Age-associated B Cells Research Articles

B cell-intrinsic IFN-γ promotes excessive CD11c+ age-associated B cell differentiation and compromised germinal center selection in lupus mice

CD11c+ age-associated B cells (ABCs) have emerged as a key component in protective and autoreactive B cell responses. Lupus is an autoimmune disorder linked to reduced efficacy of vaccines and increased susceptibility to infections. Previously, we reported that excessive CD11c+ ABCs not only significantly contribute to autoantibody production but also promote aberrant T cell activation and compromised affinity-based germinal center selection in response to immunization in lupus mice. Yet, the regulation of CD11c+ ABC differentiation is not fully understood. In this study, we show that B cell-intrinsic IFN-γ is required for excessive CD11c+ ABC differentiation in lupus mice. B cell-intrinsic IFN-γ is mainly produced by CD11c+ ABCs. IFN-γ-deficiency leads to decreased expression of ABC characteristic genes. We further show that ablating IFN-γ can normalize T cell overactivation and rescue antigen-specific GC responses in lupus mice. Our study offers insight into the crucial role of B cell-intrinsic IFN-γ in promoting excessive CD11c+ ABC differentiation, which compromises affinity-based germinal center selection and affinity maturation in lupus, providing a potential strategy to normalize vaccine responses in lupus.

Bank1 modulates the differentiation and molecular profile of key B cell populations in autoimmunity.

This study aimed at defining the role of the B cell adaptor protein BANK1 in the appearance of age-associated B cells (ABCs) in 2 SLE mouse models (TLR7.tg6 and imiquimod-induced mice), crossed with Bank1-/- mice. The absence of Bank1 led to a significant reduction in ABC levels, also affecting other B cell populations. To gain deeper insights into their differentiation pathway and the effect of Bank1 on B cell populations, a single-cell transcriptome assay was performed. In the TLR7.tg6 model, we identified 10 clusters within B cells, including an ABC-specific cluster that was decreased in Bank1-deficient mice. In its absence, ABCs exhibited an antiinflammatory gene expression profile, while being proinflammatory in Bank1-sufficient lupus-prone mice. Trajectory analyses revealed that ABCs originated from marginal zone and memory-like B cells, ultimately acquiring transcriptional characteristics associated with atypical memory cells and long-lived plasma cells. Also, Bank1 deficiency normalized the presence of naive B cells, which were nearly absent in lupus-prone mice. Interestingly, Bank1 deficiency significantly reduced a distinct cluster containing IFN-responsive genes. These findings underscore the critical role of Bank1 in ABC development, affecting early B cell stages toward ABC differentiation, and the presence of IFN-stimulated gene-containing B cells, both populations determinant for autoimmunity.

Age-associated B-cells expansion is an independent predictor of atherosclerosis and improve risk stratification in early rheumatoid arthritis

Age-associated B-cells expansion is an independent predictor of atherosclerosis and improve risk stratification in early rheumatoid arthritis

Low density granulocytes and neutrophil extracellular trap formation are increased in incomplete systemic lupus erythematosus.

To investigate the proportion of low-density granulocytes (LDGs), circulating plasma neutrophil extracellular traps (NETs), and serum-induced NET formation in patients with incomplete systemic lupus erythematosus (iSLE) and systemic lupus erythematosus (SLE). LDGs were measured cross-sectionally in 18 iSLE patients, 11 SLE patients and 14 healthy controls (HCs), whereas circulating NETs and serum-induced NET formation were assessed in 35 iSLE patients, 41 SLE patients and 16 HCs. LDGs (CD14lowCD15+) were measured in PBMCs using flow cytometry and circulating plasma NETs were measured using anti-myeloperoxidase-DNA, anti-citrullinated histone H3 and anti-elastase-DNA complex ELISAs. Serum-induced NET formation was assessed by incubating healthy neutrophils with serum from iSLE patients, SLE patients or HCs and visualizing NETs with fluorescence microscopy. Proportions of LDGs and circulating plasma NETs were similarly elevated in iSLE and SLE patients compared with those in HCs. Furthermore, patients under hydroxychloroquine (HCQ) treatment had lower proportions of LDGs than those without. Serum from iSLE and SLE patients similarly induced NET formation in healthy neutrophils. In iSLE patients, myeloperoxidase-DNA complexes were correlated with proportions of age-associated B-cells, memory B-cells and negatively with naïve B-cells, while we did not find associations between measures of NETs or serum-induced NET formation and interferon score or clinical parameters. These results show that neutrophil dysfunction, including higher proportions of LDGs, and increased NET formation, already occur in iSLE, similar to SLE, despite differences in disease manifestations. Thereby, neutrophil dysfunction may contribute to sustained exposure to autoantigens and autoreactivity in early stages of SLE.

