Immunosenescence of ageing

Aged human thymus hassall's corpuscles are immunoreactive for IGF-I and IGF-I receptor

Although Hassall's corpuscles have been proposed to act in both maturation of developing thymocytes and removal of apoptotic cells, their function remains an enigma. The involvement of insulin-like growth factor I (IGF-I) in the local autocrine and paracrine control of T-cell development in human thymus is still unclear. In this study, we investigated the structure and distribution of IGF-I and IGF-I receptor (IGF-IR)-immunopositive Hassall's corpuscles in aged human thymus using bright-field immunohistochemistry and immunoelectron microscopy. We report new immunocytochemical data for the presence of IGF-I/IGF-IR double-immunopositive Hassall's corpuscles in structurally preserved regions of age-involuted thymus and discuss the involvement of these unique thymic components in the local regulation of T-cell development and thymus plasticity during aging by IGF-I/IGF-IR-mediated cell signaling pathway.

Sympathetic innervation of the spleen in male Brown Norway rats: a longitudinal aging study

Aging leads to reduced cellular immunity with consequent increased rates of infectious disease, cancer, and autoimmunity in the elderly. The sympathetic nervous system (SNS) modulates innate and adaptive immunity via innervation of lymphoid organs. In aged Fischer 344 (F344) rats, noradrenergic (NA) nerve density in secondary lymphoid organs declines, which may contribute to immunosenescence with aging. These studies suggest there is SNS involvement in age-induced immune dysregulation. The purpose of this study was to longitudinally characterize age-related change in sympathetic innervation of the spleen and sympathetic activity/tone in male Brown Norway (BN) rats, which live longer and have a strikingly different immune profile than F344 rats, the traditional animal model for aging research. Splenic sympathetic neurotransmission was evaluated between 8 and 32 months of age by assessing (1) NA nerve fiber density, (2) splenic norepinephrine (NE) concentration, and (3) circulating catecholamine levels after decapitation. We report a decline in NA nerve density in splenic white pulp (45%) at 15 months of age compared with 8-month-old (M) rats, which is followed by a much slower rate of decline between 24 and 32 months. Lower splenic NE concentrations between 15 and 32 months of age compared with 8M rats were consistent with morphometric findings. Circulating catecholamine levels after decapitation stress generally dropped with increasing age. These findings suggest there is a sympathetic-to-immune system dysregulation beginning at middle age. Given the unique T-helper-2 bias in BN rats, altered sympathetic-immune communication may be important for understanding the age-related rise in asthma and autoimmunity.

Immunosenescence and vaccination of the elderly, I. Age-related immune impairment

The sharp increase of life expectancy and the increasing ratio of ageing population pose new challenges for the public health system. The elderly suffer from more frequent and severe infections than young people. Theoretically, vaccination could protect the elderly against several infectious diseases, but due to their age-related immune impairment, vaccination might fail in many cases. Instead of ineffective vaccination campaigns, exploration and restoration of age-dependent dysregulation of their immune functions have to be placed into the focus of recent research. Frequent comorbidities in these people augment immune defects. Immunosenescence affects both the innate and adaptive immunity. Disturbances in macrophage-derived cytokine release and reduction of the natural killer cell mediated cytotoxicity lead to increased frequency of respiratory, gastrointestinal and skin infections. Although the humoral immunity retains most of its original activity through life span, ageing dampens the ability of B cells to produce antibodies against novel antigens. Age-related declination of the cellular immunity is the consequence of thymic atrophy, reduced output of new T lymphocytes, accumulation of anergic memory cells, deficiencies in the cytokine production and uncertain antigen presentation. Persistent infection by different herpesviruses and other parasites contribute to the loss of immunosurveillance and premature exhaustion of T cells.

Premature immunosenescence in HIV-infected patients on highly active antiretroviral therapy with low-level CD4 T cell repopulation

OBJECTIVES

To analyse the role of thymic function and its association with cellular immunosenescence markers in patients with low-level CD4 T cell repopulation, despite complete HIV RNA replication control on highly active antiretroviral therapy (HAART).

METHODS

Cellular immunosenescence markers comparing patients with CD4 T cell counts <or=250 cells/mm(3) for >or=48 weeks (n = 11) and patients with a CD4 T cell count >or=500 cells/mm(3) (n = 11) were investigated. Both groups were also compared with 11 healthy volunteers of similar age. Naive CD4 T cell counts, beta- and delta-T cell rearrangement excision circles, recent thymic emigrants, replicative senescence marker, cell activation, and rate of apoptosis were analysed. The Mann-Whitney U-test was used to compare parameters between both low-level and high-level CD4 T cell repopulation groups, and healthy volunteers.

