Peritoneal cavity regulatory B cells (B10 cells) modulate IFN-γ+CD4+ T cell numbers during colitis development in mice

Peritoneal B1 and B2 cells respond differently to LPS and IL-21 stimulation

Peritoneal B cells can be divided into B1 cells (CD11b+CD19+) and B2 cells (CD11b-CD19+) based on CD11b expression. B1 cells play a crucial role in the innate immune response by producing natural antibodies and cytokines. B2 cells share similar traits with B1 cells, influenced by the peritoneal environment. However, the response of both B1 and B2 cells to the same stimuli in the peritoneum remains uncertain. We isolated peritoneal B1 and B2 cells from mice and assessed differences in Interleukin-10(IL-10) secretion, apoptosis, and surface molecule expression following exposure to LPS and Interleukin-21(IL-21). Our findings indicate that B1 cells are potent IL-10 producers, possessing surface molecules with an IgMhiCD43+CD21low profile, and exhibit a propensity for apoptosis in vitro. Conversely, B2 cells exhibit lower IL-10 production and surface markers characterized as IgMlowCD43-CD21hi, indicative of some resistance to apoptosis. LPS stimulates MAPK phosphorylation in B1 and B2 cells, causing IL-10 production. Furthermore, LPS inhibits peritoneal B2 cell apoptosis by enhancing Bcl-xL expression. Conversely, IL-21 has no impact on IL-10 production in these cells. Nevertheless, impeding STAT3 phosphorylation permits IL-21 to increase IL-10 production in peritoneal B cells. Moreover, IL-21 significantly raises apoptosis levels in these cells, a process independent of STAT3 phosphorylation and possibly linked to reduced Bcl-xL expression. This study elucidates the distinct functional and response profiles of B1 and B2 cells in the peritoneum to stimuli like LPS and IL-21, highlighting their differential roles in immunological responses and B cell diversity.

Role of Immune Cells and Immunotherapy in Multiple Myeloma

The clinical signs of multiple myeloma, a plasma cell (PC) dyscrasia, include bone loss, renal damage, and paraproteinemia. It can be defined as the uncontrolled growth of malignant PCs within the bone marrow. The distinctive bone marrow milieu that regulates the progression of myeloma disease involves interactions between plasma and stromal cells, and myeloid and lymphoid cells. These cells affect the immune system independently or because of a complicated web of interconnections, which promotes disease development and immune evasion. Due to the importance of these factors in the onset of disease, various therapeutic strategies have been created that either target or improve the immunological processes that influence disease progression. The immune system has a role in the mechanism of action of multiple myeloma treatments. The main contributions of immune cells to the bone marrow microenvironment, as well as how they interact and how immune regulation might lead to therapeutic effects, are covered in this study.

Age-associated accumulation of B cells promotes macrophage inflammation and inhibits lipolysis in adipose tissue during sepsis

Non-canonical lipolysis induced by inflammatory cytokines or Toll-like receptor ligands is required for the regulation of inflammation during endotoxemia and sepsis. Canonical lipolysis induced by catecholamines declines during aging due to factors including an expansion of lymphocytes, pro-inflammatory macrophage polarization, and an increase in chronic low-grade inflammation; however, the extent to which the non-canonical pathway of lipolysis is active and impacted by immune cells during aging remains unclear. Therefore, we aimed to define the extent to which immune cells from old mice influence non-canonical lipolysis during sepsis. We identified age-associated impairments of non-canonical lipolysis and an accumulation of dysfunctional B1 B cells in the visceral white adipose tissue (vWAT) of old mice. Lifelong deficiency of B cells results in restored non-canonical lipolysis and reductions in pro-inflammatory macrophage populations. Our study suggests that targeting the B cell-macrophage signaling axis may resolve metabolic dysfunction in aged vWAT and attenuate septic severity in older individuals.

Unraveling the diversity and functions of tissue-resident plasma cells

Antibody-secreting plasma cells (PCs) are generated in secondary lymphoid organs but are reported to reside in an emerging range of anatomical sites. Analysis of the transcriptome of different tissue-resident (Tr)PC populations revealed that they each have their own transcriptional signature indicative of functional adaptation to the host tissue environment. In contrast to expectation, all TrPCs were extremely long-lived, regardless of their organ of residence, with longevity influenced by intrinsic factors like the immunoglobulin isotype. Analysis at single-cell resolution revealed that the bone marrow is unique in housing a compendium of PCs generated all over the body that retain aspects of the transcriptional program indicative of their tissue of origin. This study reveals that extreme longevity is an intrinsic property of TrPCs whose transcriptome is imprinted by signals received both at the site of induction and within the tissue of residence.

Breg-Mediated Immunoregulation in the Skin

Wound healing is a complex process involving a coordinated series of events aimed at restoring tissue integrity and function. Regulatory B cells (Bregs) are a subset of B lymphocytes that play an essential role in fine-tuning immune responses and maintaining immune homeostasis. Recent studies have suggested that Bregs are important players in cutaneous immunity. This review summarizes the current understanding of the role of Bregs in skin immunity in health and pathology, such as diabetes, psoriasis, systemic sclerosis, cutaneous lupus erythematosus, cutaneous hypersensitivity, pemphigus, and dermatomyositis. We discuss the mechanisms by which Bregs maintain tissue homeostasis in the wound microenvironment through the promotion of angiogenesis, suppression of effector cells, and induction of regulatory immune cells. We also mention the potential clinical applications of Bregs in promoting wound healing, such as the use of adoptive Breg transfer.

Tissue-resident B cells orchestrate macrophage polarisation and function

B cells play a central role in humoral immunity but also have antibody-independent functions. Studies to date have focused on B cells in blood and secondary lymphoid organs but whether B cells reside in non-lymphoid organs (NLO) in homeostasis is unknown. Here we identify, using intravenous labeling and parabiosis, a bona-fide tissue-resident B cell population in lung, liver, kidney and urinary bladder, a substantial proportion of which are B-1a cells. Tissue-resident B cells are present in neonatal tissues and also in germ-free mice NLOs, albeit in lower numbers than in specific pathogen-free mice and following co-housing with 'pet-store' mice. They spatially co-localise with macrophages and regulate their polarization and function, promoting an anti-inflammatory phenotype, in-part via interleukin-10 production, with effects on bacterial clearance during urinary tract infection. Thus, our data reveal a critical role for tissue-resident B cells in determining the homeostatic 'inflammatory set-point' of myeloid cells, with important consequences for tissue immunity.

Noncanonical B Cells: Characteristics of Uncharacteristic B Cells

B lymphocytes were originally described as a cell type uniquely capable of secreting Abs. The importance of T cell help in Ab production was revealed soon afterward. Following these seminal findings, investigators made great strides in delineating steps in the conventional pathway that B cells follow to produce high-affinity Abs. These studies revealed generalized, or canonical, features of B cells that include their developmental origin and paths to maturation, activation, and differentiation into Ab-producing and memory cells. However, along the way, examples of nonconventional B cell populations with unique origins, age-dependent development, tissue localization, and effector functions have been revealed. In this brief review, features of B-1a, B-1b, marginal zone, regulatory, killer, NK-like, age-associated, and atypical B cells are discussed. Emerging work on these noncanonical B cells and functions, along with the study of their significance for human health and disease, represents an exciting frontier in B cell biology.

