Diversification and CXCR4-Dependent Establishment of the Bone Marrow B-1a Cell Pool Governs Atheroprotective IgM Production Linked to Human Coronary Atherosclerosis

Targeting immune cell recruitment in atherosclerosis

Atherosclerosis is the primary underlying cause of myocardial infarction and stroke. Atherosclerotic cardiovascular disease is characterized by a chronic inflammatory reaction in medium-to-large-sized arteries, with its onset and perpetuation driven by leukocytes infiltrating the subendothelial space. Activation of endothelial cells triggered by hyperlipidaemia and lipoprotein retention in the arterial intima initiates the accumulation of pro-inflammatory leukocytes in the arterial wall, fostering the progression of atherosclerosis. This inflammatory response is coordinated by an array of soluble mediators, namely cytokines and chemokines, that amplify inflammation both locally and systemically and are complemented by tissue-specific molecules that regulate the homing, adhesion and transmigration of leukocytes. Despite abundant evidence from mouse models, only a few therapies targeting leukocytes in atherosclerosis have been assessed in humans. The major challenges for the clinical translation of these therapies include the lack of tissue specificity and insufficient selectivity of inhibition strategies. In this Review, we discuss the latest research on receptor-ligand pairs and interactors that regulate leukocyte influx into the inflamed artery wall, primarily focusing on studies that used pharmacological interventions. We also discuss mechanisms that promote the resolution of inflammation and highlight how major findings from these research areas hold promise as potential therapeutic strategies for atherosclerotic cardiovascular disease.

Tipping the Scale: Atheroprotective IgM-Producing B Cells in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease whose progression is fueled by proinflammatory moieties and limited by anti-inflammatory mediators. Whereas oxidative damage and the generation of oxidation-specific epitopes that act as damage-associated molecular patterns are highly inflammatory, IgM antibodies produced by B-1 and marginal zone B cells counteract unrestricted inflammation by neutralizing and encouraging clearance of these proinflammatory signals. In this review, we focus on describing the identities of IgM-producing B cells in both mice and humans, elaborating the mechanisms underlying IgM production, and discussing the potential strategies to augment the production of atheroprotective IgM. In addition, we will discuss promising therapeutic interventions in humans to help tip the scale toward augmentation of IgM production and to provide atheroprotection.

Causal Relationships between Lymphocyte Subsets and Risk of Coronary Artery Disease: A Two-Sample Mendelian Randomization Study

Background

Currently, the causal relationship between lymphocyte subsets and coronary artery disease (CAD) remains unclear. Therefore, we utilized Mendelian randomization (MR) to assess the association between lymphocyte subsets and CAD.

Methods

We performed a two-sample MR analysis using publicly available genome-wide association studies (GWAS) datasets. The primary method of analysis to comprehensively evaluate causal effects was the inverse variance-weighted (IVW) method. The four additional MR approaches were MR-Egger, weighted median, simple mode, and weighted mode. Sensitivity analysis incorporated Cochran's Q and MR-Egger intercept tests to identify residual heterogeneity and potential horizontal pleiotropy, respectively. The MR-PRESSO distortion test was applied to identify potential pleiotropic outliers. Leave-one-out analysis confirmed that no single single-nucleotide polymorphism (SNP) significantly affected the MR estimate. We conducted reverse MR analysis to investigate the impact of variables correlated with outcomes in forward MR analysis.

Results

The IVW method revealed a significant positive association between B cell count and CAD (odds ratio (OR) = 1.08 (95% CI: 1.04, 1.11), p = 2.67 × 10-5). A similar association was observed between B cell count and myocardial infarction (MI) (OR = 1.07 (95% CI: 1.03, 1.11), p = 5.69 × 10-4). Sensitivity analyses detected no outliers, heterogeneity, or pleiotropy. The reverse MR analysis was conducted to investigate the impact of CAD and MI on B cell count, and the IVW results showed no statistical significance.

Conclusions

Our study suggests that a higher absolute B cell count is linked to an increased risk of CAD and MI.

The immunology of B-1 cells: from development to aging

B-1 cells have intricate biology, with distinct function, phenotype and developmental origin from conventional B cells. They generate a B cell receptor with conserved germline characteristics and biased V(D)J recombination, allowing this innate-like lymphocyte to spontaneously produce self-reactive natural antibodies (NAbs) and become activated by immune stimuli in a T cell-independent manner. NAbs were suggested as "rheostats" for the chronic diseases in advanced age. In fact, age-dependent loss of function of NAbs has been associated with clinically-relevant diseases in the elderly, such as atherosclerosis and neurodegenerative disorders. Here, we analyzed comprehensively the ontogeny, phenotypic characteristics, functional properties and emerging roles of B-1 cells and NAbs in health and disease. Additionally, after navigating through the complexities of B-1 cell biology from development to aging, therapeutic opportunities in the field are discussed.

B-1 lymphocytes in adipose tissue as innate modulators of inflammation linked to cardiometabolic disease

Fat is stored in distinct depots with unique features in both mice and humans and B cells reside in all adipose depots. We have shown that B cells modulate cardiometabolic disease through activities in two of these key adipose depots: visceral adipose tissue (VAT) and perivascular adipose tissue (PVAT). VAT refers to the adipose tissue surrounding organs, within the abdomen and thorax, and is comprised predominantly of white adipocytes. This depot has been implicated in mediating obesity-related dysmetabolism. PVAT refers to adipose tissue surrounding major arteries. It had long been thought to exist to provide protection and insulation for the vessel, yet recent work demonstrates an important role for PVAT in harboring immune cells, promoting their function and regulating the biology of the underlying vessel. The role of B-2 cells and adaptive immunity in adipose tissue biology has been nicely reviewed elsewhere. Given that, the predominance of B-1 cells in adipose tissue at homeostasis, and the emerging role of B-1 cells in a variety of disease states, we will focus this review on how B-1 cells function in VAT and PVAT depots to promote homeostasis and limit inflammation linked to cardiometabolic disease and factors that regulate this function.

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.

CXCR4/CXCL12 axis: "old" pathway as "novel" target for anti-inflammatory drug discovery

Inflammation is the body's defense response to exogenous or endogenous stimuli, involving complex regulatory mechanisms. Discovering anti-inflammatory drugs with both effectiveness and long-term use safety is still the direction of researchers' efforts. The inflammatory pathway was initially identified to be involved in tumor metastasis and HIV infection. However, research in recent years has proved that the CXC chemokine receptor type 4 (CXCR4)/CXC motif chemokine ligand 12 (CXCL12) axis plays a critical role in the upstream of the inflammatory pathway due to its chemotaxis to inflammatory cells. Blocking the chemotaxis of inflammatory cells by CXCL12 at the inflammatory site may block and alleviate the inflammatory response. Therefore, developing CXCR4 antagonists has become a novel strategy for anti-inflammatory therapy. This review aimed to systematically summarize and analyze the mechanisms of action of the CXCR4/CXCL12 axis in more than 20 inflammatory diseases, highlighting its crucial role in inflammation. Additionally, the anti-inflammatory activities of CXCR4 antagonists were discussed. The findings might help generate new perspectives for developing anti-inflammatory drugs targeting the CXCR4/CXCL12 axis.

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.

