Signal inhibition by the dual-specific phosphatase 4 impairs T cell-dependent B-cell responses with age

Immune senescence: A key player in cancer biology

With the rapid development of immunological techniques in recent years, our understanding of immune senescence has gradually deepened, but the role of immune senescence in cancer biology remains incompletely elucidated. Understanding these mechanisms and interactions is crucial for the development of tumor biology. This review examines five key areas: the classification and main features of immune senescence, factors influencing immune cell senescence in cancer, the reciprocal causal cycle between immune senescence and malignancy, and the potential of immune senescence as a target for cancer immunotherapy.

Enhancing vaccine effectiveness in the elderly to counter antibiotic resistance: The potential of adjuvants via pattern recognition receptors

Vaccines are an effective way to prevent the emergence and spread of antibiotic resistance by preventing diseases and establishing herd immunity. However, the reduced effectiveness of vaccines in the elderly due to immunosenescence is one of the significant contributors to the increasing antibiotic resistance. To counteract this decline and enhance vaccine effectiveness in the elderly, adjuvants play a pivotal role. Adjuvants are designed to augment the effectiveness of vaccines by activating the innate immune system, particularly through pattern recognition receptors on antigen-presenting cells. To improve vaccine effectiveness in the elderly using adjuvants, it is imperative to select the appropriate adjuvants based on an understanding of immunosenescence and the mechanisms of adjuvant functions. This review demonstrates the phenomenon of immunosenescence and explores various types of adjuvants, including their mechanisms and their potential in improving vaccine effectiveness for the elderly, thereby contributing to developing more effective vaccines for this vulnerable demographic.

The aged microenvironment impairs BCL6 and CD40L induction in CD4+ T follicular helper cell differentiation

Weakened germinal center responses by the aged immune system result in diminished immunity against pathogens and reduced efficacy of vaccines. Prolonged contacts between activated B cells and CD4+ T cells are crucial to germinal center formation and T follicular helper cell (Tfh) differentiation, but it is unclear how aging impacts the quality of this interaction. Peptide immunization confirmed that aged mice have decreased expansion of antigen-specific germinal center B cells and reduced antibody titers. Furthermore, aging was associated with accumulated Tfh cells, even in naïve mice. Despite increased numbers, aged Tfh had reduced expression of master transcription factor BCL6 and increased expression of the ectonucleotidase CD39. In vitro activation revealed that proliferative capacity was maintained in aged CD4+ T cells, but not the costimulatory molecule CD40L. When activated in vitro by aged antigen-presenting cells, young CD4+ naïve T cells generated reduced numbers of activated cells with upregulated CD40L. To determine the contribution of cell-extrinsic influences on antigen-specific Tfh induction, young, antigen-specific B and CD4+ T cells were adoptively transferred into aged hosts prior to peptide immunization. Transferred cells had reduced expansion and differentiation into germinal center B cell and Tfh and reduced antigen-specific antibody titers when compared to young hosts. Young CD4+ T cells transferred aged hosts differentiated into Tfh cells with reduced PD-1 and BCL6 expression, and increased CD39 expression, though they maintained their mitochondrial capacity. These results highlight the role of the lymphoid microenvironment in modulating CD4+ T cell differentiation, which contributes to impaired establishment and maintenance of germinal centers.

Serum cytokines profile changes in amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder, characterized by progressive limb weakness, dysphagia, dysphonia, and respiratory failure due to degeneration of upper and lower motor neurons. The pathogenesis of ALS is still unclear. Neuroinflammation has been found to be involved in its development and progression. Cytokines play a significant role in the inflammatory process. This study aims to identify novel biomarkers that may assist in the diagnosis of ALS.

Methods

In Fujian Medical University Union Hospital and Huashan Hospital Fudan University, two independent centers, we prospectively recruited 50 ALS patients, and 41 healthy controls (25 ALS and 26 controls in the first stage and 25 ALS and 15 controls in the validation stage). An 18-plex Luminex kit was used to screen the serum cytokines levels in the first stage. Commercial ELISA kits were used to measure the levels of target cytokines in the validation stage. A single-molecule array HD-X platform was applied to assess the levels of serum neurofilament light chain (NFL).

Results

The levels of serum IL-18 were markedly increased in patients with ALS in the first stage (p = 0.016). The ROC curve showed an area under the curve at 0.695 (95% CI 0.50-0.84) in distinguishing ALS patients from healthy controls. The IL-21 was decreased in elderly patients when grouped by 55 years old (the medium age). Furthermore, the IL-5, IL-13, IL-18, and NFL had a positive relationship with the disease progression of ALS. We also found that serum IL-18 was markedly increased in ALS patients in the validation stage (167.67 [148.25-175.59] vs 116.44 [102.43-122.19]pg/ml, p < 0.0015).

Conclusion

In this study, we identified systemic cytokine profile changes in the serum of ALS patients, especially the elevated IL-18, as well as the decreased IL-21 in elder patients. These changes in serum cytokine profiles may shed new light on an in-depth understanding of the immunopathogenic characteristics of ALS.

Elevated CD4+ T Cell Senescence Associates with Impaired Immune Responsiveness in Severe COVID-19

Aging is a critical risk factor for unfavorable clinical outcomes among COVID-19 patients and may impact vaccine efficacy. However, whether the senescence of T cells is associated with severe COVID-19 outcome in elderly individuals is unclear. Using flow cytometry, we analyzed the frequency of senescent T cells (Tsens) in peripheral blood from 100 hospitalized elderly COVID-19 patients and compared differences between those with mild/moderate and severe/critical illness. We also assessed correlations between the percentage of Tsens and the quantity and quality of spike-specific antibodies by ELISA, neutralizing antibody test kit, and ELISPOT assay respectively, the cytokine production profile of COVID-19 reactive T cells, and plasma soluble factors by cytometric bead array (CBA). Our study found a significantly elevated level of CD4+ Tsens in patients with severe/critical disease compared to those with mild/moderate illness. Patients with a higher level of CD4+ Tsens (>19.78%) showed a decreased survival rate compared to those with a lower level (≤19.78%). This is more pronounced among patients with breakthrough infections. The percentage of CD4+ Tsens was negatively correlated with spike-specific antibody titers, neutralization ability, and COVID-19 reactive IL-2+CD4+ T cells. In addition, spike-specific antibody levels were positively correlated with IL-2 producing T cells and plasma IL-2 amount. Mechanistically, with defective CD40L, T cells from patients with CD4+ Tsens >19.78% were unable to support B cell proliferation and differentiation. Our data demonstrate that the percentage of CD4+ Tsens in peripheral blood may serve as a reliable biomarker for the prognosis of severe COVID-19 patients, especially in breakthrough infections. Therefore, restoring the immune response of CD4+ Tsens may be key to preventing severe illness and improving vaccine efficacy in older adults.

Sustained silencing peanut allergy by xanthopurpurin is associated with suppression of peripheral and bone marrow IgE-producing B cell

Introduction

Peanut allergy is an immunoglobulin E (IgE) mediated food allergy. Rubia cordifolia L. (R. cordifolia), a Chinese herbal medicine, protects against peanut-induced anaphylaxis by suppressing IgE production in vivo. This study aims to identify IgE-inhibitory compounds from the water extract of R. cordifolia and investigate the underlying mechanisms using in vitro and in vivo models.

