Regulation of immunity and autoimmunity by B cells

Anti-inflammatory role of APRIL by modulating regulatory B cells in antigen-induced arthritis

APRIL (A Proliferation-Inducing Ligand), a member of the TNF superfamily, was initially described for its ability to promote proliferation of tumor cells in vitro. Moreover, this cytokine has been related to the pathogenesis of different chronic inflammatory diseases, such as rheumatoid arthritis. This study aimed to evaluate the ability of APRIL in regulating B cell-mediated immune response in the antigen-induced arthritis (AIA) model in mice. AIA was induced in previously immunized APRIL-transgenic (Tg) mice and their littermates by administration of antigen (mBSA) into the knee joints. Different inflammatory cell populations in spleen and draining lymph nodes were analyzed using flow cytometry and the assay was performed in the acute and chronic phases of the disease, while cytokine levels were assessed by ELISA. In the acute AIA, APRIL-Tg mice developed a less severe condition and a smaller inflammatory infiltrate in articular tissues when compared with their littermates. We also observed that the total cellularity of draining lymph nodes was decreased in APRIL-Tg mice. Flow cytometry analysis revealed an increase of CD19+IgM+CD5+ cell population in draining lymph nodes and an increase of CD19+CD21hiCD23hi (B regulatory) cells in APRIL-Tg mice with arthritis as well as an increase of IL-10 and CXCL13 production in vitro.

From neglect to spotlight: the underappreciated role of B cells in cutaneous inflammatory diseases

The skin, covering our entire body as its largest organ, manifests enormous complexities and a profound interplay of systemic and local responses. In this heterogeneous domain, B cells were considered strangers. Yet, recent studies have highlighted their existence in the skin and their distinct role in modulating cutaneous immunity across various immune contexts. Accumulating evidence is progressively shedding light on the significance of B cells in maintaining skin health and in skin disorders. Herein, we integrate current insights on the systemic and local contributions of B cells in three prevalent inflammatory skin conditions: Pemphigus Vulgaris (PV), Systemic Lupus Erythematosus (SLE), and Atopic Dermatitis (AD), underscoring the previously underappreciated importance of B cells within skin immunity. Moreover, we address the potential adverse effects of current treatments used for skin diseases, emphasizing their unintentional consequences on B cells. These comprehensive approaches may pave the way for innovative therapeutic strategies that effectively address the intricate nature of skin disorders.

CAR T-cell therapy in autoimmune diseases

Despite the tremendous progress in the clinical management of autoimmune diseases, many patients do not respond to the currently used treatments. Autoreactive B cells play a key role in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. B-cell-depleting monoclonal antibodies, such as rituximab, have poor therapeutic efficacy in autoimmune diseases, mainly due to the persistence of autoreactive B cells in lymphatic organs and inflamed tissues. The adoptive transfer of T cells engineered to target tumour cells via chimeric antigen receptors (CARs) has emerged as an effective treatment modality in B-cell malignancies. In the last 2 years treatment with autologous CAR T cells directed against the CD19 antigen has been introduced in therapy of autoimmune disease. CD19 CAR T cells induced a rapid and sustained depletion of circulating B cells, as well as in a complete clinical and serological remission of refractory systemic lupus erythematosus and dermatomyositis. In this paper, we discuss the evolving strategies for targeting autoreactive B cells via CAR T cells, which might be used for targeted therapy in autoimmune diseases.

Myeloid-derived suppressor cells cross-talk with B10 cells by BAFF/BAFF-R pathway to promote immunosuppression in cervical cancer

Immunosuppression induced by myeloid-derived suppressor cells (MDSCs) is one of the main obstacles to the efficacy of immunotherapy for cervical cancer. Recent studies on the immunosuppressive ability of MDSCs have primarily focused on T cells, but the effect of MDSCs on B cells function is still unclear. In a study of clinical specimens, we found that the accumulation of MDSCs in patients with cervical cancer was accompanied by high expression of B cell activating factor (BAFF) on the surface and high expression of interleukin (IL)-10-producing B cells (B10) in vivo. We found that the absence of BAFF could significantly inhibit tumor growth in a cervical cancer model using BAFF KO mice. Further studies showed that abundant MDSCs in cervical cancer induced B cells to differentiate into B10 cells by regulating BAFF which acted on the BAFF receptor (BAFF-R) of them. In this process, we found that a large amount of IL-10 secreted by B10 cells can activate STAT3 signaling pathway in MDSCs, and then form a positive feedback loop to promote the differentiation of B10 cells. Therefore, this study reveals a new mechanism of BAFF-mediated mutual immune regulation between MDSCs and B cells in the occurrence and development of cervical cancer.

The emerging role of regulatory cell-based therapy in autoimmune disease

Autoimmune disease, caused by unwanted immune responses to self-antigens, affects millions of people each year and poses a great social and economic burden to individuals and communities. In the course of autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and multiple sclerosis, disturbances in the balance between the immune response against harmful agents and tolerance towards self-antigens lead to an immune response against self-tissues. In recent years, various regulatory immune cells have been identified. Disruptions in the quality, quantity, and function of these cells have been implicated in autoimmune disease development. Therefore, targeting or engineering these cells is a promising therapeutic for different autoimmune diseases. Regulatory T cells, regulatory B cells, regulatory dendritic cells, myeloid suppressor cells, and some subsets of innate lymphoid cells are arising as important players among this class of cells. Here, we review the roles of each suppressive cell type in the immune system during homeostasis and in the development of autoimmunity. Moreover, we discuss the current and future therapeutic potential of each one of these cell types for autoimmune diseases.

