Plasma Cell Differentiation Research Articles

Autoimmunity promotes chronic lymphocytic leukemia progression in an indolent disease model

Chronic lymphocytic leukemia (CLL) is a heterogeneous B cell malignancy characterized by the accumulation of functionally incompetent B lymphocytes. Despite the availability of highly effective treatments, CLL remains incurable, and the factors contributing to disease progression are not fully understood. Autoimmune complications frequently arise in CLL patients and are associated with poor clinical prognosis. This study investigates the connection between plasma cell-mediated autoimmunity and CLL progression using a mouse model that expresses an active Receptor Activator of NF-κB (RANK) in B cells (RK mice), where autoimmune manifestations coexist with CLL. Transcriptional profiling of RANK-driven leukemic cells revealed a more indolent form of CLL compared to the classical TCL1 model. The discovery of near-identical CDR3 regions in both plasma and CLL cells of RK mice suggests a shared progenitor and antigen driving both conditions. Deletion of Blimp-1, which prevents plasma cell differentiation, initially enhanced B1/CLL formation in young mice but nearly halted CLL progression, highlighting the significant influence of autoimmune complications on disease outcomes. This research underscores the intertwined nature of autoimmunity and CLL, suggesting that targeting inflammatory pathways could offer therapeutic potential for managing both conditions.

Myricetin exposure reduces PC differentiation in vitro in primary human B cells

BackgroundThe process of B cell activation and plasma cell (PC) formation involves morphological, transcriptional, and metabolic changes in the B cell. Blocking or reducing PC differentiation is one approach to treat autoimmune diseases that are characterized by the presence of pathogenic autoantibodies. Recent studies have suggested the potential of myricetin, a natural flavonoid with anti-inflammatory and antioxidant properties, to block or reduce PC differentiation.MethodsPrimary human B cells were purified by using a human B cell isolation kit. B cell subsets such as IgG memory B cells, marginal zone B cells (MZ B cells), and naive B cells were isolated by flow cytometry and activated to induce PC differentiation. Quantification of PCs (CD27 + + , CD38 +) was obtained by flow cytometry. The expression of mRNA was measured by qPCR. Ig secretion in culture supernatant was measured by ELISA.ResultsMyricetin treatment significantly reduced PC differentiation in primary human B cells and all B cell subsets. Myricetin exposure reduced Ig production both IgM and IgG, in culture supernatants at day 5. Myricetin treatment led to augmented BACH2 expression and reduced IRF4, BLIMP1, and XBP1 expression compared to control cultures.ConclusionMyricetin treatment reduced PC differentiation and Ig secretion by primary human B cells. Targeting B cells in this way may be a therapeutic approach for some autoimmune diseases.Graphical

DOP030 Mucosal deficiency of mitochondria-driven humoral immunity is linked to Crohn’s Disease

Abstract Background Secretory IgA (sIgA) is critical for the maintenance of the mucosal barrier function, preventing bacterial translocation and reducing the risk of chronic inflammation. Several decades of research have revealed a dysregulation of the B-cell compartment in inflammatory bowel disease (IBD) of yet unknown origin1,2. While increased serum levels of (auto)antibodies against S. cerevisiae or the intestinal M-cell expressed FimH receptor glycoprotein 2 (GP2) are observed in patients with Crohn’s disease (CD)3, some studies indicated an impaired generation of intestinal immunoglobulin-secreting plasma cells (PCs)4. To unravel the role of mucosal humoral immunity in CD pathogenesis, we aimed to provide an in-depth characterisation of colonic PC differentiation in patients with CD. Methods In-depth phenotyping of patients with CD in remission and non-IBD controls (hospitalised normals) was performed using multi-omics analyses (spatial single-cell proteomics, proteomics, metabolomics, and transcriptomics) of plasma or colon biopsy samples. Colonic switched memory B cells (sMBCs) were sorted from lamina propria mononuclear cells (LPMNCs) by magnetic-activated cell sorting and ex vivo differentiated into PCs. The impact of mitochondrial function on colonic PC maturation was studied in mitochondrial respiratory chain complex V-deficient ATP8 mutant mice and mice that underwent nutritional intervention. Results Despite a hyperactive colonic B-cell compartment, patients with CD displayed significantly diminished mucosal dimeric IgA (dIgA) and fecal IgA compared to non-IBD controls. Polymeric immunoglobulin receptor (PIGR) expression did not differ, excluding a defective epithelial transcytosis of dIgA. Spatial single-cell proteomics uncovered that colonic plasmablasts and immature CD19+CD45+ PCs were increased at the expense of the fully mature CD19-CD45- phenotype. Consistently, PCs generated ex vivo from CD-derived sMBCs revealed impaired capacity to differentiate into IgA-secreting PCs. Metabolic phenotyping indicated a colonic mitochondrial dysfunction in patients with CD that was also reflected in colonic PCs by increased expression of the cell-surface NADase CD38 in concert with decreased expression of mitochondrially encoded transcripts. Of note, splenic PCs isolated from ATP8 mutant mice displayed a hyperproliferative and low-differentiated phenotype, while colonic IgA-secreting PCs were reduced. Conversely, feeding mice an isocaloric glucose-free, high-protein diet, which promotes mitochondrial activity, increased colonic IgA levels. Conclusion In summary, this study links mitochondrial dysfunction to impaired PC differentiation in patients with CD, resulting in reduced levels of sIgA and thereby compromised mucosal barrier integrity.

