Age-related changes in natural killer cell receptors from childhood through old age

Changes in immune cell subtypes during ageing

BACKGROUND

The immune system comprises many different types of cells, each with different functions and properties during immune defence. The numbers and types of immune cells in the circulation is highly dynamic and regulated by infections, ageing and certain types of cancers. It is recognised that immune function decreases during ageing, but the biological age at which these functional changes occur is variable, and how ageing affects the different sub-types of lymphocytes, monocytes and NK cells in the circulation is not fully defined.

METHODS

In this study, we recruited 24 healthy volunteers over the age range of 23y to 89y and measured the numbers of different subclasses of circulating cells by immuno-phenotyping and flow cytometry.

RESULTS

We show increased monocyte:lymphocyte ratios in a > 50y cohort and most T cell subsets were decreased, except for CD4+ cells, which were increased in this cohort. In addition, there was NK cell expansion and increased HLA-DR+ T cells, but decreased numbers of classical monocytes and increased numbers of CD4+ monocytes in this >50y cohort.

CONCLUSIONS

These data indicate that healthy ageing is associated with changes in both the major cell groups but also individual subclasses of cells, and these are likely to result from continuous immune challenge and impaired development.

The alteration of NK cells phenotypes related to the functions and dengue disease outcomes

Natural killer cells (NK cells) are the front line of immune cells to combat pathogens and able to influence the subsequent adaptive immune responses. One of the factors contributing to pathogenesis in dengue hemorrhagic fever (DHF) disease is aberrant immune activation during early phase of infection. This study explored the profile of NK cells in dengue infected pediatric patients with different degrees of disease severity. DHF patients contained higher frequency of activated NK cells but lower ratio of CD56dim:CD56bright NK subsets. Activated NK cells exhibited alterations in several NK receptors. Interestingly, the frequencies of NKp30 expressing activated NK cells were more pronounced in dengue fever (DF) than in DHF pediatric patients. In vitro functional analysis indicated that degranulation of NK cells in responding to dengue infected dendritic cells (DCs) required cell-cell contact and type I IFNs. Meanwhile, Interferon gamma (IFN-γ) production initially required cell-cell contact and type I IFNs followed by Interleukin-12 (IL-12), Interleukin-15 (IL-15) and Interleukin-18 (IL-18) resulting in the amplification of IFN-γ producing NK cells over time. This study highlighted the complexity and the factors influencing NK cells responses to dengue virus. Degree of activation, phenotypes of activated cells and the crosstalk between NK cells and other immune cells, could modulate the outcome of NK cells function in the dengue disease.

Lymphocyte profile in peripheral blood of patients with multiple myeloma

Multiple myeloma (MM) is a disease which remains incurable. One of the main reasons is a weakened immune system that allows MM cells to survive. Therefore, the current research is focused on the study of immune system imbalance in MM to find the most effective immunotherapy strategies. Aiming to identify the key points of immune failure in MM patients, we analysed peripheral lymphocytes subsets from MM patients (n = 57) at various stages of the disease course and healthy individuals (HI, n = 15) focusing on T, NK, iNKT, B cells and NK-cell cytokines. Our analysis revealed that MM patients exhibited immune alterations in all studied immune subsets. Compared to HI, MM patients had a significantly lower proportion of CD4 + T cells (19.55% vs. 40.85%; p < 0.001) and CD4 + iNKT cells (18.8% vs. 40%; p < 0.001), within B cells an increased proportion of CD21LCD38L subset (4.5% vs. 0.4%; p < 0.01) and decreased level of memory cells (unswitched 6.1% vs. 14.7%; p < 0.001 and switched 7.8% vs. 11.2%; NS), NK cells displaying signs of activation and exhaustion characterised by a more than 2-fold increase in SLAMF7 MFI (p < 0.001), decreased expression of NKG2D (MFI) and NKp46 (%) on CD16 + 56 + and CD16 + 56- subset respectively (p < 0.05), Effective immunotherapy needs to consider these immune defects and monitoring of the immune status of MM patients is essential to define better interventions in the future.

Donor Age Correlates With Liver-Resident Natural Killer Cell Activity in Adoptive Immunotherapy Using Donor Liver Natural Killer Cells in Liver Transplantation

BACKGROUND

Natural killer (NK) cells are involved in innate immunity and have been reported to play an important role in hepatocellular carcinoma recurrence and post-liver transplantation (LT) infection. However, the relationship between donor age and liver-resident NK cell activity remains to be elucidated.

METHODS

We successfully performed NK cell immunotherapy in 19 living donor LT recipients to prevent post-LT bloodstream infections. Liver mononuclear cells (LMNCs) were collected from the liver graft perfusate and stimulated with interleukin 2 for 3 days. Liver-resident NK cells were analyzed using flow cytometry and a chromium release assay before and after cell culture.

RESULTS

The median donor age was 44 years (range, 24-64 years). The graft weight was 492 g (range, 338-642 g), and the median number of LMNCs was 584 million cells (range, 240-1472 million cells). The proportion of NK cells before and after culture was 22% and 33%, respectively. A significant correlation was found between graft weight and the number of LMNCs. However, no correlation was found between donor age and the number or percentage of NK cells in the liver. Moreover, donor age showed a significant inverse correlation with NKp46 and NKp44 expression before culture and with NKp44, tumor necrosis factor-related apoptosis-inducing ligand, and CD69 expression after culture.

CONCLUSION

A significant inverse correlation was observed between donor age and NK cell activity in the liver. This information may be useful for cell therapy during LT.

Senescent cell-derived extracellular vesicles as potential mediators of innate immunosenescence and inflammaging

Ageing is accompanied by a decline in immune function (immunosenescence), increased inflammation (inflammaging), and more senescent cells which together contribute to age-related disease and infection susceptibility. The innate immune system is the front-line defence against infection and cancer and is also involved in the removal of senescent cells, so preventing innate immunosenescence and inflammaging is vital for health in older age. Extracellular vesicles (EVs) modulate many aspects of innate immune function, including chemotaxis, anti-microbial responses, and immune regulation. Senescent cell derived EVs (SEVs) have different cargo to that of non-senescent cell derived EVs, suggesting alterations in EV cargo across the lifespan may influence innate immune function, possibly contributing to immunosenescence and inflammaging. Here we review current understanding of the potential impact of miRNAs, lipids and proteins, found in higher concentrations in SEVs, on innate immune functions and inflammation to consider whether SEVs are potential influencers of innate immunosenescence and inflammaging. Furthermore, senolytics have demonstrated an ability to return plasma EV content closer to that of non-senescent EVs, therefore the potential use of senotherapeutics (senolytics and senostatics) to ameliorate the effects of SEVs on immunosenescence and inflammaging is also considered as a possible strategy for extending health-span in older adults.

Increased PD-1+ NK Cell Subset in the Older Population

Background

The aging of the immune system is associated with various diseases. It is worth exploring the changes of the immune system in aging. Previous studies have shown that aged T cells have enhanced expression of co-inhibitory molecules. However, it remains unclear whether aged NK cells exhibit similar characteristics to aged T cells. The objective of our research was to clarify this aspect.

Patients and Methods

This study included 98 adults aged 24-90 years (50 males and 48 females). We detected the subset of peripheral blood NK cells and the expression of various receptors on NK cells among donors of different age groups by flow cytometry. Immune subsets were initially defined by forward and side-scatter characteristics and then staining with the appropriate marker.

Results

The absolute number and subset distribution of NK cells were not associated with age. However, CD57 expression and CD69 expression were correlated with age. Furthermore, we found that PD-1 was up-regulated on NK cells in older people, associated with aging, while no such change was observed in other co-inhibitory molecules, including 2B4, CTLA-4, TIM-3, BTLA, CD70, CD39, CD160, and TIGIT. PD-1+ NK cells expressed high levels of CD57 and CD69, indicating PD-1+ NK cells displayed a phenotype of over-activation and aging.

