To 'B' regulated: B cells as members of the regulatory workforce

CD200R activation on naïve T cells by B cells induces suppressive activity of T cells via IL-24

CD200 is an anti-inflammatory protein that facilitates signal transduction through its receptor, CD200R, in cells, resulting in immune response suppression. This includes reducing M1-like macrophages, enhancing M2-like macrophages, inhibiting NK cell cytotoxicity, and downregulating CTL responses. Activation of CD200R has been found to modulate dendritic cells, leading to the induction or enhancement of Treg cells expressing Foxp3. However, the precise mechanisms behind this process are still unclear. Our previous study demonstrated that B cells in Peyer's patches can induce Treg cells, so-called Treg-of-B (P) cells, through STAT6 phosphorylation. This study aimed to investigate the role of CD200 in Treg-of-B (P) cell generation. To clarify the mechanisms, we used wild-type, STAT6 deficient, and IL-24 deficient T cells to generate Treg-of-B (P) cells, and antagonist antibodies (anti-CD200 and anti-IL-20RB), an agonist anti-CD200R antibody, CD39 inhibitors (ARL67156 and POM-1), a STAT6 inhibitor (AS1517499), and soluble IL-20RB were also applied. Our findings revealed that Peyer's patch B cells expressed CD200 to activate the CD200R on T cells and initiate the process of Treg-of-B (P) cells generation. CD200 and CD200R interaction triggers the phosphorylation of STAT6, which regulated the expression of CD200R, CD39, and IL-24 in T cells. CD39 regulated the expression of IL-24, which sustained the expression of CD223 and IL-10 and maintained the cell viability. In summary, the generation of Treg-of-B (P) cells by Peyer's patch B cells was through the CD200R-STAT6-CD39-IL-24 axis pathway.

Helminth-induced CD9+ B-cell subset alleviates obesity-associated inflammation via IL-10 production

It has been shown that helminth infection can protect against obesity and improve insulin sensitivity to a certain extent, based on epidemiological investigations and animal experiments. Meanwhile, helminths induce a network of regulatory immune cells, including regulatory B cells (Bregs). However, the molecule characteristics and function of these Bregs in improving whole-body metabolic homeostasis remains largely unclear. We established a mouse model with chronic Schistosoma japonicum infection, and compared the differences in B10 cells (CD19⁺CD5⁺CD1d^hi) and B10^- cells (CD19⁺CD5^-CD1d^-) from splenic B cells of infected mice using RNA-seq. A unique Breg population was identified. Furthermore, these Bregs were evaluated for their ability to produce inhibitory cytokines in vitro and suppress obesity when adoptively transferred into mice on a high-fat diet. We found that schistosome infection could expand Breg cell populations in mice. CD9 was demonstrated to be a key surface marker for most murine IL-10⁺ B cells in spleen. CD19⁺CD9⁺ B cells produced more IL-10 than conventional B10 cells. Adoptive transfer of CD9⁺ B cells had the capacity to alleviate obesity-associated inflammation via promoting Tregs, Th2 cells and decreasing Th1, Th17 cells in high-fat diet mice. In conclusion, schistosome infection can induce regulatory CD9⁺ B cell production, which plays a critical role in the regulation of metabolic disorders through IL-10 production.

Effects of Peptide-Induced Immune Tolerance on Murine Lupus

The regulation of autoimmunity and the molecular mechanisms by which different immune cells, including T cells, polymorphonuclear leukocytes (PMN-granulocytes), and B cells suppress autoimmune diseases is complex. We have shown previously that BWF1 lupus mice are protected from autoimmunity after i.v. injection or oral administration of tolerogenic doses of pCons, an artificial synthetic peptide based on sequences containing MHC class I and MHC class II determinants in the VH region of a J558-encoded BWF1 anti-DNA Ab. Several T cell subsets can transfer this tolerance. In this study, we determined the potential roles of granulocytes, B cells and regulatory T cells altered by pCons treatment in the BWF1 (NZB/NZW) mouse model of lupus. Immunophenotyping studies indicated that pCons treatment of BWF1 mice significantly increased CD4⁺FoxP3⁺ T cells, reduced the percent of B cells expressing CD19⁺CD5⁺ but increased the percent of CD19⁺CD1d⁺ regulatory B cells and increased the ability of the whole B cell population to suppress IgG anti-DNA production in vitro. pCons treatment significantly decreased the expression of CTLA-4 (cytotoxic T-lymphocyte-associated protein-4) in CD8⁺ T cells. In addition, peptide administration modified granulocytes so they became suppressive. We co-cultured sorted naïve B cells from mice making anti-DNA Ab (supported by addition of sorted naive CD4⁺ and CD8⁺ T cells from young auto-antibody-negative BWF1 mice) with sorted B cells or granulocytes from tolerized mice. Both tolerized granulocytes and tolerized B cells significantly suppressed the production of anti-DNA in vitro. In granulocytes from tolerized mice compared to saline-treated littermate controls, real-time PCR analysis indicated that expression of interferon-induced TNFAIP2 increased more than 2-fold while Ptdss2 and GATA1 mRNA were up-regulated more than 10-fold. In contrast, expression of these genes was significantly down-regulated in tolerized B cells. Further, another IFN-induced protein, Bcl2, was reduced in tolerized B cells as determined by Western blot analyses. In contrast, expression of FoxP3 was significantly increased in tolerized B cells. Together, these data suggest that B cells and granulocytes are altered toward suppressive functions by in vivo tolerization of BWF1 mice with pCons and it is possible these cell types participate in the clinical benefits seen in vivo.

