B cells regulate autoimmunity by provision of IL-10

Kidney allograft rejection is associated with an imbalance of B cells, regulatory T cells and differentiated CD28-CD8+ T cells: analysis of a cohort of 1095 graft biopsies

Introduction

The human immune system contains cells with either effector/memory or regulatory functions. Besides the well-established CD4+CD25hiCD127lo regulatory T cells (Tregs), we and others have shown that B cells can also have regulatory functions since their frequency and number are increased in kidney graft tolerance and B cell depletion as induction therapy may lead to acute rejection. On the other hand, we have shown that CD28-CD8+ T cells represent a subpopulation with potent effector/memory functions. In the current study, we tested the hypothesis that kidney allograft rejection may be linked to an imbalance of effector/memory and regulatory immune cells.

Methods

Based on a large cohort of more than 1000 kidney graft biopsies with concomitant peripheral blood lymphocyte phenotyping, we investigated the association between kidney graft rejection and the percentage and absolute number of circulating B cells, Tregs, as well as the ratio of B cells to CD28-CD8+ T cells and the ratio of CD28-CD8+ T cells to Tregs. Kidney graft biopsies were interpreted according to the Banff classification and divided into 5 biopsies groups: 1) normal/subnormal, 2) interstitial fibrosis and tubular atrophy grade 2/3 (IFTA), 3) antibody-mediated rejection (ABMR), 4) T cell mediated-rejection (TCMR), and 5) borderline rejection. We compared group 1 with the other groups as well as with a combined group 3, 4, and 5 (rejection of all types) using multivariable linear mixed models.

Results and discussion

We found that compared to normal/subnormal biopsies, rejection of all types was marginally associated with a decrease in the percentage of circulating B cells (p=0.06) and significantly associated with an increase in the ratio of CD28-CD8+ T cells to Tregs (p=0.01). Moreover, ABMR, TCMR (p=0.007), and rejection of all types (p=0.0003) were significantly associated with a decrease in the ratio of B cells to CD28-CD8+ T cells compared to normal/subnormal biopsies. Taken together, our results show that kidney allograft rejection is associated with an imbalance between immune cells with effector/memory functions and those with regulatory properties.

Leveraging the tolerogenic potential of TNF-α and regulatory B cells in organ transplantation

A subset of B-cells with tolerogenic functions, termed B-regulatory cells or Bregs, is characterized by the expression of anti-inflammatory/tolerogenic cytokines, namely IL-10, TGF-β, and IL-35, that contribute to their regulatory functions. Breg regulation favors graft acceptance within a tolerogenic milieu. As organ transplantation invariably triggers inflammation, new insights into the crosstalk between cytokines with dual properties and the inflamed milieu are needed to tailor their function toward tolerance. Using TNF-α as a proxy of dual-function cytokines involved in immune-related diseases and transplantation settings, the current review highlights the multifaceted role of TNF-α. It focuses on therapeutic approaches that have revealed the complexity of TNF-α properties tested in clinical settings where total TNF-α inhibition has proven ineffective and often detrimental to clinical outcomes. To improve the efficacy of current TNF-α inhibiting therapeutics, we propose a three-prong strategy to upregulate the tolerogenic pathway engaging the TNFR2 receptor while simultaneously inhibiting the inflammatory mechanisms associated with TNFR1 engagement. When combined with additional administrations of Bregs-TLR that activate Tregs, this approach may become a potential therapeutic in overcoming transplant rejection and promoting graft tolerance.

Cytokine production by human B cells: role in health and autoimmune disease

B cells are classically considered solely as antibody-producing cells driving humoral immune responses to foreign antigens in infections and vaccinations as well as self-antigens in pathological settings such as autoimmunity. However, it has now become clear that B cells can also secrete a vast array of cytokines, which influence both pro- and anti-inflammatory immune responses. Indeed, similarly to T cells, there is significant heterogeneity in cytokine-driven responses by B cells, ranging from the production of pro-inflammatory effector cytokines such as IL-6, through to the release of immunosuppressive cytokines such as IL-10. In this review, focusing on human B cells, we summarize the key findings that have revealed that cytokine-producing B cell subsets have critical functions in healthy immune responses and contribute to the pathophysiology of autoimmune diseases.

Circulating Regulatory B-Lymphocytes in Patients with Acute Myocardial Infarction: A Pilot Study

Background: Inflammation plays on important role in plaque instability and acute coronary syndromes. The anti-inflammatory effects of B-regulatory lymphocytes (B-regs) in atherosclerosis was tested mainly in animal models with inconclusive results. Herein, we studied for the first time, levels of circulating B-regs in patients with acute myocardial infarction (MI). Methods: We examined circulating levels of B-regs by flow cytometry in 29 patients with recent ST-segment elevation MI and 18 patients with stable angina pectoris (SAP) and coronary artery disease. We re-assessed B-reg levels on average 4 months later. Results: The mean level of CD20+ cells was similar in patients with MI and patients with SAP (p = 0.60). The levels of CD24hiCD38hi cells among CD20+ cells were 5.7 ± 4% and 11.6 ± 6% in patients with MI and SAP, respectively, (p < 0.001). The level of CD24hiCD38hi B-regs remained related to acute MI after correcting for age, gender, and risk factors. Circulating levels of CD24hiCD38hi B-regs in patients with MI did not change significantly at follow-up in a small patient groups (p = 0.408). Conclusions: Circulating B-regs are reduced in patients with MI compared to patients with SAP. This finding may shed further light on the inflammatory pathophysiologic factors related to plaque rupture.

The emerging role of regulatory cell-based therapy in autoimmune disease

Autoimmune disease, caused by unwanted immune responses to self-antigens, affects millions of people each year and poses a great social and economic burden to individuals and communities. In the course of autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and multiple sclerosis, disturbances in the balance between the immune response against harmful agents and tolerance towards self-antigens lead to an immune response against self-tissues. In recent years, various regulatory immune cells have been identified. Disruptions in the quality, quantity, and function of these cells have been implicated in autoimmune disease development. Therefore, targeting or engineering these cells is a promising therapeutic for different autoimmune diseases. Regulatory T cells, regulatory B cells, regulatory dendritic cells, myeloid suppressor cells, and some subsets of innate lymphoid cells are arising as important players among this class of cells. Here, we review the roles of each suppressive cell type in the immune system during homeostasis and in the development of autoimmunity. Moreover, we discuss the current and future therapeutic potential of each one of these cell types for autoimmune diseases.

IL-10 producing regulatory B cells are decreased in blood from smokers and COPD patients

Background

Two opposing B cell subsets have been defined based on their cytokine profile: IL-6 producing effector B cells (B-effs) versus IL-10 producing regulatory B cells (B-regs) that respectively positively or negatively regulate immune responses. B-regs are decreased and/or impaired in many autoimmune diseases and inflammatory conditions. Since there is increasing evidence that links B cells and B cell-rich lymphoid follicles to the pathogenesis of COPD, the aim of this study was to investigate the presence and function of B-regs in COPD.

Methods

First, presence of IL-10 producing regulatory B cells in human lung tissue was determined by immunohistochemistry. Secondly, quantification of IL-10 + B-regs and IL-6 + B-effs in peripheral blood mononuclear cells (PBMCs) from healthy controls, smokers without airflow limitation, and COPD patients (GOLD stage I-IV) was performed by flow cytometry. Thirdly, we exposed blood-derived B cells from COPD patients in vitro to cigarette smoke extract (CSE) and quantified IL-10 + B-regs and IL-6 + B-effs. Furthermore, we aimed at restoring the perturbed IL10 production by blocking BAFF. Fourthly, we determined mRNA expression of transcription factors involved in IL-10 production in FACS sorted memory- and naive B cells upon exposure to medium or CSE.

