B cell regulation of CD4+CD25+ T regulatory cells and IL-10 via B7 is essential for recovery from experimental autoimmune encephalomyelitis

A Novel Subset of Regulatory T Cells Induced by B Cells Alleviate the Severity of Immunological Diseases

Regulatory T (Treg) cells are crucial for maintaining immune tolerance by suppressing response to self-antigens and harmless antigens to prevent autoimmune diseases and uncontrolled immune responses. Therefore, using Treg cells is considered a therapeutic strategy treating inflammatory diseases. Based on their origin, Treg cells are classified into thymus-derived, peripherally induced, and in vitro induced Treg cells. Our group discovered a novel Treg cell subset, namely, Treg-of-B (Treg/B) cells, generated by culturing CD4+CD25- T cells with B cells, including Peyer's patch B cells, splenic B cells and peritoneal B1a cells, for 3 days. Treg/B cells express CD44, OX40 (CD134), cytotoxic T-lymphocyte-associated antigen-4 (CD152), glucocorticoid-induced tumor necrosis factor receptor family-related protein (CD357), interleukin-10 receptor, lymphocyte activation gene-3 (CD223), inducible co-stimulator (CD278), programmed-death 1 (CD279), tumor necrosis factor receptor II, and high levels of IL-10, but not forkhead box protein P3, similar to type 1 Treg (Tr1) cells. However, unlike Tr1 cells, Treg/B cells do not express CD103, CD226, and latency-associated peptide. Treg/B cells have been applied for the treatment of some murine models of inflammatory diseases, including allergic asthma, inflammatory bowel disease, collagen-induced arthritis, gout, psoriasis and primary biliary cholangitis. This review summarizes the current knowledge of Treg/B cells.

Engineering nanoparticle therapeutics for food allergy

Food allergy is a growing public health issue among children and adults that can lead to life-threatening anaphylaxis following allergen exposure. The criterion standard for disease management includes food avoidance and emergency epinephrine administration because current allergen-specific immunotherapy treatments are limited by adverse events and unsustained desensitization. A promising approach to remedy these shortcomings is the use of nanoparticle-based therapies that disrupt disease-driving immune mechanisms and induce more sustained tolerogenic immune pathways. The pathophysiology of food allergy includes multifaceted interactions between effector immune cells, including lymphocytes, antigen-presenting cells, mast cells, and basophils, mainly characterized by a TH2 cell response. Regulatory T cells, TH1 cell responses, and suppression of other major allergic effector cells have been found to be major drivers of beneficial outcomes in these nanoparticle therapies. Engineered nanoparticle formulations that have shown efficacy at reducing allergic responses and revealed new mechanisms of tolerance include polymeric-, lipid-, and emulsion-based nanotherapeutics. This review highlights the recent engineering design of these nanoparticles, the mechanisms induced by them, and their future potential therapeutic targets.

Therapeutic targeting of gut-originating regulatory B cells in neuroinflammatory diseases

Regulatory B cells (Bregs) are immunosuppressive cells that support immunological tolerance by the production of IL-10, IL-35, and TGF-β. Bregs arise from different developmental stages in response to inflammatory stimuli. In that regard, mounting evidence points towards a direct influence of gut microbiota on mucosal B cell development, activation, and regulation in health and disease. While an increasing number of diseases are associated with alterations in gut microbiome (dysbiosis), little is known about the role of microbiota on Breg development and induction in neuroinflammatory disorders. Notably, gut-originating, IL-10- and IgA-producing regulatory plasma cells have recently been demonstrated to egress from the gut to suppress inflammation in the CNS raising fundamental questions about the triggers and functions of mucosal-originating Bregs in systemic inflammation. Advancing our understanding of Bregs in neuroinflammatory diseases could lead to novel therapeutic approaches. Here, we summarize the main aspects of Breg differentiation and functions and evidence about their involvement in neuroinflammatory diseases. Further, we highlight current data of gut-originating Bregs and their microbial interactions and discuss future microbiota-regulatory B cell-targeted therapies in immune-mediated diseases.

Neuroinflammatory Biomarkers in the Brain, Cerebrospinal Fluid, and Blood After Ischemic Stroke

The most frequent type of stroke, known as ischemic stroke (IS), is a significant global public health issue. The pathological process of IS and post-IS episodes has not yet been fully explored, but neuroinflammation has been identified as one of the key processes. Biomarkers are objective indicators used to assess normal or pathological processes, evaluate responses to treatment, and predict outcomes, and some biomarkers can also be used as therapeutic targets. After IS, various molecules are produced by different cell types, such as microglia, astrocytes, infiltrating leukocytes, endothelial cells, and damaged neurons, that participate in the neuroinflammatory response within the ischemic brain region. These molecules may either promote or inhibit neuroinflammation and may be released into extracellular spaces, including cerebrospinal fluid (CSF) and blood, due to reasons such as BBB damage. These neuroinflammatory molecules should be valued as biomarkers to monitor whether their expression levels in the blood, CSF, and brain correlate with the diagnosis and prognosis of IS patients or whether they have potential as therapeutic targets. In addition, although some molecules do not directly participate in the process of neuroinflammation, they have been reported to have potential diagnostic or therapeutic value against post-IS neuroinflammation, and these molecules will also be listed. In this review, we summarize the neuroinflammatory biomarkers in the brain, CSF, and blood after an IS episode and the potential value of these biomarkers for the diagnosis, treatment, and prognosis of IS patients.

Histamine H4 Receptor Agonist, 4-Methylhistamine, Aggravates Disease Progression and Promotes Pro-Inflammatory Signaling in B Cells in an Experimental Autoimmune Encephalomyelitis Mouse Model

We sought to assess the impact of 4-Methylhistamine (4-MeH), a specific agonist targeting the Histamine H4 Receptor (H4R), on the progression of experimental autoimmune encephalomyelitis (EAE) and gain insight into the underlying mechanism. EAE is a chronic autoimmune, inflammatory, and neurodegenerative disease of the central nervous system (CNS) characterized by demyelination, axonal damage, and neurodegeneration. Over the past decade, pharmacological research into the H4R has gained significance in immune and inflammatory disorders. For this study, Swiss Jim Lambert EAE mice were treated with 4-MeH (30 mg/kg/day) via intraperitoneal administration from days 14 to 42, and the control group was treated with a vehicle. Subsequently, we evaluated the clinical scores. In addition, flow cytometry was employed to estimate the impact of 4-Methylhistamine (4-MeH) on NF-κB p65, GM-CSF, MCP-1, IL-6, and TNF-α within CD19+ and CXCR5+ spleen B cells. Additionally, we investigated the effect of 4-MeH on the mRNA expression levels of Nf-κB p65, Gmcsf, Mcp1, Il6, and Tnfα in the brain of mice using RT-PCR. Notably, the clinical scores of EAE mice treated with 4-MeH showed a significant increase compared with those treated with the vehicle. The percentage of cells expressing CD19+NF-κB p65+, CXCR5+NF-κB p65+, CD19+GM-CSF+, CXCR5+GM-CSF+, CD19+MCP-1+, CXCR5+MCP-1+, CD19+IL-6+, CXCR5+IL-6+, CD19+TNF-α+, and CXCR5+TNF-α+ exhibited was more pronounced in 4-MeH-treated EAE mice when compared to vehicle-treated EAE mice. Moreover, the administration of 4-MeH led to increased expression of NfκB p65, Gmcsf, Mcp1, Il6, and Tnfα mRNA in the brains of EAE mice. This means that the H4R agonist promotes pro-inflammatory mediators aggravating EAE symptoms. Our results indicate the harmful role of H4R agonists in the pathogenesis of MS in an EAE mouse model.

