Cbl and Cbl-b control the germinal center reaction by facilitating naive B cell antigen processing

CBL/Cbl-b mediates Fas degradation to reduce neuronal damage in experimental autoimmune encephalomyelitis

Fas has been shown to positively regulate the differentiation of T helper 17 (Th17) cells in mouse models of experimental autoimmune encephalomyelitis (EAE). Fas protein expression is regulated by ubiquitination but has not been further studied. In this study, we investigated the role of the Fas ubiquitin ligase in Th17 cell differentiation and highlighted its potential as a therapeutic target for EAE. The E3 ubiquitin ligase CBL of Fas was predicted using the online prediction software ubibrowser. Overexpression of CBL significantly reduced Fas protein levels but did not affect mRNA levels. The decrease in Fas protein mediated by CBL overexpression was rescued by the proteasome inhibitor MG132. Co-IP analysis revealed that CBL interacted with Fas. Further results suggested that CBL regulated Fas expression through ubiquitination, thereby affecting Th17 cell differentiation. Cbl-b, a homologue of CBL, significantly promoted the degradation of Fas protein and increased its ubiquitination modification. Furthermore, CBL and Cbl-b could synergistically regulate Fas to influence Th17 cell differentiation. The same conclusion was also reached in animal models. Luxol Fast Blue staining showed that myelinated fibres in the spinal cord were significantly increased after CBL/Cbl-b overexpression in EAE. Finally, flow cytometry and immunofluorescence staining showed that overexpression of CBL or Cbl-b decreased the proportion of Th17 cells in the spinal cord of EAE mice, ultimately reducing neuronal damage. Taken together, these data demonstrate that CBL and Cbl-b can synergistically regulate Fas to inhibit Th17 cell differentiation, thereby alleviating spinal cord nerve injury in the EAE model.

Exploring the diagnostic value of endothelial cell and angiogenesis-related genes in Hashimoto's thyroiditis based on transcriptomics and single cell RNA sequencing

(1) BACKGROUND: Hashimoto's thyroiditis (HT) can cause angiogenesis in the thyroid gland. However, the molecular mechanism of endothelial cells and angiogenesis related genes (ARGs) has not been extensively studied in HT. (2) METHODS: The HRA001684, GSE29315 and GSE163203 datasets were included in this study. Using single-cell analysis, weighted gene co-expression network analysis (WGCNA), functional enrichment analysis, machine learning algorithms and expression analysis for exploration. And receiver operator characteristic (ROC) curves was draw. Gene set enrichment analysis (GSEA) was utilized to investigate the biological function of the biomarkers. Meanwhile, we investigated into the relationship between biomarkers and different types of immune cells. Additionally, the expression of biomarkers in the TCGA-TC dataset was examined and the mRNA-drug interaction network was constructed. (3) RESULTS: We found 14 cell subtypes were obtained in HT samples after single-cell analysis. A total of 5 biomarkers (CD52, CD74, CD79A, HLA-B and RGS1) were derived, and they had excellent diagnostic performance. Then, 27 drugs targeting biomarkers were predicted. The expression analysis showed that CD74 and HLA-B were significantly up-regulated in HT samples. (4) CONCLUSION: In this study, 5 biomarkers (CD52, CD74, CD79A, HLA-B and RGS1) were screened and their expressions in endothelial cells was compared to offer a new reference for the recognition and management of HT.

Csk restrains BCR-mediated ROS production and contributes to germinal center selection and affinity maturation

Compared with naïve B cells, the B cell receptor (BCR) signal in germinal center (GC) B cells is attenuated; however, the significance of this signaling attenuation has not been well defined. Here, to investigate the role of attenuation of BCR signaling, we employed a Csk mutant mouse model in which Csk deficiency in GC B cells resulted in augmentation of net BCR signaling with no apparent effect on antigen presentation. We found that Csk is required for GC maintenance and efficient antibody affinity maturation. Mechanistically, ROS-induced apoptosis was exacerbated concomitantly with mitochondrial dysfunction in Csk-deficient GC B cells. Hence, our data suggest that attenuation of the BCR signal restrains hyper-ROS production, thereby protecting GC B cells from apoptosis and contributing to efficient affinity maturation.