Human and Murine Toll-like Receptor-Driven Disease in Systemic Lupus Erythematosus.

The pathogenesis of systemic lupus erythematosus (SLE) is linked to the differential roles of toll-like receptors (TLRs), particularly TLR7, TLR8, and TLR9. TLR7 overexpression or gene duplication, as seen with the Y-linked autoimmune accelerator (Yaa) locus or TLR7 agonist imiquimod, correlates with increased SLE severity, and specific TLR7 polymorphisms and gain-of-function variants are associated with enhanced SLE susceptibility and severity. In addition, the X-chromosome location of TLR7 and its escape from X-chromosome inactivation provide a genetic basis for female predominance in SLE. The absence of TLR8 and TLR9 have been shown to exacerbate the detrimental effects of TLR7, leading to upregulated TLR7 activity and increased disease severity in mouse models of SLE. The regulatory functions of TLR8 and TLR9 have been proposed to involve competition for the endosomal trafficking chaperone UNC93B1. However, recent evidence implies more direct, regulatory functions of TLR9 on TLR7 activity. The association between age-associated B cells (ABCs) and autoantibody production positions these cells as potential targets for treatment in SLE, but the lack of specific markers necessitates further research for precise therapeutic intervention. Therapeutically, targeting TLRs is a promising strategy for SLE treatment, with drugs like hydroxychloroquine already in clinical use.

P160 High levels of CD19 expression is a characteristic feature of age-associated B cells in ageing and autoimmunity

Abstract Background/Aims Recent evidence implicates an important role for age-associated B cells (ABCs), defined as CD19+IgD-CD27-T-bet+ B cells, in healthy ageing, following viral infection and in active SLE. We know that co-receptors of the B cell receptor (BCR) such as CD19 and other activating receptors can influence B cell activation through distinct pathways. Therefore, we compared the expression of CD19 in B cell subpopulations including ABCs in ageing and SLE. Methods Peripheral blood was obtained from six young (<45 years) healthy participants, seven elderly (>65 years) healthy participants and eight patients with SLE (25-65 years). We performed flow cytometry on peripheral blood mononuclear cells to analyse the expression of extracellular and intracellular markers. We performed statistical analysis using GraphPad Prism v7. Results CD19hi B cell frequency was at least 10-fold higher in T-bet+ cells as a whole and particularly enriched in IgD-CD27-T-bet+, ABCs, in all groups, p < 0.05. The geometric mean fluorescent intensity (gMFI, expression) of CD40 was significantly lower in IgD-CD27-T-bet+ subpopulations compared to IgD-CD27-T-bet- B cell subpopulations in all groups (Table). In all groups, in CD19+T-bet+ cells, compared to CD19+T-bet- cells, there was a significantly increased frequency of IFNγR+ cells, TLR4+ cells, TLR7+ cells and TLR9+ cells (p < 0.05 for all) with remarkable difference noted in SLE patients for TLR7 and TLR9, p < 0.01 (Table). In the switched memory IgD-CD27+ and ABCs, TLR7 expression was significantly higher (p < 0.01) in SLE patients (mean 43.8% and 18.5% respectively) compared to elderly participants (mean 13.5% compared to 4.3% respectively). Conclusion High levels of expression of CD19 is a characteristic feature of ABCs and CD19hiT-bet+ cells predominantly belong to the IgD-CD27-T-bet+ ABC subpopulation. CD19hi IgD-CD27-T-bet+ cells also had significantly lower expression of CD40 and higher expression of IFNγR and TLR7 and TLR9, suggesting that CD19 plays a significant role in moderating activation of ABCs triggered through T-independent, IFNγR-TLR-T-bet pathway. Taken together with the significant role of CD19 in regulating signalling threshold of B cell activation, and its stable expression across different B cell developmental stages, these data provide compelling mechanistic rationale for targeting CD19 to deplete B cells, including potentially pathogenic age-associated, in autoimmune disease such as SLE. Disclosure K. Shah: None. V. Poon: None. S.J. Taylor: None. C. Klein: Corporate appointments; CK is employed by Roche. Shareholder/stock ownership; CK has patents and stock ownership at Roche. F. Kollert: Corporate appointments; FK is employed by Roche. Shareholder/stock ownership; FK has stock ownership at Roche. F. Schuler: Corporate appointments; FS is employed by Roche. Shareholder/stock ownership; FS has patents and stock ownership at Roche. S. Mathur: None. M. Castelino: None. D. Sen: None. J. Cambridge: None. M. Cragg: None. M. Leandro: None. A. Akbar: None. V. Reddy: None.