Under the influence: environmental factors as modulators of neuroinflammation through the IL-10/IL-10R axis

The IL-10/IL-10 receptor (IL-10R) axis plays an important role in attenuating neuroinflammation in animal models of Multiple Sclerosis (MS) and increased IL-10 has been associated with a positive response to MS disease modifying therapy. Because environmental factors play an important role in MS susceptibility and disease course, identification of environmental factors that impact the IL-10/IL-10R axis has therapeutic potential. In this review, we provide historical and updated perspectives of how IL-10R signaling impacts neuroinflammation, discuss environmental factors and intestinal microbes with known impacts on the IL-10/IL-10R axis, and provide a hypothetical model for how B cells, via their production of IL-10, may be important in conveying environmental "information" to the inflamed central nervous system.

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.

The absence of B cells disrupts splenic and myocardial Treg homeostasis in coxsackievirus B3-induced myocarditis

Although B cells are essential for humoral immunity and show noteworthy immunomodulatory activity through antibody-independent functions, the role of B cells in regulating Treg cell responses remains controversial. Tregs (CD4+CD25+Foxp3+) are considered to play an immunoprotective role in viral myocarditis (VMC) by controlling autoimmune effector T cells. Here, we proved that B-cell knockout can not only lead to significant reductions in Tregs in the spleen, blood, and heart of VMC mice but also decrease the activation and immune function of splenic Tregs, which was reversed by adoptive transfer of B cells; the transcription levels of TGF-β and Foxp3 in the myocardium were also significantly reduced. B-cell depletion by anti-CD20 impaired the anti-inflammatory function of splenic Tregs and the homeostasis of myocardial Tregs population. Moreover, B cells can convert CD4+CD25- T cells into Foxp3+ and Foxp3-, two functionally suppressive Treg subgroups. Although the reduction in myocardial inflammation in BKO mice indicates that B cells may play a proinflammatory role, the beneficial side of B cells cannot be ignored, that is, to control autoimmunity by maintaining Treg numbers. The results observed in the animal model of VMC highlight the potential harm of rituximab in the nonselective depletion of B cells in clinical applications.

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.

Development and validation of a nomogram based on lymphocyte subsets to distinguish bipolar depression from major depressive disorder

OBJECTIVE

Bipolar depression (BD) and major depressive disorder (MDD) are both common affective disorders. The common depression episodes make it difficult to distinguish between them, even for experienced clinicians. Failure to properly diagnose them in a timely manner leads to inappropriate treatment strategies. Therefore, it is important to distinguish between BD and MDD. The aim of this study was to develop and validate a nomogram model that distinguishes BD from MDD based on the characteristics of lymphocyte subsets.

MATERIALS AND METHODS

A prospective cross-sectional study was performed. Blood samples were obtained from participants who met the inclusion criteria. The least absolute shrinkage and selection operator (LASSO) regression model was used for factor selection. A differential diagnosis nomogram for BD and MDD was developed using multivariable logistic regression and the area under the curve (AUC) with 95% confidence interval (CI) was calculated, as well as the internal validation using a bootstrap algorithm with 1,000 repetitions. Calibration curve and decision curve analysis (DCA) were used to evaluate the calibration and clinical utility of the nomogram, respectively.

RESULTS

A total of 166 participants who were diagnosed with BD (83 cases) or MDD (83 cases), as well as 101 healthy controls (HCs) between June 2018 and January 2022 were enrolled in this study. CD19⁺ B cells, CD3⁺ T cells, CD3^-CD16/56⁺ NK cells, and total lymphocyte counts were strong predictors of the diagnosis of BD and MDD and were included in the differential diagnosis nomogram. The AUC of the nomogram and internal validation were 0.922 (95%; CI, 0.879-0.965), and 0.911 (95% CI, 0.838-0.844), respectively. The calibration curve used to discriminate BD from MDD showed optimal agreement between the nomogram and the actual diagnosis. The results of DCA showed that the net clinical benefit was significant.

CONCLUSION

This is an easy-to-use, repeatable, and economical nomogram for differential diagnosis that can help clinicians in the individual diagnosis of BD and MDD patients, reduce the risk of misdiagnosis, facilitate the formulation of appropriate treatment strategies and intervention plans.

Regulatory T Cells in Autoimmunity and Cancer: A Duplicitous Lifestyle

Regulatory T (Treg) cells, possess a strategic role in the maintenance of immune homeostasis, and their function has been closely linked to development of diverse pathologies including autoimmunity and cancer. Comprehensive studies in various disease contexts revealed an increased plasticity as a characteristic of Treg cells. Although Treg cell plasticity comes in various flavors, the major categories enclose the loss of Foxp3 expression, which is the master regulator of Treg cell lineage, giving rise to “ex-Treg” cells and the “fragile” Treg cells in which FOXP3 expression is retained but accompanied by the engagement of an inflammatory program and attenuation of the suppressive activity. Treg cell plasticity possess a tremendous therapeutic potential either by inducing Treg cell de-stabilization to promote anti-tumor immunity, or re-enforcing Treg cell stability to attenuate chronic inflammation. Herein, we review the literature on the Treg cell plasticity with lessons learned in autoimmunity and cancer and discuss challenges and open questions with potential therapeutic implications.

Cross-Talk of the CNS With Immune Cells and Functions in Health and Disease

The immune system's role is much more than merely recognizing self vs. non-self and involves maintaining homeostasis and integrity of the organism starting from early development to ensure proper organ function later in life. Unlike other systems, the central nervous system (CNS) is separated from the peripheral immune machinery that, for decades, has been envisioned almost entirely as detrimental to the nervous system. New research changes this view and shows that blood-borne immune cells (both adaptive and innate) can provide homeostatic support to the CNS via neuroimmune communication. Neurodegeneration is mostly viewed through the lens of the resident brain immune populations with little attention to peripheral circulation. For example, cognition declines with impairment of peripheral adaptive immunity but not with the removal of microglia. Therapeutic failures of agents targeting the neuroinflammation framework (inhibiting immune response), especially in neurodegenerative disorders, call for a reconsideration of immune response contributions. It is crucial to understand cross-talk between the CNS and the immune system in health and disease to decipher neurodestructive and neuroprotective immune mechanisms for more efficient therapeutic strategies.

