Ageing adversely affects the migration and function of marginal zone B cells

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.

Age-Dependent Effect of Calcitriol on Mouse Regulatory T and B Lymphocytes

The hormonally active vitamin D3 metabolite, calcitriol, functions as an important modulator of the immune system. We assumed that calcitriol exerts different effects on immune cells and cytokine production, depending on the age of the animal; therefore, we analyzed its effects on regulatory T lymphocytes and regulatory B lymphocytes in healthy young and old female C57Bl/6/Foxp3GFP mice. In the lymph nodes of young mice, calcitriol decreased the percentage of Tregs, including tTregs and pTregs, and the expression of GITR, CD103, and CD101; however, calcitriol increased the level of IL-35 in adipose tissue. In the case of aged mice, calcitriol decreased the percentages of tTregs and CD19+ cells in lymph nodes and the level of osteopontin in the plasma. Additionally, increases in the levels of IgG and the lowest levels of IFN-γ, IL-10, and IL-35 were observed in the adipose tissue of aged mice. This study showed that calcitriol treatment had different effects, mainly on Treg phenotypes and cytokine secretion, in young and old female mice; it seemed that calcitriol enhanced the immunosuppressive properties of the lymphatic organs and adipose tissue of healthy young mice but not of healthy aged mice, where the opposite effects were observed.

B Cells from Aged Mice Do Not Have Intrinsic Defects in Affinity Maturation in Response to Immunization

Affinity maturation, the progressive increase in serum Ab affinity after vaccination, is an essential process that contributes to an effective humoral response against vaccines and infections. Germinal centers are key for affinity maturation, because they are where B cells undergo somatic hypermutation of their Ig genes in the dark zone before going through positive selection in the light zone via interactions with T follicular helper cells and follicular dendritic cells. In aged mice, affinity maturation has been shown to be impaired after immunization, but whether B cell-intrinsic factors contribute to this defect remains unclear. In this study, we show that B cells from aged BCR transgenic mice are able to become germinal center B cells, which are capable of receiving positive selection signals to a similar extent as B cells from young adult mice. Consistent with this, aging also does not impact the ability of B cells to undergo somatic hypermutation and acquire affinity-enhancing mutations. By contrast, transfer of B cells from young adult BCR mice into aged recipients resulted in the impaired acquisition of affinity-enhancing mutations, demonstrating that the aged microenvironment causes altered affinity maturation.

Inflammation and aging: signaling pathways and intervention therapies

Aging is characterized by systemic chronic inflammation, which is accompanied by cellular senescence, immunosenescence, organ dysfunction, and age-related diseases. Given the multidimensional complexity of aging, there is an urgent need for a systematic organization of inflammaging through dimensionality reduction. Factors secreted by senescent cells, known as the senescence-associated secretory phenotype (SASP), promote chronic inflammation and can induce senescence in normal cells. At the same time, chronic inflammation accelerates the senescence of immune cells, resulting in weakened immune function and an inability to clear senescent cells and inflammatory factors, which creates a vicious cycle of inflammation and senescence. Persistently elevated inflammation levels in organs such as the bone marrow, liver, and lungs cannot be eliminated in time, leading to organ damage and aging-related diseases. Therefore, inflammation has been recognized as an endogenous factor in aging, and the elimination of inflammation could be a potential strategy for anti-aging. Here we discuss inflammaging at the molecular, cellular, organ, and disease levels, and review current aging models, the implications of cutting-edge single cell technologies, as well as anti-aging strategies. Since preventing and alleviating aging-related diseases and improving the overall quality of life are the ultimate goals of aging research, our review highlights the critical features and potential mechanisms of inflammation and aging, along with the latest developments and future directions in aging research, providing a theoretical foundation for novel and practical anti-aging strategies.

Ectopic lymphoid structures in the aged lacrimal glands

Aging is a complex biological process in which many organs are pathologically affected. We previously reported that aged C57BL/6J had increased lacrimal gland (LG) lymphoid infiltrates that suggest ectopic lymphoid structures. However, these ectopic lymphoid structures have not been fully investigated. Using C57BL/6J mice of different ages, we analyzed the transcriptome of aged murine LGs and characterized the B and T cell populations. Age-related changes in the LG include increased differentially expressed genes associated with B and T cell activation, germinal center formation, and infiltration by marginal zone-like B cells. We also identified an age-related increase in B1+ cells and CD19+B220+ cells. B220+CD19+ cells were GL7+ (germinal center-like) and marginal zone-like and progressively increased with age. There was an upregulation of transcripts related to T follicular helper cells, and the number of these cells also increased as mice aged. Compared to a mouse model of Sjögren syndrome, aged LGs have similar transcriptome responses but also unique ones. And lastly, the ectopic lymphoid structures in aged LGs are not exclusive to a specific mouse background as aged diverse outbred mice also have immune infiltration. Altogether, this study identifies a profound change in the immune landscape of aged LGs where B cells become predominant. Further studies are necessary to investigate the specific function of these B cells during the aged LGs.