RESULTS

Our results showed a lower thymic activity in patients with low-level CD4 T cell repopulation, leading to a decline in CD4 T cell production. On the other hand, a higher activation along with a higher replicative senescence of CD4 T cells contributed to a higher rate of apoptotic CD4 T cells in this group of patients.

CONCLUSIONS

We propose a model with several different related mechanisms involved in premature immune senescence in HIV-infected patients with low-level CD4 repopulation on HAART. The understanding of such different mechanisms could help find effective strategies to prevent immune decay.

Ageing in a variable habitat: environmental stress affects senescence in parasite resistance in St Kilda Soay sheep

Despite widespread empirical evidence for a general deterioration in the majority of traits with advancing age, it is unclear whether the progress of senescence is chronologically determined, or whether factors such as environmental conditions experienced over the lifespan are more important. We explored the relative importance of ‘chronological’ and ‘environmental’ measures of age to changes in parasite resistance across the lifespan of free-living Soay sheep. Our results show that individuals experience an increase in parasite burden, as indicated by gastrointestinal helminth faecal egg count (FEC) with chronological age. However, chronological age fails to fully explain changes in FEC because a measure of environmental age, cumulative environmental stress, predicts an additional increase in FEC once chronological age has been accounted for. Additionally, we show that in females age-specific changes are dependent upon the environmental conditions experienced across individuals' life histories: increases in FEC with age were greatest among individuals that had experienced the highest degree of stress. Our results illustrate that chronological age alone may not always correspond to biological age, particularly in variable environments. In these circumstances, measures of age that capture the cumulative stresses experienced by an individual may be useful for understanding the process of senescence.

The role of immunity in elderly cancer

The increased incidence of malignancies in elderly patients living in industrialized countries has led to both identify the causes that alter the normal homeostatic balance in elderly and designate the specific treatments. The progressive decline of the immune system (immunosenescence) involving cellular and molecular alterations impact both innate and adaptive immunity. The immunosenescence leads to increased incidence of infectious diseases morbidity and mortality as well as heightened rates of other immune disorders such as autoimmunity, cancer, and inflammatory conditions. Here, we summarize the knowledge on the major changes in the immune system associated with aging in primary lymphoid organs as well as a description of molecular mechanisms, and the impact on cancer development.

Zinc supplementation increases zinc status and thymopoiesis in aged mice

The age-related decline in lymphocyte development and function coincides with impaired zinc status in the elderly. Thymic involution and reduced immune responsiveness are classic hallmarks of both aging and zinc deficiency, resulting in decreased host defense and an increased susceptibility to infections. Thus, compromised zinc status associated with aging may be an important contributing factor in reduced thymopoiesis and impaired immune functions. Our goal in this study was to understand how dietary zinc supplementation affects thymopoiesis in aged mice. We hypothesized that impaired zinc status associated with aging would mediate the decline in thymic function and output and that restoring plasma zinc concentrations via zinc supplementation would improve thymopoiesis and thymic functions. In this study, groups of young (8 wk) and aged (22 mo) mice were fed a zinc-adequate (30 mg/kg zinc) or zinc-supplemented diet (300 mg/kg) for 25 d. Aged mice had impaired zinc status, with zinc supplementation restoring plasma zinc to a concentration not different from those of young male C57Bl/6 mice. Zinc supplementation in aged mice improved thymopoiesis, as assessed by increased total thymocyte numbers. In addition, improved thymic output was mediated in part by reducing the age-related accumulation of immature CD4(-)CD8(-)CD44(+)CD25(-) thymocytes, as well as by decreasing the expression of stem cell factor, a thymosuppressive cytokine. Taken together, our results showed that in mice, zinc supplementation can reverse some age-related thymic defects and may be of considerable benefit in improving immune function and overall health in elderly populations.