Results

The presence of IL-10 producing regulatory B cells in parenchyma and lymphoid follicles in lungs was confirmed by immunohistochemistry. The percentage of IL-10 + B-regs was significantly decreased in blood-derived memory B cell subsets from smokers without airflow limitation and patients with COPD, compared to never smokers. Furthermore, the capacity of B cells to produce IL-10 was reduced upon in vitro exposure to CSE and this could not be restored by BAFF-blockade. Finally, upon CSE exposure, mRNA levels of the transcription factors IRF4 and HIF-1α, were decreased in memory B cells.

Conclusion

Decreased numbers and impaired function of B-regs in smokers and patients with COPD might contribute to the initiation and progression of the disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02208-1.

Current Perspectives: Evidence to Date on BTK Inhibitors in the Management of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system leading to demyelination and neurodegeneration. Basic and translational studies have shown that B cells and myeloid cells are critical players for the development and course of the disease. Bruton's tyrosine kinase (BTK) is essential for B cell receptor-mediated B cell activation and for normal B cell development and maturation. In addition to its role in B cells, BTK is also involved in several functions of myeloid cells. Although significant number of disease-modifying treatments (DMTs) have been approved for clinical use in MS patients, novel targeted therapies should be studied in refractory patients and patients with progressive forms of the disease. On the basis of its role in B cells and myeloid cells, BTK inhibitors can provide attractive therapeutic benefits for MS. In this article, we review the main effects of BTK inhibitors on different cell types involved in the pathogenesis of MS and summarise recent advances in the development of BTK inhibitors as novel therapeutic approaches in different MS clinical trials. Available data regarding the efficacy and safety of these drugs are described.

Identification of IL-10 competent B cells in swine

Progress in the phenotypic characterisation of porcine B cells is ongoing, with recent advances in the identification of B1 cell subsets and plasma cells. However, regulatory B cells, commonly identified by interleukin (IL)-10 production, have not been studied in pigs so far. Here we investigate IL-10 expression in B cell subsets in response to CpG-oligodeoxynucleotides, phorbol 12-myristate 13-acetate and ionomycin stimulation in vitro. Our results reflect similar findings in human and mice. We identify a small subset of IL-10 competent B cells, present within both porcine B1 and B2 cell subsets across blood, spleen, mediastinal lymph nodes and lung tissue, with varied differentiation statuses. The capacity for IL-10 production coincided with CD95 expression, suggesting an activated phenotype of IL-10 competent B cells. These findings support the emerging paradigm that B cell IL-10 production is a function of various B cell subsets influenced by activation history and microenvironmental factors.

Heterogeneity and Functions of Tumor-Infiltrating Antibody Secreting Cells: Lessons from Breast, Ovarian, and Other Solid Cancers

Simple Summary

B cells are gaining increasing recognition as important contributors to the tumor microenvironment, influencing, positively or negatively, tumor growth, patient survival, and response to therapies. Antibody secreting cells (ASCs) constitute a variable fraction of tumor-infiltrating B cells in most solid tumors, and they produce tumor-specific antibodies that can drive distinct immune responses depending on their isotypes and specificities. In this review, we discuss the current knowledge of the heterogeneity of ASCs infiltrating solid tumors and how both their canonical and noncanonical functions shape antitumor immunity, with a special emphasis on breast and ovarian cancers.

Abstract

Neglected for a long time in cancer, B cells and ASCs have recently emerged as critical actors in the tumor microenvironment, with important roles in shaping the antitumor immune response. ASCs indeed exert a major influence on tumor growth, patient survival, and response to therapies. The mechanisms underlying their pro- vs. anti-tumor roles are beginning to be elucidated, revealing the contributions of their secreted antibodies as well as of their emerging noncanonical functions. Here, concentrating mostly on ovarian and breast cancers, we summarize the current knowledge on the heterogeneity of tumor-infiltrating ASCs, we discuss their possible local or systemic origin in relation to their immunoglobulin repertoire, and we review the different mechanisms by which antibody (Ab) subclasses and isoforms differentially impact tumor cells and anti-tumor immunity. We also discuss the emerging roles of cytokines and other immune modulators produced by ASCs in cancer. Finally, we propose strategies to manipulate the tumor ASC compartment to improve cancer therapies.

Suppressive mechanisms of regulatory B cells in mice and humans

B cells include immune-suppressive fractions, called regulatory B cells (Bregs), which regulate inflammation primarily through an interleukin 10 (IL-10)-mediated inhibitory mechanism. Several B-cell fractions have been reported as IL-10-producing Bregs in murine disease models and human inflammatory responses including autoimmune diseases, infectious diseases, cancer and organ-transplant rejection. Although the suppressive functions of Bregs have been explored through the hallmark molecule IL-10, inhibitory cytokines and membrane-binding molecules other than IL-10 have also been demonstrated to contribute to Breg activities. Transcription factors and surface antigens that are characteristically expressed in Bregs are also being elucidated. Nevertheless, defining Bregs is still challenging because their active periods and differentiation stages vary among disease models. The identity of the diverse Breg fractions is also under debate. In the first place, since regulatory functions of Bregs are mostly evaluated by ex vivo stimulation, the actual in vivo phenotypes and functions may not be reflected by the ex vivo observations. In this article, we provide a historical overview of studies that established the characteristics of Bregs and review the various suppressive mechanisms that have been reported to be used by Bregs in murine and human disease conditions. We are only part-way through but the common phenotypes and functions of Bregs are still emerging.

B cell-T cell interplay in immune regulation: A focus on follicular regulatory T and regulatory B cell functions

B cells are the core components of humoral immunity. A mature B cell can serve in multiple capacities, including antibody production, antigen presentation, and regulatory functions. Forkhead box P3 (FoxP3)-expressing regulatory T cells (Tregs) are key players in sustaining immune tolerance and keeping inflammation in check. Mounting evidence suggests complex communications between B cells and Tregs. In this review, we summarize the yin-yang regulatory relationships between B cells and Tregs mainly from the perspectives of T follicular regulatory (Tfr) cells and regulatory B cells (Bregs). We discuss the regulatory effects of Tfr cells on B cell proliferation and the germinal center response. Additionally, we review the indispensable role of B cells in ensuring homeostatic Treg survival and describe the function of Bregs in promoting Treg responses. Finally, we introduce a new subset of Tregs, termed Treg-of-B cells, which are induced by B cells, lake the expression of FoxP3 but still own immunomodulatory effects. In this article, we also enumerate a sequence of research from clinical patients and experimental models to clarify the role of Tfr cells in germinal centers and the role of convention B cells and Bregs to Tregs in the context of different diseases. This review offers an updated overview of immunoregulatory networks and unveils potential targets for therapeutic interventions against cancer, autoimmune diseases and allograft rejection.

TLR9/FCRL3 regulates B cell viability, apoptosis, and antibody and IL-10 production through ERK1/2, p38, and STAT3 signaling pathways

B cells play a role in the progression of multiple sclerosis (MS) and are closely related to Fc-receptor like-3 (FCRL3), but little is known about FCRL3 in B cells and MS. Activation of TLR9 in B cells with CpG found that CpG promoted FCRL3 expression in a dose- and time-dependent manner. CpG significantly activated ERK1/2, p38, and STAT3 pathways, and FCRL3 overexpression further promoted the activation of these pathways, while FCRL3 siRNA significantly inhibited the activation of these pathways by CpG. CpG stimulation significantly promoted the viability of B cells, inhibited cell apoptosis, and enhanced the production of antibodies and secretion of IL-10 by B cells. FCRL3 siRNA blocked most of the above regulatory effects of CpG, but promoted the further production of antibodies by B cells. FCRL3 overexpression enhanced the pro-survival, anti-apoptotic, and IL-10-inducing effects of CpG, but inhibited the effect of CpG on promoting antibody production. After adding inhibitors of ERK1/2, p38, and STAT3 pathways, respectively, the effects of CpG on promoting cell viability, antibody production, and IL-10 secretion were significantly reduced, but the anti-apoptotic effect of CpG was only affected by the blockade of STAT3 pathway. In addition, FCRL3 regulated B cell antibody and IL-10 secretion mainly through its ITIMs. These results indicate that TLR9 activation affects B cell proliferation, apoptosis, antibody production, and IL-10 secretion by upregulating FCRL3 expression, and is associated with ERK1/2, p38, and STAT3 pathways. Therefore, FCRL3 may be an important target for the diagnosis and treatment of B cell-related diseases.

