Causes, consequences, and reversal of immune system aging

Uncontrolled sepsis: a systematic review of translational immunology studies in intensive care medicine

BACKGROUND

The design of clinical immunology studies in sepsis presents several fundamental challenges to improving the translational understanding of pathologic mechanisms. We undertook a systematic review of bed-to-benchside studies to test the hypothesis that variable clinical design methodologies used to investigate immunologic function in sepsis contribute to apparently conflicting laboratory data, and identify potential alternatives that overcome various obstacles to improve experimental design.

METHODS

We performed a systematic review of the design methodology employed to study neutrophil function (respiratory burst), monocyte endotoxin tolerance and lymphocyte apoptosis in the intensive care setting, over the past 15 years. We specifically focussed on how control samples were defined, taking into account age, gender, ethnicity, concomitant therapies, timing of sample collection and the criteria used to diagnose sepsis.

RESULTS

We identified 57 eligible studies, the majority of which (74%) used case-control methodology. Healthy volunteers represented the control population selected in 83% of studies. Comprehensive demographic data on age, gender and ethnicity were provided in ≤48% of case control studies. Documentation of diseases associated with immunosuppression, malignancy and immunomodulatory therapies was rare. Less than half (44%) of studies undertook independent adjudication for the diagnosis of sepsis while 68% provided microbiological data. The timing of sample collection was defined by highly variable clinical criteria. By contrast, surgical studies avoided many such confounders, although only one study in surgical patients monitored the study group for development of sepsis.

CONCLUSIONS

We found several important and common limitations in the clinical design of translational immunologic studies in human sepsis. Major elective surgery overcame many of these methodological limitations. The failure of adequate clinical design in mechanistic studies may contribute to the lack of translational therapeutic progress in intensive care medicine.

Changing treatment paradigms for patients with plasma cell myeloma: impact upon immune determinants of infection

Plasma cell myeloma (PCM) is increasing in prevalence in older age groups and infective complications are a leading cause of mortality. Patients with PCM are at increased risk of severe infections, having deficits in many arms of the immune system due to disease and treatment-related factors. Treatment of PCM has evolved over time with significant impacts on immune function resulting in changing rates and pattern of infection. Recently, there has been a paradigm shift in the treatment of PCM with the use of immunomodulatory drugs and proteasome inhibitors becoming the standard of care. These drugs have wide-ranging effects on the immune system but their impact on infection risk and aetiology remain unclear. The aims of this review are to discuss the impact of patient, disease and treatment factors on immune function over time for patients with PCM and to correlate immune deficits with the incidence and aetiology of infections seen clinically in these patients. Preventative measures and the need for clinically relevant tools to enable infective profiling of patients with PCM are discussed.

IBD across the age spectrum: is it the same disease?

IBD is a chronic disorder with disease onset ranging from early childhood to beyond the sixth decade of life. The factors that determine the age of onset currently remain unexplained. Is timing of occurrence a random event or is it indicative of different pathophysiological pathways leading to different phenotypes across the age spectrum? Over the past decade, several studies have suggested that the characteristics and natural history of IBD seem to be different according to age of onset. This heterogeneity suggests that the respective contributions of genetics, host immune system and environment to the aetiology and phenotype of Crohn's disease and ulcerative colitis are different across ages. Critical reviews that focus on differences characterizing IBD between age groups are scarce. Therefore, this Review updates the knowledge of the differences in epidemiology, clinical characteristics, and natural history of paediatric, adult and elderly-onset IBD. In addition, potential differences in host-gene-microbial interactions according to age are highlighted.

