Blimp-1 Contributes to the Development and Function of Regulatory B Cells

CRISPR-Cas Genome Editing in Ex Vivo Human Lungs to Rewire the Translational Path of Genome-Targeting Therapeutics

The ongoing advancements in CRISPR-Cas technologies can significantly accelerate the preclinical development of both in vivo and ex vivo organ genome-editing therapeutics. One of the promising applications is to genetically modify donor organs prior to implantation. The implantation of optimized donor organs with long-lasting immunomodulatory capacity holds promise for reducing the need for lifelong potent whole-body immunosuppression in recipients. However, assessing genome-targeting interventions in a clinically relevant manner prior to clinical trials remains a major challenge owing to the limited modalities available. This study introduces a novel platform for testing genome editing in human lungs ex vivo, effectively simulating preimplantation genetic engineering of donor organs. We identified gene regulatory elements whose disruption via Cas nucleases led to the upregulation of the immunomodulatory gene interleukin 10 (IL-10). We combined this approach with adenoviral vector-mediated IL-10 delivery to create favorable kinetics for early (immediate postimplantation) graft immunomodulation. Using ex vivo organ machine perfusion and precision-cut tissue slice technology, we demonstrated the feasibility of evaluating CRISPR genome editing in human lungs. To overcome the assessment limitations in ex vivo perfused human organs, we conducted an in vivo rodent study and demonstrated both early gene induction and sustained editing of the lung. Collectively, our findings lay the groundwork for a first-in-human-organ study to overcome the current translational barriers of genome-targeting therapeutics.

Single-cell BCR and transcriptome analysis reveals peripheral immune signatures in patients with thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is the most prevalent orbital disease in adults caused by an autoimmune disorder, which can lead to disfigurement and vision impairment. Developing effective treatments for this condition presents challenges due to our limited understanding of its underlying immune aberrations. In this study, we profiled the immune components in the peripheral blood of patients with TAO as well as healthy individuals, utilizing single-cell RNA sequencing and B-cell receptor repertoires (BCR) analysis. We observed a significant reduction in the proportions of regulatory B cells (Bregs) and type 2 conventional dendritic cells (DCs) in patients with TAO during the active phase. Conversely, there was a significant increase in the proportion of type 1 DCs. Further analysis of cell differentiation trajectory revealed potential impairment in the transition of B cells towards Breg phenotype during the active phase of TAO. Besides, the activation process of TAO appeared to involve inflammation and immune dysfunction, as indicated by the dynamic changes in the activities of key regulators. The abnormalities in the peripheral immune system, such as the reduced capacity of Bregs to suppress inflammation, were primarily driven by the enhanced interaction among Breg, DCs, and monocytes (i.e., CD22-PTPRC and BTLA-TNFRSF14). Collectively, our findings offer a comprehensive insight into the molecular regulation and cellular reconfiguration during the active phase of TAO at the single-cell level, in order to explore the pathogenesis of TAO and provide new ideas for the future treatment of TAO.

Schistosoma japonicum-derived peptide SJMHE1 ameliorates allergic symptoms and responses in mice with allergic rhinitis

Helminth derived excretory/secretory molecules have shown efficacy in the treatment of allergic asthma in mice, but their roles in allergic rhinitis (AR) are little known. In this study, we aimed to determine the intervention effect of SJMHE1, a Schistosoma japonicum derived small molecular peptide, on ovalbumin (OVA)-induced AR mice and investigate its possible mechanism. AR was induced in BALB/c mice, following which the mice were treated with phosphate-buffered saline (PBS), OVA323-339 and SJMHE1 respectively. SJMHE1 treatment improved clinical symptoms (rubbing and sneezing), suppressed infiltrates of inflammatory cells and eosinophils in nasal mucosa, modulated the production of type-2 (IL-4 and IL-13) and anti-inflammatory (IL-10) cytokines in the nasal lavage fluids (NLF), spleen, and serum. To investigate the underlying mechanism, fluorescein isothiocyanate (FITC)-labeled SJMHE1 was subcutaneously injected into AR mice, and we found that the FITC-SJMHE1 could accumulate in spleen, but not in nasal mucosa. FITC-SJMHE1 mainly bound to CD19 positive cells (B cells), and the SJMHE1 treatment significantly increased the proportion of regulatory B cells (Bregs) and B10 cells, along with the enhancement of PR domain containing protein 1 (Prdm1) protein levels. SJMHE1 may alleviate AR by upregulating Bregs, and has great potential as a new avenue for the AR treatment.

