B Cell Homeostasis and Functional Properties Are Altered in an Hypochlorous Acid-Induced Murine Model of Systemic Sclerosis

α7nAChR on B cells directs T cell differentiation to prevent viral myocarditis

Patients with viral myocarditis (VMC) exhibit evident autonomic nervous system imbalance, and adverse cardiac remodeling is involved in impaired cholinergic function. The α7 nicotinic acetylcholine receptor (α7nAChR), which is a neurotransmitter receptor, exerts immunoregulatory effects. Recent advances have illuminated the evolution and functions of peripheral and cardiac B cells in heart disease. However, the role of α7nAChR expressed by B cells in the progression of VMC has not been established. We revealed the neuroimmune communication landscape in the heart and found that the phenotypes of cardiac and splenic B cells and their α7nAChR expression changed dynamically during the progression of VMC to dilated cardiomyopathy. α7nAChR on B cells serves as a negative regulator by inhibiting their proinflammatory functions and signaling pathways. B cell-specific α7nAChR deficiency exacerbated myocardial inflammation, fibrosis, and cardiac dysfunction. However, these effects were abrogated in non-B cells from mice with IL-17A knockdown. Enhanced degradation of acetylcholine leads to an imbalance in cholinergic signaling, resulting in impaired neurotransmission. The acetylcholinesterase inhibitor pyridostigmine bromide could improve cardiac remodeling and prevent the progression of VMC to the chronic phase, which was partly dependent on the α7nAChR on B cells. Our findings provide notable insights into cardiac-neural-immune communication during myocardial injury.

Beyond circulating B cells: Characteristics and role of tissue-infiltrating B cells in systemic sclerosis

B cells play a key role in the pathophysiology of systemic sclerosis (SSc). While they are less characterized than their circulating counterparts, tissue-infiltrating B cells may have a more direct pathological role in tissues. In this review, we decipher the multiple evidence of B cells infiltration in the skin and lungs of SSc patients and animal models of SSc but also of other chronic fibrotic diseases with similar pathological mechanisms such as chronic graft versus host disease, idiopathic pulmonary fibrosis or morphea. We also recapitulate the current knowledge about mechanisms of B cells infiltration and their functions in tissues. Finally, we discuss B cell targeted therapies, and their specific impact on infiltrated B cells. Understanding the local consequences of infiltrating B cells is an important step for a better management of patients and the improvement of therapies in SSc.

Effector and regulatory B-cell imbalance in systemic sclerosis: cooperation or competition?

B cells play a central role in the pathogenesis of systemic sclerosis (SSc). Most B-cell studies have focused on their pathological role as antibody producers. However, in addition to immunoglobulin secretion, these cells have a wide range of functions in the immune response, including antigen presentation to T cells and cytokine production. Importantly, not all B-cell subsets promote the immune response. Regulatory B cells (Bregs) attenuate inflammation and contribute to the maintenance of immune tolerance. However, effector B cells (Beffs) positively modulate the immune response through the production of various cytokines. In SSc, Bregs are insufficient and/or dysfunctional. B-cell-targeting biologics have been trialled with promising results in the treatment of SSc. These therapies can affect Bregs or Beffs, which can potentially limit their long-term efficacy. Future strategies might involve the modulation of effector B cells in combination with the stimulation of regulatory subsets. Additionally, the monitoring of individual B-cell subsets in patients may lead to the discovery of novel biomarkers that could help predict disease relapse or progression. The purpose of this review is to summarize the relevant literatures and explain how Bregs and Beffs jointly participate in the pathogenesis of SSc.

Baicalein alleviates fibrosis and inflammation in systemic sclerosis by regulating B-cell abnormalities

BACKGROUND

Systemic sclerosis (SSc; also known as "scleroderma") is an autoimmune disorder characterized by extensive fibrosis, vascular changes, and immunologic dysregulation. Baicalein (phenolic flavonoid derived from Scutellaria baicalensis Georgi) has been used to treat the pathological processes of various fibrotic and inflammatory diseases. In this study, we investigated the effect of baicalein on the major pathologic characteristics of SSc: fibrosis, B-cell abnormalities, and inflammation.

