Toll-like receptor 7 (TLR7)-driven accumulation of a novel CD11c⁺ B-cell population is important for the development of autoimmunity

Elevated transferrin receptor 1 promoting B-cell autoimmunity in systemic lupus erythematosus

BACKGROUND

Transferrin receptor 1 (TFR1), a major iron receptor for immune cells, could impair T cell metabolism and function in systemic lupus erythematosus (SLE), leading us to investigate the effects of TFR1 and possible mechanisms on lupus B cells.

METHODS

B cells from lupus mouse models and systemic lupus erythematosus (SLE) patients were evaluated using flow cytometry (FCM) for levels of TFR1, intracellular iron deposition, reactive oxygen species (ROS), lipid peroxidation, and B-cell subsets. Transcript levels of TFR1 were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and upstream regulatory molecules were identified by in vitro gene silencing.

RESULTS

An agonist of toll-like receptor 7 (TLR7), R848 treatment significantly increased TFR1 expression in B cells from C57BL/6 (B6) mice but not those from MRL/lpr mice. In in vitro cultures of mouse splenocytes, TLR7 dose-dependently promoted TFR1 expression, and its effect was probably mediated by P53. Anti-TFR1 antibody effectively inhibited intracellular iron deposition in lupus B cells, reduced ROS and lipid peroxidation, and prevented the production of plasmablasts and autoantibodies. Among different B cell subsets, TFR1 was predominantly expressed in double negative (DN) B cells, with a more pronounced effect on DN2 B cells, which could be normalized by ROS inhibitors. Similarly, in human studies, TFR1 was highly expressed in B cells of SLE patients and closely correlated with TLR7 expression and disease activity scores, as well as iron deposition and ROS production. A significant reduction in ROS production was observed after blocking TFR1.

CONCLUSIONS

TLR7-regulated TFR1 may drive B-cell autoimmunity by promoting ROS production, thus contributing to SLE pathogenesis.

IL-4 alters TLR7-induced B cell developmental program in lupus

TLR7 stimulation of T-bet+CD11c+IgD-CD27- double-negative 2 (DN2) B cells is crucial for autoantibody formation in systemic lupus erythematosus (SLE). Here, we show that administration of IL-4 for five weeks significantly reduced autoantibodies and T-bet+CD11c+ IgD- B cells in autoimmune BXD2 mice treated with R848, a TLR7 agonist. Single-cell transcriptomics analysis indicates that following two doses of in vivo administration, IL-4 redirected development toward follicular, CD23+ germinal center (GC), and DN4-like memory B cells compared to treatment with R848 alone. While IL-4 enhanced genes related to antigen processing and presentation, it also suppressed R848-induced Ki67+ GC B cells in vivo. In vitro stimulation of SLE patient B cells with a DN2 polarizing cocktail revealed that IL-4 reduced the expression of interferon response and DN2 signature genes, promoting a population of CD23+T-bet- DN4 B population. These findings suggest that developmental reprogramming by IL-4 counteracts TLR7-promoted DN2 and GC B cells in SLE.

Aging in Granulomatosis with Polyangiitis and Microscopic Polyangiitis: From Pathophysiology to Clinical Management

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) predominantly affect individuals aged 55-75 years, with granulomatosis with polyangiitis (GPA) being diagnosed most often between 55 and 65 years and microscopic polyangiitis (MPA) between 65 and 75 years. Owing to the general increase in life expectancy, the average age at diagnosis increases, encompassing also those over 75 years old. Unfortunately, the exclusion of these older patients from many clinical trials has limited our understanding of the progression of these diseases in older subjects. The role of immunosenescence and aging in AAV pathogenesis and progression is underexplored, despite potential implications in the understanding of the disease, and potentially for disease management. Although AAV manifestations are largely consistent across age groups, certain features, such as renal involvement and the association with interstitial lung disease, may be more prevalent in older patients. Frailty must be a key consideration in therapeutic decision-making, especially when balancing the efficacy of immunosuppressants with potential side effects. Recent evidence supports the use of rituximab in addition to low-dose glucocorticoids for remission induction in life- or organ-threatening AAV, including in older populations. Furthermore, preliminary evidence supports that avacopan might be as efficient as glucocorticoids in these patients. The immunosuppressive treatment of AAV reduces the immune response to environmental pathogens, with rituximab worsening age-related hypogammaglobulinemia. Thus, prophylactic measures, including vaccination and Pneumocystis pneumonia prevention, as well as strategies to mitigate glucocorticoid side effects, should be implemented in AAV management.

What's atypical about human B cells after allogeneic stem cell transplantation?

Atypical B cells or age-associated B cells represent an alternative lineage of memory B cells. Emerging evidence suggests that context influences the apparent functional heterogeneity of age-associated B cells. While data support a protective role for age-associated B cells in the setting of infection, multiple other studies suggest that these cells play a pathogenic role in the setting of autoimmunity. After treatment with allogeneic hematopoietic stem cell transplantation, the memory B-cell compartment is altered in patients who develop an autoimmune-like syndrome called chronic graft-versus-host disease. Patients with chronic graft-versus-host disease have significantly increased proportions of CD11c+ age-associated B cells within the peripheral compartment that develop under constant exposure to host alloantigens and persist under conditions when B-cell tolerance is not achieved. Herein, we review what is currently known about the molecular alterations in the heterogeneous memory B-cell compartment of hematopoietic stem cell transplantation patients, especially patients with chronic graft-versus-host disease who have developed autoimmune manifestations. In this mini-review, we summarize intrinsic factors in age-associated B cells found in autoimmune states that likely influence their extrafollicular localization, differentiation potential into autoantibody-secreting cells, and function. We highlight lessons from B-cell studies in chronic graft-versus-host disease to provide unique insights into the molecular underpinnings of the diverse functions of age-associated B cells.

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.

Coordinated Regulation of Extrafollicular B Cell Responses by IL-12 and IFNγ

Upon activation, B cells undergo either the germinal center (GC) or extrafollicular (EF) response. While GC are known to generate high-affinity memory B cells and long-lived plasma cells, the role of the EF response is less well understood. Initially, it was thought to be limited to that of a source of fast but lower-quality antibodies until the GC can form. However, recent evidence strongly supports the EF response as an important component of the humoral response to infection. EF responses are now also recognized as a source of pathogenic B cells in autoimmune diseases. The EF response itself is dynamic and regulated by pathways that are only recently being uncovered. We have identified that the cytokine IL-12 acts as a molecular switch, enhancing the EF response and suppressing GC through multiple mechanisms. These include direct effects on both B cells themselves and the coordinated differentiation of helper CD4 T cells. Here, we explore this pathway in relation to other recent advancements in our understanding of the EF response's role and highlight areas for future research. A better understanding of how the EF response forms and is regulated is essential for advancing treatments for many disease states.