The yin and yang of B cells in a constant state of battle: intestinal inflammation and inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the gastrointestinal tract, defined by a clinical relapse-remitting course. Affecting people worldwide, the origin of IBD is still undefined, arising as a consequence of the interaction between genes, environment, and microbiota. Although the root cause is difficult to identify, data clearly indicate that dysbiosis and pathogenic microbial taxa are connected with the establishment and clinical course of IBD. The composition of the microbiota is shaped by plasma cell IgA secretion and binding, while cytokines such as IL10 or IFN-γ are important fine-tuners of the immune response in the gastrointestinal environment. B cells may also influence the course of inflammation by promoting either an anti-inflammatory or a pro-inflammatory milieu. Here, we discuss IgA-producing B regulatory cells as an anti-inflammatory factor in intestinal inflammation. Moreover, we specify the context of IgA and IgG as players that can potentially participate in mucosal inflammation. Finally, we discuss the role of B cells in mouse infection models where IL10, IgA, or IgG contribute to the outcome of the infection.

Dual Role of B Cells in Multiple Sclerosis

B cells have emerged as an important immune cell type that can be targeted for therapy in multiple sclerosis (MS). Depleting B cells with anti-CD20 antibodies is effective in treating MS. Yet, atacicept treatment, which blocks B-cell Activating Factor (BAFF) and A Proliferation-Inducing Ligand (APRIL), two cytokines important for B cell development and function, paradoxically increases disease activity in MS patients. The reason behind the failure of atacicept is not well understood. The stark differences in clinical outcomes with these therapies demonstrate that B cells have both inflammatory and anti-inflammatory functions in MS. In this review, we summarize the importance of B cells in MS and discuss the different B cell subsets that perform inflammatory and anti-inflammatory functions and how therapies modulate B cell functions in MS patients. Additionally, we discuss the potential anti-inflammatory functions of BAFF and APRIL on MS disease.

JMJD family proteins in cancer and inflammation

The occurrence of cancer entails a series of genetic mutations that favor uncontrollable tumor growth. It is believed that various factors collectively contribute to cancer, and there is no one single explanation for tumorigenesis. Epigenetic changes such as the dysregulation of enzymes modifying DNA or histones are actively involved in oncogenesis and inflammatory response. The methylation of lysine residues on histone proteins represents a class of post-translational modifications. The human Jumonji C domain-containing (JMJD) protein family consists of more than 30 members. The JMJD proteins have long been identified with histone lysine demethylases (KDM) and histone arginine demethylases activities and thus could function as epigenetic modulators in physiological processes and diseases. Importantly, growing evidence has demonstrated the aberrant expression of JMJD proteins in cancer and inflammatory diseases, which might serve as an underlying mechanism for the initiation and progression of such diseases. Here, we discuss the role of key JMJD proteins in cancer and inflammation, including the intensively studied histone lysine demethylases, as well as the understudied group of JMJD members. In particular, we focused on epigenetic changes induced by each JMJD member and summarized recent research progress evaluating their therapeutic potential for the treatment of cancer and inflammatory 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.

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.

The effect of inulin-type fructans on the intestinal immune function of antibiotic-treated mice

This study aimed to evaluate the effect of supplementation with inulin-type fructans (ITFs) on the intestinal immune function in the context of dysbiosis resulting from antibiotic cocktail (ABx) treatment. BALB/c mice (8-9 weeks of age) were treated with an ABx for 3 weeks and then allowed to recover spontaneously or with ITF supplementation (5%) for 4 weeks. Our results showed that ABx treatment can induce gut microbiota dysbiosis and intestinal inflammation in mice. After 4 weeks of recovery, ITF supplementation restored the composition of the intestinal microbial community. However, compared with spontaneous recovery, ITF supplementation delayed inflammation recovery in the intestine and upregulated diamine oxidase (DAO) activity and increased lipopolysaccharide (LPS) content in serum. In addition, ITF supplementation delayed the regulatory T (Treg) cell and B cell recovery in the lamina propria (LP). Furthermore, compared with spontaneous recovery, ITF supplementation inhibited the relative expression of certain proinflammatory genes, such as for inducible nitric oxide synthase (iNOS) and tumour necrosis factor α (Tnf-α), in the colon, but it reduced the secretion of the anti-inflammatory mediator transforming growth factor β1 (TGF-β1) in serum, reduced the secretion of secretory immunoglobulin A (SIgA) in the colon and promoted the secretion of the proinflammatory cytokine interleukin (IL)-17A. In conclusion, these data supported the hypothesis that the influence of ITFs on the host's intestinal status is not always beneficial in the context of ABx-induced biological disorder. However, the significance of these findings needs to be determined by advanced studies KEY POINTS: • ITFs did not promote the recovery of microbial community composition. • ITFs delayed the recovery of ABx-induced colonic inflammation. • ITFs reduced the secretion of TGF-β1 and SIgA. • ITFs delayed the recovery of Treg and B cells in the LP.

Intraperitoneally Delivered Mesenchymal Stem Cells Alleviate Experimental Colitis Through THBS1-Mediated Induction of IL-10-Competent Regulatory B Cells

Mesenchymal stem cells (MSCs) show promising therapeutic potential in treating inflammatory bowel disease (IBD), and intraperitoneal delivery of MSCs have become a more effective route for IBD treatment. However, the underlying mechanisms are still poorly understood. Here, we found that intraperitoneally delivered MSCs significantly alleviated experimental colitis. Depletion of peritoneal B cells, but not macrophages, clearly impaired the therapeutic effects of MSCs. Intraperitoneally delivered MSCs improved IBD likely by boosting the IL-10-producing B cells in the peritoneal cavity, and a single intraperitoneal injection of MSCs could significantly prevent disease severity in a recurrent mouse colitis model, with lower proinflammation cytokines and high level of IL-10. The gene expression profile revealed that thrombospondin-1 (THBS1) was dramatically upregulated in MSCs after coculture with peritoneal lavage fluid from colitis mice. Knockout of THBS1 expression in MSCs abolished their therapeutic effects in colitis and the induction of IL-10-producing B cells. Mechanistically, THBS1 modulates the activation of transforming growth factor-β (TGF-β), which combines with TGF-β receptors on B cells and contributes to IL-10 production. Blocking the interaction between THBS1 and latent TGF-β or inhibiting TGF-β receptors (TGF-βR) significantly reversed the THBS1-mediated induction of IL-10-producing B cells and the therapeutic effects on colitis. Collectively, our study revealed that intraperitoneally delivered MSCs secreted THBS1 to boost IL-10⁺Bregs and control the progression and recurrence of colitis, providing new insight for the prevention and treatment of IBD.