Novel Sarcoidosis Epitope Augments MHCII, CD80/CD86 Expression, Promotes B-Cell Differentiation and IgG Production.

Numerous chronic human disorders are associated with immune activation by obscure antigen(s). We identified a novel sarcoidosis-epitope (ChainA) by immunoscreening of a novel T7 phage library and confirmed an abundance of ChainA IgG-antibody in sarcoidosis. We tested whether ChainA epitope elicits immune responses through B-cell activation, plasma cell differentiation and antibody production. PBMCs from healthy controls and sarcoidosis patients were challenged by chemically synthesized ChainA epitope, and assessed cellular activation markers of B-cells, T-cells, MHC classes, plasma cell differentiation and Unfolded Protein Response (UPR) transcription factors. Chain A increased expression of MHCII class and CD80/CD86 costimulatory molecules. ChainA significantly augmented the transition of naïve B-cells to memory B-cells and plasma cells in sarcoidosis PBMCs compared to healthy PBMCs. B-Cells differentiation to antibody-secreting plasma cells requires activation of UPR, B lymphocyte-induced maturation protein 1 (Blimp-1) and X-box binding protein 1 (XBP-1). ChainA treatment upregulated the expression of Blimp-1 and spliced form of XBP-1, a transcriptional activator of endoplasmic reticulum (ER) stress response. Furthermore, the transition of B cells to plasma cells in response to ChainA induced the production of anti-ChainA IgG. In parallel to human PBMCs, utilizing murine splenocytes, we validated our observations that ChainA challenge augments MHCII expression, a robust UPR responses, and an increased production of IgG specific antibody against ChainA. These results indicate ChainA epitope may be involved in the pathogenesis of sarcoidosis, as it activates MHCII, memory B-cells, plasma cell differentiation and production of ChainA specific IgG.

Allergic Reactivity and Memory Occur Independently of Sequential Switching Through IgG1.

Allergic reactions to foods are primarily driven by allergen-binding immunoglobulin (Ig)E antibodies. IgE-expressing cells can be generated through direct switching from IgM to IgE or a sequential class switching pathway where activated B cells first switch to an intermediary isotype, most frequently IgG1, and then to IgE. It has been proposed that sequential class switch recombination is involved in augmenting the severity of allergic reactions, generating high affinity IgE, differentiation of IgE plasma cells, and in holding the memory of IgE responses. We directly tested these possibilities by comparing the allergic immunity of wild-type and IgG1-deficient (hMT) mice. We found that sequential switching through IgG1 was not required to maintain the binding capacity of IgE nor for its ability to promote degranulation and elicit anaphylaxis against bona fide food allergens. Furthermore, the absence of sequential switching modestly impacted IgE affinity and clinical reactivity against hapten antigens, suggesting that the nature of the antigen impacts the requirement for sequential switching. At a cellular level, the capacity to undergo sequential switching through IgG1 provided no competitive advantage for subsequent IgE expression among germinal center B cells or plasma cells. Furthermore, the recall of allergic immunity at memory timepoints was preserved in the absence of sequential switching through IgG1, a finding that corresponded with intact type 2 memory B cell polarization. Together, these data demonstrate that sequential switching through IgG1 is redundant in sensitization, anaphylaxis, and the persistence of allergy, ultimately revealing that IgE derived from any switching source should be targeted by novel therapeutics seeking to ameliorate allergic diseases.

