Activation of CD4⁺ Foxp3⁺ regulatory T cells proceeds normally in the absence of B cells during EAE

Toll-like receptors control the accumulation of neutrophils in lymph nodes that expand CD4+ T cells during experimental autoimmune encephalomyelitis

Toll-like receptors (TLR) control the activation of dendritic cells that prime CD4⁺ T cells in draining lymph nodes, where these T cells then undergo massive clonal expansion. The mechanisms controlling this clonal T cell expansion are poorly defined. Using the CD4⁺ T cell-mediated disease experimental autoimmune encephalomyelitis (EAE), we show here that this process is markedly suppressed when TLR9 signaling is increased, without noticeably affecting the transcriptome of primed T cells, indicating a purely quantitative effect on CD4⁺ T cell expansion. Addressing the underpinning mechanisms revealed that CD4⁺ T cell expansion was preceded and depended on the accumulation of neutrophils in lymph nodes a few days after immunization. Underlying the importance of this immune regulation pathway, blocking neutrophil accumulation in lymph nodes by treating mice with a TLR9 agonist inhibited EAE progression in mice with defects in regulatory T cells or regulatory B cells, which otherwise developed a severe chronic disease. Collectively, this study demonstrates the key role of neutrophils in the quantitative regulation of antigen-specific CD4⁺ T cell expansion in lymph nodes, and the counter-regulatory role of TLR signaling in this process.

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

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

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

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

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

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

The role of T cells in the pathogenesis of Parkinson's disease

Recent evidence has shown that neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). However, different components of the brain's immune system may exert diverse effects on neuroinflammatory events in PD. The adaptive immune response, especially the T cell response, can trigger type 1 pro-inflammatory activities and suppress type 2 anti-inflammatory activities, eventually resulting in deregulated neuroinflammation and subsequent dopaminergic neurodegeneration. Additionally, studies have increasingly shown that therapies targeting T cells can alleviate neurodegeneration and motor behavior impairment in animal models of PD. Therefore, we conclude that abnormal T cell-mediated immunity is a fundamental pathological process that may be a promising translational therapeutic target for Parkinson's disease.

Gestational Hypothyroxinemia Affects Its Offspring With a Reduced Suppressive Capacity Impairing the Outcome of the Experimental Autoimmune Encephalomyelitis

Hypothyroxinemia (Hpx) is a thyroid hormone deficiency (THD) condition highly frequent during pregnancy, which although asymptomatic for the mother, it can impair the cognitive function of the offspring. Previous studies have shown that maternal hypothyroidism increases the severity of experimental autoimmune encephalomyelitis (EAE), an autoimmune disease model for multiple sclerosis (MS). Here, we analyzed the immune response after EAE induction in the adult offspring gestated in Hpx. Mice gestated in Hpx showed an early appearance of EAE symptoms and the increase of all parameters of the disease such as: the pathological score, spinal cord demyelination, and immune cell infiltration in comparison to the adult offspring gestated in euthyroidism. Isolated CD4⁺CD25⁺ T cells from spleen of the offspring gestated in Hpx that suffer EAE showed reduced capacity to suppress proliferation of effector T cells (T_Eff) after being stimulated with anti-CD3 and anti-CD28 antibodies. Moreover, adoptive transfer experiments of CD4⁺CD25⁺ T cells from the offspring gestated in Hpx suffering EAE to mice that were induced with EAE showed that the receptor mice suffer more intense EAE pathological score. Even though, no significant differences were detected in the frequency of T_reg cells and IL-10 content in the blood, spleen, and brain between mice gestated in Hpx or euthyroidism, T cells CD4⁺CD25⁺ from spleen have reduced capacity to differentiate in vitro to T_reg and to produce IL-10. Thus, our data support the notion that maternal Hpx can imprint the immune response of the offspring suffering EAE probably due to a reduced capacity to trigger suppression. Such “imprints” on the immune system could contribute to explaining as to why adult offspring gestated in Hpx suffer earlier and more intense EAE.