Radon Improves Clinical Response in an Animal Model of Rheumatoid Arthritis Accompanied by Increased Numbers of Peripheral Blood B Cells and Interleukin-5 Concentration

Radon treatment is used as an established therapy option in chronic painful inflammatory diseases. While analgesic effects are well described, little is known about the underlying molecular effects. Among the suspected mechanisms are modulations of the anti-oxidative and the immune system. Therefore, we aimed for the first time to examine the beneficial effects of radon exposure on clinical outcome as well as the underlying mechanisms by utilizing a holistic approach in a controlled environment of a radon chamber with an animal model: K/BxN serum-induced arthritic mice as well as isolated cells were exposed to sham or radon irradiation. The effects on the anti-oxidative and the immune system were analyzed by flow-cytometry, qPCR or ELISA. We found a significantly improved clinical disease progression score in the mice, alongside significant increase of peripheral blood B cells and IL-5. No significant alterations were visible in the anti-oxidative system or regarding cell death. We conclude that neither cell death nor anti-oxidative systems are responsible for the beneficial effects of radon exposure in our preclinical model. Rather, radon slightly affects the immune system. However, more research is still needed in order to fully understand radon-mediated effects and to carry out reasonable risk-benefit considerations.

GILZ as a Regulator of Cell Fate and Inflammation

One of the human body’s initial responses to stress is the adrenal response, involving the release of mediators that include adrenaline and glucocorticoids (GC). GC are involved in controlling the inflammatory and immune response mechanisms. Of these, the molecular mechanisms that contribute to anti-inflammatory effects warrant more investigation. Previously, we found that GC induced GILZ (glucocorticoid-induced leucine zipper) quickly and widely in thymocytes, T lymphocytes, and other leukocytes. GILZ regulates the activation of cells and is an essential mediator of endogenous GC and the majority of GC anti-inflammatory effects. Further research in this regard could lead to the development of an anti-inflammatory treatment that yields the therapeutic outcomes of GC but without their characteristic adverse effects. Here, we examine the mechanisms of GILZ in the context of GC. Specifically, we review its role in the proliferation and differentiation of cells and in apoptosis. We also examine its involvement in immune cells (macrophages, neutrophils, dendritic cells, T and B lymphocytes), and in non-immune cells, including cancer cells. In conclusion, GILZ is an anti-inflammatory molecule that could mediate the immunomodulatory activities of GC, with less adverse effects, and could be a target molecule for designing new therapies to treat inflammatory diseases.

Immunomodulatory and immunoregulatory nanomedicines for autoimmunity

Autoimmune diseases, caused by cellularly and molecularly complex immune responses against self-antigens, are largely treated with broad-acting, non-disease-specific anti-inflammatory drugs. These compounds can attenuate autoimmune inflammation, but tend to impair normal immunity against infection and cancer, cannot restore normal immune homeostasis and are not curative. Nanoparticle (NP)- and microparticle (MP)-based delivery of immunotherapeutic agents affords a unique opportunity to not only increase the specificity and potency of broad-acting immunomodulators, but also to elicit the formation of organ-specific immunoregulatory cell networks capable of inducing bystander immunoregulation. Here, we review the various NP/MP-based strategies that have so far been tested in models of experimental and/or spontaneous autoimmunity, with a focus on mechanisms of action.

Impaired granzyme B-producing regulatory B cells in systemic lupus erythematosus

Granzyme B (GrB)-producing B cells are proposed to be a kind of regulatory B cells (Bregs) and have been revealed to be implicated in the pathogenesis of autoimmune diseases. Nevertheless, their role in SLE remains elusive. In this study, the frequencies of GrB-producing Bregs in peripheral blood of heathy control (HC) and systemic lupus erythematosus (SLE) were evaluated by flow cytometry, and their correlation with SLE patient clinical and immunological features were analyzed. The expression of GrB in HC and SLE B cells were also further detected by RT-qPCR analysis and ELISpot. The function of GrB-producing Bregs in HC and SLE patients was further investigated by in vitro CD4⁺ effector T cells-B cells co-culture assays with GrB blockade. We found that GrB-producing Bregs were significantly decreased in SLE patients and correlated with the clinical and immunological features. Moreover, these cells were functionally impaired under SLE circumstance. The negative correlation between GrB-producing Bregs and CD4⁺ T cells observed in healthy individuals disappeared in SLE patients. In vitro cell co-culture assay further showed that GrB-producing Bregs from SLE patients failed to suppress the Th1, Th2 and Th17 cell inflammatory responses, partially due to the dampened capacity of down-regulating TCR zeta and inducing T cell apoptosis. Taken together, these results revealed the disturbance of GrB-producing Bregs in SLE that might contribute to the disease initiation and progression.

Regulatory B Cells Involvement in Autoimmune Phenomena Occurring in Pediatric Graves' Disease Patients

Graves’s disease is the most common type of autoimmune hyperthyroidism. Numerous studies indicate different factors contributing to the onset of the disease. Despite years of research, the exact pathomechanism of Graves’ disease still remains unresolved, especially in the context of immune response. B cells can play a dual role in autoimmune reactions, on the one hand, as a source of autoantibody mainly targeted in the thyroid hormone receptor (TSHR) and, on the other, by suppressing the activity of proinflammatory cells (as regulatory B cells). To date, data on the contribution of Bregs in Graves’ pathomechanism, especially in children, are scarce. Here, we investigated the frequencies of Bregs before and during a methimazole therapy approach. We reported higher Foxp3+ and IL-10+ Breg levels with CD38- phenotype and reduced numbers of CD38 + Foxp3 + IL-10+ in pediatric Graves’ patients. In addition, selected Breg subsets were found to correlate with TSH and TRAb levels significantly. Noteworthy, certain subpopulations of Bregs were demonstrated as prognostic factors for methimazole therapy outcome. Our data demonstrate the crucial role of Bregs and their potential use as a biomarker in Graves’ disease management.

Interpreting Immunoregulation in Lung Fibrosis: A New Branch of the Immune Model

Immunostimulation is recognized as an important contribution in lung fibrosis in some animal models and patient subsets. With this review, we illustrate an additional scenario covering the possible implication of immunoregulation during fibrogenesis. Available animal and human data indicate that pulmonary fibrosis also includes diverse and discrete immunoregulating populations comprising regulatory lymphocytes (T and B regs) and myeloid cells (immunosuppressive macrophages and myeloid-derived suppressive cells; MDSC). They are initially recruited to limit the establishment of deleterious inflammation but participate in the development of lung fibrosis by producing immunoregulatory mediators (mainly TGF-β1 and IL-10) that directly or indirectly stimulate fibroblasts and matrix protein deposition. The existence of this silent immunoregulatory environment sustains an alternative mechanism of fibrosis that explains why in some conditions neither pro-inflammatory cytokine deficiency nor steroid and immunosuppressive therapies limit lung fibrosis. Therefore, the persistent presence of immunoregulation is an important parameter to consider for refining therapeutical strategies in lung fibrotic disorders under non-immunostimulatory conditions.