A protective role for B-1 cells and oxidation-specific epitope IgM in lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a morbid fibrotic lung disease with limited treatment options. The pathophysiology of IPF remains poorly understood, and elucidation of the cellular and molecular mechanisms of IPF pathogenesis is key to the development of new therapeutics. B-1 cells are an innate B cell population which play an important role linking innate and adaptive immunity. B-1 cells spontaneously secrete natural IgM and prevent inflammation in several disease states. One class of these IgM recognize oxidation-specific epitopes (OSE), which have been shown to be generated in lung injury and to promote fibrosis. A main B-1 cell reservoir is the pleural space, adjacent to the typical distribution of fibrosis in IPF. In this study, we demonstrate that B-1 cells are recruited to the lung during injury where they secrete IgM to OSE (IgM OSE ). We also show that the pleural B-1 cell reservoir responds to lung injury through regulation of the chemokine receptor CXCR4. Mechanistically we show that the transcription factor Id3 is a novel negative regulator of CXCR4 expression. Using mice with B-cell specific Id3 deficiency, a model of increased B-1b cells, we demonstrate decreased bleomycin-induced fibrosis compared to littermate controls. Furthermore, we show that mice deficient in secretory IgM ( sIgM -/- ) have higher mortality in response to bleomycin-induced lung injury, which is partially mitigated through airway delivery of the IgM OSE E06. Additionally, we provide insight into potential mechanisms of IgM in attenuation of fibrosis through RNA sequencing and pathway analysis, highlighting complement activation and extracellular matrix deposition as key differentially regulated pathways.

The role of B-1 cells in cancer progression and anti-tumor immunity

In recent years, in addition to the well-established role of T cells in controlling or promoting tumor growth, a new wave of research has demonstrated the active involvement of B cells in tumor immunity. B-cell subsets with distinct phenotypes and functions play various roles in tumor progression. Plasma cells and activated B cells have been linked to improved clinical outcomes in several types of cancer, whereas regulatory B cells have been associated with disease progression. However, we are only beginning to understand the role of a particular innate subset of B cells, referred to as B-1 cells, in cancer. Here, we summarize the characteristics of B-1 cells and review their ability to infiltrate tumors. We also describe the potential mechanisms through which B-1 cells suppress anti-tumor immune responses and promote tumor progression. Additionally, we highlight recent studies on the protective anti-tumor function of B-1 cells in both mouse models and humans. Understanding the functions of B-1 cells in tumor immunity could pave the way for designing more effective cancer immunotherapies.

Loss of TET2 increases B-1 cell number and IgM production while limiting CDR3 diversity

Recent studies have demonstrated a role for Ten-Eleven Translocation-2 (TET2), an epigenetic modulator, in regulating germinal center formation and plasma cell differentiation in B-2 cells, yet the role of TET2 in regulating B-1 cells is largely unknown. Here, B-1 cell subset numbers, IgM production, and gene expression were analyzed in mice with global knockout of TET2 compared to wildtype (WT) controls. Results revealed that TET2-KO mice had elevated numbers of B-1a and B-1b cells in their primary niche, the peritoneal cavity, as well as in the bone marrow (B-1a) and spleen (B-1b). Consistent with this finding, circulating IgM, but not IgG, was elevated in TET2-KO mice compared to WT. Analysis of bulk RNASeq of sort purified peritoneal B-1a and B-1b cells revealed reduced expression of heavy and light chain immunoglobulin genes, predominantly in B-1a cells from TET2-KO mice compared to WT controls. As expected, the expression of IgM transcripts was the most abundant isotype in B-1 cells. Yet, only in B-1a cells there was a significant increase in the proportion of IgM transcripts in TET2-KO mice compared to WT. Analysis of the CDR3 of the BCR revealed an increased abundance of replicated CDR3 sequences in B-1 cells from TET2-KO mice, which was more clearly pronounced in B-1a compared to B-1b cells. V-D-J usage and circos plot analysis of V-J combinations showed enhanced usage of VH11 and VH12 pairings. Taken together, our study is the first to demonstrate that global loss of TET2 increases B-1 cell number and IgM production and reduces CDR3 diversity, which could impact many biological processes and disease states that are regulated by IgM.

Single-cell profiling of CD11c+ B cells in atherosclerosis

Circulating CD11c+ B cells, a novel subset of activated B cells, have been linked to autoimmunity and shown to expand with age. Atherosclerosis is an age-associated disease that involves innate and adaptive immune responses to modified self-antigens. Yet, the expression of CD11c on specific B-cell subtypes and its link to atherosclerosis are poorly understood. In this study, we characterized the frequency of CD11c+ B cells in tissues in mice with aging. We observed an age-associated increase in CD11c+ B cells in the spleen and bone marrow of ApoE-/- mice, and this was associated with an increase in aortic plaque. In addition, we also utilized single-cell multi-omics profiling of 60 human subjects undergoing advanced imaging for coronary artery disease (CAD) to subtype CD11c+ B cells and determine their frequency in subjects with high and low severity of CAD. Using unsupervised clustering, we identified four distinct clusters of CD11c+ B cells, which include CD27 and IgD double negative 2 (DN2), age-associated (ABC), CD11c+ unswitched memory (USWM), and activated Naïve (aNav) B cells. We observed an increase in the frequency of both ABC B cells and DN2 B cells in patients with high CAD severity. Pathway analysis further demonstrated augmentation of autophagy, IFNg signaling, and TLR signaling in DN2 cells in high-severity CAD patients. On the other hand, an increase in the negative regulator of BCR signaling through CD72 was found in ABC cells in low-severity CAD patients. Through investigating scRNAseq of atheroma, these DN2 cells were also found to infiltrate human coronary atheroma.

Atherosclerosis antigens as targets for immunotherapy

Atherosclerosis is a chronic inflammatory disease of the arteries that can lead to thrombosis, infarction and stroke, underlying the first cause of mortality worldwide. Adaptive immunity plays critical roles in atherosclerosis, and numerous studies have ascribed both atheroprotective and atherogenic functions to specific subsets of T and B cells. However, less is known on how antigen specificity determines the protective or adverse outcome of such adaptive responses. Understanding antigen triggers in atherosclerosis is crucial to delve deeper into mechanisms of disease initiation and progression and to implement specific immunotherapeutic approaches, including vaccination strategies. Here we review the role of adaptive immunity in atherosclerosis and the insights that single-cell technology has provided into the function of distinct immune cell subsets. We outline the most relevant atherosclerosis antigens and antibodies reported to date and examine their immunotherapeutic potential. Finally, we review the most promising vaccination-based clinical trials targeting the adaptive immune system.

Human circulating CD24hi marginal zone B cells produce IgM targeting atherogenic antigens and confer protection from vascular disease

IgMs that inactivate oxidation-specific epitopes (IgMOSE), which are secondary products of lipid peroxidization, protect against inflammatory diseases, including diet-induced atherosclerosis. However, the human B cell subtype that produces IgMOSE remains unknown. In this study, we used single-cell mass cytometry and adoptive transfer of B cell subtypes to NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice to identify B27+IgM+CD24hi cells as the major producers of IgMOSE in humans. Notably, these cells have characteristics of human circulatory marginal zone B (MZB) cells, which are known to be atheoroprotective IgM producers in mice. CD24 antibody treatment to reduce MZB cells and IgM in a hyperlipidemic humanized mouse model provides the evidence that MZB cells protect against vascular inflammation. Consistent with these findings, the frequency of B27+IgM+CD24hi cells (MZB) in patients inversely correlates with coronary artery disease severity.