Evolving Approach to Clinical Cytometry for Immunodeficiencies and Other Immune Disorders

Primary immunodeficiencies were initially identified on the basis of recurrent, severe or unusual infections. Subsequently, it was noted that these diseases can also manifest with autoimmunity, autoinflammation, allergy, lymphoproliferation and malignancy, hence a conceptual change and their renaming as inborn errors of immunity. Ongoing advances in flow cytometry provide the opportunity to expand or modify the utility and scope of existing laboratory tests in this field to mirror this conceptual change. Here we have used the B cell subset, variably known as CD21low B cells, age-associated B cells and T-bet+ B cells, as an example to demonstrate this possibility.

Immunological biomarkers of aging

The immune system has long been recognized for its critical role in the elimination of pathogens and the development of autoimmune diseases, but recent evidence demonstrates that it also contributes to noncommunicable diseases associated with biological aging processes, such as cancer, cardiovascular disease, neurodegeneration, and frailty. This review examines immunological biomarkers of aging, focusing on how the immune system evolves with age and its impact on health and disease. It discusses the historical development of immunological assessments, technological advancements, and the creation of novel biomarkers and models to study immune aging. We also explore the clinical implications of immune aging, such as increased susceptibility to infectious diseases, poor vaccine responses, and a higher incidence of noncommunicable diseases. In summary, we provide a comprehensive overview of current research, highlight the clinical relevance of immune aging, and identify gaps in knowledge that require further investigation.

Two distinct durable human class-switched memory B cell populations are induced by vaccination and infection

Memory lymphocytes are durable cells that persist in the absence of antigen, but few human B cell subsets have been characterized in terms of durability. The relative durability of eight non-overlapping human B cell sub-populations covering 100% of all human class-switched B cells was interrogated. Only two long-lived B cell populations persisted in the relative absence of antigen. In addition to canonical germinal center-derived switched-memory B cells with an IgD-CD27+CXCR5+ phenotype, a second, non-canonical, but distinct memory population of IgD-CD27-CXCR5+ DN1 B cells was also durable, exhibited a unique TP63-linked transcriptional and anti-apoptotic signature, had low levels of somatic hypermutation, but was more clonally expanded than canonical switched-memory B cells. DN1 B cells likely evolved to preserve immunological breadth and may represent the human counterparts of rodent extrafollicular memory B cells that, unlike canonical memory B cells, can enter germinal centers and facilitate B cell and antibody evolution.

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.

Inflammatory CD11c+ B Cells Induced by the TREM2 Signal Accelerate Sepsis Development

CD11c+ B cells are an age-associated subset emerging in infections and autoimmune diseases. However, their role in sepsis is poorly clarified. This study identified a class of CD11c+ B cells with a proinflammatory phenotype that is expended in septic patients and mice. Notably, the transfer of these cells accelerates sepsis-induced lung injury and death in mice. Furthermore, the CD11c+ B cells were induced by the triggering receptor expressed on myeloid cells 2 (TREM2) signal, which promotes their generation via the interferon regulatory factor 4 (IRF4) pathway. Moreover, TREM2 directly participates in sepsis regulation mediated by CD11c+ B cells. This study reveals the proinflammatory role of CD11c+ B cells in sepsis and identifies TREM2 as a contributing factor in CD11c+ B-cell-mediated inflammatory injury during sepsis.

Aging immunity: unraveling the complex nexus of diet, gut microbiome, and immune function

Aging is associated with immune senescence and gut dysbiosis, both of which are heavily influenced by the diet. In this review, we summarize current knowledge regarding the impact of diets high in fiber, protein, or fat, as well as different dietary components (tryptophan, omega-3 fatty acids, and galacto-oligosaccharides) on the immune system and the gut microbiome in aging. Additionally, this review discusses how aging alters tryptophan metabolism, contributing to changes in immune function and the gut microbiome. Understanding the relationship between diet, the gut microbiome, and immune function in the context of aging is critical to formulate sound dietary recommendations for older individuals, and these personalized nutritional practices will ultimately improve the health and longevity of the elderly.

Distinct type 1 immune networks underlie the severity of restrictive lung disease after COVID-19

The variable origins of persistent breathlessness after coronavirus disease 2019 (COVID-19) have hindered efforts to decipher the immunopathology of lung sequelae. Here we analyzed hundreds of cellular and molecular features in the context of discrete pulmonary phenotypes to define the systemic immune landscape of post-COVID lung disease. Cluster analysis of lung physiology measures highlighted two phenotypes of restrictive lung disease that differed according to their impaired diffusion and severity of fibrosis. Machine learning revealed marked CCR5+CD95+CD8+ T cell perturbations in milder lung disease but attenuated T cell responses hallmarked by elevated CXCL13 in more severe disease. Distinct sets of cells, mediators and autoantibodies distinguished each restrictive phenotype and differed from those of patients without substantial lung involvement. These differences were reflected in divergent T cell-based type 1 networks according to the severity of lung disease. Our findings, which provide an immunological basis for active lung injury versus advanced disease after COVID-19, might offer new targets for treatment.

Nucleic acid triggers of autoimmunity and autoinflammation

The key role of nucleic acid sensing receptors in the development of autoimmune and autoinflammatory diseases is becoming increasingly apparent. Activation of these sensors has been attributed to the failure of professional scavenger cells to adequately clear cell debris, in many cases due to defective scavenger receptors. However, as now summarized in this review, numerous gain-of-function mutations in the nucleic acid sensing receptors, or in molecules that regulate sensor activity, have now been evaluated in gene-targeted murine strains, and critical components of their downstream pathways have been identified as therapeutic targets. In addition, we are beginning to understand how DNases and RNases play crucial roles in both generating and eliminating the distinct ligands that engage the various nucleic acid sensors. Murine models of disease have further provided important insights regarding the function of and synergy between individual endosomal and cytosolic receptors, as well as cell type restricted functions.

Compromised B-cell homeostasis: Unraveling the link between major depression, infection and autoimmune disorders

BACKGROUND

Major depression can increase susceptibility to viral infections and autoimmune diseases. B cell responses are crucial for immune defense against infections but can trigger autoimmunity when deregulated. However, it remains unclear whether compromised B-cell homeostasis in major depression contributes to an increased risk of infection and autoimmunity.