IgD+ age-associated B cells are the progenitors of the main T-independent B cell response to infection that generates protective Ab and can be induced by an inactivated vaccine in the aged

Age-associated B cells (ABC) accumulate with age and are associated with autoimmunity and chronic infection. However, their contributions to acute infection in the aged and their developmental pathways are unclear. We find that the response against influenza A virus infection in aged mice is dominated by a Fas+ GL7- effector B cell population we call infection-induced ABC (iABC). Most iABC express IgM and include antibody-secreting cells in the spleen, lung, and bone marrow. We find that in response to influenza, IgD+ CD21- CD23- ABC are the precursors of iABC and become memory B cells. These IgD+ ABC develop in germ-free mice, so are independent of foreign antigen recognition. The response of ABC to influenza infection, resulting in iABC, is T cell independent and requires both extrinsic TLR7 and TLR9 signals. In response to influenza infection, IgD+ ABC can induce a faster recovery of weight and higher total anti-influenza IgG and IgM titers that can neutralize virus. Immunization with whole inactivated virus also generates iABC in aged mice. Thus, in unimmunized aged mice, whose other B and T cell responses have waned, IgD+ ABC are likely the naive B cells with the potential to become Ab-secreting cells and to provide protection from infection in the aged.

B cell-intrinsic changes with age do not impact antibody-secreting cell formation but delay B cell participation in the germinal centre reaction

Vaccines typically protect against (re)infections by generating pathogen-neutralising antibodies. However, as we age, antibody-secreting cell formation and vaccine-induced antibody titres are reduced. Antibody-secreting plasma cells differentiate from B cells either early post-vaccination through the extrafollicular response or from the germinal centre (GC) reaction, which generates long-lived antibody-secreting cells. As the formation of both the extrafollicular antibody response and the GC requires the interaction of multiple cell types, the impaired antibody response in ageing could be caused by B cell intrinsic or extrinsic factors, or a combination of the two. Here, we show that B cells from older people do not have intrinsic defects in their proliferation and differentiation into antibody-secreting cells in vitro compared to those from the younger donors. However, adoptive transfer of B cells from aged mice to young recipient mice showed that differentiation into extrafollicular plasma cells was favoured at the expense of B cells entering the GC during the early stages of GC formation. In contrast, by the peak of the GC response, GC B cells derived from the donor cells of aged mice had expanded to the same extent as those from the younger donors. This indicates that age-related intrinsic B cell changes delay the GC response but are not responsible for the impaired antibody-secreting response or smaller peak GC response in ageing. Collectively, this study shows that B cells from aged individuals are not intrinsically defective in responding to stimulation and becoming antibody-secreting cells, implicating B cell-extrinsic factors as the primary cause of age-associated impairment in the humoral immunity.

Immune phenotype of the CD4+ T cells in the aged lymphoid organs and lacrimal glands

Aging is associated with a massive infiltration of T lymphocytes in the lacrimal gland. Here, we aimed to characterize the immune phenotype of aged CD4⁺ T cells in this tissue as compared with lymphoid organs. To perform this, we sorted regulatory T cells (Tregs, CD4⁺CD25⁺GITR⁺) and non-Tregs (CD4⁺CD25^negGITR^neg) in lymphoid organs from female C57BL/6J mice and subjected these cells to an immunology NanoString® panel. These results were confirmed by flow cytometry, live imaging, and tissue immunostaining in the lacrimal gland. Importantly, effector T helper 1 (Th1) genes were highly upregulated on aged Tregs, including the master regulator Tbx21. Among the non-Tregs, we also found a significant increase in the levels of EOMES^med/high, Tbet^negIFN-γ⁺, and CD62L⁺CD44^negCD4⁺ T cells with aging, which are associated with cell exhaustion, immunopathology, and the generation of tertiary lymphoid tissue. At the functional level, aged Tregs from lymphoid organs are less able to decrease proliferation and IFN-γ production of T responders at any age. More importantly, human lacrimal glands (age range 55-81 years) also showed the presence of CD4⁺Foxp3⁺ cells. Further studies are needed to propose potential molecular targets to avoid immune-mediated lacrimal gland dysfunction with aging.

Pannexin Channel Regulation of Cell Migration: Focus on Immune Cells

The role of Pannexin (PANX) channels during collective and single cell migration is increasingly recognized. Amongst many functions that are relevant to cell migration, here we focus on the role of PANX-mediated adenine nucleotide release and associated autocrine and paracrine signaling. We also summarize the contribution of PANXs with the cytoskeleton, which is also key regulator of cell migration. PANXs, as mechanosensitive ATP releasing channels, provide a unique link between cell migration and purinergic communication. The functional association with several purinergic receptors, together with a plethora of signals that modulate their opening, allows PANX channels to integrate physical and chemical cues during inflammation. Ubiquitously expressed in almost all immune cells, PANX1 opening has been reported in different immunological contexts. Immune activation is the epitome coordination between cell communication and migration, as leukocytes (i.e., T cells, dendritic cells) exchange information while migrating towards the injury site. In the current review, we summarized the contribution of PANX channels during immune cell migration and recruitment; although we also compile the available evidence for non-immune cells (including fibroblasts, keratinocytes, astrocytes, and cancer cells). Finally, we discuss the current evidence of PANX1 and PANX3 channels as a both positive and/or negative regulator in different inflammatory conditions, proposing a general mechanism of these channels contribution during cell migration.