Methods

Compounds were isolated from R. cordifolia water extract and their bioactivity on IgE production was assessed using a human myeloma U266 cell line. The purified active compound, xanthopurpurin (XPP), was identified by LC-MS and NMR. Peanut-allergic C3H/HeJ mice were orally administered with or without XPP at 200µg or 400µg per mouse per day for 4 weeks. Serum peanut-specific IgE levels, symptom scores, body temperatures, and plasma histamine levels were measured at challenge. Cytokines in splenocyte cultures were determined by ELISA, and IgE + B cells were analyzed by flow cytometry. Acute and sub-chronic toxicity were evaluated. IL-4 promoter DNA methylation, RNA-Seq, and qPCR analysis were performed to determine the regulatory mechanisms of XPP.

Results

XPP significantly and dose-dependently suppressed the IgE production in U266 cells. XPP significantly reduced peanut-specific IgE (>80%, p <0.01), and plasma histamine levels and protected the mice against peanut-allergic reactions in both early and late treatment experiments (p < 0.05, n=9). XPP showed a strong protective effect even 5 weeks after discontinuing the treatment. XPP significantly reduced the IL-4 level without affecting IgG or IgA and IFN-γ production. Flow cytometry data showed that XPP reduced peripheral and bone marrow IgE + B cells compared to the untreated group. XPP increased IL-4 promoter methylation. RNA-Seq and RT-PCR experiments revealed that XPP regulated the gene expression of CCND1, DUSP4, SDC1, ETS1, PTPRC, and IL6R, which are related to plasma cell IgE production. All safety testing results were in the normal range.

Conclusions

XPP successfully protected peanut-allergic mice against peanut anaphylaxis by suppressing IgE production. XPP suppresses murine IgE-producing B cell numbers and inhibits IgE production and associated genes in human plasma cells. XPP may be a potential therapy for IgE-mediated food allergy.

A silver bullet for ageing medicine?: clinical relevance of T-cell checkpoint receptors in normal human ageing

Immunosenescence describes dysregulation of the immune system with ageing manifested in both the innate and adaptive immunity, including changes in T-cell checkpoint signaling. Through complex and nuanced process, T-cells lose excitatory signaling pathways and upregulate their inhibitory signaling, leading to ineffective immune responses that contribute to the formation of the ageing phenotype. Here we expand on the expression, function, and clinical potential of targeting the T-cell checkpoint signaling in age and highlight interventions offering the most benefits to older adults' health. Notably, modifications in vaccination such as with mTOR inhibitors show immediate clinical relevance and good tolerability. Other proposed treatments, including therapies with monoclonal antibodies fail to show clinical efficacy or tolerability needed for implementation at present. Although T-cell co-signaling fits a valuable niche for translational scientists to manage immunosenescence, future study would benefit from the inclusion of older adults with multiple long-term conditions and polypharmacy, ensuring better applicability to actual patients seen in clinical settings.

Accumulation of immune-suppressive CD4 + T cells in aging - tempering inflammaging at the expense of immunity

The 'immune risk profile' has been shown to predict mortality in the elderly, highlighting the need to better understand age-related immune dysfunction. While aging leads to many defects affecting all arms of the immune system, this review is focused on the accrual of immuno-suppressive CD4 + T cell populations, including FoxP3 + regulatory T cells, and subsets of IL-10-producing T follicular helper cells. New data suggest that such accumulations constitute feedback mechanisms to temper the ongoing progressive low-grade inflammation that develops with age, the so-called "inflammaging", and by doing so, how they have the potential to promote healthier aging. However, they also impair effector immune responses, notably to infections, or vaccines. These studies also reinforce the idea that the aged immune system should not be considered as a poorly functional version of the young one, but more as a dynamic system in which CD4 + T cells, and other immune/non-immune subsets, differentiate, interact with their milieu and function differently than in young hosts. A better understanding of these unique interactions is thus needed to improve effector immune responses in the elderly, while keeping inflammaging under control.

ATM-AMPKα mediated LAG-3 expression suppresses T cell function in prostate cancer

Immunotherapy for prostate cancer (PCa) faces serious challenges. Therefore, the co-inhibitory receptors that regulate T cell function of PCa must be elucidated. Here we identified that the inhibitory receptor LAG3 was significantly induced in T cells from PCa patients. Gene array analysis revealed that insufficient ataxia telangiectasia mutated (ATM) gene expression in PCa T cells was responsible for the elevated LAG3 expression. Mechanistically, insufficient ATM expression impaired its ability to activate AMPKα signaling and CD4+ T cell functions, which further enhances the binding of the transcription factors XBP1 and EGR2 to LAG3 promoter. Reconstitution of ATM and inhibition of XBP1 or EGR2 in PCa T cells suppressed LAG3 expression and restored the effector function of CD4+ T cells from PCa. Our study revealed the mechanism of LAG3 upregulation in CD4+ T lymphocytes of PCa patients and may provide insights for the development of immunotherapeutic strategies for PCa treatment.

Age-dependent changes in T follicular helper cells shape the humoral immune response to vaccination

Vaccination is an excellent strategy to limit the morbidity and mortality associated with infectious disease. Vaccination creates protective, long-lived antibody-mediated immunity by inducing the germinal centre response, an intricate immune reaction that produces memory B cells and long-lived antibody-secreting plasma cells that provide protection against (re)infection. The magnitude and quality of the germinal centre response declines with age, contributing to poor vaccine-induced immunity in older individuals. T follicular helper cells are essential for the formation and function of the germinal centre response. This review will discuss how age-dependent changes in T follicular helper cells influence the germinal centre response, and the evidence that age-dependent changes need not be a barrier to successful vaccination in the later years of life.

Age-dependent immune responses in COVID-19-mediated liver injury: focus on cytokines

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is potentially pathogenic and causes severe symptoms; in addition to respiratory syndromes, patients might experience other severe conditions such as digestive complications and liver complications injury. The abnormality in the liver is manifested by hepatobiliary dysfunction and enzymatic elevation, which is associated with morbidity and mortality. The direct cytopathic effect, immune dysfunction, cytokine storm, and adverse effects of therapeutic regimens have a crucial role in the severity of liver injury. According to aging and immune system alterations, cytokine patterns may also change in the elderly. Moreover, hyperproduction of cytokines in the inflammatory response to SARS-CoV-2 can lead to multi-organ dysfunction. The mortality rate in elderly patients, particularly those with other comorbidities, is also higher than in adults. Although the pathogenic effect of SARS-CoV-2 on the liver has been widely studied, the impact of age and immune-mediated responses at different ages remain unclear. This review discusses the association between immune system responses in coronavirus disease 2019 (COVID-19) patients of different ages and liver injury, focusing on cytokine alterations.

Transcriptomic profiles of multiple organ dysfunction syndrome phenotypes in pediatric critical influenza

Background

Influenza virus is responsible for a large global burden of disease, especially in children. Multiple Organ Dysfunction Syndrome (MODS) is a life-threatening and fatal complication of severe influenza infection.