METHODS

Chronic unpredictable mild stress (CUMS) procedure was applied to adult C57BL/6 J mice to generate a reliable depression model. Mice were immunized with (4-hydroxy-3-nitrophenyl) acetyl (NP) keyhole limpet hemocyanin (NP-KLH) to elicit B-cell-mediated humoral immune responses. CUMS mice were subjected to a collagen-induced arthritis model or a Bm12-induced systemic lupus erythematosus model to assess the contribution of major depression to autoimmunity. RNA sequencing was performed to understand the effects of CUMS on B-cell homeostasis at the transcriptomic level.

RESULTS

CUMS mice exhibited an impaired humoral immune response, as evidenced by reduced germinal centers (GCs), plasma cells, and antigen-specific antibodies. Unimmunized CUMS mice displayed aberrant spontaneous expansion of GC B cells, plasma cells, age-associated B cells and autoantibody production. CUMS mice also demonstrated a greater exacerbation of autoimmune manifestations. RNA sequencing revealed that genes involved in B-cell-mediated immune response were downregulated in B cells from CUMS mice, while the pathways related to autoimmunity seem to be upregulated.

LIMITATIONS

Further research is needed to understand the specific targets, mechanisms, and role of B cell dysfunction in major depression.

CONCLUSIONS

Our results provide novel insights into B-cell-dependent mechanisms that involve the association of increased susceptibility to infections and autoimmunity in major depression.

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.

Comparison of B lymphocyte profile between membranous nephropathy and idiopathic nephrotic syndrome pediatric patients

BACKGROUND

Membranous nephropathy (MN) and idiopathic nephrotic syndrome (INS) are two B-cell mediated rare glomerular diseases that benefit from treatment with B-cell depleting anti-CD20 monoclonal antibody rituximab. Different B-cell dysregulations have been described in pediatric INS patients and in adults affected by MN. In adult MN patients, an increased level of mature-naïve cells and atypical memory B cells and a significant reduction in IgM memory and switched memory B cells have been previously described compared to healthy individuals. To date, there is no information available about B-cell immunophenotyping in pediatric MN.

METHODS

In this monocentric retrospective case-control study, we analyzed by flow cytometry the B-cell profile in rituximab-naïve (n = 15) children affected by MN, compared with pediatric INS patients (n = 15) selected by propensity score matching, and both evaluated during active disease. Age-matched controls (n = 15) with non-immune-mediated kidney diseases were also characterized. Demographical, clinical, laboratory, and immunosuppressive treatment data were registered.

RESULTS

We found that children with MN and INS had significantly higher circulating levels of total CD19+, mature-naïve, and atypical memory B cells and similar levels of transitional B cells when compared to age-matched controls. Circulating levels of total memory B cells, IgM memory B cells, and plasmablasts/plasmacells were significantly higher in INS patients compared to both MN patients and age-matched controls.

CONCLUSIONS

Our study indicated that children affected by MN had a specific B-cell profile and that high levels of memory B-cell subsets are specific to INS pediatric patients independently of proteinuria intensity.

Cytosolic nucleic acid sensing as driver of critical illness: mechanisms and advances in therapy

Nucleic acids from both self- and non-self-sources act as vital danger signals that trigger immune responses. Critical illnesses such as acute respiratory distress syndrome, sepsis, trauma and ischemia lead to the aberrant cytosolic accumulation and massive release of nucleic acids that are detected by antiviral innate immune receptors in the endosome or cytosol. Activation of receptors for deoxyribonucleic acids and ribonucleic acids triggers inflammation, a major contributor to morbidity and mortality in critically ill patients. In the past decade, there has been growing recognition of the therapeutic potential of targeting nucleic acid sensing in critical care. This review summarizes current knowledge of nucleic acid sensing in acute respiratory distress syndrome, sepsis, trauma and ischemia. Given the extensive research on nucleic acid sensing in common pathological conditions like cancer, autoimmune disorders, metabolic disorders and aging, we provide a comprehensive summary of nucleic acid sensing beyond critical illness to offer insights that may inform its role in critical conditions. Additionally, we discuss potential therapeutic strategies that specifically target nucleic acid sensing. By examining nucleic acid sources, sensor activation and function, as well as the impact of regulating these pathways across various acute diseases, we highlight the driving role of nucleic acid sensing in critical illness.

Sex Differences in B Cells From the Joints of Children With Oligoarticular Juvenile Idiopathic Arthritis

OBJECTIVE

Disordered T peripheral helper (Tph)-B cell interactions have been implicated in several forms of inflammatory arthritis, including oligoarticular (oligo) juvenile idiopathic arthritis (JIA). We sought to evaluate the Tph-B cell axis in oligo JIA through an analysis of intra-articular B cells.

METHODS

B cells from the blood and synovial fluid (SF) of 44 children with oligo JIA were compared to those from the blood and tonsils of controls. Flow cytometry, B cell receptor (BCR) repertoire analysis, and autoantibody profiling were used to characterize B cells.

RESULTS

Memory B (Bmem) cells and heterogeneous subsets of CD21lo B cells were enriched in oligo JIA-SF versus blood of patients and controls. Compared to male patients, female patients with oligo JIA had greater proportions of intra-articular Tph cells that expressed B cell help factors as well as Bmem cells, plasmablasts, and age-/autoimmune-associated B cells. The sex differences in B cells were observed only in the joints and were not found in the blood or tonsil, nor were they explained by other disease features such as age at onset, antinuclear antibody status, or severity. Bmem cells in SF from female patients displayed characteristics of autoreactivity, including longer complementarity determining region 3 lengths and increased usage of autoreactive BCR gene segments, which were not found in blood Bmem cells. A diverse array of autoantibodies accumulated in the SF of female patients with oligo JIA compared to the blood of patients with JIA and controls.

CONCLUSION

These findings demonstrate prominent B cell dysregulation in oligo JIA and implicate sex as an important biologic factor in B cell responses in this disease.

Polarization of the memory B-cell response

Memory B cells are long-lived cells that are induced following infection or vaccination. Upon antigen re-encounter, memory B cells rapidly differentiate into antibody-secreting or germinal center B cells. While memory B cells are an important component of long-term protective immunity following vaccination, they also contribute to the progression of diseases such as autoimmunity and allergy. Numerous subsets of memory B cells have been identified in mice and humans that possess important phenotypic and functional differences. Here, we review the transcriptional circuitry governing memory B-cell differentiation and function. We then summarize emerging evidence that the inflammatory environment in which memory B cells develop has an important role in shaping their phenotype and examine the pathways regulating the development of memory B cells during a type 1-skewed and type 2-skewed immune response.