Mechanisms underpinning poor antibody responses to vaccines in ageing

Vaccines are a highly effective intervention for conferring protection against infections and reducing the associated morbidity and mortality in vaccinated individuals. However, ageing is often associated with a functional decline in the immune system that results in poor antibody production in older individuals after vaccination. A key contributing factor of this age-related decline in vaccine efficacy is the reduced size and function of the germinal centre (GC) response. GCs are specialised microstructures where B cells undergo affinity maturation and diversification of their antibody genes, before differentiating into long-lived antibody-secreting plasma cells and memory B cells. The GC response requires the coordinated interaction of many different cell types, including B cells, T follicular helper (Tfh) cells, T follicular regulatory (Tfr) cells and stromal cell subsets like follicular dendritic cells (FDCs). This review discusses how ageing affects different components of the GC reaction that contribute to its limited output and ultimately impaired antibody responses in older individuals after vaccination. An understanding of the mechanisms underpinning the age-related decline in the GC response is crucial in informing strategies to improve vaccine efficacy and extend the healthy lifespan amongst older people.

Follicular dendritic cells

Follicular dendritic cells (FDCs) are unique accessory immune cells that contribute to the regulation of humoral immunity. They are multitasker cells essential for the organization and maintenance of the lymphoid architecture, induction of germinal center reaction, production of B memory cells, and protection from autoimmune disorders. They perform their activities through both antigen-driven and chemical signaling to B cells. FDCs play a crucial role in the physiological regulation of the immune response. Dis-regulation of this immune response results when FDCs retain antigens for years. This provides a constant antigenic stimulation for B cells resulting in the development of immune disorders. Antigen trapped on FDCs is resistant to therapeutic intervention causing chronicity and recurrences. Beyond their physiological immunoregulatory functions, FDCs are involved in the pathogenesis of several immune-related disorders including HIV/AIDS, prion diseases, chronic inflammatory, and autoimmune disorders. FDCs have also been recently implicated in rare neoplasms of lymphoid and hematopoietic tissues. Understanding FDC biology is essential for better control of humoral immunity and opens the gate for therapeutic management of FDC-mediated immune disorders. Thus, the biology of FDCs has become a hot research area in the last couple of decades. In this review, we aim to provide a comprehensive overview of FDCs and their role in physiological and pathological conditions.

Patho-Physiology of Aging and Immune-Senescence: Possible Correlates With Comorbidity and Mortality in Middle-Aged and Old COVID-19 Patients

During the last 2 years, the entire world has been severely devastated by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic (COVID-19) as it resulted in several million deaths across the globe. While the virus infects people indiscriminately, the casualty risk is higher mainly in old, and middle-aged COVID-19 patients. The incidences of COVID-19 associated co-morbidity and mortality have a great deal of correlation with the weakened and malfunctioning immune systems of elderly people. Presumably, due to the physiological changes associated with aging and because of possible comorbidities such as diabetes, hypertension, obesity, cardiovascular, and lung diseases, which are more common in elderly people, may be considered as the reason making the elderly vulnerable to the infection on one hand, and COVID-19 associated complications on the other. The accretion of senescent immune cells not only contributes to the deterioration of host defense, but also results in elevated inflammatory phenotype persuaded immune dysfunction. In the present review, we envisage to correlate functioning of the immune defense of older COVID-19 patients with secondary/super infection, increased susceptibility or aggravation against already existing cancer, infectious, autoimmune, and other chronic inflammatory diseases. Moreover, we have discussed how age-linked modulations in the immune system affect therapeutic response against administered drugs as well as immunological response to various prophylactic measures including vaccination in the elderly host. The present review also provides an insight into the intricate pathophysiology of the aging and the overall immune response of the host to SARS-CoV-2 infection. A better understanding of age-related immune dysfunction is likely to help us in the development of targeted preemptive strategies for deadly COVID-19 in elderly patients.

Aging-Related Cellular, Structural and Functional Changes in the Lymph Nodes: A Significant Component of Immunosenescence? An Overview

Aging affects all tissues and organs. Aging of the immune system results in the severe disruption of its functions, leading to an increased susceptibility to infections, an increase in autoimmune disorders and cancer incidence, and a decreased response to vaccines. Lymph nodes are precisely organized structures of the peripheral lymphoid organs and are the key sites coordinating innate and long-term adaptive immune responses to external antigens and vaccines. They are also involved in immune tolerance. The aging of lymph nodes results in decreased cell transport to and within the nodes, a disturbance in the structure and organization of nodal zones, incorrect location of individual immune cell types and impaired intercellular interactions, as well as changes in the production of adequate amounts of chemokines and cytokines necessary for immune cell proliferation, survival and function, impaired naïve T- and B-cell homeostasis, and a diminished long-term humoral response. Understanding the causes of these stromal and lymphoid microenvironment changes in the lymph nodes that cause the aging-related dysfunction of the immune system can help to improve long-term immune responses and the effectiveness of vaccines in the elderly.