CA-30, an oligosaccharide fraction derived from Liuwei Dihuang decoction, ameliorates cognitive deterioration via the intestinal microbiome in the senescence-accelerated mouse prone 8 strain

Mounting evidence points to alterations in the gut microbiota-neuroendocrine immunomodulation (NIM) network that might drive Alzheimer’s Disease (AD) pathology. In previous studies, we found that Liuwei Dihuang decoction (LW) had beneficial effects on the cognitive impairments and gastrointestinal microbiota dysbiosis in an AD mouse model. In particular, CA-30 is an oligosaccharide fraction derived from LW. We sought to determine the effects of CA-30 on the composition and function of the intestinal microbiome in the senescence-accelerated mouse prone 8 (SAMP8) mouse strain, an AD mouse model. Treatment with CA-30 delayed aging processes, ameliorated cognition in SAMP8 mice. Moreover, CA-30 ameliorated abnormal NIM network in SAMP8 mice. In addition, we found that CA-30 mainly altered the abundance of four genera and 10 newborn genera. Advantageous changes in carbohydrate-active enzymes of SAMP8 mice following CA-30 treatment, especially GH85, were also noted. We further found that seven genera were significantly correlated with the NIM network and cognitive performance. CA-30 influenced the relative abundance of these intestinal microbiomes in SAMP8 mice and restored them to SAMR1 mouse levels. CA-30 ameliorated the intestinal microbiome, rebalanced the NIM network, improved the AD-like cognitive impairments in SAMP8 mice, and can thus be a potential therapeutic agent for AD.

The Traditional Chinese Medicine Fufang Shatai Heji (STHJ) Enhances Immune Function in Cyclophosphamide-Treated Mice

Fufang Shatai Heji (STHJ) is a mixture of traditional Chinese medicines, such as Radix Adenophorae, Radix Pseudostellariae, and Radix Astragali. STHJ is commonly used to treat diseases caused by low immune function, for example, Sjögren's syndrome (SS). The primary objective of this study was to assess the immunopotentiating effect of STHJ using an immunosuppressive mouse model receiving cyclophosphamide (CTX). Following CTX treatment, STHJ was administered by oral gavage for 30 consecutive days. The percentage of specific lymphocyte subpopulations in the spleen was measured by flow cytometry. Levels of inflammatory factors in serum were detected by enzyme-linked immunosorbent assays (ELISAs). The administration of STHJ significantly elevated thymus and spleen indices, increased B cell and natural killer (NK) cell activities, and decreased CD8⁺ T, CD8⁺CD122⁺ T, NKT, and γδT cell activities in the CTX-treated mice. In addition, STHJ upregulated the expression of interleukin- (IL-) 2, IL-6, and tumor necrosis factor-α (TNF-α) and downregulated IL-10 expression in CTX-treated mice. In conclusion, STHJ effectively remitted CTX-induced immunosuppression by modulating the balance of lymphocyte subsets and cytokines. Our results suggest STHJ treatment could be used as an effective therapeutic approach to improve immune function in patients with low immunity.

Amelioration of autoimmune arthritis by adoptive transfer of Foxp3-expressing regulatory B cells is associated with the Treg/Th17 cell balance

BACKGROUND

Foxp3 is a key regulator of the development and function of regulatory T cells (Tregs), and its expression is thought to be T cell-restricted. We found that B cells in mice can express Foxp3 and B cells expressing Foxp3 may play a role in preventing the development of collagen-induced arthritis (CIA) in DBA/1J mice.

METHODS

Foxp3 expression was modulated in CD19(+) B cells by transfection with shRNA or using an over-expression construct. In addition, Foxp3-transfected B cells were adoptively transferred to CIA mice. We found that LPS or anti-IgM stimulation induced Foxp3 expression in B cells. Foxp3-expressing B cells were found in the spleens of mice.

RESULTS

Over-expression of Foxp3 conferred a contact-dependent suppressive ability on proliferation of responder T cells. Down-regulation of Foxp3 by shRNA caused a profound induction in proliferation of responder T cells. Adoptive transfer of Foxp3(+)CD19(+) B cells attenuated the clinical symptoms of CIA significantly with concomitant suppression of IL-17 production and enhancement of Foxp3 expression in CD4(+) T cells from splenocytes.