Adult thymic epithelium contains nonsenescent label-retaining cells

Progress in our understanding of thymic epithelial cell (TEC) renewal and homeostasis is hindered by the lack of markers for TEC progenitors. Stem and progenitor cell populations display remarkable diversity in their proliferative behavior. In some but not all tissues, stemness is associated with quiescence. The primary goal of our study was to discover whether quiescent cells were present in neonatal and adult TECs. To this end, we used a transgenic label-retaining cell (LRC) assay in which a histone H2B-GFP fusion protein is expressed under the control of the reverse tetracycline-controlled transactivator and the tetracycline operator minimal promoter. In adult mice, we found that both cortical and medullary TECs (cTECs and mTECs) proliferated more actively in females than males. Moreover, we observed three main differences between neonatal and adult TECs: 1) neonatal TECs proliferated more actively than adult TECs; 2) whereas cTECs and mTECs had similar turnover rates in young mice, the turnover of mTECs was more rapid than that of cTECs in adults; and 3) although no LRCs could be detected in young mice, LRCs were detectable after a 16-wk chase in adults. In female mice, LRCs were found almost exclusively among cTECs and expressed relatively low levels of p16INK4a, p19ARF, and Serpine1, and high levels of Bmi1, Foxn1, Trp63, and Wnt4. We conclude that LRCs in adult TECs are not senescent postmitotic cells and may represent the elusive progenitors responsible for TEC maintenance in the adult thymus.

Differences and interactions between risk factors for coronary spasm and atherosclerosis--smoking, aging, inflammation, and blood pressure

Objective Coronary spasm as well as atherosclerosis plays an important role in the pathogenesis of coronary heart disease. However, the relationship between coronary spasm and atherosclerosis is not well known. The purpose of the present study was to examine the differences and interactions between risk factors for coronary spasm and atherosclerosis and thereby explore the pathogenesis of coronary spasm. Methods The study subjects consisted of 938 patients with chest discomfort (522 men and 416 women, mean age 65.2±11.0) who underwent intracoronary-acetylcholine provocation tests for coronary spasm. Coronary risk factors, including age, gender, body mass index, blood pressure, high-sensitivity C-reactive protein (hsCRP), white blood cells, glucose, lipid profiles, and other laboratory chemistries were examined. Results Four hundred and ninety-six patients (315 men and 181 women, mean age: 65.1±11.4) were diagnosed with coronary spastic angina (CSA), while the remaining 442 patients (207 men and 235 women, mean age: 65.3±10.7) were diagnosed with non-CSA. A multiple logistic regression analysis revealed men, smoking, hsCRP, and low diastolic blood pressure (DBP) to be predictors (p=0.001, p=0.009, p=0.034, and p=0.041, respectively) for CSA, while age, diabetes mellitus, low high-density lipoprotein-cholesterol, systolic blood pressure (SBP), uric acid and male gender were found to be predictors (p<0.001, p<0.001, p<0.001, p=0.002, p=0.006 and p=0.029, respectively) for atherosclerosis. Conclusion Predictors for coronary spasm were smoking, hsCRP and low DBP, whereas those for atherosclerosis were age, diabetes mellitus, high SBP, and uric acid in that order. These findings suggest that the pathogenesis of coronary spasm differs from that of atherosclerosis.

p53 isoforms regulate aging- and tumor-associated replicative senescence in T lymphocytes

Cellular senescence contributes to aging and decline in tissue function. p53 isoform switching regulates replicative senescence in cultured fibroblasts and is associated with tumor progression. Here, we found that the endogenous p53 isoforms Δ133p53 and p53β are physiological regulators of proliferation and senescence in human T lymphocytes in vivo. Peripheral blood CD8+ T lymphocytes collected from healthy donors displayed an age-dependent accumulation of senescent cells (CD28-CD57+) with decreased Δ133p53 and increased p53β expression. Human lung tumor-associated CD8+ T lymphocytes also harbored senescent cells. Cultured CD8+ blood T lymphocytes underwent replicative senescence that was associated with loss of CD28 and Δ133p53 protein. In poorly proliferative, Δ133p53-low CD8+CD28- cells, reconstituted expression of either Δ133p53 or CD28 upregulated endogenous expression of each other, which restored cell proliferation, extended replicative lifespan and rescued senescence phenotypes. Conversely, Δ133p53 knockdown or p53β overexpression in CD8+CD28+ cells inhibited cell proliferation and induced senescence. This study establishes a role for Δ133p53 and p53β in regulation of cellular proliferation and senescence in vivo. Furthermore, Δ133p53-induced restoration of cellular replicative potential may lead to a new therapeutic paradigm for treating immunosenescence disorders, including those associated with aging, cancer, autoimmune diseases, and HIV infection.