The Dynamics of B Cell Aging in Health and Disease

Aging is considered to be an important risk factor for several inflammatory diseases. B cells play a major role in chronic inflammatory diseases by antibody secretion, antigen presentation and T cell regulation. Different B cell subsets have been implicated in infections and multiple autoimmune diseases. Since aging decreases B cell numbers, affects B cell subsets and impairs antibody responses, the aged B cell is expected to have major impacts on the development and progression of these diseases. In this review, we summarize the role of B cells in health and disease settings, such as atherosclerotic disease. Furthermore, we provide an overview of age-related changes in B cell development and function with respect to their impact in chronic inflammatory diseases.

Long-Term Recovery of the Adaptive Immune System in Rhesus Macaques After Total Body Irradiation

PURPOSE

Ionizing radiation causes acute damage to hematopoietic and immune cells, but the long-term immunologic consequences of irradiation are poorly understood. We therefore performed a prospective study of the delayed immune effects of radiation using a rhesus macaque model.

METHODS AND MATERIALS

Ten macaques received 4 Gy high-energy x-ray total body irradiation (TBI) and 6 control animals received sham irradiation. TBI caused transient lymphopenia that resolved over several weeks. Once white blood cell counts recovered, flow cytometry was used to immunophenotype the circulating adaptive immune cell populations 4, 9, and 21 months after TBI. Data were fit using a mixed-effects model to determine age-dependent, radiation-dependent, and interacting effects. T cell receptor (TCR) sequencing and quantification of TCR Excision Circles were used to determine relative contributions of thymopoiesis and peripheral expansion to T cell repopulation. Two years after TBI, the cohort was vaccinated with a 23-valent pneumococcal polysaccharide vaccine and a tetravalent influenza hemagglutinin vaccine.

RESULTS

Aging, but not TBI, led to significant changes in the frequencies of dendritic cells, CD4 and CD8 T cells, and B cells. However, irradiated animals exhibited increased frequencies of central memory T cells and decreased frequencies of naïve T cells. These consequences of irradiation were time-dependent and more prolonged in the CD8 T cell population. Irradiation led to transient increases in CD8+ T cell TCR Excision Circles and had no significant effect on TCR sequence entropy, indicating T cell recovery was partially mediated by thymopoiesis. Animals that were irradiated and then vaccinated showed normal immunoglobulin G binding and influenza neutralization titers in response to the 4 protein antigens but weaker immunoglobulin G binding titers to 10 of the 23 polysaccharide antigens.

CONCLUSIONS

These findings indicate that TBI causes subtle but long-lasting immune defects that are evident years after recovery from lymphopenia.

Cellular senescence in lymphoid organs and immunosenescence

Immunosenescence is a multi-faceted phenomenon at the root of age-associated immune dysfunction. It can lead to an array of pathological conditions, including but not limited to a decreased capability to surveil and clear senescent cells (SnCs) and cancerous cells, an increased autoimmune responses leading to tissue damage, a reduced ability to tackle pathogens, and a decreased competence to illicit a robust response to vaccination. Cellular senescence is a phenomenon by which oncogene-activated, stressed or damaged cells undergo a stable cell cycle arrest. Failure to efficiently clear SnCs results in their accumulation in an organism as it ages. SnCs actively secrete a myriad of molecules, collectively called senescence-associated secretory phenotype (SASP), which are factors that cause dysfunction in the neighboring tissue. Though both cellular senescence and immunosenescence have been studied extensively and implicated in various pathologies, their relationship has not been greatly explored. In the wake of an ongoing pandemic (COVID-19) that disproportionately affects the elderly, immunosenescence as a function of age has become a topic of great importance. The goal of this review is to explore the role of cellular senescence in age-associated lymphoid organ dysfunction and immunosenescence, and provide a framework to explore therapies to rejuvenate the aged immune system.

Macrophage-fibroblast circuits in the spleen

Macrophages are an integral part of all organs in the body, where they contribute to immune surveillance, protection, and tissue-specific homeostatic functions. This is facilitated by so-called niches composed of macrophages and their surrounding stroma. These niches structurally anchor macrophages and provide them with survival factors and tissue-specific signals that imprint their functional identity. In turn, macrophages ensure appropriate functioning of the niches they reside in. Macrophages thus form reciprocal, mutually beneficial circuits with their cellular niches. In this review, we explore how this concept applies to the spleen, a large secondary lymphoid organ whose primary functions are to filter the blood and regulate immunity. We first outline the splenic micro-anatomy, the different populations of splenic fibroblasts and macrophages and their respective contribution to protection of and key physiological processes occurring in the spleen. We then discuss firmly established and potential cellular circuits formed by splenic macrophages and fibroblasts, with an emphasis on the molecular cues underlying their crosstalk and their relevance to splenic functionality. Lastly, we conclude by considering how these macrophage-fibroblast circuits might be impaired by aging, and how understanding these changes might help identify novel therapeutic avenues with the potential of restoring splenic functions in the elderly.