Multifaceted, unique role of CD11c in leukocyte biology

CD11c is widely known as a dendritic cell surface marker but its non-dendritic cell expression profiles as well as its functional role have been gradually delineated. As a member of leukocyte-specific β2 integrin family, CD11c forms a heterodimer with CD18. CD11c/CD18 takes different conformations, which dictate its ligand binding. Here we reviewed CD11c current state of art, in comparison to its sister proteins CD11a, CD11b, and CD11d, illustrating its unique feature in leukocyte biology.

Know Your ABCs: Discovery, Differentiation, and Targeting of T-Bet+ B Cells

Since their first description in 2008, T-bet+ B cells have emerged as a clinically important B cell subset. Now commonly known as ABCs (Age-associated B Cells), they are uniquely characterized by their expression of the transcription factor T-bet. Indeed, this singular factor defines this B cell subset. This review will describe the discovery of T-bet+ B cells, their role in bacterial infection as T cell-independent (TI) plasmablasts, as well as long-term follicular helper T cell-dependent (TD) IgM+ and switched memory cells (i.e., T-bet+ ABCs), and later discoveries of their role(s) in diverse immunological responses. These studies highlight a critical, although limited, role of T-bet in IgG2a class switching, a function central to the cells' role in immunity and autoimmunity. Given their association with autoimmunity, pharmacological targeting is an attractive strategy for reducing or eliminating the B cells. T-bet+ ABCs express a number of characteristic cell surface markers, including CD11c, CD11b, CD73, and the adenosine 2a receptor (A2aR). Accordingly, A2aR agonist administration effectively targeted T-bet+ ABCs in vivo. Moreover, agonist treatment of lupus-prone mice reduced autoantibodies and disease symptoms. This latter work highlights the potential therapeutic use of adenosine agonists for treating autoimmune diseases involving T-bet+ ABCs.

Signaling Activation and Modulation in Extrafollicular B Cell Responses

The differentiation of naive follicular B cells into either the germinal center (GC) or extrafollicular (EF) pathway plays a critical role in shaping the type, affinity, and longevity of effector B cells. This choice also governs the selection and survival of autoreactive B cells, influencing their potential to enter the memory compartment. During the first 2-3 days following antigen encounter, initially activated B cells integrate activating signals from T cells, Toll-like receptors (TLRs), and cytokines, alongside inhibitory signals mediated by inhibitory receptors. This integration modulates the intensity of signaling, particularly of the PI3K/AKT/mTOR pathway, which plays a central role in guiding developmental decisions. These early signaling events determine whether B cells undergo GC maturation or differentiate rapidly into antibody-secreting cells (ASCs) via the EF pathway. Dysregulation of these signaling pathways-whether through excessive activation or defective regulatory mechanisms-can disrupt the balance between GC and EF fates, predisposing individuals to autoimmunity. Accordingly, aberrant PI3K/AKT/mTOR signaling has been implicated in the defective selection of autoreactive B cells, increasing the risk of autoimmune disease. This review focuses on the signaling events in newly activated B cells, with an emphasis on the induction and regulation of the PI3K/AKT/mTOR pathway. It also highlights gaps in our understanding of how alternative B cell fates are regulated. Both the physiological context and the implications of inborn errors of immunity (IEIs) and complex autoimmune conditions will be discussed in this regard.

Innate Immune Receptors as Dynamic Modulators of Extrafollicular Autoimmune B Cell Response

The immune system relies on carefully calibrated cellular machineries to enable distinction between endogenous and foreign molecules, with autoimmunity arising when this balance is disrupted. As potent autoantibody factories, B cells are major drivers of many autoimmune diseases. A significant fraction of patients affected by chronic autoimmune diseases such as systemic lupus erythematosus (SLE) exhibit pathogenic accumulation of B-cell subsets that are believed to be derived from the extrafollicular (EF) differentiation pathway. These B-cell subsets, although variously named and exhibiting intrinsic heterogeneity, are all poised producers of autoantibodies that correlate with patient pathophysiology. In addition, they are often characterized by biomarkers known to drive the innate immune response, including toll-like receptors and complement receptors. Although many innate receptors have well-established functions in myeloid cells and other immune cell types, their B cell-specific functions are still under active investigation and are crucial for understanding the molecular pathways that drive B-cell breaks of tolerance. In this review, we summarize studies on innate immune receptors that serve prominent roles in regulating EF B-cell activation in health and autoimmunity. By discussing independent and collaborative functions of these receptors, we hope to provide new perspectives in autoimmune disease signature research.

B cell immunometabolism in health and disease

B cells have crucial roles in the initiation and progression of many pathological conditions, and several therapeutic strategies have targeted the function of these cells. The advent of immunometabolism has provided compelling evidence that the metabolic reprogramming of immune cells can dramatically alter physiopathological immune activities. A better knowledge of the metabolic profiles of B cells can provide valuable means for developing therapies tuning defined cell pathways. Here we review the cellular and molecular mechanisms by which immunometabolism controls the physiology and pathophysiology of B cells and discuss the experimental evidence linking B cell metabolism to health, autoimmunity, and cancer. Considering that several metabolic pathways in B cells are involved differently, or even in opposite ways, in health and disease, we discuss how targeted modulation of B cell immunometabolism could be exploited mechanistically to rebalance abnormal B cell functions that have become altered in disease states.

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.

Roadmap for alleviating the manifestations of ageing in the cardiovascular system

Ageing of the cardiovascular system is associated with frailty and various life-threatening diseases. As global populations grow older, age-related conditions increasingly determine healthspan and lifespan. The circulatory system not only supplies nutrients and oxygen to all tissues of the human body and removes by-products but also builds the largest interorgan communication network, thereby serving as a gatekeeper for healthy ageing. Therefore, elucidating organ-specific and cell-specific ageing mechanisms that compromise circulatory system functions could have the potential to prevent or ameliorate age-related cardiovascular diseases. In support of this concept, emerging evidence suggests that targeting the circulatory system might restore organ function. In this Roadmap, we delve into the organ-specific and cell-specific mechanisms that underlie ageing-related changes in the cardiovascular system. We raise unanswered questions regarding the optimal design of clinical trials, in which markers of biological ageing in humans could be assessed. We provide guidance for the development of gerotherapeutics, which will rely on the technological progress of the diagnostic toolbox to measure residual risk in elderly individuals. A major challenge in the quest to discover interventions that delay age-related conditions in humans is to identify molecular switches that can delay the onset of ageing changes. To overcome this roadblock, future clinical trials need to provide evidence that gerotherapeutics directly affect one or several hallmarks of ageing in such a manner as to delay, prevent, alleviate or treat age-associated dysfunction and diseases.

