IgA class-switched CD27-CD21+ B cells in IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN) is characterised by the production of galactose-deficient IgA1 (GdIgA1) antibodies. As the source of pathogenic antibodies, B cells are central to IgAN pathogenesis, but the B cell activation pathways as well as the potential B cell source of dysregulated IgA-secretion remain unknown. METHODS: We carried out flow cytometry analysis of peripheral blood B cells in patients with IgA nephropathy and control subjects with a focus on IgA-expressing B cells to uncover the pathways of B cell activation in IgAN and how these could give rise to pathogenic GdIgA1 antibodies. RESULTS: In addition to global changes in the B cell landscape - expansion of naive and reduction in memory B cells - IgAN patients present with an increased frequency of IgA-expressing B cells that lack the classical memory marker CD27, but are CD21pos. IgAN patients further have an expanded population of IgApos antibody-secreting cells, which correlate with serum IgA levels. Both IgApos plasmabalsts and CD27neg B cells co-express GdIgA1. Implicating dysregulation at mucosal surfaces as the driver of such B cell differentiation, we found a correlation between lipopolysaccharide (LPS) in the serum and IgAposCD27neg B cell frequency. CONCLUSION: We propose that dysregulated immunity in the mucosa may drive de novo B cell activation within germinal centres, giving rise to IgAposCD27neg B cells and subsequently IgA-producing plasmablasts. These data integrate B cells into the paradigm of IgAN pathogenesis and allow to further investigate this pathway to uncover biomarkers and develop therapeutic interventions.

Effect of ß-glucans on rainbow trout (Oncorhynchus mykiss) IgM+ B cells.

ß-glucans are carbohydrates present in the cell wall of many fungi, which are often used as immunostimulants in feeds for farmed species. Their capacity to activate innate immune responses directly acting on innate cell populations has been widely documented in fish. However, whether they can affect the functionality of adaptive immune cells has been scarcely explored. In this context, in the current work, we have determined the effects of ß-glucans on rainbow trout blood IgM+ B cells in the presence or absence of 2,4,6-trinitrophenyl hapten conjugated to lipopolysaccharide (TNP-LPS), a model antigen. For this, rainbow trout peripheral blood leukocytes were incubated with different doses of ß-glucans or media alone in the presence or absence of TNP-LPS for 48 h. The size, levels of expression of surface MHC II, antigen processing and phagocytic capacities and proliferation of IgM+ B cells were then studied by flow cytometry. The number of IgM-secreting cells in the cultures was also estimated by ELISpot. ß-glucans significantly decreased the levels of surface MHC II expression and the antigen processing capacities of these cells, especially in the presence of TNP-LPS, while they increased their phagocytic activity. On their own, ß-glucans slightly activated the proliferation of IgM+ B cells but reduced that induced by TNP-LPS. In contrast, ß-glucans significantly increased the number of cells secreting IgM in the cultures. This effect of ß-glucans on the IgM-secreting capacity of B cells was also confirmed through a feeding experiment, in which the IgM-secreting capacity of blood leukocytes obtained from fish fed a ß-glucan-supplemented diet for one month was compared to that of leukocytes obtained from fish fed a control diet. Altogether, these findings contribute to increase our knowledge regarding the effects of ß-glucans on fish adaptive responses.

Evaluation of Regulatory B Cell Subpopulations CD24++CD38++, CD24++CD27+, Plasmablasts and Their Correlation with T Regs CD3+CD4+CD25+FOXP3+ in Dialysis Patients and Early Post-Transplant Rejection-Free Kidney Recipients.