Aging and Options to Halt Declining Immunity to Virus Infections

Immunosenescence is a process associated with aging that leads to dysregulation of cells of innate and adaptive immunity, which may become dysfunctional. Consequently, older adults show increased severity of viral and bacterial infections and impaired responses to vaccinations. A better understanding of the process of immunosenescence will aid the development of novel strategies to boost the immune system in older adults. In this review, we focus on major alterations of the immune system triggered by aging, and address the effect of chronic viral infections, effectiveness of vaccination of older adults and strategies to improve immune function in this vulnerable age group.

Deficiency of β-arrestin2 exacerbates inflammatory arthritis by facilitating plasma cell formation

β-arrestin2 (β-arr2) is, a key protein that mediates desensitization and internalization of G protein-coupled receptors and participates in inflammatory and immune responses. Deficiency of β-arr2 has been found to exacerbate collagen antibody-induced arthritis (CAIA) through unclear mechanisms. In this study we tried to elucidate the molecular mechanisms underlying β-arr2 depletion-induced exacerbation of CAIA. CAIA was induced in β-arr2-/- and wild-type (WT) mice by injection of collagen antibodies and LPS. The mice were sacrificed on d 13 after the injection, spleen, thymus and left ankle joints were collected for analysis. Arthritis index (AI) was evaluated every day or every 2 days. We showed that β-arr2-/- mice with CAIA had a further increase in the percentage of plasma cells in spleen as compared with WT mice with CAIA, which was in accordance with elevated serum IgG1 and IgG2A expression and aggravating clinical performances, pathologic changes in joints and spleen, joint effusion, and joint blood flow. Both LPS stimulation of isolated B lymphocytes in vitro and TNP-LPS challenge in vivo led to significantly higher plasma cell formation and antibodies production in β-arr2-/- mice as compared with WT mice. LPS treatment induced membrane distribution of toll-like receptor 4 (TLR4) on B lymphocytes, accordingly promoted the nuclear translocation of NF-κB and the transcription of Blimp1. Immunofluorescence analysis confirmed that more TLR4 colocalized with β-arr2 in B lymphocytes in response to LPS stimulation. Depletion of β-arr2 restrained TLR4 on B lymphocyte membrane after LPS treatment and further enhanced downstream NF-κB signaling leading to additional increment in plasma cell formation. In summary, β-arr2 depletion exacerbates CAIA and further increases plasma cell differentiation and antibody production through inhibiting TLR4 endocytosis and aggravating NF-κB signaling.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

Multiple Levels of Immunological Memory and Their Association with Vaccination

Immunological memory is divided into many levels to counteract the provocations of diverse and ever-changing infections. Fast functions of effector memory and the superposition of both quantitatively and qualitatively plastic anticipatory memory responses together form the walls of protection against pathogens. Here we provide an overview of the role of different B and T cell subsets and their interplay, the parallel and independent functions of the B1, marginal zone B cells, T-independent- and T-dependent B cell responses, as well as functions of central and effector memory T cells, tissue-resident and follicular helper T cells in the memory responses. Age-related limitations in the immunological memory of these cell types in neonates and the elderly are also discussed. We review how certain aspects of immunological memory and the interactions of components can affect the efficacy of vaccines, in order to link our knowledge of immunological memory with the practical application of vaccination.

Autoimmune encephalitis mediated by B-cell response against N-methyl-d-aspartate receptor

Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis is a neuropsychiatric disease characterized by an antibody-mediated autoimmune response against NMDAR. Recent studies have shown that anti-NMDAR antibodies are involved in the pathophysiology of the disease. However, the upstream immune and inflammatory processes responsible for this pathogenic response are still poorly understood. Here, we immunized mice against the region of NMDA receptor containing the N368/G369 amino acids, previously implicated in a pathogenic response. This paradigm induced encephalopathy characterized by blood-brain barrier opening, periventricular T2-MRI hyperintensities and IgG deposits into the brain parenchyma. Two weeks after immunization, mice developed clinical symptoms reminiscent of encephalitis: anxiety- and depressive-like behaviours, spatial memory impairment (without motor disorders) and increased sensitivity to seizures. This response occurred independently of overt T-cell recruitment. However, it was associated with B220+ (B cell) infiltration towards the ventricles, where they differentiated into CD138+ cells (plasmocytes). Interestingly, these B cells originated from peripheral lymphoid organs (spleen and cervical lymphoid nodes). Finally, blocking the B-cell response using a depleting cocktail of antibodies reduced the severity of symptoms in encephalitis mice. This study demonstrates that the B-cell response can lead to an autoimmune reaction against NMDAR that drives encephalitis-like behavioural impairments. It also provides a relevant platform for dissecting encephalitogenic mechanisms in an animal model, and enables the testing of therapeutic strategies targeting the immune system in anti-NMDAR encephalitis.