Discussion

This study indicated that PD-1+ NK cells were one of the characteristics of NK cells in older people.

Conclusion

This study indicated that PD-1+ NK cells were one of the characteristics of NK cells in older people. Those findings provided new ideas to explore the underlying drivers of NK aging.

The role of CD56bright NK cells in neurodegenerative disorders

Emerging evidence suggests a potential role for natural killer (NK) cells in neurodegenerative diseases, such as multiple sclerosis, Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. However, the precise function of NK cells in these diseases remains ambiguous. The existence of two NK cell subsets, CD56bright and CD56dim NK cells, complicates the understanding of the contribution of NK cells in neurodegeneration as their functions within the context of neurodegenerative diseases may differ significantly. CD56bright NK cells are potent cytokine secretors and are considered more immunoregulatory and less terminally differentiated than their mostly cytotoxic CD56dim counterparts. Hence, this review focusses on NK cells, specifically on CD56bright NK cells, and their role in neurodegenerative diseases. Moreover, it explores the mechanisms underlying their ability to enter the central nervous system. By consolidating current knowledge, we aim to provide a comprehensive overview on the role of CD56bright NK cells in neurodegenerative diseases. Elucidating their impact on neurodegeneration may have implications for future therapeutic interventions, potentially ameliorating disease pathogenesis.

Comprehensive analysis of senescence-associated genes in sepsis based on bulk and single-cell sequencing data

Background: Sepsis is a pathological state resulting from dysregulated immune response in host during severe infection, leading to persistent organ dysfunction and ultimately death. Senescence-associated genes (SAGs) have manifested their potential in controlling the proliferation and dissemination of a variety of diseases. Nevertheless, the correlation between sepsis and SAGs remains obscure and requires further investigation. Methods: Two RNA expression datasets (GSE28750 and GSE57065) specifically related to sepsis were employed to filter hub SAGs, based on which a diagnostic model predictive of the incidence of sepsis was developed. The association between the expression of the SAGs identified and immune-related modules was analyzed employing Cell-type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) and Microenvironment Cell Populations-counter (MCP-counter) analysis. The identified genes in each cohort were clustered by unsupervised agreement clustering analysis and weighted gene correlation network analysis (WGCNA). Results: A diagnostic model for sepsis established based on hub genes (IGFBP7, GMFG, IL10, IL18, ETS2, HGF, CD55, and MMP9) exhibited a strong clinical reliability (AUC = 0.989). Sepsis patients were randomly assigned and classified by WGCNA into two clusters with distinct immune statuses. Analysis on the single-cell RNA sequencing (scRNA-seq) data revealed high scores of SAGs in the natural killer (NK) cells of the sepsis cohort than the healthy cohort. Conclusion: These findings suggested a close association between SAGs and sepsis alterations. The identified hub genes had potential to serve as a viable diagnostic marker for sepsis.

Natural killer cells immunosenescence and the impact of lifestyle management

Natural killer cells (NKs) are lymphocytes of the innate immune system that quickly respond to viruses, infections, and tumors during their short cell life cycle. However, it was recently found that NKs undergo quantitative, distributional, structural, and functional phenotypic changes during aging that suppress immune responses, which is known as immunosenescence. The aging host environment, cytokine regulation, cytomegalovirus status, and hypothalamic‒pituitary‒adrenal axis have significant effects on NK function. Different lifestyle management interventions modulate the number and cytotoxic activity of NKs, which are essential for rebuilding the immune barrier against pathogens in elderly individuals. Based on recent studies, we review the phenotypic changes of and potential threats of NKs during aging and explore the underlying mechanisms. By summarizing the effects of lifestyle management on NKs and their application prospects, we aim to provide evidence for enhancing immune system function against immune diseases in elderly individuals.

Global Prevalence of Obstructive Sleep Apnea in the Elderly and Related Factors: A Systematic Review and Meta-Analysis Study

PURPOSE

The aims of current meta-analysis was to combine data and statistics on the global prevalence of OSA and related factors in older adults.

DESIGN

A systematic review and meta-analysis.

METHODS

To find related studies, various databases were searched including Embase, PubMed, Scopus, Web of Science (WoS), MagIran, and SID (two local databases) using appropriate keywords, MeSH and controlled vocabulary, with no time limitation up to June, 2021. Heterogeneity of studies was evaluated using I2, and Egger's regression intercept was used to detect publication bias.

FINDINGS

39 studies with a total sample size of 33,353 people were included. The pooled prevalence of OSA in older adults was 35.9% (95% confidence interval: 28.7%-43.8%; I2 = 98.81%). Considering the high heterogeneity of included studies, subgroup analysis was conducted and yielded the most prevalent in Asia continent with 37.0% (95% CI: 22.4%-54.5%; I2 = 97.32%). However, heterogeneity was remained at high level. In the majority of studies, OSA was significantly and positively related to obesity, increased BMI, age, cardiovascular diseases, diabetes, and daytime sleepiness.

CONCLUSIONS

Results of this study showed that global prevalence of OSA in older adults is high and is significantly related to obesity, increased BMI, age, cardiovascular diseases, diabetes, and daytime sleepiness. These findings can be used by experts working on the diagnosis and management of OSA in the geriatric population. These findings can be used by experts on the diagnosis and treatment of OSA in the older adults. Due to high heterogeneity, findings should be interpreted with great caution.

Interleukin-6 Drives Mitochondrial Dysregulation and Accelerates Physical Decline: Insights From an Inducible Humanized IL-6 Knock-In Mouse Model

Chronic activation of inflammatory pathways (CI) and mitochondrial dysfunction are independently linked to age-related functional decline and early mortality. Interleukin 6 (IL-6) is among the most consistently elevated chronic activation of inflammatory pathways markers, but whether IL-6 plays a causative role in this mitochondrial dysfunction and physical deterioration remains unclear. To characterize the role of IL-6 in age-related mitochondrial dysregulation and physical decline, we have developed an inducible human IL-6 (hIL-6) knock-in mouse (TetO-hIL-6mitoQC) that also contains a mitochondrial-quality control reporter. Six weeks of hIL-6 induction resulted in upregulation of proinflammatory markers, cell proliferation and metabolic pathways, and dysregulated energy utilization. Decreased grip strength, increased falls off the treadmill, and increased frailty index were also observed. Further characterization of skeletal muscles postinduction revealed an increase in mitophagy, downregulation of mitochondrial biogenesis genes, and an overall decrease in total mitochondrial numbers. This study highlights the contribution of IL-6 to mitochondrial dysregulation and supports a causal role of hIL-6 in physical decline and frailty.

Immunosenescence as a convergence pathway in neurodegeneration

Immunity refers to the body's defense mechanism to protect itself against illness or to produce antibodies against pathogens. Senescence is a cellular phenomenon that integrates a sustainable growth restriction, other phenotypic abnormalities and including a pro-inflammatory secretome. It is highly involved in regulating developmental stages, tissue homeostasis, and tumor proliferation monitoring. Contemporary experimental reports imply that abolition of senescent cells employing evolved genetic and therapeutic approaches augment the chances of survival and boosts the health span of an individual. Immunosenescence is considered as a process in which dysfunction of the immune system occurs with aging and greatly includes remodeling of lymphoid organs. This in turn causes fluctuations in the immune function of the elderly that has strict relation with the expansion of autoimmune diseases, infections, malignant tumors and neurodegenerative disorders. The interaction of the nervous and immune systems during aging is marked by bi-directional influence and mutual correlation of variations. The enhanced systemic inflammatory condition in the elderly, and the neuronal immune cell activity can be modulated by inflamm-aging and peripheral immunosenescence resulting in chronic low-grade inflammatory processes in the central Nervous system known as neuro-inflammaging. For example, glia excitation by cytokines and glia pro-inflammatory productions contribute significantly to memory injury as well as in acute systemic inflammation, which is associated with high levels of Tumor necrosis factor -α and a rise in cognitive decline. In recent years its role in the pathology of Alzheimer's disease has caught research interest to a large extent. This article reviews the connection concerning the immune and nervous systems and highlights how immunosenescence and inflamm-aging can affect neurodegenerative disorders.

