Gammaherpesvirus infection drives age-associated B cells toward pathogenicity in EAE and MS

The role of age-associated B cells in systemic lupus erythematosus

Age-associated B cells (ABCs) are a distinct subset of B cells. This B-cell population expands in the elderly but is also abnormally expanded in patients with autoimmune diseases like systemic lupus erythematosus (SLE). ABC differentiation requires unique signaling stimuli, including BCR stimulation, TLR7 and TLR9 signaling, and the action of cytokines. The role of ABCs in the pathogenesis and treatment strategies of SLE has been a research hotspot in recent years. Possible pathogenic mechanisms include the production of autoantibodies and cytokines, as well as stimulation of spontaneous germinal center. Specifically targeting ABCs is a promising strategy for treating SLE. This article reviews the role of ABCs in SLE. Understanding the origin and differentiation of ABCs and their role in SLE will facilitate the discovery of novel drug targets for the treatment of SLE.

Critical roles of chronic BCR signaling in the differentiation of anergic B cells into age-associated B cells in aging and autoimmunity

Age-associated B cells (ABCs) with autoreactive properties accumulate with age and expand prematurely in autoimmune diseases. However, the mechanisms behind ABC generation and maintenance remain poorly understood. We show that continuous B cell receptor (BCR) signaling is essential for ABC development from anergic B cells in aged and autoimmune mice. ABCs exhibit constitutive BCR activation, with surface BCRs being internalized. Notably, anergic B cells, but not nonautoreactive B cells, contributed to ABC formation in these models. Anergic B cells also showed a greater propensity for in vitro differentiation into ABCs, which was inhibited by the expression of the transcription factor Nr4a1. Bruton's tyrosine kinase (Btk), a key BCR signaling component, was constitutively activated in ABCs from aged and autoimmune mice as well as patients with lupus. Inhibiting Btk reduced ABC numbers and ameliorated the pathogenicity of lupus mice. Our findings reveal critical mechanisms underlying ABC development and offer previously unrecognized therapeutic insights for autoimmune diseases.

Multiple sclerosis and infection: history, EBV, and the search for mechanism

SUMMARYInfection has long been hypothesized as the cause of multiple sclerosis (MS), and recent evidence for Epstein-Barr virus (EBV) as the trigger of MS is clear and compelling. This clarity contrasts with yet uncertain viral mechanisms and their relation to MS neuroinflammation and demyelination. As long as this disparity persists, it will invigorate virologists, molecular biologists, immunologists, and clinicians to ascertain how EBV potentiates MS onset, and possibly the disease's chronic activity and progression. Such efforts should take advantage of the diverse body of basic and clinical research conducted over nearly two centuries since the first clinical descriptions of MS plaques. Defining the contribution of EBV to the complex and multifactorial pathology of MS will also require suitable experimental models and techniques. Such efforts will broaden our understanding of virus-driven neuroinflammation and specifically inform the development of EBV-targeted therapies for MS management and, ultimately, prevention.

T-bet+ CXCR3+ B cells drive hyperreactive B-T cell interactions in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). Self-peptide-dependent autoproliferation (AP) of B and T cells is a key mechanism in MS. Here, we show that pro-inflammatory B-T cell-enriched cell clusters (BTECs) form during AP and mirror features of a germinal center reaction. T-bet+CXCR3+ B cells are the main cell subset amplifying and sustaining their counterpart Th1 cells via interferon (IFN)-γ and are present in highly inflamed meningeal tissue. The underlying B cell activation signature is reflected by epigenetic modifications and receptor-ligand interactions with self-reactive T cells. AP+ CXCR3+ B cells show marked clonal evolution from memory to somatically hypermutated plasmablasts and upregulation of IFN-γ-related genes. Our data underscore a key role of T-bet+CXCR3+ B cells in the pathogenesis of MS in both the peripheral immune system and the CNS compartment, and thus they appear to be involved in both early relapsing-remitting disease and the chronic stage.

T-bet-expressing B cells promote atherosclerosis in apolipoprotein E-deficient mice

The humoral immune system influences the development of atherosclerosis, but the contributions of specific memory B cell subsets and IgG isotypes are poorly understood. We assessed the relationship between atherosclerosis and age-associated B cells (ABCs), a T-bet-expressing memory B cell subset that is enriched for IgG2c production and implicated in humoral autoimmunity. We found increased numbers of splenic CD11c+ ABCs in 6-mo-old, chow-fed Apoe-/- mice versus C57BL/6 control mice, which were exacerbated by high-fat diet. Deletion of T-bet in the B lineage in high-fat diet-fed Apoe-/- mice reduced aortic lesion area, and this correlated with decreased splenic CD11c+ B cells and reduced serum oxidized low-density lipoprotein-specific IgG2c. Our findings suggest that T-bet-expressing B cells are atherogenic agents in the Apoe-/- model and indicate that interventions to inhibit a T-bet-driven humoral response may improve atherosclerotic disease.