METHODS

The effect of baicalein on collagen accumulation and expression of fibrogenic markers in human dermal fibroblasts were analyzed. SSc mice were produced by injecting bleomycin and treated with baicalein (25, 50, or 100 mg/kg). The antifibrotic features of baicalein and its mechanisms were investigated by histologic examination, hydroxyproline assay, enzyme-linked immunosorbent assay, western blotting and flow cytometry.

RESULTS

Baicalein (5-120 μM) significantly inhibited the accumulation of the extracellular matrix and fibroblast activation in transforming growth factor (TGF)-β1- and platelet derived growth factor (PDGF)-induced human dermal fibroblasts, as evidenced by abrogated deposition of total collagen, decreased secretion of soluble collagen, reduced collagen contraction capability and downregulation of various fibrogenesis molecules. In a bleomycin-induced model of dermal fibrosis in mice, baicalein (25-100 mg/kg) restored dermal architecture, ameliorated inflammatory infiltrates, and attenuated dermal thickness and collagen accumulation in a dose-dependent manner. According to flow cytometry, baicalein reduced the proportion of B cells (B220⁺ lymphocytes) and increased the proportion of memory B cells (B220⁺CD27⁺ lymphocytes) in the spleens of bleomycin-induced mice. Baicalein treatment potently attenuated serum levels of cytokines (interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-17A, tumor necrosis factor-α), chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1 beta) and autoantibodies (anti-scleroderma 70 (Scl-70), anti-polymyositis-scleroderma (PM-Scl), anti-centromeres, anti-double stranded DNA (dsDNA). In addition, baicalein treatment can significantly inhibit the activation of TGF-β1 signaling in dermal fibroblasts and bleomycin-induce mice of SSc, evidenced by reducing the expression of TGF-β1 and IL-11, as well as inhibiting both small mother against decapentaplegic homolog 3 (SMAD3) and extracellular signal-related kinase (ERK) activation.

CONCLUSIONS

These findings suggest that baicalein has therapeutic potential against SSc, exerting modulating B-cell abnormalities, anti-inflammatory effects, and antifibrosis.

Dysregulated B cell function and disease pathogenesis in systemic sclerosis

Systemic sclerosis (SSc) is a complex, immune-mediated rheumatic disease characterised by excessive extracellular matrix deposition in the skin and internal organs. B cell infiltration into lesional sites such as the alveolar interstitium and small blood vessels, alongside the production of defined clinically relevant autoantibodies indicates that B cells play a fundamental role in the pathogenesis and development of SSc. This is supported by B cell and fibroblast coculture experiments revealing that B cells directly enhance collagen and extracellular matrix synthesis in fibroblasts. In addition, B cells from SSc patients produce large amounts of profibrotic cytokines such as IL-6 and TGF-β, which interact with other immune and endothelial cells, promoting the profibrotic loop. Furthermore, total B cell counts are increased in SSc patients compared with healthy donors and specific differences can be found in the content of naïve, memory, transitional and regulatory B cell compartments. B cells from SSc patients also show differential expression of activation markers such as CD19 which may shape interactions with other immune mediators such as T follicular helper cells and dendritic cells. The key role of B cells in SSc is further supported by the therapeutic benefit of B cell depletion with rituximab in some patients. It is notable also that B cell signaling is impaired in SSc patients, and this could underpin the failure to induce tolerance in B cells as has been shown in murine models of scleroderma.

Increased expression of the ectoenzyme CD38 in peripheral blood plasmablasts and plasma cells of patients with systemic sclerosis

Objective

CD38 is a type II glycoprotein highly expressed on plasmablasts and on short- and long-lived plasma cells, but weakly expressed by lymphoid, myeloid, and non-hematopoietic cells. CD38 is a target for therapies aimed at depleting antibody-producing plasma cells. Systemic sclerosis (SSc) is an immune-mediated disease with a well-documented pathogenic role of B cells. We therefore analyzed CD38 expression in different subsets of peripheral blood mononuclear cells (PBMCs) from a cohort of SSc patients.

Methods

Cell surface expression of CD38 was evaluated on PBMCs from SSc patients using eight-color flow cytometry analysis performed with a FacsCanto II (BD). Healthy individuals were used as controls (HC).