Experimental Murine Periodontitis Increases Salivary Gland IgA-Producing B Cells Following Oral Dysbiosis.

The oral microbiome is closely involved in the maintenance of host health and the development of systemic diseases. The salivary glands play an essential role in homeostasis in the oral cavity. Here, we investigated the effects of periodontal inflammation on salivary gland function and the oral microbiome. In experimental periodontitis model mice, an increase in IgA⁺ cells in the salivary glands were observed 1 week after treatment. Alteration of the oral microbiome was also induced in this model. Gene expression analysis of the salivary glands showed changes in the expression of genes related to B-cell maturation and plasma cell differentiation and an increase in the expression of genes related to macrophage activation upon experimental periodontitis induction. Furthermore, the relationship between disruption of oral microflora and salivary gland function was examined using a cohousing model in which experimental periodontitis model mice and untreated mice were reared in the same cage. We found that cohoused normal mice underwent alteration of the oral microbiome, with increases in IgA⁺ cells and macrophages in the salivary glands. In summary, our results suggest that, in the oral cavity, there is a close link between oral bacterial flora and immune cells in the salivary glands. Our results also show that localized inflammation disrupts the homeostasis in the oral cavity, inducing pathological conditions such as dysbiosis. Our study suggests the importance of the interaction among local oral inflammation, salivary gland function, and oral microflora, and provides new insights into the mechanisms by which oral health is maintained.

Immune regulatory adjuvant approach to mitigate subcutaneous immunogenicity of monoclonal antibodies.

Immunogenicity continues to be a challenge for development and clinical utility of monoclonal antibodies, and there are gaps in our current ability to prevent anti-drug antibody development in a safe and antigen-specific manner. To mitigate immunogenicity of monoclonal antibodies administered subcutaneously, O-phospho-L-serine (OPLS)-the head group of the tolerance-inducing phospholipid, phosphatidylserine-was investigated as an immunoregulatory adjuvant. Formulations of adalimumab, trastuzumab or rituximab with OPLS showed reduction in relative immunogenicity in mice compared to vehicle formulations, indicated by reduced anti-drug antibody development and significant reductions in CD138+ plasma cell differentiation in bone marrow. Titer development toward recombinant human hyaluronidase, a dispersion enhancer that was co-formulated with monoclonal antibodies, was similarly reduced. Subcutaneous administration of adalimumab with OPLS resulted in a two-fold increase in expression of type 1 regulatory (Tr1) T cell subset in the spleen. This is consistent with in vitro studies where co-culturing of dendritic cells primed with ovalbumin in the presence and absence of OPLS and antigen specific T-cells induced expression of Tr1 phenotype on live CD4+ T cells. This adjuvant does not impact immune competence of non-human primates and mice, and repeated administration of the adjuvant does not show renal or hepatic toxicity. Formulation of monoclonal antibodies with the immunoregulatory adjuvant, OPLS, was found to be safe and effective at mitigating immunogenicity.

Abstract IA018: Determinants of B cell fate and function in cancer

Abstract Effector B cell responses in solid malignancies are associated with favorable response to immunotherapy. B cells can amplify anti-tumor immune responses via antibody production, antigen presentation, and pro-inflammatory cytokine release; yet B cells in cancer patients and tumor-bearing mice often fail to support these functions. We have evaluated the contribution of either systemic inflammatory cues or antigenic quality to B cell differentiation and function in cancer. First, we identify dysregulated transcriptional programs activated in pancreatic cancer-associated B cells that promote differentiation of naïve into immunosuppressive B cells and inhibit differentiation of anti-tumor plasma cells. Second, we find that systemic exposure to STING agonists potentiates expansion of immunosuppressive regulatory human and mouse IL35+ B lymphocytes. Finally, using a system where a B cell neoantigen is either soluble or tethered to the surface of cancer cells, we demonstrate that membrane-tethered antigen is sufficient to elicit activation of anti-tumor immunity and reduce tumor growth in a NK cell-dependent manner. Thus, inflammation and quality of antigen impact basic mechanisms governing B cell differentiation and the resulting immune response to solid malignancy with implications for vaccine engineering. Citation Format: Yuliya Pylayeva-Gupta. Determinants of B cell fate and function in cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr IA018.