Age-Associated B Cells in Autoimmune Diseases: Pathogenesis and Clinical Implications

As a heterogeneous B cell subset, age-associated B cells (ABCs) exhibit distinct transcription profiles, extrafollicular differentiation processes, and multiple functions in autoimmunity. TLR7 and TLR9 signals, along with IFN-γ and IL-21 stimulation, are both essential for ABC differentiation, which is also regulated by chemokine receptors including CXCR3 and CCR2 and integrins including CD11b and CD11c. Given their functions in antigen uptake and presentation, autoantibody and proinflammatory cytokine secretion, and T helper cell activation, ABCs display potential in the prognosis, diagnosis, and therapy for autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, multiple sclerosis, neuromyelitis optica spectrum disorders, and ankylosing spondylitis. Specifically targeting ABCs by inhibiting T-bet and CD11c and activating CD11b and ARA2 represents potential therapeutic strategies for SLE and RA. Although single-cell sequencing technologies have recently revealed the heterogeneous characteristics of ABCs, further investigations to explore and validate ABC-target therapies are still warranted.

Combination of proviral and antiviral roles of B cell-intrinsic STAT1 expression defines parameters of chronic gammaherpesvirus infection

Gammaherpesviruses are species-specific, ubiquitous pathogens that establish lifelong infection in their hosts and are associated with cancers, including B cell lymphomas. Type I and II interferons (IFNs) are critical for the control of acute and chronic gammaherpesvirus infection. However, the cell type-specific role of IFN signaling during natural infection is poorly defined and is masked by the altered viral pathogenesis observed in hosts with global IFN deficiencies. STAT1 is a constitutively expressed transcription factor that is critical for the effector function of type I and II IFNs. In this study, we defined the impact of B cell-specific STAT1 expression on gammaherpesvirus infection using murine gammaherpesvirus 68 (MHV68). While the acute stage of MHV68 infection was not affected, we found opposite, anatomic site-dependent effects of B cell-intrinsic STAT1 expression during chronic infection. Consistent with the antiviral role of STAT1, B cell-specific STAT1 expression attenuated the latent viral reservoir in peritoneal B cells of chronically infected mice. In contrast, STAT1 expression in splenic B cells supported the establishment of the latent MHV68 reservoir in germinal center B cells, revealing an unexpected proviral role of B cell-intrinsic STAT1 expression during chronic gammaherpesvirus infection. These STAT1-dependent MHV68 chronic infection phenotypes were fully recapitulated in the peritoneal cavity but not the spleen of mice with B cell-specific deficiency of type I IFN receptor. In summary, our study uncovers the intriguing combination of proviral and antiviral roles of B cell-intrinsic STAT1 expression during chronic gammaherpesvirus infection.IMPORTANCEInterferons (IFNs) execute broadly antiviral roles during acute and chronic viral infections. The constitutively expressed transcription factor STAT1 is a critical downstream effector of IFN signaling. Our studies demonstrate that B cell-intrinsic STAT1 expression has opposing and anatomic site-dependent roles during chronic gammaherpesvirus infection. Specifically, B cell-intrinsic STAT1 expression restricted gammaherpesvirus latent reservoir in the peritoneal cavity, consistent with the classical antiviral role of STAT1. In contrast, decreased STAT1 expression in splenic B cells led to the attenuated establishment of gammaherpesvirus latency and decreased latent infection of germinal center B cells, highlighting a novel proviral role of B cell-intrinsic STAT1 expression during chronic infection with a B cell-tropic gammaherpesvirus. Interestingly, B cell-specific type I IFN receptor deficiency primarily recapitulated the antiviral role of B cell-intrinsic STAT1 expression, suggesting the compensatory function of B cell-intrinsic type II IFN signaling or an IFN-independent proviral role of B cell-intrinsic STAT1 expression during chronic gammaherpesvirus infection.

CD9 and Aryl Hydrocarbon Receptor Are Markers of Human CD19+CD14+ Atypical B Cells and Are Dysregulated in Systemic Lupus Erythematous Disease

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor whose expression regulates immune cell differentiation. Single-cell transcriptomic profiling was used to ascertain the heterogeneity of AHR expression in human B cell subpopulations. We identified a unique population of B cells marked by expression of AHR, CD9, and myeloid genes such as CD14 and CXCL8. Results were confirmed directly in human PBMCs and purified B cells at the protein level. TLR9 signaling induced CD14, CD9, and IL-8 protein expression in CD19+ B cells. CD14-expressing CD9+ B cells also highly expressed AHR and atypical B cell markers such as CD11c and TBET. In patients with active lupus disease, CD14+ and CD9+ B cells are dysregulated, with loss of CD9+ B cells strongly predicting disease severity and demonstrating the relevance of CD9+ B cells in systemic lupus erythematosus and autoimmune disease.