Background: B and T regulatory cells, also known as Bregs and Tregs, are involved in kidney transplantation. The purpose of this study is to monitor changes in the frequency and absolute numbers of Tregs (CD3+CD4+CD25+FoxP3+), transitional Bregs (tBregs) (CD24++CD38++), memory Bregs (mBregs) (CD24++CD27+), and plasmablasts before (T0) and six months (T6) after transplantation. Additionally, we aim to investigate any correlation between Tregs and tBregs, mBregs, or plasmablasts and their relationship with graft function. Methods: Flow cytometry was used to immunophenotype cells from 50 kidney recipients who did not experience rejection. Renal function was assessed using the estimated glomerular filtration rate (eGFR). Results: At T6, there was a significant decrease in the frequency of Tregs, plasmablasts, and tBregs, as well as in the absolute number of tBregs. The frequency of mBregs, however, remained unchanged. Graft function was found to have a positive correlation with the frequency of tBregs and plasmablasts. A significant correlation was observed between the frequency and absolute number of tBregs only when the eGFR was greater than 60 but not at lower values. At an eGFR greater than 60, there was a positive correlation between the absolute numbers of Tregs and mBregs but not between Tregs and tBregs. No correlation was observed for any cell population in dialysis patients. Conclusions: The data show a correlation between the frequency and absolute number of tBregs and the absolute number of Tregs and mBregs with good renal function in the early post-transplant period.

Jchain-DTR Mice Allow for Diphtheria Toxin-Mediated Depletion of Antibody-Secreting Cells and Evaluation of Their Differentiation Kinetics.

Antibody-secreting cells (ASCs) are generated following B cell activation and constitutively secrete antibodies. As such, ASCs are key mediators of humoral immunity whether it be in the context of pathogen exposure, vaccination or even homeostatic clearance of cellular debris. Therefore, understanding basic tenants of ASC biology such as their differentiation kinetics following B cell stimulation is of importance. Towards that aim, we developed a mouse model which expresses simian HBEGF (a.k.a., diphtheria toxin receptor (DTR)) under the control of the endogenous Jchain locus (or J-DTR). ASCs from these mice expressed high levels of cell surface DTR and were acutely depleted following diphtheria toxin treatment. Furthermore, proof-of-principle experiments demonstrated the ability to use these mice to track ASC reconstitution following depletion in 3 distinct organs. Overall, J-DTR mice provide a new and highly effective genetic tool allowing for the study of ASC biology in a wide range of potential applications.

Role of TAM Receptors in Antimalarial Humoral Immune Response.

Immune response against malaria and the clearance of Plasmodium parasite relies on germinal-center-derived B cell responses that are temporally and histologically layered. Despite a well-orchestrated germinal center response, anti-Plasmodium immune response seldom offers sterilizing immunity. Recent studies report that certain pathophysiological features of malaria such as extensive hemolysis, hypoxia as well as the extrafollicular accumulation of short-lived plasmablasts may contribute to this suboptimal immune response. In this review, we summarize some of those studies and attempt to connect certain host intrinsic features in response to the malarial disease and the resultant gaps in the immune response.

Abnormal frequency of the memory B cell subsets and plasmablasts in patients with congenital severe hemophilia A: correlation with "Inhibitor" formation.

BACKGROUND: Development of antibodies against infused Factor VIII (FVIII) or "inhibitors" represents a major challenge following FVIII replacement therapy in patients with hemophilia A (HA). Recent studies have shown that certain cellular compartments of the immune system contribute to the production of such antibodies. Herein, we determined the frequency of class-switched CD19+IgD-CD27+/non-class-switched CD19+IgD+CD27+ memory B cell subsets and CD19+CD27hiCD38hi plasmablasts in patients with severe HA and their association with the development of inhibitors in these patients. METHODS: This cross-sectional case-control study enrolled 32 patients with severe HA, including 8 with and 24 without inhibitors, and 24 healthy individuals. The frequencies of the memory B cell subsets and plasmablasts were determined using flow cytometry. RESULTS: The frequency of CD19+IgD+CD27+ non-class-switched memory B cells was significantly lower in patients with HA (including both patients with and without inhibitors) than in healthy controls. The percentages of both CD19+IgD-CD27+ class-switched and CD19+IgD+CD27+ non-class-switched memory B cells did not differ significantly between patients with and without inhibitors. HA patients with inhibitors had significantly higher proportions of CD19+CD27hiCD38hi plasmablasts than the control group as well as the inhibitor (-) ones. No significant correlation was observed between the inhibitor levels with the percentages of memory B cell subsets and plasmablasts. CONCLUSION: This study is the first to demonstrate a dysregulated proportion of CD19+IgD+CD27+ non-class-switched memory B cells and CD19+CD27hiCD38hi plasmablasts in patients with severe HA. Therefore, strategies targeting memory B-cell/plasmablast differentiation may have promising outcomes in the management of inhibitor formation in patients with severe HA.