CONCLUSION

Our data indicate that Foxp3 expression is not restricted to T cells. The expression of Foxp3 in B cells is critical for the immunoregulation of T cells and limits autoimmunity in a mouse model.

A novel splenic B1 regulatory cell subset suppresses allergic disease through phosphatidylinositol 3-kinase-Akt pathway activation

BACKGROUND

IL-10-producing regulatory B (B10) cells potently suppress allergic diseases, such as contact hypersensitivity (CHS). Splenic B10 cells share overlapping phenotypic markers with CD5⁺ B1 B cells, CD1d^hiCD21⁺CD23^- marginal zone (MZ) B cells, and CD1d^hiCD21⁺CD23⁺ T2-MZ precursor B cells but do not exclusively belong to either subset.

OBJECTIVE

In this study we investigated the signaling mechanisms and a novel phenotypic parameter of B10 cells.

METHOD

We performed microarray analysis comparing IL-10⁺ and IL-10^- B cells. B cell-specific phosphatase and tensin homolog (PTEN)-deficient mice, which exhibit aberrant activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway in B cells, were examined.

RESULTS

Microarray analysis revealed that the PI3K-Akt pathway is important for IL-10 production in B cells. PI3K-Akt pathway inhibitors reduced B10 cell numbers in vitro. B10 cell numbers were significantly increased in B cell-specific PTEN-deficient mice. The CHS response was significantly diminished in PTEN-deficient mice. Unexpectedly, splenic B10 cells in these mice were found within the B1 B-cell subset but not within the MZ B-cell subset. In wild-type mice not only MZ B10 cells but also B1-B10 cells were identified in the spleen. In addition, these 2 B10 cell subsets were predominantly found within the CD9⁺CD80⁺ B-cell fraction.

CONCLUSION

A novel splenic B1 regulatory cell subset (B1-B10 cells) was identified. Our findings show that the PI3K-Akt pathway in B cells is critical for B10 cell development and CHS response and that CD9/CD80 coexpression is a novel phenotypic parameter for both MZ-B10 and B1-B10 cells.

Role of IL-10-Producing Regulatory B Cells in Chronic Hepatitis B Virus Infection

BACKGROUND

A subset of interleukin (IL)-10-producing regulatory B (Breg) cells that suppress T-cell-mediated immunity was recently identified; however, their role in chronic hepatitis B (CHB) remains elusive.

AIM

To explore the possible role of Breg in the interaction with Th cells and consequent pathogenesis of CHB.

METHODS

The prevalence of Breg as well as 3 major effector T-cell subsets--CD4(+)CD25(high)Foxp3(+) regulatory T (Treg) cells, T helper 1 cells (Th1), and T helper 2 cells (Th2)--was assessed in the peripheral blood of 31 patients with CHB, 28 patients with acute hepatitis B (AHB), and 25 healthy controls (HC).

RESULTS

Compared to patients with AHB and HC, the prevalence of Breg and Treg cells and the concentration of IL-10 in the supernatant of cultured peripheral blood mononuclear cells (PBMCs) were greatly increased in patients with CHB. A significantly decreased proportion of Th1 cells was also observed in patients with CHB and was demonstrated to have a negative correlation with the prevalence of Breg. Furthermore, depletion of Treg cells in the PBMCs of patients with CHB did not alter the frequency of Breg cells or their ability to produce IL-10, indicating little, if any, impact of Treg cells on the generation and maintenance of Breg cells.

CONCLUSIONS

Our data indicate that increased Breg cells might be a major source of elevated IL-10 in CHB and represent a critical and independent regulatory force in the development of impaired anti-HBV immunity, consequently contributing to the pathogenesis of CHB.

Age-associated aberrations in mouse cellular and humoral immune responses

BACKGROUND AND AIMS

Several contradictions and inconsistent reports regarding nature of dysfunction of immune system with age are known. The lack of multipoint age comparisons in immune functions contributes to the observed ambiguity in understanding immunosenescence. Thus, the present study aimed at a concurrent analysis of different immune cells in an attempt to delineate the nature of dysregulation with progressive aging in mice.

METHODS

4, 8, 12 and 16 months old mice were analyzed for various immune parameters involving neutrophils, peripheral blood lymphocytes, peritoneal macrophages, splenocytes, inflamm-aging markers in plasma and humoral immune response in intestine.

RESULTS

Neutrophils registered a remarkable decrease in activities of respiratory burst enzymes and phagocytosis, while macrophages recorded a decrease in TLR-2 and TLR-4 expression. MCP-1 and CRP levels increased in plasma, whereas stimulation index and CD28 expression decreased in lymphocytes. Interleukins analysis (IFN-γ, IL-4, IL-10) showed a remarkable shift towards Th2 response which further resulted in increased IgG1/IgG2a ratio and IgE levels in intestine.