Age-associated B cell infiltration in salivary glands represents a hallmark of Sjögren's-like disease in aging mice.

Sjögren's disease (SjD), characterized by circulating autoantibodies and exocrine gland inflammation, is typically diagnosed in women over 50years of age. However, the contribution of age to SjD pathogenesis is unclear. C57BL/6 female mice at different ages were studied to investigate how aging influences the dynamics of salivary gland inflammation. Salivary glands were characterized for immune cell infiltration, inflammatory gene expression, and saliva production. At 8months, gene expression of several chemokines involved in immune cell trafficking was significantly elevated. At this age, age-associated B cells (ABCs), a unique subset of B cells expressing the myeloid markers CD11b and/or CD11c, were preferentially enriched in the salivary glands compared to other organs like the spleen or liver. The salivary gland ABCs increased with age and positively correlated with increased CD4 T follicular helper cells. By 14months, lymphocytic foci of well-organized T and B cells spontaneously developed in the salivary glands. In addition, the mice progressively developed high titers of serum autoantibodies. A subset of aged mice developed salivary gland dysfunction mimicking SjD patients. Our data demonstrates that aging is a significant confounding factor for SjD. Thus, aged female C57BL/6 mice are more appropriate and a valuable preclinical model for investigating SjD pathogenesis and novel therapeutic interventions.

In-depth human immune cellular profiling from newborn to frail.

Immune functional decline and remodeling accompany aging and frailty. It is still largely unknown how changes in the immune cellular composition differentiate healthy individuals from those become frail at a relatively early age. Our aim in this exploratory study was to investigate immunological changes from newborn to frailty, and the association between health statute and various immune cell subtypes. The participants analyzed in this study covered human cord blood cells and peripheral blood cells collected from young adults, healthy and frail old individuals. A total of 30 immune cell subsets was performed by flow cytometry based on the surface markers of immune cells. Furthermore, frailty was investigated for its relations with various leukocyte subpopulations. Frail individuals exhibited a higher CD4/CD8 ratio, a higher proportion of CD4+ central memory T (TCM) cells, CD8+ effector memory T cells, CD27- switched memory B (CD27-BSM) cells, CD27+ switched memory B cells, age-associated B cells (ABCs) and CD38-CD24- B cells, and a lower proportion of naïve CD8 + T cells and progenitor B cells. The Frailty index score was found to be associated with naïve T cells, CD4/CD8 ratio, ABCs, CD27-BSM cells, and CD4+ TCM cells. Our findings conducted a relatively comprehensive and extensive atlas of age- and frailty-related changes in peripheral leukocyte subpopulations from newborn to frailty. The immune phenotypes identified in this study can contribute to a deeper understanding of immunosenescence in frailty and may provide a rationale for future interventions and diagnosis.