A combination of the percentages of IFN-γ+CD4+T cells and granzyme B+CD19+B cells is associated with acute hepatic rejection: a case control study

Background

T cells and B cells play a key role in alloimmune responses. We aimed to characterize the shift of T cell subsets and B cell subsets during acute hepatic rejection, and further determine whether they could serve as a prognostic marker.

Methods

Blood samples together with the clinical data from liver transplant recipients with and without acute hepatic rejection were collected and analyzed as well as from a validation cohort.

Results

Upon activation the expression of TGF-β and granzyme B in CD19⁺B cells, and the expression of IL-2 and IFN-γ in CD4⁺T cells were higher in acute hepatic rejection. However, only the frequencies of granzyme B⁺CD19⁺B cells and IFN-γ⁺CD4⁺T cells correlated with liver function in addition to with each other. A combination of the two cell subsets as a novel marker could classify rejection versus non-rejection (area under the curve 0.811, p = 0.001) with the cut-off value of 62.93%, which was more sensitive for worse histological changes (p = 0.027). Moreover, the occurrence rate of acute rejection was higher in the group with the novel marker > 62.93% (p = 0.000). The role of the novel marker was further confirmed in a validation cohort, which was identified to be the only significant independent risk factor for acute rejection (odds ratio: 0.923; 95% CI confidence interval: 0.885–0.964; p = 0.000).

Conclusions

A combination of the percentages of IFN-γ⁺CD4⁺T cells and granzyme B⁺CD19⁺B cells can distinguish rejection from non-rejection, which can be used as a potential prognostic marker for acute rejection in liver transplant recipients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02855-w.

Checkpoint Receptor TIGIT Expressed on Tim-1+ B Cells Regulates Tissue Inflammation

Tim-1, a phosphatidylserine receptor expressed on B cells, induces interleukin 10 (IL-10) production by sensing apoptotic cells. Here we show that mice with B cell-specific Tim-1 deletion develop tissue inflammation in multiple organs including spontaneous paralysis with inflammation in the central nervous system (CNS). Transcriptomic analysis demonstrates that besides IL-10, Tim-1⁺ B cells also differentially express a number of co-inhibitory checkpoint receptors including TIGIT. Mice with B cell-specific TIGIT deletion develop spontaneous paralysis with CNS inflammation, but with limited inflammation in other organs. Our findings suggest that Tim-1⁺ B cells are essential for maintaining self-tolerance and restraining tissue inflammation, and that Tim-1 signaling-dependent TIGIT expression on B cells is essential for maintaining CNS-specific tolerance. A possible critical role of aryl hydrocarbon receptor (AhR) in regulating the B cell function is discussed, as we find that AhR is among the preferentially expressed transcription factors in Tim-1⁺ B cells and regulates their TIGIT and IL-10 expression.

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.

Adoptive Transfer of Regulatory Immune Cells in Organ Transplantation

Chronic graft rejection remains a significant barrier to solid organ transplantation as a treatment for end-organ failure. Patients receiving organ transplants typically require systemic immunosuppression in the form of pharmacological immunosuppressants for the duration of their lives, leaving these patients vulnerable to opportunistic infections, malignancies, and other use-restricting side-effects. In recent years, a substantial amount of research has focused on the use of cell-based therapies for the induction of graft tolerance. Inducing or adoptively transferring regulatory cell types, including regulatory T cells, myeloid-derived suppressor cells, and IL-10 secreting B cells, has the potential to produce graft-specific tolerance in transplant recipients. Significant progress has been made in the optimization of these cell-based therapeutic strategies as our understanding of their underlying mechanisms increases and new immunoengineering technologies become more widely available. Still, many questions remain to be answered regarding optimal cell types to use, appropriate dosage and timing, and adjuvant therapies. In this review, we summarize what is known about the cellular mechanisms that underly the current cell-based therapies being developed for the prevention of allograft rejection, the different strategies being explored to optimize these therapies, and all of the completed and ongoing clinical trials involving these therapies.

B-Cell Control of Regulatory T Cells in Friend Virus Infection

B lymphocytes have well-established effector roles during viral infections, including production of antibodies and functioning as antigen-presenting cells for CD4+ and CD8+ T cells. B cells have also been shown to regulate immune responses and induce regulatory T cells (Tregs). In the Friend virus (FV) model, Tregs are known to inhibit effector CD8+ T-cell responses and contribute to virus persistence. Recent work has uncovered a role for B cells in the induction and activation of Tregs during FV infection. In addition to inducing Tregs, B cell antibody production and antigen-presenting cell activity is a target of Treg suppression. This review focuses on the dynamic interactions between B cells and Tregs during FV infection.

Characterization of the Cell Surface Phenotype and Regulatory Activity of B-Cell IgD Low (BDL) Regulatory B Cells

B-cell IgD Low (BD_L) B cells have been shown to promote immunological tolerance by inducing proliferation of CD4⁺Foxp3⁺ T-regulatory cells (Treg) in a glucocorticoid-induced tumor necrosis factor receptor-related protein ligand (GITRL, Tnfsf18)-dependent manner. BD_L cells constitute a small subset of splenic B lymphocytes that, in mice, are characterized by the B220⁺IgM^intCD21^intCD23⁺CD93^-IgD^low/- cell surface expression profile. In this chapter, we show the flow cytometry gating strategy developed to identify and purify BD_L. In addition, we describe an in vitro assay and two in vivo assays to assess BD_L regulatory activity by quantitating Treg expansion/proliferation and indicate how they can be used in mouse models of disease. Collectively, these methods are useful to track and quantitate BD_L and Treg numbers and assess their regulatory activity in inflammatory disease models.

The frequency of follicular T helper cells differs in acute and chronic neuroinflammation

Beyond the major role of T cells in the pathogenesis of the autoimmune neuroinflammatory disorder multiple sclerosis (MS), recent studies have highlighted the impact of B cells on pathogenic inflammatory processes. Follicular T helper cells (Tfh) are essential for the promotion of B cell-driven immune responses. However, their role in MS and its murine model, experimental autoimmune encephalomyelitis (EAE), is poorly investigated. A first step to achieving a better understanding of the contribution of Tfh cells to the disease is the consideration of Tfh cell localization in relation to genetic background and EAE induction method. Here, we investigated the Tfh cell distribution during disease progression in disease relevant organs in three different EAE models. An increase of Tfh frequency in the central nervous system (CNS) was observed during peak of C57BL/6 J EAE, paralleling chronic disease activity, whereas in relapsing-remitting SJL EAE mice Tfh cell frequencies were increased during remission. Furthermore, transferred Tfh-skewed cells polarized in vitro induced mild clinical symptoms in B6.Rag1^-/- mice. We identified significantly higher levels of Tfh cells in the dura mater than in the CNS both in C57BL/6 and in SJL/J mice. Overall, our study emphasizes diverse, non-static roles of Tfh cells during autoimmune neuroinflammation.