Inflammation and autoimmunity in pulmonary hypertension: is there a role for endothelial adhesion molecules? (2017 Grover Conference Series)

While pulmonary hypertension (PH) has traditionally not been considered as a disease that is directly linked to or, potentially, even caused by inflammation, a rapidly growing body of evidence has demonstrated the accumulation of a variety of inflammatory and immune cells in PH lungs, in and around the wall of remodeled pulmonary resistance vessels and in the vicinity of plexiform lesions, respectively. Concomitantly, abundant production and release of various inflammatory mediators has been documented in both PH patients and experimental models of PH. While these findings unequivocally demonstrate an inflammatory component in PH, they have fueled an intense and presently ongoing debate as to the nature of this inflammatory aspect: is it a mere bystander of or response to the actual disease process, or is it a pathomechanistic contributor or potentially even a trigger of endothelial injury, smooth muscle hypertrophy and hyperplasia, and the resulting lung vascular remodeling? In this review, we will discuss the present evidence for an inflammatory component in PH disease with a specific focus on the potential role of the endothelium in this scenario and highlight future avenues of experimental investigation which may lead to novel therapeutic interventions.

IL-10-Producing B Cells Regulate T Helper Cell Immune Responses during 1,3-β-Glucan-Induced Lung Inflammation

With the rapid development of industry and farm, fungi contamination widely exists in occupational environment. Inhalation of fungi-contaminated organic dust results in hypersensitivity pneumonitis. 1,3-β-Glucan is a major cell wall component of fungus and is considered as a biomarker of fungi exposure. Current studies showed that 1,3-β-glucan exposure induced lung inflammation, which involved uncontrolled T helper (Th) cell immune responses, such as Th1, Th2, Th17, and regulatory T cell (Treg). A recently identified IL-10-producing B cells (B10) was reported in regulating immune homeostasis. However, its regulatory role in hypersensitivity pneumonitis is still subject to debate. In our study, we comprehensively investigated the role of B10 and the relationship between B10 and Treg in 1,3-β-glucan-induced lung inflammation. Mice with insufficient B10 exhibited more inflammatory cells accumulation and severer pathological inflammatory changes. Insufficient B10 led to increasing Th1, Th2, and Th17 responses and restricted Treg function. Depletion of Treg before the onset of inflammation could suppress B10. Whereas, Treg depletion only at the late stage of inflammation failed to affect B10. Our study demonstrated that insufficient B10 aggravated the lung inflammation mediated by dynamic shifts in Th immune responses after 1,3-β-glucan exposure. The regulatory function of B10 on Th immune responses might be associated with Treg and IL-10. Treg could only interact with B10 at an early stage.

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.

Role of IL-10-producing regulatory B cells in modulating T-helper cell immune responses during silica-induced lung inflammation and fibrosis

Silicosis is characterized by chronic lung inflammation and fibrosis, which are seriously harmful to human health. Previous research demonstrated that uncontrolled T-helper (Th) cell immune responses were involved in the pathogenesis of silicosis. Lymphocytes also are reported to have important roles. Existing studies on lymphocyte regulation of Th immune responses were limited to T cells, such as the regulatory T (Treg) cell, which could negatively regulate inflammation and promote the process of silicosis. However, other regulatory subsets in silicosis have not been investigated in detail, and the mechanism of immune homeostasis modulation needs further exploration. Another regulatory lymphocyte, the regulatory B cell, has recently drawn increasing attention. In this study, we comprehensively showed the role of IL-10-producing regulatory B cell (B10) in a silicosis model of mice. B10 was inducible by silica instillation. Insufficient B10 amplified inflammation and attenuated lung fibrosis by promoting the Th1 immune response. Insufficient B10 clearly inhibited Treg and decreased the level of IL-10. Our study indicated that B10 could control lung inflammation and exacerbate lung fibrosis by inhibiting Th1 response and modulating the Th balance. The regulatory function of B10 could be associated with Treg induction and IL-10 secretion.