Impact of Epstein-Barr Virus Nuclear Antigen 1 on Neuroinflammation in PARK2 Knockout Mice

This study aimed to explore the intricate relationship between mitochondrial dysfunction, infection, and neuroinflammation, focusing specifically on the impact of pathogenic epitopes of the Epstein-Barr Virus (EBV) nuclear antigen 1 (EBNA1) in a mouse model of mitochondrial dysfunctions. The investigation included female middle-aged PARK2-/- and C57BL/6J wild-type mice immunized with EBNA1386-405 or with active experimental autoimmune encephalomyelitis (EAE) induction by the myelin oligodendrocyte glycoprotein (MOG)35-55 peptide. The PARK2-/- mice developed more severe EAE than the wild-type mice. Following immunization with EBNA1386-405, only PARK2-/- exhibited symptoms resembling EAE. During the acute phase, PARK2-/- mice immunized with either MOG35-55 or EBNA1386-405 exhibited a similar infiltration of the T cells and macrophages in the spinal cord and decreased glial fibrillary acidic protein (GFAP) expression in the brain. However, the EBNA1386-405 -immunized PARK2-/- mice showed significantly increased frequencies of CD8a+ T cells and CD11c+ B cells, and distinct cytokine profiles in the periphery compared to the wild-type controls. These findings highlight the role of EBV in exacerbating inflammation, particularly in the context of mitochondrial deficiencies.

Multiple sclerosis patient-derived spontaneous B cells have distinct EBV and host gene expression profiles in active disease

Epstein-Barr virus (EBV) is an aetiologic risk factor for the development of multiple sclerosis (MS). However, the role of EBV-infected B cells in the immunopathology of MS is not well understood. Here we characterized spontaneous lymphoblastoid cell lines (SLCLs) isolated from MS patients and healthy controls (HC) ex vivo to study EBV and host gene expression in the context of an individual's endogenous EBV. SLCLs derived from MS patient B cells during active disease had higher EBV lytic gene expression than SLCLs from MS patients with stable disease or HCs. Host gene expression analysis revealed activation of pathways associated with hypercytokinemia and interferon signalling in MS SLCLs and upregulation of forkhead box protein 1 (FOXP1), which contributes to EBV lytic gene expression. We demonstrate that antiviral approaches targeting EBV replication decreased cytokine production and autologous CD4+ T cell responses in this ex vivo model. These data suggest that dysregulation of intrinsic B cell control of EBV gene expression drives a pro-inflammatory, pathogenic B cell phenotype that can be attenuated by suppressing EBV lytic gene expression.

Ocrelizumab B cell depletion has no effect on HERV RNA expression in PBMC in MS patients

BACKGROUND

Epstein barr virus (EBV) infection of B cells is now understood to be one of the triggering events for the development of Multiple Sclerosis (MS), a progressive immune-mediated disease of the central nervous system. EBV infection is also linked to expression of human endogenous retroviruses (HERVs) of the HERV-W group, a further risk factor for the development of MS. Ocrelizumab is a high-potency disease-modifying treatment (DMT) for MS, which depletes B cells by targeting CD20.

OBJECTIVES

We studied the effects of ocrelizumab on gene expression in peripheral blood mononuclear cells (PBMC) from paired samples from 20 patients taken prior to and 6 months after beginning ocrelizumab therapy. We hypothesised that EBV and HERV-W loads would be lower in post-treatment samples.

METHODS

Samples were collected in Paxgene tubes, subject to RNA extraction and Illumina paired end short read mRNA sequencing with mapping of sequence reads to the human genome using Salmon and differential gene expression compared with DeSeq2. Mapping was also performed separately to the HERV-D database of HERV sequences and the EBV reference sequence.

RESULTS

Patient samples were more strongly clustered by individual rather than disease type (relapsing/remitting or primary progressive), treatment (pre and post), age, or sex. Fourteen genes, all clearly linked to B cell function were significantly down regulated in the post treatment samples. Interestingly only one pre-treatment sample had detectable EBV RNA and there were no significant differences in HERV expression (of any group) between pre- and post-treatment samples.

CONCLUSIONS

While EBV and HERV expression are clearly linked to triggering MS pathogenesis, it does not appear that high level expression of these viruses is a part of the ongoing disease process or that changes in virus load are associated with ocrelizumab treatment.