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.

The Immunomodulatory Effects of Mesenchymal Stem Cells on Regulatory B Cells

The therapeutic potential of mesenchymal stem cells (MSCs) has been investigated in many preclinical and clinical studies. This potential is dominantly based on the immunosuppressive properties of MSCs. Although the therapeutic profiles of MSC transplantation are still not fully characterized, accumulating evidence has revealed that B cells change after MSC infusion, in particular inducing regulatory B cells (Bregs). The immunosuppressive effects of Bregs have been demonstrated, and these cells are being evaluated as new targets for the treatment of inflammatory diseases. MSCs are capable of educating B cells and inducing regulatory B cell production via cell-to-cell contact, soluble factors, and extracellular vesicles (EVs). These cells thus have the potential to complement each other's immunomodulatory functions, and a combined approach may enable synergistic effects for the treatment of immunological diseases. However, compared with investigations regarding other immune cells, investigations into how MSCs specifically regulate Bregs have been superficial and insufficient. In this review, we discuss the current findings related to the immunomodulatory effects of MSCs on regulatory B cells and provide optimal strategies for applications in immune-related disease treatments.

Interleukin 35 Regulatory B Cells

B lymphocytes play a central role in host immunity. They orchestrate humoral immune responses that modulate activities of other immune cells and produce neutralizing antibodies that confer lasting immunity to infectious diseases including smallpox, measles and poliomyelitis. In addition to these traditional functions is the recent recognition that B cells also play critical role in maintaining peripheral tolerance and suppressing the development or severity of autoimmune diseases. Their immune suppressive function is attributed to relatively rare populations of regulatory B cells (Bregs) that produce anti-inflammatory cytokines including interleukin 10 (IL-10), IL-35 and transforming growth factor-β. The IL-35-producing B cell (i35-Breg) is the newest Breg subset described. i35-Bregs suppress central nervous system autoimmune diseases by inducing infectious tolerance whereby conventional B cells acquire regulatory functions that suppress pathogenic Th17 responses. In this review, we discuss immunobiology of i35-Breg cell, i35-Breg therapies for autoimmune diseases and potential therapeutic strategies for depleting i35-Bregs that suppress immune responses against pathogens and tumor cells.

Cell Therapy in Solid Organ Transplantation

Transplantation is the only cure for end-stage organ failure. Current immunosuppressive drugs have two major limitations: 1) non antigen specificity, which increases the risk of cancer and infection diseases, and 2) chronic toxicity. Cell therapy appears to be an innovative and promising strategy to minimize the use of immunosuppression in transplantation and to improve long-term graft survival. Preclinical studies have shown efficacy and safety of using various suppressor cells, such as regulatory T cells, regulatory B cells and tolerogenic dendritic cells. Recent clinical trials using cellbased therapies in solid organ transplantation also hold out the promise of improving efficacy. In this review, we will briefly go over the rejection process, current immunosuppressive drugs, and the potential therapeutic use of regulatory cells in transplantation.

Discovery and Function of B-Cell IgD Low (BDL) B Cells in Immune Tolerance

It is now appreciated that in addition to their role in humoral immunity, B cells also exert regulatory mechanisms that lead to attenuation of inflammatory responses. The concept of B-cell regulation became well recognized when mice deficient in B cells due to genetic disruption were shown to be refractory to recovery from the signs of experimental autoimmune encephalomyelitis (EAE), the mouse model of multiple sclerosis. This seminal study spurred the search for B-cell regulatory phenotypes and mechanisms of action. Our approach was to utilize differential B-cell depletion with anti-CD20 to retain B cells whose presence were required to achieve EAE recovery. Utilizing flow cytometry, adoptive cell therapy and genetic approaches, we discovered a new B-cell subset that, upon adoptive transfer into B cell-deficient mice, was sufficient to promote EAE recovery. This B-cell subset is IgM⁺, but due to low/negative IgD cell surface expression, it was named B-cell IgD low (BD_L). Mechanistically, we found that in the absence of BD_L, the absolute cell number of CD4⁺Foxp3⁺ T regulatory cells (Treg), essential for immune tolerance, was significantly reduced. Furthermore, we found that BD_L expression of glucocorticoid-induced tumor necrosis factor ligand (GITRL) was essential for induction of Treg proliferation and maintenance of their homeostasis. Thus, we have identified a new B-cell subset that is critical for immunological tolerance through interactions with Treg.

Regulatory B Cells Normalize CNS Myeloid Cell Content in a Mouse Model of Multiple Sclerosis and Promote Oligodendrogenesis and Remyelination

The unmet medical need of patients with multiple sclerosis (MS) is the inexorable loss of CNS myelin and latterly neurons leading to permanent neurologic disability. Solicitation of endogenous oligodendrocytes progenitor cells, the precursor of oligodendrocytes, to remyelinate axons may abort the onset of disability. In female mice with experimental autoimmune encephalomyelitis (EAE), a murine model of MS, adoptive transfer of IL-10⁺ regulatory B cells (B_regs) has been shown to reverse EAE by promoting the expansion of peripheral and CNS-infiltrating IL-10⁺ T cells. Here, we examined whether B_regs treatment and its bystander effect on regulatory T cells are associated with CNS repair as reflected by oligodendrogenesis and remyelination. We have found that transfusion of B_regs reverses established clinical EAE and that clinical improvement is associated with a significant increase in spinal cord remyelination as reflected by g-ratio analysis within the thoracic and lumbar spine. We further observed in the spinal cords of EAE B_regs-treated mice that CNS resident CD11b/CD45^intLy6C^- microglia, and infiltrating CD11b⁺/CD45^high monocytes/macrophages content reverts to normal and polarize to a M2-like CD206⁺ phenotype. Concurrently, there was a substantial increase in neo-oligodendrogenesis as manifest by an increase in CD45^-/low CNS cells expressing A2B5, an early marker in oligodendrocytes progenitor cell differentiation as well as GalC⁺/O1⁺ premyelinating and myelin basic protein⁺/myelin oligodendrocyte glycoprotein⁺ mature oligodendrocytes with reciprocal downregulation of paired related homeobox protein 1. These results demonstrate that the clinical benefit of B_regs is associated with normalization of CNS immune milieu and concurrent activation of oligodendrocyte progenitor cells with subsequent remyelination.SIGNIFICANCE STATEMENT In multiple sclerosis patients, demyelination progresses with aging and disease course, leading to irreversible disability. In this study, we have discovered, using a mouse model of multiple sclerosis, that the transfusion of autologous regulatory B cells (B_regs) is able to ameliorate, cure, and sustain the durable remission of the disease. We show that the adoptive transfer of B_regs dramatically decreased the frequency of myeloid-derived cells, both infiltrating monocytes/macrophages and resident microglia, and converted their phenotype to an immunosuppressive-like phenotype. Moreover, we showed that CNS oligodendrocyte progenitor cells are activated following B_regs treatment and differentiate into myelinating oligodendrocytes, which results in neo-oligodendrogenesis and remyelination of spinal cords.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Resolution of inflammation during multiple sclerosis