Regulatory T and B lymphocytes in a spontaneous autoimmune polyneuropathy

B7-2(-/-) non-obese diabetic (NOD) mice develop a spontaneous autoimmune polyneuropathy (SAP) that mimics the progressive form of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). In this study, we focused on the role of regulatory T cells (Tregs ) and regulatory B cells (Bregs ) in SAP. We found that deletion of B7-2 in female NOD mice led to a lower frequency and number of Tregs and Bregs in spleens and lymph nodes. Tregs but not Bregs suppressed antigen-stimulated splenocyte proliferation, whereas Bregs inhibited the T helper type 1 (Th1) cytokine response. Both Tregs and Bregs induced an increase in CD4(+) interleukin (IL)-10(+) cells, although less effectively in the absence of B7-2. Adoptive transfer studies revealed that Tregs , but not Bregs , suppressed SAP, while Bregs attenuated disease severity when given prior to symptom onset. B cell deficiency in B cell-deficient (muMT)/B7-2(-/-) NOD mice prevented the development of SAP, which would indicate that the pathogenic role of B cells predominates over its regulatory role in this model. We conclude that Bregs and Tregs control the immunopathogenesis and progression of SAP in a non-redundant fashion, and that therapies aimed at expansion of Bregs and Tregs may be an effective approach in autoimmune neuropathies.

A regulatory CD9(+) B-cell subset inhibits HDM-induced allergic airway inflammation

BACKGROUND

Exposure to respiratory allergens triggers airway hyperresponsiveness and inflammation characterized by the expansion of TH 2 cells and the production of allergen specific IgE. Allergic asthma is characterized by an alteration in immune regulatory mechanisms leading to an imbalance between pro- and anti-inflammatory components of the immune system.

AIMS

Recently B cells have been described as central regulators of exacerbated inflammation, notably in the case of autoimmunity. However, to what extent these cells can regulate airway inflammation and asthma remains to be elucidated.

MATERIALS & METHODS

We took advantage of a allergic asthma model in mice induced by percutaneous sensitization and respiratory challenge with an extract of house dust mite.

RESULTS

In this study, we showed that the induction of allergic asthma alters the homeostasis of IL-10(+) Bregs and favors the production of inflammatory cytokines by B cells. Deeper transcriptomic and phenotypic analysis of Bregs revealed that they were enriched in a CD9(+) B cell subset. In asthmatic mice the adoptive transfer of CD9(+) B cells normalized airway inflammation and lung function by inhibiting TH 2- and TH 17-driven inflammation in an IL-10-dependent manner, restoring a favorable immunological balance in lung tissues. Indeed we further showed that injection of CD9(+) Bregs controls the expansion of lung effector T cells allowing the establishment of a favorable regulatory T cells/effector T cells ratio in lungs.

CONCLUSION

This finding strengthens the potential for Breg-targeted therapies in allergic asthma.

Regulatory T cells in B-cell-deficient and wild-type mice differ functionally and in expression of cell surface markers

NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) with chronic inflammation of thyroids by T and B cells. B-cell deficient (B(-/-) ) mice are resistant to SAT but develop SAT if regulatory T (Treg) cells are transiently depleted. We established a transfer model using splenocytes from CD28(-/-)  B(-/-) mice (effector cells and antigen-presenting cells) cultured with or without sorted Treg cells from Foxp3-GFP wild-type (WT) or B(-/-) mice. After transfer to mice lacking T cells, mice given Treg cells from B(-/-) mice had significantly lower SAT severity scores than mice given Treg cells from WT mice, indicating that Treg cells in B(-/-) mice are more effective suppressors of SAT than Treg cells in WT mice. Treg cells from B(-/-) mice differ from WT Treg cells in expression of CD27, tumour necrosis factor receptor (TNFR) II p75, and glucocorticoid-induced TNFR-related protein (GITR). After transient depletion using anti-CD25 or diphtheria toxin, the repopulating Treg cells in B(-/-) mice lack suppressor function, and expression of CD27, GITR and p75 is like that of WT Treg cells. If B(-/-) Treg cells develop with B cells in bone marrow chimeras, their phenotype is like that of WT Treg cells. Addition of B cells to cultures of B(-/-) Treg and T effector cells abrogates their suppressive function and their phenotype is like that of WT Treg cells. These results establish for the first time that Treg cells in WT and B(-/-) mice differ both functionally and in expression of particular cell surface markers. Both properties are altered after transient depletion and repopulation of B(-/-) Treg cells, and by the presence of B cells during Treg cell development or during interaction with effector T cells.