Aging, Immunity, and COVID-19: How Age Influences the Host Immune Response to Coronavirus Infections?

The novel coronavirus severe acute respiratory syndrome coronavirus 2 causing the Coronavirus disease (COVID-19) pandemic has ravaged the world with over 72 million total cases and over 1.6 million deaths worldwide as of early December 2020. An overwhelming preponderance of cases and deaths is observed within the elderly population, and especially in those with pre-existing conditions and comorbidities. Aging causes numerous biological changes in the immune system, which are linked to age-related illnesses and susceptibility to infectious diseases. Age-related changes influence the host immune response and therefore not only weaken the ability to fight respiratory infections but also to mount effective responses to vaccines. Immunosenescence and inflamm-aging are considered key features of the aging immune system wherein accumulation of senescent immune cells contribute to its decline and simultaneously increased inflammatory phenotypes cause immune dysfunction. Age-related quantitative and qualitative changes in the immune system affect cells and soluble mediators of both the innate and adaptive immune responses within lymphoid and non-lymphoid peripheral tissues. These changes determine not only the susceptibility to infections, but also disease progression and clinical outcomes thereafter. Furthermore, the response to therapeutics and the immune response to vaccines are influenced by age-related changes within the immune system. Therefore, better understanding of the pathophysiology of aging and the immune response will not only help understand age-related diseases but also guide targeted management strategies for deadly infectious diseases like COVID-19.

Ageing promotes early T follicular helper cell differentiation by modulating expression of RBPJ

Ageing profoundly changes our immune system and is thought to be a driving factor in the morbidity and mortality associated with infectious disease in older people. We have previously shown that the impaired immunity to vaccination that occurs in aged individuals is partly attributed to the effect of age on T follicular helper (Tfh) cell formation. In this study, we examined how age intrinsically affects Tfh cell formation in both mice and humans. We show increased formation of Tfh precursors (pre-Tfh) but no associated increase in germinal centre (GC)-Tfh cells in aged mice, suggesting age-driven promotion of only early Tfh cell differentiation. Mechanistically, we show that ageing alters TCR signalling which drives expression of the Notch-associated transcription factor, RBPJ. Genetic or chemical modulation of RBPJ or Notch rescues this age-associated early Tfh cell differentiation, and increased intrinsic Notch activity recapitulates this phenomenon in younger mice. Our data offer mechanistic insight into the age-induced changes in T-cell activation that affects the differentiation and ultimately the function of effector T cells.

Dysregulation of leukocyte trafficking in ageing: Causal factors and possible corrective therapies

Ageing is a universal biological phenomenon that is accompanied by the development of chronic, low-grade inflammation and remodelling of the immune system resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under homeostatic and inflammatory conditions is dysregulated in ageing. We particularly highlight the age-related changes in the expression of adhesion molecules and chemokine receptor/ligands, and the accumulation of senescent cells that drive modulated leukocyte trafficking. These age-related changes to leukocyte trafficking are multifactorial and specific to leukocyte subset, tissue, type of vascular bed, and inflammatory status. However, dysregulated leukocyte trafficking ultimately affects immune responses in older adults. We therefore go on to discuss approved drugs, including anti-integrins, anti-chemokines and statins, as well as novel therapeutics that may be used to target dysregulated leukocyte trafficking in ageing, improve immune responses and delay the onset of age-related diseases.

Peripherally-sourced myeloid antigen presenting cells increase with advanced aging

Aging is associated with dysfunction of the gut microbiota-immune-brain axis, a major regulatory axis in both brain health and in central nervous system (CNS) diseases. Antigen presenting cells (APCs) play a major role in sensing changes in the gut microbiota and regulation of innate and adaptive immune responses. APCs have also been implicated in various chronic inflammatory conditions, including age-related neurodegenerative diseases. The increase in chronic low-level inflammation seen with aging has also been linked to behavioral decline. Despite their acknowledged importance along the gut microbiota-immune-brain axis, there is limited evidence on how APCs change with aging. In this study, we examined age-related changes in myeloid APCs in the gut, spleen, and brain as well as changes in the gut microbiota and behavioral phenotype in mice ranging in age from 2 months up to 32 months of both sexes. Our data show that the number of peripherally-sourced myeloid APCs significantly increases with advanced aging in the brain. In addition, our data showed that age-related changes in APCs are subset-specific in the gut and sexually dimorphic in the spleen. Our work highlights the importance of studying myeloid APCs in an age-, tissue-, and sex-specific manner.