Targeting a cell-specific microRNA repressor of CXCR4 ameliorates atherosclerosis in mice

The CXC chemokine receptor 4 (CXCR4) in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) is crucial for vascular integrity. The atheroprotective functions of CXCR4 in vascular cells may be counteracted by atherogenic functions in other nonvascular cell types. Thus, strategies for cell-specifically augmenting CXCR4 function in vascular cells are crucial if this receptor is to be useful as a therapeutic target in treating atherosclerosis and other vascular disorders. Here, we identified miR-206-3p as a vascular-specific CXCR4 repressor and exploited a target-site blocker (CXCR4-TSB) that disrupted the interaction of miR-206-3p with CXCR4 in vitro and in vivo. In vitro, CXCR4-TSB enhanced CXCR4 expression in human and murine ECs and VSMCs to modulate cell viability, proliferation, and migration. Systemic administration of CXCR4-TSB in Apoe-deficient mice enhanced Cxcr4 expression in ECs and VSMCs in the walls of blood vessels, reduced vascular permeability and monocyte adhesion to endothelium, and attenuated the development of diet-induced atherosclerosis. CXCR4-TSB also increased CXCR4 expression in B cells, corroborating its atheroprotective role in this cell type. Analyses of human atherosclerotic plaque specimens revealed a decrease in CXCR4 and an increase in miR-206-3p expression in advanced compared with early lesions, supporting a role for the miR-206-3p-CXCR4 interaction in human disease. Disrupting the miR-206-3p-CXCR4 interaction in a cell-specific manner with target-site blockers is a potential therapeutic approach that could be used to treat atherosclerosis and other vascular diseases.

Impact of Immunity on Coronary Artery Disease: An Updated Pathogenic Interplay and Potential Therapeutic Strategies

Coronary artery disease (CAD) is the leading cause of death worldwide. It is a result of the buildup of atherosclerosis within the coronary arteries. The role of the immune system in CAD is complex and multifaceted. The immune system responds to damage or injury to the arterial walls by initiating an inflammatory response. However, this inflammatory response can become chronic and lead to plaque formation. Neutrophiles, macrophages, B lymphocytes, T lymphocytes, and NKT cells play a key role in immunity response, both with proatherogenic and antiatherogenic signaling pathways. Recent findings provide new roles and activities referring to endothelial cells and vascular smooth muscle cells, which help to clarify the intricate signaling crosstalk between the involved actors. Research is ongoing to explore immunomodulatory therapies that target the immune system to reduce inflammation and its contribution to atherosclerosis. This review aims to summarize the pathogenic interplay between immunity and CAD and the potential therapeutic strategies, and explore immunomodulatory therapies that target the immune system to reduce inflammation and its contribution to atherosclerosis.

Novel mechanisms and therapeutic targets in atherosclerosis: inflammation and beyond

This review based on the ESC William Harvey Lecture in Basic Science 2022 highlights recent experimental and translational progress on the therapeutic targeting of the inflammatory components in atherosclerosis, introducing novel strategies to limit side effects and to increase efficacy. Since the validation of the inflammatory paradigm in CANTOS and COLCOT, efforts to control the residual risk conferred by inflammation have centred on the NLRP3 inflammasome-driven IL-1β-IL6 axis. Interference with the co-stimulatory dyad CD40L-CD40 and selective targeting of tumour necrosis factor-receptor associated factors (TRAFs), namely the TRAF6-CD40 interaction in macrophages by small molecule inhibitors, harbour intriguing options to reduce established atherosclerosis and plaque instability without immune side effects. The chemokine system crucial for shaping immune cell recruitment and homoeostasis can be fine-tuned and modulated by its heterodimer interactome. Structure-function analysis enabled the design of cyclic, helical, or linked peptides specifically targeting or mimicking these interactions to limit atherosclerosis or thrombosis by blunting myeloid recruitment, boosting regulatory T cells, inhibiting platelet activity, or specifically blocking the atypical chemokine MIF without notable side effects. Finally, adventitial neuroimmune cardiovascular interfaces in advanced atherosclerosis show robust restructuring of innervation from perivascular ganglia and employ sensory neurons of dorsal root ganglia to enter the central nervous system and to establish an atherosclerosis-brain circuit sensor, while sympathetic and vagal efferents project to the celiac ganglion to create an atherosclerosis-brain circuit effector. Disrupting this circuitry by surgical or chemical sympathectomy limited disease progression and enhanced plaque stability, opening exciting perspectives for selective and tailored intervention beyond anti-inflammatory strategies.

B-1 plasma cells require non-cognate CD4 T cell help to generate a unique repertoire of natural IgM

Evolutionarily conserved, "natural" (n)IgM is broadly reactive to both self and foreign antigens. Its selective deficiency leads to increases in autoimmune diseases and infections. In mice, nIgM is secreted independent of microbial exposure to bone marrow (BM) and spleen B-1 cell-derived plasma cells (B-1PC), generating the majority of nIgM, or by B-1 cells that remain non-terminally differentiated (B-1sec). Thus, it has been assumed that the nIgM repertoire is broadly reflective of the repertoire of body cavity B-1 cells. Studies here reveal, however, that B-1PC generate a distinct, oligoclonal nIgM repertoire, characterized by short CDR3 variable immunoglobulin heavy chain regions, 7-8 amino acids in length, some public, many arising from convergent rearrangements, while specificities previously associated with nIgM were generated by a population of IgM-secreting B-1 (B-1sec). BM, but not spleen B-1PC, or B-1sec also required the presence of TCRαβ CD4 T cells for their development from fetal precursors. Together, the studies identify important previously unknown characteristics of the nIgM pool.

Age-related changes in antigen-specific natural antibodies are influenced by sex

Introduction

Natural antibody (NAb) derived from CD5+ B-1 cells maintains tissue homeostasis, controls inflammation, aids in establishing long-term protective responses against pathogens, and provides immediate protection from infection. CD5+ B-1 cell NAbs recognize evolutionarily fixed epitopes, such as phosphatidylcholine (PtC), found on bacteria and senescent red blood cells. Anti-PtC antibodies are essential in protection against bacterial sepsis. CD5+ B-1 cell-derived NAbs have a unique germline-like structure that lacks N-additions, a feature critical for providing protection against infection. Previously, we demonstrated the repertoire and germline status of PtC+CD5+ B-1 cell IgM obtained from male mice changes with age depending on the anatomical location of the B-1 cells. More recently, we demonstrated serum antibody from aged female mice maintains protection against pneumococcal infection, whereas serum antibody from male mice does not provide protection.

Results

Here, we show that aged female mice have significantly more splenic PtC+CD5+ B-1 cells and more PtC specific serum IgM than aged male mice. Furthermore, we find both age and biological sex related repertoire differences when comparing B cell receptor (BCR) sequencing results of PtC+CD5+ B-1 cells. While BCR germline status of PtC+CD5+ B-1 cells from aged male and female mice is similar in the peritoneal cavity, it differs significantly in the spleen, where aged females retain germline configuration and aged males do not. Nucleic acid sensing toll-like receptors are critical in the maintenance of PtC+ B-1 cells; therefore, to begin to understand the mechanism of differences observed between the male and female PtC+CD5+ B-1 cell repertoire, we analyzed levels of cell-free nucleic acids and found increases in aged females.

Conclusion

Our results suggest the antigenic milieu differs between aged males and females, leading to differential selection of antigen-specific B-1 cells over time. Further elucidation of how biological sex differences influence the maintenance of B-1 cells within the aging environment will be essential to understand sex and age-related disparities in the susceptibility to bacterial infection and will aid in the development of more effective vaccination and/or therapeutic strategies specific for males and females.

Single-cell genomics identifies distinct B1 cell developmental pathways and reveals aging-related changes in the B-cell receptor repertoire

Background

B1 cells are self-renewing innate-like B lymphocytes that provide the first line of defense against pathogens. B1 cells primarily reside in the peritoneal cavity and are known to originate from various fetal tissues, yet their developmental pathways and the mechanisms underlying maintenance of B1 cells throughout adulthood remain unclear.