B10 cells: a functionally defined regulatory B cell subset

B cells are commonly thought to enhance inflammatory immune responses. However, specific regulatory B cell subsets recently were identified that downregulate adaptive and innate immunity, inflammation, and autoimmunity through diverse molecular mechanisms. In both mice and humans, a rare, but specific, subset of regulatory B cells is functionally characterized by its capacity to produce IL-10, a potent inhibitory cytokine. For clarity, this regulatory B cell subset has been labeled as B10 cells, because their ability to downregulate immune responses and inflammatory disease is fully attributable to IL-10, and their absence or loss exacerbates disease symptoms in mouse models. This review preferentially focuses on what is known about mouse B10 cell development, phenotype, and effector function, as well as on mechanistic studies that demonstrated their functional importance during inflammation, autoimmune disease, and immune responses.

The Gateway Reflex, which is mediated by the inflammation amplifier, directs pathogenic immune cells into the CNS

The brain-blood barrier (BBB) tightly limits immune cell migration into the central nervous system (CNS), avoiding unwanted inflammation under the normal state. However, immune cells can traverse the BBB when inflammation occurs within the CNS, suggesting a certain signal that creates a gateway that bypasses the BBB might exist. We revealed the inflammation amplifier as a mechanism of this signal, and identified dorsal vessels of the fifth lumber (L5) spinal cord as the gateway. The inflammation amplifier is driven by a simultaneous activation of NF-κB and STATs in non-immune cells, causing the production of a large amount of inflammatory chemokines to open the gateway at L5 vessels. It was found that the activation of the amplifier can be modulated by neural activation and artificially operated by electric pulses followed by establishment of new gateways, Gateway Reflex, at least in mice. Furthermore, genes required for the inflammation amplifier have been identified and are highly associated with various inflammatory diseases and disorders in the CNS. Thus, physical and/or pharmacological manipulation of the inflammation amplifier holds therapeutic value to control neuro-inflammation.

Single dose of glycoengineered anti-CD19 antibody (MEDI551) disrupts experimental autoimmune encephalomyelitis by inhibiting pathogenic adaptive immune responses in the bone marrow and spinal cord while preserving peripheral regulatory mechanisms

Plasma cells and the autoreactive Abs they produce are suspected to contribute to the pathogenesis of multiple sclerosis, but recent attempts to target these components of humoral immunity have failed. MEDI551, an anti-CD19 Ab that depletes mature B cells including plasma cells may offer a compelling alternative that reduces pathogenic adaptive immune responses while sparing regulatory mechanisms. Indeed, our data demonstrate that a single dose of MEDI551, given before or during ongoing experimental autoimmune encephalomyelitis, disrupts development of the disease. Leukocyte infiltration into the spinal cord is significantly reduced, as well as short-lived and long-lived autoreactive CD138(+) plasma cells in the spleen and bone marrow, respectively. In addition, potentially protective CD1d(hi)CD5(+) regulatory B cells show resistance to depletion, and myelin-specific Foxp3(+) regulatory T cells are expanded. Taken together, these results demonstrate that MEDI551 disrupts experimental autoimmune encephalomyelitis by inhibiting multiple proinflammatory components whereas preserving regulatory populations.

