Reversing B cell aging

Generation of a single-cell B cell atlas of antibody repertoires and transcriptomes to identify signatures associated with antigen specificity

Although new genomics-based pipelines have potential to augment antibody discovery, these methods remain in their infancy due to an incomplete understanding of the selection process that governs B cell clonal selection, expansion, and antigen specificity. Furthermore, it remains unknown how factors such as aging and reduction of tolerance influence B cell selection. Here we perform single-cell sequencing of antibody repertoires and transcriptomes of murine B cells following immunizations with a model therapeutic antigen target. We determine the relationship between antibody repertoires, gene expression signatures, and antigen specificity across 100,000 B cells. Recombinant expression and characterization of 227 monoclonal antibodies revealed the existence of clonally expanded and class-switched antigen-specific B cells that were more frequent in young mice. Although integrating multiple repertoire features such as germline gene usage and transcriptional signatures failed to distinguish antigen-specific from nonspecific B cells, other features such as immunoglobulin G (IgG) subtype and sequence composition correlated with antigen specificity.

Gastric DLBCL clonal evolution as function of patient age

Diffuse large B cell lymphoma (DLBCL) is the most common type of NHL, accounting for about 40% of NHL cases, and is one of the most aggressive lymphomas. DLBCL is widespread in individuals aged more than 50 years old, with a maximum incidence in the seventh decade, but it may also occur in younger patients. DLBCL may occur in any immune system tissue, including those around the gastrointestinal tract, and even in the stomach, though gastric DLBCL has yet to be sufficiently investigated. This study aimed to understand changes in gastric Diffuse Large B cell lymphoma (gastric DLBCL) development with age. Immunoglobulin (Ig) heavy chain variable region genes were amplified from sections of nine preserved biopsies, from patients whose age varied between 25 and 89 years, sequenced and analyzed. We show first that identification of the malignant clone based on the biopsies is much less certain than was previously assumed; and second that, contrary to expectations, the repertoire of gastric B cell clones is more diverse among the elderly DLBCL patients than among the young.

Compromised levels of CD6 and reduced T cell activation in the aged immune system

The CD6 molecule, a cell surface marker, is involved in immunological synapse formation between T cell and antigen-presenting cell and T lymphocyte activation for adequate immune response. Geriatric individuals fail to mount a satisfactory immunological response against pathogens thus, insights into the functionality of CD6 may provide information for competence building in elderly immune cells. However, limited information is available regarding the status of CD6 in geriatric individuals. In this study, various isoforms of CD6 were analysed in aged mononuclear cells (MNCs) and compared with young individuals. In geriatric individuals, protein and mRNA expressions of CD6 molecule/isoforms were found to be decreased compared to their young counterparts. Furthermore, geriatric MNCs failed to show any change in CD6 levels and its isoforms upon polyclonal activation compared to young MNCs, marked by reduced Ca⁺⁺ release and IL-2 expression. We suggest an overall decrease in CD6 levels in geriatric MNCs and T cells with suboptimal T cell activation in aged individuals.

Bullous Pemphigoid: Trigger and Predisposing Factors

Bullous pemphigoid (BP) is the most frequent autoimmune subepidermal blistering disease provoked by autoantibodies directed against two hemidesmosomal proteins: BP180 and BP230. Its pathogenesis depends on the interaction between predisposing factors, such as human leukocyte antigen (HLA) genes, comorbidities, aging, and trigger factors. Several trigger factors, such as drugs, thermal or electrical burns, surgical procedures, trauma, ultraviolet irradiation, radiotherapy, chemical preparations, transplants, and infections may induce or exacerbate BP disease. Identification of predisposing and trigger factors can increase the understanding of BP pathogenesis. Furthermore, an accurate anamnesis focused on the recognition of a possible trigger factor can improve prognosis by promptly removing it.

Immunological aging and clinical consequences

Immunosenescence is defined as the changes in the immune system associated with age. It is a progressive and irreversible process involving a decrease in the number of naïve T and B cells, NK cells cytotoxic and activity, and disruption of pro and anti-inflammatory balance by altering the production of IL-2, -4, -6, -10, -10, TNF-α, interferon γ and others. With age there is an increase in autoimmunity and generalized inflammation with simultaneous immunodeficiency, which results in greater susceptibility to infectious diseases, a decrease in reactivity to prophylactic vaccinations, the incidence of autoimmune diseases, and increased risk of infectious injury complications, exacerbation of symptoms of chronic diseases and an insufficient response to the presence of cells cancer. For years, based on the analysis of the frequency of viral and bacterial infections, immunological indicators and inflammation, attempts have been made to develop the immune risk profile (IRP) and effective methods of preventing disorders of the immune system and prolonging the functional capacity of the elderly.