B-cell intrinsic regulation of antibody mediated immunity by histone H2A deubiquitinase BAP1

Introduction

BAP1 is a deubiquitinase (DUB) of the Ubiquitin C-terminal Hydrolase (UCH) family that regulates gene expression and other cellular processes, through its direct catalytic activity on the repressive epigenetic mark histone H2AK119ub, as well as on several other substrates. BAP1 is also a highly important tumor suppressor, expressed and functional across many cell types and tissues. In recent work, we demonstrated a cell intrinsic role of BAP1 in the B cell lineage development in murine bone marrow, however the role of BAP1 in the regulation of B cell mediated humoral immune response has not been previously explored.

Methods and results

In the current study, we demonstrate that a B-cell intrinsic loss of BAP1 in activated B cells in the Bap1 fl/fl Cγ1-cre murine model results in a severe defect in antibody production, with altered dynamics of germinal centre B cell, memory B cell, and plasma cell numbers. At the cellular and molecular level, BAP1 was dispensable for B cell immunoglobulin class switching but resulted in an impaired proliferation of activated B cells, with genome-wide dysregulation in histone H2AK119ub levels and gene expression.

Conclusion and discussion

In summary, our study establishes the B-cell intrinsic role of BAP1 in antibody mediated immune response and indicates its central role in the regulation of the genome-wide landscapes of histone H2AK119ub and downstream transcriptional programs of B cell activation and humoral immunity.

SYK ubiquitination by CBL E3 ligases restrains cross-presentation of dead cell-associated antigens by type 1 dendritic cells

Cross-presentation of dead cell-associated antigens by conventional dendritic cells type 1 (cDC1s) is critical for CD8+ T cells response against many tumors and viral infections. It is facilitated by DNGR-1 (CLEC9A), an SYK-coupled cDC1 receptor that detects dead cell debris. Here, we report that DNGR-1 engagement leads to rapid activation of CBL and CBL-B E3 ligases to cause K63-linked ubiquitination of SYK and terminate signaling. Genetic deletion of CBL E3 ligases or charge-conserved mutation of target lysines within SYK abolishes SYK ubiquitination and results in enhanced DNGR-1-dependent antigen cross-presentation. We also find that cDC1 deficient in CBL E3 ligases are more efficient at cross-priming CD8+ T cells to dead cell-associated antigens and promoting host resistance to tumors. Our findings reveal a role for CBL-dependent ubiquitination in limiting cross-presentation of dead cell-associated antigens and highlight an axis of negative regulation of cDC1 activity that could be exploited to increase anti-tumor immunity.

Epstein-Barr virus and genetic risk variants as determinants of T-bet+ B cell-driven autoimmune diseases

B cells expressing the transcription factor T-bet are found to have a protective role in viral infections, but are also considered major players in the onset of different types of autoimmune diseases. Currently, the exact mechanisms driving such 'atypical' memory B cells to contribute to protective immunity or autoimmunity are unclear. In addition to general autoimmune-related factors including sex and age, the ways T-bet+ B cells instigate autoimmune diseases may be determined by the close interplay between genetic risk variants and Epstein-Barr virus (EBV). The impact of EBV on T-bet+ B cells likely relies on the type of risk variants associated with each autoimmune disease, which may affect their differentiation, migratory routes and effector function. In this hypothesis-driven review, we discuss the lines of evidence pointing to such genetic and/or EBV-mediated influence on T-bet+ B cells in a range of autoimmune diseases, including systemic lupus erythematosus (SLE) and multiple sclerosis (MS). We provide examples of how genetic risk variants can be linked to certain signaling pathways and are differentially affected by EBV to shape T-bet+ B-cells. Finally, we propose options to improve current treatment of B cell-related autoimmune diseases by more selective targeting of pathways that are critical for pathogenic T-bet+ B-cell formation.

Tumor-derived exosomes deliver the tumor suppressor miR-3591-3p to induce M2 macrophage polarization and promote glioma progression