CD1d(hi)CD5+ B cells expanded by GM-CSF in vivo suppress experimental autoimmune myasthenia gravis

IL-10-competent subset within CD1d(hi)CD5(+) B cells, also known as B10 cells, has been shown to regulate autoimmune diseases. Whether B10 cells can prevent or suppress the development of experimental autoimmune myasthenia gravis (EAMG) has not been studied. In this study, we investigated whether low-dose GM-CSF, which suppresses EAMG, can expand B10 cells in vivo, and whether adoptive transfer of CD1d(hi)CD5(+) B cells would prevent or suppress EAMG. We found that treatment of EAMG mice with low-dose GM-CSF increased the proportion of CD1d(hi)CD5(+) B cells and B10 cells. In vitro coculture studies revealed that CD1d(hi)CD5(+) B cells altered T cell cytokine profile but did not directly inhibit T cell proliferation. In contrast, CD1d(hi)CD5(+) B cells inhibited B cell proliferation and its autoantibody production in an IL-10-dependent manner. Adoptive transfer of CD1d(hi)CD5(+) B cells to mice could prevent disease, as well as suppress EAMG after disease onset. This was associated with downregulation of mature dendritic cell markers and expansion of regulatory T cells resulting in the suppression of acetylcholine receptor-specific T cell and B cell responses. Thus, our data have provided significant insight into the mechanisms underlying the tolerogenic effects of B10 cells in EAMG. These observations suggest that in vivo or in vitro expansion of CD1d(hi)CD5(+) B cells or B10 cells may represent an effective strategy in the treatment of human myasthenia gravis.

B cells with immune-regulating function in transplantation

In transplantation, the contribution of B cells to the rejection or acceptance of the allograft is a topic of major interest. The presence of donor-specific antibodies in transplant recipients is often associated with decreased graft function and rejection, clearly indicating a pathogenetic role of B cells in transplantation. However, data from studies in humans and rodents suggest that under certain conditions, B cells have the capacity to control or regulate the immune response to a transplanted organ. Although a great deal of attention has been focused on B cells in human and murine models of autoimmunity, our understanding of the role of these cells in transplantation is limited at present. Indeed, results in this setting are controversial and seem to depend on the model system used or the clinical situation studied. Here, we review the current understanding of the various phenotypes and roles that have been associated with immune-regulating B cells. We also discuss the mechanisms employed by subsets of these regulatory B cells to control the immune response in transplant recipients and in animal models of transplantation.

B-type suppression: a role played by "regulatory B cells" or "regulatory plasma cells"?

B-cell depletion can improve disease in some patients with rheumatoid arthritis or multiple sclerosis, indicating the pathogenic contribution of B cells to autoimmunity. However, studies in mice have demonstrated that B cells have immunosuppressive functions as well, with IL-10 being a critical mediator of B-cell-mediated suppression. IL-10-secreting B cells have been shown to promote disease remission in some mouse models of autoimmune disorders. Human B cells also produce IL-10, and evidence is accumulating that human IL-10-producing B cells might inhibit immunity. There is considerable interest in identifying the phenotype of B cells providing IL-10 in a suppressive manner, which would facilitate the analysis of the molecular mechanisms controlling this B-cell property. Here, we review current knowledge on the B-cell subpopulations found to provide suppressive functions in mice, considering both the pathological context in which they were identified and the signals that control their induction. We discuss the phenotype of B cells that have IL-10-dependent regulatory activities in mice, which leads us to propose that antibody-secreting cells are, in some cases at least, the major source of B-cell-derived regulatory IL-10 in vivo. Anti-inflammatory cytokine production by antibody-secreting cells offers a novel mechanism for the coordination of innate and humoral immune responses.

IL-35-producing B cells are critical regulators of immunity during autoimmune and infectious diseases