B- and Plasma Cell Subsets in Autoimmune Diseases: Translational Perspectives

B lymphocytes play a central role in immunity owing to their unique antibody-producing capacity that provides protection against certain infections and during vaccination. In autoimmune diseases, B cells can gain pathogenic relevance through autoantibody production, antigen presentation, and proinflammatory cytokine secretion. Recent data indicate that B and plasma cells can function as regulators through the production of immunoregulatory cytokines and/or employing checkpoint molecules. In this study, we review the key findings that define subsets of B and plasma cells with pathogenic and protective functions in autoimmunity. In addition to harsh B-cell depletion, we discuss the strategies that have the potential to reinstall the balance of pathogenic and protective B cells with the potential of more specific and personalized therapies.

Indoleamine 2, 3-Dioxygenase Promotes Aryl Hydrocarbon Receptor-Dependent Differentiation Of Regulatory B Cells in Lung Cancer

Regulatory B cells (Breg) are IL-10 producing subsets of B cells that contribute to immunosuppression in the tumor microenvironment (TME). Breg are elevated in patients with lung cancer; however, the mechanisms underlying Breg development and their function in lung cancer have not been adequately elucidated. Herein, we report a novel role for Indoleamine 2, 3- dioxygenase (IDO), a metabolic enzyme that degrades tryptophan (Trp) and the Trp metabolite L-kynurenine (L-Kyn) in the regulation of Breg differentiation in the lung TME. Using a syngeneic mouse model of lung cancer, we report that Breg frequencies significantly increased during tumor progression in the lung TME and secondary lymphoid organs, while Breg were reduced in tumor-bearing IDO deficient mice (IDO^-/-). Trp metabolite L-Kyn promoted Breg differentiation in-vitro in an aryl hydrocarbon receptor (AhR), toll-like receptor-4-myeloid differentiation primary response 88, (TLR4-MyD88) dependent manner. Importantly, using mouse models with conditional deletion of IDO in myeloid-lineage cells, we identified a significant role for immunosuppressive myeloid-derived suppressor cell (MDSC)-associated IDO in modulating in-vivo and ex-vivo differentiation of Breg. Our studies thus identify Trp metabolism as a therapeutic target to modulate regulatory B cell function during lung cancer progression.

Characterization of Organ-Specific Regulatory B Cells Using Single-Cell RNA Sequencing

Regulatory B cells (Breg) are considered as immunosuppressive cells. Different subsets of Breg cells have been identified both in human beings and in mice. However, there is a lack of unique markers to identify Breg cells, and the heterogeneity of Breg cells in different organs needs to be further illuminated. In this study, we performed high-throughput single-cell RNA sequencing (scRNA-seq) and single-cell B-cell receptor sequencing (scBCR-seq) of B cells from the murine spleen, liver, mesenteric lymph nodes, bone marrow, and peritoneal cavity to better define the phenotype of these cells. Breg cells were identified based on the expression of immunosuppressive genes and IL-10-producing B (B10) cell-related genes, to define B10 and non-B10 subsets in Breg cells based on the score of the B10 gene signatures. Moreover, we characterized 19 common genes significantly expressed in Breg cells, including Fcrl5, Zbtb20, Ccdc28b, Cd9, and Ptpn22, and further analyzed the transcription factor activity in defined Breg cells. Last, a BCR analysis was used to determine the clonally expanded clusters and the relationship of Breg cells across different organs. We demonstrated that Atf3 may potentially modulate the function of Breg cells as a transcription factor and that seven organ-specific subsets of Breg cells are found. Depending on gene expression and functional modules, non-B10 Breg cells exhibited activated the TGF-β pathway, thus suggesting that non-B10 Breg cells have specific immunosuppressive properties different from conventional B10 cells. In conclusion, our work provides new insights into Breg cells and illustrates their transcriptional profiles and BCR repertoire in different organs under physiological conditions.

Immunoregulation by antibody secreting cells in inflammation, infection, and cancer

Antibody-secreting cells (ASCs) are considered work horses of the humoral immune response for their tireless effort to produce large amounts of antibodies that fulfill an array of functions in host defense, inflammation, and maintenance of homeostasis. While traditionally considered largely senescent cells, surprising recent findings demonstrate that subsets of ASCs downmodulate ongoing immune responses independent of antibody formation. Such regulatory ASCs produce IL-10 or IL-35 and are implicated in maintaining tissue and immune homeostasis. They also serve to suppress pathogenic leukocytes in infection, allergy, and inflammatory diseases that affect tissues, such as the central nervous system and the respiratory tract. Additionally, regulatory ASCs infiltrate various cancer types and restrict effective anti-tumor T cell responses. While incompletely understood, there is significant overlap in factors that control ASC differentiation, IL-10 expression by B cells and the generation of ASCs that secrete both antibodies and IL-10. In this review, we will cover the biology, phenotype, generation, maintenance and function of regulatory ASCs in various tissues under pathological and steady states. An improved understanding of the development of regulatory ASCs and their biological roles will be critical for generating novel ASC-targeted therapies for the treatment of inflammatory diseases, infection, and cancer.

Regulatory B cells improve ventricular remodeling after myocardial infarction by modulating monocyte migration

Overactivated inflammatory responses contribute to adverse ventricular remodeling after myocardial infarction (MI). Regulatory B cells (Bregs) are a newly discovered subset of B cells with immunomodulatory roles in many immune and inflammation-related diseases. Our study aims to determine whether the expansion of Bregs exerts a beneficial effect on ventricular remodeling and explore the mechanisms involved. Here, we showed that adoptive transfer of Bregs ameliorated ventricular remodeling in a murine MI model, as demonstrated by improved cardiac function, decreased scar size and attenuated interstitial fibrosis without changing the survival rate. Reduced Ly6C^hi monocyte infiltration was found in the hearts of the Breg-transferred mice, while the infiltration of Ly6C^lo monocytes was not affected. In addition, the replenishment of Bregs had no effect on the myocardial accumulation of T cells or neutrophils. Mechanistically, Bregs reduced the expression of C-C motif chemokine receptor 2 (CCR2) in monocytes, which inhibited proinflammatory monocyte recruitment to the heart from the peripheral blood and mobilization from the bone marrow. Breg-mediated protection against MI was abrogated by treatment with an interleukin 10 (IL-10) antibody. Finally, IL-10 neutralization reversed the effect of Bregs on monocyte migration and CCR2 expression. The present study suggests a therapeutic value of Bregs in limiting ventricular remodeling after MI through decreasing CCR2-mediated monocyte recruitment and mobilization.