Increased cytotoxic natural killer cells in the endometrium alone cannot be considered the immunological cause of recurrent miscarriage

OBJECTIVE

To study the distribution and gene expression of endometrial immune cell populations, especially natural killer (NK) subsets, between assisted reproductive technology patients and healthy donors and explore a possible relationship of these results with patients' killer cell immunoglobulin-like receptor (KIR) genotypes and KIR-human antigen leukocyte-C (HLA-C) binding.

DESIGN

Prospective observational cohort study.

SETTING

Clinic and university laboratories.

PATIENT(S)

Participants included 39 women with recurrent miscarriages who had undergone in vitro fertilization cycles with donated oocytes and 21 healthy oocyte donors with proven fertility.

INTERVENTION(S)

Endometrial biopsy samples were collected from both patients and donors, and the KIR genotypes of the assisted reproductive technology patients were analyzed.

MAIN OUTCOME MEASURE(S)

Endometrial gene expression (cluster of differentiation [CD] antigens and anti-inflammatory and proinflammatory interleukins) and the number and percentage of regulatory T and NK cell populations in patients and donors were determined. Subsequently, the results obtained were categorized in the group of patients by KIR genotype. Killer cell immunoglobulin-like receptor-HLA-C binding was also examined in patients, considering their KIRs.

RESULT(S)

A higher percentage of CD56dimCD16+ NK cells were observed in patients than those in healthy donors. Nevertheless, when categorizing patients by KIR genotype and comparing the KIR AA (35.9%), AB (43.6%), and BB (20.5%) groups, no statistically significant difference was observed in either endometrial gene expression or any of the immune cell populations analyzed. Finally, no differences in binding between KIR and HLA-C molecules were registered among these 3 sets of patients.

CONCLUSION(S)

The reported increase in the number of NK cells with a cytotoxic profile in the endometrium of women with a history of recurrent miscarriages cannot alone explain these events because no relationship is observed between such cellular increase and the KIR genotypes, which individually, and in combination with the different HLA-C alleles, have also been associated, by previous studies, with negative reproductive outcomes.

CLINICAL TRIAL REGISTRATION NUMBER

1405-MAD-025-JG.

Age-related changes of the innate immune system of the palatine tonsil in a healthy cohort

Although tonsillectomy is performed frequently, the role of palatine tonsils in life long immune protection or tolerance is still debated and the consequences of their removal for the immune system are of general interest. We analysed the tonsillar myeloid compartment in healthy subjects across a wide range of age (64% male; age range: 3 - 85 years) and compared its composition to the peripheral blood. We could observe a strong accumulation of all granulocyte subsets in the aging tonsil, which was most pronounced for basophils and mast cells. On functional level, an increase of CD163 and CD206 expression among monocytes and an increase of neutrophils expressing the inhibitory FcγRIIb correlated with increasing age. While the age-related shift of the leukocyte composition towards monocytes in blood is not reflected in tonsils, the increasing immunoregulatory phenotype of tonsilar monocytes is potentially counteracting the phenomenon of inflammaging at higher age.

Maladaptive Immune Activation in Age-Related Decline of Muscle Function

Age-related changes in immune competency and inflammation play a role in the decline of physical function. In this review of the conference on Function-Promoting Therapies held in March 2022, we discuss the biology of aging and geroscience with an emphasis on decline in physical function and the role of age-related changes in immune competence and inflammation. More recent studies in skeletal muscle and aging highlighting a crosstalk between skeletal muscle, neuromuscular feedback, and immune cell subsets are also discussed. The value of strategies targeting specific pathways that affect skeletal muscle and more systems-wide approaches that provide benefits in muscle homeostasis with aging are underscored. Goals in clinical trial design and the need for incorporating differences in life history when interpreting results from these intervention strategies are important. Where applicable, references are made to papers presented at the conference. We conclude by underscoring the need to incorporate age-related immune competency and inflammation when interpreting results from interventions that target specific pathways predicted to promote skeletal muscle function and tissue homeostasis.

Natural killer cells in aging and age-related diseases

Aging leads to escalated systemic inflammation. As the sentinel of immune system, natural killer (NK) cells are early responders that sense cues and signals from target organs and swiftly orchestrate local inflammation upon their arrival. Emerging evidence indicates a profound role of NK cells in the initiation and evolution of neuroinflammation in aging and age-related diseases. Here we discuss recent advances in NK cell biology and the organ-specific features of NK cells in normal brain aging, Alzheimer's disease, Parkinson's disease and stroke. Our increasing understanding of NK cells and their unique features in aging and age-related diseases may facilitate the future design of immune therapies targeting NK cells to benefit the old population.

Sex/gender-related differences in inflammaging

Geroscience puts mechanisms of aging as a driver of the most common age-related diseases and dysfunctions. Under this perspective, addressing the basic mechanisms of aging will produce a better understanding than addressing each disease pathophysiology individually. Worldwide, despite greater functional impairment, life expectancy is higher in women than in men. Gender differences in the prevalence of multimorbidity lead mandatory to the understanding of the mechanisms underlying gender-related differences in multimorbidity patterns and disability-free life expectancy. Extensive literature suggested that inflammaging is at the crossroad of aging and age-related diseases. In this review, we highlight the main evidence on sex/gender differences in the mechanisms that foster inflammaging, i.e. the age-dependent triggering of innate immunity, modifications of adaptive immunity, and accrual of senescent cells, underpinning some biomarkers of inflammaging that show sex-related differences. In the framework of the "gender medicine perspective", we will also discuss how sex/gender differences in inflammaging can affect sex differences in COVID-19 severe outcomes.

Age-related changes in CD4+ T and NK cell compartments may contribute to the occurrence of pregnancy loss in advanced maternal age

A recent study characterized novel immune cell subsets (T, NK, and γδ T cell subsets) related to recurrent pregnancy loss (RPL). This study aims to assess whether these RPL-related immune cell subsets are affected by aging. The percentages of peripheral blood immunes cells from nulligravida women (NGW), women with a history of normal pregnancy (NP), and women with a history of pregnancy loss (PL) were detected by flow cytometry. The correlations between maternal age and cell percentages were assessed. We found a significant positive correlation between PL and maternal age. The percentages of effector memory CD4⁺ T (CD3⁺ CD4⁺ CD45RA¯ CCR7¯), terminally differentiated CD4⁺ T (CD3⁺ CD4⁺ CD45RA⁺ CCR7¯), and mature NK cells (CD3¯ CD56^+lo) significantly increased with maternal age. A significant decrease in the percentage of Naïve CD4⁺ T cells (CD3⁺ CD4⁺ CD45RA⁺ CCR7⁺) with age was observed in women from the NP group. Women aged 35 or older had significantly higher percentages of effector memory CD4⁺ T cells, terminally differentiated CD4⁺ T cells, and mature NK cells than younger women. Maternal age positively correlates with terminally differentiated CD4⁺ T, effector memory CD4⁺ T, and mature NK cell percentages. In contrast, an inverse correlation was observed between Naïve CD4⁺ T cell and age among women from the NP group. Our findings indicate that age-related CD4⁺ T and NK cell dysregulation might be involved in the pathogenesis of PL in women with advanced maternal age. The underlying mechanism needs further investigation.

Markers of systemic inflammation are positively associated with influenza vaccine antibody responses with a possible role for ILT2(+)CD57(+) NK-cells

Background

With increasing age, overall health declines while systemic levels of inflammatory mediators tend to increase. Although the underlying mechanisms are poorly understood, there is a wealth of data suggesting that this so-called “inflammaging” contributes to the risk of adverse outcomes in older adults. We sought to determine whether markers of systemic inflammation were associated with antibody responses to the seasonal influenza vaccine.