Pathogenesis and pathology of anti-neutrophil cytoplasmic antibody（ANCA）-associated vasculitis

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AAV is characterized by necrotizing small vessel vasculitis with positive serum ANCA.

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MPO/PR3-ANCA and neutrophils play central roles in AAV pathogenicity.

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Dysregulated complement system primes neutrophils.

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MPO-ANCA directly activates neutrophils to induce NETosis followed by releasing NETs.

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B cells, T cells, and dendritic cells also contribute to the pathogenicity of AAV.

Suppression of IL-23-mediated psoriasis-like inflammation by regulatory B cells

Psoriasis is an inflammatory cutaneous disease mediated by T-cell dependent immune responses; however, B cells are also considered to play an important role its development. Regulatory B cells (Bregs) regulate immune responses negatively through interleukin-10 (IL-10) production. This study aimed to investigate the role of Bregs in IL-23-mediated psoriasis-like inflammation in mice. Psoriasis-like inflammation was induced in B cell-specific phosphatase and tensin homolog (PTEN)-deficient mice, in which Bregs were significantly expanded, and in their controls, by intradermal injection of 20 μL phosphate-buffered saline (PBS) containing 0.5 μg rmIL-23 into one ear, every other day for 16 days. IL-23-mediated psoriasis-like inflammation was suppressed in B cell-specific PTEN-deficient mice along with decreased ear thickness and epidermal thickness on day 15. Moreover, adoptive transfer of B1 B cells suppressed IL-23-mediated psoriasis-like inflammation. rmIL-23-injected B cell-specific PTEN-deficient mice showed expanded regulatory T cells (Tregs) in the spleen and draining lymph nodes along with increased Bregs. Further, T helper (Th) 17 differentiation in the rmIL-23-injected ear was suppressed in B cell-specific PTEN-deficient mice. Overall, these results indicate that increased Bregs suppress IL-23-mediated psoriasis-like inflammation through Treg expansion and inhibition of Th17 differentiation. Thus, targeting Bregs may be a feasible treatment strategy for psoriasis.

The Multiple Functions of B Cells in Chronic HBV Infection

Chronic hepatitis B virus (HBV) infection is one of the main causes of liver diseases, of which the natural history and clinical outcomes are associated with the role of B cells. As humoral immune cells, B cells play a critical role in the process of anti-HBV antibody production. In addition, some studies have also characterized other B cell subsets involved in antigen presentation and regulating the immune response beyond antibody secretion. However, not all B cell subsets play a positive role in the immune response to chronic HBV infection, and various B cell subsets jointly mediate persistent HBV infection, tolerance, and liver damage. Thus, we further sought to elucidate the multiple functions of B cells to gain novel insight into the understanding of chronic hepatitis B (CHB) pathogenesis. We also reviewed the current immunotherapies targeting B cells to explore novel therapeutic interventions for the treatment of chronic HBV infection.

Regulatory B Cells and Their Cytokine Profile in HCV-Related Hepatocellular Carcinoma: Association with Regulatory T Cells and Disease Progression

Although regulatory B cells (Bregs) have been proven to play a suppressive role in autoimmune diseases, infections and different tumors, little is known regarding hepatocellular carcinoma (HCC), especially in hepatitis C-related settings. Herein, we analyzed the frequency of circulating Bregs, serum levels of IL-10, IL-35 and B-cell activating factor (BAFF) and investigated their association with regulatory T cells (Tregs) and disease progression in HCV-related HCC. For comparative purposes, four groups were enrolled; chronic HCV (CHC group, n = 35), HCV-related liver cirrhosis (HCV-LC group, n = 35), HCV-related HCC (HCV-HCC group, n = 60) and an apparently healthy control (Control-group, n = 20). HCC diagnosis and staging were in concordance with the Barcelona Clinic Liver Cancer (BCLC) staging system. Analysis of the percentage of Breg cells and peripheral lymphocyte subsets (Treg) was performed by flow cytometry. Serum cytokine levels of IL-10, IL-35 and B-cell activating factor (BAFF) were measured by ELISA. The frequency of Bregs was significantly higher in the HCV-HCC group compared to the other groups and controls. A significant increase was noted in late-HCC versus those in the early stages. The frequency of Bregs was positively correlated with Tregs, serum IL-10, IL-35 and BAFF. In conclusion, Peripheral Bregs were positively correlated with the frequency of Tregs, IL-10, IL-35 and BAFF, and may be associated with HCV-related HCC progression.

Biologics for Allergic Dermatologic Diseases

PURPOSE OF REVIEW

Atopic dermatitis (AD), chronic spontaneous urticaria (CSU), and allergic contact dermatitis (ACD) represent three important allergic dermatoses with many unmet therapeutic needs. The development of biologic agents has opened the door to both new treatment options and improved understanding of the underlying pathophysiology, both shared and unique for these entities. With several FDA-approved medications available and many more in development, the biologic revolution has begun for allergic dermatoses.

RECENT FINDINGS

This is a narrative review on the current state of pathomechanisms and appropriately targeted biologic agents for these three common allergic skin conditions. The importance of Th2 inflammation and the effect of inflammatory cytokines on the skin barrier may help explain the impressive efficacy of biologic agents, while maintaining relative safety. While some of the biologic agents show efficacy across multiple allergic dermatoses, more often it seems these more targeted pathways show accordingly precise efficacy. However, in each disease, multiple agents hold promise, and may be differentiated by safety and adverse effect profile rather than simply by efficacy. New understanding of the pathogenesis of the allergic dermatoses has ushered in a new era of biologic therapies. Competing mechanisms and molecules will continue to be developed and vetted in trials with hopes of continuously refined precision therapies with optimized safety and efficacy profiles.