Aging enhances release of exosomal cytokine mRNAs by Aβ1-42-stimulated macrophages

Amyloid-β1-42 (Aβ) peptide effects on human models of central nervous system (CNS)-patrolling macrophages (Ms) and CD4 memory T-cells (CD4-Tms) were investigated to examine immune responses to Aβ in Alzheimer's disease. Aβ and lipopolysaccharide (LPS) elicited similar M cytokine and exosomal mRNA (ex-mRNA) responses. Aβ- and LPS-stimulated Ms from 20 ≥65-yr-old subjects generated significantly more IL-1, TNF-α, and IL-6, but not IL-8 or IL-12, and significantly more ex-mRNAs for IL-6, TNF-α, and IL-12, but not for IL-8 or IL-1, than Ms from 20 matched 21- to 45-yr-old subjects. CD4-Tm generation of IL-2, IL-4, and IFN-γ and, for young subjects, IL-10, but not IL-6, evoked by Aβ was significantly lower than with anti-T-cell antigen receptor antibodies (Abs). Abs significantly increased all CD4-Tm ex-mRNAs, but only IL-2 and IL-6 ex-mRNAs were increased by Aβ. There were no significant differences between cytokine and ex-mRNA responses of CD4-Tms from the old compared to the young subjects. M-derived serum exosomes from the old subjects had significantly higher IL-6 and IL-12 ex-mRNA levels than those from the young subjects, whereas there were no differences for CD4-Tm-derived serum exosomes. An Aβ level relevant to neurodegeneration elicited broad M cytokine and ex-mRNA responses that were significantly greater in the old subjects, but only narrow and age-independent CD4-Tm responses.

Human lymphocyte repertoires in ageing

Deterioration of adaptive immunity with ageing may reflect changes in the repertoire of T cells and B cells available to respond to antigenic challenges, due to altered proportions and absolute numbers of lymphocyte subpopulations as well as changes in the repertoire of antigen receptor genes expressed by these cells. High-throughput DNA sequencing (HTS) now facilitates examination of immunoglobulin and T cell receptor gene rearrangements, and initial studies using these methods to study immune system ageing in humans have demonstrated age-related alterations in the receptor populations within lymphocyte subsets, as well as in repertoires responding to vaccination. Accurate measurement of repertoire diversity remains an experimental challenge. Studies of larger numbers of human subjects, analysis of defined lymphocyte subpopulations including antigen-specific populations, and controlling for factors such as chronic viral infections, will be important for gaining additional understanding of the impact of ageing on human lymphocyte populations.

Immunosenescence and novel vaccination strategies for the elderly

Vaccination remains the most effective prophylactic intervention for infectious disease in the healthcare professional's toolkit. However, the efficacy and effectiveness of vaccines decrease with age. This becomes most apparent after an individual reaches 65-70 years old, and results from complex changes in the immune system that occur during aging. As such, new vaccine formulations and strategies that can accommodate age-related changes in immunity are required to protect this expanding population. Here, we summarize the consequences of immunosenescence on vaccination and how novel vaccination strategies can be designed to accommodate the aging immune system. We conclude that current vaccination protocols are not sufficient to protect our aging population and, in some cases, are an inefficient use of healthcare resources. However, researchers and clinicians are developing novel vaccination strategies that include modifying who and when we vaccinate and capitalize on existing vaccines, in addition to formulating new vaccines specifically tailored to the elderly in order to remedy this deficiency.

Coming of age: molecular drivers of aging and therapeutic opportunities

Aging is like the weather: everyone talks about it, but no one seems to do anything about it. We believe this may soon change, as an improved understanding of the molecular and genetic pathways underlying aging suggests it is possible to therapeutically target the aging process and increase health span. This Review series focuses on fundamental cellular mechanisms of aging and their relationship to human disease. These pathways include telomere dysfunction in cellular senescence and induction of the senescence-associated secretory phenotype (SASP) in systemic aging, sirtuin family regulation of metabolism and aging-associated diseases, mitochondrial metabolism in aging, the mechanistic target of rapamycin (mTOR) signaling pathway and the use of mTOR inhibitors to increase longevity, the progressive decline of the immune system with age, and aging-associated changes to pancreatic islet β cells that may contribute to diabetes. Together, these articles explore pathways affecting aging and possible interventional targets to slow or delay the onset of age-related pathologies.