CONCLUSION

A decline in cell-mediated immune response, chronic inflammation and aggravation of humoral immunity was evident which conclusively suggests a skewed Th2 pathway during aging.

The immune potential and immunopathology of cytokine-producing B cell subsets: a comprehensive review

B lymphocytes are generally recognized for their potential to mediate humoral immunity by producing different antibody isotypes and being involved in opsonization and complement fixation. Nevertheless, the non-classical, antibody-independent immune potential of B cell subsets has attracted much attention especially in the past decade. These B cells can release a broad variety of cytokines (such as IL-2, IL-4, IL-6, IL-10, IL-17, IFN-α, IFN-γ, TNF-α, TGF-β, LT), and can be classified into distinct subsets depending on the particular cytokine profile, thus emerging the concept of cytokine-producing B cell subsets. Although there is still controversy surrounding the key cell surface markers, intracellular factors and cellular origins of cytokine-producing B cell subsets, accumulating evidence indicates that these B cells are endowed with great potential to regulate both innate and adaptive arms of immune system though releasing cytokines. On the one hand, they promote immune responses through mounting Th1/Th2/Th17 and neutrophil response, inducing DC maturation and formation of lymphoid structures, increasing NK cell and macrophage activation, enhancing development of themselves and sustaining antibody production. On the other hand, they can negatively regulate immune responses by suppressing Th cell responses, inhibiting Tr1 cell and Foxp3(+) Treg differentiation, impairing APC function and pro-inflammatory cytokine release by monocytes, and inducing CD8(+) T cell anergy and CD4(+) T cell apoptosis. Therefore, cytokine-producing B cell subsets have multifunctional functions in health and diseases, playing pathologic as well as protective roles in autoimmunity, infection, allergy, and even malignancy. In this review, we revisit the history of discovering cytokine-producing B cells, describe the identification of cytokine-producing B cell subsets, introduce the origins of cytokine-producing B cell subsets as well as molecular and cellular mechanisms for their differentiation, and summarize the recent progress made toward understanding the unexpectedly complex and potentially opposing roles of cytokine-producing B cells in immunological disorders.

IL-10-producing regulatory B cells (B10 cells) in autoimmune disease

B cell abnormalities contribute to the development and progress of autoimmune disease. Traditionally, the role of B cells in autoimmune disease was thought to be predominantly limited to the production of autoantibodies. Nevertheless, in addition to autoantibody production, B cells have other functions potentially relevant to autoimmunity. Such functions include antigen presentation to and activation of T cells, expression of co-stimulatory molecules and cytokine production. Recently, the ability of B cells to negatively regulate cellular immune responses and inflammation has been described and the concept of regulatory B cells has emerged. A variety of cytokines produced by regulatory B cell subsets have been reported, with IL-10 being the most studied. In this review, this specific IL-10-producing subset of regulatory B cells has been labeled B10 cells to highlight that the regulatory function of these rare B cells is mediated by IL-10, and to distinguish them from other B cell subsets that regulate immune responses through different mechanisms. B10 cells are a functionally defined subset currently identified only by their competency to produce and secrete IL-10 following appropriate stimulation. Although B10 cells share surface markers with other previously defined B cell subsets, currently there is no cell surface or intracellular phenotypic marker or set of markers unique to B10 cells. The recent discovery of an effective way to expand B10 cells ex vivo opens new horizons in the potential therapeutic applications of this rare B cell subset. This review highlights the current knowledge on B10 cells and discusses their potential as novel therapeutic agents in autoimmunity.

Role of Peroxisome Proliferator-Activated Receptor-γ in Vascular Inflammation

Vascular inflammation plays a crucial role in atherosclerosis, and its regulation is important to prevent cerebrovascular and coronary artery disease. The inflammatory process in atherogenesis involves a variety of immune cells including monocytes/macrophages, lymphocytes, dendritic cells, and neutrophils, which all express peroxisome proliferator-activated receptor-γ (PPAR-γ). PPAR-γ is a nuclear receptor and transcription factor in the steroid superfamily and is known to be a key regulator of adipocyte differentiation. Increasing evidence from mainly experimental studies has demonstrated that PPAR-γ activation by endogenous and synthetic ligands is involved in lipid metabolism and anti-inflammatory activity. In addition, recent clinical studies have shown a beneficial effect of thiazolidinediones, synthetic PPAR-γ ligands, on cardiovascular disease beyond glycemic control. These results suggest that PPAR-γ activation is an important regulator in vascular inflammation and is expected to be a therapeutic target in the treatment of atherosclerotic complications. This paper reviews the recent findings of PPAR-γ involvement in vascular inflammation and the therapeutic potential of regulating the immune system in atherosclerosis.