Regulatory Role of B Cells and Its Subsets in Hepatitis E Virus Infection

Antibodies as well as memory B cells are the potential correlates of a protective immune response against hepatitis E virus (HEV) infection. Literature on the role of B regulatory cells (Bregs) in acute viral infections is limited. We have evaluated the role of IL-10 expressing Bregs in HEV infection. A total of 108 acute hepatitis E patients, 55 hepatitis E recovered individuals and 128 HEV naïve healthy controls were enrolled. The percentages of peripheral CD19⁺, immature CD19⁺CD24^hiCD38^hi, mature CD19⁺CD24^intCD38^int and memory CD19⁺CD24^hiCD38⁻ B cells were analyzed by flowcytometry. Intracellular cytokine staining for IL-10 and TGF-β, HEV-rORF2p specific T cell response (IFN-γ expression) pre/post IL-10/IL-10R blocking and CD19⁺IL-10⁺ B cells-depletion based assays were carried out to assess the functionality of Bregs. The percentage of HEV-rORF2p specific immature B cell phenotype was significantly higher in acute hepatitis E patients compared to hepatitis E recovered individuals and controls. Significantly higher IL-10 expression on B and HEV-rORF2p stimulated immature B cells of acute hepatitis E patients compared to controls indicated that Bregs are functional and HEV-rORF2p specific. Enhanced IFN-γ expression on CD8⁺ T cells upon IL-10/IL-10R blocking and also post CD19⁺IL-10⁺ B cells depletion suggested that CD3⁺CD8⁺IFN-γ⁺ T cells corroborate the regulatory potential of Bregs via IL-10 dependent mechanism. We have identified HEV specific functional, immature CD19⁺CD24^hiCD38^hi B cells having IL-10 mediated regulatory activities and a potential to modulate IFN-γ mediated T cell response in Hepatitis E. The prognostic/pathogenic role of Bregs in recovery from severe hepatitis E needs evaluation.

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

Does the use of the Bruton Tyrosine Kinase inhibitors and the c-kit inhibitor masitinib result in clinically significant outcomes among patients with various forms of multiple sclerosis?

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system accompanied by chronic inflammation, axonal loss, and neurodegeneration. Traditionally, MS has been thought of as a T-cell mediated disease, but research over the past decade has demonstrated the importance of B cells in both acute demyelination and disease progression. The highly selective irreversible Bruton Tyrosine Kinase (BTK) inhibitors evobrutinib, tolebrutinib, and orelabrutinib, and the reversible BTK inhibitor fenebrutinib, all target B-cell activation and aspects of innate immunity, including macrophage and microglia biology. The c-KIT inhibitor masitinib mitigates neuroinflammation by controlling the survival, migration, and degranulation of mast cells, leading to the inhibition of proinflammatory and vasoactive molecular cascades that result from mast cell activation. This article will review and critically appraise the ongoing clinical trials of two classes of receptor tyrosine kinase inhibitors that are emerging as potential medical treatments for the varying subtypes of MS: BTK inhibitors and c-KIT inhibitors. Specifically, this review will attempt to answer whether BTK inhibitors have measurable positive clinical effects on patients with RRMS, SPMS with relapses, relapse-free SPMS, and PPMS through their effect on MRI T1 lesions; annualized relapse rate; EDSS scale; MSFC score; and time to onset of composite 12-week confirmed disability progression. Additionally, this review will examine the literature to determine if masitinib has positive clinical effects on patients with PPMS or relapse-free SPMS through its effect on EDSS or MSFC scores.

Polygenic autoimmune disease risk alleles impacting B cell tolerance act in concert across shared molecular networks in mouse and in humans

Most B cells produced in the bone marrow have some level of autoreactivity. Despite efforts of central tolerance to eliminate these cells, many escape to periphery, where in healthy individuals, they are rendered functionally non-responsive to restimulation through their antigen receptor via a process termed anergy. Broad repertoire autoreactivity may reflect the chances of generating autoreactivity by stochastic use of germline immunoglobulin gene segments or active mechanisms may select autoreactive cells during egress to the naïve peripheral B cell pool. Likewise, it is unclear why in some individuals autoreactive B cell clones become activated and drive pathophysiologic changes in autoimmune diseases. Both of these remain central questions in the study of the immune system(s). In most individuals, autoimmune diseases arise from complex interplay of genetic risk factors and environmental influences. Advances in genome sequencing and increased statistical power from large autoimmune disease cohorts has led to identification of more than 200 autoimmune disease risk loci. It has been observed that autoantibodies are detectable in the serum years to decades prior to the diagnosis of autoimmune disease. Thus, current models hold that genetic defects in the pathways that control autoreactive B cell tolerance set genetic liability thresholds across multiple autoimmune diseases. Despite the fact these seminal concepts were developed in animal (especially murine) models of autoimmune disease, some perceive a disconnect between human risk alleles and those identified in murine models of autoimmune disease. Here, we synthesize the current state of the art in our understanding of human risk alleles in two prototypical autoimmune diseases - systemic lupus erythematosus (SLE) and type 1 diabetes (T1D) along with spontaneous murine disease models. We compare these risk networks to those reported in murine models of these diseases, focusing on pathways relevant to anergy and central tolerance. We highlight some differences between murine and human environmental and genetic factors that may impact autoimmune disease development and expression and may, in turn, explain some of this discrepancy. Finally, we show that there is substantial overlap between the molecular networks that define these disease states across species. Our synthesis and analysis of the current state of the field are consistent with the idea that the same molecular networks are perturbed in murine and human autoimmune disease. Based on these analyses, we anticipate that murine autoimmune disease models will continue to yield novel insights into how best to diagnose, prognose, prevent and treat human autoimmune diseases.

Deconvolution of B cell receptor repertoire in multiple sclerosis patients revealed a delay in tBreg maturation

Background

B lymphocytes play a pivotal regulatory role in the development of the immune response. It was previously shown that deficiency in B regulatory cells (Bregs) or a decrease in their anti-inflammatory activity can lead to immunological dysfunctions. However, the exact mechanisms of Bregs development and functioning are only partially resolved. For instance, only a little is known about the structure of their B cell receptor (BCR) repertoires in autoimmune disorders, including multiple sclerosis (MS), a severe neuroinflammatory disease with a yet unknown etiology. Here, we elucidate specific properties of B regulatory cells in MS.

Methods

We performed a prospective study of the transitional Breg (tBreg) subpopulations with the CD19+CD24highCD38high phenotype from MS patients and healthy donors by (i) measuring their content during two diverging courses of relapsing-remitting MS: benign multiple sclerosis (BMS) and highly active multiple sclerosis (HAMS); (ii) analyzing BCR repertoires of circulating B cells by high-throughput sequencing; and (iii) measuring the percentage of CD27+ cells in tBregs.

Results

The tBregs from HAMS patients carry the heavy chain with a lower amount of hypermutations than tBregs from healthy donors. The percentage of transitional CD24highCD38high B cells is elevated, whereas the frequency of differentiated CD27+ cells in this transitional B cell subset was decreased in the MS patients as compared with healthy donors.

Conclusions

Impaired maturation of regulatory B cells is associated with MS progression.