Effects of short-chain fatty acids in inhibiting HDAC and activating p38 MAPK are critical for promoting B10 cell generation and function

B10 cells are regulatory B cells capable of producing IL-10 for maintaining immune homeostasis. Dysregulation of B10 cells occurs in autoimmune and inflammatory diseases. Modulation or adoptive transfer of B10 cells is a promising therapeutic strategy. The short-chain fatty acids (SCFAs), the metabolites of microbiota, play a critical role in maintaining immune homeostasis and are the potential drugs for the modulation of B10 cells. It is not clear whether and how SCFAs upregulate the frequency of B10 cells. Here, we found that SCFAs could promote murine and human B10 cell generation in vitro. Upregulation of B10 cells by butyrate or pentanoate was also observed in either healthy mice, mice with dextran sodium sulfate (DSS)-induced colitis, or mice with collagen-induced arthritis. Moreover, SCFA treatment could ameliorate clinical scores of colitis and arthritis. Adoptive transfer of B cells pretreated with butyrate showed more alleviation of DSS-induced colitis than those without butyrate. A further study demonstrates that SCFAs upregulate B10 cells in a manner dependent on their histone deacetylase (HDAC) inhibitory activity and independent of the G-protein-coupled receptor pathway. Transcriptomic analysis indicated that the MAPK signaling pathway was enriched in B10 cells treated with butyrate. A study with inhibitors of ERK, JNK, and p38 MAPK demonstrated that activating p38 MAPK by butyrate is critical for the upregulation of B10 cells. Moreover, HDAC inhibitor has similar effects on B10 cells. Our study sheds light on the mechanism underlying B10 cell differentiation and function and provides a potential therapeutic strategy with SCFAs and HDAC inhibitors for inflammation and autoimmune diseases.

The Role of Regulatory B cells in Kidney Diseases

B cells, commonly regarded as proinflammatory antibody-producing cells, are detrimental to individuals with autoimmune diseases. However, in recent years, several studies have shown that regulatory B (Breg) cells, an immunosuppressive subset of B cells, may exert protective effects against autoimmune diseases by secretion of inhibitory cytokines such as IL-10. In practice, Breg cells are identified by their production of immune-regulatory cytokines, such as IL-10, TGF-β, and IL-35, however, no specific marker or Breg cell-specific transcription factor has been identified. Multiple phenotypes of Breg cells have been found, whose functions vary according to their phenotype. This review summarizes the discovery, phenotypes, development, and function of Breg cells and highlights their potential therapeutic value in kidney 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.

The identification, development and therapeutic potential of IL-10-producing regulatory B cells in multiple sclerosis

Regulatory B cells are a rare B-cell subset widely known to exert their immunosuppressive function via the production of interleukin-10 (IL-10) and other mechanisms. B10 cells are a special subset of regulatory B cells with immunoregulatory function that is fully attributed to IL-10. Their unique roles in the animal model of multiple sclerosis (MS) have been described, as well as their relevance in MS patients. This review specifically focuses on the identification and development of B10 cells, the signals that promote IL-10 production in B cells, the roles of B10 cells in MS, and the potential and major challenges of the application of B10-based therapies for MS.

B regulatory cells in allergy

B cells have classically been recognized for their unique and indispensable role in the production of antibodies. Their potential as immunoregulatory cells with anti-inflammatory functions has received increasing attention during the last two decades. Herein, we highlight pioneering studies in the field of regulatory B cell (Breg) research. We will review the literature on Bregs with a particular focus on their role in the regulation of allergic inflammation.

Construction of a nitro-oxidative stress-driven, mechanistic model of mood disorders: A nomothetic network approach

Major depression is accompanied by increased IgM-mediated autoimmune responses to oxidative specific epitopes (OSEs) and nitric oxide (NO)-adducts. These responses were not examined in bipolar disorder type 1 (BP1) and BP2. IgM responses to malondialdehyde (MDA), phosphatidinylinositol, oleic acid, azelaic acid, and NO-adducts were determined in 35 healthy controls, and 47 major depressed (MDD), 29 BP1, and 25 BP2 patients. We also measured serum peroxides, IgG to oxidized LDL (oxLDL), and IgM/IgA directed to lipopolysaccharides (LPS). IgM responses to OSEs and NO-adducts (OSENO) were significantly higher in MDD and BP1 as compared with controls, and IgM to OSEs higher in MDD than in BP2. Partial Least Squares (PLS) analysis showed that 57.7% of the variance in the clinical phenome of mood disorders was explained by number of episodes, a latent vector extracted from IgM to OSENO, IgG to oxLDL, and peroxides. There were significant specific indirect effects of IgA/IgM to LPS on the clinical phenome, which were mediated by peroxides, IgM OSENO, and IgG oxLDL. Using PLS we have constructed a data-driven nomothetic network which ensembled causome (increased plasma LPS load), adverse outcome pathways (namely neuro-affective toxicity), and clinical phenome features of mood disorders in a data-driven model. Based on those feature sets, cluster analysis discovered a new diagnostic class characterized by increased plasma LPS load, peroxides, autoimmune responses to OSENO, and increased phenome scores. Using the new nomothetic network approach, we constructed a mechanistically transdiagnostic diagnostic class indicating neuro-affective toxicity in 74.3% of the mood disorder patients.

Therapeutic Potential of B-1a Cells in COVID-19

Coronavirus disease 2019 (COVID-19) is a life-threatening respiratory illness caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Its clinical presentation can vary from the asymptomatic state to acute respiratory distress syndrome (ARDS) and multi-organ dysfunction. Due to our insufficient understanding of its pathophysiology and lack of effective treatment, the morbidity and mortality of severe COVID-19 patients are high. Patients with COVID-19 develop ARDS fueled by exaggerated neutrophil influx into the lungs and cytokine storm. B-1a cells represent a unique subpopulation of B lymphocytes critical for circulating natural antibodies, innate immunity, and immunoregulation. These cells spontaneously produce natural IgM, interleukin (IL)-10, and granulocyte-monocyte colony stimulating factor (GM-CSF). Natural IgM neutralizes viruses and opsonizes bacteria, IL-10 attenuates the cytokine storm, and GM-CSF induces IgM production by B-1a cells in an autocrine manner. Indeed, B-1a cells have been shown to ameliorate influenza virus infection, sepsis, and pneumonia, all of which are similar to COVID-19. The recent discovery of B-1a cells in humans further reinforces their potentially critical role in the immune response against SARS-CoV-2 and their anticipated translational applications against viral and microbial infections. Given that B-1a cells protect against ARDS via immunoglobulin production and the anti-COVID-19 effects of convalescent plasma treatment, we recommend that studies be conducted to further examine the role of B-1a cells in the pathogenesis of COVID-19 and explore their therapeutic potential to treat COVID-19 patients.