Regulatory T cells induced by mucosal B cells alleviate allergic airway hypersensitivity

Asthma is one of the most common chronic airway inflammatory diseases. The induction of immunologic tolerance via mucosa has been used for treating allergic diseases. B cells, which comprise the major cell population in Peyer's patches, were shown to induce the development of regulatory T (Treg) cells. This study investigated the role of B cells in Peyer's patches regarding the induction of tolerance and Treg cell functions. An in vitro suppressive assay and ELISA were used to evaluate the function of T cells stimulated by Peyer-patch B cells (Treg-of-B cells). The therapeutic potential of Treg-of-B cells was then evaluated by an animal model of airway inflammation. Treg-of-B cells were found to exert a suppressive function on T-cell proliferation. Antigen-loaded B cells isolated from Peyer's patches were more tolerogenic, and had the potential to generate more suppressive Treg-of-B cells via the production of IL-10 and cell-cell contacts. Treg-of-B cells expressed cytotoxic T lymphocyte antigen 4, inducible costimulator, OX40 (CD134), programmed death 1, and TNF-RII, and produced lower concentrations of IL-2 and higher concentrations of IL-10. In a murine model of asthma, an adoptive transfer of Treg-of-B cells before or after immunization sufficiently suppressed Th2 cytokine production and eosinophilic infiltration, and alleviated asthmatic symptoms. B cells isolated from gut-associated lymphoid tissues can generate regulatory T cells that may be important in oral tolerance, and that may be applicable to the alleviation of allergic symptoms.

B-lymphocyte effector functions in health and disease

B-lymphocytes have traditionally been thought to contribute to immunity and autoimmune disease through terminal differentiation into plasma cells that secrete antibody. However, studies in mice and recent clinical studies have demonstrated that genetically altered B-cell function and B-cell-targeted therapies can significantly affect autoimmune diseases that were predominantly thought to be T-cell-mediated. B-cell depletion in mouse models of disease has also led to the identification of alternative B-cell effector functions that regulate normal immune responses and autoimmune disease. This review highlights multiple B-cell effector mechanisms, including the promotion of cellular immunity, the negative regulation of immune responses, and the production of pathogenic antibodies.

Amplified B lymphocyte CD40 signaling drives regulatory B10 cell expansion in mice

BACKGROUND

Aberrant CD40 ligand (CD154) expression occurs on both T cells and B cells in human lupus patients, which is suggested to enhance B cell CD40 signaling and play a role in disease pathogenesis. Transgenic mice expressing CD154 by their B cells (CD154(TG)) have an expanded spleen B cell pool and produce autoantibodies (autoAbs). CD22 deficient (CD22(-/-)) mice also produce autoAbs, and importantly, their B cells are hyper-proliferative following CD40 stimulation ex vivo. Combining these 2 genetic alterations in CD154(TG)CD22(-/-) mice was thereby predicted to intensify CD40 signaling and autoimmune disease due to autoreactive B cell expansion and/or activation.

METHODOLOGY/PRINCIPAL FINDINGS

CD154(TG)CD22(-/-) mice were assessed for their humoral immune responses and for changes in their endogenous lymphocyte subsets. Remarkably, CD154(TG)CD22(-/-) mice were not autoimmune, but instead generated minimal IgG responses against both self and foreign antigens. This paucity in IgG isotype switching occurred despite an expanded spleen B cell pool, higher serum IgM levels, and augmented ex vivo B cell proliferation. Impaired IgG responses in CD154(TG)CD22(-/-) mice were explained by a 16-fold expansion of functional, mature IL-10-competent regulatory spleen B cells (B10 cells: 26.7×10(6)±6 in CD154(TG)CD22(-/-) mice; 1.7×10(6)±0.4 in wild type mice, p<0.01), and an 11-fold expansion of B10 cells combined with their ex vivo-matured progenitors (B10+B10pro cells: 66×10(6)±3 in CD154(TG)CD22(-/-) mice; 6.1×10(6)±2 in wild type mice, p<0.01) that represented 39% of all spleen B cells.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate for the first time that the IL-10-producing B10 B cell subset has the capacity to suppress IgG humoral immune responses against both foreign and self antigens. Thereby, therapeutic agents that drive regulatory B10 cell expansion in vivo may inhibit pathogenic IgG autoAb production in humans.

[Regulatory B cell and autoimmune disease]

Regulatory B cells that produce IL-10 are now recognized as an important component of the immune system. Hallmark papers from a number of distinguished laboratories have identified phenotypically diverse B cell subsets with regulatory functions during distinct autoimmune diseases, including IL-10-producing B cells, CD5(+) B-1a cells, CD1d(+) marginal zone B cells, and transitional 2-marginal zone precursor B cells. Most recently, a numerically rare and phenotypically unique CD1d(hi)CD5(+)CD19(hi) subset of regulatory B cells has been identified in the spleens of both normal and autoimmune mice. Remarkably, regulatory B cells are potent negative regulators of inflammation and autoimmunity in mouse models of disease in vivo. Herein, our current understanding of regulatory B cell function is reviewed in the context of previous studies that have identified and characterized regulatory B cells.