CgBlimp-1 inhibits granulocytes proliferation and interleukin production in the immune response of oyster Crassostrea gigas

B lymphocyte-inducible maturation protein 1 (Blimp-1) is a SET domain and zinc fingers containing transcriptional repressor, which is necessary for regulating the development of many immune cell lineages and keeping immune homeostasis. In the present study, a Blimp-1 homologue (designated as CgBlimp-1) was identified from oyster Crassostrea gigas, which contained a conserved SET domain and five ZnF_C2H2 domains and shared high homology with Blimp-1 from other species. The mRNA transcripts of CgBlimp-1 were highly expressed in gill and hepatopancreas. CgBlimp-1 protein was detected to be specifically expressed in granulocytes. After V. splendidus stimulation, the mRNA expression level of CgBlimp-1 in haemocytes up-regulated significantly at 24, 48, and 96 h, which was 4.39-fold (p < 0.05), 7.68-fold (p < 0.01) and 2.65-fold (p < 0.05) of that in control group, respectively. When the expression of CgBlimp-1 was knocked-down in vivo by RNAi, the mRNA expressions of downstream transcription factor CgMyc-A (1.63-fold of that in control group, p < 0.05) and cell cycle related gene CgCDK2 (1.70-fold, p < 0.05) increased significantly at 24 h after V. splendidus stimulation. Concomitantly, the ratio of EdU⁺ haemocytes increased notably (p < 0.01) while the proportion of haemocytes in G0/G1 phase decreased dramatically (p < 0.001), compared to that in control group. More specifically, the proportion of granulocytes in total haemocytes increased apparently (p < 0.05) in CgBlimp-1-RNAi oysters, together with up-regulation (p < 0.05) of the ratio of EdU⁺ granulocytes and down-regulation (p < 0.001) of the proportion of granulocytes in G0/G1 phase. Furthermore, the mRNA expression levels of CgIL17-1, CgIL17-2 and CgIL17-4 in haemocytes increased significantly in CgBlimp-1-RNAi oysters, which was 1.71-fold (p < 0.05), 144.70-fold (p < 0.01) and 1.93-fold (p < 0.05) of that in control group, respectively. Aforementioned results suggested that CgBlimp-1 could reduce the proliferation of granulocytes by arresting cell cycle in G1/G0 phase and avoid over-expression of interleukin to maintain homeostasis in the immune response of oyster.

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.

Molecular Mechanisms Driving IL-10- Producing B Cells Functions: STAT3 and c-MAF as Underestimated Central Key Regulators?

Regulatory B cells (Bregs) have been highlighted in very different pathology settings including autoimmune diseases, allergy, graft rejection, and cancer. Improving tools for the characterization of Bregs has become the main objective especially in humans. Transitional, mature B cells and plasma cells can differentiate into IL-10 producing Bregs in both mice and humans, suggesting that Bregs are not derived from unique precursors but may arise from different competent progenitors at unrestricted development stages. Moreover, in addition to IL-10 production, regulatory B cells used a broad range of suppressing mechanisms to modulate the immune response. Although Bregs have been consistently described in the literature, only a few reports described the molecular aspects that control the acquisition of the regulatory function. In this manuscript, we detailed the latest reports describing the control of IL-10, TGFβ, and GZMB production in different Breg subsets at the molecular level. We focused on the understanding of the role of the transcription factors STAT3 and c-MAF in controlling IL-10 production in murine and human B cells and how these factors may represent an important crossroad of several key drivers of the Breg response. Finally, we provided original data supporting the evidence that MAF is expressed in human IL-10- producing plasmablast and could be induced in vitro following different stimulation cocktails. At steady state, we reported that MAF is expressed in specific human B-cell tonsillar subsets including the IgD⁺ CD27⁺ unswitched population, germinal center cells and plasmablast.