T-bet+ B cells are activated by and control endogenous retroviruses through TLR-dependent mechanisms

Endogenous retroviruses (ERVs) are an integral part of the mammalian genome. The role of immune control of ERVs in general is poorly defined as is their function as anti-cancer immune targets or drivers of autoimmune disease. Here, we generate mouse-strains where Moloney-Murine Leukemia Virus tagged with GFP (ERV-GFP) infected the mouse germline. This enables us to analyze the role of genetic, epigenetic and cell intrinsic restriction factors in ERV activation and control. We identify an autoreactive B cell response against the neo-self/ERV antigen GFP as a key mechanism of ERV control. Hallmarks of this response are spontaneous ERV-GFP+ germinal center formation, elevated serum IFN-γ levels and a dependency on Age-associated B cells (ABCs) a subclass of T-bet+ memory B cells. Impairment of IgM B cell receptor-signal in nucleic-acid sensing TLR-deficient mice contributes to defective ERV control. Although ERVs are a part of the genome they break immune tolerance, induce immune surveillance against ERV-derived self-antigens and shape the host immune response.

The transcription factor ZEB2 drives the formation of age-associated B cells.

Age-associated B cells (ABCs) accumulate during infection, aging, and autoimmunity, contributing to lupus pathogenesis. In this study, we screened for transcription factors driving ABC formation and found that zinc finger E-box binding homeobox 2 (ZEB2) is required for human and mouse ABC differentiation in vitro. ABCs are reduced in ZEB2 haploinsufficient individuals and in mice lacking Zeb2 in B cells. In mice with toll-like receptor 7 (TLR7)-driven lupus, ZEB2 is essential for ABC formation and autoimmune pathology. ZEB2 binds to +20-kb myocyte enhancer factor 2b (Mef2b)'s intronic enhancer, repressing MEF2B-mediated germinal center B cell differentiation and promoting ABC formation. ZEB2 also targets genes important for ABC specification and function, including Itgax. ZEB2-driven ABC differentiation requires JAK-STAT (Janus kinase-signal transducer and activator of transcription), and treatment with JAK1/3 inhibitor reduces ABC accumulation in autoimmune mice and patients. Thus, ZEB2 emerges as a driver of B cell autoimmunity.

Expansion and surface makers of age-associated B cells in IgG4-related disease.

To assess the expression of age-associated B cells (ABCs), and characterise the surface markers of ABCs in patients with IgG4-related disease (IgG4-RD). Fifty-one newly diagnosed patients with IgG4-RD, 18 IgG4-RD patients with disease remission, 34 patients with other autoimmune diseases, and 61 age- and sex-matched healthy controls (HCs) were included. Circulating ABCs, as well as surface markers were detected by flow cytometry, and tissue infiltration of ABCs were assessed by immunofluorescence (IF). The expression of ABCs in the affected organs of LatY136F knock-in (LAT) mouse models (IgG4-RD mouse model) were explored by flow cytometry and IF. The percentages and absolute numbers of ABCs (gated as CD21-T-bet+CD11c+) in CD19+ B cells raised remarkably in untreated IgG4-RD patients than HC, and reduced significantly after treatment. The percentage of CD27+ABCs, DN2 B cells and activated naive B cells was higher in patients with IgG4-RD than in HCs and patients with multiple autoimmune diseases, whereas the percentage was comparable with that in patients with systemic lupus erythematosus. Phenotypical analysis revealed upregulated levels of CD86, TACI, CD38, and downregulated level of CXCR3 in peripheral CD19+CD21-CD11c+ B cells of IgG4-RD patients compared with that of HC. In IgG4-RD patients, CD19+CD21- CD11c+ cells expressed higher levels of CD80, CXCR3, TACI, CD95, and BAFF-R, while lower levels of CD86, CD27, CD38, and CXCR5 compared with CD19+ CD21- CD11c- B cells. ABCs (CD11c+T-bet+ gated in B220+ cells) were increased significantly in lungs of LAT mice than that of wild type (WT) mice. ABCs were expanded both in the peripheral blood and affected tissues of patients with IgG4-RD as well as in the lungs of LAT mice, indicating the potential roles of ABCs in IgG4-RD pathogenesis.