Identifying regulatory B cells (B10 cells) that produce IL-10 in mice

Regulatory B cells that produce IL-10 are now recognized as an important component of the immune system. We have identified a rare antigen-specific regulatory B-cell subset with a unique CD1d(hi)CD5(+)CD19(hi) phenotype in the spleens of wild-type mice. We call these cells B10 cells because they are responsible for most B cell IL-10 production, they appear to only produce IL-10 after 5 h of in vitro stimulation, and to distinguish them from other potential regulatory B cell subsets. B10 progenitor (B10pro) cells have also been identified within the spleen CD1d(hi)CD5(+)CD19(hi) B-cell subset, and within other lymphoid tissues. Herein, four methods for identifying and isolating regulatory IL-10-producing B10 cells in mice are provided. The first two methods are used to identify and enumerate B10 and B10pro cells based on their cell surface phenotypes and cytoplasmic IL-10 staining. The last two methods are used to isolate viable B10 cells for adoptive transfer and functional studies. These methods should facilitate the study of B10 cells in inflammation, autoimmune disease, immune responses, and cancer therapy.

Regulatory B cells (B10 cells) and regulatory T cells have independent roles in controlling experimental autoimmune encephalomyelitis initiation and late-phase immunopathogenesis

Experimental autoimmune encephalomyelitis (EAE) is a T lymphocyte-mediated autoimmune disease of the CNS. Significant roles for B cells and a rare IL-10-producing CD1d(high)CD5(+) regulatory B cell subset (B10 cells) have been identified during the initiation and progression of EAE. Whether and how the regulatory functions of B10 cells and FoxP3(+) T regulatory cells (Tregs) overlap or influence EAE immunopathogenesis independently has remained unanswered. This study demonstrates that the number of endogenous or adoptively transferred B10 cells directly influenced EAE pathogenesis through their production of IL-10. B10 cell numbers expanded quickly within the spleen, but not CNS following myelin oligodendrocyte glycoprotein(35-55) immunization, which paralleled B10 cell regulation of disease initiation. The adoptive transfer of myelin oligodendrocyte glycoprotein(33-35)-sensitized B10 cells into wild-type mice reduced EAE initiation dramatically. However, B10 cells did not suppress ongoing EAE disease. Rather, Treg numbers expanded significantly within the CNS during disease progression, which paralleled their negative regulation of late-phase disease. Likewise, the preferential depletion of B10 cells in vivo during disease initiation enhanced EAE pathogenesis, whereas Treg depletion enhanced late-phase disease. B10 cells did not regulate T cell proliferation during in vitro assays, but significantly altered CD4(+) T cell IFN-gamma and TNF-alpha production. Furthermore, B10 cells downregulated the ability of dendritic cells to act as APCs and thereby indirectly modulated T cell proliferation. Thus, B10 cells predominantly control disease initiation, whereas Tregs reciprocally inhibit late-phase disease, with overlapping B10 cell and Treg functions shaping the normal course of EAE immunopathogenesis.

B10 cells and regulatory B cells balance immune responses during inflammation, autoimmunity, and cancer

The ability of B cells to negatively regulate cellular immune responses and inflammation has only recently been described. Hallmark papers from a number of distinguished laboratories have identified phenotypically diverse B-cell subsets with regulatory functions during distinct autoimmune diseases, including IL-10-producing B cells, CD5+ B-1a cells, CD1d+ marginal zone B cells, and transitional-2-marginal zone precursor B cells. Most recently, a numerically rare and phenotypically unique CD1dhiCD5+CD19hi subset of regulatory B cells has been identified in the spleens of both normal and autoimmune mice. CD1dhiCD5+ B cells with the capacity to produce IL-10 have been named B10 cells as they produce IL-10 exclusively and are the predominant B-cell source of IL-10. Remarkably, B10 cells are potent negative regulators of inflammation and autoimmunity in mouse models of disease in vivo. Herein, our current understanding of B10-cell development and function is reviewed in the context of previous studies that have identified and characterized regulatory B cells, emerging evidence for B10-cell regulation of tumor immunity, and the likelihood that B10 cells exist in humans.

Translational Mini-Review Series on B Cell-Directed Therapies: The pathogenic role of B cells in autoantibody-associated autoimmune diseases--lessons from B cell-depletion therapy

B cell depletion therapy with rituximab (BCDT) is a licensed treatment for rheumatoid arthritis and has shown promising results in the treatment of severe, refractory patients with other autoantibody-associated autoimmune diseases (AAID). The exact role that B cells play in the pathogenesis of AAID and consequently the mechanisms by which BCDT is effective are not known. The two more widely discussed hypotheses are that BCDT is effective because it removes the precursors of plasma cells producing pathogenic autoantibody species, or because it depletes a critical mass of autoreactive B cell clones that present antigen to pathogenic autoreactive T cells. This review will focus on the effects of BCDT and whether the response of patients with AAID to BCDT could be due ultimately to its effects on autoantibodies. A better knowledge of the main role that B cells play in the pathogenesis of the different diseases and a better understanding of the most likely mechanism of relapse following an earlier response to BCDT would help to guide further developments of B cell targeting therapies and potentially increase the chance of designing a protocol that could induce a long-term remission.