FoxO1 suppresses IL-10 producing B cell differentiation via negatively regulating Blimp-1 expression and contributes to allergic asthma progression

IL-10-producing B cells (B10) are involved in the prevention of autoimmune and allergic responses but its mechanisms remain poorly understood. We took advantage of the ovalbumin-induced asthma mouse model to demonstrate that the activity of FoxO1 is upregulated in lung B cells and correlates inversely with B10 cells, while showing decreased activity in ex vivo and in vitro induced B10 cells. We further observed that FoxO1 deficiency leads to increased frequency of B10 cells. These observations have in vivo clinical evidence, as B cell specific FoxO1 deficiency leads to reduced lung eosinophils and asthma remission in mice, and there are reduced regulatory B cells and increased FoxO1 activity in B cells of asthma patients. Single cell RNA-sequencing data demonstrated a negative correlation between the expression of Foxo1 and Il10 in B cells from the mouse spleen and lung and the human lung. For a biological mechanism, FoxO1 inhibits the expression of Prdm1, which encodes Blimp-1, a transcription factor of B10 cells. Our experimental evidence in both murine and human asthma demonstrates that FoxO1 is a negative regulator of B10 cell differentiation via negatively regulating Prdm1 and its expression in B cells contributes to allergic asthma disease.

Blimp-1 Upregulation by Multiple Ligands via EGFR Transactivation Inhibits Cell Migration in Keratinocytes and Squamous Cell Carcinoma

B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor and plays a crucial role in the regulation of development and functions of various immune cells. Currently, there is limited understanding about the regulation of Blimp-1 expression and cellular functions in keratinocytes and cancer cells. Previously we demonstrated that EGF can upregulate Blimp-1 gene expression in keratinocytes, playing a negative role in regulation of cell migration and inflammation. Because it remains unclear if Blimp-1 can be regulated by other stimuli beyond EGF, here we further investigated multiple stimuli for their regulation of Blimp-1 expression in keratinocytes and squamous cell carcinoma (SCC). We found that PMA, TNF-α, LPS, polyIC, H₂O₂ and UVB can upregulate the protein and/or mRNA levels of Blimp-1 in HaCaT and SCC cells. Concomitant EGFR activation was observed by these stimuli, and EGFR inhibitor gefitinib and Syk inhibitor can block Blimp-1 gene expression caused by PMA. Reporter assay of Blimp-1 promoter activity further indicated the involvement of AP-1 in PMA-, TNF-α-, LPS- and EGF-elicited Blimp-1 mRNA expression. Confocal microscopic data indicated the nuclear loclization of Blimp-1, and such localization was not changed by stimuli. Moreover, Blimp-1 silencing enhanced SCC cell migration. Taken together, Blimp-1 can be transcriptionally upregulated by several stimuli in keratinocytes and SCC via EGFR transactivation and AP-1 pathway. These include growth factor PMA, cytokine TNF-α, TLR ligands (LPS and polyIC), and ROS insults (H₂O₂ and UVB). The function of Blimp-1 as a negative regulator of cell migration in SCC can provide a new therapeutic target in SCC.