Regulation of neuroinflammation by B cells and plasma cells

The remarkable success of anti-CD20 B cell depletion therapies in reducing the burden of multiple sclerosis (MS) disease has prompted significant interest in how B cells contribute to neuroinflammation. Most focus has been on identifying pathogenic CD20⁺ B cells. However, an increasing number of studies have also identified regulatory functions of B lineage cells, particularly the production of IL-10, as being associated with disease remission in anti-CD20-treated MS patients. Moreover, IL-10-producing B cells have been linked to the attenuation of inflammation in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. In addition to IL-10-producing B cells, antibody-producing plasma cells (PCs) have also been implicated in suppressing neuroinflammation. This review will examine regulatory roles for B cells and PCs in MS and EAE. In addition, we speculate on the involvement of regulatory PCs and the cytokine BAFF in the context of anti-CD20 treatment. Lastly, we explore how the microbiota could influence anti-inflammatory B cell behavior. A better understanding of the contributions of different B cell subsets to the regulation of neuroinflammation, and factors that impact the development, maintenance, and migration of such subsets, will be important for rationalizing next-generation B cell-directed therapies for the treatment of MS.

A TLR4-TRIF-dependent signaling pathway is required for protective natural tumor-reactive IgM production by B1 cells

Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Our previous studies demonstrated a toll-like receptor 4 (TLR4) and C-type lectin receptor (CLR; Mincle/MCL) agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6'-dicorynomycolate (TDCM) effectively inhibits peritoneal tumor growth and ascites development through a mechanism dependent upon B1a cell-produced natural IgM, complement, and phagocytes. In the current study, we investigated the requirement for TLR4 and Fc receptor common γ chain (FcRγ), required for Mincle/MCL signaling, in the MPL/TDCM-elicited response. MPL/TDCM significantly increased macrophages and Ly6Chi monocytes in the peritoneal cavity of both TLR4-/- and FcRγ-/- mice, suggesting redundancy in the signals required for monocyte/macrophage recruitment. However, B1 cell activation, antibody secreting cell differentiation, and tumor-reactive IgM production were defective in TLR4-/-, but not FcRγ-/- mice. TRIF was required for production of IgM reactive against tumor- and mucin-related antigens, but not phosphorylcholine, whereas TLR4 was required for production of both types of reactivities. Consistent with this, B1 cells lacking TLR4 or TRIF did not proliferate or differentiate into tumor-reactive IgM-producing cells in vitro and did not reconstitute MPL/TDCM-dependent protection against peritoneal carcinomatosis in CD19-/- mice. Our results indicate a TLR4/TRIF-dependent pathway is required by B1 cells for MPL/TDCM-elicited production of protective tumor-reactive natural IgM. The dependency on TRIF signaling for tumor-reactive, but not phosphorylcholine-reactive, IgM production reveals unexpected heterogeneity in TLR4-dependent regulation of natural IgM production, thereby highlighting important differences to consider when designing vaccines or therapies targeting these specificities.

Plasma Cells: From Cytokine Production to Regulation in Experimental Autoimmune Encephalomyelitis

B cells are a critical arm of the adaptive immune system. After encounter with antigen, B cells are activated and differentiate into plasmablasts (PBs) and plasma cells (PCs). Although their frequency is low, PB/PCs can be found in all lymphoid organs including peripheral lymph nodes and spleen. Upon immunization, depending on the location of where B cells encounter their antigen, PB/PCs subsequently home to and accumuate in the bone marrow and the intestine where they can survive as long-lived plasma cells for years, continually producing antibody. Recent evidence has shown that, in addition to producing antibodies, PB/PCs can also produce cytokines such as IL-17, IL-10, and IL-35. In addition, PB/PCs that produce IL-10 have been shown to play a regulatory role during experimental autoimmune encephalomyelitis, an animal model of neuroinflammation. The purpose of this review is to describe the phenotype and function of regulatory PB/PCs in the context of experimental autoimmune encephalomyelitis and in patients with multiple sclerosis.

Specialized immune responses in the peritoneal cavity and omentum

The peritoneal cavity is a fluid filled space that holds most of the abdominal organs, including the omentum, a visceral adipose tissue that contains milky spots or clusters of leukocytes that are organized similar to those in conventional lymphoid tissues. A unique assortment of leukocytes patrol the peritoneal cavity and migrate in and out of the milky spots, where they encounter Ags or pathogens from the peritoneal fluid and respond accordingly. The principal role of leukocytes in the peritoneal cavity is to preserve tissue homeostasis and secure tissue repair. However, when peritoneal homeostasis is disturbed by inflammation, infection, obesity, or tumor metastasis, specialized fibroblastic stromal cells and mesothelial cells in the omentum regulate the recruitment of peritoneal leukocytes and steer their activation in unique ways. In this review, the types of cells that reside in the peritoneal cavity, the role of the omentum in their maintenance and activation, and how these processes function in response to pathogens and malignancy will be discussed.

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.

Role of regulatory B cells in autoimmune diseases of the digestive system

Recently, regulatory B cells (Breg), a subset of functional B cells, have been reported to participate in the negative regulation of immunity in autoimmune diseases by producing interleukin (IL)-10, IL-35, and transforming growth factor-β. However, a specific surface marker for Breg has not been identified and their potential therapeutic role requires further study. This review discusses the function of Breg in autoimmune diseases of the digestive system, with the purpose of highlighting their regulation of immune responses and their potential as a therapeutic target for the treatment of these diseases.

Rejection of xenogeneic porcine islets in humanized mice is characterized by graft-infiltrating Th17 cells and activated B cells

Xenogeneic porcine islet transplantation is a promising potential therapy for type 1 diabetes (T1D). Understanding human immune responses against porcine islets is crucial for the design of optimal immunomodulatory regimens for effective control of xenogeneic rejection of porcine islets in humans. Humanized mice are a valuable tool for studying human immune responses and therefore present an attractive alternative to human subject research. Here, by using a pig-to-humanized mouse model of xenogeneic islet transplantation, we described the human immune response to transplanted porcine islets, a process characterized by dense islet xenograft infiltration of human CD45⁺ cells comprising activated human B cells, CD4⁺ CD44⁺ IL-17⁺ Th17 cells, and CD68⁺ macrophages. In addition, we tested an experimental immunomodulatory regimen in promoting long-term islet xenograft survival, a triple therapy consisting of donor splenocytes treated with ethylcarbodiimide (ECDI-SP), and peri-transplant rituximab and rapamycin. We observed that the triple therapy effectively inhibited graft infiltration of T and B cells as well as macrophages, promoted transitional B cells both in the periphery and in the islet xenografts, and provided a superior islet xenograft protection. Our study therefore indicates an advantage of donor ECDI-SP treatment in controlling human immune cells in promoting long-term islet xenograft survival.

