MZ B cells migrate in a T-bet dependent manner and might contribute to the remission of collagen-induced arthritis by the secretion of IL-10

Single-cell RNA sequencing analysis reveals the heterogeneity of IL-10 producing regulatory B cells in lupus-prone mice

Introduction

B cells can have both pathogenic and protective roles in autoimmune diseases, including systemic lupus erythematosus (SLE). Deficiencies in the number or immunosuppressive function of IL-10 producing regulatory B cells (Bregs) can cause exacerbated autoimmune inflammation. However, the exact role of Bregs in lupus pathogenesis has not been elucidated.

Methods

We carried out gene expression analysis by scRNA-seq to characterize differences in splenic Breg subsets and molecular profiles through stages of disease progression in lupus-prone mice. Transcriptome-based changes in Bregs from mice with active disease were confirmed by phenotypic analysis.

Results

We found that a loss of marginal zone (MZ) lineage Bregs, an increase in plasmablast/plasma cell (PB-PC) lineage Bregs, and overall increases in inflammatory gene signatures were characteristic of active disease as compared to Bregs from the pre-disease stage. However, the frequencies of both MZ Bregs and PB-PCs expressing IL-10 were significantly decreased in active-disease mice.

Conclusion

Overall, we have identified changes to the repertoire and transcriptional landscape of Breg subsets associated with active disease that provide insights into the role of Bregs in lupus pathogenesis. These results could inform the design of Breg-targeted therapies and interventions to restore Breg suppressive function in autoimmunity.

JAK inhibitors differentially modulate B cell activation, maturation and function: A comparative analysis of five JAK inhibitors in an in-vitro B cell differentiation model and in patients with rheumatoid arthritis

Background

Janus kinase (JAK) inhibitors have been approved for the treatment of several immune-mediated diseases (IMIDs) including rheumatoid arthritis (RA) and psoriatic arthritis and are in clinical trials for numerous other IMIDs. However, detailed studies investigating the effects of different JAK inhibitors on B cells are missing. Within this study, we therefore aimed to characterize the effect of JAK inhibition on the B cell compartment.

Methods

To this end, we investigated the B cell compartment under JAK inhibition and compared the specific effects of the different JAK inhibitors tofacitinib (pan-JAK), baricitinib (JAK1/2), ruxolitinib (JAK1/2), upadacitinib (JAK1/2) as well as filgotinib (selective JAK1) on in-vitro B cell activation, proliferation, and class switch recombination and involved pathways.

Results

While B cell phenotyping of RA patients showed an increase in marginal zone (MZ) B cells under JAK inhibition, comparison with healthy donors revealed that the relative frequency of MZ B cells was still lower compared to healthy controls. In an in-vitro model of T-cell-independent B cell activation we observed that JAK1/2 and selective JAK1 inhibitor treatment led to a dose-dependent decrease of total B cell numbers. We detected an altered B cell differentiation with a significant increase in MZ-like B cells and an increase in plasmablast differentiation in the first days of culture, most pronounced with the pan-JAK inhibitor tofacitinib, although there was no increase in immunoglobulin secretion in-vitro. Notably, we further observed a profound reduction of switched memory B cell formation, especially with JAK1/2 inhibition. JAK inhibitor treatment led to a dose-dependent reduction of STAT3 expression and phosphorylation as well as STAT3 target gene expression and modulated the secretion of pro- and anti-inflammatory cytokines by B cells.

Conclusion

JAK inhibition has a major effect on B cell activation and differentiation, with differential outcomes between JAK inhibitors hinting towards distinct and unique effects on B cell homeostasis.

Age/autoimmunity-associated B cells in inflammatory arthritis: An emerging therapeutic target

Age/autoimmunity-associated B cells (ABCs) are a novel B cell subpopulation with a unique transcriptional signature and cell surface phenotype. They are not sensitive to BCR but rely on TLR7 or TLR9 in the context of T cell-derived cytokines for the differentiation. It has been established that aberrant expansion of ABCs is linked to the pathogenesis of systemic autoimmune diseases such as systemic lupus erythematosus. Recently, we and other groups have shown that increased ABCs is associated with rheumatoid arthritis (RA) disease activity and have demonstrated their pathogenic role in RA, indicating that targeting specific B cell subsets is a promising strategy for the treatment of inflammatory arthritis. In this review, we summarize the current knowledge of ABCs, focusing on their emerging role in the pathogenesis of inflammatory arthritis. A deep understanding of the biology of ABCs in the context of inflammatory settings in vivo will ultimately contribute to the development of novel targeted therapies for the treatment of inflammatory arthritis.