Multiple sclerosis (MS) is a frequent autoimmune demyelinating disease of the central nervous system (CNS). There are three clinical forms described: relapsing-remitting multiple sclerosis (RRMS), the most common initial presentation (85%) among which, if not treated, about half will transform, into the secondary progressive multiple sclerosis (SPMS) and the primary progressive MS (PPMS) (15%) that is directly progressive without superimposed clinical relapses. Inflammation is present in all subsets of MS. The relapsing/remitting form could represent itself a particular interest for the study of inflammation resolution even though it remains incomplete in MS. Successful resolution of acute inflammation is a highly regulated process and dependent on mechanisms engaged early in the inflammatory response that are scarcely studied in MS. Moreover, recent classes of disease-modifying treatment (DMTs) that are effective against RRMS act by re-establishing the inflammatory imbalance, taking advantage of the pre-existing endogenous suppressor. In this review, we will discuss the active role of regulatory immune cells in inflammation resolution as well as the role of tissue and non-hematopoietic cells as contributors to inflammation resolution. Finally, we will explore how DMTs, more specifically induction therapies, impact the resolution of inflammation during MS.

The emerging role of regulatory T cells following lung transplantation

Regulatory T cells (Treg) have proven to be a powerful immunologic force in nearly every organ system and hold therapeutic potential for a wide range of diseases. Insights gained from non-transplant pathologies, such as infection, cancer, and autoimmunity, are now being translated to the field of solid organ transplantation, particularly for livers and kidneys. Recent insights from animal models of lung transplantation have established that Tregs play a vital role in suppressing rejection and facilitating tolerance of lung allografts, and such discoveries are being validated in human studies and preclinical trials. Given that long-term outcomes following lung transplantation remain profoundly limited by chronic rejection, Treg therapy holds the potential to significantly improve patient outcomes and should be aggressively investigated.

Critical roles of regulatory B and T cells in helminth parasite-induced protection against allergic airway inflammation

The prevalence of allergic asthma and incidences of helminth infections in humans are inversely correlated. Although experimental studies have established the causal relation between parasite infection and allergic asthma, the mechanism of the parasite-associated immunomodulation is not fully elucidated. Using a murine model of asthma and nematode parasite Heligmosomoides polygyrus, we investigated the roles of regulatory B cells (B_reg ) and T cells (T_reg ) in mediation of the protection against allergic asthma by parasite. H. polygyrus infection significantly suppressed ovalbumin (OVA)-induced allergic airway inflammation (AAI) evidenced by alleviated lung histopathology and reduced numbers of bronchoalveolar inflammatory cell infiltration, and induced significant responses of interleukin (IL)-10⁺ B_reg , IL-10⁺ T_reg and forkhead box protein 3 (FoxP3)⁺ T_reg in mesenteric lymph node and spleen of the mice. Adoptive transfer of IL-10⁺ B_reg and IL-10⁺ T_reg cell prevented the lung immunopathology in AAI mice. Depletion of FoxP3⁺ T_reg cells in FoxP3-diphtheria toxin (DT) receptor transgenic mice by diphtheria toxin (DT) treatment exacerbated airway inflammation in parasite-free AAI mice and partially abrogated the parasite-induced protection against AAI. IL-10⁺ B_reg cells were able to promote IL-10⁺ T_reg expansion and maintain FoxP3⁺ T_reg cell population. These two types of T_regs failed to induce CD19⁺ B cells to transform into IL-10⁺ B_reg cells. These results demonstrate that B_reg , IL-10⁺ T_reg and FoxP3⁺ T_reg cells contribute in A discrepant manner to the protection against allergic airway immunopathology by parasiteS. B_reg cell might be a key upstream regulatory cell that induces IL-10⁺ T_reg response and supports FoxP3⁺ T_reg cell population which, in turn, mediate the parasite-imposed immunosuppression of allergic airway inflammation. These results provide insight into the immunological relationship between parasite infection and allergic asthma.

Potential role of regulatory B cells in immunological diseases

Regulatory B cells (Bregs) are immune-modulating cells that affect the immune system by producing cytokines or cellular interactions. These cells have immunomodulatory effects on the immune system by cytokine production. The abnormalities in Bregs could be involved in various disorders such as autoimmunity, chronic infectious disease, malignancies, allergies, and primary immunodeficiencies are immune-related scenarios. Ongoing investigation could disclose the biology and the exact phenotype of these cells and also the assigned mechanisms of action of each subset, as a result, potential therapeutic strategies for treating immune-related anomalies. In this review, we collect the findings of human and mouse Bregs and the therapeutic efforts to change the pathogenicity of these cells in diverse disease.

Mature IgDlow/- B cells maintain tolerance by promoting regulatory T cell homeostasis

A number of different B cell subsets have been shown to exhibit regulatory activity using a variety of mechanisms to attenuate inflammatory diseases. Here we show, using anti-CD20-mediated partial B cell depletion in mice, that a population of mature B cells distinguishable by IgD^low/- expression maintains tolerance by, at least in part, promoting CD4⁺Foxp3⁺ regulatory T cell homeostatic expansion via glucocorticoid-induced tumor necrosis factor receptor ligand, or GITRL. Cell surface phenotyping, transcriptome analysis and developmental study data show that B cells expressing IgD at a low level (BD_L) are a novel population of mature B cells that emerge in the spleen from the transitional-2 stage paralleling the differentiation of follicular B cells. The cell surface phenotype and regulatory function of BD_L are highly suggestive that they are a new B cell subset. Human splenic and peripheral blood IgD^low/- B cells also exhibit BD_L regulatory activity, rendering them of therapeutic interest.