Results

We performed high-throughput single-cell analysis of the transcriptomes and B-cell receptor repertoires of peritoneal B cells of neonates, young adults, and elderly mice. Gene expression analysis of 31,718 peritoneal B cells showed that the neonate peritoneal cavity contained many B1 progenitors, and neonate B cell specific clustering revealed two trajectories of peritoneal B1 cell development, including pre-BCR dependent and pre-BCR independent pathways. We also detected profound age-related changes in B1 cell transcriptomes: clear difference in senescence genetic program was evident in differentially aged B1 cells, and we found an example that a B1 subset only present in the oldest mice was marked by expression of the fatty-acid receptor CD36. We also performed antibody gene sequencing of 15,967 peritoneal B cells from the three age groups and discovered that B1 cell aging was associated with clonal expansion and two B1 cell clones expanded in the aged mice had the same CDR-H3 sequence (AGDYDGYWYFDV) as a pathogenically linked cell type from a recent study of an atherosclerosis mouse model.

Conclusions

Beyond offering an unprecedent data resource to explore the cell-to-cell variation in B cells, our study has revealed that B1 precursor subsets are present in the neonate peritoneal cavity and dissected the developmental pathway of the precursor cells. Besides, this study has found the expression of CD36 on the B1 cells in the aged mice. And the single-cell B-cell receptor sequencing reveals B1 cell aging is associated with clonal expansion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00795-6.

B-1b Cells Have Unique Functional Traits Compared to B-1a Cells at Homeostasis and in Aged Hyperlipidemic Mice With Atherosclerosis

Immunoglobulin M (IgM) to oxidation specific epitopes (OSE) are inversely associated with atherosclerosis in mice and humans. The B-1b subtype of B-1 cells secrete IgM to OSE, and unlike B-1a cells, are capable of long-lasting IgM memory. What attributes make B-1b cells different than B-1a cells is unknown. Our objectives were to determine how B-1b cells produce more IgM compared to B-1a cells at homeostatic condition and to see the differences in the B-1a and B-1b cell distribution and IgM CDR-H3 sequences in mice with advanced atherosclerosis. Here, in-vivo studies demonstrated greater migration to spleen, splenic production of IgM and plasma IgM levels in ApoE^-/-Rag1^-/- mice intraperitoneally injected with equal numbers of B-1b compared to B-1a cells. Bulk RNA seq analysis and flow cytometry of B-1a and B-1b cells identified CCR6 as a chemokine receptor more highly expressed on B-1b cells compared to B-1a. Knockout of CCR6 resulted in reduced B-1b cell migration to the spleen. Moreover, B-1b cell numbers were significantly higher in spleen of aged atherosclerotic ApoE^-/- mice compared to young ApoE^-/- mice. Single cell sequencing results of IgHM in B-1a and B-1b cells from peritoneal cavity and spleen of atherosclerotic aged ApoE^-/- mice revealed significantly more N additions at the V-D and D-J junctions, greater diversity in V region usage and CDR-H3 sequences in B-1b compared to B-1a cells. In summary, B-1b cells demonstrated enhanced CCR6-mediated splenic migration, IgM production, and IgM repertoire diversification compared to B-1a cells. These findings suggest that potential strategies to selectively augment B-1b cell numbers and splenic trafficking could lead to increased and more diverse IgM targeting OSE to limit atherosclerosis.

The Forgotten Brother: The Innate-like B1 Cell in Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS), traditionally considered a chronic autoimmune attack against the insulating myelin sheaths around axons. However, the exact etiology has not been identified and is likely multi-factorial. Recently, evidence has been accumulating that implies that autoimmune processes underlying MS may, in fact, be triggered by pathological processes initiated within the CNS. This review focuses on a relatively unexplored immune cell-the "innate-like" B1 lymphocyte. The B1 cell is a primary-natural-antibody- and anti-inflammatory-cytokine-producing cell present in the healthy brain. It has been recently shown that its frequency and function may differ between MS patients and healthy controls, but its exact involvement in the MS pathogenic process remains obscure. In this review, we propose that this enigmatic cell may play a more prominent role in MS pathology than ever imagined. We aim to shed light on the human B1 cell in health and disease, and how dysregulation in its delicate homeostatic role could impact MS. Furthermore, novel therapeutic avenues to restore B1 cells' beneficial functions will be proposed.

Modified Lipoproteins Induce Arterial Wall Inflammation During Atherogenesis

Circulating apolipoprotein B-containing lipoproteins, notably the low-density lipoproteins, enter the inner layer of the arterial wall, the intima, where a fraction of them is retained and modified by proteases, lipases, and oxidizing agents and enzymes. The modified lipoproteins and various modification products, such as fatty acids, ceramides, lysophospholipids, and oxidized lipids induce inflammatory reactions in the macrophages and the covering endothelial cells, initiating an increased leukocyte diapedesis. Lipolysis of the lipoproteins also induces the formation of cholesterol crystals with strong proinflammatory properties. Modified and aggregated lipoproteins, cholesterol crystals, and lipoproteins isolated from human atherosclerotic lesions, all can activate macrophages and thereby induce the secretion of proinflammatory cytokines, chemokines, and enzymes. The extent of lipoprotein retention, modification, and aggregation have been shown to depend largely on differences in the composition of the circulating lipoprotein particles. These properties can be modified by pharmacological means, and thereby provide opportunities for clinical interventions regarding the prevention and treatment of atherosclerotic vascular diseases.

B-1b Cells Possess Unique bHLH-Driven P62-Dependent Self-Renewal and Atheroprotection

BACKGROUND

B1a and B1b lymphocytes produce IgM that inactivates oxidation-specific epitopes (IgM^OSE) on LDL (low-density lipoprotein) and protects against atherosclerosis. Loss of ID3 (inhibitor of differentiation 3) in B cells selectively promotes B1b but not B1a cell numbers, leading to higher IgM^OSE production and reduction in atherosclerotic plaque formation. Yet, the mechanism underlying this regulation remains unexplored.

METHODS

Bulk RNA sequencing was utilized to identify differentially expressed genes in B1a and B1b cells from Id3KO and Id3WT mice. CRISPR/Cas9 and lentiviral genome editing coupled with adoptive transfer were used to identify key Id3-dependent signaling pathways regulating B1b cell proliferation and the impact on atherosclerosis. Biospecimens from humans with advanced coronary artery disease imaging were analyzed to translate murine findings to human subjects with coronary artery disease.

RESULTS

Through RNA sequencing, P62 was found to be enriched in Id3KO B1b cells. Further in vitro characterization reveals a novel role for P62 in mediating BAFF (B-cell activating factor)-induced B1b cell proliferation through interacting with TRAF6 and activating NF-κB (nuclear factor kappa B), leading to subsequent C-MYC upregulation. Promoter-reporter assays reveal that Id3 inhibits the E2A protein from activating the P62 promoter. Mice adoptively transferred with B1 cells overexpressing P62 exhibited an increase in B1b cell number and IgM^OSE levels and were protected against atherosclerosis. Consistent with murine mechanistic findings, P62 expression in human B1 cells was significantly higher in subjects harboring a function-impairing SNP (rs11574) in the ID3 gene and directly correlated with plasma IgM^OSE levels.

CONCLUSIONS

This study unveils a novel role for P62 in driving BAFF-induced B1b cell proliferation and IgM^OSE production to attenuate diet-induced atherosclerosis. Results identify a direct role for Id3 in antagonizing E2A from activating the p62 promoter. Moreover, analysis of putative human B1 cells also implicates these pathways in coronary artery disease subjects, suggesting P62 as a new immunomodulatory target for treating atherosclerosis.