Th1-related transcription factors and cytokines in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an inflammatory disorder related to immunity dysfunction. The Th1 cell family including Th1 cells, transcription factor T-bet, and related cytokines IFNγ, TNFα, IL-2, IL-18, TGF-β, and IL-12 have been widely discussed in autoimmunity, such as SLE. In this review, we will comprehensively discuss the expression profile of the Th1 cell family in both SLE patients and animal models and clarify how the family members are involved in lupus development. Interestingly, T-bet-related age-associated B cells (ABCs) and low-dose IL-2 treatment in lupus were emergently discussed as well. Collection of the evidence will better understand the roles of the Th1 cell family in lupus pathogenesis, especially targeting IL-2 in lupus.

Mechanisms of Aging Vary with Developmental Stages in the Human Hematopoietic Trajectory

Background : Hematopoietic stem and progenitor cells (HSPCs) undergo functional changes with age. An unresolved issue is whether aging is induced by a shift in intrinsic state in which all HSPCs undergo coordinated changes in functional potential, or by clonal evolution of a senescent population.Identification of senescent cells in human hematopoiesis poses another challenge. In this study, we have identified lineage-specific, senescence-associated pathways at different developmental stages of HSPCs and have developed an “aging signature HSC” for non-primed human HSCs. Methods: HSPCs (CD34+ cells) were isolated from the bone marrow of healthy human subjects (old = >60 years; young = 21 to <35 years). Single-cell RNA-sequencing (scRNAseq) studies and downstream analysis were performed using different R packages for normalization, dimension reduction, clustering, classification, pseudotime ordering, and developmental trajectory analyses. Gene Set Enrichment Analysis, GSEA (version 4.3.2., Broad Institute, Inc) was applied to identify pathways and processes that were coordinately up- or down-regulated with aging. Results: HSPCs (CD34+ cells) were derived from 13 healthy human subjects (old subjects n = 6; young subjects n = 7). There were 26,076 genes identified. The HSPCs were ordered and classified along their developmental trajectory during differentiation processes from (1) hematopoietic stem cells (HSC) to (2) myeloid-lymphoid progenitors (MLP), (3) megakaryocyte-erythrocyte progenitors (MEP), (4) granulocytic-monocytic progenitors (GMP), (5) granulocyte- (G), and (6) monocyte- (Mono) progenitors, (7) dendritic cell (DC), (8) erythroid progenitors (E), as well as various subsets of lymphocytes (Ly1 to Ly4). The results are depicted in Figure 1A. Remarkable are the increases in HSCs (p < 0.05) and in Ly4 (p < 0.001) in old subjects. The Kolmogorov-Smirnov test showed a significant delay in the developmental “pseudotimes” of HSCs (p < 0.001) and of Ly4 (p < 0.05). We then compared the differences in GSEA between old and young subjects in each of the following clusters: (A) whole HSPCs; (B) HSPCs along myeloid pathway (mye-HSPC); (C) HSC-MLP-MEP; (D) HSC. The major findings relevant to aging are summarized in Fig. 1B. Pathways that are significantly increased in the old subjects and throughout all comparisons include: “Formation of senescence associated heterochromatin foci”, “Aging signature HSC”, “DNA damage telomere stress induced senescence”, and “TNFR1 induced NFKB signaling pathway”. “Hypoxia”, “P53 pathway”, “IL2 signaling”, “TNFA signaling via NFKB” were elevated upon enrichment of the primitive HSC population, while other pathways decreased: “Senescence associated secretory phenotype (SASP)”, “DNA methylation”. “Cell cycle” and “DNA repair” are consistently more abundant in young subjects. We analyzed the 512 cells in the HSC cluster with higher resolution and were able to identify a sub-cluster “MPP2A” that is significantly increased in old subjects (4.5% of all HSPCs and 28.5% of HSCs, versus 1.9% and 12.9% respectively in young subjects; p < 0.005). The results are depicted in the highlighted circles in Fig. 1A. This population is quiescent and is highly enriched in “aging signature HSC” in old subjects (p <0.0001). Prominent examples of these signature genes within this list are shown in Fig. 1C). Further along the trajectory, a unique population of B cells “Ly4” was found predominantly in old subjects. The transcriptome profile Ly4 is similar to immature and age-associated B cells (ABCs). This cluster of lymphoid cells may represent the precursors of ABCs described thus far only in peripheral blood, providing another evidence that the aging mechanisms at various differentiation stages are different. Conclusions: In this study, we have defined specific pathways that distinctly separate aging HSCPs from young ones, and shown that the definition of “aging signature” varies with developmental stages. The accumulation a small cluster in the non-primed HSC compartment, with “aging signature HSC” and cell cycle arrest in old subjects indicates that aging of human hematopoiesis is induced by clonal evolution. The abundance of a unique population among lymphoid precursors with expression profiles similar to ABCs demonstrates that lymphoid and myeloid progenitors age differently.