Results

Forty-six SSc patients (mean age 56, range 23-79 years; 38 females and 8 males), and thirty-two age- and sex-matched HC were studied. Twenty-eight patients had the limited cutaneous form and eighteen the diffuse cutaneous form of SSc. The mean disease duration was 7 years. Fourteen patients were on immunosuppressive therapy (14 MMF, 5 RTX). The total percentages of T, B and NK cells were not different between SSc and HC. Compared to HC, SSc patients had higher levels of CD3+CD38+ T cells (p<0.05), higher percentage (p<0.001) of CD3+CD4+CD25+FOXP3+ regulatory T cells, lower percentage (p<0.05) of CD3+CD56+ NK T cells. Moreover, SSc patients had higher levels of CD24^highCD19+CD38^high regulatory B cells than HC (p<0.01), while the amount of CD24+CD19+CD38+CD27+ memory B cells was lower (p<0.001). Finally, the percentages of circulating CD38^highCD27+ plasmablasts and CD138+CD38^high plasma cells were both higher in the SSc group than in HC (p<0.001). We did not observe any correlations between these immunophenotypes and disease subsets or duration, and ongoing immunosuppressive treatment.

Conclusions

The increased expression of CD38 in peripheral blood plasmablasts and plasma cells of SSc patients may suggest this ectoenzyme as a candidate therapeutic target, under the hypothesis that depletion of these cells may beneficially downregulate the chronic immune response in SSc patients. Validation of this data in multicenter cohorts shall be obtained prior to clinical trials with existing anti-CD38 drugs.

Soluble markers of B cell activation suggest a role of B cells in the pathogenesis of systemic sclerosis-associated pulmonary arterial hypertension

Introduction

Soluble markers of B cell activation are interesting diagnostic and prognostic tools in autoimmune diseases. Data in systemic sclerosis (SSc) are scarce and few studies focused on their association with disease characteristics.

Methods

1. Serum levels of 14 B cell biomarkers (β2-microglobulin, rheumatoid factor (RF), immunoglobulins (Ig) G, IgA, IgM, BAFF, APRIL, soluble (s)TACI, sBCMA sCD21, sCD23, sCD25, sCD27, CXCL13) were measured in SSc patients and healthy controls (HC). 2. Associations between these biomarkers and SSc characteristics were assessed. 3. The pathophysiological relevance of identified associations was explored by studying protein production in B cell culture supernatant.

Results

In a discovery panel of 80 SSc patients encompassing the broad spectrum of disease manifestations, we observed a higher frequency of RF positivity, and increased levels of β2-microglobulin, IgG and CXCL13 compared with HC. We found significant associations between several biomarkers and SSc characteristics related to disease phenotype, activity and severity. Especially, serum IgG levels were associated with pulmonary hypertension (PH); β2-microglobulin with Nt-pro-BNP and DLCO; and BAFF with peak tricuspid regurgitation velocity (TRV). In a validation cohort of limited cutaneous SSc patients without extensive ILD, we observed lower serum IgG levels, and higher β2-microglobulin, sBCMA, sCD23 and sCD27 levels in patients with pulmonary arterial hypertension (PAH). BAFF levels strongly correlated with Nt-pro-BNP levels, FVC/DLCO ratio and peak TRV in SSc-PAH patients. Cultured SSc B cells showed increased production of various angiogenic factors (angiogenin, angiopoietin-1, VEGFR-1, PDGF-AA, MMP-8, TIMP-1, L-selectin) and decreased production of angiopoietin-2 compared to HC.

Conclusion

Soluble markers of B cell activation could be relevant tools to assess organ involvements, activity and severity in SSc. Their associations with PAH could plead for a role of B cell activation in the pathogenesis of pulmonary microangiopathy. B cells may contribute to SSc vasculopathy through production of angiogenic mediators.