Age-associated B cells in autoimmune diseases

Age-associated B cells (ABCs) are a transcriptionally and functionally unique B cell population. In addition to arising with age and following infection, ABCs are expanded during autoimmune disease, including those with systemic lupus erythematosus, multiple sclerosis, and rheumatoid arthritis. The exact nature of how ABCs impact disease remains unclear. Here, we review what is known regarding ABC development and distribution during diseases including systemic lupus erythematosus, multiple sclerosis, and rheumatoid arthritis. We discuss possible mechanisms by which ABCs could contribute to disease, including the production of cytokines and autoantibodies or stimulation of T cells. Finally, we speculate on how ABCs might act as mediators between sex, infection, and autoimmune disease, and discuss avenues for further research.

Marginal Zone B-Cell Populations and Their Regulatory Potential in the Context of HIV and Other Chronic Inflammatory Conditions

Inflammation in the context of Human Immunodeficiency Virus (HIV) establishes early and persists beyond antiretroviral therapy (ART). As such, we have shown excess B-cell activating factor (BAFF) in the blood of HIV-infected progressors, as soon as in the acute phase, and despite successful ART. Excess BAFF was associated with deregulation of the B-cell compartment; notably, with increased frequencies of a population sharing features of both transitional immature (TI) and marginal zone (MZ) B-cells, we termed Marginal Zone precursor-like (MZp). We have reported similar observations with HIV-transgenic mice, Simian Immunodeficiency Virus (SIV)-infected macaques, and more recently, with HIV-infected Beninese commercial sex workers, which suggests that excess BAFF and increased frequencies of MZp B-cells are reliable markers of inflammation in the context of HIV. Importantly, we have recently shown that in healthy individuals, MZps present an important regulatory B-cell (Breg) profile and function. Herein, we wish to review our current knowledge on MZ B-cell populations, especially their Breg status, and that of other B-cell populations sharing similar features. BAFF and its analog A Proliferation-Inducing Ligand (APRIL) are important in shaping the MZ B-cell pool; moreover, the impact that excess BAFF—encountered in the context of HIV and several chronic inflammatory conditions—may exert on MZ B-cell populations, Breg and antibody producing capacities is a threat to the self-integrity of their antibody responses and immune surveillance functions. As such, deregulations of MZ B-cell populations contribute to autoimmune manifestations and the development of MZ lymphomas (MZLs) in the context of HIV and other inflammatory diseases. Therefore, further comprehending the mechanisms regulating MZ B-cell populations and their functions could be beneficial to innovative therapeutic avenues that could be deployed to restore MZ B-cell immune competence in the context of chronic inflammation involving excess BAFF.

T-bet represses collagen-induced arthritis by suppressing Th17 lineage commitment through inhibition of RORγt expression and function

T-bet is a key transcription factor for the T helper 1 lineage and its expression level is negatively correlated to inflammation in patients with rheumatoid arthritis (RA). Our previous study using T-bet transgenic mice revealed over-expression of T-bet completely suppressed collagen-induced arthritis (CIA), a murine model of RA, indicating a potential suppressive role of T-bet in the pathogenesis of autoimmune arthritis. Here, we show T-bet-deficiency exacerbated CIA. T-bet in CD4 + T cells, but not in CD11c + dendritic cells, was critical for regulating the production of IL-17A, IL-17F, IL-22, and TNFα from CD4 + T cells. T-bet-deficient CD4 + T cells showed higher RORγt expression and increased IL-17A production in RORγt-positive cells after CII immunization. In addition, T-bet-deficient naïve CD4 + T cells showed accelerated Th17 differentiation in vitro. CIA induced in CD4-Cre T-bet^fl/fl (cKO) mice was more severe and T-bet-deficient CD4 + T cells in the arthritic joints of cKO mice showed higher RORγt expression and increased IL-17A production. Transcriptome analysis of T-bet-deficient CD4 + T cells revealed that expression levels of Th17-related genes were selectively increased. Our results indicate that T-bet in CD4 + T cells repressed RORγt expression and function resulting in suppression of arthritogenic Th17 cells and CIA.