β2-Adrenergic Receptor Expression and Intracellular Signaling in B Cells Are Highly Dynamic during Collagen-Induced Arthritis

The sympathetic nervous system (SNS) has either a pro-inflammatory or anti-inflammatory effect, depending on the stage of arthritis. In the past, treatment of arthritic B cells with a β2-adrenergic receptor (β2-ADR) agonist has been shown to attenuate arthritis. In this study, the expression and signaling of β2-ADR in B cells during collagen-induced arthritis (CIA) were investigated to provide an explanation of why only B cells from arthritic mice are able to improve CIA. Splenic B cells were isolated via magnetic-activated cell sorting (MACS). Adrenergic receptors on B cells and intracellular β2-ADR downstream molecules (G protein-coupled receptor kinase 2 (GRK-2), β-Arrestin 2, p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB)) were analyzed at different time points in naïve and arthritic B cells with and without stimulation of β2-ADR agonist terbutaline by flow cytometry. β2-ADR-expressing B cells increase during CIA without a change in receptor density. Moreover, we observed a profound downregulation of GRK-2 shortly after induction of arthritis and an increase in β-Arrestin 2 only at late stage of arthritis. The second messengers studied (p38, ERK1/2 and CREB) followed a biphasic course, characterized by a reduction at onset and an increase in established arthritis. Stimulation of CIA B cells with the β-ADR agonist terbutaline increased pp38 MAPK independent of the timepoint, while pERK1/2 and pCREB were enhanced only in the late phase of arthritis. The phosphorylation of p38 MAPK, ERK1/2 and CREB in the late phase of arthritis was associated with increased IL-10 produced by B10 cells. The change of β2-ADR expression and signaling during sustained inflammation might be an integral part of the switch from pro- to anti-inflammatory action of sympathetic mechanisms in late arthritis.

The role of B cells in cancer development

B cells play a critical role in adaptive immune responses mainly due to antigen presentation and antibody production. Studies about the tumor-infiltrating immune cells so far demonstrated that the function of B cells in tumor immunity is quite different among various tumor types. The antigen presentation of B cells is mainly anti-tumoral, while the role of antibody production is controversial. Moreover, the immunosuppressive regulatory B cells are detrimental to anti-tumor immunity via the secretion of various anti-inflammatory cytokines. This review briefly summarizes the different roles of B cells classified by the primary function of B cells, antigen presentation, antibody production, and immunity regulation. Further, it discusses the potential therapeutic target of B cells in tumor immunity.

The phenotype of HLA-binding B cells from sensitized kidney transplant recipients correlates with clinically prognostic patterns of interferon-γ production against purified HLA proteins

B cells play crucial roles in cell-mediated alloimmune responses. In vitro, B cells can support or regulate indirect T-cell alloreactivity in response to donor antigens on ELISpot and these patterns associate with clinical outcome. Previous reports of associations between B-cell phenotype and function have examined global phenotypes and responses to polyclonal stimuli. We hypothesized that studying antigen-specific B cells, using samples from sensitized patients, would inform further study to identify novel targets for intervention. Using biotinylated HLA proteins, which bind HLA-specific B cells via the B-cell receptor in a dose-dependent fashion, we report the specific phenotype of HLA-binding B cells and define how they associated with patterns of anti-HLA response in interferon-γ ELISpot. HLA-binding class-switched and IgM+CD27+ memory cells associated strongly with B-dependent interferon-γ production and appeared not suppressible by endogenous Tregs. When the predominant HLA-binding phenotype was naïve B cells, the associated functional ELISpot phenotype was determined by other cells present. High numbers of non-HLA-binding transitional cells associated with B-suppressed interferon-γ production, especially if Tregs were present. However, high frequencies of HLA-binding marginal-zone precursors associated with B-dependent interferon-γ production that appeared suppressible by Tregs. Finally, non-HLA-binding marginal zone precursors may also suppress interferon-γ production, though this association only emerged when Tregs were absent from the ELISpot. Thus, our novel data provide a foundation on which to further define the complexities of interactions between HLA-specific T and B cells and identify new targets for intervention in new therapies for chronic rejection.

Oxidative Phosphorylation Regulates Interleukin-10 Production in Regulatory B Cells via the Extracellular Signal-related Kinase Pathway

Regulatory B cells (Bregs) are immune cells that constrain autoimmune response and restrict inflammation via their expression of interleukin (IL)-10. However, the molecular mechanisms underlying Breg differentiation and IL-10 secretion remain unclear. Previous data suggest that cellular metabolism determines both the fate and function of these cells. Here, we suggest an essential role for mitochondrial oxidative phosphorylation (OXPHOS) in the regulation of IL-10 in these Bregs. We found that IL-10⁺ B cells from IL-10-green fluorescent protein-expressing mice had higher oxygen consumption rate than IL-10^- B cells. In addition, inhibition of OXPHOS decreased the expression of IL-10 in B cells. Further, suppression of OXPHOS diminished the expression of surface markers for Bregs and impaired their therapeutic effects in dextran sulfate sodium (DSS)-induced colitis. Mechanistically, mitochondrial OXPHOS was found to regulate the transcription factor HIF-1α through the extracellular signal-related kinase pathway. Taken together, this study reveals a strong correlation between mitochondrial OXPHOS and Breg phenotype/function, indicating OXPHOS as a therapeutic target in autoimmune diseases driven by Breg dysfunction.

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.

Full spectrum of vitamin D immunomodulation in multiple sclerosis: mechanisms and therapeutic implications

Vitamin D deficiency has been associated with the risk of multiple sclerosis, disease activity and progression. Results from in vitro experiments, animal models and analysis of human samples from randomized controlled trials provide comprehensive data illustrating the pleiotropic actions of Vitamin D on the immune system. They globally result in immunomodulation by decreasing differentiation of effector T and B cells while promoting regulatory subsets. Vitamin D also modulates innate immune cells such as macrophages, monocytes and dendritic cells, and acts at the level of the blood–brain barrier reducing immune cell trafficking. Vitamin D exerts additional activity within the central nervous system reducing microglial and astrocytic activation. The immunomodulatory role of Vitamin D detected in animal models of multiple sclerosis has suggested its potential therapeutic use for treating multiple sclerosis. In this review, we focus on recent published data describing the biological effects of Vitamin D in animal models of multiple sclerosis on immune cells, blood–brain barrier function, activation of glial cells and its potential neuroprotective effects. Based on the current knowledge, we also discuss optimization of therapeutic interventions with Vitamin D in patients with multiple sclerosis, as well as new technologies allowing in-depth analysis of immune cell regulations by vitamin D.

Cell type-specific mechanistic target of rapamycin-dependent distortion of autophagy pathways in lupus nephritis

Pro-inflammatory immune system development, metabolomic defects, and deregulation of autophagy play interconnected roles in driving the pathogenesis of systemic lupus erythematosus (SLE). Lupus nephritis (LN) is a leading cause of morbidity and mortality in SLE. While the causes of SLE have not been clearly delineated, skewing of T and B cell differentiation, activation of antigen-presenting cells, production of antinuclear autoantibodies and pro-inflammatory cytokines are known to contribute to disease development. Underlying this process are defects in autophagy and mitophagy that cause the accumulation of oxidative stress-generating mitochondria which promote necrotic cell death. Autophagy is generally inhibited by the activation of the mammalian target of rapamycin (mTOR), a large protein kinase that underlies abnormal immune cell lineage specification in SLE. Importantly, several autophagy-regulating genes, including ATG5 and ATG7, as well as mitophagy-regulating HRES-1/Rab4A have been linked to lupus susceptibility and molecular pathogenesis. Moreover, genetically-driven mTOR activation has been associated with fulminant lupus nephritis. mTOR activation and diminished autophagy promote the expansion of pro-inflammatory Th17, Tfh and CD3⁺CD4^-CD8^- double-negative (DN) T cells at the expense of CD8⁺ effector memory T cells and CD4⁺ regulatory T cells (Tregs). mTOR activation and aberrant autophagy also involve renal podocytes, mesangial cells, endothelial cells, and tubular epithelial cells that may compromise end-organ resistance in LN. Activation of mTOR complexes 1 (mTORC1) and 2 (mTORC2) has been identified as biomarkers of disease activation and predictors of disease flares and prognosis in SLE patients with and without LN. This review highlights recent advances in molecular pathogenesis of LN with a focus on immuno-metabolic checkpoints of autophagy and their roles in pathogenesis, prognosis and selection of targets for treatment in SLE.