Chemokine Receptor Activation Enhances Memory B Cell Class Switching Linked to IgE Sensitization to Alpha Gal and Cardiovascular Disease

Background: Recent studies have suggested that IgE sensitization to α-gal is associated with coronary artery disease (CAD). However, the B cell subtype(s) responsible for production of IgE to α-gal and mechanisms mediating this production remain elusive. Methods: Single cell multi-omics sequencing, was utilized to phenotype B cells obtained from 60 subjects that had undergone coronary angiography in whom serum IgE was evaluated by ImmunoCAP. Bioinformatics approaches were used to identify B cell subtype(s) and transcriptomic signatures associated with α-gal sensitization. In vitro characterization of chemokine/chemokine receptor pairs on switched memory B cells associated with IgE to α-gal was performed. Results: Of the 60 patients, 17 (28%) were positive for IgE to α-gal. CITESeq identified CCR6+ class-switched memory (SWM) B cells and CXCR4 expresssion on these CCR6+ SWM B cells as significantly associated with IgE sensitization to α-gal but not to other common allergens (peanut or inhalants). In vitro studies of enriched human B cells revealed significantly greater IgE on SWM B cells with high CCR6 and CXCR4 expression 10 days after cells were treated with IL-4 and CD40 to stimulate class switch recombination. Both CCL20 (CCR6 ligand) and CXCL12 (ligand for CXCR4) increased the expression of IgE on SWM B cells expressing their receptors. However, they appeared to have unique pathways mediating this effect as only CCL20 increased activation-induced cytidine deaminase (AID), while CXCL12 drove proliferation of CXCR4+ SWM B cells. Lastly, correlation analysis indicated an association between CAD severity and the frequency of both CCR6+ SWM and CXCR4+ SWM B cells. Conclusions: CCR6+ SWM B cells were identified as potential producers of IgE to α-gal in CAD patients. Additionally, our findings highlighted non-chemotaxis roles of CCL20/CCR6 and CXCL12/CXCR4 signaling in mediating IgE class switching and cell proliferation of SWM B cells respectively. Results may have important implications for a better understanding and better therapeutic approaches for subjects with IgE sensitization to α-gal.

Two paralogs of CXCR4 in the Japanese sea bass (Lateolabrax japonica) are involved in the immune response of B lymphocytes

CXC chemokine receptor 4 (CXCR4), a member of the G-protein-coupled receptor family, plays an important role in host immune responses. Within the teleost lineage, there are two paralogs of CXCR4; however, the role of CXCR4 in teleost B cells is poorly understood. In this study, we determined the cDNA sequences of the two CXCR4 paralogs from the Japanese sea bass (Lateolabrax japonica; LjCXCR4a and LjCXCR4b). Sequence and phylogenetic tree analyses revealed that LjCXCR4a and LjCXCR4b are most closely related to CXCR4a and CXCR4b, respectively, in the large yellow croaker (Larimichthys crocea). CXCR4 transcripts were mainly expressed in the gills, and their expression in different tissues was altered upon infection with Vibrio harveyi. LjCXCR4a and LjCXCR4b protein levels were upregulated in infected B cells. Knockdown of LjCXCR4a and LjCXCR4b in B cells by RNA interference, the phagocytic activity of B cells was not affected. Furthermore, knockdown of LjCXCR4a, not of LjCXCR4b, was observed to inhibit LjIgM expression in lipopolysaccharide-stimulated B cells. In addition, knockdown of LjCXCR4a, not of LjCXCR4b, was found to reduce reactive oxygen species levels in B cells. Our results indicate that LjCXCR4a and LjCXCR4b modulate the immune response of Japanese sea bass B cells against bacterial infection, albeit via different pathways.

Role and implications of the CXCL12/CXCR4/CXCR7 axis in atherosclerosis: still a debate

Atherosclerosis is one of the leading causes of mortality and morbidity worldwide. Chemokines and their receptors are implicated in the pathogenesis of atherosclerosis. CXCL12 is a member of the chemokine family exerting a myriad role in atherosclerosis through its classical CXCR4 and atypical ACKR3 (CXCR7) receptors. The modulatory and regulatory functional spectrum of CXCL12/CXCR4/ACKR3 axis in atherosclerosis spans from proatherogenic, prothrombotic and proinflammatory to atheroprotective, plaque stabilizer and dyslipidemia rectifier. This diverse continuum is executed in a wide range of biological units including endothelial cells (ECs), progenitor cells, macrophages, monocytes, platelets, lymphocytes, neutrophils and vascular smooth muscle cells (VSMCs) through complex heterogeneous and homogenous coupling of CXCR4 and ACKR3 receptors, employing different downstream signalling pathways, which often cross-talk among themselves and with other signalling interactomes. Hence, a better understanding of this structural and functional heterogeneity and complex phenomenon involving CXCL12/CXCR4/ACKR3 axis in atherosclerosis would not only help in formulation of novel therapeutics, but also in elucidation of the CXCL12 ligand and its receptors, as possible diagnostic and prognostic biomarkers.Key messagesThe role of CXCL12 per se is proatherogenic in atherosclerosis development and progression.The CXCL12 receptors, CXCR4 and ACKR3 perform both proatherogenic and athero-protective functions in various cell typesDue to functional heterogeneity and cross talk of CXCR4 and ACKR3 at receptor level and downstream pathways, regional boosting with specific temporal and spatial modulators of CXCL12, CXCR4 and ACKR3 need to be explored.

B Cell-Activating Factor Antagonism Attenuates the Growth of Experimental Abdominal Aortic Aneurysm

B cell-activating factor (BAFF), part of a tumor necrosis factor family of cytokines, was recently identified as a regulator of atherosclerosis; however, its role in aortic aneurysm has not been determined. Here, the study examined the effect of selective BAFF antagonism using an anti-BAFF antibody (blocks binding of BAFF to receptors BAFF receptor 3, transmembrane activator and CAML interactor, and B-cell maturation antigen) and mBaffR-mFc (blocks binding of BAFF to BAFF receptor 3) on a murine model of abdominal aortic aneurysm (AAA). In a prevention strategy, the antagonists were injected before the induction of AAA, and in an intervention strategy, the antagonists were injected after the induction of AAA. Both strategies attenuated the formation of AAA. In the intervention group, BAFF antagonism depleted most of the mature B-cell subsets in spleen and circulation, leading to enhanced resolution of inflammation in AAA as indicated by decreased infiltration of B cells and proinflammatory macrophages and a reduced number of apoptotic cells. In AAA tissues, B cells and macrophages were found in close contact. In vitro, B cells, irrespective of treatment with BAFF, impaired the efferocytosis activity of macrophages, suggesting a direct innate role of B cells on macrophage function. Altogether, BAFF antagonism affects survival of the mature B cells, promotes resolution of inflammation in the aorta, and attenuates the growth of AAA in mice.

B Lymphocyte-Deficiency in Mice Causes Vascular Dysfunction by Inducing Neutrophilia

B lymphocytes have been implicated in the development of insulin resistance, atherosclerosis and certain types of hypertension. In contrast to these studies, which were performed under pathological conditions, the present study provides evidence for the protective effect of B lymphocytes in maintaining vascular homeostasis under physiological conditions. In young mice not exposed to any known risk factors, the lack of B cells led to massive endothelial dysfunction. The vascular dysfunction in B cell-deficient mice was associated with an increased number of neutrophils in the circulating blood. Neutrophil depletion in B cell-deficient mice resulted in the complete normalization of vascular function, indicating a causal role of neutrophilia. Moreover, vascular function in B cell-deficient mice could be restored by adoptive transfer of naive B-1 cells isolated from wild-type mice. Interestingly, B-1 cell transfer also reduced the number of neutrophils in the recipient mice, further supporting the involvement of neutrophils in the vascular pathology caused by B cell-deficiency. In conclusion, we report in the present study the hitherto undescribed role of B lymphocytes in regulating vascular function. B cell dysregulation may represent a crucial mechanism in vascular pathology.