Methods

We measured RNA expression of 469 biologically plausible candidate genes in children admitted to North American pediatric intensive care units with severe influenza virus infection with and without MODS. Whole blood samples from 191 influenza-infected children (median age 6.4 years, IQR: 2.2, 11) were collected a median of 27 hours following admission; for 45 children a second blood sample was collected approximately seven days later. Extracted RNA was hybridized to NanoString mRNA probes, counts normalized, and analyzed using linear models controlling for age and bacterial co-infections (FDR q<0.05).

Results

Comparing pediatric samples collected near admission, children with Prolonged MODS for ≥7 days (n=38; 9 deaths) had significant upregulation of nine mRNA transcripts associated with neutrophil degranulation (RETN, TCN1, OLFM4, MMP8, LCN2, BPI, LTF, S100A12, GUSB) compared to those who recovered more rapidly from MODS (n=27). These neutrophil transcripts present in early samples predicted Prolonged MODS or death when compared to patients who recovered, however in paired longitudinal samples, they were not differentially expressed over time. Instead, five genes involved in protein metabolism and/or adaptive immunity signaling pathways (RPL3, MRPL3, HLA-DMB, EEF1G, CD8A) were associated with MODS recovery within a week.

Conclusion

Thus, early increased expression of neutrophil degranulation genes indicated worse clinical outcomes in children with influenza infection, consistent with reports in adult cohorts with influenza, sepsis, and acute respiratory distress syndrome.

Mitochondrial Dysfunction in CD4+ T Effector Memory RA+ Cells

Human ageing is accompanied by poor responses to infection and decreased vaccine efficacy. While the causes of this can be attributed to defects in the immune system that increase with age, it is unknown whether mitochondrial dysfunction may also contribute to these phenomena. This study aims to assess mitochondrial dysfunction in CD4+ terminal effector memory T cells re-expressing CD45RA (TEMRA) cells and other CD4+ memory T cell subtypes, which are increased in number in the elderly population, with respect to how their metabolic responses to stimulation are altered compared to CD4+ naïve T cells. In this study, we show that CD4+ TEMRA cells exhibit altered mitochondrial dynamics compared to CD4+ naïve cells and CD4+ central and effector memory cells, with a 25% reduction in OPA1 expression. CD4+ TEMRA and memory cells show increased upregulation of Glucose transporter 1 following stimulation and higher levels of mitochondrial mass compared to CD4+ naïve T cells. Additionally, TEMRA cells exhibit a decrease in mitochondrial membrane potential compared to other CD4+ memory cell subsets by up to 50%. By comparing young to aged individuals, more significant mitochondria mass and lower membrane potential were observed in CD4+ TEMRA of young individuals. In conclusion, we suggest that CD4+ TEMRA cells may be impaired with respect to their metabolic response to stimulation, possibly contributing to impaired responses to infection and vaccination.

Elevated CD153 Expression on Aged T Follicular Helper Cells is Vital for B cell Responses

Our recent data showed that an aberrant IL-10-producing T follicular helper population (Tfh10) accumulates dramatically with age and is associated with age-related declines in vaccine responsiveness. Through single cell gene expression and chromatin accessibility analysis of IL-10+ and IL-10- memory CD4+ T cells from young and aged mice, we identified increased expression of CD153 on aged Tfh and Tfh10 cells. Mechanistically, we linked inflammaging (increased IL-6 levels) to elevated CD153 expression of Tfh cells through c-Maf. Surprisingly, blockade of CD153 in aged mice significantly reduced their vaccine-driven antibody response, which was associated with decreased expression of ICOS on antigen-specific Tfh cells. Combined, these data show that an IL-6/c-Maf/CD153 circuit is critical for maintaining ICOS expression. Thus, although overall Tfh-mediated B cell responses are reduced in the context of vaccines and aging, our data suggest that elevated expression of CD153 on Tfh cells potentiates the remaining Tfh function in aged mice.

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

AgeAnno: a knowledgebase of single-cell annotation of aging in human

Aging is a complex process that accompanied by molecular and cellular alterations. The identification of tissue-/cell type-specific biomarkers of aging and elucidation of the detailed biological mechanisms of aging-related genes at the single-cell level can help to understand the heterogeneous aging process and design targeted anti-aging therapeutics. Here, we built AgeAnno (https://relab.xidian.edu.cn/AgeAnno/#/), a knowledgebase of single cell annotation of aging in human, aiming to provide comprehensive characterizations for aging-related genes across diverse tissue-cell types in human by using single-cell RNA and ATAC sequencing data (scRNA and scATAC). The current version of AgeAnno houses 1 678 610 cells from 28 healthy tissue samples with ages ranging from 0 to 110 years. We collected 5580 aging-related genes from previous resources and performed dynamic functional annotations of the cellular context. For the scRNA data, we performed analyses include differential gene expression, gene variation coefficient, cell communication network, transcription factor (TF) regulatory network, and immune cell proportionc. AgeAnno also provides differential chromatin accessibility analysis, motif/TF enrichment and footprint analysis, and co-accessibility peak analysis for scATAC data. AgeAnno will be a unique resource to systematically characterize aging-related genes across diverse tissue-cell types in human, and it could facilitate antiaging and aging-related disease research.

NUTMEG: A randomized phase II study of nivolumab and temozolomide versus temozolomide alone in newly diagnosed older patients with glioblastoma

Background

There is an immunologic rationale to evaluate immunotherapy in the older glioblastoma population, who have been underrepresented in prior trials. The NUTMEG study evaluated the combination of nivolumab and temozolomide in patients with glioblastoma aged 65 years and older.

Methods

NUTMEG was a multicenter 2:1 randomized phase II trial for patients with newly diagnosed glioblastoma aged 65 years and older. The experimental arm consisted of hypofractionated chemoradiation with temozolomide, then adjuvant nivolumab and temozolomide. The standard arm consisted of hypofractionated chemoradiation with temozolomide, then adjuvant temozolomide. The primary objective was to improve overall survival (OS) in the experimental arm.

Results

A total of 103 participants were randomized, with 69 in the experimental arm and 34 in the standard arm. The median (range) age was 73 (65-88) years. After 37 months of follow-up, the median OS was 11.6 months (95% CI, 9.7-13.4) in the experimental arm and 11.8 months (95% CI, 8.3-14.8) in the standard arm. For the experimental arm relative to the standard arm, the OS hazard ratio was 0.85 (95% CI, 0.54-1.33). In the experimental arm, there were three grade 3 immune-related adverse events which resolved, with no unexpected serious adverse events.

Conclusions

Due to insufficient evidence of benefit with nivolumab, the decision was made not to transition to a phase III trial. No new safety signals were identified with nivolumab. This complements the existing series of immunotherapy trials. Research is needed to identify biomarkers and new strategies including combinations.