B lymphocytes have critical roles as positive and negative regulators of immunity. Their inhibitory function has been associated primarily with interleukin 10 (IL-10) because B-cell-derived IL-10 can protect against autoimmune disease and increase susceptibility to pathogens. Here we identify IL-35-producing B cells as key players in the negative regulation of immunity. Mice in which only B cells did not express IL-35 lost their ability to recover from the T-cell-mediated demyelinating autoimmune disease experimental autoimmune encephalomyelitis (EAE). In contrast, these mice displayed a markedly improved resistance to infection with the intracellular bacterial pathogen Salmonella enterica serovar Typhimurium as shown by their superior containment of the bacterial growth and their prolonged survival after primary infection, and upon secondary challenge, compared to control mice. The increased immunity found in mice lacking IL-35 production by B cells was associated with a higher activation of macrophages and inflammatory T cells, as well as an increased function of B cells as antigen-presenting cells (APCs). During Salmonella infection, IL-35- and IL-10-producing B cells corresponded to two largely distinct sets of surface-IgM(+)CD138(hi)TACI(+)CXCR4(+)CD1d(int)Tim1(int) plasma cells expressing the transcription factor Blimp1 (also known as Prdm1). During EAE, CD138(+) plasma cells were also the main source of B-cell-derived IL-35 and IL-10. Collectively, our data show the importance of IL-35-producing B cells in regulation of immunity and highlight IL-35 production by B cells as a potential therapeutic target for autoimmune and infectious diseases. This study reveals the central role of activated B cells, particularly plasma cells, and their production of cytokines in the regulation of immune responses in health and disease.

Interleukin-10-producing B cells and the regulation of immunity

B cells are usually considered primarily for their unique capacity to produce antibodies after differentiation into plasma cells. In addition to their roles as antibody-producing cells, it has become apparent during the last 10 years that B cells also perform important functions in immunity through the production of cytokines. In particular, it was shown that B cells could negatively regulate immunity through provision of interleukin (IL)-10 during autoimmune and infectious diseases in mice. Here, we review data on the suppressive functions of B cells in mice with particular emphasis on the signals controlling the acquisition of such suppressive functions by B cells, the phenotype of the B cells involved in the negative regulation of immunity, and the processes targeted by this inhibitory circuit. Finally, we discuss the possibility that human B cells might also perform similar inhibitory functions through the provision of IL-10, and review data suggesting that such B cell-mediated regulatory activities might be impaired in patients with autoimmune diseases.

Peripheral CD4(+) T-cell tolerance is induced in vivo by rare antigen-bearing B cells in follicular, marginal zone, and B-1 subsets

B cells are efficient APCs when they internalize antigen via BCR-mediated uptake. Adoptively transferred antigen-presenting B cells can induce T-cell tolerance to foreign and self antigens; however, it is unknown whether endogenous B cells presenting self-peptides interact with naïve T cells and contribute to peripheral T-cell self-tolerance. Moreover, the relative abilities of mature B-cell subsets to induce T-cell tolerance have not been examined. To address these questions, we created a new mouse model wherein a very small fraction of B cells expresses an antigen transgene that cannot be transferred to other APCs. We limited antigen expression to follicular, marginal zone, or B-1 B-cell subsets and found that small numbers of each subset interacted with naïve antigen-specific T cells. Although antigen expressed by B-1 B cells induced the most T-cell division, divided T cells subsequently disappeared from secondary lymphoid tissues. Independent of which B-cell subset presented antigen, the remaining T cells were rendered hypo-responsive, and this effect was not associated with Foxp3 expression. Our data show that physiologically relevant proportions of B cells can mediate peripheral T-cell tolerance, and suggest that the mechanisms of tolerance induction might differ among follicular, marginal zone, and B-1 B-cell subsets.

Dynamic cross-regulation of antigen-specific effector and regulatory T cell subpopulations and microglia in brain autoimmunity

Background

Multiple Sclerosis (MS) is considered a T-cell-mediated autoimmune disease with a prototypical oscillatory behavior, as evidenced by the presence of clinical relapses. Understanding the dynamics of immune cells governing the course of MS, therefore, has many implications for immunotherapy. Here, we used flow cytometry to analyze the time-dependent behavior of antigen-specific effector (T_eff) and regulatory (T_reg) T cells and microglia in mice model of MS, Experimental Autoimmune Encephalomyelitis (EAE), and compared the observations with a mathematical cross-regulation model of T-cell dynamics in autoimmune disease.