TLR7 activation of age-associated B cells mediates disease in a mouse model of primary Sjögren's disease.

Primary Sjögren's disease (pSD) (also referred to as Sjögren's syndrome) is an autoimmune disease that primarily occurs in women. In addition to exocrine gland dysfunction, pSD patients exhibit B cell hyperactivity. B cell-intrinsic TLR7 activation is integral to the pathogenesis of systemic lupus erythematosus, a disease that shares similarities with pSD. The role of TLR7-mediated B cell activation in pSD, however, remains poorly understood. We hypothesized that age-associated B cells (ABCs) were expanded in pSD and that TLR7-stimulated ABCs exhibited pathogenic features characteristic of disease. Our data revealed that ABC expansion and TLR7 expression were enhanced in a pSD mouse model in a Myd88-dependent manner. Splenocytes from pSD mice showed enhanced sensitivity to TLR7 agonism as compared with those derived from control animals. Sort-purified marginal zone B cells and ABCs from pSD mice showed enhanced inflammatory cytokine secretion and were enriched for antinuclear autoantibodies following TLR7 agonism. Finally, IgG from pSD patient sera showed elevated antinuclear autoantibodies, many of which were secreted preferentially by TLR7-stimulated murine marginal zone B cells and ABCs. These data indicate that pSD B cells are hyperresponsive to TLR7 agonism and that TLR7-activated B cells contribute to pSD through cytokine and autoantibody production. Thus, therapeutics that target TLR7 signaling cascades in B cells may have utility in pSD patients.

Genetics of SLE: mechanistic insights from monogenic disease and disease-associated variants.

The past few years have provided important insights into the genetic architecture of systemic autoimmunity through aggregation of findings from genome-wide association studies (GWAS) and whole-exome or whole-genome sequencing studies. In the prototypic systemic autoimmune disease systemic lupus erythematosus (SLE), monogenic disease accounts for a small fraction of cases but has been instrumental in the elucidation of disease mechanisms. Defects in theclearance or digestion of extracellular or intracellular DNA or RNA lead to increased sensing of nucleic acids, which can break B cell tolerance and induce the production of type I interferons leading to tissue damage. Current data suggest that multiple GWAS SLE risk alleles act in concert with rare functional variants to promote SLE development. Moreover, introduction of orthologous variant alleles into mice has revealed that pathogenic X-linked dominant and recessive SLE can be caused by novel variants in TLR7 and SAT1, respectively. Such bespoke models of disease help tounravel pathogenic pathways and can be used to test targeted therapies. Cell type-specific expression data revealed that most GWAS SLE risk genes are highly expressed in age-associated B cells (ABCs), which supports the view that ABCs produce lupus autoantibodies and contribute to end-organ damage by persisting in inflamed tissues, including the kidneys. ABCs have thus emerged as key targets of promising precision therapeutics.