The Effects of Immune System Modulation on Prion Disease Susceptibility and Pathogenesis

Prion diseases are a unique group of infectious chronic neurodegenerative disorders to which there are no cures. Although prion infections do not stimulate adaptive immune responses in infected individuals, the actions of certain immune cell populations can have a significant impact on disease pathogenesis. After infection, the targeting of peripherally-acquired prions to specific immune cells in the secondary lymphoid organs (SLO), such as the lymph nodes and spleen, is essential for the efficient transmission of disease to the brain. Once the prions reach the brain, interactions with other immune cell populations can provide either host protection or accelerate the neurodegeneration. In this review, we provide a detailed account of how factors such as inflammation, ageing and pathogen co-infection can affect prion disease pathogenesis and susceptibility. For example, we discuss how changes to the abundance, function and activation status of specific immune cell populations can affect the transmission of prion diseases by peripheral routes. We also describe how the effects of systemic inflammation on certain glial cell subsets in the brains of infected individuals can accelerate the neurodegeneration. A detailed understanding of the factors that affect prion disease transmission and pathogenesis is essential for the development of novel intervention strategies.

Assessment of Lymph Node Stromal Cells as an Underlying Factor in Age-Related Immune Impairment

Aging negatively impacts immunity, resulting in inefficient responses to vaccinations and infections. Fibroblastic reticular cells (FRCs) are the major stromal cell subset in lymph nodes (LNs) and play an intricate role in the orchestration and control of adaptive immune responses. Although stromal cells have a major impact on immune responses, the impact of aging on LN stromal cells remains unclear. Quantitative analysis of LN stromal cells by flow cytometry revealed that there are no significant differences in the number of stromal cells in young and aged LN at steady state but after influenza infection aged FRCs have delayed expansion as a result of reduced proliferation. Aged LNs also produce reduced levels of homeostatic chemokines, which correlates with reduced homing of naive T cells. Image analysis reveals that young and aged T-cell zone FRCs have similar morphology at steady state and after infection. Furthermore, aged FRCs did not appear to be a contributing factor in the reduced proliferation of young T cells transferred into aged LNs after influenza infection. These results demonstrate that aging alters LN stromal cell response to challenge and these age-related changes may be an underlying contributor to impaired immune responses in the elderly people.

Allergological Study of 565 Elderly Patients Previously Labeled as Allergic to Penicillins

Purpose

Elderly people thought to have an allergy to beta-lactams (BLs) may tolerate the drugs in subsequent exposures due to initial false labeling of allergies, the spontaneous loss of sensitivity to BLs over time or age-related decline in sensitization. As a result, they may be treated with less appropriate antibiotics, causing more side effects and entailing increased costs for health systems. The aim of this investigation was to assess whether patients in the third and fourth age with previously confirmed allergies to BLs had lost sensitization and could tolerate these antibiotics.

Patients and methods

Patients allergic to BLs were divided into group A (aged 60-79 years) and B (aged ≥80 years). Clinical history, skin testing, drug challenge tests (DCT) and evaluation of resensitization were used to classify participants as showing immediate reactions, non-immediate reactions, or tolerance. We compared clinical entities, drugs involved, and final outcome by age group.

Results

Of 1362 cases evaluated, 565 underwent an allergological study. The skin was the most common organ involved. Anaphylaxis and side chain reactions were more frequent in group A (p<0.01), as were positive DCT. Classical benzylpenicillin determinants (benzylpenicilloyl and/or minor determinant mixture) were more frequent triggers in group B (p< 0.01). Resensitization after challenge occurred in very few participants.

Conclusion

The risk for allergy to BLs decreases with age and a history of anaphylaxis by BLs is a predictor of positive results in skin tests (ST). Both immunoglobin E (IgE) and T-cell-mediated responses can disappear in elderly people, who can develop tolerance to these antibiotics. These results are of clinical relevance to patients who need to be treated with antibiotics from this family.

Unaltered intravenous prion disease pathogenesis in the temporary absence of marginal zone B cells

Prion diseases are a unique, infectious, neurodegenerative disorders that can affect animals and humans. Data from mouse transmissions show that efficient infection of the host after intravenous (IV) prion exposure is dependent upon the early accumulation and amplification of the prions on stromal follicular dendritic cells (FDC) in the B cell follicles. How infectious prions are initially conveyed from the blood-stream to the FDC in the spleen is uncertain. Addressing this issue is important as susceptibility to peripheral prion infections can be reduced by treatments that prevent the early accumulation of prions upon FDC. The marginal zone (MZ) in the spleen contains specialized subsets of B cells and macrophages that are positioned to continuously monitor the blood-stream and remove pathogens, toxins and apoptotic cells. The continual shuttling of MZ B cells between the MZ and the B-cell follicle enables them to efficiently capture and deliver blood-borne antigens and antigen-containing immune complexes to splenic FDC. We tested the hypothesis that MZ B cells also play a role in the initial shuttling of prions from the blood-stream to FDC. MZ B cells were temporarily depleted from the MZ by antibody-mediated blocking of integrin function. We show that depletion of MZ B cells around the time of IV prion exposure did not affect the early accumulation of blood-borne prions upon splenic FDC or reduce susceptibility to IV prion infection. In conclusion, our data suggest that the initial delivery of blood-borne prions to FDC in the spleen occurs independently of MZ B cells.