NOD1 Agonist Induces Proliferation and Plasma Cell Differentiation of Mouse B Cells Especially CD23high B Cells

ABSTRACT Background Like innate cells, B cells also express Pattern Recognition Receptors (PRRs) to detect danger signal such as tissue damage or pathogen intrusion. Production of specific antibodies by plasma cells results from the activation and differentiation of B cells following three signals: (i) antigen recognition by B Cell Receptors, (ii) recognition of danger and (iii) T-cell help. However, it is unclear whether T-cell help is dispensable for B cell activation and differentiation or not. Few studies have investigated the role of cytosolic PRRs such as NOD1 in B cell differentiation. Methods We used splenic C57BL6J B cells to evaluate NOD1 expression and then assessed the effect of stimulation with C12-iE-DAP, a NOD1 ligand, with or without CD40L as a T-cell help signal on B-cell responses globally or according to their CD23 expression level. Results We showed that murine B cells express NOD1 and that the presence of C12-iE-DAP induces activation, proliferation and initiates differentiation in plasma cells even in the absence of a T-dependent signal. Surprisingly, CD23high B cells are more sensitive than CD23low B cells to stimulation. Conclusion Our results suggest that the NLR pathway could induce antibody development during infections and be exploited to develop more effective vaccination.

Clinical and immunological characteristics of high-risk double-hit multiple myeloma

At present, the characteristics of double-hit multiple myeloma (DHMM) are unknown. We retrospectively analyzed the clinical data from 433 new diagnosed MM patients and found that DHMM have a higher β2-MG level and percentage of bone marrow plasma cell. Cox regression analysis showed that the prognosis of DHMM was not limited by clinical indicators. The abnormal proliferation of bone marrow in DHMM is obvious, and the proportion of poorly differentiated plasma cell is high. By collecting specimens from our center and performing flow cytometry to analyze the immunophenotypic and functional characteristics of lymphocyte subpopulations, we found that DHMM had a higher ratio of Tregs cells, and the proportion of iTregs cells was also significantly higher than non-DHMM (P < 0.05). Moreover, DHMM had higher levels of TGF-β1 and IL-10, and TGF-β1 and IL-10 were positively correlated with iTregs (P < 0.05). In addition, DHMM was highly expressed PD-1 on CD8 + T cells and had a higher proportion of CD38highTregs cells. In vitro we have shown that the addition of TGF-β1 antibody or CD38 antibody can effectively inhibit the proportion of CD38high Tregs. This study describes the characteristics of DHMM based on bicentric data, which is helpful to better provide theoretical support for the treatment of DHMM.

Increased PRP19 in Hepatocyte Impedes B Cell Function to Promote Hepatocarcinogenesis.

Tumor immune microenvironment is strongly associated with the malignancy behavior of hepatocellular carcinoma (HCC). However, the immune function and regulatory mechanisms of B cells in HCC remain unclear. The expression differences between B cell high- and low-infiltration HCC samples are explored to identify the key regulator. Pre-mRNA processing factor 19 (PRP19) expression is increased in B cell low-infiltrated tissues and negatively correlated with the B cell marker, CD20. Inhibition of PRP19 expression promoted B cell infiltration in tumor tissue and impeded HCC growth. Mechanically, the co-immunoprecipitation (Co-IP) assay revealed that PRP19 interacts with DEAD-box helicase 5 (DDX5), leading to ubiquitination and degradation of the DDX5 protein. The attenuated DDX5 impairs CXCL12 mRNA stability to suppress B cell recruitment and plasma cell differentiation via CXCL12/CXCR4 axis. Moreover, the adoptive transfer of CXCR4+ B cells combined with CXCL12 treatment in mice models effectively inhibits HCC development by reshaping the immune response. The expression of PRP19, DDX5, and infiltrating B cells are recognized as clinical prognosis indicators for HCC patients. Overall, this study provides valuable insights into the clinical benefits of HCC immunotherapy by targeting PRP19 and modulating tumor-infiltrating B cell immune function.