B-cell-specific-peroxisome proliferator-activated receptor γ deficiency augments contact hypersensitivity with impaired regulatory B cells

Nuclear receptor peroxisome proliferator-activated receptor γ (PPAR-γ) activation can prevent immunoinflammatory disorders and diabetes. B cells play protective roles during inflammation as well. However, the roles of endogenous PPAR-γ in the regulatory properties of B cells to relieve inflammation remain unknown. Here, we developed B-cell-specific PPAR-γ knockout (B-PPAR-γ^-/- ) mice and found that the conditional deletion of PPAR-γ in B cells resulted in exaggerated contact hypersensitivity (CHS). Meanwhile, interferon-γ (IFN-γ) of CD4⁺ CD8⁺ T cells was up-regulated in B-PPAR-γ^-/- mice in CHS. This showed that the regulatory function of B cells in B-PPAR-γ^-/- mice declined in vivo. Whereas splenic CD5⁺ CD1d^hi regulatory B-cell numbers and peripheral regulatory T-cell numbers were not changed in naive B-PPAR-γ^-/- mice. Loss of PPAR-γ in B cells also did not affect either CD86 or FasL expression in splenic CD5⁺ CD1d^hi regulatory B cells after activation. Notably, interleukin-10 (IL-10) production in CD5⁺ CD1d^hi regulatory B cells reduced in B-PPAR-γ-deficient mice. In addition, functional IL-10-producing CD5⁺ CD1d^hi regulatory B cells decreased in B-PPAR-γ^-/- mice in the CHS model. These findings were in accordance with augmented CHS. The current work indicated the involvement of endogenous PPAR-γ in the regulatory function of B cells by disturbing the expansion of IL-10-positive regulatory B cells.

Regulatory B cells and advances in transplantation

The effects of B cell subsets with regulatory activity on the immune response to an allograft have evoked increasing interest. Here, we summarize the function and signaling of regulatory B cells (Bregs) and their potential effects on transplantation. These cells are able to suppress the immune system directly via ligand-receptor interactions and indirectly by secretion of immunosuppressive cytokines, particularly IL-10. In experimental animal models, the extensively studied IL-10-producing B cells have shown unique therapeutic advantages in the transplant field. In addition, adoptive transfer of B cell subsets with regulatory activity may reveal a new approach to prolonging allograft survival. Recent clinical observations on currently available therapies targeting B cells have revealed that Bregs play an important role in immune tolerance and that these cells are expected to become a new target of immunotherapy for transplant-related diseases.

CD19+IgM+ cells demonstrate enhanced therapeutic efficacy in type 1 diabetes mellitus

We describe a protective effect on autoimmune diabetes and reduced destructive insulitis in NOD.scid recipients following splenocyte injections from diabetic NOD donors and sorted CD19+ cells compared with NOD.scid recipients receiving splenocytes alone. This protective effect was age specific (only CD19+ cells from young NOD donors exerted this effect; P < 0.001). We found that the CD19+IgM+ cell is the primary subpopulation of B cells that delayed transfer of diabetes mediated by diabetogenic T cells from NOD mice (P = 0.002). Removal of IgM+ cells from the CD19+ pool did not result in protection. Notably, protection conferred by CD19+IgM+ cotransfers were not dependent on the presence of Tregs, as their depletion did not affect their ability to delay onset of diabetes. Blockade of IL-10 with neutralizing antibodies at the time of CD19+ cell cotransfers also abrogated the therapeutic effect, suggesting that IL-10 secretion was an important component of protection. These results were strengthened by ex vivo incubation of CD19+ cells with IL-5, resulting in enhanced proliferation and IL-10 production and equivalently delayed diabetes progression (P = 0.0005). The potential to expand CD19+IgM+ cells, especially in response to IL-5 stimulation or by pharmacologic agents, may be a new therapeutic option for type 1 diabetes.

Helminths-based bi-functional molecule, tuftsin-phosphorylcholine (TPC), ameliorates an established murine arthritis

A novel small molecule named tuftsin-phosphorylcholine (TPC), which is linked to the biological activity of helminths, was constructed. The current study address the effect of TPC treatment in established collagen-induced arthritis (CIA) mice and propose TPC bi-functional activity. TPC treatment was initiated when clinical score was 2 to 4. Arthritis scores in TPC treated mice were lower compared to mice treated with vehicle (P < 0.001). Joint staining showed normal joint structure in TPC-treated mice compared to control groups treated with phosphate buffered saline (PBS), phosphorylcholine, or tuftsin, which exhibited severely inflamed joints. TPC enhanced anti-inflammatory response due to increased IL-10 secretion, and reduced pro-inflammatory cytokine secretion (IL-1-β, IL-6, TNF-αP < 0.001). Furthermore, TPC therapy increased expansion of CD4⁺CD25⁺FOXP3⁺T regulatory cells and IL-10⁺CD5⁺CD1d⁺B regulatory cells. We propose that the immunomodulatory activity of TPC can be a result of a bi-specific activity of TPC: (a) The tuftsin part of the TPC shifts RAW macrophage cells from pro-inflammatory macrophages M1 to anti-inflammatory M2-secreting IL-10 (P < 0.001) through neuropilin-1 and (b) TPC significantly reduce mouse TLR4 expression via NFkB pathway by HEK^TM cells (P < 0.02) via the phosphorylcholine site of the molecule. Our results indicate that TPC, significantly ameliorated established CIA by its immunomodulatory activity. These data could lead to a novel self bi-functional small molecule for treating patients with progressive RA.

Role of TFH Cells in Promoting T Helper 17-Induced Neuroinflammation

Both T cells and B cells are implicated in the pathology of multiple sclerosis (MS), but how these cells cooperate to drive disease remains unclear. Recent studies using experimental autoimmune encephalomyelitis (EAE) demonstrated that the TH17 pathway is correlated with increased numbers of ectopic B-cell follicles in the central nervous system (CNS). As follicular T helper (TFH) cells are regulators of B cell responses, we sought to examine the role of TFH cells in EAE induced by the transfer of myelin-specific TH17 cells (TH17-EAE). In this study, we first confirmed previous reports that B-cells are a major cell type infiltrating the CNS during TH17-EAE. In addition, we found that B cells contribute to the severity of TH17-EAE. Class-switched B-cells in the CNS were positively correlated with disease and, strikingly, the severity TH17-EAE was diminished in B cell deficient mice. We next focused on the role TFH cells play in TH17-EAE. We found substantial numbers of CXCR5⁺PD1⁺CD4⁺ TFH cells in the CNS tissue of TH17-EAE mice and that at the peak of disease, the number of infiltrating TFHs was correlated with the number of infiltrating B-cells. Using congenic CD45.1⁺ donor mice and CD45.2⁺ recipient mice, we determined that the TFH cells were recipient-derived, whereas IL-17⁺ cells were donor-derived. We assessed whether myelin-specific TFH cells are capable of inducing EAE in recipient mice and found that transferring TFH cells failed to induce EAE. Finally, we tested the effects of blocking TFH trafficking in TH17-EAE using an antagonistic antibody against CXCL13, the chemokine ligand for CXCR5 on TFH cells. We found anti-CXCL13 treatment significantly reduced TH17-EAE disease. This treatment blocked CD4⁺ T cells from entering the CNS, but had no effect on infiltration of B cells. Strikingly, this antibody treatment had no measurable effect on TH17 disease in B cell-deficient mice. These data demonstrate that infiltrating TFH cells are a key cell type that contributes to an inflammatory B cell response in TH17-EAE and provide evidence for targeting TFH cells as a treatment for neuro-autoimmune diseases like MS.