IL-2, IL-6 and chitinase 3-like 2 might predict early relapse activity in multiple sclerosis

Background

The possibility to better predict the severity of the disease in a patient newly diagnosed with multiple sclerosis would allow the treatment strategy to be personalized and lead to better clinical outcomes. Prognostic biomarkers are highly needed.

Objective

To assess the prognostic value of intrathecal IgM synthesis, cerebrospinal fluid and serum IL-2, IL-6, IL-10, chitinase 3-like 2 and neurofilament heavy chains obtained early after the onset of the disease.

Methods

58 patients after the first manifestation of multiple sclerosis were included. After the initial diagnostic assessment including serum and cerebrospinal fluid biomarkers, all patients initiated therapy with either glatiramer acetate, teriflunomide, or interferon beta. To assess the evolution of the disease, we followed the patients clinically and with MRI for two years.

Results

The IL-2:IL-6 ratio (both in cerebrospinal fluid) <0.48 (p = 0.0028), IL-2 in cerebrospinal fluid ≥1.23pg/ml (p = 0.026), and chitinase 3-like 2 in cerebrospinal fluid ≥7900pg/ml (p = 0.033), as well as baseline EDSS ≥1.5 (p = 0.0481) and age <22 (p = 0.0312), proved to be independent markers associated with shorter relapse free intervals.

Conclusion

The IL-2:IL-6 ratio, IL-2, and chitinase 3-like 2 (all in cerebrospinal fluid) might be of value as prognostic biomarkers in early phases of multiple sclerosis.

Contribution of Dysregulated B-Cells and IgE Antibody Responses to Multiple Sclerosis

Multiple sclerosis (MS), a debilitating autoimmune inflammatory disease that affects the brain and spinal cord, causes demyelination of neurons, axonal damage, and neurodegeneration. MS and the murine experimental autoimmune encephalomyelitis (EAE) model have been viewed mainly as T-cell-mediated diseases. Emerging data have suggested the contribution of B-cells and autoantibodies to the disease progression. However, the underlying mechanisms by which dysregulated B-cells and antibody response promote MS and EAE remain largely unclear. Here, we provide an updated review of this specific subject by including B-cell biology and the role of B-cells in triggering autoimmune neuroinflammation with a focus on the regulation of antibody-producing B-cells. We will then discuss the role of a specific type of antibody, IgE, as it relates to the potential regulation of microglia and macrophage activation, autoimmunity and MS/EAE development. This knowledge can be utilized to develop new and effective therapeutic approaches to MS, which fits the scope of the Research Topic "Immune Mechanism in White Matter Lesions: Clinical and Pathophysiological Implications".

Age-Associated B Cell Features of the Murine High-Grade B Cell Lymphoma Bc.DLFL1 and Its Extranodal Expansion in Abdominal Adipose Tissues

Diffuse large B cell lymphoma comprises a heterogeneous group of B cell-derived tumors, with different degrees of aggressiveness, as defined by their cellular origin and tissue microenvironment. Using the spontaneous Bc.DLFL1 lymphoma originating from a BALB/c mouse as a diffuse large B cell lymphoma model, in this study we demonstrate that the lymphoma cells display surface phenotype, IgH V-region somatic mutations, transcription factor characteristics and in vivo location to splenic extrafollicular regions of age-associated B cells (ABCs), corresponding to T-bet⁺ and Blimp-1⁺/CD138^- plasmablasts derivation. The expansion of lymphoma cells within lymphoid tissues took place in a close arrangement with CD11c⁺ dendritic cells, whereas the extranodal infiltration occurred selectively in the mesentery and omentum containing resident gp38/podoplanin⁺ fibroblastic reticular cells. Antagonizing BAFF-R activity by mBR3-Fc soluble receptor fusion protein led to a significant delay of disease progression. The extranodal expansion of Bc.DLFL1 lymphoma within the omental and mesenteric adipose tissues was coupled with a significant change of the tissue cytokine landscape, including both shared alterations and tissue-specific variations. Our findings indicate that while Bc.DLFL1 cells of ABC origin retain the positioning pattern within lymphoid tissues of their physiological counterpart, they also expand in non-lymphoid tissues in a BAFF-dependent manner, where they may alter the adipose tissue microenvironment to support their extranodal growth.

Chronic Rhinosinusitis, S. aureus Biofilm and Secreted Products, Inflammatory Responses, and Disease Severity

Chronic rhinosinusitis (CRS) is a persistent inflammation of the nasal cavity and paranasal sinuses associated with tissue remodelling, dysfunction of the sinuses' natural defence mechanisms, and induction of different inflammatory clusters. The etiopathogenesis of CRS remains elusive, and both environmental factors, such as bacterial biofilms and the host's general condition, are thought to play a role. Bacterial biofilms have significant clinical relevance due to their potential to cause resistance to antimicrobial therapy and host defenses. Despite substantial medical advances, some CRS patients suffer from recalcitrant disease that is unresponsive to medical and surgical treatments. Those patients often have nasal polyps with tissue eosinophilia, S. aureus-dominant mucosal biofilm, comorbid asthma, and a severely compromised quality of life. This review aims to summarise the contemporary knowledge of inflammatory cells/pathways in CRS, the role of bacterial biofilm, and their impact on the severity of the disease. Here, an emphasis is placed on S. aureus biofilm and its secreted products. A better understanding of these factors might offer important diagnostic and therapeutic perceptions for recalcitrant disease.

Regulatory B cell repertoire defects predispose lung cancer patients to immune-related toxicity following checkpoint blockade

Checkpoint blockade with Pembrolizumab, has demonstrated durable clinical responses in advanced non-small cell lung cancer, however, treatment is offset by the development of high-grade immune related adverse events (irAEs) in some patients. Here, we show that in these patients a deficient Breg checkpoint fails to limit self-reactive T cell enhanced activity and auto-antibody formation enabled by PD-1/PD-L1 blockade, leading to severe auto-inflammatory sequelae. Principally a failure of IL-10 producing regulatory B cells as demonstrated through functional ex vivo assays and deep phenotyping mass cytometric analysis, is a major and significant finding in patients who develop high-grade irAEs when undergoing treatment with anti-PD1/PD-L1 checkpoint blockade. There is currently a lack of biomarkers to identify a priori those patients at greatest risk of developing severe auto-inflammatory syndrome. Pre-therapy B cell profiling could provide an important tool to identify lung cancer patients at high risk of developing severe irAEs on checkpoint blockade.

Trichinella-induced immunomodulation: Another tale of helminth success

Trichinella spiralis is a unique parasite in that both the adults and larvae survive in two different intracellular niches in the same host. The immune response, albeit intense, is highly modulated to ensure the survival of both the host and the parasite. It is skewed to T helper 2 and regulatory arms. Diverse cells from both the innate and adaptive compartments of immunity, including dendritic cells, T regulatory cells, and alternatively activated macrophages are thought to mediate such immunomodulation. The parasite has also an outstanding ability to evade the immune system by several elaborate processes. The molecules derived from the parasites including Trichinella, particularly the components of the excretory-secretory products, are being continually identified and explored for the potential of ameliorating the immunopathology in animal models of diverse inflammatory and autoimmune human diseases. Herein we discuss the various aspects of Trichinella-induced immunomodulation with a special reference to the practical implications of the immune system manipulation in alleviating or possibly curing human diseases.