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.

Senescence-associated T cells in immunosenescence and diseases

Age-related changes in the immune system, referred to as immunosenescence, appear to evolve with rather paradoxical manifestations, a diminished adaptive immune capacity, and an increased propensity for chronic inflammation often with autoimmunity, which may underlie the development of diverse disorders with age. Immunosenescent phenotypes are associated with the emergence of unique lymphocyte subpopulations of both T and B lineages. We report that a CD153+ programmed cell death protein 1 (PD-1)+ CD4+ T-cell subpopulation with severely attenuated T-cell receptor (TCR)-responsiveness, termed senescence-associated T (SAT) cells, co-evolve with potentially autoreactive CD30+ B cells, such as spontaneous germinal center B cells and age-associated B cells, in aging mice. SAT cells and CD30+ B cells are reciprocally activated with the aid of the interaction of CD153 with CD30 in trans and with the TCR complex in cis, resulting in the restoration of TCR-mediated proliferation and secretion of abundant pro-inflammatory cytokines in SAT cells and the activation and production of autoantibodies by CD30+ B cells. Besides normal aging, the development of SAT cells coupled with counterpart B cells may be robustly accelerated and accumulated in the relevant tissues of lymphoid or extra-lymphoid organs under chronic inflammatory conditions, including autoimmunity, and may contribute to the pathogenesis and aggravation of the disorders. This review summarizes and discusses recent advances in the understanding of SAT cells in the contexts of immunosenescent phenotypes, as well as autoimmune and chronic inflammatory diseases, and it provides a novel therapeutic clue.

Impact of Fli1 deletion on B cell populations: A focus on age-associated B cells and transcriptional dynamics

BACKGROUND

Altered Fli1 expression is associated with various autoimmune diseases, yet its impact on B cells remains unexplored.

OBJECTIVE

This study investigated the direct effects of Fli1 depletion on B cell populations, focusing on age-associated B cells (ABCs).

METHODS

Splenocytes of Fli1 BcKO (Cd19-Cre+/-; Fli1flox/flox) and Cd19-Cre+/- mice were analyzed flow cytometrically. Transcriptional/epigenetic profiles of Cd11b+Cd11c+ ABCs were examined by RNA-sequencing and ATAC-sequencing.

RESULTS

Fli1 BcKO mice displayed a notable reduction in follicular and marginal zone B cells, with a concurrent rise in newly formed B cells compared to Cd19-Cre+/- mice. Additionally, a striking increase in B-1 B cells, as well as Cd11b+Cd11c+ or T-bet+Cd11c+ ABCs, was observed in Fli1 BcKO mice. Furthermore, these mice exhibited elevated Cd138 levels in follicular B cells. Conducting transcriptional analyses of Fli1-depleted ABCs unveiled upregulated genes associated with cell-cell adhesion, coupled with downregulated genes linked to cell activation or immune responses. Exploring the chromatin landscape found that Fli1 depletion dysregulated the chromatin accessibility of the interferon regulatory factor family, implying potential roles in autoimmunity.

CONCLUSION

These findings suggest complex modulations of B cell populations and immune-related gene expression due to Fli1 deficiency, shedding light on its involvement in autoimmune processes.

Immunosenescence and age-related immune cells: causes of age-related diseases

Immunosenescence is a weakening of the immune system due to aging, characterized by changes in immune cells and dysregulated immune function. Age-related immune cells are increasing with aging. They are associated with chronic prolonged inflammation, causing tissue dysfunction and age-related diseases. Here, we discuss increased pro-inflammatory activity of aged macrophages, accumulation of lymphocytes with an age-associated phenotype, and specific alterations in both functions and characteristics of these immune cells. These cellular changes are associated with development of age-related diseases. Additionally, we reviewed various therapeutic strategies targeting age-related immunosenescence, providing pathways to mitigate effects of age-related diseases.

Circulatory age-associated B cells: Their distinct transcriptomic characteristics and clinical significance in drug-naïve patients with rheumatoid arthritis

Age-associated B cells (ABCs) have been implicated in the pathogenesis of autoimmune diseases. However, the global gene expression and clinical significance of circulatory ABCs in rheumatoid arthritis (RA) remain poorly understood. Here, single-cell RNA sequencing identified nine B cell subsets in peripheral blood of RA patients, including ABCs. Increased phagocytosis and antigen presentation were functionally enriched by the genes expressed differentially in ABCs. Network analysis and in vitro experiments demonstrated SYK as a key regulator defining the myeloid-like phenotypes in ABCs. Flow cytometry showed that the proportion of ABCs correlated with RA activity and serum tumor necrosis factor-alpha level. Notably, ABCs above a cutoff threshold specifically distinguished RA from healthy controls and indicated higher disease activity. This study highlights the myeloid characteristics of circulatory ABCs regulated by SYK in RA. Increased ABCs may reflect disease activity and could serve as a potential biomarker in RA.

Characterization of T-bet expressing B cells in lupus patients indicates a putative prognostic and therapeutic value of these cells for the disease

OBJECTIVE

To investigate whether T-bet+ B cells, as well as age-associated B cells/ABCs (CD19 + CD21-CD11c + T-bet+) and double-negative B cells/DN (CD19 + IgD-CD27- CXCR5-T-bet+), serve as prognostic and/or therapeutic tools for systemic lupus erythematosus (SLE) in humans.

METHODS

Flow cytometry was used for enumerating T-bet+ B cells and ABCs/DN subsets, found in the peripheral blood of 10 healthy donors and 22 active SLE patients. Whole blood assay cultures, combined with in vitro pharmacological treatments, were performed to evaluate the effects of hydroxychloroquine, anifrolumab, and fasudil (a ROCK kinase inhibitor) on T-bet+ B cells' percentage. Moreover, previously published single-cell RNA sequencing (scRNA-seq) data were used in a meta-analysis to allow characterization of genes and pathways associated with the biology of T-bet in B cells.

RESULTS

T-bet+ B cells displayed an expansion in SLE patients [1.47 (1.9-0.7) vs 10.85 (37.4-3.6)]. Similarly, both ABCs and DN were found to be expanded. Interestingly, percentages of T-bet+ B cells positively correlated with patients' SLEDAI scores (rs = 0.55, P = 0.007). Cell culture experiments conducted revealed that all three agents tested can deplete T-bet + B cells (without affecting the cell viability of lymphocytes, T cells, and B cells). According to bioinformatics analyses, T-bet is highly expressed in two B-cell clusters with pathogenic characteristics for SLE (designated as atypical memory B cells and activated naïve B cells). These clusters can be targeted for therapeutic interventions.