Expanding Diversity and Common Goal of Regulatory T and B Cells. I: Origin, Phenotype, Mechanisms

Immunosuppressive activity of regulatory T and B cells is critical to limit autoimmunity, excessive inflammation, and pathological immune response to conventional antigens or allergens. Both types of regulatory cells are intensively investigated, however, their development and mechanisms of action are still not completely understood. Both T and B regulatory cells represent highly differentiated populations in terms of phenotypes and origin, however, they use similar mechanisms of action. The most investigated CD4+CD25+ regulatory T cells are characterized by the expression of Foxp3+ transcription factor, which is not sufficient to maintain their lineage stability and suppressive function. Currently, it is considered that specific epigenetic changes are critical for defining regulatory T cell stability in the context of their suppressive function. It is not yet known if similar epigenetic regulation determines development, lineage stability, and function of regulatory B cells. Phenotype diversity, confirmed or hypothetical developmental pathways, multiple mechanisms of action, and role of epigenetic changes in these processes are the subject of this review.

B Cell Requirement for Robust Regulatory T Cell Responses to Friend Retrovirus Infection

Regulatory T cells (Tregs) are immunosuppressive cells of the immune system that control autoimmune reactivity. Tregs also respond during immune reactions to infectious agents in order to limit immunopathological damage from potent effectors such as CD8⁺ cytolytic T lymphocytes. We have used the Friend virus (FV) model of retroviral infection in mice to investigate how viral infections induce Tregs. During acute FV infection, there is significant activation and expansion of thymus-derived (natural) Tregs that suppress virus-specific CD8⁺ T cell responses. Unlike conventional T cells, the responding Tregs are not virus specific, so the mechanisms that induce their expansion are of great interest. We now show that B cells provide essential signals for Treg expansion during FV infection. Treg responses are greatly diminished in B cell-deficient mice but can be restored by adoptive transfers of B cells at the time of infection. The feeble Treg responses in B cell-deficient mice are associated with enhanced virus-specific CD8⁺ T cell responses and accelerated virus control during the first 2 weeks of infection. In vitro experiments demonstrated that B cells promote Treg activation and proliferation through a glucocorticoid-induced receptor superfamily member 18 (GITR) ligand-dependent mechanism. Thus, B cells play paradoxically opposing roles during FV infection. They provide proliferative signals to immunsosuppressive Tregs, which slows early virus control, and they also produce virus-specific antibodies, which are essential for long-term virus control.

When infectious agents invade a host, numerous immunological mechanisms are deployed to limit their replication, neutralize their spread, and destroy the host cells harboring the infection. Since immune responses also have a strong capacity to damage host cells and tissues, their magnitude, potency, and duration are under regulatory control. Regulatory T cells are an important component of this control, and the mechanisms that induce them to respond and exert immunosuppressive regulation are of great interest. In the current report, we show that B cells, the cells responsible for making pathogen-specific antibodies, are also involved in promoting the expansion of regulatory T cells during a retroviral infection. In vitro studies demonstrated that they do so via stimulation of the Tregs through interactions between cell surface molecules: GITR interactions with its ligand (GITRL) on B cells and GITR on regulatory T cells. These findings point the way toward therapeutics to better treat infections and autoimmune diseases.

B cells control maternofetal priming of allergy and tolerance in a murine model of allergic airway inflammation

BACKGROUND

Allergic asthma is a chronic lung disease resulting from inappropriate immune responses to environmental antigens. Early tolerance induction is an attractive approach for primary prevention of asthma.

OBJECTIVE

We analyzed the mechanisms of perinatal tolerance induction to allergens, with particular focus on the role of B cells in preconception and early intrauterine immune priming.

METHODS

Wild-type (WT) and B cell-deficient mice received ovalbumin (OVA) intranasally before mating. Their offspring were analyzed in a murine model of allergic airway inflammation.

RESULTS

Although antigen application before conception protected WT progeny from allergy, it aggravated allergic airway inflammation in B cell-deficient offspring. B-cell transfer restored protection, demonstrating the crucial role of B cells in perinatal tolerance induction. Effective diaplacentar allergen transfer was detectable in pregnant WT mice but not in pregnant B-cell knockout dams, and antigen concentrations in WT amniotic fluid (AF) were higher than in IgG-free AF of B cell-deficient dams. Application of OVA/IgG immune complexes during pregnancy boosted OVA uptake by fetal dendritic cells (DCs). Fetal DCs in human subjects and mice expressed strikingly higher levels of Fcγ receptors compared with DCs from adults and were highly efficient in taking up OVA/IgG immune complexes. Moreover, murine fetal DCs effectively primed antigen-specific forkhead box P3⁺ regulatory T cells after in vitro coincubation with OVA/IgG-containing AF.

CONCLUSION

Our data support a decisive role for B cells and immunoglobulins during in utero tolerance priming. These findings improve the understanding of perinatal immunity and might support the development of effective primary prevention strategies for allergy and asthma in the future.

TLR4 supports the expansion of FasL+CD5+CD1dhi regulatory B cells, which decreases in contact hypersensitivity

Certain B cells termed as "regulatory B cells" (Bregs) can suppress the ongoing immune responses and a splenic CD5⁺CD1d^hi Breg subset identified earlier was shown to exert its regulatory functions through secretion of IL-10. Though FasL expression is an alternative mechanism of immune suppression used by B cells, little is known about the FasL expressing CD5⁺CD1d^hi Bregs. In this study, we isolated splenocytes or splenic CD19⁺ B cells and compared the efficiency of toll-like receptor(TLR)4 ligand (lipopolysaccharide) with TLR9 ligand (CpG), anti-CD40 and TLR9 ligand (CpG) plus anti-CD40 on the FasL expression of splenic CD5⁺CD1d^hi Bregs by flow cytometry. FasL expression in CD5⁺CD1d^hi B cells was rapidly increased after TLR4 ligation. Intriguingly, anti-CD40 and CpG plus anti-CD40 combinations failed to stimulate FasL expression in CD5⁺CD1d^hi B cells although the IL-10 production was up-regulated in this subset. In addition, LPS and other B10-cell inducers increased the expression of surface molecules like CD86 and CD25, which are correlated to the regulatory functions of B cells. Furthermore, NF-κB and NF-AT inhibitors decreased the TLR4-activated FasL expression in CD5⁺CD1d^hi B cells. Then we sorted splenic CD5⁺CD1d^hi Bregs using flow cytometry and found that TLR4-activated CD5⁺CD1d^hi Bregs suppressed the proliferation of CFSE-labeled CD4⁺ T cells in vitro, which was partly blocked by anti-FasL antibody. In oxazolone-sensitized mice having contact hypersensitivity, FasL expression in splenic CD5⁺CD1d^hi B cells was decreased compared to the control group after TLR4 ligation. Our findings suggest that the regulatory function of CD5⁺CD1d^hi B cells could be partly mediated by Fas-FasL pathway and this FasL expressing CD5⁺CD1d^hi Bregs might participate in the regulation of inflammatory diseases.

