinguished. In this review, we consider recent work in the field highlighting roles for glycation in obesity and atherosclerosis and discuss emerging strategies to block the adverse consequences of AGEs. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Natural Antibodies as Rheostats for Susceptibility to Chronic Diseases in the Aged

Natural antibodies are spontaneously produced in the absence of infection or immunization, and are both anti-microbial and autoreactive. Autoreactive natural antibodies can bind noxious molecules, such as those involved in clinical situations of atherosclerosis (oxLDL), malignancy (NGcGM3), and neurodegeneration (amyloid, tau) and can affect the fate of their targets or the cells bearing them to maintain homeostasis. Clinically relevant natural antibodies have been shown to decline with advancing age in those few situations where measurements have been made. Consistent with this, human B-1 cells that are thought to be responsible for generating natural antibodies also decline with advancing age. These findings together suggest that an age-related decline in amount or efficacy of homeostatic natural antibodies is associated with relative loss of protection against molecules involved in several diseases whose incidence rises in the older age population, and that those individuals experiencing greatest loss are at greatest risk. In this view, natural antibodies act as rheostats for susceptibility to several age-related diseases. These considerations suggest that administration of natural antibodies, or of factors that maintain B-1 cells and/or enhance production of natural antibodies by B-1 cells, may serve to counteract the onset or progression of age-related chronic illness.

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.

Distinctions among Circulating Antibody-Secreting Cell Populations, Including B-1 Cells, in Human Adult Peripheral Blood

Human Ab-secreting cell (ASC) populations in circulation are not well studied. In addition to B-1 (CD20(+)CD27(+)CD38(lo/int)CD43(+)) cell and conventional plasmablast (PB) (CD20-CD27(hi)CD38(hi)) cell populations, in this study, we identified a novel B cell population termed 20(+)38(hi) B cells (CD20(+)CD27(hi)CD38(hi)) that spontaneously secretes Ab. At steady-state, 20(+)38(hi) B cells are distinct from PBs on the basis of CD20 expression, amount of Ab production, frequency of mutation, and diversity of BCR repertoire. However, cytokine treatment of 20(+)38(hi) B cells induces loss of CD20 and acquisition of CD138, suggesting that 20(+)38(hi) B cells are precursors to PBs or pre-PBs. We then evaluated similarities and differences among CD20(+)CD27(+)CD38(lo/int)CD43(+) B-1 cells, CD20(+)CD27(hi)CD38(hi) 20(+)38(hi) B cells, CD20(-)CD27(hi)CD38(hi) PBs, and CD20(+)CD27(+)CD38(lo/int)CD43(-) memory B cells. We found that B-1 cells differ from 20(+)38(hi) B cells and PBs in a number of ways, including Ag expression, morphological appearance, transcriptional profiling, Ab skewing, Ab repertoire, and secretory response to stimulation. In terms of gene expression, B-1 cells align more closely with memory B cells than with 20(+)38(hi) B cells or PBs, but differ in that memory B cells do not express Ab secretion-related genes. We found that B-1 cell Abs use Vh4-34, which is often associated with autoreactivity, 3- to 6-fold more often than other B cell populations. Along with selective production of IgM anti-phosphoryl choline, these data suggest that human B-1 cells might be preferentially selected for autoreactivity/natural specificity. In summary, our results indicate that human healthy adult peripheral blood at steady-state consists of three distinct ASC populations.