Exosomes can selectively secrete harmful metabolic substances from cells to maintain cellular homeostasis, and complex crosstalk occurs between exosomes and tumor-associated macrophages (TAMs) in the glioma immune microenvironment. However, the precise mechanisms by which these exosome-encapsulated cargos create an immunosuppressive microenvironment remain unclear. Herein, we investigated the effect of glioma-derived exosomes (GDEs) on macrophage polarization and glioma progression. We performed sequencing analysis of cerebrospinal fluid (CSF) and tumor tissues from glioma patients to identify functional microRNAs (miRNAs). High levels of miR-3591-3p were found in CSF and GDEs but not in normal brain tissue or glial cells. Functionally, GDEs and miR-3591-3p significantly induced M2 macrophage polarization and increased the secretion of IL10 and TGFβ1, which in turn promoted glioma invasion and migration. Moreover, miR-3591-3p overexpression in glioma cell lines resulted in G2/M arrest and markedly increased apoptosis. Mechanistically, miR-3591-3p can directly target CBLB and MAPK1 in macrophages and glioma cells, respectively, and further activate the JAK2/PI3K/AKT/mTOR, JAK2/STAT3, and MAPK signaling pathways. In vivo experiments confirmed that macrophages lentivirally transduced with miR-3591-3p can significantly promote glioma progression. Thus, our study demonstrates that tumor-suppressive miR-3591-3p in glioma cells can be secreted via exosomes and target TAMs to induce the formation of an immunosuppressive microenvironment. Collectively, these findings provide new insights into the role of glioma exosomal miRNAs in mediating the establishment of an immunosuppressive tumor microenvironment and show that miR-3591-3p may be a valuable biomarker and that blocking the encapsulation of miR-3591-3p into exosomes may become a novel immunotherapeutic strategy for glioma.

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

The Ins and Outs of Antigen Uptake in B cells

A review of our current knowledge of B cell antigen uptake mechanisms, the relevance of these processes to pathology, and outstanding questions in the field. Specific antigens induce B cell activation through the B cell receptor (BCR) which initiates downstream signaling and undergoes endocytosis. While extensive research has shed light on the signaling pathways in health and disease, the endocytic mechanisms remain largely uncharacterized. Given the importance of BCR-antigen internalization for antigen presentation in initiating adaptive immune responses and its role in autoimmunity and malignancy, understanding the molecular mechanisms represents critical, and largely untapped, potential therapeutics. In this review, we discuss recent advancements in our understanding of BCR endocytic mechanisms and the role of the actin cytoskeleton and post-translational modifications in regulating BCR uptake. We discuss dysregulated BCR endocytosis in the context of B cell malignancies and autoimmune disorders. Finally, we pose several outstanding mechanistic questions which will critically advance our understanding of the coordination between BCR endocytosis and B cell activation.

Plasmablasts derive from CD23- activated B cells after the extinction of IL-4/STAT6 signaling and IRF4 induction

The terminal differentiation of B cells into antibody-secreting cells (ASCs) is a critical component of adaptive immune responses. However, it is a very sensitive process, and dysfunctions lead to a variety of lymphoproliferative neoplasias including germinal center-derived lymphomas. To better characterize the late genomic events that drive the ASC differentiation of human primary naive B cells, we used our in vitro differentiation system and a combination of RNA sequencing and Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC sequencing). We discovered 2 mechanisms that drive human terminal B-cell differentiation. First, after an initial response to interleukin-4 (IL-4), cells that were committed to an ASC fate downregulated the CD23 marker and IL-4 signaling, whereas cells that maintained IL-4 signaling did not differentiate. Second, human CD23- cells also increased IRF4 protein to levels required for ASC differentiation, but they did that independently of the ubiquitin-mediated degradation process previously described in mice. Finally, we showed that CD23- cells carried the imprint of their previous activated B-cell status, were precursors of plasmablasts, and had a phenotype similar to that of in vivo preplasmablasts. Altogether, our results provide an unprecedented genomic characterization of the fate decision between activated B cells and plasmablasts, which provides new insights into the pathological mechanisms that drive lymphoma biology.

New insights into B cells as antigen presenting cells

In addition to their role as antibody producing cells, B cells make a critical contribution to adaptive immune responses by functioning as professional antigen-presenting cells (APC). Distinctive features of B cells as APC include the expression of the B cell receptor (BCR) for antigen and regulated expression of HLA-DO. Here, we discuss recent progress in investigation of B cells as APC. We start with an update on the canonical MHC class II antigen presentation pathway in B cells and alternative pathways, including generation of extracellular vesicles. Turning to APC function, we highlight the roles of B cells as thymic APC, as APC for T follicular helper (T_FH), as APC for CD4 memory T cells and as presenters of idiotypic BCR determinants. We also note recent examples that link B cell Ag-presentation to disease. Emerging evidence indicates that, in addition to unique features of B cells compared to other professional APC, there is appreciable heterogeneity among B cells, arising from, for example, B cell activation state or the microenvironment.

Cbls boost B cells

T cell regulation of antibody-mediated immunity is critical for health. In this issue of JEM, Li et al. (https://doi.org/10.1084/jem.20191537) identify the Cbl family of E3 ubiquitin ligases as B cell-intrinsic gatekeepers of T cell-dependent humoral immunity.