B cells induced by Schistosoma japonicum infection display diverse regulatory phenotypes and modulate CD4+ T cell response

Background

The increased activity of regulatory B cells (Breg) is known to be involved in immunosuppression during helminth infection, which is characterized by inducing IL-10-producing Breg cells. However, the current knowledge of B cell subsets differentiation and IL-10-independent immunoregulatory mechanisms of B cells in schistosomiasis is insufficient.

Methods

BALB/c mice were percutaneously infected with cercariae for investigating the profile of B cell subsets during Schistosoma japonicum infection. B cells isolated from the spleen or peritoneal cavity were analyzed for the regulatory phenotype after stimulation with soluble egg antigens (SEA) in vitro. CD4⁺ T cells were then cocultured with B cells pretreated with or without anti-PD-L1 antibody for investigating the role of B cells from infected mice on regulating CD4⁺ T cells. Furthermore, the in vivo administration of anti-PD-L1 antibody was conducted to investigate the role of PD-L1 in regulating host immunity during infection.

Results

The percentages of peritoneal and splenic B-1a cells, as well as marginal zone B (MZB) cells were decreased at eight and twelve weeks after infection compared to those from uninfected mice. In splenic B cells, TGF-β expression was increased at eight weeks but declined at twelve weeks of infection, and PD-L1 expression was elevated at both eight and twelve weeks of infection. In addition, SEA stimulation in vitro significantly promoted the expression of IL-10 in peritoneal B cells and CD5 in splenic B cells, and the SEA-stimulated splenic and peritoneal B cells preferentially expressed PD-L1 and TGF-β. The splenic B cells from infected mice were able to suppress the function of Th1 and Th2 cells in vitro but to expand the expression of Tfh transcription factor Bcl6, which was further enhanced by blocking PD-L1 of B cells before co-cultivation. Moreover, Th2 response and Bcl6 expression in CD4⁺ T cells were also increased in vivo by blocking PD-L1 after infection, although the hepatic pathology was slightly influenced.

Conclusions

Our findings revealed that S. japonicum infection modulates the differentiation of B cell subsets that have the capability to affect the CD4⁺ T cell response. This study contributes to a better understanding of B cells immune response during schistosomiasis.

Antigen-dependent interactions between regulatory B cells and T cells at the T:B border inhibit subsequent T cell interactions with DCs

IL-10+ regulatory B cells (Bregs) inhibit immune responses in various settings. While Bregs appear to inhibit inflammatory cytokine expression by CD4+ T cells and innate immune cells, their reported impact on CD8+ T cells is contradictory. Moreover, it remains unclear which effects of Bregs are direct versus indirect. Finally, the subanatomical localization of Breg suppressive function and the nature of their intercellular interactions remain unknown. Using novel tamoxifen-inducible B cell-specific IL-10 knockout mice, we found that Bregs inhibit CD8+ T cell proliferation and inhibit inflammatory cytokine expression by both CD4+ and CD8+ T cells. Sort-purified Bregs from IL-10-reporter mice were adoptively transferred into wild-type hosts and examined by live-cell imaging. Bregs localized to the T:B border, specifically entered the T cell zone, and made more frequent and longer contacts with both CD4+ and CD8+ T cells than did non-Bregs. These Breg:T cell interactions were antigen-specific and reduced subsequent T:DC contacts. Thus, Bregs inhibit T cells through direct cognate interactions that subsequently reduce DC:T cell interactions.

Characterization of intratumoral and circulating IL-10-producing B cells in gastric cancer

The tumor microenvironment harbors multiple immunosuppressive mechanisms, many of which involve suppressive immune cells. B regulatory (Breg) cells, as critical regulators of immune responses, were investigated in patients with gastric carcinoma. In the present study, the B cells that expressed IL-10 were highly enriched in tumor-infiltrating B cells, and could also be found at reduced frequencies in circulating B cells. These cells expressed high CD19 and CD20, and were almost exclusively CD27⁺CD10^-. The IL-10 expression was significantly higher in CD27⁺CD10^--sorted B cells than in CD27^-CD10^--sorted B cells. In an in vitro coculture of B cells and autologous T cells, CD27⁺CD10^- B cells were capable of reducing the levels of CD4 T cell-mediated IFNγ, TNF, and IL-17 expression and the levels of CD8 T cell-mediated IFNγ and TNF expression. These regulatory effects were dependent on IL-10 as well as CD80/CD86. Interestingly, CD27⁺CD10^- B cells also significantly elevated IL-10 production from CD4 and CD8 T cells in an IL-10-dependent manner. Overall, we here report enrichment of IL-10-expressing CD27⁺CD10^- B cells in the intratumoral environment, which could significantly alter the cytokine production profile by CD4 and CD8 T cells.

Immune Tolerance and Rejection in Organ Transplantation

In this chapter, we describe the history of transplantation, the multiple cell types, and mechanisms that are involved in rejection and tolerance of a transplanted organ, as well as summarize the common and promising new therapeutics used in transplant patients.

New Predictor of Organ Failure in Acute Pancreatitis: CD4+ T Lymphocytes and CD19+ B Lymphocytes

OBJECTIVE

Lymphocytes are one of the main effector cells in the inflammatory response of acute pancreatitis (AP). The purpose of the study was to evaluate whether peripheral blood lymphocyte (PBL) subsets at admission change during AP based on clinical outcomes and to explore whether these changes vary by aetiology of AP. Hence, we performed a prospective study to find a predictor in lymphocyte subsets that might allow easier, earlier, and more accurate prediction of clinical outcomes.

METHODS

Patients with AP were enrolled from December 2017 to June 2018 at the First Affiliated Hospital of Nanjing Medical University. Age, sex, clinical and biochemical parameters, and aetiology of AP were obtained at admission. PBL counts were assessed within 24 hours after admission. Clinical outcomes were observed as endpoints. The areas under the curve (AUCs) of different predictors were calculated using the receiver operating characteristic (ROC) curve.