Results

Over four seasons, hemagglutination inhibition antibody titres and ex vivo bulk peripheral blood mononuclear cell (PBMC) responses to live influenza viruses assessed via interferon (IFN)-γ/interleukin (IL)-10 production, were measured pre- and 4-weeks post-vaccination in young adults (n = 79) and older adults randomized to standard- or high-dose inactivated vaccine (n = 612). Circulating tumour necrosis factor (TNF), interleukin (IL)-6 and C-reactive protein (CRP) were also measured pre-vaccination. Post-vaccination antibody titres were significantly associated with systemic inflammatory levels; specifically, IL-6 was positively associated with A/H3N2 titres in young adults (Cohen’s d = 0.36), and in older high-dose, but not standard-dose recipients, all systemic inflammatory mediators were positively associated with A/H1N1, A/H3N2 and B titres (d = 0.10–0.45). We further show that the frequency of ILT2(+)CD57(+) CD56-Dim natural killer (NK)-cells was positively associated with both plasma IL-6 and post-vaccination A/H3N2 titres in a follow-up cohort of older high-dose recipients (n = 63). Pathway analysis suggested that ILT2(+)CD57(+) Dim NK-cells mediated 40% of the association between IL-6 and A/H3N2 titres, which may be related to underlying participant frailty.

Conclusions

In summary, our data suggest a complex relationship amongst influenza vaccine responses, systemic inflammation and NK-cell phenotype in older adults, which depends heavily on age, vaccine dose and possibly overall health status. While our results suggest that “inflammaging” may increase vaccine immunogenicity in older adults, it is yet to be determined whether this enhancement contributes to improved protection against influenza disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00284-x.

Age-dependent NK cell dysfunctions in severe COVID-19 patients

Natural Killer (NK) cells are key innate effectors of antiviral immune response, and their activity changes in ageing and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Here, we investigated the age-related changes of NK cell phenotype and function during SARS-CoV-2 infection, by comparing adult and elderly patients both requiring mechanical ventilation. Adult patients had a reduced number of total NK cells, while elderly showed a peculiar skewing of NK cell subsets towards the CD56lowCD16high and CD56neg phenotypes, expressing activation markers and check-point inhibitory receptors. Although NK cell degranulation ability is significantly compromised in both cohorts, IFN-γ production is impaired only in adult patients in a TGF-β-dependent manner. This inhibitory effect was associated with a shorter hospitalization time of adult patients suggesting a role for TGF-β in preventing an excessive NK cell activation and systemic inflammation. Our data highlight an age-dependent role of NK cells in shaping SARS-CoV-2 infection toward a pathophysiological evolution.

The diseased kidney: aging and senescent immunology

Immunosenescence is the deterioration of the innate and adaptive immune systems associated with aging and is primarily characterized by a reduction in T cell production and accumulation of atypical subsets. Age-related immunological dysfunction leads to impaired immune protection and persistent low-grade chronic inflammation, resulting in a decreased vaccination response and increased vulnerability to infection, cancer, cardiovascular disease, and autoimmune disease in the elderly. As the elderly constitute a growing proportion of the population with renal disease, immunosenescence is a normal aging process that is prevalent among older people. In addition, immunosenescence seems to be more pronounced in patients with kidney diseases than in healthy controls, as shown by severe chronic inflammation, accumulation of immune cells with the senescent phenotype (CD28− T cells, CD14+CD16+ monocytes), and proinflammatory cytokine production. Immunosenescence inhibits immunological clearance and renal tissue regeneration, thereby increasing the risk of permanent renal damage, infection, and cardiovascular events in patients with kidney disease, lowering the prognosis, and even influencing the efficacy of renal replacement treatment. Biological drugs (senomorphics and senolytics) target the aging immune system and exert renoprotective effects. This review aims to emphasize the features of immunosenescence and its influence on kidney diseases and immunotherapy, highlighting the future directions of kidney disease treatment using senescence-focused techniques.

Mucosal-homing natural killer cells are associated with aging in persons living with HIV

Natural killer (NK) cells are critical modulators of HIV transmission and disease. Recent evidence suggests a loss of NK cell cytotoxicity during aging, yet analysis of NK cell biology and aging in people with HIV (PWH) is lacking. Herein, we perform comprehensive analyses of people aging with and without HIV to determine age-related NK phenotypic changes. Utilizing high-dimensional flow cytometry, we analyze 30 immune-related proteins on peripheral NK cells from healthy donors, PWH with viral suppression, and viremic PWH. NK cell phenotypes are dynamic across aging but change significantly in HIV and on antiretroviral drug therapy (ART). NK cells in healthy aging show increasing ⍺4β7 and decreasing CCR7 expression and a reverse phenomenon in PWH. These HIV-associated trafficking patterns could be due to NK cell recruitment to HIV reservoir formation in lymphoid tissue or failed mucosal signaling in the HIV-infected gut but appear to be tight delineators of age-related NK cell changes.

Cellular Senescence in Immunity against Infections

Cellular senescence is characterized by irreversible cell cycle arrest in response to different triggers and an inflammatory secretome. Although originally described in fibroblasts and cell types of solid organs, cellular senescence affects most tissues with advancing age, including the lymphoid tissue, causing chronic inflammation and dysregulation of both innate and adaptive immune functions. Besides its normal occurrence, persistent microbial challenge or pathogenic microorganisms might also accelerate the activation of cellular aging, inducing the premature senescence of immune cells. Therapeutic strategies counteracting the detrimental effects of cellular senescence are being developed. Their application to target immune cells might have the potential to improve immune dysfunctions during aging and reduce the age-dependent susceptibility to infections. In this review, we discuss how immune senescence influences the host’s ability to resolve more common infections in the elderly and detail the different markers proposed to identify such senescent cells; the mechanisms by which infectious agents increase the extent of immune senescence are also reviewed. Finally, available senescence therapeutics are discussed in the context of their effects on immunity and against infections.

Impact of natural killer cells on outcomes after allogeneic hematopoietic stem cell transplantation: A systematic review and meta-analysis

Background

Natural killer (NK) cells play a vital role in early immune reconstitution following allogeneic hematopoietic stem cell transplantation (HSCT).

Methods

A literature search was performed on PubMed, Cochrane, and Clinical trials.gov through April 20, 2022. We included 21 studies reporting data on the impact of NK cells on outcomes after HSCT. Data was extracted following the PRISMA guidelines. Pooled analysis was done using the meta-package (Schwarzer et al.). Proportions with 95% confidence intervals (CI) were computed.

Results

We included 1785 patients from 21 studies investigating the impact of NK cell reconstitution post-HSCT (8 studies/1455 patients), stem cell graft NK cell content (4 studies/185 patients), therapeutic NK cell infusions post-HSCT (5 studies/74 patients), and pre-emptive/prophylactic NK cell infusions post-HSCT (4 studies/77 patients). Higher NK cell reconstitution was associated with a better 2-year overall survival (OS) (high: 77%, 95%CI 0.73-0.82 vs low: 55%, 95%CI 0.37-0.72; n=899), however, pooled analysis for relapse rate (RR) or graft versus host disease (GVHD) could not be performed due to insufficient data. Higher graft NK cell content demonstrated a trend towards a better pooled OS (high: 65.2%, 95%CI 0.47-0.81 vs low: 46.5%, 95%CI 0.24-0.70; n=157), lower RR (high: 16.9%, 95%CI 0.10-0.25 vs low: 33%, 95%CI 0.04-0.72; n=157), and lower acute GVHD incidence (high: 27.6%, 95%CI 0.20-0.36 vs low: 49.7%, 95%CI 0.26-0.74; n=157). Therapeutic NK or cytokine-induced killer (CIK) cell infusions for hematologic relapse post-HSCT reported an overall response rate (ORR) and complete response (CR) of 48.9% and 11% with CIK cell infusions and 82.8% and 44.8% with NK cell infusions, respectively. RR, acute GVHD, and chronic GVHD were observed in 55.6% and 51.7%, 34.5% and 20%, and 20.7% and 11.1% of patients with CIK and NK cell infusions, respectively. Pre-emptive donor-derived NK cell infusions to prevent relapse post-HSCT had promising outcomes with 1-year OS of 69%, CR rate of 42%, ORR of 77%, RR of 28%, and acute and chronic GVHD rates of 24.9% and 3.7%, respectively.