The stressed host response to infection: the disruptive signals and rhythms of systemic inflammation

The cognate signals from sterile or pathogen-induced sources converge on the same recognition or response pathways. In the surgical patient, a systemic response to infection most often occurs in the context of ongoing inflammatory stress. Such an inflammatory response is modulated initially by the magnitude of injury and by patient-specific (endogenous) factors, such as confounding illness, age, and genetic variation. Over an extended period of stress, treatmentrelated (exogenous) factors add unpredictability to host responses to subsequent challenges, such as acquired infection. The host response is discussed in the context of how existing sterile stressors may modify the response to acquired infection in surgical patients.

Thymic involution and immune reconstitution

Chronic thymus involution associated with aging results in less efficient T-cell development and decreased emigration of naïve T cells to the periphery. Thymic decline in the aged is linked to increased morbidity and mortality in a wide range of clinical settings. Negative consequences of these effects on global health make it of paramount importance to understand the mechanisms driving thymic involution and homeostatic processes across the lifespan. There is growing evidence that thymus tissue is plastic and that the involution process might be therapeutically halted or reversed. We present here progress on the exploitation of thymosuppressive and thymostimulatory pathways using factors such as keratinocyte growth factor, interleukin 7 or sex steroid ablation for therapeutic thymus restoration and peripheral immune reconstitution in adults.

B cells and aging: molecules and mechanisms

Recent advances allow aging-associated changes in B-cell function to be approached at a mechanistic level. Reduced expression of genes crucial to lineage commitment and differentiation yield diminished B-cell production. Moreover, intrinsic differences in the repertoire generated by B-cell precursors in aged individuals, coupled with falling B-cell generation rates and life-long homeostatic competition, result in narrowed clonotypic diversity. Similarly, reductions in gene products crucial for immunoglobulin class switch recombination and somatic hypermutation impact the efficacy of humoral immune responses. Together, these findings set the stage for integrated analyses of how age-related changes at the molecular, cellular and population levels interact to yield the overall aging phenotype.

Immune senescence and brain aging: can rejuvenation of immunity reverse memory loss?

The factors that determine brain aging remain a mystery. Do brain aging and memory loss reflect processes occurring only within the brain? Here, we present a novel view, linking aging of adaptive immunity to brain senescence and specifically to spatial memory deterioration. Inborn immune deficiency, in addition to sudden imposition of immune malfunction in young animals, results in cognitive impairment. As a corollary, immune restoration at adulthood or in the elderly results in a reversal of memory loss. These results, together with the known deterioration of adaptive immunity in the elderly, suggest that memory loss does not solely reflect chronological age; rather, it is an outcome of the gap between an increasing demand for maintenance (age-related risk-factor accumulation) and the reduced ability of the immune system to meet these needs.

Thymopoiesis in elderly human is associated with systemic inflammatory status

Immunosenescence studies of age-related immune system damage focused on clinical lymphopenic situations or androgenic blockade have revealed new insights about adult human immune reconstitution. However, as far as we know, the extent of lymphopoiesis in the thymus of elderly humans remains unclear. To this effect, we have analyzed 65 adult human thymuses (from 36 to 81 years; median age 68.6 years) obtained from patients who underwent cardiac surgery. Our results show a correlation between CD4(+)CD8(+) double-positive (DP) cells and both the age (inverse) and percentage (direct) of peripheral naive T cells, indicating that the thymus is still able to affect the peripheral lymphocyte pool even in the elderly. We also found significant correlation between the degree of thymopoiesis and the inflammation markers, as shown by the inverse correlations between DP and the percentage of neutrophils and IL-6 levels and the percentage of peripheral lymphocytes. Furthermore, in a multivariate linear regression the percentage of DP and IL-7 levels, but not age, were independently associated with the percentage of neutrophils. In conclusion, the thymus maintains, even in the elderly, an active thymopoiesis that rejuvenates the peripheral naive T-cell pool. Moreover, age-related thymopoietic decay is associated with the peripheral inflammation markers.

BONE MARROW, THYMUS AND BLOOD: CHANGES ACROSS THE LIFESPAN

The aim of this review is to present age-related changes in the bone marrow and thymus and their effects in later life. Age-related hematologic changes are marked by a decline in marrow cellularity, increased risk of myeloproliferative disorders and anemia, and a decline in adaptive immunity. The exact mechanisms that produce these changes remain undefined. For the most part, the changes in function that are a consequence of aging alone rarely have meaningful clinical consequences. However, in the face of the stresses induced by other illnesses, the decreased physiologic reserve can slow or prevent an appropriate response to the stressors.