RESULTS

Overall, 133 patients were included. Patients (n=24) with organ failure (OF) had significantly lower CD4+ T lymphocyte levels than those (n=109) with No OF (NOF) (39.60 (33.94-46.13) vs. 32.41 (26.51-38.00), P=0.004). The OF group exhibited significantly higher CD19+ B lymphocytes than the NOF group (16.07 (10.67-21.06) vs. 23.78 (17.84-29.45), P=0.001). Of the AP cases, 68.8% were caused by gallstones; 10.1% were attributed to alcohol; 16.5% were due to hyperlipidaemia; and 4.6% had other causes. Across all aetiologies, a lower CD4+ T lymphocyte level was significantly related to OF (P<0.05). However, CD19+ B lymphocytes were significant only in gallstone pancreatitis (P<0.05). The ROC curve results showed that the AUC values of CD4+T lymphocytes, CD19+ B lymphocytes, and combined CD4+T lymphocytes and CD19+ B lymphocytes were similar to those of traditional scoring systems, such as APACHEII and Ranson.

CONCLUSIONS

CD4+ T and CD19+ B lymphocytes during the early phase of AP can predict OF.

Regulatory B cells: New players in inflammatory and autoimmune rheumatic diseases

OBJECTIVE

Regulatory B cells (Bregs) are a new subset of B cells with immunoregulatory functions, mainly through IL-10 production. Bregs suppress inflammatory Th1 and Th17 differentiation and induce Tregs suppressing autoimmune diseases. The aim of the study was to review the literature related to Bregs in autoimmune rheumatic diseases (ARDs).

METHODS

A literature review of publications in PUBMED published in English was performed using the relevant combinations of terms.

RESULTS

All relevant publications are discussed. Overall, recent studies in rheumatic diseases found Bregs to be decreased in ANCA-associated vasculitides (AAV) and in systemic sclerosis (SSc), particularly in SSc-associated lung fibrosis. In AAV Bregs levels are negatively correlated with autoantibody levels whereas in SSc this association is less clear but there is an inverse association with Th1 and Th17 cells. In rheumatoid arthritis (RA), Bregs were decreased, particularly in RA-associated lung fibrosis. In psoriatic arthritis IL-10 + Bregs are decreased and inversely associated with Th1 and Th17 cells. In systemic lupus erythematosus (SLE), the role of Bregs is unclear. In experimental diseases, when Bregs were expanded ex-vivo, they ameliorated established disease.

CONCLUSION

Bregs appear to be a new player in the pathogenesis of ARDs, and may offer a new strategy for therapeutic intervention.

Coexistence of regulatory B cells and regulatory T cells in tumor-infiltrating lymphocyte aggregates is a prognostic factor in patients with breast cancer

BACKGROUND

Tumors can acquire tolerance to tumor immunity and develop enhanced proliferation. Regulatory B cells (Bregs), whose role in immune tolerance is similar to that of regulatory T cells (Tregs), appear to be involved in tumor immunity. Recently, Bregs were found to induce Tregs against tumor immunity. However, the platform for the coexistence of Bregs and Tregs in cancer patients and its clinical significance remain unclear; thus, they were evaluated in breast cancer patients.

METHODS

In 489 breast cancer patients, CD25- and IL10-positive Bregs and Foxp3-positive Tregs were immunohistochemically evaluated in tumor-infiltrating lymphocyte aggregates (TIL aggregates) that consisted of CD19-positive B-cell follicles and CD3-positive T-cell parafollicles. Then the correlations of the localization and existence of these cells with metastasis-free survival (MFS) were evaluated in breast cancer patients.

RESULTS

TIL aggregates were observed in marginal regions of tumors in breast cancer patients. In the TIL aggregates, the existence of Bregs was closely related to that of Tregs (p < 0.0001). On multivariate analysis, the coexistence of Bregs and Tregs in TIL aggregates was correlated with MFS in breast cancer patients (p = 0.007). Furthermore, MFS was significantly shorter for patients with the coexistence of Tregs and Bregs in TIL aggregates than in those with Tregs alone without Bregs (p = 0.0475).

CONCLUSIONS

The present results suggest that Bregs are related to the induction of Tregs in TIL aggregates and the development of metastasis of breast cancer cells. Bregs are expected to be a new diagnostic and therapeutic target in breast cancer patients.

The Immunologic Paradoxes of IgG4-Related Disease

IgG4-related disease (IgG4-RD), which usually occurs in middle-aged and elderly men, is a newly recognized fibroinflammatory condition characterized by swelling and sclerosis of involved organs, increased IgG4-positive plasma cell infiltration in lesions, and elevated IgG4 concentration in serum. Despite growing interest in the research, the pathophysiological mechanism remains elusive. Most IgG4-RD patients respond well to steroid therapy initially, but recurrent and refractory cases are common, especially in advanced fibrotic stage. Recent studies have documented the heterogeneity of the B cell lineages, which suggests their multiple functions in IgG4-RD beyond IgG4 production, such as cytokine secretion, antigen presentation, autoantibody production, and modulation of T and B cell interactions. Thus, a critical balance exists between pathogenic and regulatory B subsets to prevent immunopathology. A prompt response to B cell depletion therapy reported in recent cases strongly suggests the imbalance within B cell lineages in IgG4-RD. A more precise understanding of the pathogenesis of IgG4-RD will open up new perspectives for therapeutic strategy. With a particular emphasis on the novel B cell-targeted therapeutic strategies, this review highlights the immunologic features of IgG4-RD and the possible roles of B cell lineages in the pathogenesis of IgG4-RD.

B Lymphocytes in Rheumatoid Arthritis and the Effects of Anti-TNF-α Agents on B Lymphocytes: A Review of the Literature

PURPOSE

The aim of this article was to review published research related to B lymphocytes in rheumatoid arthritis, their role in the pathogenesis of the disease, the effects of tumor necrosis factor (TNF)-α inhibitors on B lymphocytes, the risk for infection, and responses to vaccines.

METHODS

A PubMed search was conducted to review recent advances related to B lymphocytes and the effects of anti-TNF-α on B lymphocytes in rheumatoid arthritis.