Immunosenescence, Inflammaging, and Lung Senescence in Asthma in the Elderly

Prevalence of asthma in older adults is growing along with increasing global life expectancy. Due to poor clinical consequences such as high mortality, advancement in understanding the pathophysiology of asthma in older patients has been sought to provide prompt treatment for them. Age-related alterations of functions in the immune system and lung parenchyma occur throughout life. Alterations with advancing age are promoted by various stimuli, including pathobionts, fungi, viruses, pollutants, and damage-associated molecular patterns derived from impaired cells, abandoned cell debris, and senescent cells. Age-related changes in the innate and adaptive immune response, termed immunosenescence, includes impairment of phagocytosis and antigen presentation, enhancement of proinflammatory mediator generation, and production of senescence-associated secretory phenotype. Immnunosenescence could promote inflammaging (chronic low-grade inflammation) and contribute to late-onset adult asthma and asthma in the elderly, along with age-related pulmonary disease, such as chronic obstructive pulmonary disease and pulmonary fibrosis, due to lung parenchyma senescence. Aged patients with asthma exhibit local and systemic type 2 and non-type 2 inflammation, associated with clinical manifestations. Here, we discuss immunosenescence’s contribution to the immune response and the combination of type 2 inflammation and inflammaging in asthma in the elderly and present an overview of age-related features in the immune system and lung structure.

How Can We Improve the Vaccination Response in Older People? Part II: Targeting Immunosenescence of Adaptive Immunity Cells

The number of people that are 65 years old or older has been increasing due to the improvement in medicine and public health. However, this trend is not accompanied by an increase in quality of life, and this population is vulnerable to most illnesses, especially to infectious diseases. Vaccination is the best strategy to prevent this fact, but older people present a less efficient response, as their immune system is weaker due mainly to a phenomenon known as immunosenescence. The adaptive immune system is constituted by two types of lymphocytes, T and B cells, and the function and fitness of these cell populations are affected during ageing. Here, we review the impact of ageing on T and B cells and discuss the approaches that have been described or proposed to modulate and reverse the decline of the ageing adaptive immune system.

Upregulation of microRNA-96-5p is associated with adolescent idiopathic scoliosis and low bone mass phenotype

Bone densitometry revealed low bone mass in patients with adolescent idiopathic scoliosis (AIS) and its prognostic potential to predict curve progression. Recent studies showed differential circulating miRNAs in AIS but their diagnostic potential and links to low bone mass have not been well-documented. The present study aimed to compare miRNA profiles in bone tissues collected from AIS and non-scoliotic subjects, and to explore if the selected miRNA candidates could be useful diagnostic biomarkers for AIS. Microarray analysis identified miR-96-5p being the most upregulated among the candidates. miR-96-5p level was measured in plasma samples from 100 AIS and 52 healthy girls. Our results showed significantly higher plasma levels of miR-96-5p in AIS girls with an area under the curve (AUC) of 0.671 for diagnostic accuracy. A model that was composed of plasma miR-96-5p and patient-specific parameters (age, body weight and years since menarche) gave rise to an improved AUC of 0.752. Ingenuity Pathway Analysis (IPA) indicated functional links between bone metabolic pathways and miR-96-5p. In conclusion, differentially expressed miRNAs in AIS bone and plasma samples represented a new source of disease biomarkers and players in AIS etiopathogenesis, which required further validation study involving AIS patients of both genders with long-term follow-up.

Hallmarks of the aging T-cell system

The adaptive immune system has the enormous challenge to protect the host through the generation and differentiation of pathogen-specific short-lived effector T cells while in parallel developing long-lived memory cells to control future encounters with the same pathogen. A complex regulatory network is needed to preserve a population of naïve cells over lifetime that exhibit sufficient diversity of antigen receptors to respond to new antigens, while also sustaining immune memory. In parallel, cells need to maintain their proliferative potential and the plasticity to differentiate into different functional lineages. Initial signs of waning immune competence emerge after 50 years of age, with increasing clinical relevance in the 7th-10th decade of life. Morbidity and mortality from infections increase, as drastically exemplified by the current COVID-19 pandemic. Many vaccines, such as for the influenza virus, are poorly effective to generate protective immunity in older individuals. Age-associated changes occur at the level of the T-cell population as well as the functionality of its cellular constituents. The system highly relies on the self-renewal of naïve and memory T cells, which is robust but eventually fails. Genetic and epigenetic modifications contribute to functional differences in responsiveness and differentiation potential. To some extent, these changes arise from defective maintenance; to some, they represent successful, but not universally beneficial adaptations to the aging host. Interventions that can compensate for the age-related defects and improve immune responses in older adults are increasingly within reach.

Young but not older adults exhibit an expansion of CD45RA+CCR7+CD95+ T follicular helper cells in response to tetanus vaccine

A subset of CD4⁺ T cells, known as T follicular helper (Tfh), provides co-stimulating signals required to establish long-term humoral immunity. Recent studies have shown a reduced frequency and functionality of this population in older adults in comparison to young adults, in response to vaccination. To evaluate whether memory generation of circulating Tfh (cTfh) cells contributes to this phenomenon, the memory subpopulations of cTfh, and their activation degree, were evaluated both ex-vivo and in-vitro, in response to the model antigen tetanus toxoid (TT) after the first dose of tetanus vaccine. Here, we report a lower frequency of cTfh after vaccination in older adults compared to young adults. Moreover, whereas cTfh from older adults preferably expanded with an effector memory phenotype, young adults experienced a temporal increase of CCR7⁺CD45RA⁺ cTfh cells, which also displayed higher levels of CD95, CD40L, CXCR3, and Bcl-6 upon antigen re-encounter. This phenotype was confirmed using automatized algorithm. In conclusion, our results suggest that an age-related loss of heterogeneity and an expansion of more differentiated memory cells within the cTfh compartment could affect the responsiveness of older individuals to vaccines, making this phenotype a characteristic feature of immunosenescence.

The MAPK dual specific phosphatase (DUSP) proteins: A versatile wrestler in T cell functionality

The functional state of T cells is diverse and under dynamic control for adapting to the changes of microenvironment. Reversible protein phosphorylation represents an important post-translational modification that not only involves in the immediate early response of T cells, but also affects their functionality in the long run. Perturbation of global phosphorylation profile and/or phosphorylation of specific signaling nodes result in aberrant T cell activity. Dual specific phosphatases (DUSPs), which target MAPKs and beyond, have increasingly been emerged as a versatile regulator in T cell biology. Herein in this mini review, we sought to summarize and discuss the impact of DUSP proteins on the regulation of effector T cell activity, T cell polarization, regulatory T cell development and T cell senescence/exhaustion. Given the distinctive engagement of each DUSP member under various disease settings such as chronic infection, autoimmune disorders, cancer and age-related diseases, DUSP proteins likely hold the promise to become a druggable target other than the existing therapeutics that are predominantly by manipulating protein kinase activity.

Ageing of T-dependent B cell responses

The human immune system is in continuous interaction with environmental factors (pathogens, exercise, stress, pollutants, diet, vaccines, and therapeutics) that condition its efficiency by promoting or moderating multiple immune mechanisms. While the deleterious impact of external factors can be avoided or limited, the immune system itself grows weaker with age. Immune cells persist in the elderly, and the observed decline of cellular immunity is related to cellular senescence. Immunosenescence, which affects both T and B cells, erodes lymphocyte-dependent responses to vaccines and pathogens. Germinal centers (GCs), the organized lymphoid structures where B cells engage in affinity maturation, are regulated by follicular helper (Tfh) and follicular regulatory (Tfr) T cells, the major T cell components of GCs. This review discusses how age-related changes affect Tfh and Tfr cells as key components of B cell immunity, and how they ultimately shape the response of the ageing immune system to vaccines and infectious challenges.