Single-cell profiling reveals age-associated immunity in atherosclerosis.

Aging is a dominant driver of atherosclerosis and induces a series of immunological alterations, called immunosenescence. Given the demographic shift towards elderly, elucidating the unknown impact of aging on the immunological landscape in atherosclerosis is highly relevant. While the young Western diet-fed Ldlr-deficient (Ldlr-/-) mouse is a widely used model to study atherosclerosis, it does not reflect the gradual plaque progression in the context of an aging immune system as occurs in humans. Here, we show that aging promotes advanced atherosclerosis in chow diet-fed Ldlr-/- mice, with increased incidence of calcification and cholesterol crystals. We observed systemic immunosenescence, including myeloid skewing and T-cells with more extreme effector phenotypes. Using a combination of single-cell RNA-sequencing and flow cytometry on aortic leucocytes of young vs. aged Ldlr-/- mice, we show age-related shifts in expression of genes involved in atherogenic processes, such as cellular activation and cytokine production. We identified age-associated cells with pro-inflammatory features, including GzmK+CD8+ T-cells and previously in atherosclerosis undefined CD11b+CD11c+T-bet+ age-associated B-cells (ABCs). ABCs of Ldlr-/- mice showed high expression of genes involved in plasma cell differentiation, co-stimulation, and antigen presentation. In vitro studies supported that ABCs are highly potent antigen-presenting cells. In cardiovascular disease patients, we confirmed the presence of these age-associated T- and B-cells in atherosclerotic plaques and blood. Collectively, we are the first to provide comprehensive profiling of aged immunity in atherosclerotic mice and reveal the emergence of age-associated T- and B-cells in the atherosclerotic aorta. Further research into age-associated immunity may contribute to novel diagnostic and therapeutic tools to combat cardiovascular disease.

Age-associated B cells predict impaired humoral immunity after COVID-19 vaccination in patients receiving immune checkpoint blockade

Age-associated B cells (ABC) accumulate with age and in individuals with different immunological disorders, including cancer patients treated with immune checkpoint blockade and those with inborn errors of immunity. Here, we investigate whether ABCs from different conditions are similar and how they impact the longitudinal level of the COVID-19 vaccine response. Single-cell RNA sequencing indicates that ABCs with distinct aetiologies have common transcriptional profiles and can be categorised according to their expression of immune genes, such as the autoimmune regulator (AIRE). Furthermore, higher baseline ABC frequency correlates with decreased levels of antigen-specific memory B cells and reduced neutralising capacity against SARS-CoV-2. ABCs express high levels of the inhibitory FcγRIIB receptor and are distinctive in their ability to bind immune complexes, which could contribute to diminish vaccine responses either directly, or indirectly via enhanced clearance of immune complexed-antigen. Expansion of ABCs may, therefore, serve as a biomarker identifying individuals at risk of suboptimal responses to vaccination.

Cutting Edge: IL-21 and Tissue-Specific Signals Instruct Tbet+CD11c+ B Cell Development following Viral Infection.

Tbet+CD11c+ B cells, also known as age-associated B cells (ABCs), are pivotal contributors to humoral immunity following infection and in autoimmunity, yet their invivo generation is incompletely understood. We used a mouse model of systemic acute lymphocytic choriomeningitis virus infection to examine the developmental requirements of ABCs that emerged in the spleen and liver. IL-21 signaling through STAT3 was indispensable for ABC development. In contrast, IFN-γ signaling through STAT1 was required for B cell activation and proliferation. Mice that underwent splenectomy or were deficient in lymphotoxin α generated hepatic ABCs despite the lack of secondary lymphoid organ contributions, suggesting that the liver supported de novo generation of these cells separately from their development in lymphoid organs. Thus, IFN-γ and IL-21 signaling have distinct, stage-specific roles in ABC differentiation, while the tissue microenvironment provides additional cues necessary for their development.