FINDINGS

B lymphocytes play an important role in the pathogenesis of rheumatoid arthritis. In this review, we summarize the major mechanisms by which B lymphocytes play a pathologic role in the development and propagation of the disease, as B lymphocytes are recruited to the synovial fluid, where they contribute to local inflammation through the secretion of pro-inflammatory mediators (cytokines, chemokines, micro-RNAs) and present antigens to T cells. We discuss the effects of TNF-α, either direct or indirect, on B lymphocytes expressing receptors for this cytokine. We also show that total B-cell numbers have been reported to be reduced in the blood of patients with rheumatoid arthritis versus healthy controls, but are significantly increased up to normal levels in patients undergoing anti-TNF-α therapy. As for B-cell subsets, controversial results have been reported, with studies showing decreased frequencies of total memory B cells (and memory subsets) and others showing no differences in patients versus healthy controls. Studies investigating the effects of anti-TNF-α therapy have also given controversial results, with therapy found to increase (or not) the frequency of memory B lymphocytes, in patients with rheumatoid arthritis versus healthy controls. Those highly variable results could have been due to differences in patient characteristics and limited numbers of subjects. Finally, we summarize the effects of blocking TNF-α with anti-TNF-α agents on possible infections that patients with rheumatoid arthritis may contract, as well as on responses to vaccination.

IMPLICATIONS

B lymphocytes play a significant role in the pathogenesis of rheumatoid arthritis, and B cell-depletion therapy has a major effect on the course of the disease. The advances in treatment of rheumatoid arthritis include the development of targeted therapies. Anti-TNF-α therapies are widely used despite potentially serious adverse events. The data on the effects of anti-TNF-α therapies on B lymphocytes are limited and conflicting. There is a need for larger studies to better understand the effects of newly discovered therapies on the different cells of the immune system.

Pathogenic roles of B lymphocytes in systemic sclerosis

Systemic sclerosis (SSc) is a collagen disease characterized by autoimmunity and excessive extracellular matrix deposition in the skin and visceral organs. Although the pathogenic relationship between systemic autoimmunity and the clinical manifestations of SSc remains unknown, SSc patients show a variety of abnormal immune activation including the production of disease-specific autoantibodies and cytokine production. Many recent studies have demonstrated that immune cells, including T cells, B cells, and macrophages, have a variety of immunological abnormalities in SSc. So far, several groups and our group reported that B cells play a critical role in systemic autoimmunity and disease expression through various functions, such as cytokine production, lymphoid organogenesis, and induction of other immune cell activation in addition to autoantibody production. Recent studies show that B cells from SSc patients demonstrate an up-regulated CD19 expression, a crucial regulator of B cell activation, which induces chronic hyper-reactivity of memory B cells and SSc-specific autoantibody production and also causes fibrosis of several organs. Furthermore, in SSc-model mice, such as tight-skin mice, bleomycin-induced SSc model mice, and DNA topoisomerase I and complete Freund's adjuvant-induced SSc model mice, have abnormal B cell activation which associates with skin and lung fibrosis. Indeed, B cell depletion therapy using anti-CD20 Ab, Rituximab, is considered to one potential beneficial treatment for patients with SSc. However, there is no direct evidence which can explain how B cells, especially autoantigen-reactive B cells, progress or regulate disease manifestations of SSc. Collectively, B cell abnormalities in SSc is most likely participating in fibrosis and tissue damage of SSc. If the relationship between SSc-specific tissue damage and B cell abnormalities is revealed, these findings lead to novel effective therapy for SSc.

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

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

B lymphocytes in systemic sclerosis: Abnormalities and therapeutic targets

Systemic sclerosis (SSc) is a connective tissue disease characterized by excessive extracellular matrix deposition in the skin and visceral organs with an autoimmune background. Although the pathogenic relationship between systemic autoimmunity and the clinical manifestations remains unknown, SSc patients have immunological abnormalities including the production of disease-specific autoantibodies. Recent studies have demonstrated that B cells play a crucial role in systemic autoimmunity and disease expression via various functions in addition to autoantibody production. Recent studies show that B cells from SSc patients demonstrate an upregulated CD19 signaling pathway, which is a crucial regulator of B-cell activation, that induces SSc-specific autoantibody production in SSc. In addition, B cells from SSc patients exhibit an overexpression of CD19. Consistently, in CD19 transgenic mice, CD19 overexpression induces SSc-specific autoantibody production. SSc patients have also intrinsic B-cell abnormalities characterized by chronic hyperreactivity of memory B cells, possibly due to CD19 overexpression. Similarly, B cells from a tight-skin mouse, a genetic model of SSc, show augmented CD19 signaling and chronic hyperreactivity. Furthermore, in bleomycin-induced SSc model mice, endogenous ligands for Toll-like receptors, induced by bleomycin treatment, stimulate B cells to produce various fibrogenic cytokines and autoantibodies. Remarkably, CD19 loss results in inhibition of B-cell hyperreactivity and elimination of autoantibody production, which is associated with improvement of fibrosis. Taken together, altered B-cell function may result in tissue fibrosis, as well as autoimmunity, in SSc. Although further studies and greater understanding are needed, B cells are potential therapeutic target in SSc.

B Cell-Activating Factor (BAFF)-Targeted B Cell Therapies in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) involve dysregulated immune responses to gut antigens in genetically predisposed individuals. While a better elucidation of IBD pathophysiology has considerably increased the number of treatment options, the need for more effective therapeutic strategies remains a pressing priority. Defects of both non-hematopoietic (epithelial and stromal) and hematopoietic (lymphoid and myeloid) cells have been described in patients with IBD. Within the lymphoid system, alterations of the T cell compartment are viewed as essential in the pathogenesis of IBD. However, growing evidence points to the additional perturbations of the B cell compartment. Indeed, the intestinal lamina propria from IBD patients shows an increased presence of antibody-secreting plasma cells, which correlates with enhanced pro-inflammatory immunoglobulin G production and changes in the quality of non-inflammatory IgA responses. These B cell abnormalities are compounded by the emergence of systemic antibody responses to various autologous and microbial antigens, which predates the clinical diagnosis of IBD and identifies patients with complicated disease. It is presently unclear whether such antibody responses play a pathogenetic role, as B cell depletion with the CD20-targeting monoclonal antibody rituximab did not ameliorate ulcerative colitis in a clinical trial. However, it must be noted that unresponsiveness to rituximab is also observed also in some patients with autoimmune disorders usually responsive to B cell-depleting therapies. In this review, we discussed mechanistic aspects of B cell-based therapies and their potential role in IBD with a special interest on BAFF and BAFF-targeting therapies buoyed by the success of anti-BAFF treatments in rheumatologic disorders.