ICOS agonist vopratelimab modulates follicular helper T cells and improves B cell function in common variable immunodeficiency.

Common variable immunodeficiency (CVID) is an immune defect characterized by hypogammaglobulinemia and impaired development of B cells into plasma cells. As follicular helper T cells (TFH) play a central role in humoral immunity, we examined TFH cells in CVID, and investigated whether an inducible T cell co-stimulator (ICOS) agonist, vopratelimab, could modulate TFH, B cell interactions and enhance immunoglobulin production. CVID subjects had decreased TFH17 and increased TFH1 subsets; this was associated with increased transitional B cells and decreased IgG+ B and IgD-IgM-CD27+ memory B cells. ICOS expression on CVID CD4+ T cells was also decreased. However, ICOS activation of CD4+ T cells by vopratelimab significantly increased total CVID TFH, TFH2, cell numbers, as well as IL-4, IL-10 and IL-21 secretion in vitro. Vopratelimab treatment also increased plasma cells, IgG+ B cells, reduced naïve & transitional B cells and significantly increased IgG1 secretion by CVID B cells. Interestingly, vopratelimab treatment also restored IgA secretion in PBMCs from several CVID patients who had a complete lack of endogenous serum IgA. Our data demonstrate the potential of TFH modulation in restoring TFH and enhancing B cell maturation in CVID. The effects of an ICOS agonist in antibody defects warrants further investigation. This biologic may also be of therapeutic interest in other clinical settings of antibody deficiency.

Alterations of B-Cell subsets in Peripheral Blood from Adult Patients with Idiopathic Membranous Nephropathy.

OBJECTIVES: Idiopathic membranous nephropathy (MN) is an autoimmune disease characterized by specific antibodies. However, the underlying mechanisms by which lymphocytes promote the development of MN remain poorly understood. This study aims to determine the changes of B-cell subsets and their clinical significance in MN patients. METHODS: We included a cohort of 21 idiopathic MN patients with new onset or a relapse, 19 healthy controls (HCs) and 10 patients with minimal change disease (MCD). Immunohistochemistry and flow cytometry were performed to assess the B-cell infiltration in renal biopsy tissues and peripheral blood, respectively. RESULTS: Idiopathic MN patients (including new-onset and relapse groups) had lower percentages of marginal-zone B (MZB) and non-switched memory B cells, and higher percentages of plasmablasts than HCs (P < 0.01). Particularly, the new-onset group had lower percentages of switched memory B cells and MZB cells, and higher percentages of Naïve B cells than HCs (P<0.05). Interestingly, the percentage of plasmablasts was significantly correlated with urine protein to creatinine ratio, serum albumin, IgG, anti-M-type phospholipase A2 receptor antibody level and age in MN patients (P < 0.05). MN with Ehrenreich-Churg stage Ⅱ-Ⅳ had a lower median percentage of MZB and non-switched memory B cells, while a higher median percentage of plasmablasts than those in MN patients with stage Ehrenreich-Churg I (P < 0.05). CONCLUSION: Idiopathic MN patients had specific changes in B-cell subsets proportions in peripheral blood. Further studies are needed to precisely determine the roles of B-cell subsets in MN.