Regulatory B cells in infection, inflammation, and autoimmunity

Regulatory B (Breg) cells are characterized by differential expression of CD5 and CD1d in mouse and CD24 and CD38 in human immune systems. The Breg family also includes LAG-3⁺CD138^hi plasma cells, CD1d CD5 CD21 CD23 cells, Tim1, PD-L1, PD-L2, CD200- expressing B cells, and CD39^hiKi67⁺ cells originating from the transitional, marginal zone or germinal centre of the spleen. Breg cells produce IL10 and IL35 and to cause immunosuppression. These cells respond to TLR2, TLR4, and TLR9 agonists, CD40 ligands, IL12p35 and heat shock proteins. Emerging evidence suggests that TLR signalling component Myd88 impacts the modulation of Breg cell responses and the host's susceptibility to infection. Breg cells are found to reduce relapsing-remitting experimental autoimmune encephalomyelitis. However, the Breg-mediated mechanism used to control T cell-mediated immune responses is still unclear. Here, we review the existing literature to find gaps in the current knowledge and to build a pathway to further research.

Isolation of functional mature peritoneal macrophages from healthy humans

Macrophages play an important role in the inflammatory response. Their various biological functions are induced by different membrane receptors, including Toll-like receptors, which trigger several intracellular signaling cascades and activate the inflammasomes, which in turn elicit the release of inflammatory mediators such as cytokines. In this study, we present a novel method for the isolation of human mature peritoneal macrophages. This method can be easily implemented by gynecologists who routinely perform laparoscopy for sterilization by tubal ligation or surgically intervene in benign gynecological pathologies. Our method confirms that macrophages are the main peritoneal leukocyte subpopulation isolated from the human peritoneum in homeostasis. We showed that primary human peritoneal macrophages present phagocytic and oxidative activities, and respond to activation of the main proinflammatory pathways such as Toll-like receptors and inflammasomes, resulting in the secretion of different proinflammatory cytokines. Therefore, this method provides a useful tool for characterizing primary human macrophages as control cells for studies of molecular inflammatory pathways in steady-state conditions and for comparing them with those obtained from pathologies involving the peritoneal cavity. Furthermore, it will facilitate advances in the screening of anti-inflammatory compounds in the human system.

Skin-Associated B Cells in Health and Inflammation

Traditionally, the skin was believed to be devoid of B cells, and studies of the skin immune system have largely focused on other types of leukocytes. Exciting recent data show that B cells localize to the healthy skin of humans and other mammalian species with likely homeostatic functions in host defense, regulation of microbial communities, and wound healing. Distinct skin-associated B cell subsets drive or suppress cutaneous inflammatory responses with important clinical implications. Localized functions of skin-associated B cell subsets during inflammation comprise Ab production, interactions with skin T cells, tertiary lymphoid tissue formation, and production of proinflammatory cytokines but also include immunosuppression by providing IL-10. In this review, we delve into the intriguing new roles of skin-associated B cells in homeostasis and inflammation.

The role of B regulatory (B10) cells in inflammatory disorders and their potential as therapeutic targets

Over the past decade, studies have identified subset of B cells, which play suppressive functions in additions to the conventional functions of B cells: antigen processing and presentation, activation of T cells and antibody productions. Because of their regulatory function, they were named as B regulatory cells (Bregs). Bregs restrict the severity of autoimmune disorders in animal disease models such as experimental autoimmune myocarditis (EAM), experimental autoimmune encephalitis (EAE), and collagen-induced arthritis (CIA) but can contribute to the development of infection and cancer. In humans, the roles of B regulatory cells in autoimmune diseases have not been clearly established because of the inconsistent findings from many researchers. This is believed to arise from the speculated fact that Bregs lack specific marker, which can be used to identify and characterize them in human diseases. The CD19⁺CD24^hiCD38^hiCD1d^hiB cells have been associated with the regulatory function. Available evidences highlight the relevance of increasing IL-10-producing B cells in autoimmune diseases and the possibility of serving as new therapeutic targets in inflammatory disorders. This review empanels the functions of Bregs in autoimmune diseases in both human and animal models, and further evaluates the possibility of Bregs as therapeutic targets in inflammatory disorders. Consequently, this might help identify possible research gaps, which need to be clarified as researchers speculate the possibility of targeting some subsets of Bregs in the treatment of inflammatory disorders.

Role of environmental factors in the pathogenesis of Crohn's disease: a critical review

PURPOSE

To review role of environmental factors in the pathogenesis of Crohn's disease.

METHODS

We systematically reviewed trials and systematic reviews using PubMed and Web of science databases. Here, we review the current information on the causative factors and mechanisms of CD, including smoking, exercise, diet, animal protein, breastfeeding, history of childhood infection and vaccination, oral contraceptives, and antibiotics of CD. We also highlight important knowledge gaps that need to be filled in order to advance the field of CD research.

RESULTS

Epidemiological studies have indicated the significance of environmental factors in the disease behavior and outcome of Crohn's disease (CD). There are a few recognized environmental factors, such as cigarette smoking, exercise, dietary habits, and breastfeeding, which are associated with the pathogenesis of CD. These factors are hypothesized to change the epithelial barrier function, which disturbs both the innate and adaptive immune systems and the intestinal flora. However, the effect of several risk factors, such as appendectomy and pharmaceutical use, differs across several studies, indicating the need for more rigorous research. Furthermore, few studies have examined effective interventions based on environmental factors that can improve disease outcomes. Recent studies have indicated that the pathogenesis of CD is related to environmental and genetic factors.

CONCLUSION

We review the current information on the causative factors and mechanisms of CD, including smoking, exercise, diet, animal protein, breastfeeding, history of childhood infection and vaccination, oral contraceptives, and antibiotics of CD. However, further studies are needed to understand knowledge gaps in the field of CD.

Mannose-capped lipoarabinomannan-induced B10 cells decrease severity of dextran sodium sulphate-induced inflammatory bowel disease in mice

Inflammatory bowel disease (IBD) is a chronic, non‐specific, inflammatory gastrointestinal disease that mainly consists of Crohn's disease and ulcerative colitis. However, the aetiology and pathogenesis of IBD are still unclear. B10 (IL‐10 producing regulatory B) cells, a subset of regulatory B cells, are known to contribute to intestinal homeostasis and the aberrant frequency of B10 cells is associated with IBD. We have recently reported that B10 cells can be induced by ManLAM (mannose‐capped lipoarabinomannan), a major cell‐wall lipoglycan of M tb (Mycobacterium tuberculosis). In the current study, the ManLAM‐induced B10 cells were adoptively transferred into IL(interleukin)‐10^−/− mice and the roles of ManLAM‐induced B10 cells were investigated in DSS (dextran sodium sulphate)‐induced IBD model. ManLAM‐induced B10 cells decrease colitis severity in the mice. The B10 cells downregulate Th1 polarization in spleen and MLNs (mesenteric lymph nodes) of DSS‐treated mice. These results suggest that IL‐10 production by ManLAM‐treated B cells contributes to keeping the balance between CD4⁺ T cell subsets and protect mice from DSS‐induced IBD.