The Placebo-Controlled Effect of Percutaneous Coronary Intervention on Exercise Induced Changes in Anti-Malondialdehyde-LDL Antibody Levels in Stable Coronary Artery Disease: A Substudy of the ORBITA Trial

Aim: Malondialdehyde-modified low-density lipoprotein (MDA-LDL) forms a significant component of oxidised LDL. The effects of exercise on levels of MDA-LDL and anti-MDA-LDL antibodies are not well-understood. Furthermore, it is not known whether these can be modified in patients with coronary artery disease by percutaneous coronary intervention (PCI). Methods: The Objective Randomised Blinded Investigation with optimal medical Therapy of Angioplasty in stable angina (ORBITA) trial was the first blinded, multi-centre randomised trial of PCI vs. placebo procedure for angina relief. Serum samples were available at four time-points: pre-randomisation pre- (P1) and post- (P2) exercise and post-randomisation (6-weeks following the PCI or placebo procedure), pre- (P3) and post- (P4) exercise. ELISAs were performed using laboratory-developed assays for MDA-LDL (adjusted for Apolipoprotein B) and anti-MDA-LDL antibodies. Results: One hundred ninety-six of the 200 patients (age 66.1 [SD 8.99] years, 28% female) with severe single vessel coronary artery disease suitable for PCI enrolled in the ORBITA trial had blood available for analysis. With exercise at pre-randomisation (P2-P1) there was no significant change in adjusted MDA-LDL (-0.001, 95% CI -0.004 to 0.001; p = 0.287); however, IgG and IgM anti-MDA-LDL significantly declined (-0.022, 95% CI -0.029 to -0.014, p < 0.0001; -0.016, 95% CI -0.024 to -0.008, p = 0.0002, respectively). PCI did not have a significant impact on either the pre-exercise values (P3 controlling for P1) of MDA-LDL (p = 0.102), IgG (p = 0.444) or IgM anti-MDA-LDL (p = 0.909). Nor did PCI impact the exercise induced changes in these markers (P4 controlling for P1, P2, and P3) for MDA-LDL (p = 0.605), IgG (p = 0.725) or IgM anti-MDA-LDL (p = 0.171). Pre-randomisation ischaemia on stress echo did not impact these interactions. Conclusions: Exercise results in an acute reduction in anti-oxLDL antibodies in patients with severe single vessel coronary disease, possibly indicating an induction in homoeostatic clearance via the innate immune system. However, PCI did not ameliorate this effect.

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.

Therapeutic Potential of B-1a Cells in Intestinal Ischemia-reperfusion Injury

BACKGROUND

Acute mesenteric ischemia is a common surgical emergency. Restoration of blood flow is a critical objective of treating this pathology. However, many patients suffer from ischemia-reperfusion (I/R) injuries at the time of revascularization, requiring prolonged hospitalizations. B-1a cells are a subtype of B lymphocytes with roles in regulating inflammation and tissue injury by spontaneous release of natural IgM and IL-10. We hypothesized that treatment with B-1a cells protects mice from intestinal I/R.

METHODS

Mesenteric ischemia was induced in mice by placing a vascular clip on the superior mesenteric artery for 60 minutes. At the time of reperfusion, B-1a cells or PBS control were instilled into the peritoneal cavity (PerC) of mice. PerC lavage, blood, intestine, and lungs were collected 4 h after reperfusion. Serum organ injury and inflammatory markers such as ALT, AST, LDH, lactate, IL-6, as well as lung and gut histology and myeloperoxidase (MPO) were assessed.

RESULTS

In intestinal I/R, B-1a cell frequency and number in the PerC were significantly decreased compared to sham-operated mice. There was an increase in the serum levels of ALT, AST, LDH, lactate, and IL-6 when comparing the vehicle group with the sham group. These increases were significantly reduced in the B-1a cell treated group. B-1a cell treatment significantly decreased the intestine and lung injury scores as well as MPO content, compared to vehicle treated mice. B-1a cell treatment resulted in a reduction of apoptotic cells in these tissues. Serum IgM levels were decreased in intestinal I/R, while treatment with B-1a cells significantly increased their levels towards normal levels.

CONCLUSIONS

B-1a cell treatment at the time of mesenteric reperfusion ameliorates end organ damage and reduces systemic inflammation through the improvement of serum IgM levels. Preserving B-1a cells pool could serve as a novel therapeutic avenue in intestinal I/R injury.

Anti-inflammatory and Immunomodulatory Therapies in Atherosclerosis

Hypercholesterolemia is a major risk factor in atherosclerosis development and lipid-lowering drugs (i.e., statins) remain the treatment of choice. Despite effective reduction of LDL cholesterol in patients, a residual cardiovascular risk persists in some individuals, highlighting the need for further therapeutic intervention. Recently, the CANTOS trial paved the way toward the development of specific therapies targeting inflammation, a key feature in atherosclerosis progression. The pre-existence of multiple drugs modulating both innate and adaptive immune responses has significantly accelerated the number of translational studies applying these drugs to atherosclerosis. Additional preclinical research has led to the discovery of new therapeutic targets, offering promising perspectives for the treatment and prevention of atherosclerosis. Currently, both drugs with selective targeting and broad unspecific anti-inflammatory effects have been tested. In this chapter, we aim to give an overview of current advances in immunomodulatory treatment approaches for atherosclerotic cardiovascular diseases.

Targeting the chemokine network in atherosclerosis

Chemokines and their receptors represent a potential target for immunotherapy in chronic inflammation. They comprise a large family of cytokines with chemotactic activity, and their cognate receptors are expressed on all cells of the body. This network dictates leukocyte recruitment and activation, angiogenesis, cell proliferation and maturation. Dysregulation of chemokine and chemokine receptor expression as well as function participates in many pathologies including cancer, autoimmune diseases and chronic inflammation. In atherosclerosis, a lipid-driven chronic inflammation of middle-sized and large arteries, chemokines and their receptors participates in almost all stages of the disease from initiation of fatty streaks to mature atherosclerotic plaque formation. Atherosclerosis and its complications are the main driver of mortality and morbidity in cardiovascular diseases (CVD). Hence, exploring new fields of therapeutic targeting of atherosclerosis is of key importance. This review gives an overview of the recent advances on the role of key chemokines and chemokine receptors in atherosclerosis, addresses chemokine-based biomarkers at biochemical, imaging and genetic level in human studies, and highlights the clinial trials targeting atherosclerosis.

B Cells in Atherosclerosis: Mechanisms and Potential Clinical Applications

•

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

•

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.

•

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

•

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

•

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.