Análise do transcriptoma de diferentes tipos de células únicas do sangue periférico de pacientes infectados com o vírus da Dengue para detalhamento da massiva geração de células secretoras de anticorpos / Evaluation of the tryptophan metabolism in the massive generation of antibody-secreting cells in Dengue patients through the transcriptome of single blood cells

A Dengue induz uma resposta exacerbada e transitória das células secretoras de anticorpos (ASCs) no sangue de pacientes cerca de sete dias após o início dos sintomas. A frequência dessas ASCs chega a representar mais de 50% de todas as células B circulantes neste período. No entanto, ainda é desconhecido se a magnitude dessa resposta tem relação com a gravidade da Dengue. Nosso grupo de pesquisa já mostrou que a cultura de células nucleares do sangue periférico (PBMCs) de indivíduos saudáveis com partículas do vírus da Dengue (DENV), por 7 dias, levava a diferenciação de células B em ASCs em magnitude similar àquelas estimuladas por mitógenos. Essas culturas apresentavam um consumo significativamente maior de triptofano (TRP), associado à maior expressão das enzimas IDO1 e IDO2, e, consequentemente, maior síntese de quinurenina (KYN) em relação ao estímulo por mitógenos. Considerando que as concentrações de TRP e KYN detectadas nos sobrenadantes dessas culturas eram diretamente proporcionais ao aumento de ASCs, decidimos investigar o papel desse metabolismo do TRP e de seus respectivos metabólitos na diferenciação das ASCs. Para isso, análises do transcriptoma público de células únicas do sangue periférico de pacientes com Dengue (estudo E-MTAB- 9467) foram realizadas para inferir a real participação do metabolismo do TRP na geração de ASCs. Com o programa R foram executadas análises de Downstream. Identificamos um aumento massivo das ASCs nas amostras dos pacientes infectados com Dengue. No entanto, os principais genes desencadeadores da ativação do metabolismo do TRP (IDO1 e IDO2) não foram expressos nas subpopulações de células B, mas sim em células dendríticas e monócitos CD14+ respectivamente. Isso sugeriria que esta via não seria ativada nos linfócitos B. Por outro lado, genes codificadores de outros participantes da via do TRP (HSD17B10, ECHS1 e SIRT3) foram detectados em células B e podem estar relacionados com a proliferação das ASCs. Além disso, a análise de enriquecimento mostrou uma aumentada expressão de genes associados com moléculas de MHC de classe II em plasmablastos e plasmócitos de pacientes com Dengue. Porém, com a expressão aumentada de ENTPD1 nessas células durante a fase sintomatológica, nossos dados sugerem também que um eventual papel de plasmablastos e plasmócitos como apresentadoras de antígenos na Dengue poderia induzir uma resposta supressora de células T

Dengue can cause an exacerbated and transient antibody-secreting cell (ASC) response in the blood of patients nearly 7 days of symptomatology. The ASC frequency reaches more than 50% of all circulating B cells during that period. However, it is still unknown whether the magnitude of this response may be directly related to the severity of Dengue. Our research group has already shown that the culture of peripheral blood mononuclear cells (PBMCs) from healthy individuals with Dengue virus (DENV) particles for 7 days led to a differentiation of B cells into ASCs to a magnitude similar to those stimulated by mitogens. These cultures showed significantly higher consumption of tryptophan (TRP), associated with higher expression of enzymes IDO1 and IDO2, and consequently, higher synthesis of quinurenine (KYN) compared to mitogen stimulation. The concentrations of TRP and KYN detected in the supernatants of these cultures were directly proportional to ASC frequency increase. Thus, we have decided to investigate the role of TRP metabolism and its respective metabolites in ASC differentiation. For this, we performed an analysis of single-cell transcriptome with peripheral blood from Dengue patients (dataset from E-MTAB-9467 study). Downstream analyses were performed with R software. Corroborating with literature, we identified a massive increase in ASC frequency of Dengue infected patients. However, the main genes triggering TRP metabolism activation (IDO1 and IDO2) were not expressed in B-cell subsets, but in dendritic cells and CD14+ monocytes, respectively. This would suggest that this pathway would not be activated in B lymphocytes. Nevertheless, genes encoding other participants in the TRP pathway (HSD17B10, ECHS1, and SIRT3) were detected in B cells and may be related to ASC proliferation. Futhermore, a Gene Ontology analysis showed an increased expression of genes associated with MHC class II molecules in plasmablasts and plasma cells of Dengue patients. As these cells also presented an increased expression of ENTPD1 during the symptomatic phase, our data suggest a potential role of plasmablasts and plasma cells as antigen-presenting cells associated with a suppressive T cell response in Dengue

