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

Exogenous binding immunoglobulin protein (BiP) enhance immune regulatory phenotype in ex-vivo Mtb infected PBMCs stratified based on QuantiFERON response

Even though anti-tuberculosis (TB) treatment is readily available, Mycobacterium tuberculosis (Mtb) infection continues to be a global threat with a high death rate recorded from a single infectious agent. This highlights the significance of developing new strategies to curb the growing Mtb infection cases. Host-directed therapies (HDT) offer a promising approach that includes both drug discovery and drug repurposing, aimed at identifying host targets and promoting immune cell populations that can lead to better infection outcomes. In this context, we investigated the potential of exogenous Binding Immunoglobulin Protein (BiP) to induce such changes ex-vivo using PBMCs from healthy (QFN-) and Mtb exposed (QFN+) individuals. We analysed cell surface expression and cytokine profiles across eight different stimulation conditions including human full-length BiP protein (20 μg/ml), TLR-9a (0.5 μM), BiP/TLR-9a combination, isoniazid (1 μM), H37Rv (MOI: 1: 10), and pooled bronchoalveolar lavage (BAL) samples collected at TB diagnosis (TBdx) and at month 6 (M6) of anti-TB treatment. Our results revealed that BiP-stimulated PBMCs showed a significant reduction of interleukin (IL)-10 secretion, along with increased IL-4, IL-5, IL-13, and soluble Fas-L (sFasL) secretion. We also observed that BiP stimulation enhanced the expression of membrane bound Fas-L (CD178) and IL5Ra (CD125) in B-cells isolated from both QFN- and QFN+ groups. Additionally, BiP exhibited a synergistic effect with TLR-9a, further boosting this co-expression. Moreover, we observed that BiP induced IL5Ra expression in both CD3+CD5lo and CD3+CD5hi T-cell populations. This study explores the effects of exogenous BiP on cell functionality and provides valuable insights into its potential to modulate host cell responses, which could be explored as a host-directed therapy for TB in the future.

When the allergy alarm bells toll: The role of Toll-like receptors in allergic diseases and treatment

Toll-like receptors of the human immune system are specialized pathogen detectors able to link innate and adaptive immune responses. TLR ligands include among others bacteria-, mycoplasma- or virus-derived compounds such as lipids, lipo- and glycoproteins and nucleic acids. Not only are genetic variations in TLR-related genes associated with the pathogenesis of allergic diseases, including asthma and allergic rhinitis, their expression also differs between allergic and non-allergic individuals. Due to a complex interplay of genes, environmental factors, and allergen sources the interpretation of TLRs involved in immunoglobulin E-mediated diseases remains challenging. Therefore, it is imperative to dissect the role of TLRs in allergies. In this review, we discuss i) the expression of TLRs in organs and cell types involved in the allergic immune response, ii) their involvement in modulating allergy-associated or -protective immune responses, and iii) how differential activation of TLRs by environmental factors, such as microbial, viral or air pollutant exposure, results in allergy development. However, we focus on iv) allergen sources interacting with TLRs, and v) how targeting TLRs could be employed in novel therapeutic strategies. Understanding the contributions of TLRs to allergy development allow the identification of knowledge gaps, provide guidance for ongoing research efforts, and built the foundation for future exploitation of TLRs in vaccine design.

Deficiency in TLR4 impairs regulatory B cells production induced by Schistosome soluble egg antigen

Regulatory B cells (Bregs) producing IL-10 have negative regulatory function. Several studies have shown the important roles for Toll-like receptor 2 (TLR2), TLR4, and TLR9 ligation in the development of Bregs. We have reported that Schistosome soluble egg antigen (SEA) induced the production of Bregs. However, it remains unclear whether such activation is via the TLR pathway. The present study showed that IL-10 and TLR4 mRNA expression in spleen B cells of significantly increased in C57BL/10 J mice spleen B cells following SEA stimulation. The level of secreted IL-10 and IL-10⁺ B cell proportion decreased in spleen B cells derived from TLR4-deficient C57BL/10ScNJ (TLR4^-/^-) mice following SEA or LPS stimulation compared with C57BL/10 J mice. The CD1d^hiCD5⁺ B cells proportion decreased in spleen B cells of TLR4^-/^- mice following SEA stimulation compared with control mice. NF-κB, ERK, p38MAPK and JNK signal transduction inhibitors significantly suppressed IL-10 secretion in CD1d^hiCD5⁺ B cells induced by SEA or LPS. The phosphorylation levels of IκBα, p65, ERK, JNK and p38 were increased in CD1d^hiCD5⁺ B cell of C57BL/10 J mice treated with LPS or SEA. In conclusion, this study suggests that TLR4 plays a critical role in Bregs activation induced by SEA. And the TLR4-triggered NF-κB and MAPK pathways activation in CD1d^hiCD5⁺ B cells stimulated with SEA. The findings elucidated the mechanism of SEA induction of CD1d^hiCD5⁺ B cells and helped us to understand the immune regulation during Schistosoma japonicum infection.