Trypanosoma cruzi Induces B Cells That Regulate the CD4+ T Cell Response

Trypanosoma cruzi infection induces a polyclonal B cell proliferative response characterized by maturation to plasma cells, excessive generation of germinal centers, and secretion of parasite-unrelated antibodies. Although traditionally reduced to the humoral response, several infectious and non-infectious models revealed that B lymphocytes could regulate and play crucial roles in cellular responses. Here, we analyze the trypomastigote-induced effect on B cells, their effects on CD4+ T cells, and their correlation with in vivo findings. The trypomastigotes were able to induce the proliferation and the production of IL-10 or IL-6 of naïve B cells in co-culture experiments. Also, we found that IL-10-producing B220lo cells were elicited in vivo. We also found up-regulated expression of FasL and PD-L1, proteins involved in apoptosis induction and inhibition of TCR signaling, and of BAFF and APRIL mRNAs, two B-cell growth factors. Interestingly, it was observed that IL-21, which plays a critical role in regulatory B cell differentiation, was significantly increased in B220+/IL-21+ in in vivo infections. This is striking since the secretion of IL-21 is associated with T helper follicular cells. Furthermore, trypomastigote-stimulated B-cell conditioned medium dramatically reduced the proliferation and increased the apoptotic rate on CD3/CD28 activated CD4+ T cells, suggesting the development of effective regulatory B cells. In this condition, CD4+ T cells showed a marked decrease in proliferation and viability with marginal IL-2 or IFNγ secretion, which is counterproductive with an efficient immune response against T. cruzi. Altogether, our results show that B lymphocytes stimulated with trypomastigotes adopt a particular phenotype that exerts a strong regulation of this T cell compartment by inducing apoptosis, arresting cell division, and affecting the developing of a proinflammatory response.

Properties of regulatory B cells regulating B cell targets

Regulatory B cells (Bregs) have shown promise as anti-rejection therapy applied to organ transplantation. However, less is known about their effect on other B cell populations that are involved in chronic graft rejection. We recently uncovered that naïve B cells, stimulated by TLR ligand agonists, converted into B cells with regulatory properties (Bregs-TLR) that prevented allograft rejection. Here, we examine the granular phenotype and regulatory properties of Breg-TLR cells suppressing B cells. Cocultures of Bregs-TLR with LPS-activated B cells showed a dose-dependent suppression of targeted B cell proliferation. Adoptive transfers of Bregs-TLR induced a decline in antibody responses to antigenically disparate skin grafts. The role of Breg BCR specificity in regulation was assessed using B cell-deficient mice replenished with transgenic BCR (OB1) and TCR (OT-II) lymphocytes of matching antigenic specificity. Results indicated that proliferation of OB1 B cells, mediated through help from CD4⁺ OT-II cells, was suppressed by OB1 Bregs of similar specificity. Transcriptomic analyses indicated that Bregs-TLR suppression is associated with a block in targeted B cell differentiation controlled by PRDM1 (Blimp1). This work uncovered the regulatory properties of a new brand of Breg cells and provided mechanistic insights into potential applications of Breg therapy in transplantation.

Metabolic Program of Regulatory B Lymphocytes and Influence in the Control of Malignant and Autoimmune Situations

Metabolic pathways have been studied for a while in eukaryotic cells. During glycolysis, glucose enters into the cells through the Glut1 transporter to be phosphorylated and metabolized generating ATP molecules. Immune cells can use additional pathways to adapt their energetic needs. The pentose phosphate pathway, the glutaminolysis, the fatty acid oxidation and the oxidative phosphorylation generate additional metabolites to respond to the physiological requirements. Specifically, in B lymphocytes, these pathways are activated to meet energetic demands in relation to their maturation status and their functional orientation (tolerance, effector or regulatory activities). These metabolic programs are differentially involved depending on the receptors and the co-activation molecules stimulated. Their induction may also vary according to the influence of the microenvironment, i.e. the presence of T cells, cytokines … promoting the expression of particular transcription factors that direct the energetic program and modulate the number of ATP molecule produced. The current review provides recent advances showing the underestimated influence of the metabolic pathways in the control of the B cell physiology, with a particular focus on the regulatory B cells, but also in the oncogenic and autoimmune evolution of the B cells.