CD30 influences germinal center B-cell dynamics and the expansion of IgG1-switched B cells

Initially, identified as a Hodgkin lymphoma marker, CD30 was subsequently detected on a subset of human B cells within and around germinal centers (GCs). While CD30 expression is typically restricted to a few B cells, expansion of CD30-expressing B cells occurs in certain immune disorders and during viral infections. The role of CD30 in B cells remains largely unclear. To address this gap in knowledge, we established a conditional CD30-knockin mouse strain. In these mice, B-cell-specific CD30 expression led to a normal B-cell phenotype in young mice, but most aged mice exhibited significant expansion of B cells, T cells and myeloid cells and increased percentages of GC B cells and IgG1-switched cells. This may be driven by the expansion of CD4+ senescence-associated T cells and T follicular helper cells, which partially express CD30-L (CD153) and may stimulate CD30-expressing B cells. Inducing CD30 expression in antigen-activated B cells accelerates the GC reaction and augments plasma cell differentiation, possibly through the posttranscriptional upregulation of CXCR4. Furthermore, CD30 expression in GC B cells promoted the expansion of IgG1-switched cells, which displayed either a GC or memory-like B-cell phenotype, with abnormally high IgG1 levels compared with those in controls. These findings shed light on the role of CD30 signaling in GC B cells and suggest that elevated CD30+ B-cell numbers lead to pathological lymphocyte activation and proliferation.

Developing a workflow for the isolation of hybridoma cells producing fully human antigen-specific antibodies using a surface IgG detection method

The antigen-mediated B cell isolation method, based on the detection of surface IgG (sIgG), has increased the efficiency of therapeutic antibody (Ab) discovery. However, the reduction in sIgG expression on B cells during plasma cell differentiation presents challenges as it enables Ab production from only a small subset of B cells (e.g., memory B cells). The present study aimed to addressed this problem by developing a workflow to isolate human-IgG-secreting hybridoma cells produced by cell fusion, the majority of which express sIgG. We showed that our sIgG-based antigen-coated bead separation method efficiently enriched hybridoma cells expressing antigen-specific Abs with a yield of 83.5% (from the cell fusion pool) and a positive rate of 73.2%. Furthermore, because the separation could be performed after only a short (1–2-day) culture period following cell fusion, diverse hybridoma clones could be obtained, minimizing clonal selection and the incidence of duplicates. Given that the expression of membrane-bound IgG and sIgG are regulated by different splicing mechanisms, we speculate that the cell fusion step potentially attenuated the suppression of human sIgG expression. Overall, our proposed method is expected to markedly improve the efficiency of therapeutic Ab candidate production, which will have important clinical implications.

Variations in the germinal center response revealed by genetically diverse mouse strains.

The humoral response is complex and involves multiple cellular populations and signaling pathways. Bacterial and viral infections, as well as immunization regimens, can trigger this type of response, promoting the formation of microanatomical cellular structures called germinal centers (GCs). GCs formed in secondary lymphoid organs support the differentiation of high-affinity plasma cells and memory B cells. There is growing evidence that the quality of the humoral response is influenced by genetic variants. Using 12 genetically divergent mouse strains, we assessed the impact of genetics on GC cellular traits. At steady state, in the spleen, lymph nodes and Peyer's patches, we quantified GC B cells, plasma cells and follicular helper Tcells. These traits were also quantified in the spleen of mice following immunization with a foreign antigen, namely, sheep red blood cells, in addition to the number and size of GCs. We observed both strain- and organ-specific variations in cell type abundance, as well as for GC number and size. Moreover, we find that some of these traits are highly heritable. Importantly, the results of this study inform on the impact of genetic diversity in shaping the GC response and identify the traits that are the most impacted by genetic background.

The ICF2 gene Zbtb24 specifically regulates the differentiation of B1 cells via promoting heme synthesis