CONCLUSIONS

T-bet+ B cells can serve as a putative prognostic biomarker of lupus severity. Circumstantial data suggest that these cells may promote disease pathogenesis and may represent a novel therapeutic target.

Recent Evidence of the Role of CD4+ T Cell Subsets in IgG4-related Disease

CD4+ T cells, the so-called T helper cells, are one of the main players in the human immune system, which can regulate acquired immunity. Dysfunction of the acquired immune system induces various chronic inflammatory diseases such as malignancies and autoimmune diseases. IgG4-related disease (IgG4-RD) is also a chronic inflammatory disease that is characterized by elevated serum IgG4 concentration and infiltration of IgG4-positive plasma cells in affected tissues. Despite that remarkable advances in understanding the pathogenesis of IgG4-RD have been on the rise, the detailed mechanisms by which IgG4-RD develops are still unknown. In fact, CD4+ T cells abundantly infiltrate at lesions of IgG4-RD, and they are also associated with the pathogenesis of other refractory chronic inflammatory diseases. Therefore, our focus was on CD4+ T cells, and we previously reported the roles of their subsets including regulatory T cells, CD4 cytotoxic T lymphocytes, T follicular helper (Tfh) cells, T follicular regulatory cells, and T peripheral helper (Tph) cells in IgG4-RD. Among the subsets, Tph cells play an important role in generating ectopic lymphoid structures at inflammatory sites. Moreover, we found that circulating Tph cells are increased in IgG4-RD patients. Unlike Tfh cells, Tph cells express high levels of chemokine receptors and cytotoxic molecules. Thus, they can infiltrate affected tissues and exert a cytotoxic function. Additionally, our latest observations demonstrated that Tph cells interact with extrafollicular B cells in affected tissues. Hence, Tph cells may collaborate with a specific B-cell subset, and they play a role in the maintenance of persistent fibroinflammation in lesions of IgG4-RD. Tph cells may have an important role to play in the pathogenesis of not only IgG4-RD but also other chronic inflammatory diseases. This review summarizes and discusses the possible pathologic roles of CD4+ T cell subsets including Tph cells in IgG4-RD.

Immune Aging in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a life-long autoimmune disease caused by the confluence of genetic and environmental variables that lead to loss of self-tolerance and persistent joint inflammation. RA occurs at the highest incidence in individuals >65 years old, implicating the aging process in disease susceptibility. Transformative approaches in molecular immunology and in functional genomics have paved the way for pathway paradigms underlying the replacement of immune homeostasis with autodestructive immunity in affected patients, including the process of immune aging. Patients with RA have a signature of premature immune aging, best understood for CD4+ T cells, which function as pathogenic effectors in this HLA class II-associated disease. Premature immune aging is present in healthy HLA-DRB1*04+ individuals, placing accelerated immune aging before joint inflammation. Aging-related molecular abnormalities directly implicated in turning RA CD4+ T cells into proinflammatory effector cells are linked to malfunction of subcellular organelles, such as mitochondria, lysosomes, lipid droplets, and the endoplasmic reticulum. Resulting changes in T cell behavior include cellular hypermobility, tissue invasiveness, unopposed mammalian target of rapamycin complex (mTORC)1 activation, excessive release of tumor necrosis factor, lysosomal failure, clonal expansion, and immunogenic cell death. Aged and metabolically reprogrammed T cells in patients with RA are accompanied by age-associated B cells, which specialize in autoantibody production. Clonal hematopoiesis drives myeloid cell aging by producing aged monocytes and hypermetabolic macrophages, which sustain the process of inflammaging. Here, we synthesize insights into the relationship of RA risk and immune aging and discuss mechanisms through which immune aging can cause autoimmunity.

Function and Regulation of Age-Associated B Cells in Diseases

The aging process often leads to immune-related diseases, including infections, tumors, and autoimmune disorders. Recently, researchers identified a special subpopulation of B cells in elderly female mice that increases with age and accumulates prematurely in mouse models of autoimmune diseases or viral infections; these B cells are known as age-related B cells (ABCs). These cells possess distinctive cell surface phenotypes and transcriptional characteristics, and the cell population is widely recognized as CD11c+CD11b+T-bet+CD21-CD23- cells. Research has shown that ABCs are a heterogeneous group of B cells that originate independently of the germinal center and are insensitive to B-cell receptor (BCR) and CD40 stimulation, differentiating and proliferating in response to toll-like receptor 7 (TLR7) and IL-21 stimulation. Additionally, they secrete self-antibodies and cytokines to regulate the immune response. These issues have aroused widespread interest among researchers in this field. This review summarizes recent research progress on ABCs, including the functions and regulation of ABCs in aging, viral infection, autoimmune diseases, and organ transplantation.

Molecular underpinnings of aging contributing to systemic sclerosis pathogenesis

PURPOSE OF REVIEW

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by diffuse organ fibrosis and vasculopathy. Aberrant aging has been increasingly implicated in fibrotic diseases of the lung and other organs. The aim of this review is to summarize the established mechanisms of aging and how they may contribute to the pathogenesis of SSc.

RECENT FINDINGS

Shortened telomeres are present in SSc patients with interstitial lung disease (SSc-ILD) and associate with disease severity and mortality. Although the cause of telomere length shortening is unknown, immune mechanisms may be at play. Senescent cells accumulate in affected organs of SSc patients and contribute to a pathologic cellular phenotype that can be profibrotic and inflammatory. In addition to identifying patients with a more severe phenotype, biomarkers of aging may help identify patients who have worse outcomes with immunosuppression.

SUMMARY

Aging mechanisms, including telomere dysfunction and cellular senescence, likely contribute to the progressive fibrosis, vasculopathy, and immune dysfunction of SSc. Further work is needed to understand whether aberrant aging is an initiator or perpetuator of disease, and whether this is cell or organ specific. A better understanding of the role aging mechanisms play in SSc will contribute to our understanding of the underlying pathobiology and may also influence management of patients exhibiting the aging phenotype.