Role of B-Cell in the Pathogenesis of Systemic Sclerosis

Systemic sclerosis (SSc) is a rare multisystem autoimmune disease, characterized by fibrosis, vasculopathy, and autoimmunity. Recent advances have highlighted the significant implications of B-cells in SSc. B-cells are present in affected organs, their subpopulations are disrupted, and they display an activated phenotype, and the regulatory capacities of B-cells are impaired, as illustrated by the decrease in the IL-10+ producing B-cell subpopulation or the inhibitory membrane co-receptor density. Recent multi-omics evidence highlights the role of B-cells mainly in the early stage of SSc and preferentially during severe organ involvement. This dysregulated homeostasis partly explains the synthesis of anti-endothelial cell autoantibodies (AECAs) or anti-fibroblast autoantibodies (AFAs), proinflammatory or profibrotic cytokines (interleukin-6 and transforming growth factor-β) produced by B and plasma cells. That is associated with cell-to-cell interactions with endothelial cells, fibroblasts, vascular smooth muscle cells, and other immune cells, altogether leading to cell activation and proliferation, cell resistance to apoptosis, the impairment of regulatory mechanisms, and causing fibrosis of several organs encountered in the SSc. Finally, alongside these exploratory data, treatments targeting B-cells, through their depletion by cytotoxicity (anti-CD20 monoclonal antibody), or the cytokines produced by the B-cell, or their costimulation molecules, seem interesting, probably in certain profiles of early patients with severe organic damage.

Simple gene signature to assess murine fibroblast polarization

We provide an original multi-stage approach identifying a gene signature to assess murine fibroblast polarization. Prototypic polarizations (inflammatory/fibrotic) were induced by seeded mouse embryonic fibroblasts (MEFs) with TNFα or TGFß1, respectively. The transcriptomic and proteomic profiles were obtained by RNA microarray and LC-MS/MS. Gene Ontology and pathways analysis were performed among the differentially expressed genes (DEGs) and proteins (DEPs). Balb/c mice underwent daily intradermal injections of HOCl (or PBS) as an experimental murine model of inflammation-mediated fibrosis in a time-dependent manner. As results, 1456 and 2215 DEGs, and 289 and 233 DEPs were respectively found in MEFs in response to TNFα or TGFß1, respectively. Among the most significant pathways, we combined 26 representative genes to encompass the proinflammatory and profibrotic polarizations of fibroblasts. Based on principal component analysis, this signature deciphered baseline state, proinflammatory polarization, and profibrotic polarization as accurately as RNA microarray and LC-MS/MS did. Then, we assessed the gene signature on dermal fibroblasts isolated from the experimental murine model. We observed a proinflammatory polarization at day 7, and a mixture of a proinflammatory and profibrotic polarizations at day 42 in line with histological findings. Our approach provides a small-size and convenient gene signature to assess murine fibroblast polarization.

Can Antinuclear Antibodies Have a Pathogenic Role in Systemic Sclerosis?

Systemic sclerosis (SSc) is a connective tissue disease characterized by extensive fibrosis of the skin and internal organs, associated with vasculopathy and autoimmune features. Antinuclear antibodies (ANA) are found in almost all SSc patients and constitute strong diagnosis and prognosis biomarkers. However, it remains unclear whether ANA are simple bystanders or if they can have a role in the pathophysiology of the disease. One might think that the nuclear nature of their targets prevents any accessibility to autoantibodies. Nevertheless, recent data suggest that ANA could be pathogenic or at least contribute to the perennation of the disease. We review here first the indirect clues of the contribution of ANA to SSc: they are associated to the disease subtypes, they may precede disease onset, their titer correlates with disease activity and severity, there is an association between molecular subsets, and some patients can respond to B-cell targeting therapy. Then, we describe in a second part the mechanisms of ANA production in SSc from individual genetic background to post-transcriptional modifications of neoantigens. Finally, we elaborate on the potential mechanisms of pathogenicity: ANA could be pathogenic through immune-complex-mediated mechanisms; other processes potentially involve molecular mimicry and ANA penetration into the target cell, with a focus on anti-topoisomerase-I antibodies, which are the most probable candidate to play a role in the pathophysiology of SSc. Finally, we outline some technical and conceptual ways to improve our understanding in this field.