Conclusion

NK cells have a favorable impact on outcomes after HSCT. The optimal use of NK cell infusions post-HSCT may be in a pre-emptive fashion to prevent disease relapse.

Characterization of the immune system of Ellegaard Göttingen Minipigs - An important large animal model in experimental medicine

Interest in Ellegaard Göttingen Minipigs (EGMs) as a model in experimental medicine is continuously growing. The aim of this project is to increase the knowledge of the immune system of EGMs as information is still scarce. Therefore, we studied the postnatal maturation of their immune system from birth until 126 weeks of age. For the first 26 weeks of the study, animals were kept under pathogen-reduced conditions (SPF) and afterwards under conventional housing conditions. The development of the immune system was analyzed by monitoring changes in total numbers of leukocytes and lymphocytes of ten individuals and the composition of leukocyte populations by multi-color flow cytometry (FCM). We followed the presence of monocytes using monoclonal antibodies (mAbs) against CD172a+ and CD163+ and B cells based on the expression of CD79a. NK cells were distinguished as CD3-CD16+CD8α+/dim cells and further subdivided using NKp46 (CD335) expression into NKp46-, NKp46+, and NKp46high NK cells. T-cell receptor (TCR) γδ T cells were defined by the expression of TCR-γδ and different subsets were determined by their CD2 and perforin expression. TCR-αβ T cells were classified by their CD8β+ or CD4 expression. For monitoring their differentiation, expression of CD27 and perforin was investigated for CD8β++ T cells and CD8α together with CD27 for CD4+ T cells. We clearly detected a postnatal development of immune cell composition and identified phenotypes indicative of differentiation within the respective leukocyte subsets. Examination of the development of the antigen-specific immune system after transfer to different distinct housing conditions and after vaccination against common porcine pathogens such as porcine circovirus 2 (PCV2) revealed a markedly increased presence of more differentiated CD8+ and CD4+ T cells with central and effector memory T-cell phenotypes. To complement the findings, a PCV2 vaccine-specific antigen was used for in vitro restimulation experiments. We demonstrated antigen-specific proliferation of CD4+CD8α+CD27+ central and CD4+CD8α+CD27- effector memory T cells as well as antigen-specific production of TNF-α and IFN-γ. This study of postnatal immune development defines basic cellular immune parameters of EGMs and represents an important milestone for the use of EGMs for immunological questions in experimental medicine.

Changes in immunological parameters by ageing in rural healthy Indian adults and their associations with sex and lifestyle

Several factors including sex and lifestyle have been reported to contribute to the age-related alteration of immune functions. The study was undertaken to determine age-related differences in the proportion of peripheral blood mononuclear lymphocytes in the Indian population using blood samples from 67 healthy adults (33 females and 34 males) aged between 20 and 80 years old. In the linear regression analysis to estimate the relationship with age categories, there was a significant increase in the frequency of natural killer cells with ageing, while their cytolytic activity significantly declined. The frequency of CD4+ T cells increased with age, whereas that of CD8+ T cells decreased, resulting in the age-associated increase of the CD4/CD8 ratio. The subsets of B cells did not show any significant relationship with age. Although there were variations between the male and female subgroups in effect size of ageing, the trends were in the same direction in all the parameters. Reduced fat intake was associated with a lower frequency of CD4+ T cells, and higher serum cotinine level was associated with a higher CD4/CD8 ratio. The results indicate that cellular immunity in the Indian population is affected by ageing, while humoral immunity is less susceptible to ageing.

Investigating population-level immunosenescence: From bench to bedside

The immune response is remodeled with aging in a process called immunosenescence. Some immunologists conceive immunosenescence as an adaptation of immunity to the aged immune-environment rather than a merely collapsed reactivity of immune cells against microbes and tumor cells. Others believe on an uninterrupted activation of the innate immune system with aging, leading to a low grade, sterile and chronic proinflammatory state called inflammaging. For instance, it is possible that chronic infection by cytomegalovirus leads to persistent production of viral load. This phenomenon offers periodic stimuli to the immune system that ultimately contribute to the remodeling of the immune response. If investigating immunosenescence at the cellular level is already a difficult task, considering the population level is much more complex. However, by studying immunosenescence at the population level, we can extract valuable results with viable applications. While studies with animal models allow scientists to deepen their understanding of the mechanisms of immunosenescence, studying large populations can bring practical innovations to medicine and the health system. Many researchers and funders have dedicated themselves to producing methods for the evaluation of immunosenescence on a large scale, aiming to elucidate new mechanisms by which diseases are established in the elderly. The description of how the immune response is remodeled with aging emerges as a new tool to identify the subset of subjects in which unhealthy aging is a matter of time, to help better individualize clinical management and select patients who may benefit. of early interventions. This review focuses on functional assays as valuable methods for measuring the remodeling of the immune response with aging and discuss their clinical impact. We also recall fundamental concepts for understanding the aging process of the immune response. In addition, we highlight future prospects for immunosenescence research.

What Inhibits Natural Killers’ Performance in Tumour

Natural killer cells are innate lymphocytes with the ability to lyse tumour cells depending on the balance of their activating and inhibiting receptors. Growing numbers of clinical trials show promising results of NK cell-based immunotherapies. Unlike T cells, NK cells can lyse tumour cells independent of antigen presentation, based simply on their activation and inhibition receptors. Various strategies to improve NK cell-based therapies are being developed, all with one goal: to shift the balance to activation. In this review, we discuss the current understanding of ways NK cells can lyse tumour cells and all the inhibitory signals stopping their cytotoxic potential.

Circulating biomarkers of inflammaging as potential predictors of COVID-19 severe outcomes

The COVID-19 pandemic caused by SARS-CoV-2 infection has been of unprecedented clinical and socio-economic worldwide relevance. The case fatality rate for COVID-19 grows exponentially with age and the presence of comorbidities. In the older patients, COVID-19 manifests predominantly as a systemic disease associated with immunological, inflammatory, and procoagulant responses. Timely diagnosis and risk stratification are crucial steps to define appropriate therapies and reduce mortality, especially in the older patients. Chronically and systemically activated innate immune responses and impaired antiviral responses have been recognized as the results of a progressive remodeling of the immune system during aging, which can be described by the words 'immunosenescence' and 'inflammaging'. These age-related features of the immune system were highlighted in patients affected by COVID-19 with the poorest clinical outcomes, suggesting that the mechanisms underpinning immunosenescence and inflammaging could be relevant for COVID-19 pathogenesis and progression. Increasing evidence suggests that senescent myeloid and endothelial cells are characterized by the acquisition of a senescence-associated pro-inflammatory phenotype (SASP), which is considered as the main culprit of both immunosenescence and inflammaging. Here, we reviewed this evidence and highlighted several circulating biomarkers of inflammaging that could provide additional prognostic information to stratify COVID-19 patients based on the risk of severe outcomes.

Single-cell transcriptomics reveal a unique memory-like NK cell subset that accumulates with ageing and correlates with disease severity in COVID-19

Background

Natural killer (NK) cells are innate lymphoid cells that mediate antitumour and antiviral responses. However, very little is known about how ageing influences human NK cells, especially at the single-cell level.