Targeting Inflammation and Immunosenescence to Improve Vaccine Responses in the Elderly

One of the most appreciated consequences of immunosenescence is an impaired response to vaccines with advanced age. While most studies report impaired antibody responses in older adults as a correlate of vaccine efficacy, it is now widely appreciated that this may fail to identify important changes occurring in the immune system with age that may affect vaccine efficacy. The impact of immunosenescence on vaccination goes beyond the defects on antibody responses as T cell-mediated responses are reshaped during aging and certainly affect vaccination. Likewise, age-related changes in the innate immune system may have important consequences on antigen presentation and priming of adaptive immune responses. Importantly, a low-level chronic inflammatory status known as inflammaging has been shown to inhibit immune responses to vaccination and pharmacological strategies aiming at blocking baseline inflammation can be potentially used to boost vaccine responses. Yet current strategies aiming at improving immunogenicity in the elderly have mainly focused on the use of adjuvants to promote local inflammation. More research is needed to understand the role of inflammation in vaccine responses and to reconcile these seemingly paradoxical observations. Alternative approaches to improve vaccine responses in the elderly include the use of higher vaccine doses or alternative routes of vaccination showing only limited benefits. This review will explore novel targets and potential new strategies for enhancing vaccine responses in older adults, including the use of anti-inflammatory drugs and immunomodulators.

Immunosenescence is both functional/adaptive and dysfunctional/maladaptive

Alterations in the immune system with aging are considered to underlie many age-related diseases. However, many elderly individuals remain healthy until even a very advanced age. There is also an increase in numbers of centenarians and their apparent fitness. We should therefore change our unilaterally detrimental consideration of age-related immune changes. Recent data taking into consideration the immunobiography concept may allow for meaningful distinctions among various aging trajectories. This implies that the aging immune system has a homeodynamic characteristic balanced between adaptive and maladaptive aspects. The survival and health of an individual depends from the equilibrium of this balance. In this article, we highlight which parts of the aging of the immune system may be considered adaptive in contrast to those that may be maladaptive.

The emerging role of T follicular helper (TFH) cells in aging: Influence on the immune frailty

The world population is undergoing a rapid expansion of older adults. Aging is associated with numerous changes that affect all organs and systems, including every component of the immune system. Immunosenescence is a multifaceted process characterized by poor response to vaccine and higher incidence of bacterial and viral infections, cancer, cardiovascular and autoimmune diseases. Immunosenescence has been associated with chronic low-grade inflammation referred to as inflammaging, whose underlying mechanisms remain incompletely elucidated, including age-related changes affecting components of the innate and adaptive immune system. T follicular helper (T_FH) cells, present in lymphoid organs and in peripheral blood, are specialized in providing cognate help to B cells and are required for the production of immunoglobulins. Several subsets of T_FH cells have been identified in humans and mice and modifications in T_FH cell phenotype and function progressively occur with age. Dysfunctional T_FH cells play a role in cancer, autoimmune and cardiovascular diseases, all conditions particularly prevalent in elderly subjects. A specialized population of Treg cells, named T follicular regulatory (T_FR) cells, present in lymphoid organs and in peripheral blood, exerts opposing roles to T_FH cells in regulating immunity. Indeed, changes in T_FH/T_FR cell ratio constitute a relevant feature of aging. Herein we discuss the cellular and molecular changes in both T_FH cells and T_FR cells that occur in aging and recent findings suggesting that T_FH cells and/or their subsets could be involved in atherosclerosis, cancer, and autoimmunity.

Ecto-NTPDase CD39 is a negative checkpoint that inhibits follicular helper cell generation

Vaccination is a mainstay in preventive medicine, reducing morbidity and mortality from infection, largely by generating pathogen-specific neutralizing antibodies. However, standard immunization strategies are insufficient with increasing age due to immunological impediments, including defects in T follicular helper (Tfh) cells. Here, we found that Tfh generation is inversely linked to the expression of the ecto-NTPDase CD39 that modifies purinergic signaling. The lineage-determining transcription factor BCL6 inhibited CD39 expression, while increased Tfh frequencies were found in individuals with a germline polymorphism preventing transcription of ENTPD1, encoding CD39. In in vitro human and in vivo mouse studies, Tfh generation and germinal center responses were enhanced by reducing CD39 expression through the inhibition of the cAMP/PKA/p-CREB pathway, or by blocking adenosine signaling downstream of CD39 using the selective adenosine A2a receptor antagonist istradefylline. Thus, purinergic signaling in differentiating T cells can be targeted to improve vaccine responses, in particular in older individuals who have increased CD39 expression.

Human Regulatory T Cells From Umbilical Cord Blood Display Increased Repertoire Diversity and Lineage Stability Relative to Adult Peripheral Blood

The human T lymphocyte compartment is highly dynamic over the course of a lifetime. Of the many changes, perhaps most notable is the transition from a predominantly naïve T cell state at birth to the acquisition of antigen-experienced memory and effector subsets following environmental exposures. These phenotypic changes, including the induction of T cell exhaustion and senescence, have the potential to negatively impact efficacy of adoptive T cell therapies (ACT). When considering ACT with CD4+CD25+CD127-/lo regulatory T cells (Tregs) for the induction of immune tolerance, we previously reported ex vivo expanded umbilical cord blood (CB) Tregs remained more naïve, suppressed responder T cells equivalently, and exhibited a more diverse T cell receptor (TCR) repertoire compared to expanded adult peripheral blood (APB) Tregs. Herein, we hypothesized that upon further characterization, we would observe increased lineage heterogeneity and phenotypic diversity in APB Tregs that might negatively impact lineage stability, engraftment capacity, and the potential for Tregs to home to sites of tissue inflammation following ACT. We compared the phenotypic profiles of human Tregs isolated from CB versus the more traditional source, APB. We conducted analysis of fresh and ex vivo expanded Treg subsets at both the single cell (scRNA-seq and flow cytometry) and bulk (microarray and cytokine profiling) levels. Single cell transcriptional profiles of pre-expansion APB Tregs highlighted a cluster of cells that showed increased expression of genes associated with effector and pro-inflammatory phenotypes (CCL5, GZMK, CXCR3, LYAR, and NKG7) with low expression of Treg markers (FOXP3 and IKZF2). CB Tregs were more diverse in TCR repertoire and homogenous in phenotype, and contained fewer effector-like cells in contrast with APB Tregs. Interestingly, expression of canonical Treg markers, such as FOXP3, TIGIT, and IKZF2, were increased in CB CD4+CD127+ conventional T cells (Tconv) compared to APB Tconv, post-expansion, implying perinatal T cells may adopt a default regulatory program. Collectively, these data identify surface markers (namely CXCR3) that could be depleted to improve purity and stability of APB Tregs, and support the use of expanded CB Tregs as a potentially optimal ACT modality for the treatment of autoimmune and inflammatory diseases.