Age-Associated B Cells

The age-associated B cell subset has been the focus of increasing interest over the last decade. These cells have a unique cell surface phenotype and transcriptional signature, and they rely on TLR7 or TLR9 signals in the context of Th1 cytokines for their formation and activation. Most are antigen-experienced memory B cells that arise during responses to microbial infections and are key to pathogen clearance and control. Their increasing prevalence with age contributes to several well-established features of immunosenescence, including reduced B cell genesis and damped immune responses. In addition, they are elevated in autoimmune and autoinflammatory diseases, and in these settings they are enriched for characteristic autoantibody specificities. Together, these features identify age-associated B cells as a subset with pivotal roles in immunological health, disease, and aging. Accordingly, a detailed understanding of their origins, functions, and physiology should make them tractable translational targets in each of these settings.

Loss of OcaB Prevents Age-Induced Fat Accretion and Insulin Resistance by Altering B-Lymphocyte Transition and Promoting Energy Expenditure

The current demographic shift toward an aging population has led to a robust increase in the prevalence of age-associated metabolic disorders. Recent studies have demonstrated that the etiology of obesity-related insulin resistance that develops with aging differs from that induced by high-calorie diets. Whereas the role of adaptive immunity in changes in energy metabolism driven by nutritional challenges has recently gained attention, its impact on aging remains mostly unknown. Here we found that the number of follicular B2 lymphocytes and expression of the B-cell-specific transcriptional coactivator OcaB increase with age in spleen and in intra-abdominal epididymal white adipose tissue (eWAT), concomitantly with higher circulating levels of IgG and impaired glucose homeostasis. Reduction of B-cell maturation and Ig production-especially that of IgG2c-by ablation of OcaB prevented age-induced glucose intolerance and insulin resistance and promoted energy expenditure by stimulating fatty acid utilization in eWAT and brown adipose tissue. Transfer of wild-type bone marrow in OcaB^-/- mice replenished the eWAT B2-cell population and IgG levels, which diminished glucose tolerance, insulin sensitivity, and energy expenditure while increasing body weight gain in aged mice. Thus these findings demonstrate that upon aging, modifications in B-cell-driven adaptive immunity contribute to glucose intolerance and fat accretion.

Characterization and redox mechanism of asthma in the elderly

Asthma is a chronic disease characterized by reversible airflow limitation, coughing, bronchial constriction, and an inflammatory immune response. While asthma has frequently been categorized as emerging in childhood, evidence has begun to reveal that the elderly population is certainly susceptible to late-onset, or even long-standing asthma. Non-atopic asthma, most commonly found in elderly patients is associated with elevated levels of serum and sputum neutrophils and may be more detrimental than atopic asthma. The mortality of asthma is high in the elderly since these patients often possess more severe symptoms than younger populations. The redox mechanisms that mediate inflammatory reactions during asthma have not been thoroughly interpreted in the context of aging. Thus, we review the asthmatic symptoms related to reactive oxygen species (ROS) and reactive nitrogen species (RNS) in seniors. Moreover, immune status in the elderly is weakened in part by immunosenescence, which is broadly defined as the decline in functionality of the immune system that corresponds with increasing age. The effects of immunosenescence on the expression of biomarkers potentially utilized in the clinical diagnosis of asthma remain unclear. It has also been shown that existing asthma treatments are less effective in the elderly. Thus, it is necessary that clinicians approach the diagnosis and treatment of asthmatic senior patients using innovative methods. Asthma in the elderly demands more intentional diagnostic and therapeutic research since it is potentially one of the few causes of mortality and morbidity in the elderly that is largely reversible.

B Cell Development in the Bone Marrow Is Regulated by Homeostatic Feedback Exerted by Mature B Cells

Cellular homeostasis in the B cell compartment is strictly imposed to balance cell production and cell loss. However, it is not clear whether B cell development in the bone marrow is an autonomous process or subjected to regulation by the peripheral B cell compartment. To specifically address this question, we used mice transgenic for human CD20, where effective depletion of B lineage cells is obtained upon administration of mouse anti-human CD20 antibodies, in the absence of any effect on other cell lineages and/or tissues. We followed the kinetics of B cell return to equilibrium by BrdU labeling and flow cytometry and analyzed the resulting data by mathematical modeling. Labeling was much faster in depleted mice. Compared to control mice, B cell-depleted mice exhibited a higher proliferation rate in the pro-/pre-B compartment, and higher cell death and lower differentiation in the immature B cell compartment. We validated the first result by analysis of the expression of Ki67, the nuclear protein expressed in proliferating cells, and the second using Annexin V staining. Collectively, our results suggest that B lymphopoiesis is subjected to homeostatic feedback mechanisms imposed by mature B cells in the peripheral compartment.