BackgroundLoss-of-function mutations of ZBTB24 cause immunodeficiency, centromeric instability, and facial anomalies syndrome 2 (ICF2). ICF2 is a rare autosomal recessive disorder with immunological defects in serum antibodies and circulating memory B cells, resulting in recurrent and sometimes fatal respiratory and gastrointestinal infections. The genotype–phenotype correlation in patients with ICF2 indicates an essential role of ZBTB24 in the terminal differentiation of B cells.MethodsWe used the clustered regularly interspaced short palindromic repeats (CRISPER)/Cas9 technology to generate B cell specific Zbtb24-deficient mice and verified the deletion specificity and efficiency by quantitative polymerase chain reaction (Q-PCR) and western blotting analyses in fluorescence-activated cell sorting (FACS)-sorted cells. The development, phenotype of B cells and in vivo responses to T cell dependent or independent antigens post immunization were analyzed by flow cytometry and enzyme-linked immunosorbent assay (ELISA). Adoptive transfer experiment in combination with in vitro cultures of FACS-purified B cells and RNA-Seq analysis were utilized to specifically determine the impact of Zbtb24 on B cell biology as well as the underlying mechanisms.ResultsZbtb24 is dispensable for B cell development and maintenance in naive mice. Surprisingly, B cell specific deletion of Zbtb24 does not evidently compromise germinal center reactions and the resulting primary and secondary antibody responses induced by T cell dependent antigens (TD-Ags), but significantly inhibits T cell independent antigen-elicited antibody productions in vivo. At the cellular level, Zbtb24-deficiency specifically impedes the plasma cell differentiation of B1 cells without impairing their survival, activation and proliferation in vitro. Mechanistically, Zbtb24-ablation attenuates heme biosynthesis partially through mTORC1 in B1 cells, and addition of exogenous hemin abrogates the differentiation defects of Zbtb24-null B1 cells.ConclusionsZbtb24 seems to regulate antibody responses against TD-Ags B cell extrinsically, but it specifically promotes the plasma cell differentiation of B1 cells via heme synthesis in mice. Our study also suggests that defected B1 functions contribute to recurrent infections in patients with ICF2.

Increased autoreactivity and maturity of EBI2+ antibody-secreting cells from nasal polyps.

Elevated numbers of antibody-secreting cells (ASCs) and anti-double-stranded DNA (anti-dsDNA) antibodies are found in nasal polyp (NP) tissue. The presence of anti-dsDNA IgG in tissue prospectively predicts recurrent NP but the characteristics of the source ASCs are unknown. Here, we investigated whether NP B cells expressing the extrafollicular marker EBI2 have increased propensity for autoantibody production and evaluated the molecular characteristics of NP ASCs. NPs showed increased frequencies of anti-dsDNA IgG and total IgG ASCs compared with tonsils, with more pronounced differences among EBI2+ cells. In NPs, EBI2+ cells were frequently double negative (IgD-CD27-) and ASCs. Single-cell RNA-Seq analysis of tonsils and NPs revealed substantial differences in B lineage composition, including differences in percentages of ASCs, germinal centers, proliferative cells, and non-ASCs. NPs exhibited higher expression of specific isotypes (IGHE, IGHA1, IGHA2, and IGHG4) and mature plasma genes, including SDC1 and XBP1, than tonsils. Gene Ontology biological processes indicated upregulated NF-κB and downregulated apoptosis pathways in NP ASCs. Together, these data indicate that NP EBI2+ ASCs secret increased total and anti-dsDNA IgG compared with those from tonsils and had molecular features of mature plasma cell differentiation.

Iguratimod suppresses plasma cell differentiation and ameliorates experimental Sjögren's syndrome in mice by promoting TEC kinase degradation.

Primary Sjögren's syndrome (pSS) is a chronic inflammatory autoimmune disease with an unclear pathogenesis, and there is currently no approved drug for the treatment of this disease. Iguratimod, as a novel clinical anti-rheumatic drug in China and Japan, has shown remarkable efficacy in improving the symptoms of patients with pSS in clinical studies. In this study we investigated the mechanisms underlying the therapeutic effect of iguratimod in the treatment of pSS. Experimental Sjögren's syndrome (ESS) model was established in female mice by immunizing with salivary gland protein. After immunization, ESS mice were orally treated with iguratimod (10, 30, 100 mg·kg-1·d-1) or hydroxychloroquine (50 mg·kg-1·d-1) for 70 days. We showed that iguratimod administration dose-dependently increased saliva secretion, and ameliorated ESS development by predominantly inhibiting B cells activation and plasma cell differentiation. Iguratimod (30 and 100 mg·kg-1·d-1) was more effective than hydroxychloroquine (50 mg·kg-1·d-1). When the potential target of iguratimod was searched, we found that iguratimod bound to TEC kinase and promoted its degradation through the autophagy-lysosome pathway in BAFF-activated B cells, thereby directly inhibiting TEC-regulated B cells function, suggesting that the action mode of iguratimod on TEC was different from that of conventional kinase inhibitors. In addition, we found a crucial role of TEC overexpression in plasma cells of patients with pSS. Together, we demonstrate that iguratimod effectively ameliorates ESS via its unique suppression of TEC function, which will be helpful for its clinical application. Targeting TEC kinase, a new regulatory factor for B cells, may be a promising therapeutic option.