T cells, aging and senescence

The T cell compartment undergoes characteristic changes with age, which contribute to increased incidence and severity of infections and reduced immunogenicity and efficacy of many vaccines in the older population. Production of naïve T cells is severely impaired due to a decreased output of lymphoid cells from the bone marrow and the involution of the thymus. At the same time, antigen-experienced, highly differentiated T cells accumulate resulting in a diminished T cell receptor repertoire. These cells show some similarities with senescent cells, such as shorter telomers, accumulated DNA damage and metabolic changes. Latent infection with Cytomegalovirus also impacts the T cell compartment and aggravates several of its age-associated changes. Loss of CD28 expression is one hallmark of T cells after repeated antigenic stimulation, but CD28- T cells cannot be considered truly senescent as e.g. they are still able to proliferate upon adequate stimulation. Several additional markers have been suggested in order to define a potential fully senescent T cell population, but no consensus definition has been reached so far. It has been postulated that highly differentiated senescent-like T cells are unable to eliminate other senescent cell types. Removal of senescent non-immune cells has been shown to be beneficial for the organism and a reliable definition of senescent T cells is essential for an extension of this concept to T cells.

Strain specificities in influence of ageing on germinal centre reaction to inactivated influenza virus antigens in mice: Sex-based differences

Considering variability in vaccine responsiveness across human populations, in respect to magnitude and quality, and importance of vaccines in the elderly, the influence of recipient genetic background on the kinetics of age-related changes in the serum IgG antibody responses to seasonal trivalent inactivated split-virus influenza bulk (TIV) was studied in BALB/c and C57BL/6 mice showing quantitative and qualitative differences in this responses in young adult ages. With ageing the total serum IgG response to influenza viruses declined, in a strain-specific manner, so the strain disparity observed in young adult mice (the greater magnitude of IgG response in BALB/c mice) disappeared in aged mice. However, the sexual dimorphisms in this response (more prominent in females of both strains) remained in aged ones. The strain-specific differences in age-related decline in the magnitude of IgG response to TIV correlated with the number of germinal centre (GC) B splenocytes. The age-related decline in GC B cell number was consistent with the decrease in the proliferation of B cells and CD4+ cells in splenocyte cultures upon restimulation with TIV. Additionally, the age-related decrease in the magnitude of IgG response correlated with the increase in follicular T regulatory (fTreg)/follicular T helper (fTh) and fTreg/GC B splenocyte ratios (reflecting decrease in fTh and GC B numbers without changes in fTreg number), and the frequency of CD4+ splenocytes producing IL-21, a key factor in balancing the B cell and fTreg cell activity. With ageing the avidity of virus influenza-specific antibody increased in females of both strains. Moreover, ageing affected IgG2a/IgG1 and IgG2c/IgG1 ratios (reflecting Th1/Th2 balance) in male BALB/c mice and female C57BL/6 mice, respectively. Consequently, differently from young mice exhibiting the similar ratios in male and female mice, in aged female mice of both strains IgG2a(c)/IgG1 ratios were shifted towards a less effective IgG1 response (stimulated by IL-4 cytokines) compared with males. The age-related alterations in IgG subclass profiles in both strains correlated with those in IFN-γ/IL-4 production level ratio in splenocyte cultures restimulated with TIV. These findings stimulate further research to formulate sex-specific strategies to improve efficacy of influenza vaccine in the elderly.

A validated composite model to predict risk of curve progression in adolescent idiopathic scoliosis

BACKGROUND

In adolescent idiopathic scoliosis (AIS), the continuous search for effective prognostication of significant curve progression at the initial clinical consultation to inform decision for timely treatment and to avoid unnecessary overtreatment remains a big challenge as evidence of the multifactorial etiopathogenic nature is increasingly reported. This study aimed to formulate a composite model composed of clinical parameters and circulating markers in the prediction of curve progression.

METHOD

This is a two-phase study consisting of an exploration cohort (120 AIS, mean Cobb angle of 25°± 8.5 at their first clinical visit) and a validation cohort (51 AIS, mean Cobb angle of 23° ± 5.0° at the first visit). Patients with AIS were followed-up for a minimum of six years to formulate a composite model for prediction. At the first visit, clinical parameters were collected from routine clinical practice, and circulating markers were assayed from blood.

FINDING

We constructed the composite predictive model for curve progression to severe Cobb angle > 40° with a high HR of 27.9 (95% CI of 6.55 to 119.16). The area under curve of the composite model is higher than that of individual parameters used in current clinical practice. The model was validated by an independent cohort and achieved a sensitivity of 72.7% and a specificity of 90%.

INTERPRETATION

This is the first study proposing and validating a prognostic composite model consisting of clinical and circulating parameters which could quantitatively evaluate the probability of curve progression to a severe curvature in AIS at the initial consultation. Further validation in clinic will facilitate application of composite model in assisting objective clinical decision.

Metabolic reprogramming in memory CD4 T cell responses of old adults

To determine whether aging affects the ability of T cells to undergo metabolic reprogramming upon activation, we compared CD4 T cell responses after polyclonal in vitro stimulation. Compared to younger adults, CD4 memory T cells from healthy older individuals exhibited a higher upregulation of oxidative phosphorylation with increased production of reactive oxygen species and intracellular and secreted ATP. Increased ATP secretion led to increased purinergic signaling and P2X7-dependent increases in cytoplasmic calcium. The increased mitochondrial activity was not due to a difference in activation-induced mitochondrial biogenesis. Expression of carnitine palmitoyl transferase 1 was higher, conversely that of fatty acid synthase was reduced in older T cells, resulting in increased fatty acid oxidation, while depleting intracellular lipid stores. The aged CD4 memory T cells therefore maintain a more catabolic state in lipid metabolism, while their ability to upregulate glycolysis upon activation is preserved.

Dual-Specificity Phosphatases in Immunity and Infection: An Update

Kinase activation and phosphorylation cascades are key to initiate immune cell activation in response to recognition of antigen and sensing of microbial danger. However, for balanced and controlled immune responses, the intensity and duration of phospho-signaling has to be regulated. The dual-specificity phosphatase (DUSP) gene family has many members that are differentially expressed in resting and activated immune cells. Here, we review the progress made in the field of DUSP gene function in regulation of the immune system during the last decade. Studies in knockout mice have confirmed the essential functions of several DUSP-MAPK phosphatases (DUSP-MKP) in controlling inflammatory and anti-microbial immune responses and support the concept that individual DUSP-MKP shape and determine the outcome of innate immune responses due to context-dependent expression and selective inhibition of different mitogen-activated protein kinases (MAPK). In addition to the canonical DUSP-MKP, several small-size atypical DUSP proteins regulate immune cells and are therefore also reviewed here. Unexpected and complex findings in DUSP knockout mice pose new questions regarding cell type-specific and redundant functions. Another emerging question concerns the interaction of DUSP-MKP with non-MAPK binding partners and substrate proteins. Finally, the pharmacological targeting of DUSPs is desirable to modulate immune and inflammatory responses.