Results

We found that T_eff and T_reg cells specific to myelin olygodendrocyte glycoprotein (MOG) developed coupled oscillatory dynamics with a 4- to 5-day period and decreasing amplitude that was always higher for the T_eff populations, in agreement with the mathematical model. Microglia activation followed the oscillations of MOG-specific T_eff cells in the secondary lymphoid organs, but they were activated before MOG-specific T-cell peaks in the CNS. Finally, we assessed the role of B-cell depletion induced by anti-CD20 therapy in the dynamics of T cells in an EAE model with more severe disease after therapy. We observed that B-cell depletion decreases T_eff expansion, although its oscillatory behavior persists. However, the effect of B cell depletion was more significant in the T_reg population within the CNS, which matched with activation of microglia and worsening of the disease. Mathematical modeling of T-cell cross-regulation after anti-CD20 therapy suggests that B-cell depletion may influence the dynamics of T cells by fine-tuning their activation.

Conclusions

The oscillatory dynamics of T-cells have an intrinsic origin in the physiological regulation of the adaptive immune response, which influences both disease phenotype and response to immunotherapy.

Adaptive immune responses in CNS autoimmune disease: mechanisms and therapeutic opportunities

The processes underlying autoimmune CNS inflammation are complex, but key roles for autoimmune lymphocytes seem inevitable, based on clinical investigations in multiple sclerosis (MS) and related diseases such as neuromyelitis optica, together with the known pathogenic activity of T cells in experimental autoimmune encephalomyelitis (EAE) models. Despite intense investigation, the details of etiopathology in these diseases have been elusive. Here we describe recent advances in the rodent models that begin to allow a map of pathogenic and protective immunity to be drawn. This map might illuminate previous successful and unsuccessful therapeutic strategies targeting particular pathways, whilst also providing better opportunities for the future, leading to tailored intervention based on understanding the quality of each individual's autoimmune response.

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.

Decreased levels of circulating CD4+CD25+Foxp3+ regulatory T cells in patients with primary antiphospholipid syndrome

INTRODUCTION

CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cell dysfunction has been documented in various autoimmune disorders, but not in antiphospholipid syndrome (APS) so far.

METHODS

In this cross-sectional study, we aim to investigate CD4(+)CD25(+)Foxp3(+) Treg cells, CD3(+)CD19(-) T cells and CD3(-)CD19(+) B cells in patients with primary APS and healthy controls. Cell subtypes were immunophenotyped using specific monoclonal antibodies (anti-CD3 CY5, anti-CD4 FITC, anti-CD25, anti-Foxp3, anti-CD19 PE) and flow cytometry.

RESULTS

Twenty patients with APS and 20 age- and sex-matched controls were studied. The percentage of total lymphocytes, activated Th cells (CD4+CD25+), Treg cells and CD3(-)CD19(+) B cells were found significantly lower in APS patients as compared to controls (all p < 0.05).

CONCLUSION

A dysfunction in CD4(+)CD25(+)Foxp3(+) Treg cells may represent one of the mechanisms leading to autoimmunity in APS patients. The decreased number of CD3(-)CD19(+) B cells of APS patients warrants further elucidation.

Regulatory B cells control T-cell autoimmunity through IL-21-dependent cognate interactions

B cells regulate immune responses by producing antigen-specific antibodies. However, specific B-cell subsets can also negatively regulate T-cell immune responses, and have been termed regulatory B cells. Human and mouse regulatory B cells (B10 cells) with the ability to express the inhibitory cytokine interleukin-10 (IL-10) have been identified. Although rare, B10 cells are potent negative regulators of antigen-specific inflammation and T-cell-dependent autoimmune diseases in mice. How B10-cell IL-10 production and regulation of antigen-specific immune responses are controlled in vivo without inducing systemic immunosuppression is unknown. Using a mouse model for multiple sclerosis, here we show that B10-cell maturation into functional IL-10-secreting effector cells that inhibit in vivo autoimmune disease requires IL-21 and CD40-dependent cognate interactions with T cells. Moreover, the ex vivo provision of CD40 and IL-21 receptor signals can drive B10-cell development and expansion by four-million-fold, and generate B10 effector cells producing IL-10 that markedly inhibit disease symptoms when transferred into mice with established autoimmune disease. The ex vivo expansion and reinfusion of autologous B10 cells may provide a novel and effective in vivo treatment for severe autoimmune diseases that are resistant to current therapies.