Increased Tc17 cell levels and imbalance of naïve/effector immune response in Parkinson's disease patients in a two-year follow-up: a case control study

BACKGROUND

Neuroinflammation has been proved to play a role in dopaminergic neuronal death in Parkinson's disease (PD). This link highlights the relevance of the immune response in the progression of the disease. However, little is known about the impact of peripheral immune response on the disease. This study is aimed to evaluate how immune cell populations change in untreated PD patients followed-up for 2 years.

METHODS

Thirty-two patients with no previous treatment (PD-0 yr) and twenty-two healthy subjects (controls) were included in the study. PD patients were sampled 1 and 2 years after the start of the treatment. CD4 T cells (naïve/central memory, effector, and activated), CD8 T cells (activated, central memory, effector memory, NKT, Tc1, Tc2, and Tc17), and B cells (activated, plasma, and Lip-AP) were characterized by flow cytometry.

RESULTS

We observed decreased levels of naïve/central memory CD4 and CD8 T cells, Tc1, Tc2, NKT, and plasma cells, and increased levels of effector T cells, activated T cells, and Tc17.

CONCLUSIONS

PD patients treated for 2 years showed an imbalance in the naive/effector immune response. Naïve and effector cell levels were associated with clinical deterioration. These populations are also correlated to aging. On the other hand, higher Tc17 levels suggest an increased inflammatory response, which may impact the progression of the disease. Our results highlight the relevant effect of treatment on the immune response, which could improve our management of the disease.

Immunoregulation by antibody secreting cells in inflammation, infection, and cancer

Antibody-secreting cells (ASCs) are considered work horses of the humoral immune response for their tireless effort to produce large amounts of antibodies that fulfill an array of functions in host defense, inflammation, and maintenance of homeostasis. While traditionally considered largely senescent cells, surprising recent findings demonstrate that subsets of ASCs downmodulate ongoing immune responses independent of antibody formation. Such regulatory ASCs produce IL-10 or IL-35 and are implicated in maintaining tissue and immune homeostasis. They also serve to suppress pathogenic leukocytes in infection, allergy, and inflammatory diseases that affect tissues, such as the central nervous system and the respiratory tract. Additionally, regulatory ASCs infiltrate various cancer types and restrict effective anti-tumor T cell responses. While incompletely understood, there is significant overlap in factors that control ASC differentiation, IL-10 expression by B cells and the generation of ASCs that secrete both antibodies and IL-10. In this review, we will cover the biology, phenotype, generation, maintenance and function of regulatory ASCs in various tissues under pathological and steady states. An improved understanding of the development of regulatory ASCs and their biological roles will be critical for generating novel ASC-targeted therapies for the treatment of inflammatory diseases, infection, and cancer.

MicroRNA-10a Negatively Regulates CD4+ T Cell IL-10 Production through Suppression of Blimp1

An uncontrolled CD4⁺ T cell response is a critical hallmark of autoimmune diseases. IL-10, which can be produced by both effector and regulatory CD4⁺ T cells, plays an essential role in the inhibition of autoimmunity. MicroRNAs are key molecules involved in regulating immune responses. However, how miR-10a regulates CD4⁺ T cell function in the pathogenesis of intestinal immune responses is not fully understood. In this study, we show that the mice with deficient miR-10a in CD4⁺ T cells were more resistant to intestinal inflammation upon inflammatory insult. miR-10a-deficient CD4⁺CD45Rb^hi T cells were less colitogenic in Rag ^-/- mice, in which CD4⁺ T cell production of IL-10 was increased. miR-10a-deficient CD4⁺ T cells expressed a higher expression of IL-10 in vitro. Blocking the IL-10/IL-10R pathway in vivo aggravated colitis induced by miR-10a-deficient CD4⁺CD45Rb^hi T cells. Mechanically, miR-10a suppressed CD4⁺ T cell production of IL-10 through targeting Prdm1, which encodes Blimp1. We further show that that CD4⁺ T cells lacking Blimp1 produced lower levels of IL-10 and induced more severe colitis in Rag ^-/- mice. These data thus establish the role of miR-10a in the inhibition of IL-10 production in CD4⁺ T cells to regulate intestinal homeostasis.