Acteoside promotes B cell-derived IL-10 production and ameliorates autoimmunity

IL-10-producing regulatory B (Breg) cells are well recognized for maintaining immune tolerance. The impaired Breg cell function with decreased IL-10-producing capacity has been found in autoimmune diseases, such as rheumatoid arthritis, lupus, and primary Sjogren's syndrome (pSS). However, seldom therapeutic agents targeting Breg cells are available to treat those autoimmune diseases. Here, we showed that acteoside (AC), a caffeoyl phenylethanoid glycoside from a medicinal herb Radix Rehmanniae, could promote IL-10 production from both human and murine B cells via critically regulating the TLR4/PI3K axis. Moreover, TLR4 was found increased in Breg cells from mice with experimental SS (ESS), a mouse model that recapitulates human pSS. Thus, B cells from the ESS mice were susceptible to AC treatment, showing higher IL-10-producing capacity than those from naïve controls. In addition, AC treatment also promoted the production of IL-10 from TLR4⁺ CXCR4⁺ plasma cells of ESS mice. Notably, we found that AC was able to enter lymphoid organs upon oral administration. AC treatment effectively increased IL-10⁺ B cells in ESS mice and ameliorated disease pathology accompanied by reduced T effector cells, including Th17 and T follicular helper cells in the ESS mice. In conclusion, AC could promote Breg cell function and attenuate ESS pathology in vivo, which may be a promising drug candidate for treating pSS and other autoimmune diseases.

Antigen receptor-engineered Tregs inhibit CNS autoimmunity in cell therapy using non-redundant immune mechanisms in mice

CD4⁺FOXP3⁺ Tregs are currently explored to develop cell therapies against immune‐mediated disorders, with an increasing focus on antigen receptor‐engineered Tregs. Deciphering their mode of action is necessary to identify the strengths and limits of this approach. Here, we addressed this issue in an autoimmune disease of the CNS, EAE. Following disease induction, autoreactive Tregs upregulated LAG‐3 and CTLA‐4 in LNs, while IL‐10 and amphiregulin (AREG) were increased in CNS Tregs. Using genetic approaches, we demonstrated that IL‐10, CTLA‐4, and LAG‐3 were nonredundantly required for the protective function of antigen receptor‐engineered Tregs against EAE in cell therapy whereas AREG was dispensable. Treg‐derived IL‐10 and CTLA‐4 were both required to suppress acute autoreactive CD4⁺ T‐cell activation, which correlated with disease control. These molecules also affected the accumulation in the recipients of engineered Tregs themselves, underlying complex roles for these molecules. Noteworthy, despite the persistence of the transferred Tregs and their protective effect, autoreactive T cells eventually accumulated in the spleen of treated mice. In conclusion, this study highlights the remarkable power of antigen receptor‐engineered Tregs to appropriately provide multiple suppressive factors nonredundantly necessary to prevent autoimmune attacks.

Inflammation and atherosclerosis: signaling pathways and therapeutic intervention

Atherosclerosis is a chronic inflammatory vascular disease driven by traditional and nontraditional risk factors. Genome-wide association combined with clonal lineage tracing and clinical trials have demonstrated that innate and adaptive immune responses can promote or quell atherosclerosis. Several signaling pathways, that are associated with the inflammatory response, have been implicated within atherosclerosis such as NLRP3 inflammasome, toll-like receptors, proprotein convertase subtilisin/kexin type 9, Notch and Wnt signaling pathways, which are of importance for atherosclerosis development and regression. Targeting inflammatory pathways, especially the NLRP3 inflammasome pathway and its regulated inflammatory cytokine interleukin-1β, could represent an attractive new route for the treatment of atherosclerotic diseases. Herein, we summarize the knowledge on cellular participants and key inflammatory signaling pathways in atherosclerosis, and discuss the preclinical studies targeting these key pathways for atherosclerosis, the clinical trials that are going to target some of these processes, and the effects of quelling inflammation and atherosclerosis in the clinic.

Human IL-10-producing B cells have diverse states that are induced from multiple B cell subsets

Regulatory B cells (Bregs) suppress immune responses through the secretion of interleukin-10 (IL-10). This immunomodulatory capacity holds therapeutic potential, yet a definitional immunophenotype for enumeration and prospective isolation of B cells capable of IL-10 production remains elusive. Here, we simultaneously quantify cytokine production and immunophenotype in human peripheral B cells across a range of stimulatory conditions and time points using mass cytometry. Our analysis shows that multiple functional B cell subsets produce IL-10 and that no phenotype uniquely identifies IL-10+ B cells. Further, a significant portion of IL-10+ B cells co-express the pro-inflammatory cytokines IL-6 and tumor necrosis factor alpha (TNFα). Despite this heterogeneity, operationally tolerant liver transplant recipients have a unique enrichment of IL-10+, but not TNFα+ or IL-6+, B cells compared with transplant recipients receiving immunosuppression. Thus, human IL-10-producing B cells constitute an induced, transient state arising from a diversity of B cell subsets that may contribute to maintenance of immune homeostasis.

B Cells Specific CpG Induces High IL-10 and IL-6 Expression In Vitro in Neuro-Behçet's Disease

Remitting-RelapsingMultiple Sclerosis (RRMS) and Neuro-Behçet Disease (NBD) are two chronic neuroinflammatory disorders leading to neurological damage. Herein, we investigated in these patients the IL-10-producing cells during the early stages of these disorders. Cellular and molecular investigations were carried out on treatment naive patients suffering from RRMS and NBD recruited at the first episode of clinical relapse. Our findings demonstrate that CSF-B cells from NBD patients, but not RRMS, are the major source of intrathecal IL-10 as compared to T-CD4 cells. Moreover, we showed a lower expression of TGF-β and IL35, in the CSF cells of NBD patients as compared to the control group. Specific in vitro CpG stimulation of peripheral blood B cells from NBD patients resulted in a concomitant early mRNA expression of IL6 and IL10 but was limited to IL10 for RRMS patients. Furthermore, mRNA expression of IL-6 and IL-10 receptors was assessed and intriguingly IL6ST receptor subunit was significantly lower in NBD CSF, but not RRMS while IL10RB was increased in both. Deciphering the role of increased IL-10-producing B cells and IL10RB despite relapsing disease as well as the discordant expression of IL6 and IL6ST may pave the way for a better understanding of the pathophysiology of these neuro-inflammatory disorders.

B cells and tertiary lymphoid structures as determinants of tumour immune contexture and clinical outcome

B cells are a major component of the tumour microenvironment, where they are predominantly associated with tertiary lymphoid structures (TLS). In germinal centres within mature TLS, B cell clones are selectively activated and amplified, and undergo antibody class switching and somatic hypermutation. Subsequently, these B cell clones differentiate into plasma cells that can produce IgG or IgA antibodies targeting tumour-associated antigens. In tumours without mature TLS, B cells are either scarce or differentiate into regulatory cells that produce immunosuppressive cytokines. Indeed, different tumours vary considerably in their TLS and B cell content. Notably, tumours with mature TLS, a high density of B cells and plasma cells, as well as the presence of antibodies to tumour-associated antigens are typically associated with favourable clinical outcomes and responses to immunotherapy compared with those lacking these characteristics. However, polyclonal B cell activation can also result in the formation of immune complexes that trigger the production of pro-inflammatory cytokines by macrophages and neutrophils. In complement-rich tumours, IgG antibodies can also activate the complement cascade, resulting in the production of anaphylatoxins that sustain tumour-promoting inflammation and angiogenesis. Herein, we review the phenotypic heterogeneity of intratumoural B cells and the importance of TLS in their generation as well as the potential of B cells and TLS as prognostic and predictive biomarkers. We also discuss novel therapeutic approaches that are being explored with the aim of increasing mature TLS formation, B cell differentiation and anti-tumour antibody production within tumours.