Effector and regulatory B cells in Multiple Sclerosis

The role of B cells in the pathogenesis of Multiple Sclerosis (MS), an autoimmune neurodegenerative disease, is becoming eminent in recent years, but the specific contribution of the distinct B cell subsets remains to be elucidated. Several B cell subsets have shown regulatory, anti-inflammatory capacities in response to stimuli in vitro, as well as in the animal model of MS: Experimental Autoimmune Encephalomyelitis (EAE). However, the functional role of the B regulatory cells (Bregs) in vivo and specifically in the human disease is yet to be clarified. In the present review, we have summarized the updated information on the roles of effector and regulatory B cells in MS and the immune-modulatory effects of MS therapeutic agents on their phenotype and function.

Schistosome-induced pulmonary B cells inhibit allergic airway inflammation and display a reduced Th2-driving function

Chronic schistosome infections protect against allergic airway inflammation (AAI) via the induction of IL-10-producing splenic regulatory B (Breg) cells. Previous experiments have demonstrated that schistosome-induced pulmonary B cells can also reduce AAI, but act independently of IL-10. We have now further characterized the phenotype and inhibitory activity of these protective pulmonary B cells. We excluded a role for regulatory T (Treg) cell induction as putative AAI-protective mechanisms. Schistosome-induced B cells showed increased CD86 expression and reduced cytokine expression in response to Toll-like receptor (TLR) ligands compared with control B cells. To investigate the consequences for T cell activation we cultured ovalbumin (OVA)-pulsed, schistosome-induced B cells with OVA-specific transgenic T cells and observed less Th2 cytokine expression and T cell proliferation compared with control conditions. This suppressive effect was preserved even under optimal T cell stimulation by anti-CD3/28. Blocking of the inhibitory cytokines IL-10 or TGF-β only marginally restored Th2 cytokine induction. These data suggest that schistosome-induced pulmonary B cells are impaired in their capacity to produce cytokines to TLR ligands and to induce Th2 cytokine responses independent of their antigen-presenting function. These findings underline the presence of distinct B cell subsets with different stimulatory or inhibitory properties even if induced by the same type of helminth.

PPAR-γ agonist ameliorates liver pathology accompanied by increasing regulatory B and T cells in high-fat-diet mice

OBJECTIVE

Peroxisome proliferator-activated receptor (PPAR)-γ plays critical roles in human metabolic disorders. However, the mechanism remains incompletely understood. Regulatory cells contribute to these metabolic improvements; therefore, whether PPAR-γ agonist regulates regulatory cells was investigated.

METHODS

C57BL/6J mice received a normal or high-fat diet (HFD) with or without pioglitazone treatment. Mice were sacrificed for detecting the metabolic parameters. Lymphocytes from spleen and visceral adipose tissue (VAT) were collected and analyzed for ST2⁺ Tregs and Bregs by flow cytometry. IL-10 in the liver or VAT was detected by immunofluorescence and ELISA. Correlation analysis between IL-10 and liver weight or serum total cholesterol was made by Pearson correlation analysis.

RESULTS

Pioglitazone increased VAT weight but reduced serum total cholesterol, hepatic steatosis, and cholesterol crystallization formation. Pioglitazone treatment enhanced ST2⁺ Tregs and Bregs in the VAT and spleen of HFD-fed mice (all P < 0.05). Pioglitazone treatment increased IL-10 in the livers or VAT of HFD-fed mice (all P < 0.05). The expression of IL-10 in the liver was significantly negatively correlated with liver weight or serum total cholesterol in pioglitazone-treated HFD-fed mice (r²  = 0.74, P < 0.05; r²  = 0.58, P < 0.05).

CONCLUSIONS

PPAR-γ signaling plays a critical role in the regulation of metabolic disorders through promoting regulatory cell response.

Regulatory B Cells in Pregnancy: Lessons from Autoimmunity, Graft Tolerance, and Cancer

The success of pregnancy is contingent on the maternal immune system recognizing and accommodating a growing semi-allogeneic fetus. Specialized subsets of lymphocytes capable of negative regulation are fundamental in this process, and include the regulatory T cells (Tregs) and potentially, regulatory B cells (Bregs). Most of our current understanding of the immune regulatory role of Bregs comes from studies in the fields of autoimmunity, transplantation tolerance, and cancer biology. Bregs control autoimmune diseases and can elicit graft tolerance by inhibiting the differentiation of effector T cells and dendritic cells (DCs), and activating Tregs. Furthermore, in cancer, Bregs are hijacked by neoplastic cells to promote tumorigenesis. Pregnancy therefore represents a condition that reconciles these fields-mechanisms must be in place to ensure maternal immunological tolerance throughout gravidity to allow the semi-allogeneic fetus to grow within. Thus, the mechanisms underlying Breg activities in autoimmune diseases, transplantation tolerance, and cancer may take place during pregnancy as well. In this review, we discuss the potential role of Bregs as guardians of pregnancy and propose an endocrine-modulated feedback loop highlighting the Breg-Treg-tolerogenic DC interface essential for the induction of maternal immune tolerance.

Mechanisms by Which B Cells and Regulatory T Cells Influence Development of Murine Organ-Specific Autoimmune Diseases

Experiments with B cell-deficient (B−/−) mice indicate that a number of autoimmune diseases require B cells in addition to T cells for their development. Using B−/− Non-obese diabetic (NOD) and NOD.H-2h4 mice, we demonstrated that development of spontaneous autoimmune thyroiditis (SAT), Sjogren’s syndrome and diabetes do not develop in B−/− mice, whereas all three diseases develop in B cell-positive wild-type (WT) mice. B cells are required early in life, since reconstitution of adult mice with B cells or autoantibodies did not restore their ability to develop disease. B cells function as important antigen presenting cells (APC) to initiate activation of autoreactive CD4+ effector T cells. If B cells are absent or greatly reduced in number, other APC will present the antigen, such that Treg are preferentially activated and effector T cells are not activated. In these situations, B−/− or B cell-depleted mice develop the autoimmune disease when T regulatory cells (Treg) are transiently depleted. This review focuses on how B cells influence Treg activation and function, and briefly considers factors that influence the effectiveness of B cell depletion for treatment of autoimmune diseases.