[Regulatory B cells in human autoimmune diseases]

B cells have been generally considered to be positive regulators of immune responses because of their ability to produce antigen-specific antibodies and to activate T cells through antigen presentation. Impairment of B cell development and function may cause autoimmune diseases. Recently, specific B cell subsets that can negatively regulate immune responses have been described in mouse models of a wide variety of autoimmune diseases. The concept of those B cells, termed regulatory B cells, is now recognized as important in the murine immune system. Among several regulatory B cell subsets, IL-10-producing regulatory B cells are the most widely investigated. On the basis of discoveries from studies of such mice, human regulatory B cells that produce IL-10 in most cases are becoming an active area of research. There have been emerging data suggesting the importance of human regulatory B cells in various diseases. Revealing the immune regulation mechanisms of human regulatory B cells in human autoimmune diseases could lead to the development of novel B cell targeted therapies. This review highlights the current knowledge on regulatory B cells, mainly IL-10-producing regulatory B cells, in clinical research using human samples.

Cryopreserved vitamin D3-tolerogenic dendritic cells pulsed with autoantigens as a potential therapy for multiple sclerosis patients

Background

Tolerogenic dendritic cells (tolDC) have been postulated as a potent immunoregulatory therapy for autoimmune diseases such as multiple sclerosis (MS). In a previous study, we demonstrated that the administration of antigen-specific vitamin D₃ (vitD3) tolDC in mice showing clinical signs of experimental autoimmune encephalomyelitis (EAE; the animal model of MS) resulted in abrogation of disease progression. With the purpose to translate this beneficial therapy to the clinics, we have investigated the effectivity of vitD3-frozen antigen-specific tolDC pulsed with myelin oligodendrocyte glycoprotein 40-55 peptide (f-tolDC-MOG) since it would reduce the cost, functional variability and number of leukapheresis to perform to the patients.

Methods

Mice showing EAE clinical signs were treated with repetitive doses of f-tolDC-MOG. Tolerogenic mechanisms induced by the therapy were analysed by flow cytometry and T cell proliferation assays.

Results

Treatment with f-tolDC-MOG was effective in ameliorating clinical signs of mice with EAE, inhibiting antigen-specific reactivity and inducing Treg. In addition, the long-term treatment was well tolerated and leading to a prolonged maintenance of tolerogenicity mediated by induction of Breg, reduction of NK cells and activation of immunoregulatory NKT cells.

Conclusions

The outcomes of this study show that the use of antigen-specific f-tolDC promotes multiple and potent tolerogenic mechanisms. Moreover, these cells can be kept frozen maintaining their tolerogenic properties, which is a relevant step for their translation to the clinic. Altogether, vitD3 f-tolDC-MOG is a potential strategy to arrest the autoimmune destruction in MS patients.

Fingolimod therapy modulates circulating B cell composition, increases B regulatory subsets and production of IL-10 and TGFβ in patients with Multiple Sclerosis

Fingolimod, an oral therapeutic agent approved for patients with relapsing-remitting Multiple Sclerosis (MS), has been shown to prevent lymphocyte egress from secondary lymphoid tissues; however the specific drug effect on B cells in fingolimod-treated patients remains to be fully elucidated. We present here a comprehensive analysis on the proportions of B cell subsets in the periphery, and the levels of activation, functional surface markers and cytokine profile of B cells in MS patients, following initiation of fingolimod therapy, using flow cytometry and cytokine bead array. Fingolimod therapy increased the ratio of naïve to memory cells, elevated the percentage of plasma cells and highly increased the proportion of transitional B cells as well as additional regulatory subsets, including: IL10(+), CD25(+) and CD5(+) B cells. The percentage of activated CD69(+) cells was highly elevated in the remaining circulating B cells, which produced increased levels of IL10, TGFβ, IL6, IL4, LTα, TNFα and IFNγ cytokines, with an overall increased ratio of TGFβ to pro-inflammatory cytokines. Furthermore, fingolimod therapy reduced ICAM-1(+) cells, suggesting a possible reduction in antigen-presenting capacity. Phosphorylated-fingolimod was shown in vitro to reduce S1PR1 RNA and protein, to slightly increase viability and to activate anti-apoptotic Bcl2 in transformed B cells of patients with MS. In conclusion, fingolimod therapy modulates significantly the composition of circulating B cells, promoting regulatory subsets and an anti-inflammatory cytokine repertoire.

IL-10-Producing Regulatory B Cells Are Decreased in Patients with Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immunodeficiency in adults. CVID patients often present changes in the frequency and function of B lymphocytes, reduced number of Treg cells, chronic immune activation, recurrent infections, high incidence of autoimmunity and increased risk for malignancies. We hypothesized that the frequency of B10 cells would be diminished in CVID patients because these cells play an important role in the development of Treg cells and in the control of T cell activation and autoimmunity. Therefore, we evaluated the frequency of B10 cells in CVID patients and correlated it with different clinical and immunological characteristics of this disease. Forty-two CVID patients and 17 healthy controls were recruited for this study. Cryopreserved PBMCs were used for analysis of T cell activation, frequency of Treg cells and characterization of B10 cells by flow cytometry. IL-10 production by sorted B cells culture and plasma sCD14 were determined by ELISA. We found that CVID patients presented decreased frequency of IL-10-producing CD24^hiCD38^hi B cells in different cell culture conditions and decreased frequency of IL-10-producing CD24^hiCD27⁺ B cells stimulated with CpG+PIB. Moreover, we found that CVID patients presented lower secretion of IL-10 by sorting-purified B cells when compared to healthy controls. The frequency of B10 cells had no correlation with autoimmunity, immune activation and Treg cells in CVID patients. This work suggests that CVID patients have a compromised regulatory B cell compartment which is not correlated with clinical and immunological characteristics presented by these individuals.