Influence of acute epinephrine infusion on endotoxin-induced parameters of heart rate variability: a randomized controlled trial

OBJECTIVE

To determine whether the acute anti-inflammatory influence of epinephrine (EPI) extends to changes in heart rate variability (HRV) induced by the prototypical inflammatory stimulus, endotoxin (lipopolysaccharide [LPS]).

SUMMARY BACKGROUND DATA

HRV reflects fluctuating cardiac autonomic inputs and is acutely reduced during the systemic inflammation induced by LPS as well as during severe critical illnesses such as sepsis and traumatic injury. While EPI may diminish proinflammatory cytokine release, it is unknown whether this net anti-inflammatory activity extends to HRV.

METHODS

Healthy volunteers (n = 17) were randomized to either saline + LPS (2 ng/kg) or LPS + antecedent EPI infusion (30 ng/kg/min) from -3 to 6 hours relative to LPS. HRV and blood samples were obtained before EPI and LPS as well as hourly afterward. Plasma cytokines were measured by ELISA. Statistical analysis was by repeated measures analysis of variance. This study was registered at Clinicaltrials.gov and is listed under the following ID number: NCT00753402.

RESULTS

LPS acutely influenced all measured parameters of HRV including standard deviation of the average beat to beat intervals over a 5-minute period, percentage of interval differences of successive interbeat intervals greater than 50 milliseconds and square root of the mean squared differences, high frequency (HF), low frequency, low frequency/HF, and very low frequency (all P < 0.01). EPI infusion reduced the inflammatory cytokine response to LPS as measured by decreased TNFalpha, IL-6, and IL-8 (P < 0.01). Relative to the saline + LPS group, antecedent EPI infusion was associated with further reductions in parameters of HRV measuring vagal/parasympathetic activity including, percentage of interval differences of successive interbeat intervals greater than 50 milliseconds, square root of the mean squared differences, and HF (P < 0.05).

CONCLUSION

Prior EPI exposure exerts anti-inflammatory influences but also may reduce vagus nerve activity. Hence, acute EPI administration may be protective against early inflammatory challenges but diminish vagal nerve responsiveness to subsequent stimuli.

TLR4 polymorphisms and ageing: implications for the pathophysiology of age-related diseases

INTRODUCTION

Innate immunity provides a first line of host defense against infection by recognizing and killing microbes while simultaneously activating an instructive immune response. Toll-like receptors (TLRs) are principal mediators of rapid microbial recognition and function mainly by detection of pathogen-associated molecular patterns that do not exist in the host. Recognition of their ligands leads to a series of signaling events resulting in acute host responses, involved in killing pathogens.

DISCUSSION

We describe the involvement of TLR4 polymorphisms in ageing, and in particular in age-related diseases, suggesting the crucial role of molecules of innate immunity in pathophysiology of these diseases. Hence, we observed that pro-inflammatory alleles may be related to unsuccessful ageing, such as Alzheimer's disease, prostate cancer, and atherosclerosis; in contrast, the control of inflammation by anti-inflammatory alleles may result in increased longevity and successful ageing. Finally, a possible therapeutic approach to delay age-related diseases is outlined.

Age-associated parallel increase of Foxp3(+)CD4(+) regulatory and CD44(+)CD4(+) memory T cells in SJL/J mice

Effector/memory T cells (Tem) are required to maintain successful immunity, while regulatory T cells (Treg) are required to prevent excessive/uncontrolled inflammation and/or autoimmunity. Although both Tem and Treg cells are increased during aging, the relationship between the increased proportion of Foxp3(+) Treg cells and CD44(+) Tem cells with aging is not clearly understood. We found in this report that Foxp3(+) Treg cells are increased in parallel with CD44(+) Tem cells in SJL/J mice with aging, and that all Foxp3(+) Treg cells are of CD44(+) Tem phenotype, suggesting that the increased Foxp3(+) Treg cells originated from the expanded pool of CD44(+) Tem cells with aging. Our in vitro kinetic studies further suggested that Foxp3(+) Treg cells are converted through the CD44(+) stage. Furthermore, we observed that although the balance between Foxp3(+) Treg and CD44(+)Foxp3(-) Tem cells remained with aging, the aged mice have higher ratios of both Tem and Treg cells vs. naïve T cells resulting in the "shrunken" naïve T cell pools. Our results suggest that an age-associated imbalance of T cell repertoire is a mechanism that contributes to spontaneous occurrence of Hodgkin's-like lymphoma in aged SJL/J mice.