A Spontaneous Model of Experimental Autoimmune Encephalomyelitis Provides Evidence of MOG-Specific B Cell Recruitment and Clonal Expansion

The key role of B cells in the pathophysiology of multiple sclerosis (MS) is supported by the presence of oligoclonal bands in the cerebrospinal fluid, by the association of meningeal ectopic B cell follicles with demyelination, axonal loss and reduction of astrocytes, as well as by the high efficacy of B lymphocyte depletion in controlling inflammatory parameters of MS. Here, we use a spontaneous model of experimental autoimmune encephalomyelitis (EAE) to study the clonality of the B cell response targeting myelin oligodendrocyte glycoprotein (MOG). In particular, 94% of SJL/j mice expressing an I-A^s: MOG_92-106 specific transgenic T cell receptor (TCR¹⁶⁴⁰) spontaneously develop a chronic paralytic EAE between the age of 60-500 days. The immune response is triggered by the microbiota in the gut-associated lymphoid tissue, while there is evidence that the maturation of the autoimmune demyelinating response might occur in the cervical lymph nodes owing to local brain drainage. Using MOG-protein-tetramers we tracked the autoantigen-specific B cells and localized their enrichment to the cervical lymph nodes and among the brain immune infiltrate. MOG-specific IgG1 antibodies were detected in the serum of diseased TCR¹⁶⁴⁰ mice and proved pathogenic upon adoptive transfer into disease-prone recipients. The ontogeny of the MOG-specific humoral response preceded disease onset coherent with their contribution to EAE initiation. This humoral response was, however, not sufficient for disease induction as MOG-antibodies could be detected at the age of 69 days in a model with an average age of onset of 197 days. To assess the MOG-specific B cell repertoire we FACS-sorted MOG-tetramer binding cells and clonally expand them in vitro to sequence the paratopes of the IgG heavy chain and kappa light chains. Despite the fragility of clonally expanding MOG-tetramer binding effector B cells, our results indicate the selection of a common CDR-3 clonotype among the Igk light chains derived from both disease-free and diseased TCR¹⁶⁴⁰ mice. Our study demonstrates the pre-clinical mobilization of the MOG-specific B cell response within the brain-draining cervical lymph nodes, and reiterates that MOG antibodies are a poor biomarker of disease onset and progression.

CD4+ T-cell-derived IL-10 promotes CNS inflammation in mice by sustaining effector T cell survival

Interleukin (IL)-10 is considered a prototypical anti-inflammatory cytokine, significantly contributing to the maintenance and reestablishment of immune homeostasis. Accordingly, it has been shown in the intestine that IL-10 produced by Tregs can act on effector T cells, thereby limiting inflammation. Herein, we investigate whether this role also applies to IL-10 produced by T cells during central nervous system (CNS) inflammation. During neuroinflammation, both CNS-resident and -infiltrating cells produce IL-10; yet, as IL-10 has a pleotropic function, the exact contribution of the different cellular sources is not fully understood. We find that T-cell-derived IL-10, but not other relevant IL-10 sources, can promote inflammation in experimental autoimmune encephalomyelitis. Furthermore, in the CNS, T-cell-derived IL-10 acts on effector T cells, promoting their survival and thereby enhancing inflammation and CNS autoimmunity. Our data indicate a pro-inflammatory role of T-cell-derived IL-10 in the CNS.

Microbial metabolite butyrate promotes induction of IL-10+IgM+ plasma cells

The microbially-derived short-chain fatty acid butyrate is a central inhibitor of inflammatory innate and adaptive immune responses. Emerging evidence suggests that butyrate induces differentiation of IL-10-producing (IL-10+) regulatory B cells. However, the underlying mechanisms of butyrate-driven modulation of B cell differentiation are not fully defined. Given the dominant role of regulatory plasma cells (PCs) as the main source of anti-inflammatory cytokines including IL-10 and the observation that butyrate also induces the differentiation of PCs, we here investigated the effect of the microbial metabolite butyrate on the induction of regulatory IL-10+ PCs and underlying mechanisms. Here we show that butyrate induces the differentiation of IL-10+IgM+ PCs. Ex vivo, butyrate, but hardly propionate, another microbially-derived short-chain fatty acid, induced the differentiation of IL-10+IgM+ CD138high PCs from isolated splenic murine B cells. In vivo, administration of butyrate via drinking water or by daily intraperitoneal injection increased the number of IL-10+IgM+ CD138high PCs in the spleens of Ovalbumin (Ova)/complete Freund’s adjuvant-immunized mice. The induction of these regulatory PCs was associated with an increase of anti-Ova IgM, but a reduction of anti-Ova class-switched pathogenic IgG2b serum antibodies. Based on the knowledge that butyrate inhibits histone deacetylases (HDACs) thereby increasing histone acetylation, we identified here that HDAC3 inhibition was sufficient to induce PC differentiation and IL-10+ expression. Furthermore, reduced mitochondrial superoxide levels following butyrate treatment and HDAC3 inhibition were necessary for PC differentiation, but not IL-10 expression. In summary, the microbial metabolite butyrate promotes the differentiation of IgM+ PCs and their expression of IL-10. HDAC3 inhibition may be involved as an underlying pathway for both PC differentiation and IL-10 expression, while reduced mitochondrial superoxide levels are crucial only for PC differentiation. The induction of regulatory IL-10+IgM+ PCs and the inhibition of class switching to antigen-specific pathogenic IgG subclasses might represent important pathways of butyrate to limit inflammation.

IgG4 Autoantibodies in Organ-Specific Autoimmunopathies: Reviewing Class Switching, Antibody-Producing Cells, and Specific Immunotherapies

Organ-specific autoimmunity is often characterized by autoantibodies targeting proteins expressed in the affected tissue. A subgroup of autoimmunopathies has recently emerged that is characterized by predominant autoantibodies of the IgG4 subclass (IgG4-autoimmune diseases; IgG4-AID). This group includes pemphigus vulgaris, thrombotic thrombocytopenic purpura, subtypes of autoimmune encephalitis, inflammatory neuropathies, myasthenia gravis and membranous nephropathy. Although the associated autoantibodies target specific antigens in different organs and thus cause diverse syndromes and diseases, they share surprising similarities in genetic predisposition, disease mechanisms, clinical course and response to therapies. IgG4-AID appear to be distinct from another group of rare immune diseases associated with IgG4, which are the IgG4-related diseases (IgG4-RLD), such as IgG4-related which have distinct clinical and serological properties and are not characterized by antigen-specific IgG4. Importantly, IgG4-AID differ significantly from diseases associated with IgG1 autoantibodies targeting the same organ. This may be due to the unique functional characteristics of IgG4 autoantibodies (e.g. anti-inflammatory and functionally monovalent) that affect how the antibodies cause disease, and the differential response to immunotherapies of the IgG4 producing B cells/plasmablasts. These clinical and pathophysiological clues give important insight in the immunopathogenesis of IgG4-AID. Understanding IgG4 immunobiology is a key step towards the development of novel, IgG4 specific treatments. In this review we therefore summarize current knowledge on IgG4 regulation, the relevance of class switching in the context of health and disease, describe the cellular mechanisms involved in IgG4 production and provide an overview of treatment responses in IgG4-AID.

Chronic immune thrombocytopenia in a child with X-linked agammaglobulinemia-an uncommon phenotype

Autoimmune disorders are common in patients with primary immunodeficiency diseases (PIDs). However, the prevalence of autoimmunity is low in patients with X-linked agammaglobulinemia (XLA), mostly due to the absence of antibodies. Chronic or persistent immune thrombocytopenia (ITP), which is usually considered an antibody-mediated disease, is uncommon in patients with XLA. In this study, we detailly described a surprising autoimmune phenomenon, chronic ITP, in a small boy diagnosed with XLA. This is an interesting phenotype found in XLA, and it is helpful to understand the immune pathogenesis of autoimmunity in patients with XLA.

B Cell IL-4 Drives Th2 Responses In Vivo, Ameliorates Allograft Rejection, and Promotes Allergic Airway Disease

B cells can be polarized to express various cytokines. The roles of IFNγ and IL-10, expressed respectively by B effector 1 (Be1) and Bregs, have been established in pathogen clearance, tumor growth, autoimmunity and allograft rejection. However, the in vivo role of B cell IL-4, produced by Be2 cells, remains to be established. We developed B-IL-4/13 iKO mice carrying a tamoxifen-inducible B cell-specific deletion of IL-4 and IL-13. After alloimmunization, B-IL-4/13 iKO mice exhibited decreased IL-4⁺ Th2 cells and IL-10⁺ Bregs without impact on Th1, Tregs, or CD8 T cell responses. B-IL-4/13 iKO mice rejected islet allografts more rapidly, even when treated with tolerogenic anti-TIM-1 mAb. In ovalbumin-induced allergic airway disease (AAD), B-IL-4/13 iKO mice had reduced inflammatory cells in BAL, and preserved lung histology with markedly decreased infiltration by IL-4⁺ and IL-5⁺ CD4⁺ T cells. Hence, B cell IL-4 is a major driver of Th2 responses in vivo which promotes allograft survival, and conversely, worsens AAD.