Methods

We applied single-cell sequencing (scRNA-seq) to human lymphocytes and NK cells from 4 young and 4 elderly individuals and then analysed the transcriptome data using Seurat. We detected the proportion and phenotype of NK cell subsets in peripheral blood samples from a total of 62 young and 52 elderly healthy donors by flow cytometry. We also used flow cytometry to examine the effector functions of NK cell subsets upon IFN-α/IL-12+IL-15/K562/IL-2 stimulation in vitro in peripheral blood samples from a total of 64 young and 63 elderly healthy donors. We finally studied and integrated single-cell transcriptomes of NK cells from 15 young and 41 elderly COVID-19 patients with those from 12 young and 6 elderly healthy control individuals to investigate the impacts of ageing on NK cell subsets in COVID-19 disease.

Results

We discovered a memory-like NK subpopulation (NK2) exhibiting the largest distribution change between elderly and young individuals among lymphocytes. Notably, we discovered a unique NK subset that was predominantly CD52⁺ NK2 cells (NK2.1). These memory-like NK2.1 cells accumulated with age, exhibited proinflammatory characteristics, and displayed a type I interferon response state. Integrative analyses of a large-cohort COVID-19 dataset and our datasets revealed that NK2.1 cells from elderly COVID-19 patients are enriched for type I interferon signalling, which is positively correlated with disease severity in COVID-19.

Conclusions

We identified a unique memory-like NK cell subset that accumulates with ageing and correlates with disease severity in COVID-19. Our results identify memory-like NK2.1 cells as a potential target for developing immunotherapies for infectious diseases and for addressing age-related dysfunctions of the immune system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-022-01049-3.

Aging of the Immune System: Focus on Natural Killer Cells Phenotype and Functions

Aging is the greatest risk factor for nearly all major chronic diseases, including cardiovascular diseases, cancer, Alzheimer’s and other neurodegenerative diseases of aging. Age-related impairment of immune function (immunosenescence) is one important cause of age-related morbidity and mortality, which may extend beyond its role in infectious disease. One aspect of immunosenescence that has received less attention is age-related natural killer (NK) cell dysfunction, characterized by reduced cytokine secretion and decreased target cell cytotoxicity, accompanied by and despite an increase in NK cell numbers with age. Moreover, recent studies have revealed that NK cells are the central actors in the immunosurveillance of senescent cells, whose age-related accumulation is itself a probable contributor to the chronic sterile low-grade inflammation developed with aging (“inflammaging”). NK cell dysfunction is therefore implicated in the increasing burden of infection, malignancy, inflammatory disorders, and senescent cells with age. This review will focus on recent advances and open questions in understanding the interplay between systemic inflammation, senescence burden, and NK cell dysfunction in the context of aging. Understanding the factors driving and enforcing NK cell aging may potentially lead to therapies countering age-related diseases and underlying drivers of the biological aging process itself.

Enhanced co-culture and enrichment of human natural killer cells for the selective clearance of senescent cells

In the context of aging and age-associated diseases, Natural Killer (NK) cells have been revealed as a key cell type responsible for the immune clearance of senescent cells. Subsequently, NK cell-based therapies have emerged as promising alternatives to drug-based therapeutic interventions for the prevention and treatment of age-related disease and debility. Given the promise of NK cell-mediated immunotherapies as a safe and effective treatment strategy, we outline an improved method by which primary NK cells can be efficiently enriched from human peripheral blood across multiple donors (ages 20-42 years old), with a practical protocol that reliably enhances both CD56^dim and CD56^bright NK cells by 15-fold and 3-fold, respectively. Importantly, we show that our co-culture protocol can be used as an easily adaptable tool to assess highly efficient and selective killing of senescent cells by primary NK cells enriched via our method using longer co-culture durations and a low target to effector ratio, which may be more physiological than has been achieved in previous literature.

Infection in the Developing Brain: The Role of Unique Systemic Immune Vulnerabilities

Central nervous system (CNS) infections remain a major burden of pediatric disease associated with significant long-term morbidity due to injury to the developing brain. Children are susceptible to various etiologies of CNS infection partly because of vulnerabilities in their peripheral immune system. Young children are known to have reduced numbers and functionality of innate and adaptive immune cells, poorer production of immune mediators, impaired responses to inflammatory stimuli and depressed antibody activity in comparison to adults. This has implications not only for their response to pathogen invasion, but also for the development of appropriate vaccines and vaccination strategies. Further, pediatric immune characteristics evolve across the span of childhood into adolescence as their broader physiological and hormonal landscape develop. In addition to intrinsic vulnerabilities, children are subject to external factors that impact their susceptibility to infections, including maternal immunity and exposure, and nutrition. In this review we summarize the current evidence for immune characteristics across childhood that render children at risk for CNS infection and introduce the link with the CNS through the modulatory role that the brain has on the immune response. This manuscript lays the foundation from which we explore the specifics of infection and inflammation within the CNS and the consequences to the maturing brain in part two of this review series.

Interconnections between Inflammageing and Immunosenescence during Ageing

Acute inflammation is a physiological response to injury or infection, with a cascade of steps that ultimately lead to the recruitment of immune cells to clear invading pathogens and heal wounds. However, chronic inflammation arising from the continued presence of the initial trigger, or the dysfunction of signalling and/or effector pathways, is harmful to health. While successful ageing in older adults, including centenarians, is associated with low levels of inflammation, elevated inflammation increases the risk of poor health and death. Hence inflammation has been described as one of seven pillars of ageing. Age-associated sterile, chronic, and low-grade inflammation is commonly termed inflammageing-it is not simply a consequence of increasing chronological age, but is also a marker of biological ageing, multimorbidity, and mortality risk. While inflammageing was initially thought to be caused by "continuous antigenic load and stress", reports from the last two decades describe a much more complex phenomenon also involving cellular senescence and the ageing of the immune system. In this review, we explore some of the main sources and consequences of inflammageing in the context of immunosenescence and highlight potential interventions. In particular, we assess the contribution of cellular senescence to age-associated inflammation, identify patterns of pro- and anti-inflammatory markers characteristic of inflammageing, describe alterations in the ageing immune system that lead to elevated inflammation, and finally assess the ways that diet, exercise, and pharmacological interventions can reduce inflammageing and thus, improve later life health.

Platelets in pediatric and neonatal sepsis: novel mediators of the inflammatory cascade

Sepsis, a dysregulated host response to infection, has been difficult to accurately define in children. Despite a higher incidence, especially in neonates, a non-specific clinical presentation alongside a lack of verified biomarkers has prevented a common understanding of this condition. Platelets, traditionally regarded as mediators of haemostasis and thrombosis, are increasingly associated with functions in the immune system with involvement across the spectrum of innate and adaptive immunity. The large number of circulating platelets (approx. 150,000 cells per microlitre) mean they outnumber traditional immune cells and are often the first to encounter a pathogen at a site of injury. There are also well-described physiological differences between platelets in children and adults. The purpose of this review is to place into context the platelet and its role in immunology and examine the evidence where available for its role as an immune cell in childhood sepsis. It will examine how the platelet interacts with both humoral and cellular components of the immune system and finally discuss the role the platelet proteome, releasate and extracellular vesicles may play in childhood sepsis. This review also examines how platelet transfusions may interfere with the complex relationships between immune cells in infection. IMPACT: Platelets are increasingly being recognised as important "first responders" to immune threats. Differences in adult and paediatric platelets may contribute to differing immune response to infections. Adult platelet transfusions may affect infant immune responses to inflammatory/infectious stimuli.

Emerging cellular senescence-centric understanding of immunological aging and its potential modulation through dietary bioactive components

Immunological aging is strongly associated with the observable deleterious effects of human aging. Our understanding of the causes, effects, and therapeutics of aging immune cells has long been considered within the sole purview of immunosenescence. However, it is being progressively realized that immunosenescence may not be the only determinant of immunological aging. The cellular senescence-centric theory of aging proposes a more fundamental and specific role of immune cells in regulating senescent cell (SC) burden in aging tissues that has augmented the notion of senescence immunotherapy. Now, in addition, several emerging studies are suggesting that cellular senescence itself may be prevalent in aging immune cells, and that senescent immune cells exhibiting characteristic markers of cellular senescence, similar to non-leucocyte cells, could be among the key drivers of various facets of physiological aging. The present review integrates the current knowledge related to immunosenescence and cellular senescence in immune cells per se, and aims at providing a cohesive overview of these two phenomena and their significance in immunity and aging. We present evidence and rationalize that understanding the extent and impact of cellular senescence in immune cells vis-à-vis immunosenescence is necessary for truly comprehending the notion of an 'aged immune cell'. In addition, we also discuss the emerging significance of dietary factors such as phytochemicals, probiotic bacteria, fatty acids, and micronutrients as possible modulators of immunosenescence and cellular senescence. Evidence and opportunities related to nutritional bioactive components and immunological aging have been deliberated to augment potential nutrition-oriented immunotherapy during aging.