Single-Cell Transcriptomics Reveals the Cellular Heterogeneity of Cardiovascular Diseases

"A world in a wild flower, and a bodhi in a leaf," small cells contain huge secrets. The vasculature is composed of many multifunctional cell subpopulations, each of which is involved in the occurrence and development of cardiovascular diseases. Single-cell transcriptomics captures the full picture of genes expressed within individual cells, identifies rare or de novo cell subpopulations, analyzes single-cell trajectory and stem cell or progenitor cell lineage conversion, and compares healthy tissue and disease-related tissue at single-cell resolution. Single-cell transcriptomics has had a profound effect on the field of cardiovascular research over the past decade, as evidenced by the construction of cardiovascular cell landscape, as well as the clarification of cardiovascular diseases and the mechanism of stem cell or progenitor cell differentiation. The classification and proportion of cell subpopulations in vasculature vary with species, location, genotype, and disease, exhibiting unique gene expression characteristics in organ development, disease progression, and regression. Specific gene markers are expected to be the diagnostic criteria, therapeutic targets, or prognostic indicators of diseases. Therefore, treatment of vascular disease still has lots of potentials to develop. Herein, we summarize the cell clusters and gene expression patterns in normal vasculature and atherosclerosis, aortic aneurysm, and pulmonary hypertension to reveal vascular heterogeneity and new regulatory factors of cardiovascular disease in the use of single-cell transcriptomics and discuss its current limitations and promising clinical potential.

Extracellular CIRP decreases Siglec-G expression on B-1a cells skewing them towards a pro-inflammatory phenotype in sepsis

BACKGROUND

Sepsis is a life-threatening disease syndrome caused by a dysregulated host response to infection and injury. Extracellular cold-inducible RNA-binding protein (eCIRP) acts as a damage-associated molecular pattern. Peritoneal cavity (PerC) B-1a cells attenuate inflammation and tissue injury by spontaneous releasing natural IgM and IL-10. Sialic acid-binding immunoglobulin-type lectin-G (Siglec-G) is a CD33-related receptor highly expressed in B-1a cells to serve critical immunoregulatory functions. In sepsis, B-1a cell numbers in PerC are decreased. We hypothesized that eCIRP causes the reduction of PerC B-1a cells and alters their function during sepsis.

METHODS

Sepsis was induced in WT and CIRP-/- mice by cecal ligation and puncture (CLP). PerC washout cells were collected and B-1a cells and Siglec-G were assessed by flow cytometry. Mice were i.p. injected with recombinant murine (rm) CIRP and after 20 h, Siglec-G expression in PerC B-1a cells were assessed. PerC B-1a cells were treated with rmCIRP for 4 h and Siglec-G expression was assessed. PerC B-1a cells were pre-treated with anti-Siglec-G Ab and then after stimulated with rmCIRP for 24 h, IL-6 levels in the culture supernatants were assessed.

RESULTS

eCIRP levels in the PerC were elevated in septic mice. In WT mice, the frequencies and numbers of total and Siglec-G+ B-1a cells in the PerC were significantly decreased in the CLP group compared to sham group, whereas in CIRP-/- mice, their frequencies and numbers in sepsis were significantly rescued compared to WT septic mice. Mice injected with rmCIRP showed decreased frequencies and numbers of total and Siglec-G+ PerC B-1a cells compared to PBS-injected mice. In vitro treatment of PerC B-1a cells with rmCIRP demonstrated significant reduction in Siglec-G mRNA and protein compared to PBS group. PerC B-1a cells treated with anti-Siglec-G Ab had significantly higher production of IL-6 in response to rmCIRP compared to IgG control. Anti-Siglec-G Ab treated B-1a cells co-cultured with macrophages produced significantly higher levels of IL-6, and TNF-α, and lower levels of IL-10 compared to IgG-treated B-1a cells and macrophage co-cultures stimulated with rmCIRP.

CONCLUSION

eCIRP reduces PerC B-1a cell pool and skews them to a pro-inflammatory phenotype by downregulating Siglec-G expression. Targeting eCIRP will retain Siglec-G expressing B-1a cells in the PerC and preserve their anti-inflammatory function in sepsis.

Rituximab in Patients with Acute ST-elevation Myocardial Infarction (RITA-MI): an Experimental Medicine Safety Study

Aims

In pre-clinical models of acute myocardial infarction (MI), mature B cells mobilize inflammatory monocytes into the heart, leading to increased infarct size and deterioration of cardiac function, whilst anti-CD20 antibody-mediated depletion of B cells limits myocardial injury and improves cardiac function. Rituximab is a monoclonal anti-CD20 antibody targeted against human B cells. However, its use in cardiovascular disease is untested and is currently contraindicated. Therefore, we assessed the safety, feasibility, and pharmacodynamic effect of rituximab given to patients with acute ST-elevation MI (STEMI).

Methods and results

Rituximab in patients with acute ST-elevation myocardial infarction (RITA-MI) was a prospective, open-label, dose-escalation, single-arm, phase 1/2a clinical trial, which tested rituximab administered as a single intravenous dose in patients with STEMI within 48 h of symptom onset. Four escalating doses (200, 500, 700, and 1000 mg) were used. The primary endpoint was safety, whilst secondary endpoints were changes in circulating immune cell subsets including B cells, and cardiac and inflammatory biomarkers. A total of 24 patients were dosed. Rituximab appeared well tolerated. Seven serious adverse events were reported, none of which were assessed as being related to the rituximab infusion. Rituximab caused a mean 96.3% (95% confidence interval 93.8–98.8%) depletion of circulating B cells within 30 min of starting the infusion. Maximal B-cell depletion was seen at Day 6, which was significantly lower than baseline for all doses (P < 0.001). B-cell repopulation at 6 months was dose-dependent, with modulation of returning B-cell subsets. Immunoglobulin (IgG, IgM, and IgA) levels were not affected during the 6 months of follow-up.

Conclusions

A single infusion of rituximab appears safe when given in the acute STEMI setting and substantially alters circulating B-cell subsets. We provide important new insight into the feasibility and pharmacodynamics of rituximab in acute STEMI, which will inform further clinical translation of this potential therapy.

Clinical trial registration

NCT03072199 at https://www.clinicaltrials.gov/

Chemokine Receptor-6 Promotes B-1 Cell Trafficking to Perivascular Adipose Tissue, Local IgM Production and Atheroprotection

Chemokine receptor-6 (CCR6) mediates immune cell recruitment to inflammatory sites and has cell type-specific effects on diet-induced atherosclerosis in mice. Previously we showed that loss of CCR6 in B cells resulted in loss of B cell-mediated atheroprotection, although the B cell subtype mediating this effect was unknown. Perivascular adipose tissue (PVAT) harbors high numbers of B cells including atheroprotective IgM secreting B-1 cells. Production of IgM antibodies is a major mechanism whereby B-1 cells limit atherosclerosis development. Yet whether CCR6 regulates B-1 cell number and production of IgM in the PVAT is unknown. In this present study, flow cytometry experiments demonstrated that both B-1 and B-2 cells express CCR6, albeit at a higher frequency in B-2 cells in both humans and mice. Nevertheless, B-2 cell numbers in peritoneal cavity (PerC), spleen, bone marrow and PVAT were no different in ApoE ^-/- CCR6 ^-/- compared to ApoE ^-/- CCR6 ^+/+ mice. In contrast, the numbers of atheroprotective IgM secreting B-1 cells were significantly lower in the PVAT of ApoE ^-/- CCR6 ^-/- compared to ApoE ^-/- CCR6 ^+/+ mice. Surprisingly, adoptive transfer (AT) of CD43^- splenic B cells into B cell-deficient μMT ^-/- ApoE ^-/- mice repopulated the PerC with B-1 and B-2 cells and reduced atherosclerosis when transferred into ApoE ^-/- CCR6 ^+/+ sIgM ^-/- mice only when those cells expressed both CCR6 and sIgM. CCR6 expression on circulating human B cells in subjects with a high level of atherosclerosis in their coronary arteries was lower only in the putative human B-1 cells. These results provide evidence that B-1 cell CCR6 expression enhances B-1 cell number and IgM secretion in PVAT to provide atheroprotection in mice and suggest potential human relevance to our murine findings.