The Role of B Cells in Regulation of Th Cell Differentiation in Coxsackievirus B3-Induced Acute Myocarditis

Viral myocarditis (VMC) is the major cause of sudden death in adolescents. To date, no effective treatment has been identified for VMC. Studies have shown that T helper (Th) cells such as Th1, Th2, Th17, and Th22 cells are involved in the pathogenesis of VMC. However, the role of B cells and their impact on Th cells in VMC is unclear. In this study, we investigated the role of B cells in Th cell differentiation in myocardial damage in an animal model of VMC. C57BL/6 mice were infected with Coxsackievirus B3 (CVB3) intraperitoneally or injected with phosphate-buffered saline as a control condition. At day 7, samples from these mice were analyzed by histology, ELISA, flow cytometry, and gene expression assays. We found that TNF-α-, IL-6-, and IL-17-producing B cell numbers were significantly increased, while IL-4-producing B cell population was significantly reduced in acute VMC. Furthermore, we performed B cell knockout (BKO), SCID, and SCID+B cells reconstitution experiments. We found that BKO alleviated the cardiac damage following CVB3 infection, may hamper the differentiation of Th1 and Th17 cells, may promote the differentiation of Th2 cells, and proved ineffective for the differentiation of Th22 cells. In contrast, SCID+B cells reconstitution experiment exacerbated the cardiac damage. Ex vivo studies further revealed that B cells promote the differentiation of Th1 and Th17 cells and inhibit the differentiation of Th2 cells. Our study shows that B cells are activated and have strong abilities of antigen presentation and producing cytokines in VMC; B cells not only play a pathogenic role in VMC independent of T cells but also promote Th1 and Th17 cell differentiation, and hamper Th2 cell differentiation in VMC.

B cells in systemic sclerosis: from pathophysiology to treatment

Systemic sclerosis is a debilitating autoimmune disease with unknown pathogenesis. The clinical phenotype of fibrosis is preceded by vascular and immunologic aberrations. Adaptive immunity has been extensively studied in patients with the disease and B cells appear to be dysregulated. This is evident in peripheral blood B cell subsets, with activated effector B cells and impaired B regulatory function. In addition, B cells infiltrate target organs and tissues of patients with the disease, such as the skin and the lung, indicating a probable role in the pathogenesis. Impaired B cell homeostasis explains the rationale behind B cell therapeutic targeting. Indeed, several studies in recent years have shown that depletion of B cells appears to be a promising treatment alongside current established therapeutic choices, such as mycophenolate. In this review, B cell aberrations in animal models and human patients with systemic sclerosis will be presented. Moreover, we will also summarize current existing data regarding therapeutic targeting of the B cells in systemic sclerosis.

Is There a Future for Anti-CD38 Antibody Therapy in Systemic Autoimmune Diseases?

CD38 is a type II glycoprotein highly expressed on plasmablasts, short-lived and long-lived plasma cells, but weakly expressed on other lymphoid cells, myeloid cells and non-hematopoietic cells. This expression pattern makes CD38 an interesting target for a targeted therapy aiming to deplete antibody-producing plasma cells. We present data suggesting that anti-CD38 therapy may be effective for the prevention at the preclinical stage and for the treatment of established autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, Sjögren’s syndrome and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Given the high unmet need for efficacious disease-modifying treatment in these diseases, studies are warranted to determine if anti-CD38 antibody-based therapies may delay or prevent the disease progression of systemic autoimmune diseases.

Regulatory B cells: New players in inflammatory and autoimmune rheumatic diseases

OBJECTIVE

Regulatory B cells (Bregs) are a new subset of B cells with immunoregulatory functions, mainly through IL-10 production. Bregs suppress inflammatory Th1 and Th17 differentiation and induce Tregs suppressing autoimmune diseases. The aim of the study was to review the literature related to Bregs in autoimmune rheumatic diseases (ARDs).

METHODS

A literature review of publications in PUBMED published in English was performed using the relevant combinations of terms.

RESULTS

All relevant publications are discussed. Overall, recent studies in rheumatic diseases found Bregs to be decreased in ANCA-associated vasculitides (AAV) and in systemic sclerosis (SSc), particularly in SSc-associated lung fibrosis. In AAV Bregs levels are negatively correlated with autoantibody levels whereas in SSc this association is less clear but there is an inverse association with Th1 and Th17 cells. In rheumatoid arthritis (RA), Bregs were decreased, particularly in RA-associated lung fibrosis. In psoriatic arthritis IL-10 + Bregs are decreased and inversely associated with Th1 and Th17 cells. In systemic lupus erythematosus (SLE), the role of Bregs is unclear. In experimental diseases, when Bregs were expanded ex-vivo, they ameliorated established disease.

CONCLUSION

Bregs appear to be a new player in the pathogenesis of ARDs, and may offer a new strategy for therapeutic intervention.