Aging affects B-cell antigen receptor repertoire diversity in primary and secondary lymphoid tissues

The elderly immune system is characterized by reduced responses to infections and vaccines, and an increase in the incidence of autoimmune diseases and cancer. Age-related deficits in the immune system may be caused by peripheral homeostatic pressures that limit bone marrow B-cell production or migration to the peripheral lymphoid tissues. Studies of peripheral blood B-cell receptor spectratypes have shown that those of the elderly are characterized by reduced diversity, which is correlated with poor health status. In the present study, we performed for the first time high-throughput sequencing of immunoglobulin genes from archived biopsy samples of primary and secondary lymphoid tissues in old (74 ± 7 years old, range 61-89) versus young (24 ± 5 years old, range 18-45) individuals, analyzed repertoire diversities and compared these to results in peripheral blood. We found reduced repertoire diversity in peripheral blood and lymph node repertoires from old people, while in the old spleen samples the diversity was larger than in the young. There were no differences in somatic hypermutation characteristics between age groups. These results support the hypothesis that age-related immune frailty stems from altered B-cell homeostasis leading to narrower memory B-cell repertoires, rather than changes in somatic hypermutation mechanisms.

A comparative review of aging and B cell function in mice and humans

Immune system function declines with age. Here we review and compare age-associated changes in murine and human B cell pools and humoral immune responses. We summarize changes in B cell generation and homeostasis, as well as notable changes at the subcellular level; then discuss how these changes help to explain alterations in immune responses across the adult lifespan of the animal. In each section we compare and contrast findings in the mouse, arguably the best animal model of the aging immune system, with current understanding of B cell immunity in humans.

Aging affects epidermal Langerhans cell development and function and alters their miRNA gene expression profile

Immunosenescence is a result of progressive decline in immune system function with advancing age. Epidermal Langerhans cells (LCs), belonging to the dendritic cell (DC) family, act as sentinels to play key roles in the skin immune responses. However, it has not been fully elucidated how aging affects development and function of LCs. Here, we systemically analyzed LC development and function during the aging process in C57BL/6J mice, and performed global microRNA (miRNA) gene expression profiles in aged and young LCs. We found that the frequency and maturation of epidermal LCs were significantly reduced in aged mice starting at 12 months of age, while the Langerin expression and ability to phagocytose Dextran in aged LCs were increased compared to LCs from < 6 month old mice. The migration of LCs to draining lymph nodes was comparable between aged and young mice. Functionally, aged LCs were impaired in their capacity to induce OVA-specific CD4⁺ and CD8⁺ T cell proliferation. Furthermore, the expression of miRNAs in aged epidermal LCs showed a distinct profile compared to young LCs. Most interestingly, aging-regulated miRNAs potentially target TGF-β-dependent and non- TGF-β-dependent signal pathways related to LCs. Overall, our data suggests that aging affects LCs development and function, and that age-regulated miRNAs may contribute to the LC developmental and functional changes in aging.

Immunosenescence and age-related viral diseases

Immunosenescence is described as a decline in the normal functioning of the immune system associated with physiologic ageing. Immunosenescence contributes to reduced efficacy to vaccination and increased susceptibility to infectious diseases in the elderly. Extensive studies of laboratory animal models of ageing or donor lymphocyte analysis have identified changes in immunity caused by the ageing process. Most of these studies have identified phenotypic and functional changes in innate and adaptive immunity. However, it is unclear which of these defects are critical for impaired immune defense against infection. This review describes the changes that occur in innate and adaptive immunity with ageing and some age-related viral diseases where defects in a key component of immunity contribute to the high mortality rate in mouse models of ageing.

Aging and neoteny in the B lineage

Aging and the physiologic decline of tissues and cells were once thought to be irreversible. However, recent studies suggest that various tissues, especially parts of the hematopoietic system, can be rejuvenated. Here we review potential mechanisms for this process and how they may be used to reverse age-related disorders and aging in general. We propose the novel hypothesis that altering the homeostatic process during cellular depletion can reverse aging in the hematopoietic system.

Acute lymphoblastic leukemia and developmental biology: a crucial interrelationship

The latest scientific findings in the field of cancer research are redefining our understanding of the molecular and cellular basis of the disease, moving the emphasis toward the study of the mechanisms underlying the alteration of the normal processes of cellular differentiation. The concepts best exemplifying this new vision are those of cancer stem cells and tumoral reprogramming. The study of the biology of acute lymphoblastic leukemias (ALLs) has provided seminal experimental evidence supporting these new points of view. Furthermore, in the case of B cells, it has been shown that all the stages of their normal development show a tremendous degree of plasticity, allowing them to be reprogrammed to other cellular types, either normal or leukemic. Here we revise the most recent discoveries in the fields of B-cell developmental plasticity and B-ALL research and discuss their interrelationships and their implications for our understanding of the biology of the disease.