Regulatory B Cells Are Decreased and Functionally Impaired in Myasthenia Gravis Patients

Myasthenia gravis (MG) is an autoimmune disease mediated by B cells secreting autoantibodies. Regulatory B (Breg) cells confirmed to have an immunosuppressive function play an important role in many autoimmune diseases. However, what about the changes in Breg cells in the thymus and peripheral blood of MG patients? The changes in the proportion of Breg cells in the peripheral blood of 41 MG patients without any drug treatment and 30 healthy controls were detected by flow cytometry. We found that the proportions of CD19⁺ IL-10⁺ cells and CD19⁺CD24^hiCD38^hi cell subsets in MG patients were significantly lower than those in healthy controls. Then, we detected the proportion of CD19⁺ IL-10⁺ cells in thymus tissues of 10 healthy children, 4 healthy adults, and 12 MG patients by flow cytometry. However, the percentage of CD19⁺ IL-10⁺ cells was highest in healthy children (~8%), followed by healthy adults (~3%), and was lowest in MG patients (~0.5%). CD19⁺CD24^hiCD38^hi B cells exerted immunosuppressive functions in healthy people but were refractory in MG patients. Moreover, p-STAT3 downstream of CD40 may be impaired in CD24^hiCD38^hi B cells from the peripheral blood of MG patients.

Characterization of Definitive Regulatory B Cell Subsets by Cell Surface Phenotype, Function and Context

Regulatory B cell or “Breg” is a broad term that represents the anti-inflammatory activity of B cells, but does not describe their individual phenotypes, specific mechanisms of regulation or relevant disease contexts. Thus, given the variety of B cell regulatory mechanisms reported in human disease and their animal models, a more thorough and comprehensive identification strategy is needed for tracking and comparing B cell subsets between research groups and in clinical settings. This review summarizes the discovery process and mechanism of action for well-defined regulatory B cell subsets with an emphasis on the mouse model of multiple sclerosis experimental autoimmune encephalomyelitis. We discuss the importance of conducting thorough B cell phenotyping along with mechanistic studies prior to defining a particular subset of B cells as Breg. Since virtually all B cell subsets can exert regulatory activity, it is timely for their definitive identification across studies.

B cell-derived IL-27 promotes control of persistent LCMV infection

Recent studies have identified a critical role for B cell-produced cytokines in regulating both humoral and cellular immunity. Here, we show that B cells are an essential source of interleukin-27 (IL-27) during persistent lymphocytic choriomeningitis virus (LCMV) clone 13 (Cl-13) infection. By using conditional knockout mouse models with specific IL-27p28 deletion in B cells, we observed that B cell-derived IL-27 promotes survival of virus-specific CD4 T cells and supports functions of T follicular helper (Tfh) cells. Mechanistically, B cell-derived IL-27 promotes CD4 T cell function, antibody class switch, and the ability to control persistent LCMV infection. Deletion of IL-27ra in T cells demonstrated that T cell-intrinsic IL-27R signaling is essential for viral control, optimal CD4 T cell responses, and antibody class switch during persistent LCMV infection. Collectively, our findings identify a cellular mechanism whereby B cell-derived IL-27 drives antiviral immunity and antibody responses through IL-27 signaling on T cells to promote control of LCMV Cl-13 infection.

Anti-Neuronal IgG4 Autoimmune Diseases and IgG4-Related Diseases May Not Be Part of the Same Spectrum: A Comparative Study

Background

IgG4 is associated with two emerging groups of rare diseases: 1) IgG4 autoimmune diseases (IgG4-AID) and 2) IgG4-related diseases (IgG4-RLD). Anti-neuronal IgG4-AID include MuSK myasthenia gravis, LGI1- and Caspr2-encephalitis and autoimmune nodo-/paranodopathies (CNTN1/Caspr1 or NF155 antibodies). IgG4-RLD is a multiorgan disease hallmarked by tissue-destructive fibrotic lesions with lymphocyte and IgG4 plasma cell infiltrates and increased serum IgG4 concentrations. It is unclear whether IgG4-AID and IgG4-RLD share relevant clinical and immunopathological features.

Methods

We collected and analyzed clinical, serological, and histopathological data in 50 patients with anti-neuronal IgG4-AID and 19 patients with IgG4-RLD.

Results

A significantly higher proportion of IgG4-RLD patients had serum IgG4 elevation when compared to IgG4-AID patients (52.63% vs. 16%, p = .004). Moreover, those IgG4-AID patients with elevated IgG4 did not meet the diagnostic criteria of IgG4-RLD, and their autoantibody titers did not correlate with their serum IgG4 concentrations. In addition, patients with IgG4-RLD were negative for anti-neuronal/neuromuscular autoantibodies and among these patients, men showed a significantly higher propensity for IgG4 elevation, when compared to women (p = .005). Last, a kidney biopsy from a patient with autoimmune paranodopathy due to CNTN1/Caspr1-complex IgG4 autoantibodies and concomitant nephrotic syndrome did not show fibrosis or IgG4+ plasma cells, which are diagnostic hallmarks of IgG4-RLD.

Conclusion

Our observations suggest that anti-neuronal IgG4-AID and IgG4-RLD are most likely distinct disease entities.

B Cell Receptor Signaling and Protein Kinase D2 Support Regulatory B Cell Function in Pancreatic Cancer

B cells can act as potent suppressors of anti-tumor T cell immunity, presenting a mechanism of resistance to immunotherapy. In pancreatic ductal adenocarcinoma, B cells can display a T cell-suppressive or regulatory phenotype centered on the expression of the cytokine Interleukin 35 (IL-35). While B cell-mediated immunosuppression presents a barrier to anti-tumorigenic T cell function, it is not clear how regulatory B cell function could be targeted, and the signals that promote this suppressive phenotype in B cells are not well understood. Here we use a novel IL-35 reporter model to understand which signaling pathways are important for immunosuppressive properties in B cells. In vitro analysis of IL-35 reporter B cells revealed a synergy between the BCR and TLR4 signaling pathways is sufficient to induce IL-35 expression. However, in vivo, B cell receptor activation, as opposed to MyD88 signaling in B cells, is central to B cell-mediated suppression and promotion of pancreatic cancer growth. Further analysis identified protein kinase D2 (PKD2) as being a key downstream regulator of IL-35 expression in B cells. Regulatory B cells with an inactivating mutation in PKD2 failed to produce IL-35 or fully suppress effector T cell function in vitro. Furthermore, inhibition of PKD in B cells decreased tumor growth and promoted effector T cell function upon adoptive transfer into B cell-deficient mice. Collectively, these data provide insight into how regulatory B cell function is promoted in pancreatic cancer and identify potential therapeutic targets to restrain this function.

B cells in central nervous system disease: diversity, locations and pathophysiology

B cells represent a relatively minor cell population within both the healthy and diseased central nervous system (CNS), yet they can have profound effects. This is emphasized in multiple sclerosis, in which B cell-depleting therapies are arguably the most efficacious treatment for the condition. In this Review, we discuss how B cells enter and persist in the CNS and how, in many neurological conditions, B cells concentrate within CNS barriers but are rarely found in the parenchyma. We highlight how B cells can contribute to CNS pathology through antibody secretion, antigen presentation and secretion of neurotoxic molecules, using examples from CNS tumours, CNS infections and autoimmune conditions such as neuromyelitis optica and, in particular, multiple sclerosis. Overall, understanding common and divergent principles of B cell accumulation and their effects within the CNS could offer new insights into treating these devastating neurological conditions.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.