Interaction Between Adipocytes and B Lymphocytes in Human Metabolic Diseases

Diseases associated with the disorders of carbohydrate and lipid metabolism are widespread in the modern world. Interaction between the cells of adipose tissue - adipocytes - and immune system cells is an essential factor in pathogenesis of such diseases. Long-term increase in the glucose and fatty acid levels leads to adipocyte hypertrophy and increased expression of pro-inflammatory cytokines and adipokines by these cells. As a result, immune cells acquire a pro-inflammatory phenotype, and new leukocytes are recruited. Inflammation of adipose tissue leads to insulin resistance and stimulates formation of atherosclerotic plaques and development of autoimmunity. New studies show that different groups of B lymphocytes play an essential role in regulation of adipose tissue inflammation. Decrease in the number of B-2 lymphocytes suppresses development of a number of metabolic diseases, whereas decreased numbers of the regulatory B lymphocytes and B-1 lymphocytes are associated with more severe pathology. Recent studies showed that adipocytes influence B lymphocyte activity both directly and by altering activity of other immune cells. These findings provide better understanding of the molecular mechanisms of human pathologies associated with impaired carbohydrate and lipid metabolism, such as type 2 diabetes mellitus.

The interaction between the soluble programmed death ligand-1 (sPD-L1) and PD-1+ regulator B cells mediates immunosuppression in triple-negative breast cancer

Accumulating evidence suggests that regulatory B cells (Bregs) play important roles in inhibiting the immune response in tumors. Programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) are important molecules that maintain the balance of the immune response and immune tolerance. This study aims to evaluate the soluble form of PD-L1 and its function in inducing the differentiation of B lymphocytes, investigate the relationship between soluble PD-L1 (sPD-L1) and B-cell subsets, and explore the antitumor activity of T lymphocytes after PD-L1 blockade in coculture systems. In an effort to explore the role of sPD-L1 in human breast cancer etiology, we examined the levels of sPD-L1 and interleukin-10 (IL-10) in the serum of breast tumor patients and the proportions of B cells, PD-1⁺ B cells, Bregs, and PD-1⁺ Bregs in the peripheral blood of patients with breast tumors and assessed their relationship among sPD-L1, IL-10, and B-cell subsets. The levels of sPD-L1 and IL-10 in serum were found to be significantly higher in invasive breast cancer (IBCa) patients than in breast fibroadenoma (FIBma) patients. Meanwhile, the proportions and absolute numbers of Bregs and PD-1⁺ Bregs in the peripheral blood of IBCa patients were significantly higher than those of FIBma patients. Notably, they were the highest in triple-negative breast cancer (TNBC) among other subtypes of IBCa. Positive correlations of sPD-L1 and IL-10, IL-10 and PD-1⁺ Bregs, and also sPD-L1 and PD-1⁺ Bregs were observed in IBCa. We further demonstrated that sPD-L1 could induce Breg differentiation, IL-10 secretion, and IL-10 mRNA expression in a dose-dependent manner in vitro. Finally, the induction of regulatory T cells (T_regs) by Bregs was further shown to suppress the antitumor response and that PD-L1 blockade therapies could promote the apoptosis of tumor cells. Together, these results indicated that sPD-L1 could mediate the differentiation of Bregs, expand CD4⁺ T_regs and weaken the antitumor activity of CD4⁺ T cells. PD-L1/PD-1 blockade therapies might be a powerful therapeutic strategy for IBCa patients, particularly for TNBC patients with high level of PD-1⁺ Bregs.

Regulatory B Cell Therapy in Kidney Transplantation

In the context of kidney injury, the role of Bregs is gaining interest. In a number of autoimmune diseases, the number and/or the function of Bregs has been shown to be impaired or downregulated, therefore restoring their balance might be a potential therapeutic tool. Moreover, in the context of kidney transplantation their upregulation has been linked to tolerance. However, a specific marker or set of markers that define Bregs as a unique cell subset has not been found and otherwise multiple phenotypes of Bregs have been studied. A quest on the proper markers and induction mechanisms is now the goal of many researchers. Here we summarize the most recent evidence on the role of Bregs in kidney disease by describing the relevance of in vitro and in vivo Bregs induction as well as the potential use of Bregs as cell therapy agents in kidney transplantation.