Influence of aging on germinal centre reaction and antibody response to inactivated influenza virus antigens in mice: sex-based differences

The study examined sex-specificities in age-related changes in BALB/c mice IgG antibody responses to immunisation with trivalent inactivated split-virus influenza bulk. Aging diminished the total serum IgG antibody responses to H1N1 and H3N2 and B influenza virus antigens in mice of both sexes, but they remained greater in aged females. This sex difference in aged mice correlated with the greater post-immunisation increase in the frequency of spleen germinal centre (GC) B cells and more favourable T follicular regulatory (Tfr)/GC B cell ratio, as Tfr cells are suggested to control antibody production through suppression of glycolysis. The greater post-immunisation GC B cell response in aged females compared with males correlated with the greater proliferation of B cells and CD4+ cells in splenocyte cultures from aged females restimulated with inactivated split-virus influenza from the bulk. To support the greater post-immunisation increase in the frequency GC B cell in aged females was more favourable Tfr/T follicular helper (Tfh) cell ratio. Additionally, compared with aged males, in age-matched females the greater avidity of serum IgG antibodies was found. However, in aged females IgG2a/IgG1 antibody ratio, reflecting spleen Th1/Th2 cytokine balance, was shifted towards IgG1 when compared with age-matched male mice. This shift was ascribed to a more prominent decline in the titres of functionally important IgG2a antibodies in females with aging. The study suggest that biological sex should be considered as a variable in designing strategies to manipulate with immune outcome of immunisation in aged animals, and possibly, at very long distance, humans.

Polyamine Metabolism and Gene Methylation in Conjunction with One-Carbon Metabolism

Recent investigations have revealed that changes in DNA methylation status play an important role in aging-associated pathologies and lifespan. The methylation of DNA is regulated by DNA methyltransferases (DNMT1, DNMT3a, and DNMT3b) in the presence of S-adenosylmethionine (SAM), which serves as a methyl group donor. Increased availability of SAM enhances DNMT activity, while its metabolites, S-adenosyl-l-homocysteine (SAH) and decarboxylated S-adenosylmethionine (dcSAM), act to inhibit DNMT activity. SAH, which is converted from SAM by adding a methyl group to cytosine residues in DNA, is an intermediate precursor of homocysteine. dcSAM, converted from SAM by the enzymatic activity of adenosylmethionine decarboxylase, provides an aminopropyl group to synthesize the polyamines spermine and spermidine. Increased homocysteine levels are a significant risk factor for the development of a wide range of conditions, including cardiovascular diseases. However, successful homocysteine-lowering treatment by vitamins (B6, B12, and folate) failed to improve these conditions. Long-term increased polyamine intake elevated blood spermine levels and inhibited aging-associated pathologies in mice and humans. Spermine reversed changes (increased dcSAM, decreased DNMT activity, aberrant DNA methylation, and proinflammatory status) induced by the inhibition of ornithine decarboxylase. The relation between polyamine metabolism, one-carbon metabolism, DNA methylation, and the biological mechanism of spermine-induced lifespan extension is discussed.

PD-1 blockade partially recovers dysfunctional virus-specific B cells in chronic hepatitis B infection

Chronic HBV (CHB) infection suppresses virus-specific T cells, but its impact on humoral immunity has been poorly analyzed. Here, we developed a dual-staining method that utilizes hepatitis B virus (HBV) surface antigens (HBsAg) labeled with fluorochromes as "baits" for specific ex vivo detection of HBsAg-specific B cells and analysis of their quantity, function, and phenotype. We studied healthy vaccinated subjects (n = 18) and patients with resolved (n = 21), acute (n = 11), or chronic (n = 96) HBV infection and observed that frequencies of circulating HBsAg-specific B cells were independent of HBV infection status. In contrast, the presence of serum HBsAg affected function and phenotype of HBsAg-specific B cells that were unable to mature in vitro into Ab-secreting cells and displayed an increased expression of markers linked to hyperactivation (CD21lo) and exhaustion (PD-1). Importantly, B cell alterations were not limited to HBsAg-specific B cells, but affected the global B cell population. HBsAg-specific B cell maturation could be partially restored by a method involving the combination of the cytokines IL-2 and IL-21 and CD40L-expressing feeder cells and was further boosted by the addition of anti-PD-1 Abs. In conclusion, HBV infection has a marked impact on global and HBV-specific humoral immunity, yet HBsAg-specific B cells are amenable to a partial rescue by B cell-maturing cytokines and PD-1 blockade.

Dual-specificity MAP kinase phosphatases in health and disease

It is well established that a family of dual-specificity MAP kinase phosphatases (MKPs) play key roles in the regulated dephosphorylation and inactivation of MAP kinase isoforms in mammalian cells and tissues. MKPs provide a mechanism of spatiotemporal feedback control of these key signalling pathways, but can also mediate crosstalk between distinct MAP kinase cascades and facilitate interactions between MAP kinase pathways and other key signalling modules. As our knowledge of the regulation, substrate specificity and catalytic mechanisms of MKPs has matured, more recent work using genetic models has revealed key physiological functions for MKPs and also uncovered potentially important roles in regulating the pathophysiological outcome of signalling with relevance to human diseases. These include cancer, diabetes, inflammatory and neurodegenerative disorders. It is hoped that this understanding will reveal novel therapeutic targets and biomarkers for disease, thus contributing to more effective diagnosis and treatment for these debilitating and often fatal conditions.

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A comprehensive review of the dual-specificity MAP kinase Phosphatases (MKPs)

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Focus is on MKPs in the regulation of MAPK signalling in health and disease.

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Covers roles of MKPs in inflammation, obesity/diabetes, cancer and neurodegeneration

T follicular helper cell development and functionality in immune ageing

By 2050, there will be over 1.6 billion adults aged 65 years and older, making age-related diseases and conditions a growing public health concern. One of the leading causes of death in the ageing population is pathogenic infections (e.g. influenza, Streptococcus pneumoniae). This age-dependent susceptibility to infection has been linked to a reduced ability of the ageing immune system to mount protective responses against infectious pathogens, as well as to vaccines against these pathogens. The primary immune response that promotes protection is the production of antibodies by B cells - a response that is directly mediated by T follicular helper (T_FH) cells within germinal centers (GCs) in secondary lymphoid tissues. In this review, we will summarize the current knowledge on the development and functionality of T_FH cells, the use of circulating T_FH (cT_FH) cells as vaccine biomarkers, and the influence of age on these processes. Moreover, we will discuss the strategies for overcoming T_FH cell dysfunction to improve protective antibody responses in the ageing human population.

Age-related changes in immune function (immune senescence) in caries and periodontal diseases: a systematic review

AIM

To systematically review the evidence regarding immune senescence in the pathogenesis of periodontitis and dental caries.

METHODS

A systematic search of electronic databases utilizing medical subject headings (MeSH terms) supplemented by screening of review articles and other relevant texts was undertaken.

RESULTS

Seventy-three articles were included (43 for periodontitis, 30 for caries). Study results were found to be generally heterogeneous. Regarding periodontitis, human studies suggest evidence for altered neutrophil function and increased production of pro-inflammatory mediators (e.g. interleukin-1β, interleukin-6 and prostaglandin E₂ ) in older compared to younger subjects, and animal experiments suggest increased expression of genes that contribute to a pro-inflammatory state in older compared to younger animals. Regarding dental caries, research relating to changes in immune functioning and the impact of ageing is in its infancy. A small number of studies have reported components of innate and adaptive immunity that affect the composition of saliva and dental biofilms with possible impacts on caries progression.