Age-related sexual dimorphism on the longitudinal progression of blood immune cells in BALB/cByJ mice

The study of immune system aging is of relevance, considering its myriad of interactions and role in protecting and maintaining body homeostasis. While mouse models have been extensively used to study immune system aging, little is known on how the main immune populations progress over time and what is the impact of sex. To contribute to filling this gap, male and female BALB/cByJ mice were longitudinally evaluated, from 3 to 18 months old, for the main blood populations, assessed by flow cytometry. Using linear mixed-effect models, we observed that the percentages of neutrophils, monocytes, eosinophils, and total natural killer (NK) cells increase with aging, while those of B cells, T cells (including CD4⁺ and CD8⁺ subsets), and Ly6C⁺ NK cells decrease. Males present higher percentages of neutrophils and classical monocytes Ly6C^high over time, while females present higher percentages of total T cells, both CD4⁺ and CD8⁺, eosinophils, and NK cells. Males and females display similar percentages of B cells, even though with opposite accelerated progressions over time. This study revealed that mouse models recapitulate what is observed in humans during aging: an overall proportional decrease in the adaptive and an increase in the innate immune cells. Additionally, it uncovers an age-related sexual dimorphism in the proportion of immune cells in circulation, further strengthening the need to explore the impact of sex when addressing immune system aging using mouse models.

Targeting immune dysfunction in aging

Human aging is a multifactorial phenomenon that affects numerous organ systems and cellular processes, with the immune system being one of the most dysregulated. Immunosenescence, the gradual deterioration of the immune system, and inflammaging, a chronic inflammatory state that persists in the elderly, are among the plethora of immune changes that occur during aging. Almost all populations of immune cells change with age in terms of numbers and/or activity. These alterations are in general highly detrimental, resulting in an increased susceptibility to infections, reduced healing abilities, and altered homeostasis that promote the emergence of age-associated diseases such as cancer, diabetes, and other diseases associated with inflammation. Thanks to recent developments, several strategies have been proposed to target central immunological processes or specific immune subpopulations affected by aging. These therapeutic approaches could soon be applied in the clinic to slow down or even reverse specific age-induced immune changes in order to rejuvenate the immune system and prevent or reduce the impact of various diseases. Due to its systemic nature and interconnection with all the other systems in the body, the immune system is an attractive target for aging intervention because relatively targeted modifications to a small set of cells have the potential to improve the health of multiple organ systems. Therefore, anti-aging immune targeting therapies could represent a potent approach for improving healthspan. Here, we review aging changes in the major components of the immune system, we summarize the current immune-targeting therapeutic approaches in the context of aging and discuss the future directions in the field of immune rejuvenation.

Immunosuppressive network promotes immunosenescence associated with aging and chronic inflammatory conditions

The functional competence of the immune system gradually declines with aging, a process called immunosenescence. The age-related remodelling of the immune system affects both adaptive and innate immunity. In particular, a chronic low-grade inflammation, termed inflammaging, is associated with the aging process. Immunosenescence not only is present in inflammaging state, but it also occurs in several pathological conditions in conjunction with chronic inflammation. It is known that persistent inflammation stimulates a counteracting compensatory immunosuppression intended to protect host tissues. Inflammatory mediators enhance myelopoiesis and induce the generation of immature myeloid-derived suppressor cells (MDSC) which in mutual cooperation stimulates the immunosuppressive network. Immunosuppressive cells, especially MDSCs, regulatory T cells (Treg), and M2 macrophages produce immunosuppressive factors, e.g., TGF-β, IL-10, ROS, arginase-1 (ARG1), and indoleamine 2,3-dioxygenase (IDO), which suppress the functions of CD4/CD8T and B cells as well as macrophages, natural killer (NK) cells, and dendritic cells. The immunosuppressive armament (i) inhibits the development and proliferation of immune cells, (ii) decreases the cytotoxic activity of CD8T and NK cells, (iii) prevents antigen presentation and antibody production, and (iv) suppresses responsiveness to inflammatory mediators. These phenotypes are the hallmarks of immunosenescence. Immunosuppressive factors are able to control the chromatin landscape, and thus, it seems that the immunosenescence state is epigenetically regulated.

Fingolimod Therapy in Multiple Sclerosis Leads to the Enrichment of a Subpopulation of Aged NK Cells

Fingolimod is an approved oral treatment for relapsing-remitting multiple sclerosis (RRMS) that modulates agonistically the sphingosin-1-phosphate receptor (S1PR), inhibiting thereby the egress of lymphocytes from the lymph nodes. In this interventional prospective clinical phase IV trial, we longitudinally investigated the impact of fingolimod on frequencies of NK cell subpopulations by flow cytometry in 17 RRMS patients at baseline and 1, 3, 6, and 12 months after treatment initiation. Clinical outcome was assessed by the Expanded Disability Status Scale (EDSS) and annualized relapse rates (ARR). Over the study period, median EDSS remained stable from month 3 to month 12, and ARR decreased compared to ARR in the 24 months prior treatment. Treatment was paralleled by an increased frequency of circulating NK cells, due primarily to an increase in CD56dimCD94low mature NK cells, while the CD56bright fraction and CD127+ innate lymphoid cells (ILCs) decreased over time. An unsupervised clustering algorithm further revealed that a particular fraction of NK cells defined by the expression of CD56dimCD16++KIR+/-NKG2A-CD94-CCR7+/-CX3CR1+/-NKG2C-NKG2D+NKp46-DNAM1++CD127+ increased during treatment. This specific phenotype might reflect a status of aged, fully differentiated, and less functional NK cells. Our study confirms that fingolimod treatment affects both NK cells and ILC. In addition, our study suggests that treatment leads to the enrichment of a specific NK cell subset characterized by an aged phenotype. This might limit the anti-microbial and anti-tumour NK cell activity in fingolimod-treated patients.

Too young to die? How aging affects cellular innate immune responses to influenza virus and disease severity

Influenza is a respiratory viral infection that causes significant morbidity and mortality worldwide. The innate immune cell response elicited during influenza A virus (IAV) infection forms the critical first line of defense, which typically is impaired as we age. As such, elderly individuals more commonly succumb to influenza-associated complications, which is reflected in most aged animal models of IAV infection. Here, we review the important roles of several major innate immune cell populations in influenza pathogenesis, some of which being deleterious to the host, and the current knowledge of how age-associated numerical, phenotypic and functional cell changes impact disease development. Further investigation into age-related modulation of innate immune cell responses, using appropriate animal models, will help reveal how immunity to IAV may be compromised by aging and inform the development of novel therapies, tailored for use in this vulnerable group.

Potential of Mesenchymal Stem Cells in the Rejuvenation of the Aging Immune System

Rapid growth of the geriatric population has been made possible with advancements in pharmaceutical and health sciences. Hence, age-associated diseases are becoming more common. Aging encompasses deterioration of the immune system, known as immunosenescence. Dysregulation of the immune cell production, differentiation, and functioning lead to a chronic subclinical inflammatory state termed inflammaging. The hallmarks of the aging immune system are decreased naïve cells, increased memory cells, and increased serum levels of pro-inflammatory cytokines. Mesenchymal stem cell (MSC) transplantation is a promising solution to halt immunosenescence as the cells have excellent immunomodulatory functions and low immunogenicity. This review compiles the present knowledge of the causes and changes of the aging immune system and the potential of MSC transplantation as a regenerative therapy for immunosenescence.