Regulatory B Cells (Bregs) Inhibit Osteoclastogenesis and Play a Potential Role in Ameliorating Ovariectomy-Induced Bone Loss

Increasing evidence in recent years has suggested that regulatory B cells (Bregs) are one of the crucial modulators in various inflammatory disease conditions. However, no study to date has investigated the significance of Bregs in modulating osteoclastogenesis. To the best of our knowledge, in the present study, we for the first time examined the anti-osteoclastogenic potential of Bregs under in vitro conditions and observed that Bregs suppress RANKL-induced osteoclastogenesis in a dose-dependent manner. We further elucidated the mechanism behind the observed suppression of osteoclasts differentiation via Bregs. Our results clearly suggested that the observed anti-osteoclastogenic property of Bregs is mediated via the production of IL-10 cytokine. Next, we explored whether Bregs have any role in mediating inflammatory bone loss under post-menopausal osteoporotic conditions in ovx mice. Remarkably, our in vivo data clearly suggest that the frequencies of both CD19+IL-10+ Bregs and CD19+CD1dhiCD5+IL-10+ "B10" Bregs were significantly reduced in case of osteoporotic mice model. Moreover, we also found a significant reduction in serum IL-10 cytokine levels in osteoporotic mice, thereby further supporting our observations. Taken together, the present study for the first time establishes the direct role of regulatory B cells in modulating osteoclastogenesis in vitro. Further, our in vivo data suggest that modulations in the percentage of Bregs population along with its reduced potential to produce IL-10 might further exacerbate the observed bone loss in ovx mice.

Effects of short-chain fatty acids in inhibiting HDAC and activating p38 MAPK are critical for promoting B10 cell generation and function

B10 cells are regulatory B cells capable of producing IL-10 for maintaining immune homeostasis. Dysregulation of B10 cells occurs in autoimmune and inflammatory diseases. Modulation or adoptive transfer of B10 cells is a promising therapeutic strategy. The short-chain fatty acids (SCFAs), the metabolites of microbiota, play a critical role in maintaining immune homeostasis and are the potential drugs for the modulation of B10 cells. It is not clear whether and how SCFAs upregulate the frequency of B10 cells. Here, we found that SCFAs could promote murine and human B10 cell generation in vitro. Upregulation of B10 cells by butyrate or pentanoate was also observed in either healthy mice, mice with dextran sodium sulfate (DSS)-induced colitis, or mice with collagen-induced arthritis. Moreover, SCFA treatment could ameliorate clinical scores of colitis and arthritis. Adoptive transfer of B cells pretreated with butyrate showed more alleviation of DSS-induced colitis than those without butyrate. A further study demonstrates that SCFAs upregulate B10 cells in a manner dependent on their histone deacetylase (HDAC) inhibitory activity and independent of the G-protein-coupled receptor pathway. Transcriptomic analysis indicated that the MAPK signaling pathway was enriched in B10 cells treated with butyrate. A study with inhibitors of ERK, JNK, and p38 MAPK demonstrated that activating p38 MAPK by butyrate is critical for the upregulation of B10 cells. Moreover, HDAC inhibitor has similar effects on B10 cells. Our study sheds light on the mechanism underlying B10 cell differentiation and function and provides a potential therapeutic strategy with SCFAs and HDAC inhibitors for inflammation and autoimmune diseases.