Mitochondria-targeted antioxidant SkQ1 inhibits age-dependent involution of the thymus in normal and senescence-prone rats

One of the most striking changes during mammal aging is a progressive involution of the thymus, associated with an increase in susceptibility to infections, autoimmune diseases and cancer. In order to delay age-related processes, we have developed mitochondria-targeted antioxidant plastoquinonyl decyltriphenyl phosphonium (SkQ1). Here we report that, at low doses, SkQ1 (250 nmol/kg per day) inhibited age-dependent involution of the thymus in normal (Wistar) and senescence-prone (OXYS) rats. SkQ1 preserved total weight and volume of the organ, the volume of thymic cortex and medulla, the thymic cellularity, and the number of CD3+, CD4+, and CD8+ cells in the thymus. Moreover, SkQ1 was especially effective in senescence-prone rats.   Thus SkQ1 slows down age-linked decline of the immune system, explaining prevention by this compound of infection-caused death in rodents, previously described in our group.

Exclusive expression of proteasome subunit {beta}5t in the human thymic cortex

The ubiquitin-proteasome pathway, which degrades intracellular proteins, is involved in numerous cellular processes, including the supply of immunocompetent peptides to the antigen presenting machinery. Proteolysis by proteasomes is conducted by three beta subunits, beta1, beta2, and beta5, of the 20S proteasome. Recently, a novel beta subunit expressed exclusively in cortical thymic epithelial cells was discovered in mice. This subunit, designated beta5t, is a component of the thymoproteasome, a specialized type of proteasomes implicated in thymic positive selection. In this study, we show that, like its mouse counterpart, human beta5t is expressed exclusively in the thymic cortex. Human beta5t was expressed in approximately 80% of cortical thymic epithelial cells and some cortical dendritic cells. Human beta5t was incorporated into proteasomes with two other catalytically active beta subunits beta1i and beta2i, forming 20S proteasomes with subunit compositions characteristic of thymoproteasomes. The present study demonstrates, for the first time, the existence of thymoproteasomes in the human thymic cortex, indicating that thymoproteasome function is likely conserved between humans and mice.

Trends in postoperative sepsis: are we improving outcomes?

BACKGROUND AND PURPOSE

Each year, as many as two million operations are complicated by surgical site infections in the United States, and surgical patients account for 30% of patients with sepsis. The purpose of this study was to determine recent trends in sepsis incidence, severity, and mortality rate after surgical procedures and to evaluate changes in the pattern of septicemia pathogens over time.

METHODS

Analysis of the 1990-2006 hospital discharge data from the Healthcare Cost and Utilization Project (HCUP) State Inpatient Databases (SID) for New Jersey. Patients >or= 18 years who developed sepsis after surgery were identified using International Classification of Diseases, Ninth Revision, Clinical Modification codes as defined by the Patient Safety Indicator "Postoperative Sepsis" developed by the Agency for Healthcare Research and Quality (AHRQ). Severe sepsis was defined as sepsis complicated by organ dysfunction.

RESULTS

A total of 1,276,451 surgery discharges (537,843 elective [42.1%] and 738,608 non-elective [57.9%] procedures) were identified. After elective surgery, 5,865 patients (1.09%) developed postoperative sepsis, of whom 2,778 (0.52%) had severe sepsis. The incidence of postoperative sepsis after elective surgery increased from 0.67% to 1.74% (p < 0.0001) and severe sepsis after elective surgery from 0.22% to 1.12% (p < 0.0001). The sepsis mortality rate for elective procedures showed no significant change over time. The proportion of severe sepsis after elective cases increased from 32.9% to 64.6% (p < 0.0002). The rates of postoperative sepsis (4.24%) and severe sepsis (2.28%) were significantly greater for non-elective than for elective procedures (p < 0.0002). Non-elective surgical procedures had a significant increase in the rates of postoperative sepsis (3.74% to 4.51%) and severe sepsis (1.79% to 3.15%) over time (p < 0.0001) with the proportion of severe sepsis increasing from 47.7% to 69.9% (p < 0.0002). The in-hospital mortality rate after non-elective surgery decreased from 37.9% to 29.8% (p < 0.0001).