Adaptive immunity and atherosclerosis: aging at its crossroads

Adaptive immunity plays a profound role in atherosclerosis pathogenesis by regulating antigen-specific responses, inflammatory signaling and antibody production. However, as we age, our immune system undergoes a gradual functional decline, a phenomenon termed "immunosenescence". This decline is characterized by a reduction in proliferative naïve B- and T cells, decreased B- and T cell receptor repertoire and a pro-inflammatory senescence associated secretory profile. Furthermore, aging affects germinal center responses and deteriorates secondary lymphoid organ function and structure, leading to impaired T-B cell dynamics and increased autoantibody production. In this review, we will dissect the impact of aging on adaptive immunity and the role played by age-associated B- and T cells in atherosclerosis pathogenesis, emphasizing the need for interventions that target age-related immune dysfunction to reduce cardiovascular disease risk.

CD11c+ B cells in relapsing-remitting multiple sclerosis and effects of anti-CD20 therapy

OBJECTIVES

B cells are important in the pathogenesis of multiple sclerosis. It is yet unknown which subsets may be involved, but atypical B cells have been proposed as mediators of autoimmunity. In this study, we investigated differences in B-cell subsets between controls and patients with untreated and anti-CD20-treated multiple sclerosis.

METHODS

We recruited 155 participants for an exploratory cohort comprising peripheral blood and cerebrospinal fluid, and a validation cohort comprising peripheral blood. Flow cytometry was used to characterize B-cell phenotypes and effector functions of CD11c+ atypical B cells.

RESULTS

There were no differences in circulating B cells between controls and untreated multiple sclerosis. As expected, anti-CD20-treated patients had a markedly lower B-cell count. Of B cells remaining after treatment, we observed higher proportions of CD11c+ B cells and plasmablasts. CD11c+ B cells were expanded in cerebrospinal fluid compared to peripheral blood in controls and untreated multiple sclerosis. Surprisingly, the proportion of CD11c+ cerebrospinal fluid B cells was higher in controls and after anti-CD20 therapy than in untreated multiple sclerosis. Apart from the presence of plasmablasts, the cerebrospinal fluid B-cell composition after anti-CD20 therapy resembled that of controls. CD11c+ B cells demonstrated a high potential for both proinflammatory and regulatory cytokine production.

INTERPRETATION

The study demonstrates that CD11c+ B cells and plasmablasts are less efficiently depleted by anti-CD20 therapy, and that CD11c+ B cells comprise a phenotypically and functionally distinct, albeit heterogenous, B-cell subset with the capacity of exerting both proinflammatory and regulatory functions.

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

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

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 the clearance 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 to unravel 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.

Age-associated B cells are long-lasting effectors that impede latent γHV68 reactivation

Age-associated B cells (ABCs; CD19⁺CD11c⁺T-bet⁺) are a unique population that are increased in an array of viral infections, though their role during latent infection is largely unexplored. Here, we use murine gammaherpesvirus 68 (γHV68) to demonstrate that ABCs remain elevated long-term during latent infection and express IFNγ and TNF. Using a recombinant γHV68 that is cleared following acute infection, we show that ABCs persist in the absence of latent virus, though their expression of IFNγ and TNF is decreased. With a fluorescent reporter gene-expressing γHV68 we demonstrate that ABCs are infected with γHV68 at similar rates to other previously activated B cells. We find that mice without ABCs display defects in anti-viral IgG2a/c antibodies and are more susceptible to reactivation of γHV68 following virus challenges that typically do not break latency. Together, these results indicate that ABCs are a persistent effector subset during latent viral infection that impedes γHV68 reactivation.

Age-associated B cells are long-lasting effectors that impede latent γHV68 reactivation

Age-associated B cells (ABCs; CD19⁺CD11c⁺T-bet⁺) are a unique population that are increased in an array of viral infections, though their role during latent infection is largely unexplored. Here, we use murine gammaherpesvirus 68 (γHV68) to demonstrate that ABCs remain elevated long-term during latent infection and express IFNγ and TNF. Using a recombinant γHV68 that is cleared following acute infection, we show that ABCs persist in the absence of latent virus, though their expression of IFNγ and TNF is decreased. With a fluorescent reporter gene-expressing γHV68 we demonstrate that ABCs are infected with γHV68 at similar rates to other previously activated B cells. We find that mice without ABCs display defects in anti-viral IgG2a/c antibodies and are more susceptible to reactivation of γHV68 following virus challenges that typically do not break latency. Together, these results indicate that ABCs are a persistent effector subset during latent viral infection that impedes γHV68 reactivation.