CD19(+)IL-10(+) regulatory B cells affect survival of tongue squamous cell carcinoma patients and induce resting CD4(+) T cells to CD4(+)Foxp3(+) regulatory T cells

OBJECTIVES

Increase of regulatory T cells (Tregs) in the tumor microenvironment predicts worse survival of patients with various types of cancer including tongue squamous cell carcinoma (TSCC). Recently, the cross-talk between Tregs and regulatory B cells (Bregs) has been shown in several tumor models. However the relevance of Bregs to tumor immunity in humans remains elusive. Our objective was to investigate the distribution and function of Bregs in TSCC microenvironment.

MATERIALS AND METHODS

Double staining (Bregs: IL10/CD19 and Tregs: Foxp3/CD4) was performed on tissue sections of 46 TSCC, 20 metastasis lymph nodes, and tumor adjacent normal tissue. Flow cytometry analysis was used to detect the Bregs from magnetic bead-sorted B cells after co-culture with TSCC cell lines, and Tregs from sorted CD4(+)CD25(-) T cells after co-culture with stimulated B cells.

RESULTS

The immunohistochemical (IHC) results showed that the frequency of Bregs/CD19(+) B in TSCC (0.80±0.08%) was significantly higher than adjacent normal tissue (0.52±0.04% p<0.01). And the increase of Bregs in TSCC microenvironment was related to Tregs and predicts worse survival in patients. Cytological experiments indicated that frequency of Bregs increased after co-culture with TSCC cell line and that the induced B cells converted CD4(+)CD25(-) T cells into Tregs.

CONCLUSION

The increased expression of Bregs in the TSCC microenvironment plays a significant role in the differentiation of resting CD4(+) T cells and influenced the prognosis of TSCC patients.

Rapid activation and hepatic recruitment of innate-like regulatory B cells after invariant NKT cell stimulation in mice

BACKGROUND & AIMS

Invariant natural killer T (iNKT) cells are present within the liver and have been implicated in the development of many liver diseases. Upon activation by glycolipid ligands (including α-galactosylceramide; αGalCer), hepatic iNKT cells produce numerous cytokines and recruit both pro-inflammatory and regulatory immune cells. However, the involvement of B cells in this process is poorly defined.

METHODS

Wild-type (male, C57BL/6), B cell deficient, or B cell depleted mice were injected with αGalCer or vehicle, hepatic B cell phenotype and liver injury was subsequently determined.

RESULTS

iNKT cell activation resulted in liver injury and the rapid activation and hepatic recruitment of B cells (mainly innate-like B1 and MZ-like B cells) from the spleen and peritoneal cavity. B cells recruited to the liver produce IL-10 and TGFβ, and express cell surface CD73 (ectoenzyme which generates adenosine). B cell deficient mice developed augmented αGalCer-induced hepatitis, enhanced neutrophil recruitment and striking alterations in the hepatic cytokine milieu. αGalCer-induced hepatitis was unaltered in IL-10(-/-) mice, or after TGFβ neutralization, but was significantly worsened in mice treated with a CD73 inhibitor.

CONCLUSIONS

iNKT cell stimulation recruits innate-like regulatory B cells to the liver which suppress hepatic inflammation through IL-10 and TGFβ1 independent mechanisms, but involve CD73 activity. These findings highlight an important inflammation suppressing role for B cells at early time points during the development of an innate immune response within the liver, and represent a potential therapeutic target for the treatment of liver disease.

Regulatory B cells in human inflammatory and autoimmune diseases: from mouse models to clinical research

B cells have been generally considered to be positive regulators of immune responses because of their ability to produce antigen-specific antibodies and to activate T cells through antigen presentation. Impairment of B cell development and function may cause inflammatory and autoimmune diseases. Recently, specific B cell subsets that can negatively regulate immune responses have been described in mouse models of a wide variety of inflammatory and autoimmune diseases. The concept of those B cells, termed regulatory B cells, is now recognized as important in the murine immune system. Among several regulatory B cell subsets, IL-10-producing regulatory B cells are the most widely investigated. On the basis of discoveries from studies of such mice, human regulatory B cells that produce IL-10 in most cases are becoming an active area of research. There have been emerging data suggesting the importance of human regulatory B cells in various diseases. Revealing the immune regulation mechanisms of human regulatory B cells in human inflammatory and autoimmune diseases could lead to the development of novel B cell targeted therapies. This review highlights the current knowledge on regulatory B cells, mainly IL-10-producing regulatory B cells, in animal models of inflammatory and autoimmune diseases and in clinical research using human samples.

Leishmania infantum amastigotes trigger a subpopulation of human B cells with an immunoregulatory phenotype

Visceral leishmaniasis is caused by the protozoan parasites Leishmania infantum and Leishmania donovani. This infection is characterized by an uncontrolled parasitization of internal organs which, when left untreated, leads to death. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. Other studies have suggested a role for B cells in the pathology of this parasitic infection and the recent identification of a B-cell population in humans with regulatory functions, which secretes large amounts of IL-10 following activation, have sparked our interest in the context of visceral leishmaniasis. We report here that incubation of human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. as monitored by TNF and IFNγ secretion). Blockade of IL-10 activity using a soluble IL-10 receptor restored only partially TNF and IFNγ production to control levels. The parasite-mediated IL-10 secretion was shown to rely on the activity of Syk, phosphatidylinositol-3 kinase and p38, as well as to require intracellular calcium mobilization. Cell sorting experiments allowed us to identify the IL-10-secreting B-cell subset (i.e. CD19⁺CD24⁺CD27^-). In summary, exposure of human B cells to Leishmania infantum amastigotes triggers B cells with regulatory activities mediated in part by IL-10, which could favor parasite dissemination in the organism.

Leishmaniasis is an infection caused by protozoan parasites of the genus Leishmania and is a significant neglected tropical disease, with 350 million people in 98 countries at risk of developing one of the forms of the disease. Visceral leishmaniasis is characterized by an uncontrolled parasitization of internal organs, which leads to death when left untreated. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. We demonstrate that a contact between human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. TNF and IFNγ production). Blockade of IL-10 activity using a soluble IL-10 receptor restored to some degree TNF and IFNγ secretion. Cell sorting experiments allowed us to identify a major IL-10-secreting B cell subset characterized as CD24⁺ and CD27^-. Exposure of human B cells to Leishmania infantum amastigotes thus triggers B cells with regulatory activities mediated in part by IL-10, which could promote parasite dissemination in the organism.