Expansion of extrafollicular B and T cell subsets in childhood-onset systemic lupus erythematosus.

Introduction: Most childhood-onset SLE patients (cSLE) develop lupus nephritis (cLN), but only a small proportion achieve complete response to current therapies. The prognosis of children with LN and end-stage renal disease is particularly dire. Mortality rates within the first five years of renal replacement therapy may reach 22%. Thus, there is urgent need to decipher and target immune mechanisms that drive cLN. Despite the clear role of autoantibody production in SLE, targeted B cell therapies such as rituximab (anti-CD20) and belimumab (anti-BAFF) have shown only modest efficacy in cLN. While many studies have linked dysregulation of germinal center formation to SLE pathogenesis, other work supports a role for extrafollicular B cell activation in generation of pathogenic antibody secreting cells. However, whether extrafollicular B cell subsets and their T cell collaborators play a role in specific organ involvement in cLN and/or track with disease activity remains unknown. Methods: We analyzed high-dimensional mass cytometry and gene expression data from 24 treatment naïve cSLE patients at the time of diagnosis and longitudinally, applying novel computational tools to identify abnormalities associated with clinical manifestations (cLN) and disease activity (SLEDAI). Results: cSLE patients have an extrafollicular B cell expansion signature, with increased frequency of i) DN2, ii) Bnd2, iii) plasmablasts, and iv) peripheral T helper cells. Most importantly, we discovered that this extrafollicular signature correlates with disease activity in cLN, supporting extrafollicular T/B interactions as a mechanism underlying pediatric renal pathogenesis. Discussion: This study integrates established and emerging themes of extrafollicular B cell involvement in SLE by providing evidence for extrafollicular B and peripheral T helper cell expansion, along with elevated type 1 IFN activation, in a homogeneous cohort of treatment-naïve cSLE patients, a point at which they should display the most extreme state of their immune dysregulation.

The Janus face of proliferating plasmablasts in dengue and COVID-19 infections.

Introduction: B cells play an integral role in the immune response to both dengue fever and COVID-19. Prior scRNAseq analyses of peripheral plasmablasts in COVID-19 have revealed a heterogeneous population with distinct cell subsets associated with proliferation; prior studies in patients with dengue fever have likewise shown the presence of proliferative pre-plasmablasts in the circulation. These findings may have implications for disease severity. In this study, we sought to gain a mechanistic understanding of the intracellular processes in naive and memory B cells that are associated with and may lead to an expanded proliferative plasmablast population in the circulation. Methods: We analyzed age-controlled (pediatric and adult), peripheral blood mononuclear cell scRNAseq datasets from patients infected with either dengue (primary or secondary) or COVID-19 (non-severe or severe) from previously published studies. Our preliminary analysis showed that pediatric patients with dengue and adults with COVID-19 had an expanded proliferative plasmablast (p-PB) population. By contrast, neither the adults with dengue nor the children with COVID-19 in our dataset had p-PBs. We used this distinctive preliminary signature to guide our analyses design and expanded our analyses to naive and memory B cells. Results: In age/disease conditions with and without p-PBs, we found differences in cell sensing and activation, including via the B cell receptor and downstream signal transduction. Likewise, inflammation was mediated differently: relative to groups without p-PBs, those with p-PBs had increased expression of interferon response and S100 genes (particularly severe COVID-19). Furthermore, several transcription factors at the nexus of activation, inflammation, and cell fate decisions were expressed differently in groups with and without p-PBs. Discussion: We used dengue and COVID-19 infections in adult and pediatric patients (focusing on naive B, memory B, and plasmablast cells) as a model to better understand the mechanisms that may give rise to p-PB populations in the circulation. Our results indicate that a more pro-inflammatory state in naive and memory B cells correlated with - and could influence the generation of- proliferating plasmablasts. Further exploration of these mechanisms will have implications for immune memory, vaccine development, and post-viral autoimmune syndromes.