Research progress on immune aging and its mechanisms affecting geriatric diseases

Immunosenescence, also known as immune aging, refers to the degeneration, compensation, and reconstruction of the immune system with aging. Immune aging is an important factor in the increased susceptibility of the elderly to infectious diseases, malignant tumors, and a variety of chronic diseases and has long been a hotspot in geriatrics and immunology research. In this paper, the characteristics and progression of immune aging are briefly reviewed for clinicians' reference.

Capillary networks and follicular marginal zones in human spleens. Three-dimensional models based on immunostained serial sections

We have reconstructed small parts of capillary networks in the human splenic white pulp using serial sections immunostained for CD34 alone or for CD34 and CD271. The three-dimensional (3D) models show three types of interconnected networks: a network with very few long capillaries inside the white pulp originating from central arteries, a denser network surrounding follicles plus periarterial T-cell regions and a network in the red pulp. Capillaries of the perifollicular network and the red pulp network have open ends. Perifollicular capillaries form an arrangement similar to a basketball net located in the outer marginal zone. The marginal zone is defined by MAdCAM-1+ marginal reticular stromal cells. Perifollicular capillaries are connected to red pulp capillaries surrounded by CD271+ stromal capillary sheath cells. The scarcity of capillaries inside the splenic white pulp is astonishing, as non-polarised germinal centres with proliferating B-cells occur in adult human spleens. We suggest that specialized stromal marginal reticular cells form a barrier inside the splenic marginal zone, which together with the scarcity of capillaries guarantees the maintenance of gradients necessary for positioning of migratory B- and T-lymphocytes in the human splenic white pulp.

How do PrPSc Prions Spread between Host Species, and within Hosts?

Prion diseases are sub-acute neurodegenerative diseases that affect humans and some domestic and free-ranging animals. Infectious prion agents are considered to comprise solely of abnormally folded isoforms of the cellular prion protein known as PrP^Sc. Pathology during prion disease is restricted to the central nervous system where it causes extensive neurodegeneration and ultimately leads to the death of the host. The first half of this review provides a thorough account of our understanding of the various ways in which PrP^Sc prions may spread between individuals within a population, both horizontally and vertically. Many natural prion diseases are acquired peripherally, such as by oral exposure, lesions to skin or mucous membranes, and possibly also via the nasal cavity. Following peripheral exposure, some prions accumulate to high levels within the secondary lymphoid organs as they make their journey from the site of infection to the brain, a process termed neuroinvasion. The replication of PrP^Sc prions within secondary lymphoid organs is important for their efficient spread to the brain. The second half of this review describes the key tissues, cells and molecules which are involved in the propagation of PrP^Sc prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. This section also considers how additional factors such as inflammation and aging might influence prion disease susceptibility.

Immunology of Prion Protein and Prions

Many natural prion diseases are acquired peripherally, such as following the oral consumption of contaminated food or pasture. After peripheral exposure many prion isolates initially accumulate to high levels within the host's secondary lymphoid tissues. The replication of prions within these tissues is essential for their efficient spread to the brain where they ultimately cause neurodegeneration. This chapter describes our current understanding of the critical tissues, cells, and molecules which the prions exploit to mediate their efficient propagation from the site of exposure (such as the intestine) to the brain. Interactions between the immune system and prions are not only restricted to the secondary lymphoid tissues. Therefore, an account of how the activation status of the microglial in the brain can also influence progression of prion disease pathogenesis is provided. Prion disease susceptibility may also be influenced by additional factors such as chronic inflammation, coinfection with other pathogens, and aging. Finally, the potential for immunotherapy to provide a means of safe and effective prophylactic or therapeutic intervention in these currently untreatable diseases is considered.

Influence of ageing on the microarchitecture of the spleen and lymph nodes

The elderly have a decreased response to vaccination and an increased susceptibility to infectious diseases. The spleen and lymph nodes are important secondary lymphoid organs where immune cells can rapidly respond to pathogenic material in the blood and lymph in order to mount long-term adaptive immune responses to those pathogens. In aged mice and humans structural changes occur to both the spleen and lymph nodes. These structural changes affect the functioning of the immune cells within, which may ultimate result in less effective or decreased immune responses. This review describes our current understanding of the structural changes that occur to the spleen and lymph nodes of elderly mice. However, where data are available, we also discuss whether similar changes occur in tissues from elderly humans. A particular focus is made on how these structural changes are considered to impact on the functioning of the immune cells within. The world’s population is currently living longer than ever before. The increased incidence and severity of infectious diseases in the elderly has the potential to have a significant impact on the health care system if solutions are not identified. A thorough understanding of the molecular causes of these ageing-related structural changes to the spleen and lymph nodes may help to identify novel treatments that could repair them, and in doing so, improve immune responses and vaccine efficacy in the elderly.