Dysregulated translational factors and epigenetic regulations orchestrate in B cells contributing to autoimmune diseases

B cells play a crucial role in antigen presentation, antibody production and pro-/anti-inflammatory cytokine secretion in adaptive immunity. Several translational factors including transcription factors and cytokines participate in the regulation of B cell development, with the cooperation of epigenetic regulations. Autoimmune diseases are generally characterized with autoreactive B cells and high-level pathogenic autoantibodies. The success of B cell depletion therapy in mouse model and clinical trials has proven the role of B cells in pathogenesis of autoimmune diseases. The failure of B cell tolerance in immune checkpoints results in accumulated autoreactive naïve B (B_N) cells with aberrant B cell receptor signaling and dysregulated B cell response, contributing to self-antibody-mediated autoimmune reaction. Dysregulation of translational factors and epigenetic alterations in B cells has been demonstrated to correlate with aberrant B cell compartment in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome, multiple sclerosis, diabetes mellitus and pemphigus. This review is intended to summarize the interaction of translational factors and epigenetic regulations that are involved with development and differentiation of B cells, and the mechanism of dysregulation in the pathogenesis of autoimmune diseases.

Immunosuppressive Mechanisms of Regulatory B Cells

Regulatory B cells (Bregs) is a term that encompasses all B cells that act to suppress immune responses. Bregs contribute to the maintenance of tolerance, limiting ongoing immune responses and reestablishing immune homeostasis. The important role of Bregs in restraining the pathology associated with exacerbated inflammatory responses in autoimmunity and graft rejection has been consistently demonstrated, while more recent studies have suggested a role for this population in other immune-related conditions, such as infections, allergy, cancer, and chronic metabolic diseases. Initial studies identified IL-10 as the hallmark of Breg function; nevertheless, the past decade has seen the discovery of other molecules utilized by human and murine B cells to regulate immune responses. This new arsenal includes other anti-inflammatory cytokines such IL-35 and TGF-β, as well as cell surface proteins like CD1d and PD-L1. In this review, we examine the main suppressive mechanisms employed by these novel Breg populations. We also discuss recent evidence that helps to unravel previously unknown aspects of the phenotype, development, activation, and function of IL-10-producing Bregs, incorporating an overview on those questions that remain obscure.

Advances of Regulatory B Cells in Autoimmune Diseases

With the ability to induce T cell activation and elicit humoral responses, B cells are generally considered as effectors of the immune system. However, the emergence of regulatory B cells (Bregs) has given new insight into the role of B cells in immune responses. Bregs exhibit immunosuppressive functions via diverse mechanisms, including the secretion of anti-inflammatory cytokines and direct cell contact. The balance between Bregs and effector B cells is important for the immune tolerance. In this review, we focus on recent advances in the characteristics of Bregs and their functional roles in autoimmunity.

Age-Associated B Cells (ABCs) in the Prognosis, Diagnosis and Therapy of Systemic Lupus Erythematosus (SLE)

The term “age-associated B cells” (ABCs) refers to a heterogeneous B cell subset (CD19⁺,CD21⁻, CD11c⁺,T-bet⁺) which is expanded in the elderly, but also accumulates prematurely in patients with autoimmune disorders and/or infectious diseases. In healthy individuals, ABCs represent a low prevalence population that positively impacts immunosenescence. In autoimmunity and infections though, ABCs expand dramatically and produce high titers of antibodies, thus playing a role in the regulation of humoral responses. Despite the fact that these observations were made on both mice and humans, the functional features of ABCs and their exact role in human health and disease are still elusive. This review focuses on ABC and ABC-like sub-populations found in Systemic Lupus Erythematosus (SLE) patients (such as the double negative 2;DN2 population: CD19⁺,IgD⁻,CD27⁻, CXCR5⁻,T-bet⁺) and broaches the subject of their potential use as prognostic and/or diagnostic markers. The identification of novel biomarkers, via correlating the cell populations with the clinical profile of the patients, should enable better patient stratification and monitoring. Moreover, the necessity and importance of elucidating the role of transcription factor T-bet (TBX21) in the pathogenesis of human autoimmunity are addressed. T-bet, whose expression is upregulated in both mouse and human ABCs, is considered to play a major role in various aspects of autoimmunity, such as the production of autoreactive IgG, the enhanced antigen presentation to T cells and also the formation of spontaneous germinal centres (GC). Shedding light to its role in human disease, in conjunction with the characterisation of genes and pathways associated with the transcription factor itself, may lead to the discovery of novel druggable targets.

Regulatory B Cells and Its Role in Central Nervous System Inflammatory Demyelinating Diseases

Regulatory B (Breg) cells represent a population of suppressor B cells that participate in immunomodulatory processes and inhibition of excessive inflammation. The regulatory function of Breg cells have been demonstrated in mice and human with inflammatory diseases, cancer, after transplantation, and particularly in autoinflammatory disorders. In order to suppress inflammation, Breg cells produce anti-inflammatory mediators, induce death ligand-mediated apoptosis, and regulate many kinds of immune cells such as suppressing the proliferation and differentiation of effector T cell and increasing the number of regulatory T cells. Central nervous system Inflammatory demyelinating diseases (CNS IDDs) are a heterogeneous group of disorders, which occur against the background of an acute or chronic inflammatory process. With the advent of monoclonal antibodies directed against B cells, breakthroughs have been made in the treatment of CNS IDDs. Therefore, the number and function of B cells in IDDs have attracted attention. Meanwhile, increasing number of studies have confirmed that Breg cells play a role in alleviating autoimmune diseases, and treatment with Breg cells has also been proposed as a new therapeutic direction. In this review, we focus on the understanding of the development and function of Breg cells and on the diversification of Breg cells in CNS IDDs.