Identification of stromal cell proportion-related genes in the breast cancer tumor microenvironment using CorDelSFS feature selection: implications for tumor progression and prognosis.

Background: The tumor microenvironment (TME) of breast cancer (BRCA) is a complex and dynamic micro-ecosystem that influences BRCA occurrence, progression, and prognosis through its cellular and molecular components. However, as the tumor progresses, the dynamic changes of stromal and immune cells in TME become unclear. Objective: The aim of this study was to identify differentially co-expressed genes (DCGs) associated with the proportion of stromal cells in TME of BRCA, to explore the patterns of cell proportion changes, and ultimately, their impact on prognosis. Methods: A new heuristic feature selection strategy (CorDelSFS) was combined with differential co-expression analysis to identify TME-key DCGs. The expression pattern and co-expression network of TME-key DCGs were analyzed across different TMEs. A prognostic model was constructed using six TME-key DCGs, and the correlation between the risk score and the proportion of stromal cells and immune cells in TME was evaluated. Results: TME-key DCGs mimicked the dynamic trend of BRCA TME and formed cell type-specific subnetworks. The IG gene-related subnetwork, plasmablast-specific expression, played a vital role in the BRCA TME through its adaptive immune function and tumor progression inhibition. The prognostic model showed that the risk score was significantly correlated with the proportion of stromal cells and immune cells in TME, and low-risk patients had stronger adaptive immune function. IGKV1D-39 was identified as a novel BRCA prognostic marker specifically expressed in plasmablasts and involved in adaptive immune responses. Conclusions: This study explores the role of proportionate-related genes in the tumor microenvironment using a machine learning approach and provides new insights for discovering the key biological processes in tumor progression and clinical prognosis.

TRAPnSeq allows high-throughput profiling of antigen-specific antibody-secreting cells.

Following activation by cognate antigen, B cells undergo fine-tuning of their antigen receptors and may ultimately differentiate into antibody-secreting cells (ASCs). While antigen-specific B cells that express surface receptors (B cell receptors [BCRs]) can be readily cloned and sequenced following flow sorting, antigen-specific ASCs that lack surface BCRs cannot be easily profiled. Here, we report an approach, TRAPnSeq (antigen specificity mapping through immunoglobulin [Ig] secretion TRAP and Sequencing), that allows capture of secreted antibodies on the surface of ASCs, which in turn enables high-throughput screening of single ASCs against large antigen panels. This approach incorporates flow cytometry, standard microfluidic platforms, and DNA-barcoding technologies to characterize antigen-specific ASCs through single-cell V(D)J, RNA, and antigen barcode sequencing. We show the utility of TRAPnSeq by profiling antigen-specific IgG and IgE ASCs from both mice and humans and highlight its capacity to accelerate therapeutic antibody discovery from ASCs.

Quiz case: Abnormal haematopoietic cells in pleural effusion.

This case was presented because of the number of plasmablasts in a patient with a medical history of multiple myeloma. Flow cytometry is a "gold standard" technique for the diagnosis of haematological malignancies. This technique works for all fluids and should be performed in effusions (pleural, pericardial, ascites) in cases of suspected haematological malignancy. Alternatively, immunohistochemistry using appropriate markers could be performed if flow cytometry is not available. This case illustrates a pleural infiltration by plasmablasts. Myelomatous cells were characterised by immunocytochemistry and flow cytometry.

Targeting plasma cells in systemic autoimmune rheumatic diseases - Promises and pitfalls.