The development and function of regulatory B cells expressing IL-10 (B10 cells) requires antigen receptor diversity and TLR signals

Autoimmunity and inflammation are controlled in part by regulatory B cells, including a recently identified IL-10-competent CD1d(high)CD5(+) B cell subset termed B10 cells that represents 1-3% of adult mouse spleen B cells. In this study, pathways that influence B10 cell generation and IL-10 production were identified and compared with previously described regulatory B cells. IL-10-competent B cells were predominantly CD1d(high)CD5(+) in adult spleen and were the prevalent source of IL-10, but not other cytokines. B10 cell development and/or maturation in vivo required Ag receptor diversity and intact signaling pathways, but not T cells, gut-associated flora, or environmental pathogens. Spleen B10 cell frequencies were significantly expanded in aged mice and mice predisposed to autoimmunity, but were significantly decreased in mouse strains that are susceptible to exogenous autoantigen-induced autoimmunity. LPS, PMA, plus ionomycin stimulation in vitro for 5 h induced B10 cells to express cytoplasmic IL-10. However, prolonged LPS or CD40 stimulation (48 h) induced additional adult spleen CD1d(high)CD5(+) B cells to express IL-10 following PMA plus ionomycin stimulation. Prolonged LPS or CD40 stimulation of newborn spleen and adult blood or lymph node CD1d(low) and/or CD5(-) B cells also induced cytoplasmic IL-10 competence in rare B cells, with CD40 ligation uniformly inducing CD5 expression. IL-10 secretion was induced by LPS signaling through MyD88-dependent pathways, but not following CD40 ligation. LPS stimulation also induced rapid B10 cell clonal expansion when compared with other spleen B cells. Thereby, both adaptive and innate signals regulate B10 cell development, maturation, CD5 expression, and competence for IL-10 production.

Induction of CD4+ T-cell anergy and apoptosis by activated human B cells

B cells are well-known mediators of humoral immunity and serve as costimulators in the generation of T cell-mediated responses. In several mouse models, however, it was observed that B cells can also down-regulate immune reactions, suggesting a dual role for B cells. Due to this discrepancy and so far limited data, we directly tested the effects of primary human B cells on activated CD4(+) T helper cells in vitro. We found that under optimal costimulation large, activated CD25(+) B cells but not small CD25(-) B cells induced temporary T-cell anergy, determined by cell division arrest and down-regulation of cytokine production. In addition, large CD25(+) B cells directly induced CD95-independent apoptosis in a subpopulation of activated T cells. Suppression required direct B-T-cell contact and was not transferable from T to T cell, excluding potential involvement of regulatory T cells. Moreover, inhibitory effects involved an IL-2-dependent mechanism, since decreasing concentrations of IL-2 led to a shift from inhibitory toward costimulatory effects triggered by B cells. We conclude that activated CD25(+) B cells are able to costimulate or down-regulate T-cell responses, depending on activation status and environmental conditions that might also influence their pathophysiological impact.

Regulatory role of B cells in a murine model of allergic airway disease

Mice sensitized to OVA and subjected to acute OVA aerosol exposures develop allergic airway disease (AAD). However, chronic continuous Ag exposure results in resolution of AAD and the development of local inhalational tolerance (LIT). Because we have previously observed the persistence of B cells in the bronchoalveolar lavage (BAL) and hilar lymph nodes (HLN) at the resolution stage of this model, we investigated the role of B cells in the modulation of AAD. Although B cell-deficient mice developed LIT, adoptive transfer of HLN B cells from LIT mice to OVA-sensitized recipients resulted in attenuated AAD following subsequent OVA aerosol exposure, as determined by reduced BAL leukocytosis and eosinophilia, decreased tissue inflammation, and absent methacholine hyper-responsiveness. In similar adoptive transfer studies, HLN B cells from AAD mice were without effect. The protection transferred by LIT HLN B cells was Ag specific and was associated with accumulation of Foxp3(+) T regulatory cells regionally in BAL and HLN, but not systemically in the spleen. Fluorescent labeling of LIT HLN B cells before adoptive transfer demonstrated that these cells had the capacity to migrate to local inflammatory sites. In vitro assessment demonstrated that the LIT HLN B cells exerted this regulatory effect via TGF-beta induced conversion of CD4(+)CD25(-) T effector cells into functionally suppressive CD4(+)CD25(+)Foxp3(+) T regulatory cells. These findings illustrated a novel regulatory role for regional B cells in AAD and suggested a possible contributory role of B cells, along with other cell types, in the establishment of LIT.