TCL1A, B Cell Regulation and Tolerance in Renal Transplantation

Despite much progress in the management of kidney transplantation, the need for life-long immunosuppressive therapies remains a major issue representing many risks for patients. Operational tolerance, defined as allograft acceptance without immunosuppression, has logically been subject to many investigations with the aim of a better understanding of post-transplantation mechanisms and potentially how it would be induced in patients. Among proposed biomarkers, T-cell Leukemia/Lymphoma protein 1A (TCL1A) has been observed as overexpressed in the peripheral blood of operational tolerant patients in several studies. TCL1A expression is restricted to early B cells, also increased in the blood of tolerant patients, and showing regulatory properties, notably through IL-10 secretion for some subsets. TCL1A has first been identified as an oncogene, overexpression of which is associated to the development of T and B cell cancer. TCL1A acts as a coactivator of the serine threonine kinase Akt and through other interactions favoring cell survival, growth, and proliferation. It has also been identified as interacting with others major actors involved in B cells differentiation and regulation, including IL-10 production. Herein, we reviewed known interactions and functions of TCL1A in B cells which could involve its potential role in the set up and maintenance of renal allograft tolerance.

B Cells and Microbiota in Autoimmunity

Trillions of microorganisms inhabit the mucosal membranes maintaining a symbiotic relationship with the host's immune system. B cells are key players in this relationship because activated and differentiated B cells produce secretory immunoglobulin A (sIgA), which binds commensals to preserve a healthy microbial ecosystem. Mounting evidence shows that changes in the function and composition of the gut microbiota are associated with several autoimmune diseases suggesting that an imbalanced or dysbiotic microbiota contributes to autoimmune inflammation. Bacteria within the gut mucosa may modulate autoimmune inflammation through different mechanisms from commensals ability to induce B-cell clones that cross-react with host antigens or through regulation of B-cell subsets' capacity to produce cytokines. Commensal signals in the gut instigate the differentiation of IL-10 producing B cells and IL-10 producing IgA+ plasma cells that recirculate and exert regulatory functions. While the origin of the dysbiosis in autoimmunity is unclear, compelling evidence shows that specific species have a remarkable influence in shaping the inflammatory immune response. Further insight is necessary to dissect the complex interaction between microorganisms, genes, and the immune system. In this review, we will discuss the bidirectional interaction between commensals and B-cell responses in the context of autoimmune inflammation.

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.

IL-10 production by ILC2s requires Blimp-1 and cMaf, modulates cellular metabolism, and ameliorates airway hyperreactivity

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are the dominant innate lymphoid cell population in the lungs at steady state, and their release of type 2 cytokines is a central driver in responding eosinophil infiltration and increased airway hyperreactivity. Our laboratory has identified a unique subset of ILC2s in the lungs that actively produce IL-10 (ILC210s).

OBJECTIVE

Our aim was to characterize the effector functions of ILC210s in the development and pathology of allergic asthma.

METHODS

IL-4-stimulated ILC210s were isolated to evaluate cytokine secretion, transcription factor signaling, metabolic dependence, and effector functions in vitro. ILC210s were also adoptively transferred into Rag2-/-γc-/- mice, which were then challenged with IL-33 and assessed for airway hyperreactivity and lung inflammation.

RESULTS

We have determined that the transcription factors cMaf and Blimp-1 regulate IL-10 expression in ILC210s. Strikingly, our results demonstrate that ILC210s can utilize both autocrine and paracrine signaling to suppress proinflammatory ILC2 effector functions in vitro. Further, this subset dampens airway hyperreactivity and significantly reduces lung inflammation in vivo. Interestingly, ILC210s demonstrated a metabolic dependency on the glycolytic pathway for IL-10 production, shifting from the fatty acid oxidation pathway conventionally utilized for proinflammatory effector functions.

CONCLUSION

These findings provide an important and previously unrecognized role of ILC210s in diseases associated with ILC2s such as allergic lung inflammation and asthma. They also provide new insights into the metabolism dependency of proinflammatory and anti-inflammatory ILC2 phenotypes.