Inflammatory signal induced IL-10 production of marginal zone B-cells depends on CREB

IL-10 is a suppressive cytokine that has been implicated in the pathophysiology of autoimmune disorders and can be produced by different cell types such as regulatory B-cells. Our previous work showed that under inflammatory condition MZ B-cells differentiated into IL-10 producing cells and contributed to the downregulation of collagen-induced arthritis, while follicular B-cells failed to do so. Based on these observations, we aimed to investigate how inflammatory signals mediated through the BCR, TLR9 and IFN-γ receptors trigger IL-10 production in MZ B-cells but leave FO B-cells unresponsive. We particularly focused on the CREB transcription factor as it is involved in all three signalling cascades and analysed its contribution to IL-10 production. Our results demonstrate that the IL-10 production of MZ B-cells induced by the BCR, TLR9 and IFN-γ receptors is mediated by CREB. We showed that the activation of CREB is prolonged in MZ B-cells while the transcription factor only transiently phosphorylated in FO B-cells. The sustained phosphorylation of CREB is clearly associated with its prolonged binding to molecular partner CBP, whereas inhibition of their association decreased IL-10 production. We assume that sustained activation of CREB is required for IL-10 production by B-cells under inflammatory conditions.

Hypomorphic Mutations in the BCR Signalosome Lead to Selective Immunoglobulin M Deficiency and Impaired B-cell Homeostasis

B cell activation via the B cell receptor (BCR) signalosome involves participation of signaling molecules such as BTK and BLNK. Genetic defects in these molecules are known to impair B cell differentiation and subsequently lead to agammaglobulinemia. Here we identified novel mutations in BTK and BLNK in two unrelated patients that perturb the intrinsic B-cell receptor signaling pathway and lead to selective IgM deficiency, whereas production of other immunoglobulin isotypes and IgG antibody response remain intact. Currently it is unknown how BCR signaling strength affects mature B cell development in humans. Both patients show reduced levels of BCR signalosome phosphorylation as well as impaired BCR-dependent Ca²⁺ influx, which was accompanied by a marked decrease in IgD⁺IgM⁺CD27⁺ MZ-like B-cells. We further describe reduced expression of essential B cell differentiation factors such as BAFF-R and T-Bet in the patients' B-cells, which might contribute to the observed deficiency of MZ-like B cells. MZ-like B cells are known to produce natural IgM antibodies that play an essential role in immune homeostasis. By using surface plasmon resonance (SPR) technology and a synthetic blood group A trisaccharide as antigen we were able to show that both patients lack the presence of anti-blood group A IgM considered to be prototypical natural antibodies whereas IgG levels were normal. Antibody binding dynamics and binding affinity of anti-blood group A IgG were comparable between patients and healthy controls. These results indicate that human IgM deficiency can be associated with signaling defects in the BCR signalosome, defective production of natural IgM antibodies in the blood group A/B/0 system and abnormalities in B cell development.

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.

The Interplay Between Innate-Like B Cells and Other Cell Types in Autoimmunity

Studies performed in animal models and in humans indicate that the innate arm of the immune system provides an essential role in the initial protection against potential insults and in maintaining tolerance to self-antigens. In the B cell compartment, several subsets engage in both adaptive and innate functions. Whereas B cell subsets are recognized to play important roles in autoimmune diseases, understanding the intricacies of their effector functions remains challenging. In addition to B-1a cells and marginal zone B cells, the B cell compartment comprises other B cells with innate-like functions, including innate response activator B cells, T-bet positive B cells, natural killer-like B cells, IL-17-producing B cells, and human self-reactive V_H4-34-expressing B cells. Herein, we summarize the functions of recently described B cell populations that can exert innate-like roles in both animal models and humans. We also highlight the importance of the cross talk between innate-like B cells and other adaptive and innate branches of the immune system in various autoimmune and inflammatory diseases. In as much as innate immunity seems to be important in resolving inflammation, it is possible that targeting certain innate-like B cell subsets could represent a novel therapeutic approach for inducing resolution of inflammation of autoimmune and inflammatory responses.