CONCLUSION

There is evidence that immune functioning related to periodontitis and (less investigated) dental caries alters with increasing age. In both conditions, age-associated mechanistic changes in immune functioning are complex and incompletely understood and it is not clear how these relate to disease susceptibility.

Aging and the immune system: An overview

The world is witnessing a rapid demographic shift towards an older population, a trend with major medical, social, economic and political implications. Aging is a multifaceted process, involving numerous molecular and cellular mechanisms in the context of different organ systems. A crucial component of aging is a set of functional and structural alterations in the immune system that can manifest as a decreased ability to fight infection, diminished response to vaccination, increased incidence of cancer, higher prevalence of autoimmunity and constitutive low-grade inflammation, among others. In addition to cell-intrinsic changes in both innate and adaptive immune cells, alterations in the stromal microenvironment in primary and secondary lymphoid organs play an important role in age-associated immune dysfunction. This article will provide a broad overview of these phenomena and point out some of their clinical and therapeutic implications.

Immune senescence, epigenetics and autoimmunity

Aging of the immune system in humans and animals is characterized by a decline in both adaptive and innate immune responses. Paradoxically, aging is also associated with a state of chronic inflammation ("inflammaging") and an increased likelihood of developing autoimmune diseases. Epigenetic changes in non-dividing and dividing cells, including immune cells, due to environmental factors contribute to the inflammation and autoimmunity that characterize both the state and diseases of aging. Here, we review the epigenetic mechanisms involved in the development of immune senescence and autoimmunity in old age.

Immunosenescence and Inflamm-Aging As Two Sides of the Same Coin: Friends or Foes?

The immune system is the most important protective physiological system of the organism. It has many connections with other systems and is, in fact, often considered as part of the larger neuro-endocrine-immune axis. Most experimental data on immune changes with aging show a decline in many immune parameters when compared to young healthy subjects. The bulk of these changes is termed immunosenescence. Immunosenescence has been considered for some time as detrimental because it often leads to subclinical accumulation of pro-inflammatory factors and inflamm-aging. Together, immunosenescence and inflamm-aging are suggested to stand at the origin of most of the diseases of the elderly, such as infections, cancer, autoimmune disorders, and chronic inflammatory diseases. However, an increasing number of immune-gerontologists have challenged this negative interpretation of immunosenescence with respect to its significance in aging-related alterations of the immune system. If one considers these changes from an evolutionary perspective, they can be viewed preferably as adaptive or remodeling rather than solely detrimental. Whereas it is conceivable that global immune changes may lead to various diseases, it is also obvious that these changes may be needed for extended survival/longevity. Recent cumulative data suggest that, without the existence of the immunosenescence/inflamm-aging duo (representing two sides of the same phenomenon), human longevity would be greatly shortened. This review summarizes recent data on the dynamic reassessment of immune changes with aging. Accordingly, attempts to intervene on the aging immune system by targeting its rejuvenation, it may be more suitable to aim to maintain general homeostasis and function by appropriately improving immune-inflammatory-functions.

Signal transduction changes in CD4+ and CD8+ T cell subpopulations with aging

The innate and adaptive branches of the immune system display changes with aging, a fact referred to as immunosenescence. Furthermore, it has been established that adaptive immunity is more susceptible to age-related changes than innate immunity. The most prominent phenotypic changes that reflect the specific differentiation and role of each T cell subpopulation are two-fold. They are a decreased number of naïve T cells that parallels an increase in memory T cells, mainly in the cytotoxic CD8⁺ T cell population, which can be subdivided into naïve, central, effector memory and TEMRA cells. The two main T cell properties that are the most affected with aging are the altered clonal expansion and decreased cytokine production, especially IL-2. These T cell functions have been shown to be affected in the early events of signaling. The aim of the present study was to investigate the influence of age on TCR- and CD28-dependent activation of the downstream signaling effectors Lck, SHP-1, Akt, PI3K p85α and mTOR in differentiated subpopulations of CD4⁺ and CD8⁺ T cells. Results showed that lymphocytes of elderly subjects were already in an activated state that could not be upregulated by external stimulation. Results also showed that the age-related signal transduction changes were more important than phenotype in the CD4⁺ and CD8⁺ T subpopulations. These observations suggested that age-related molecular and biochemical changes have a more significant influence on T cell functions than T cell phenotype.

Aging of the Immune System. Mechanisms and Therapeutic Targets

Beginning with the sixth decade of life, the human immune system undergoes dramatic aging-related changes, which continuously progress to a state of immunosenescence. The aging immune system loses the ability to protect against infections and cancer and fails to support appropriate wound healing. Vaccine responses are typically impaired in older individuals. Conversely, inflammatory responses mediated by the innate immune system gain in intensity and duration, rendering older individuals susceptible to tissue-damaging immunity and inflammatory disease. Immune system aging functions as an accelerator for other age-related pathologies. It occurs prematurely in some clinical conditions, most prominently in patients with the autoimmune syndrome rheumatoid arthritis (RA); and such patients serve as an informative model system to study molecular mechanisms of immune aging. T cells from patients with RA are prone to differentiate into proinflammatory effector cells, sustaining chronic-persistent inflammatory lesions in the joints and many other organ systems. RA T cells have several hallmarks of cellular aging; most importantly, they accumulate damaged DNA. Because of deficiency of the DNA repair kinase ataxia telangiectasia mutated, RA T cells carry a higher burden of DNA double-strand breaks, triggering cell-indigenous stress signals that shift the cell's survival potential and differentiation pattern. Immune aging in RA T cells is also associated with metabolic reprogramming; specifically, with reduced glycolytic flux and diminished ATP production. Chronic energy stress affects the longevity and the functional differentiation of older T cells. Altered metabolic patterns provide opportunities to therapeutically target the immune aging process through metabolic interference.

Successful and Maladaptive T Cell Aging

Throughout life, the T cell system adapts to shifting resources and demands, resulting in a fundamentally restructured immune system in older individuals. Here we review the cellular and molecular features of an aged immune system and discuss the trade-offs inherent to these adaptive mechanisms. Processes include homeostatic proliferation that maintains compartment size at the expense of partial loss in stemness and incomplete differentiation and the activation of negative regulatory programs, which constrain effector T cell expansion and prevent increasing oligoclonality but also interfere with memory cell generation. We propose that immune failure occurs when adaptive strategies developed by the aging T cell system fail and also discuss how, in some settings, the programs associated with T cell aging culminates in a maladaptive response that directly contributes to chronic inflammatory disease.

Modulation of dendritic cell and T cell cross-talk during aging: The potential role of checkpoint inhibitory molecules

Dendritic cells (DCs) undergo continuous changes throughout life, and there is evidence that elderly DCs have a reduced capacity to stimulate T cells, which may contribute to impaired anti-tumour immune responses in elderly people with cancer. Changes in checkpoint inhibitory molecules/pathways during aging may be one mechanism that impairs the ability of elderly DCs to activate T cells. However, little is currently known regarding the combined effects of aging and cancer on DC and T cell inhibitory molecules/pathways. In this review, we discuss our current understanding of the influence of aging and cancer on key DC and T cell inhibitory molecules/pathways, the potential underlying cellular and molecular mechanisms contributing to their modulation, and the possibility of therapeutically targeting inhibitory molecules in elderly cancer patients.