Regulatory B Cells: Role in Type 1 Diabetes

Regulatory B cells (Bregs) have an anti-inflammatory role and can suppress autoimmunity, by employing both cytokine secretion and cell-contact mediated mechanisms. Numerous Breg subsets have been described and have overlapping phenotypes in terms of their immune expression markers or cytokine production. A hallmark feature of Bregs is the secretion of IL-10, although IL-35 and TGFβ−producing B cells have also been identified. To date, few reports have identified an impaired frequency or function of Bregs in individuals with type 1 diabetes; thus our understanding of the role played by these Breg subsets in the pathogenesis of this condition is limited. In this review we will focus on how regulatory B cells are altered in the development of type 1 diabetes, highlighting both frequency and function and discuss both human and animal studies.

Contact dermatitis

Contact dermatitis (CD) is among the most common inflammatory dermatological conditions and includes allergic CD, photoallergic CD, irritant CD, photoirritant CD (also called phototoxic CD) and protein CD. Occupational CD can be of any type and is the most prevalent occupational skin disease. Each CD type is characterized by different immunological mechanisms and/or requisite exposures. Clinical manifestations of CD vary widely and multiple subtypes may occur simultaneously. The diagnosis relies on clinical presentation, thorough exposure assessment and evaluation with techniques such as patch testing and skin-prick testing. Management is based on patient education, avoidance strategies of specific substances, and topical treatments; in severe or recalcitrant cases, which can negatively affect the quality of life of patients, systemic medications may be needed.

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.

Intricate Relationship Between Adaptive and Innate Immune System in Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a complex immunological allergic disease characterized by the interplay between the innate and adaptive immune system. Initially, the role of the innate immune system was believed to be confined to the initial sensitization phase, while adaptive immune reactions were linked with the advanced elicitation phase. However, recent data predicted a comparatively mixed and interdependent role of both immune systems throughout the disease progression. Therefore, the actual mechanisms of disease progression are more complex and interlinked. The aim of this review is to combine such findings that enhanced our understanding of the pathomechanisms of ACD. Here, we focused on the main cell types from both immune domains, which are involved in ACD, such as CD4+ and CD8+ T cells, B cells, neutrophils, and innate lymphoid cells (ILCs). Such insights can be useful for devising future therapeutic interventions for ACD.

Phenotypes, Functions, and Clinical Relevance of Regulatory B Cells in Cancer

In immune system, B cells are classically positive modulators that regulate inflammation and immune responses. Regulatory B cells (Bregs) are a subset of B cells which play crucial roles in various conditions, including infection, allergies, autoimmune diseases, transplantation, and tumors. Until now, unequivocal surface markers for Bregs still lack consensus, although numerous Breg subsets have been identified. Generally, Bregs exert their immunoregulatory functions mainly through cytokine secretion and intercellular contact. In the tumor microenvironment, Bregs suppress effector T cells, induce regulatory T cells and target other tumor-infiltrating immune cells, such as myeloid-derived suppressor cells, natural killer cells and macrophages, to hamper anti-tumor immunity. Meanwhile, the cross-regulations between Bregs and tumor cells often result in tumor escape from immunosurveillance. In addition, accumulating evidence suggests that Bregs are closely associated with many clinicopathological factors of cancer patients and might be potential biomarkers for accessing patient survival. Thus, Bregs are potential therapeutic targets for future immunotherapy in cancer patients. In this review, we will discuss the phenotypes, functions, and clinical relevance of Bregs in cancer.

Astilbin combined with lipopolysaccharide induces IL-10-producing regulatory B cells via the STAT3 signalling pathway

OBJECTIVES

Astilbin exerts immunoregulatory activities and plays anti-inflammatory effects in inflammation-associated diseases. IL-10-producing B cells are the major subset of regulatory B cells (Bregs) and inhibit inflammation and autoimmune diseases. This study aimed to analyse the inducing effect of astilbin on Bregs and investigate the involved molecular mechanisms.

METHODS

The frequencies and activities of IL-10-producing Bregs were observed using the co-treatment of astilbin and lipopolysaccharide (LPS) ex vivo. The protective effect of astilbin/LPS-induced Bregs on dextran sulphate sodium (DSS)-induced colitis was confirmed in vivo. The molecular signalling events of Breg induction were checked via Western blot. CD40^-/- and toll-like receptor (TLR) 4^-/- B cells were treated with astilbin/LPS to determine the modulatory role of CD40 or TLR4 on astilbin/LPS-induced Bregs.