Plasma cells are the antibody secretors of the immune system. Continuous antibody secretion over years can provide long-term immune protection but could also be held responsible for long-lasting autoimmunity in case of self-reactive plasma cells. Systemic autoimmune rheumatic diseases (ARD) affect multiple organ systems and are associated with a plethora of different autoantibodies. Two prototypic systemic ARDs are systemic lupus erythematosus (SLE) and Sjögren's disease (SjD). Both diseases are characterized by B-cell hyperactivity and the production of autoantibodies against nuclear antigens. Analogues to other immune cells, different subsets of plasma cells have been described. Plasma cell subsets are often defined dependent on their current state of maturation, that also depend on the precursor B-cell subset from which they derived. But, a universal definition of plasma cell subsets is not available so far. Furthermore, the ability for long-term survival and effector functions may differ, potentially in a disease-specific manner. Characterization of plasma cell subsets and their specificity in individual patients can help to choose a suitable targeting approach for either a broad or more selective plasma cell depletion. Targeting plasma cells in systemic ARDs is currently challenging because of side effects or varying depletion efficacies in the tissue. Recent developments, however, like antigen-specific targeting and CAR-T-cell therapy might open up major benefits for patients beyond current treatment options.

Single-cell transcriptomics combined with proteomics of intrathecal IgG reveal transcriptional heterogeneity of oligoclonal IgG-secreting cells in multiple sclerosis.

The phenotypes of B lineage cells that produce oligoclonal IgG in multiple sclerosis have not been unequivocally determined. Here, we utilized single-cell RNA-seq data of intrathecal B lineage cells in combination with mass spectrometry of intrathecally synthesized IgG to identify its cellular source. We found that the intrathecally produced IgG matched a larger fraction of clonally expanded antibody-secreting cells compared to singletons. The IgG was traced back to two clonally related clusters of antibody-secreting cells, one comprising highly proliferating cells, and the other consisting of more differentiated cells expressing genes associated with immunoglobulin synthesis. These findings suggest some degree of heterogeneity among cells that produce oligoclonal IgG in multiple sclerosis.

A transcriptionally distinct subset of influenza-specific effector memory B cells predicts long-lived antibody responses to vaccination in humans.

Seasonal influenza vaccination elicits hemagglutinin (HA)-specific memory B (Bmem) cells, and although multiple Bmem cell populations have been characterized, considerable heterogeneity exists. We found that HA-specific human Bmem cells differed in the expression of surface marker FcRL5 and transcriptional factor T-bet. FcRL5+T-bet+ Bmem cells were transcriptionally similar to effector-like memory cells, while T-betnegFcRL5neg Bmem cells exhibited stem-like central memory properties. FcRL5+ Bmem cells did not express plasma-cell-commitment factors but did express transcriptional, epigenetic, metabolic, and functional programs that poised these cells for antibody production. Accordingly, HA+ T-bet+ Bmem cells at day 7 post-vaccination expressed intracellular immunoglobulin, and tonsil-derived FcRL5+ Bmem cells differentiated more rapidly into antibody-secreting cells (ASCs) in vitro. The T-bet+ Bmem cell response positively correlated with long-lived humoral immunity, and clonotypes from T-bet+ Bmem cells were represented in the secondary ASC response to repeat vaccination, suggesting that this effector-like population predicts influenza vaccine durability and recall potential.

PD-1highCXCR5-CD4+ peripheral helper T cells promote CXCR3+ plasmablasts in human acute viral infection.

T cell-B cell interaction is the key immune response to protect the host from severe viral infection. However, how T cells support B cells to exert protective humoral immunity in humans is not well understood. Here, we use COVID-19 as a model of acute viral infections and analyze CD4+ T cell subsets associated with plasmablast expansion and clinical outcome. Peripheral helper T cells (Tph cells; denoted as PD-1highCXCR5-CD4+ T cells) are significantly increased, as are plasmablasts. Tph cells exhibit "B cell help" signatures and induce plasmablast differentiation in vitro. Interestingly, expanded plasmablasts show increased CXCR3 expression, which is positively correlated with higher frequency of activated Tph cells and better clinical outcome. Mechanistically, Tph cells help B cell differentiation and produce more interferon γ (IFNγ), which induces CXCR3 expression on plasmablasts. These results elucidate a role for Tph cells in regulating protective B cell response during acute viral infection.