Single-Cell Analysis Provides New Insights into the Roles of Tertiary Lymphoid Structures and Immune Cell Infiltration in Kidney Injury and Chronic Kidney Disease

Chronic kidney disease (CKD) is a global health concern with high morbidity and mortality. Acute kidney injury (AKI) is a pivotal risk factor for the progression of CKD, and the rate of AKI-to-CKD progression increases with aging. Intrarenal inflammation is a fundamental mechanism underlying AKI-to-CKD progression. Tertiary lymphoid structures (TLSs), ectopic lymphoid aggregates formed in nonlymphoid organs, develop in aged injured kidneys, but not in young kidneys, with prolonged inflammation and maladaptive repair, which potentially exacerbates AKI-to-CKD progression in aged individuals. Dysregulated immune responses are involved in the pathogenesis of various kidney diseases, such as IgA nephropathy, lupus nephritis, and diabetic kidney diseases, thereby deteriorating kidney function. TLSs also develop in several kidney diseases, including transplanted kidneys and renal cell carcinoma. However, the precise immunologic mechanisms driving AKI-to-CKD progression and development of these kidney diseases remain unclear, which hinders the development of novel therapeutic approaches. This review aims to describe recent findings from single-cell analysis of cellular heterogeneity and complex interactions among immune and renal parenchymal cells, which potentially contribute to the pathogenesis of AKI-to-CKD progression and other kidney diseases, highlighting the mechanisms of formation and pathogenic roles of TLSs in aged injured kidneys.

Immune aging and infectious diseases

ABSTRACT

The rise in global life expectancy has led to an increase in the older population, presenting significant challenges in managing infectious diseases. Aging affects the innate and adaptive immune systems, resulting in chronic low-grade inflammation (inflammaging) and immune function decline (immunosenescence). These changes would impair defense mechanisms, increase susceptibility to infections and reduce vaccine efficacy in older adults. Cellular senescence exacerbates these issues by releasing pro-inflammatory factors, further perpetuating chronic inflammation. Moreover, comorbidities, such as cardiovascular disease and diabetes, which are common in older adults, amplify immune dysfunction, while immunosuppressive medications further complicate responses to infections. This review explores the molecular and cellular mechanisms driving inflammaging and immunosenescence, focusing on genomic instability, telomere attrition, and mitochondrial dysfunction. Additionally, we discussed how aging-associated immune alterations influence responses to bacterial, viral, and parasitic infections and evaluated emerging antiaging strategies, aimed at mitigating these effects to improve health outcomes in the aging population.

Lung-resident lymphocytes and their roles in respiratory infections and chronic respiratory diseases

Recent scientific breakthroughs have blurred traditional boundaries between innate and adaptive immunity, revealing a sophisticated network of tissue-resident cells that deliver immediate, localized immune responses. These lymphocytes not only provide rapid frontline defense but also present a paradoxical role in the pathogenesis of respiratory diseases such as asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and the long-term tissue consequences of viral infections including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). This review traverses the intricate landscape of lung-resident lymphocytes, delving into their origins, diverse functions, and their dualistic impact on pulmonary health. We dissect their interactions with the microenvironment and the regulatory mechanisms guiding their activity, with an emphasis on their contribution to both immune protection and immunopathology. This review aims to elucidate the complex narrative of these cells, enhancing our understanding of the development of precise therapeutic strategies to combat acute and chronic pulmonary diseases. Through this exploration, the review aspires to shed light on the potential of harnessing lung-resident lymphocytes for the treatment of respiratory conditions.

Contributions of each of the BAFF receptors to the lymphocyte profiles in C57BL/6 mice

BAFF, a vital B cell survival and differentiation factor, has three receptors: B-cell maturation antigen (BCMA), transmembrane activator and CAML interactor (TACI) and BR3. Although B cells are greatly reduced in B6.Baff-/- (which harbour no BAFF) and B6.Br3-/- mice (which harbour supra-normal levels of BAFF), the distributions of B cell subsets and relationships between Foxp3+ and CD4+ cells in these mice differ. Using a large panel of B6 congenic knockout and/or transgenic mice, we demonstrate that (1) supra-normal levels of BAFF per se do not explain the phenotypic differences between B6.Baff-/- and B6.Br3-/- mice; (2) B cells are expanded in B6.Taci-/- mice, with preferential expansion of follicular (FO) B cells at the expense of CD19+CD21-/loCD23-/lo B cells but without the preferential expansion of Foxp3+ cells observed in B6 mice bearing a Baff transgene; (3) despite no expansion in total B cells, percentages of FO B cells and marginal zone B cells are higher and percentages of CD19+CD21-/loCD23-/lo B cells are lower in young B6.Bcma-/- mice, consistent with the inability of B6.Br3-/-.Taci-/- mice to recapitulate the B cell profile of B6.Baff-/- mice; and (4) percentages of Foxp3+ cells in B6.Br3-/-.Taci-/- mice are intermediate between those in B6.Br3-/- and B6.Taci-/- mice despite the B cell profile of B6.Br3-/-.Taci-/- mice strongly resembling that of B6.Br3-/- mice. Collectively, our findings point to a non-redundant role for each of the BAFF receptors in determining the ultimate lymphocyte profile of the host. This may have clinically relevant ramifications in that the degree that a candidate therapeutic agent blocks engagement of any given individual BAFF receptor may affect its clinical utility.

Immunometabolic regulation of germinal centers and its implications for aging

Aging, metabolism, and immunity have long been considered distinct domains. Aging is primarily associated with the gradual decline of physiological functions, metabolism regulates energy production and maintains cellular processes, and the immune system manages innate and adaptive responses against pathogens and vaccines. However, recent studies have revealed that these three systems are intricately interconnected, collectively influencing an individual's response to stress and disease. This review explores the interplay between immunometabolism, T follicular helper cells, B cells, and aging, focusing on how these interactions impact immune function in the elderly.

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 50 years 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 8 months, 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 14 months, 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.

Rise of a CD27- IgD- CD11c+ B cells population in kidney recipients achieving long-term graft stability under immunosuppression

The use of immunosuppressive treatment is required to prevent rejection events, even a long time after kidney transplantation despite rare recipients achieving long-term graft stability without the need for immunosuppressive treatment, called operationally tolerant patients (TOLs). We comprehensively investigate the immune system of long-term IS recipients (LTTs) and TOLs to highlight their shared and unique immune features. Blood immune cell phenotyping was performed by spectral cytometry. Samples from 34 individuals were analyzed, including 6 LTTs, 8 TOLs, 10 stable patients at 1 year posttransplantation (STAs), and 10 healthy volunteers. B cells differed between LTTs and TOLs with a decreased total B-cell frequency and the acquisition of a memory phenotype in LTTs whereas a naive phenotype is maintained in TOLs. The frequencies of IgD-CD27- B cells and CD11c+ memory B cells are increased in LTTs, with an exhausted phenotype, evoked by a significant decrease in CD25 expression. These CD11c+ B cells display an exhausted phenotype similar to those found in several chronic immune diseases in which they have been shown to participate in their pathophysiology, suggesting active chronic inflammation in LTTs. Altogether, these data indicate that precautions should be taken to minimize IS use.