RESULTS

Although astilbin alone could not affect Bregs, the co-treatment of astilbin and LPS remarkably induced CD19⁺ CD1d^hi and CD19⁺ TIM-1⁺ cells which produced IL-10 ex vivo. Colonic CD19⁺ CD1d^hi and CD19⁺ TIM-1⁺ cells were also increased in astilbin-treated mice with DSS-induced colitis. The adoptive transfer of CD19⁺ TIM-1⁺ cells pre-induced by astilbin/LPS directly suppressed the progression of DSS-induced colitis. Combined astilbin and LPS stimulated the STAT3 activation of CD19⁺ TIM-1⁺ cells but had no effects on SOCS3, AKT, NF-κB, Erk, JNK nor P38. Inhibiting the STAT3 phosphorylation of CD19⁺ TIM-1⁺ cells abolished Breg induction by astilbin/LPS. Furthermore, Breg induction was weakened in CD40^-/- B cells with the decrease in STAT3 activation, but had disappeared in TLR4^-/- B cells with no STAT3 activation, thereby confirming the indispensable role of TLR4 signalling in the induction of IL-10-producing Bregs.

CONCLUSIONS

This study reports the new immunoregulatory role of astilbin for promoting IL-10-producing B cells and suggests the possible use of astilbin in the therapy of inflammatory diseases.

Activation of IL-10+ B cells: A novel immunomodulatory mechanism for therapeutic bacterial suspensions

Objectives:

Bacterial components are used to improve immune responses in patients with respiratory infections. Pharmacological formulations of bacterial components include a mixture of bacterial antigens, some of which are complete inactivated bacteria, that is, named bacterial suspensions; while others are fragments of bacteria, which are presented as bacterial lysates. Although bacterial lysates have been broadly used as immune-stimulators, the biological support for the therapeutic effectiveness of bacterial suspension has not yet been studied. Thus, the aim of our study was to investigate the immunological activity induced by bacterial suspension.

Methods:

This work was an exploratory translational study. Peripheral blood mononuclear cells were obtained from healthy donors and cultured in time–dose dependent assays with a commercial bacterial suspension. Flow cytometry was used for phenotypic analysis and for determining soluble cytokines in culture supernatants.

Results:

We observed that bacterial suspension activates B cells in a dose-dependent manner. Peripheral blood mononuclear cells were able to secrete IL-6 and IL-10 after 24 h of bacterial suspension stimulation. TLR2 expression was observed mainly on CD19+ CD38^Lo B cells after 72 h of culture; remarkably, most of the TLR2+ CD19+ cells were also IL-10+.

Conclusion:

Our findings suggest that bacterial suspension induces the activation of B cell subsets as well as the secretion of IL-6 and IL-10. Expression of TLR2 on CD19+ cells could act as an activation loop of IL-10+ B regulatory cells. The clinical implications of these findings are discussed at the end of this article.

IL-10-producing regulatory B cells exhibit functional defects and play a protective role in severe endotoxic shock

Dysregulated host immune homeostasis in sepsis is life-threatening even after a successfully treated bacterial infection. Lipopolysaccharide (LPS) is an endotoxin that is a major contributor to the aberrant immune responses and endotoxic shock in gram-negative bacterial sepsis. However, the current knowledge of the role of B cells in endotoxic shock is limited. Here, we report that CD1d expression in B cells and the percentage of CD5⁺CD1d^hi regulatory B (Breg) cells decreased in a mouse model of endotoxic shock. Interestingly, IL-10 but not FasL expression in CD5⁺CD1d^hi Breg cells in response to endotoxin was dramatically reduced in severe septic shock mice, and the regulatory function of CD5⁺CD1d^hi Breg cells in vitro to control the Th1 response was also diminished. Adoptive transfer of CD5⁺CD1d^hi Breg cells from healthy WT mice but not IL-10 deficient mice downregulated the IFN-γ secretion in CD4⁺ T cells and conferred protection against severe endotoxic shock in vivo. Our findings demonstrate the change and notable therapeutic potential of IL-10-producing Breg cells in endotoxic shock.