Immunosurveillance of Cancer and Viral Infections with Regard to Alterations of Human NK Cells Originating from Lifestyle and Aging

Natural killer (NK) cells are cytotoxic immune cells with an innate capacity for eliminating cancer cells and virus- infected cells. NK cells are critical effector cells in the immunosurveillance of cancer and viral infections. Patients with low NK cell activity or NK cell deficiencies are predisposed to increased risks of cancer and severe viral infections. However, functional alterations of human NK cells are associated with lifestyles and aging. Personal lifestyles, such as cigarette smoking, alcohol consumption, stress, obesity, and aging are correlated with NK cell dysfunction, whereas adequate sleep, moderate exercise, forest bathing, and listening to music are associated with functional healthy NK cells. Therefore, adherence to a healthy lifestyle is essential and will be favorable for immunosurveillance of cancer and viral infections with healthy NK cells.

The impact of aging on innate and adaptive immunity in the human female genital tract

Mucosal tissues in the human female reproductive tract (FRT) are primary sites for both gynecological cancers and infections by a spectrum of sexually transmitted pathogens, including human immunodeficiency virus (HIV), that compromise women's health. While the regulation of innate and adaptive immune protection in the FRT by hormonal cyclic changes across the menstrual cycle and pregnancy are being intensely studied, little to nothing is known about the alterations in mucosal immune protection that occur throughout the FRT as women age following menopause. The immune system in the FRT has two key functions: defense against pathogens and reproduction. After menopause, natural reproductive function ends, and therefore, two overlapping processes contribute to alterations in immune protection in aging women: menopause and immunosenescence. The goal of this review is to summarize the multiple immune changes that occur in the FRT with aging, including the impact on the function of epithelial cells, immune cells, and stromal fibroblasts. These studies indicate that major aspects of innate and adaptive immunity in the FRT are compromised in a site‐specific manner in the FRT as women age. Further, at some FRT sites, immunological compensation occurs. Overall, alterations in mucosal immune protection contribute to the increased risk of sexually transmitted infections (STI), urogenital infections, and gynecological cancers. Further studies are essential to provide a foundation for the development of novel therapeutic interventions to restore immune protection and reverse conditions that threaten women's lives as they age.

Feed-forward regulation between cellular senescence and immunosuppression promotes the aging process and age-related diseases

Aging is a progressive degenerative process involving a chronic low-grade inflammation and the accumulation of senescent cells. One major issue is to reveal the mechanisms which promote the deposition of pro-inflammatory senescent cells within tissues. The accumulation involves mechanisms which increase cellular senescence as well as those inhibiting the clearance of senescent cells from tissues. It is known that a persistent inflammatory state evokes a compensatory immunosuppression which inhibits pro-inflammatory processes by impairing the functions of effector immune cells, e.g., macrophages, T cells and natural killer (NK) cells. Unfortunately, these cells are indispensable for immune surveillance and the subsequent clearance of senescent cells, i.e., the inflammation-induced counteracting immunosuppression prevents the cleansing of host tissues. Moreover, senescent cells can also repress their own clearance by expressing inhibitors of immune surveillance and releasing the ligands of NKG2D receptors which impair their surveillance by NK and cytotoxic CD8⁺ T cells. It seems that cellular senescence and immunosuppression establish a feed-forward process which promotes the aging process and age-related diseases. I will examine in detail the immunosuppressive mechanisms which impair the surveillance and clearance of pro-inflammatory senescent cells with aging. In addition, I will discuss several therapeutic strategies to halt the degenerative feed-forward circuit associated with the aging process and age-related diseases.

Hallmarks and detection techniques of cellular senescence and cellular ageing in immune cells

The ageing of the global population brings about unprecedented challenges. Chronic age-related diseases in an increasing number of people represent an enormous burden for health and social care. The immune system deteriorates during ageing and contributes to many of these age-associated diseases due to its pivotal role in pathogen clearance, tissue homeostasis and maintenance. Moreover, in order to develop treatments for COVID-19, we urgently need to acquire more knowledge about the aged immune system, as older adults are disproportionally and more severely affected. Changes with age lead to impaired responses to infections, malignancies and vaccination, and are accompanied by chronic, low-degree inflammation, which together is termed immunosenescence. However, the molecular and cellular mechanisms that underlie immunosenescence, termed immune cell senescence, are mostly unknown. Cellular senescence, characterised by an irreversible cell cycle arrest, is thought to be the cause of tissue and organismal ageing. Thus, better understanding of cellular senescence in immune populations at single-cell level may provide us with insight into how immune cell senescence develops over the life time of an individual. In this review, we will briefly introduce the phenotypic characterisation of aged innate and adaptive immune cells, which also contributes to overall immunosenescence, including subsets and function. Next, we will focus on the different hallmarks of cellular senescence and cellular ageing, and the detection techniques most suitable for immune cells. Applying these techniques will deepen our understanding of immune cell senescence and to discover potential druggable pathways, which can be modulated to reverse immune ageing.

Immune Cell Number, Phenotype, and Function in the Elderly with Sepsis

Sepsis is a form of life-threatening organ dysfunction caused by dysregulated host responses to an infection that can be partly attributed to immune dysfunction. Although sepsis affects patients of all ages, elderly individuals display increased susceptibility and mortality. This is partly due to immunosenescence, a decline in normal immune system function associated with physiological aging that affects almost all cell types in the innate and adaptive immune systems. In elderly patients with sepsis, these alterations in immune cells such as endothelial cells, neutrophils, monocytes, macrophages, natural killer cells, dendritic cells, T lymphocytes, and B lymphocytes, are largely responsible for their poor prognosis and increased mortality. Here, we review recent studies investigating the events affecting both innate and adaptive immune cells in elderly mice and patients with sepsis, including alterations in their number, phenotype, and function, to shed light on possible new therapeutic strategies.

Sex- and age-dependent alterations of splenic immune cell profile and NK cell phenotypes and function in C57BL/6J mice

Background

Physiological homeostasis decline, immunosenescence, and increased risk for multiple diseases, including neurodegeneration, are all hallmarks of ageing. Importantly, it is known that the ageing process is sex-biased. For example, there are sex differences in predisposition for multiple age-related diseases, including neurodegenerative and autoimmune diseases. However, sex differences in age-associated immune phenotypes are not clearly understood.

Results

Here, we examined the effects of age on immune cell phenotypes in both sexes of C57BL/6J mice with a particular focus on NK cells. We found female-specific spleen weight increases with age and concordant reduction in the number of splenocytes per gram of spleen weight compared to young females. To evaluate sex- and age-associated changes in splenic immune cell composition, we performed flow cytometry analysis. In male mice, we observed an age-associated reduction in the frequencies of monocytes and NK cells; female mice displayed a reduction in B cells, NK cells, and CD8 + T cells and increased frequency of monocytes and neutrophils with age. We then performed a whole blood stimulation assay and multiplex analyses of plasma cytokines and observed age- and sex-specific differences in immune cell reactivity and basal circulating cytokine concentrations. As we have previously illustrated a potential role of NK cells in Parkinson’s disease, an age-related neurodegenerative disease, we further analyzed age-associated changes in NK cell phenotypes and function. There were distinct differences between the sexes in age-associated changes in the expression of NK cell receptors, IFN-γ production, and impairment of α-synuclein endocytosis.

Conclusions

This study demonstrates sex- and age-specific alterations in splenic lymphocyte composition, circulating cytokine/chemokine profiles, and NK cell phenotype and effector functions. Our data provide evidence that age-related physiological perturbations differ between the sexes which may help elucidate sex differences in age-related diseases, including neurodegenerative diseases, particularly Parkinson’s disease, where immune dysfunction is implicated in their etiology.