Functional Role of B Cells in Atherosclerosis

Atherosclerosis is a lipid-driven inflammatory disease of blood vessels, and both innate and adaptive immune responses are involved in its development. The impact of B cells on atherosclerosis has been demonstrated in numerous studies and B cells have been found in close proximity to atherosclerotic plaques in humans and mice. B cells exert both atheroprotective and pro-atherogenic functions, which have been associated with their B cell subset attribution. While B1 cells and marginal zone B cells are considered to protect against atherosclerosis, follicular B cells and innate response activator B cells have been shown to promote atherosclerosis. In this review, we shed light on the role of B cells from a different, functional perspective and focus on the three major B cell functions: antibody production, antigen presentation/T cell interaction, and the release of cytokines. All of these functions have the potential to affect atherosclerosis by multiple ways and are dependent on the cellular milieu and the activation status of the B cell. Moreover, we discuss B cell receptor signaling and the mechanism of B cell activation under atherosclerosis-prone conditions. By summarizing current knowledge of B cells in and beyond atherosclerosis, we are pointing out open questions and enabling new perspectives.

Antigen Receptor Specificity and Cell Location Influence the Diversification and Selection of the B-1a Cell Pool with Age

B-1a cells provide immediate and essential protection from infection through production of natural Ig, which is germline-like due to minimal insertion of N region additions. We have previously demonstrated peritoneal B-1a cell-derived phosphorylcholine-specific and total IgM moves away from germline (as evidenced by an increase in N-additions) with age as a result of selection. In young mice, anti-phosphatidylcholine Abs, like anti-phosphorylcholine Abs, contain few N-additions, and have been shown to be essential in protection from bacterial sepsis. In this study, we demonstrate the germline-like status of phosphatidylcholine (PtC)-specific (PtC⁺) peritoneal B-1a cell IgM does not change with age. In direct contrast, the splenic PtC⁺ B-1a cell population does not preserve its IgM germline status in the aged mice. Furthermore, splenic PtC⁺ B-1a cells displayed more diverse variable gene segments of the H chain (V_H) use in both the young and aged mice as compared with peritoneal PtC⁺ B-1a cells. Whereas the peritoneal PtC⁺ population increased V_H12 use with age, we observed differential use of V_H11, V_H12, and V_H2 between the peritoneal and splenic PtC⁺ populations with age. These results suggest disparate selection pressures occur with age upon B-1a cells expressing different specificities in distinct locations. Overall, these results illuminate the need to further elucidate how B-1a cells are influenced over time in terms of production and selection, both of which contribute to the actual and available natural IgM repertoire with increasing age. Such studies would aid in the development of more effective vaccination and therapeutic strategies in the aged population.

CD1d Selectively Down Regulates the Expression of the Oxidized Phospholipid-Specific E06 IgM Natural Antibody in Ldlr-/- Mice

Natural antibodies (NAbs) are important regulators of tissue homeostasis and inflammation and are thought to have diverse protective roles in a variety of pathological states. E06 is a T15 idiotype IgM NAb exclusively produced by B-1 cells, which recognizes the phosphocholine (PC) head group in oxidized phospholipids on the surface of apoptotic cells and in oxidized LDL (OxLDL), and the PC present on the cell wall of Streptococcus pneumoniae. Here we report that titers of the E06 NAb are selectively increased several-fold in Cd1d-deficient mice, whereas total IgM and IgM antibodies recognizing other oxidation specific epitopes such as in malondialdehyde-modified LDL (MDA-LDL) and OxLDL were not increased. The high titers of E06 in Cd1d-deficient mice are not due to a global increase in IgM-secreting B-1 cells, but they are specifically due to an expansion of E06-secreting splenic B-1 cells. Thus, CD1d-mediated regulation appeared to be suppressive in nature and specific for E06 IgM-secreting cells. The CD1d-mediated regulation of the E06 NAb generation is a novel mechanism that regulates the production of this specific oxidation epitope recognizing NAb.

Beyond Macrophages and T Cells: B Cells and Immunoglobulins Determine the Fate of the Atherosclerotic Plaque

Atherosclerosis (AS) leading to myocardial infarction and stroke remains worldwide the main cause for mortality. Vulnerable atherosclerotic plaques are responsible for these life-threatening clinical endpoints. Atherosclerosis is a chronic, complex, inflammatory disease with interactions between metabolic dysfunction, dyslipidemia, disturbed microbiome, infectious triggers, vascular, and immune cells. Undoubtedly, the immune response is a most important piece of the pathological puzzle in AS. Although macrophages and T cells have been the focus of research in recent years, B cells producing antibodies and regulating T and natural killer (NKT) cell activation are more important than formerly thought. New results show that the B cells exert a prominent role with atherogenic and protective facets mediated by distinct B cell subsets and different immunoglobulin effects. These new insights come, amongst others, from observations of the effects of innovative B cell targeted therapies in autoimmune diseases like systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). These diseases associate with AS, and the beneficial side effects of B cell subset depleting (modifying) therapies on atherosclerotic concomitant disease, have been observed. Moreover, the CANTOS study (NCT01327846) showed impressive results of immune-mediated inflammation as a new promising target of action for the fight against atherosclerotic endpoints. This review will reflect the putative role of B cells in AS in an attempt to connect observations from animal models with the small spectrum of the thus far available human data. We will also discuss the clinical therapeutic potency of B cell modulations on the process of AS.

TLR2/CXCR4 coassociation facilitatesChlamydia pneumoniaeinfection-induced atherosclerosis

Toll-like receptor 2 (TLR2) and C-X-C motif chemokine receptor 4 (CXCR4) have both been shown to be involved in atherosclerosis. We demonstrate for the first time the presence of TLR2/CXCR4 coassociation during C. pneumoniae infection-induced atherosclerosis. Amazingly, blocking of both TLR2 and CXCR4 significantly retards and even almost reverses this infection-induced atherosclerosis. Our work reveals new mechanisms about C. pneumoniae infection-induced atherosclerosis and identifies potential new therapeutic targets for the prevention and treatment of atherosclerosis.

Retroviral Overexpression of CXCR4 on Murine B-1a Cells and Adoptive Transfer for Targeted B-1a Cell Migration to the Bone Marrow and IgM Production

As cell function is influenced by niche-specific factors in the cellular microenvironment, methods to dissect cell localization and migration can provide further insight on cell function. B-1a cells are a unique B cell subset in mice that produce protective natural IgM antibodies against oxidation-specific epitopes that arise during health and disease. B-1a cell IgM production differs depending on B-1a cell location, and therefore it becomes useful from a therapeutic standpoint to target B-1a localization to niches supportive of high antibody production. Here we describe a method to target B-1a cell migration to the bone marrow by retroviral-mediated overexpression of the C-X-C motif chemokine receptor 4 (CXCR4). Gene induction in primary murine B cells can be challenging and typically yields low transfection efficiencies of 10-20% depending on technique. Here we demonstrate that retroviral transduction of primary murine B-1a cells results in 30-40% transduction efficiency. This method utilizes adoptive cell transfer of transduced B-1a cells into B cell-deficient recipient mice so that donor B-1a cell migration and localization can be visualized. This protocol can be modified for other retroviral constructs and can be used in diverse functional assays post-adoptive transfer, including analysis of donor cell or host cell phenotype and function, or analysis of soluble factors secreted post B-1a cell transfer. The use of distinct donor and recipient mice differentiated by CD45.1 and CD45.2 allotype and the presence of a GFP reporter within the retroviral plasmid could also enable detection of donor cells in other, immune-sufficient mouse models containing endogenous B cell populations.

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.