Clinical value of plasmablasts in predicting disease relapse in patients with IgG4-related disease.

OBJECTIVES: To explore the value of plasmablasts in predicting disease relapse in IgG4-related diseases (IgG4-RD). METHODS: Treatment-naïve IgG4-RD patients treated with glucocorticoid (GC) monotherapy or leflunomide (LEF) and GC combination therapy diagnosed at the Chinese PLA General Hospital during February 2017 and January 2018 were included in this study. The absolute plasmablast count was measured by using the absolute count tubes with flow cytometry. Patients were categorized into high and low plasmablast level groups by defining the median number of plasmablasts as the cut-off value. The characteristics of the clinical manifestations between the two groups were compared. In addition, the correlation of plasmablast count with other indicators and its clinical value in predicting disease relapse were evaluated. RESULTS: Data of 37 treatment-naïve IgG4-RD patients were analyzed. The median (IQR) absolute count of plasmablasts was 4.0 (2.8-7.5)/µL, which was correlated with the lymphocyte percentage, serum IgG, IgG4, and IgG4/IgG. The baseline absolute count of plasmablasts was an independent risk factor for disease relapse in IgG4-RD patients (HR, 1.199; 95% CI, 1.030-1.396, P = 0.019), and the application of LEF was an independent protective factor (HR, 0.283; 95% CI, 0.106-0.759, p = 0.012). CONCLUSIONS: The present study preliminarily indicated that baseline absolute plasmablast count may independently predict disease relapse in patients with IgG4-RD treated with GC monotherapy or LEF and GC combination therapy. More efforts are still needed to be performed in the future. Key Points • The absolute count of plasmablasts is correlated with the lymphocyte percentage, serum IgG, IgG4 and IgG4/IgG. • The baseline absolute plasmablast count may predict disease relapse in patients with IgG4-RD treated with GC monotherapy or LEF and GC combination therapy. • The application of LEF is an independent protective factor for disease relapse in IgG4-RD.

A novel approach for characterization of KSHV-associated multicentric Castleman disease from effusions.

A biopsy of lymphoid tissue is currently required to diagnose Kaposi sarcoma-associated herpesvirus (KSHV)-associated multicentric Castleman disease (KSHV-MCD). Patients showing clinical manifestations of KSHV-MCD but no pathological changes of KSHV-MCD are diagnosed as KSHV inflammatory cytokine syndrome. However, a lymph node biopsy is not always feasible to make the distinction. A pathognomonic feature of lymph nodes in KSHV-MCD is the expansion of KSHV-infected, lambda-restricted but polyclonal plasmablasts. To investigate whether these cells also reside in extra-nodal sites, effusion from 11 patients with KSHV-MCD and 19 with KSHV inflammatory cytokine syndrome was analysed by multiparametric flow cytometry. A distinct, lambda-restricted plasmablastic population (LRP) with highly consistent immunophenotype was detected in effusions in 8/11 patients with KSHV-MCD. The same population was also observed in 7/19 patients with KSHV inflammatory cytokine syndrome. The detection of LRP stratified KSHV inflammatory cytokine syndrome into two clinically distinct subgroups; those with detectable LRP closely resembled KSHV-MCD, showing similar KSHV viral load, comparable severity of thrombocytopenia and hypoalbuminaemia, and similar incidences of hepatosplenomegaly. Collectively, the detection of LRP by flow cytometry can serve as a valuable tool in diagnosing KSHV-MCD. KSHV inflammatory cytokine syndrome with LRP in effusions may represent a liquid-form of KSHV-MCD.