Inhibition of ICAM-1/LFA-1 interactions prevents B-cell-dependent anti-CD45RB-induced transplantation tolerance

BACKGROUND

Allogeneic tolerance can be reliably obtained with monoclonal antibody therapy targeting CD45RB. Although regulatory T cells play an important role in the mechanism, we have recently demonstrated the active participation of host B lymphocytes. After anti-CD45RB therapy, B lymphocytes demonstrate phenotypic alterations that include up-regulation of CD54 (intercellular adhesion molecule [ICAM]-1). We have investigated the hypothesis that alteration in ICAM-1 expression is required for tolerance induction.

MATERIALS AND METHODS

Recipients of heterotopic allogeneic cardiac grafts (C3H donors into B6 recipients) were treated with anti-CD45RB, anti-ICAM, anti-lymphocyte function-associated antigen-1 (LFA), or the combination of these agents. These data were extended by performing allogeneic cardiac transplants into ICAM or LFA recipients treated with a 5-day course of anti-CD45RB. Finally, B-cell-deficient animals were reconstituted with ICAM splenocytes to create a recipient with a selective deficiency of ICAM-1 restricted to the B-cell compartment.

RESULTS

Anti-CD45RB alone or the combination of anti-LFA/anti-ICAM reliably induced transplantation tolerance. However, the triple combination was routinely unsuccessful and induced long-term graft survival in no recipients. ICAM-deficient or LFA-deficient recipients were also resistant to tolerance induced by anti-CD45RB. Finally, transfer of control splenocytes to B-cell-deficient recipients permitted anti-CD45RB-induced tolerance, whereas transfer of ICAM cells was unable to support tolerance induction.

CONCLUSIONS

Expression of ICAM-1 by B lymphocytes and interaction with LFA-1 form a central aspect of transplantation tolerance induced by anti-CD45RB therapy. These data further elucidate the cellular mechanisms used by B lymphocytes in the induction of transplantation tolerance.

CD83 modulates B cell function in vitro: increased IL-10 and reduced Ig secretion by CD83Tg B cells

The murine transmembrane glycoprotein CD83 is an important regulator for both thymic T cell maturation and peripheral T cell responses. Recently, we reported that CD83 also has a function on B cells: Ubiquitous transgenic (Tg) expression of CD83 interfered with the immunoglobulin (Ig) response to infectious agents and to T cell dependent as well as T cell independent model antigen immunization. Here we compare the function of CD83Tg B cells that overexpress CD83 and CD83 mutant (CD83mu) B cells that display a drastically reduced CD83 expression. Correlating with CD83 expression, the basic as well as the lipopolysaccharide (LPS) induced expression of the activation markers CD86 and MHC-II are significantly increased in CD83Tg B cells and reciprocally decreased in CD83mu B cells. Wild-type B cells rapidly upregulate CD83 within three hours post BCR or TLR engagement by de novo protein synthesis. The forced premature overexpression of CD83 on the CD83Tg B cells results in reduced calcium signaling, reduced Ig secretion and a reciprocally increased IL-10 production upon in vitro activation. This altered phenotype is mediated by CD83 expressed on the B cells themselves, since it is observed in the absence of accessory cells. In line with this finding, purified CD83mu B cells displayed a reduced IL-10 production and slightly increased Ig secretion upon LPS stimulation in vitro. Taken together, our data strongly suggest that CD83 is expressed by B cells upon activation and contributes to the regulation of B cell function.

Abrogation of antibody-mediated allograft rejection by regulatory CD4 T cells with indirect allospecificity

Alloantibody is an important effector mechanism for allograft rejection. In this study, we tested the hypothesis that regulatory T cells with indirect allospecificity can prevent humoral rejection by using a rat transplant model in which acute rejection of MHC class I-disparate PVG.R8 heart grafts by PVG.RT1(u) recipients is mediated by alloantibody and is dependent upon help from CD4 T cells that can recognize the disparate MHC alloantigen only via the indirect pathway. Pretransplant treatment of PVG.RT1(u) recipients with anti-CD4 mAb plus donor-specific transfusion abrogated alloantibody production and prolonged PVG.R8 graft survival indefinitely. Naive syngeneic splenocytes injected into tolerant animals did not effect heart graft rejection, suggesting the presence of regulatory mechanisms. Adoptive transfer experiments into CD4 T cell-reconstituted, congenitally athymic recipients confirmed that regulation was mediated by CD4 T cells and was alloantigen-specific. CD4 T cell regulation could be broken in tolerant animals either by immunizing with an immunodominant linear allopeptide or by depleting tolerant CD4 T cells, but surprisingly this resulted in neither alloantibody generation nor graft rejection. These findings demonstrate that anti-CD4 plus donor-specific transfusion treatment results in the development of CD4 regulatory T cells that recognize alloantigens via the indirect pathway and act in an Ag-specific manner to prevent alloantibody-mediated rejection. Their development is associated with intrinsic tolerance within the alloantigen-specific B cell compartment that persists after T cell help is made available.