Gut Antibody Deficiency in a Mouse Model of CVID Results in Spontaneous Development of a Gluten-Sensitive Enteropathy

Primary immunodeficiencies are heritable disorders of immune function. CD19 is a B cell co-receptor important for B cell development, and CD19 deficiency is a known genetic risk factor for a rare form of primary immunodeficiency known as “common variable immunodeficiency” (CVID); an antibody deficiency resulting in low levels of serum IgG and IgA. Enteropathies are commonly observed in CVID patients but the underlying reason for this is undefined. Here, we utilize CD19^−/− mice as a model of CVID to test the hypothesis that antibody deficiency negatively impacts gut physiology under steady-state conditions. As anticipated, immune phenotyping experiments demonstrate that CD19^−/− mice develop a severe B cell deficiency in gut-associated lymphoid tissues that result in significant reductions to antibody concentrations in the gut lumen. Antibody deficiency was associated with defective anti-commensal IgA responses and the outgrowth of anaerobic bacteria in the gut. Expansion of anaerobic bacteria coincides with the development of a chronic inflammatory condition in the gut of CD19^−/− mice that results in an intestinal malabsorption characterized by defects in lipid metabolism and transport. Administration of the antibiotic metronidazole to target anaerobic members of the microbiota rescues mice from disease indicating that intestinal malabsorption is a microbiota-dependent phenomenon. Finally, intestinal malabsorption in CD19^−/− mice is a gluten-sensitive enteropathy as exposure to a gluten-free diet also significantly reduces disease severity in CD19^−/− mice. Collectively, these results support an effect of antibody deficiency on steady-state gut physiology that compliment emerging data from human studies linking IgA deficiency with non-infectious complications associated with CVID. They also demonstrate that CD19^−/− mice are a useful model for studying the role of B cell deficiency and gut dysbiosis on gluten-sensitive enteropathies; a rapidly emerging group of diseases in humans with an unknown etiology.

Regulatory functions of B cells and regulatory plasma cells

B cells critically contribute to health through the production of antibodies that provide a vital line of defence against infectious agents. In addition, B cells are known to play an integrative role in immunity, acting as crucial antigen-presenting cells for T cells, and being an important source of cytokines that can target multiple cell types including stromal cells, innate cells, and adaptive lymphocytes. This review focuses on the role of B cells as negative regulators of immunity through the production of interleukin-10 (IL-10) in autoimmune, infectious, and malignant diseases. It discusses the phenotypes of the B cell subsets most competent to produce IL-10 in vitro and to exert suppressive functions in vivo upon adoptive transfer in recipient mice, the signals and transcription factors regulating IL-10 expression in B cells, and the recent identification of plasmocytes, including short-lived plasmablasts and long-lived plasma cells, as an important source of IL-10 in secondary lymphoid organs and inflamed tissues in vivo during mouse and human diseases. With our increasing knowledge of this non-canonical B cell function a coherent framework starts emerging that will help monitoring and targeting this B cell function in health and disease.

Abnormal numbers of CD4+ T lymphocytes and abnormal expression of CD4+ T lymphocyte‑secreted cytokines in patients with immune‑related haemocytopenia

In the past decade, a group of cases with persisting haemocytopenia were separated from those with idiopathic cytopenia of undetermined significance due to the optimal response of these patients to immunosuppression therapy and due to the detection of autoantibodies in the bone marrow of haemopoietic cells. This condition was termed immune-related haemocytopenia (IRH). However, the quantity of T lymphocytes remained unknown. In the present study, the percentage of CD4⁺ T-cell subsets and related cytokines was measured using flow cytometry and an enzyme-linked immunosorbent assay. An abnormal number of CD4⁺ T cell subsets was found, including increased percentages of T helper (Th)2, Th9 and Th17 cells and a decreased number of regulatory T (Treg) cells. In addition, the results showed downregulation in the levels of interleukin (IL)-2, transforming growth factor-β and IL-35, and upregulation in the levels of IL-4, IL-6, IL-17, IL-23 and interferon-γ in patients who did not receive therapy (untreated patients). These levels were significantly associated with the number of peripheral blood cells and were recovered following treatment. In conclusion, an abnormal number of CD4⁺ T cell subsets and corresponding abnormal levels of regulatory cytokines resulted in the stimulation of B1 lymphocytes to produce autoantibodies in IRH, which may be considered as markers to evaluate disease prognosis and treatment strategies.

IL-10-producing B cells attenuate cardiac inflammation by regulating Th1 and Th17 cells in acute viral myocarditis induced by coxsackie virus B3

AIMS

This work aimed to evaluate the regulatory function of IL-10-producing B cells in viral myocarditis (VMC).

MAIN METHODS

We adoptively transferred purified IL-10-producing B cells to VMC mice via the tail vein. We observed the inflammatory responses and cardiac lesions by histological analysis, examined the proportions of spleen Th1 and T17 cells by flow cytometry and expression levels of related transcription factors (T-bet and RORγt) by reverse transcription polymerase chain reaction (RT-PCR), and calculated the cardiac pathological scores and the mean survival times.

KEY FINDINGS

IL-10-producing B cells were found to be T cell-dependent in the pathogenesis of VMC. They mainly downregulated T-bet and RORγt mRNA levels to decrease the proportions of Th1 and Th17 cells, thereby restraining the inflammation and damage in the myocardium in B cell-deficient VMC mice. Adoptive transfer of IL-10-producing B cells before VMC induction also normalized the inflammatory responses and prolonged the survival time in wild-type (WT) VMC mice. While the transfer of IL-10-producing B cells on day 3 of VMC alleviated the severity of disease, it did not extend the mean survival time of VMC mice. By contrast, IL-10-producing B cells showed no effect on day 7 of VMC. In conclusion, IL-10-producing B cells downregulate the proportion of Th1 and Th17 cells to alleviate inflammatory damage in the myocardium during VMC before the induction or the early phase of disease.

SIGNIFICANCE

These findings suggest that IL-10-producing B cells may be a new therapeutic target for modulating the immune response in VMC.

IL-10 producing B cells rescue mouse fetuses from inflammation-driven fetal death and are able to modulate T cell immune responses

Understanding the mechanisms leading to fetal death following maternal subclinical infections is crucial to develop new therapeutic strategies. Here we addressed the relevance of IL-10 secreting B cells (B10) in the maintenance of the immune balance during gestation. µMT females lacking mature B cells presented normal pregnancies, although their fetuses were smaller and their Treg pool did not expand as in B cell sufficient controls. Pregnant µMT females were more susceptible to LPS despite having less Treg; their fetuses died at doses compatible with pregnancy in WT animals. Adoptive transfer of IL-10 negative B effector cells or B cells from IL-10 deficient mice did not modify this outcome. The transfer of B10 cells or application of recombinant murine IL-10 reduced the fetal loss, associated with a normalization of Treg numbers and cytokine modulation at the feto-maternal interface. B cell-derived IL-10 suppressed the production of IL-17A and IL-6 by T cells and promoted the conversion of naïve cells into Treg. B10 cells are required to restore the immune balance at the feto-maternal interface when perturbed by inflammatory signals. Our data position B cells in a central role in the maintenance of the balance between immunity and tolerance during pregnancy.