Frontiers of Autoantibodies in Autoimmune Disorders: Crosstalk Between Tfh/Tfr and Regulatory B Cells

Balance of Tfh/Tfr cell is critically important for the maintenance of immune tolerance, as evidenced by the fact that T follicular helper (Tfh) cells are central to the autoantibodies generation through providing necessary help for germinal center (GC) B cells, whereas T follicular regulatory (Tfr) cells significantly inhibit autoimmune inflammation process through restraining Tfh cell responses. However, signals underlying the regulation of Tfh and Tfr cells are largely undefined. Regulatory B cells (Bregs) is a heterogeneous subpopulation of B cells with immunosuppressive function. Considerable advances have been made in their functions to produce anti‐inflammatory cytokines and to regulate Th17, Th1, and Treg cells in autoimmune diseases. The recent identification of their correlations with dysregulated Tfr/Tfh cells and autoantibody production makes Bregs an important checkpoint in GC response. Bregs exert profound impacts on the differentiation, function, and distribution of Tfh and Tfr cells in the immune microenvironment. Thus, unraveling mechanistic information on Tfh-Breg and Tfr-Breg interactions will inspire novel implications for the establishment of homeostasis and prevention of autoantibodies in diverse diseases. This review summarizes the dysregulation of Tfh/Tfr cells in autoimmune diseases with a focus on the emerging role of Bregs in regulating the balance between Tfh and Tfr cells. The previously unsuspected crosstalk between Bregs and Tfh/Tfr cells will be beneficial to understand the cellular mechanisms of autoantibody production and evoke a revolution in immunotherapy for autoimmune diseases.

The identification, development and therapeutic potential of IL-10-producing regulatory B cells in multiple sclerosis

Regulatory B cells are a rare B-cell subset widely known to exert their immunosuppressive function via the production of interleukin-10 (IL-10) and other mechanisms. B10 cells are a special subset of regulatory B cells with immunoregulatory function that is fully attributed to IL-10. Their unique roles in the animal model of multiple sclerosis (MS) have been described, as well as their relevance in MS patients. This review specifically focuses on the identification and development of B10 cells, the signals that promote IL-10 production in B cells, the roles of B10 cells in MS, and the potential and major challenges of the application of B10-based therapies for MS.

Regulatory B cells in respiratory health and diseases

B cells are critical mediators of humoral immune responses in the airways through antibody production, antigen presentation, and cytokine secretion. In addition, a subset of B cells, known as regulatory B cells (Bregs), exhibit immunosuppressive functions via diverse regulatory mechanisms. Bregs modulate immune responses via the secretion of IL‐10, IL‐35, and tumor growth factor‐β (TGF‐β), and by direct cell contact. The balance between effector and regulatory B cell functions is critical in the maintenance of immune homeostasis. The importance of Bregs in airway immune responses is emphasized by the different respiratory disorders associated with abnormalities in Breg numbers and function. In this review, we summarize the role of immunosuppressive Bregs in airway inflammatory diseases and highlight the importance of this subset in the maintenance of respiratory health. We propose that improved understanding of signals in the lung microenvironment that drive Breg differentiation can provide novel therapeutic avenues for improved management of respiratory diseases.

Cholesterol metabolism drives regulatory B cell IL-10 through provision of geranylgeranyl pyrophosphate

Regulatory B cells restrict immune and inflammatory responses across a number of contexts. This capacity is mediated primarily through the production of IL-10. Here we demonstrate that the induction of a regulatory program in human B cells is dependent on a metabolic priming event driven by cholesterol metabolism. Synthesis of the metabolic intermediate geranylgeranyl pyrophosphate (GGPP) is required to specifically drive IL-10 production, and to attenuate Th1 responses. Furthermore, GGPP-dependent protein modifications control signaling through PI3Kδ-AKT-GSK3, which in turn promote BLIMP1-dependent IL-10 production. Inherited gene mutations in cholesterol metabolism result in a severe autoinflammatory syndrome termed mevalonate kinase deficiency (MKD). Consistent with our findings, B cells from MKD patients induce poor IL-10 responses and are functionally impaired. Moreover, metabolic supplementation with GGPP is able to reverse this defect. Collectively, our data define cholesterol metabolism as an integral metabolic pathway for the optimal functioning of human IL-10 producing regulatory B cells.