TLR7 expression increases with disease progression and mediates expansion of distinct B cell subsets in primary Sjögren’s Disease

Abstract Primary Sjögren’s Disease (pSD) is a systemic autoimmune disorder in which the exocrine tissue exhibits chronic inflammation. Additionally, patients often experience diminished tear and saliva production along with many extra-glandular disease manifestations. The causes of pSD are poorly understood and no curative treatments are available. Previous studies in our lab conducted in a pSD mouse model demonstrated that TLR7 agonism accelerates pSD pathogenesis and drives expansion of age-associated B cells (ABCs). To extend our prior work, we hypothesized that pSD splenocytes show heightened TLR7 expression and activation, and expansion of B cell subsets linked to autoimmunity relies on TLR7 in pSD mice. We harvested the spleens of pSD females at three different disease time points (pre-disease, clinical disease and advanced stage disease) and performed flow cytometry. Parallel experiments were performed using age and sex-matched healthy controls. Splenocytes were also cultured with the TLR7 agonist Imiquimod (Imq) and IL-6 secretion assessed by ELISA. In addition, spleens were isolated from TLR7-deficient pSD females at the clinical disease stage and flow cytometry was performed. We found splenocytes derived from pSD animals at the clinical disease stage secreted higher levels of IL-6 in response to Imq stimulation as compared to those derived from healthy control animals. TLR7 +B cells and ABCs (B220 +, CD23 −, CD21 −, T-bet +) increased with disease progression in pSD mice. In pSD mice lacking TLR7, ABCs and germinal center B cells were decreased compared to the TLR7-sufficient pSD parental strain. Thus, splenocytes from pSD mice show enhanced sensitivity to TLR7 and TLR7 signaling mediates expansion of ABC subset in pSD. NIH/NIDCR T32 DE023056 NIH/NIDCR R01 DE029472

Dysregulation of complement regulator CD55 in the initiation of autoimmunity

Abstract CD21 is a complement receptor involved in B cell tolerance. CD21 low age-associated B cells (ABCs) are an autoimmune-prone population of B cells that are expanded in autoimmunity. B cell receptor (BCR) and toll-like receptor 9 (TLR9) co-stimulation poise B cells for this autoimmunity-associated cell fate. We and others have discovered that BCR and TLR9 co-stimulation also causes downregulation of CD55, a complement regulatory protein that dampens complement activation by interfering with the production of complement fragments. We posit that CD55, by controlling the generation of complement fragments, regulates BCR-TLR9-triggered B cell responses in the context of autoimmunity. Congruent with this hypothesis, CD55 deficiency has been shown to cause exaggerated experimental encephalitis and disease in the MRL/lpr mouse model of lupus. Our overarching hypothesis is that CD55 regulates B cell responses in the context of autoimmune disease. For this study, we examined CD86 upregulation, proliferation, and cytokine production in B cells after knocking out CD55. We found that CD55 did not impact the CD86 upregulation or proliferation of B cells, but did induce a proinflammatory cytokine profile with increased IL-6 production. In addition, crossing CD55 deficiency onto anti-insulin B cells, a well-studied anergic model, showed that CD55 deficiency partially abrogated anergy-mediated tolerance, increasing the ability of these B cells to proliferate when stimulated through TLR9. These findings may have implications for the future use of complement inhibitors in the treatment of autoimmune disease. Iris Lee holds a Dean’s Scholars Award from the Washington University Division of Physician-Scientists, which is funded by a Burroughs Wellcome Fund Physician-Scientist Institutional Award. The Kendall lab is supported by VA Merit I01BX002882 and R01 DK084246.