Ofatumumab in the treatment of multiple sclerosis - A summary of preclinical and clinical data

B-cell targeted therapies are highly effective in multiple sclerosis (MS). Most of these therapies are administered intravenously at long intervals. Ofatumumab, an anti-CD20 antibody that is administered subcutaneously at low doses on a monthly basis due to its high affinity to the target structure, became available for the treatment of MS in 2021. An overview of practice-relevant immunological and clinical data on ofatumumab is provided. The high affinity of ofatumumab to the target structure allows low dose and low volume administration, with the release and absorption profile after subcutaneous application allowing for high concentrations in the lymph nodes and gradual depletion of B-cells. Rapid onset of action is achieved as well as B-cell repletion within a few months in case of discontinuation of therapy. Long-term data show stable IgG levels over up to four years and high efficacy with respect to relapse rate, progression, and cognition. According to current study data, the effect compared to teriflunomide is greater the earlier therapy is initiated. Ofatumumab has a specific B-cell depletion pattern. CD20 expressing B-cell progenitor cells in the bone marrow are preserved and therefore also the inducibility and differentiation of plasma cells. The formation of a humoral immunological memory is therefore possible. Four-year study data showed no abnormalities in the rate of severe infections or malignancies. Ofatumumab is an innovative B-cell targeted therapy. It is highly effective with a good safety and tolerability profile, well controllable and maintains immunocompetence against pathogens.

Role of canonical and noncanonical autophagy pathways in shaping the life journey of B cells.

Autophagy is a regulated intracellular catabolic process by which invading pathogens, damaged organelles, aggregated proteins, and other macromolecules are degraded in lysosomes. It has been widely appreciated that autophagic activity plays an important role in regulating the development, fate determination, and function of cells in the immune system, including B lymphocytes. Autophagy encompasses several distinct pathways that have been linked to B cell homeostasis and function. While B cell presentation of major histocompatibility complex (MHC) class II-restricted cytosolic antigens to T cells involves both macroautophagy and chaperone-mediated autophagy (CMA), plasma cells and memory B cells mainly rely on macroautophagy for their survival. Emerging evidence indicates that core autophagy factors also participate in processes related to yet clearly distinct from classical autophagy. These autophagy-related pathways, referred to as noncanonical autophagy or conjugation of ATG8 to single membranes (CASM), contribute to B cell homeostasis and functions, including MHC class II-restricted antigen presentation to T cells, germinal center formation, plasma cell differentiation, and recall responses. Dysregulation of B cell autophagy has been identified in several autoimmune and autoinflammatory diseases such as systemic lupus erythematosus, rheumatoid arthritis, and inflammatory bowel disease. In this review, we discuss recent advances in understanding the role of canonical and noncanonical autophagy in B cells, including B cell development and maturation, antigen processing and presentation, pathogen-specific antibody responses, cytokine secretion, and autoimmunity. Unraveling the molecular mechanisms of canonical and noncanonical autophagy in B cells will improve our understanding of B cell biology, with implications for the development of autophagy-based immunotherapies.

Fibroblast-like synoviocytes preferentially induce terminal differentiation of IgD+ memory B cells instead of naïve B cells.

Rheumatoid arthritis (RA) is a systemic autoimmune disease driven by highly active autoantibody-producing B cells. Activation of B cells is maintained within ectopic germinal centres found in affected joints. Fibroblast-like synoviocytes (FLS) present in inflamed joints support B-cell survival, activation, and differentiation. CD27+ memory B cells and naive B cells show very different responses to activation, particularly by CD40 ligand (CD40L). We show that FLS-dependent activation of human B cells is dependent on interleukin-6 (IL-6) and CD40L. FLS have been shown to activate both naive and memory B cells. Whether the activating potential of FLS is different for naive and memory B cells has not been investigated. Our results suggest that FLS-induced activation of B cells is dependent on IL-6 and CD40L. While FLS are able to induce plasma cell differentiation, isotype switching, and antibody production in memory B cells, the ability of FLS to activate naive B cells is significantly lower.