Type I interferons provide additive signals for murine regulatory B cell induction by Schistosoma mansoni eggs

The helminth Schistosoma mansoni (S. mansoni) induces a network of regulatory immune cells, including interleukin (IL)-10-producing regulatory B cells (Bregs). However, the signals required for the development and activation of Bregs are not well characterized. Recent reports suggest that helminths induce type I interferons (IFN-I), and that IFN-I drive the development of Bregs in humans. We therefore assessed the role of IFN-I in the induction of Bregs by S. mansoni. Mice chronically infected with S. mansoni or i.v. injected with S. mansoni soluble egg antigen (SEA) developed a systemic IFN-I signature. Recombinant IFN-α enhanced IL-10 production by Bregs stimulated with S. mansoni SEA in vitro, while not activating Bregs by itself. IFN-I signaling also supported ex vivo IL-10 production by SEA-primed Bregs but was dispensable for activation of S. mansoni egg-induced Bregs in vivo. These data indicate that although IFN-I can serve as a coactivator for Breg IL-10 production, they are unlikely to participate in the development of Bregs in response to S. mansoni eggs.

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

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

APRIL Induces a Novel Subset of IgA+ Regulatory B Cells That Suppress Inflammation via Expression of IL-10 and PD-L1

Regulatory B cells (Bregs) are immunosuppressive cells that modulate immune responses through multiple mechanisms. The signals required for the differentiation and activation of these cells remain still poorly understood. We have already shown that overexpression of A PRoliferation-Inducing Ligand (APRIL) reduces the incidence and severity of collagen-induced arthritis (CIA) in mice. Furthermore, we have described that APRIL, but not BAFF, promoted IL-10 production and regulatory functions in human B cells. Therefore, we hypothesized that APRIL, but not BAFF, may be involved in the induction and/or activation of IL-10 producing Bregs that suppress inflammatory responses in vitro and in vivo. Here, we describe that APRIL promotes the differentiation of naïve human B cells to IL-10-producing IgA⁺ B cells. These APRIL-induced IgA⁺ B cells display a Breg phenotype and inhibit T cell and macrophage responses through IL-10 and PD-L1. Moreover, APRIL-induced IL-10 producing Bregs suppress inflammation in vivo in experimental autoimmune encephalitis (EAE) and contact hypersensitivity (CHS) models. Finally, we showed a strong correlation between APRIL and IL-10 in the inflamed synovial tissue of inflammatory arthritis patients. Collectively, these observations indicate the potential relevance of this novel APRIL-induced IgA⁺ Breg population for immune homeostasis and immunopathology.

IgM+CD27+ B cells possessed regulatory function and represented the main source of B cell-derived IL-10 in the synovial fluid of osteoarthritis patients

Synovial inflammation is observed in patients with osteoathritis (OA) and likely contributed to its exacerbation. Regulatory B (Breg) cells are shown to suppress inflammation in various diseases, including rheumatoid arthritis (RA). To examine whether Breg cells also participated in OA, we examined the synovial fluid from OA patients, and compared with that in RA patients. In OA synovial fluid, IL-10-producing B cells were present directly ex vivo and were increased upon stimulation, indicating that B cells were a source of IL-10 directly at the affected site of OA patients. Interestingly, the frequency of IL-10⁺ cells in synovial B cells was higher in OA patients than in RA patients, but the total number of IL-10⁺ B cells in OA was lower than that in RA, suggesting that OA patients presented lower B cell infiltration than RA patients. Phenotypical analysis demonstrated that the IL-10⁺ B cells were IgM⁺ and CD27⁺, but not CD24^hi or CD38^hi. To allow functional analysis of IgM⁺CD27⁺ B cells, the IgM⁺CD27⁺ B cells in the blood of OA patients were examined. These blood IgM⁺CD27⁺ B cells expressed more IL-10, but less CD80 and CD86 than non-IgM⁺CD27⁺ B cells. Blood IgM⁺CD27⁺ B cells suppressed the proliferation and IFN-γ expression of autologous T cells, and this effect could be reverted if IL-10 was inhibited. Furthermore, we found that patients with more severe OA presented lower levels of IL-10⁺ B cells in the synovial fluid. Together, our study described an IgM⁺CD27⁺ B cell subset in OA patients, which represented the major IL-10-secreting B cell type in the synovial fluid of OA patients and possessed regulatory function.

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 cell phenotype and mechanism of action: the impact of stimulating conditions

A diverse population of regulatory B (Breg) cells reportedly exhibits significant immunomodulatory effects in various models of inflammatory responses and infectious diseases caused by bacteria, viruses or parasites. Breg cells contribute to maintenance of homeostasis via IL-10 production and multiple IL-10-independent mechanisms. The current review describes various phenotypic and functional subsets of Breg cells in autoimmune and infectious diseases and discusses the impacts of experimental conditions that have been found to drive Breg cell differentiation.