Extrafollicular CD19lowCXCR5-CD11c- double negative 3 (DN3) B cells are significantly associated with disease activity in females with systemic lupus erythematosus

Objective

B cells play a major role in the development and maintenance of systemic lupus erythematosus (SLE). Double negative (DN) B cells defined by the lack of surface expression of IgD and CD27 have attracted recent interest for their sensitivity to Toll-like receptor 7 (TLR7) ligands and their potential role in the production of autoantibodies. Here we aimed at investigating the possible association of DN B cells and their subsets with SLE disease activity specifically in female patients, in which TLR7 gene has been reported to escape X chromosome inactivation.

Methods

Peripheral blood mononuclear cells were purified from woman participating to the clinically well-characterized Swiss SLE Cohort Study (SSCS). PBMC from age-matched healthy females were used as controls. PBMC were stained for cell surface markers, intracellular Tbet and analyzed by multicolor cytofluorimetry. Single nucleotide TLR7 polymorphisms were assessed by polymerase chain reaction.

Results

The median SLE disease activity index of the 86 females was 2, IQR [0-6], all but 8 were under chronic SLE treatment. B cells co-expressing CD11c and Tbet were increased, the mean fluorescence intensity (MFI) of CD19 was considerably reduced and we observed a large increase in CD11c + CXCR5-and CD11c-CXCR5-concomitantly with a reduction of CD11c-CXCR5+ B cells in SLE compared to 40 healthy donors (HD). When focusing on the DN B cell subset, we found a reduction of DN1 (CD11c-CXCR5+) and an increase of DN2 (CD11c + CXCR5-) and most impressively of DN3 (CD11c-CXCR5-) cells. The DN subset, particularly DN3, showed the lowest level of CD19 expression. Both DN1 and DN3 percentages as well as the CD19 MFI of DN cells were associated with SLE disease activity. The use of glucocorticoids, immunosuppressants, and antimalarials impacted differentially on the frequencies of DN B cell subsets. CD19 MFI in B cells and the percentage of DN3 were the strongest biomarkers of disease activity. The TLR7 snp3858384 G allele was associated with increased percentages of B cells and CD19+CD11c-CXCR5+ and decreased CD19+CD11c-CXCR5-.

Conclusions

DN3 B cells are strongly associated with SLE clinical activity pointing to their potential involvement in disease pathogenesis, and CD19 expression level performs accurately as disease activity biomarker.

The effector function of mucosal associated invariant T cells alters with aging and is regulated by RORγt

Introduction

Mucosal-associated invariant T (MAIT) cells are a predominant subset of innate-like T cells in humans, characterized by diverse gene expression profiles and functional capabilities. However, the factors influencing the transcriptomes and effector functions of MAIT cells, particularly at mucosal barriers, remain largely unclear.

Methods

In this study, we employed single-cell RNA sequencing (scRNA-seq) and functional assays to investigate the transcriptomic and functional characteristics of intestinal MAIT cells in mouse models during aging. We also extended scRNA-seq analysis to human intestinal MAIT cells to compare their gene expression patterns with those observed in aged mice.

Results

Our findings demonstrated that the transcriptomes and functional capabilities of intestinal MAIT cells shifted from MAIT17 to MAIT1 profiles with aging in mouse models, with notable changes in the production of cytotoxic molecules. Further scRNA-seq analysis of human intestinal MAIT cells revealed a segregation into MAIT1 and MAIT17 subsets, displaying gene expression patterns that mirrored those seen in aged mouse models. The transcription factor RORγt was expressed in both MAIT1 and MAIT17 cells, acting to repress IFNγ production while promoting IL17 expression. Moreover, reduced expression of RORC and Il17A was correlated with poorer survival outcomes in colorectal cancer patients.

Discussion

These results suggest that aging induces a functional shift between MAIT1 and MAIT17 cells, which may be influenced by transcriptional regulators like RORγt. The observed alterations in MAIT cell activity could potentially impact disease prognosis, particularly in colorectal cancer. This study provides new insights into the dynamics of MAIT cell responses at mucosal barriers, highlighting possible therapeutic targets for modulating MAIT cell functions in aging and disease.

Aberrant zonal recycling of germinal center B cells impairs appropriate selection in lupus

Autoimmune diseases such as lupus are characterized by polyclonal B cell activation, leading to the production of autoantibodies. The mechanism leading to B cell dysregulation is unclear; however, the defect may lie in selection within germinal centers (GCs). GC B cells cycle between proliferation and mutation in the dark zone and selection in the light zone (LZ). Temporal assessment of GCs from mice with either persistent infection or lupus showed an accumulation of LZ B cells. Yet, only in lupus, GC B cells exhibited reduced proliferation and progressive loss of MYC and FOXO1, which regulate zonal recycling and differentiation. As lupus progressed, decreased mutational frequency and repertoire diversity were associated with reduced responsiveness to CD40 signaling, despite accumulation of plasma cells. Collectively, these findings suggest that lupus disease progression coincides with an intrinsic defect in LZ B cell signaling, altering the zonal recycling, selection, and differentiation of autoreactive B cells.

Immune Alterations with Aging: Mechanisms and Intervention Strategies

Aging is the result of a complex interplay of physical, environmental, and social factors, leading to an increased prevalence of chronic age-related diseases that burden health and social care systems. As the global population ages, it is crucial to understand the aged immune system, which undergoes declines in both innate and adaptive immunity. This immune decline exacerbates the aging process, creating a feedback loop that accelerates the onset of diseases, including infectious diseases, autoimmune disorders, and cancer. Intervention strategies, including dietary adjustments, pharmacological treatments, and immunomodulatory therapies, represent promising approaches to counteract immunosenescence. These interventions aim to enhance immune function by improving the activity and interactions of aging-affected immune cells, or by modulating inflammatory responses through the suppression of excessive cytokine secretion and inflammatory pathway activation. Such strategies have the potential to restore immune homeostasis and mitigate age-related inflammation, thus reducing the risk of chronic diseases linked to aging. In summary, this review provides insights into the effects and underlying mechanisms of immunosenescence, as well as its potential interventions, with particular emphasis on the relationship between aging, immunity, and nutritional factors.