Human Mesenchymal Stem Cell-Treated Regulatory CD23+CD43+ B Cells Alleviate Intestinal Inflammation

Rationale: Mesenchymal stem cells (MSCs) have been demonstrated to ameliorate inflammatory bowel disease by their actions on multiple immune cells, especially on regulatory B cells (Breg cells). However, the phenotypes and functions of human MSCs (hMSCs)-treated Breg cell subsets are not yet clear.

Methods: Purified B cells were cocultured with MSCs and the phenotypes and immunomodulatory functions of the B cells were analyzed by FACS and proliferation assays in vitro. Also, a trinitrobenzenesulfonic acid-induced mouse colitis model was employed to detect the function of MSC-treated Breg cells in vivo.

Results: We demonstrated that coculturing with hMSCs significantly enhanced the immunomodulatory activity of B cells by up-regulating IL-10 expression. We then identified that a novel regulatory B cell population characterized by CD23 and CD43 phenotypic markers could be induced by hMSCs. The CD23⁺CD43⁺ Breg cells substantially inhibited the inflammatory cytokine secretion and proliferation of T cells through an IL-10-dependent pathway. More significantly, intraperitoneal injection of hMSCs ameliorated the clinical and histopathological severity in the mouse experimental colitis model, accompanied by an increase in the number of CD23⁺CD43⁺ Breg cells. The adoptive transfer of CD23⁺CD43⁺ B cells effectively alleviated murine colitis, as compared with the CD23^-CD43^- B cells. Treatment with CD23⁺CD43⁺ B cells, and not hMSCs, substantially improved the symptoms of colitis in B cell-depleted mice.

Conclusion: the novel CD23⁺CD43⁺ Breg cell subset appears to be involved in the immunomodulatory function of hMSCs and sheds new light on elucidating the therapeutic mechanism of hMSCs for the treatment of inflammation-related diseases.

Microbiota maintain colonic homeostasis by activating TLR2/MyD88/PI3K signaling in IL-10-producing regulatory B cells

Resident microbiota activate regulatory cells that modulate intestinal inflammation and promote and maintain intestinal homeostasis. IL-10 is a key mediator of immune regulatory function. Our studies described the functional importance and mechanisms by which gut microbiota and specific microbial components influenced the development of intestinal IL-10-producing B cells. We used fecal transplant to germ-free (GF) Il10+/EGFP reporter and Il10-/- mice to demonstrate that microbiota from specific pathogen-free mice primarily stimulated IL-10-producing colon-specific B cells and T regulatory-1 cells in ex-GF mice. IL-10 in turn down-regulated microbiota-activated mucosal inflammatory cytokines. TLR2/9 ligands and enteric bacterial lysates preferentially induced IL-10 production and regulatory capacity of intestinal B cells. Analysis of Il10+/EGFP mice crossed with additional gene-deficient strains and B cell co-transfer studies demonstrated that microbiota-induced IL-10-producing intestinal B cells ameliorated chronic T cell-mediated colitis in a TLR2, MyD88 and PI3K-dependent fashion. In vitro studies implicated PI3Kp110δ and AKT downstream signaling. These studies demonstrated that resident enteric bacteria activated intestinal IL-10-producing B cells through TLR2, MyD88 and PI3K pathways. These B cells reduced colonic T cell activation and maintained mucosal homeostasis in response to intestinal microbiota.

B1 cells protect against Schistosoma japonicum-induced liver inflammation and fibrosis by controlling monocyte infiltration

During Schistosoma infection, lack of B cells results in more severe granulomas, inflammation, and fibrosis in the liver, but the mechanisms underlying this pathology remain unclear. This study was to clarify the mechanisms underpinning the immunomodulation of B cells in mice infected with Schistosoma japonicum (S. japonicum). We found that B cell deficiency led to aggravated liver pathology, as demonstrated by increases in the size of the egg-associated granulomas, alanine transaminase levels, and collagen deposition. Compared with infected wild-type (WT) mice, infected B cell-deficient (μMT) mice showed increased infiltration of Ly6C^hi monocytes and higher levels of proinflammatory cytokines and chemokines. Furthermore, B1 cells were increased significantly in the liver of WT mice following S. japonicum infection. Adoptively transferring B1 cells, but not B2 cells, to μMT mice significantly reduced liver pathology and liver infiltration of Ly6C^hi monocytes. Additionally, secretion of IL-10 from hepatic B cells increased significantly in infected WT mice and this IL-10 was mainly derived from B1 cells. Adoptively transferring B1 cells purified from WT mice, but not from IL-10-deficient mice, to μMT mice significantly reduced liver pathology and liver infiltration of Ly6C^hi monocytes. These reductions were accompanied by decreases in the expression levels of chemokines and inflammatory cytokines. Taken together, these data indicated that after S. japonicum infection, an increased number of hepatic B1 cells secrete IL-10, which inhibits the expression of chemokines and cytokines and suppresses the infiltration of Ly6C^hi monocytes into the liver thereby alleviating liver early inflammation and late fibrosis.

Infection with Schistosoma results in strong granulomatous inflammation caused by parasite eggs deposited in the liver. Granuloma is defined as a significant number of immune cell infiltration around the eggs intermixed with hepatocytes, which can protect the host against liver damage. But excessive infiltration and inflammation lead to severe liver injury and fibrosis. Here we found that B1 cells accumulated in the liver after infection and released IL-10 to regulate inflammation. B1 cell-derived IL-10 inhibited the expression of chemokines and then restrained excessive infiltration of Ly6C^hi monocytes into the liver thereby alleviating early inflammation and later fibrosis in the liver. Our study provides insight into the immunomodulation of B1 cells in schistosomiasis and an important step towards the development of therapeutic strategies for Schistosoma-induced liver diseases.

The Number of Regulatory B Cells is Increased in Mice with Collagen-induced Arthritis

The aim of this study is to investigate changes in regulatory B cells (Bregs) and the expression of related cytokines such as interleukin-10 (IL-10) and transforming growth factor (TGF)-β in a mouse model of collagen-induced arthritis (CIA). A total 20 DBA/1 mice (6-8 weeks old) were randomly divided into control and CIA disease groups. For the CIA disease group, animals were injected intradermally with chicken collagen type II and complete Freund's adjuvant. The calculated arthritis index score of the CIA group was significantly higher than that in control group. Hematoxylin and eosin staining showed tumid synovial cells with irregular arrangement and obvious hyperplasia, with a high degree of inflammatory cell infiltration in CIA model group. Cytometric bead array technology and quantitative RT-PCR indicated that the levels of IL-10 and TGF-β in serum, and synovial cells were significantly increased in the CIA group. The proportion of Bregs in the spleen of the CIA group was significantly increased compared to the control group. In conclusion, our findings demonstrate that the number of Bregs and the expression of TGF-β and IL-10 are enhanced in mice with CIA.