CONCLUSIONS

Sepsis and death were more likely after non-elective than elective surgery. Sepsis and severe sepsis has increased significantly after elective and non-elective procedures over the last 17 years. The hospital mortality rate was reduced significantly after non-elective surgery, but no improvements were found for elective surgery patients who developed sepsis. Disparities in age, sex, and ethnicity and the development of postoperative surgical sepsis were found. Population-based studies may assist in defining temporal trends, disparities, and outcomes in sepsis not elucidated in smaller studies.

An epithelial progenitor pool regulates thymus growth

Thymic epithelium provides an essential cellular substrate for T cell development and selection. Gradual age-associated thymic atrophy leads to a reduction in functional thymic tissue and a decline in de novo T cell generation. Development of strategies tailored toward regeneration of thymic tissue provides an important possibility to improve immune function in elderly individuals and increase the capacity for immune recovery in patients having undergone bone marrow transfer following immunoablative therapies. In this study we show that restriction of the size of the functional thymic epithelial progenitor pool affects the number of mature thymic epithelial cells. Using an embryo fusion chimera-based approach, we demonstrate a reduction in the total number of both embryonic and adult thymic epithelium, which relates to the initial size of the progenitor cell pool. The inability of thymic epithelial progenitor cells to undergo sufficient compensatory proliferation to rescue the deficit in progenitor numbers suggests that in addition to extrinsic regulation of thymus growth by provision of growth factors, intrinsic factors such as a proliferative restriction of thymic epithelial progenitors and availability of progenitor cell niches may limit thymic epithelial recovery. Collectively, our data demonstrate an important level of regulation of thymic growth and recovery at the thymic epithelial progenitor level, providing an important consideration for developing methods targeted toward inducing thymic regeneration.

Decreased MT1 and MT2 melatonin receptor expression in extrapineal tissues of the rat during physiological aging

Aging is a complex process associated with a diminished ability to respond to stress, a progressive increase in free radical generation and a decline in immune function. Melatonin, a molecule with a great functional versatility exerts anti-oxidant, oncostatic, immunomodulatory, and anti-aging properties. Melatonin levels drop during aging and it has been speculated that the loss of melatonin may accelerate aging. This study was designed to elucidate whether aging involves responsiveness to reduced melatonin. Melatonin membrane receptor (MT1 and MT2) expression and MT1 protein expression were analyzed in extrapineal tissues (thymus, spleen, liver, kidney, and heart) of 3- and 12-month-old rats using real time polymerase chain reaction and western blotting analysis. Moreover, melatonin in tissues was measured by high performance liquid chromatography. We report for the first time, an age-related reduction in mRNA MT1 and MT2 expression levels as well as MT1 protein expression in all tissues tested except the thymus, where surprisingly, both melatonin receptor levels were significantly higher in 12-month-old rats and MT1 protein expression maintained unchanged with age. Diminished melatonin concentrations were measured in spleen, liver, and heart during aging. As a conclusion, physiological aging seems to exert responsiveness to melatonin and consequently, the loss of this potent anti-oxidant may contribute to onset of aging.

Transcriptome analysis of murine thymocytes reveals age-associated changes in thymic gene expression

The decline in adaptive immunity, naïve T-cell output and a contraction in the peripheral T cell receptor (TCR) repertoire with age are largely attributable to thymic involution and the loss of critical cytokines and hormones within the thymic microenvironment. To assess the molecular changes associated with this loss of thymic function, we used cDNA microarray analyses to examine the transcriptomes of thymocytes from mice of various ages ranging from very young (1 month) to very old (24 months). Genes associated with various biological and molecular processes including oxidative phosphorylation, T- and B- cell receptor signaling and antigen presentation were observed to significantly change with thymocyte age. These include several immunoglobulin chains, chemokine and ribosomal proteins, annexin A2, vav 1 and several S100 signaling proteins. The increased expression of immunoglobulin genes in aged thymocytes could be attributed to the thymic B cells which were found to be actively producing IgG and IgM antibodies. Upon further examination, we found that purified thymic T cells derived from aged but not young thymi also exhibited IgM on their cell surface suggesting the possible presence of auto-antibodies on the surface thymocytes with advancing age. These studies provide valuable insight into the cellular and molecular mechanisms associated with thymic aging.

Premature senescence of T lymphocytes from patients with beta-thalassemia major

Several researches have demonstrated a suppressed cell mediated immunity in patients with beta-thalassemia major. To know whether the premature aging of T cells is involved in abnormalities of cell mediated immunity, the biomarkers of immunosenescence including telomerase activity, apoptosis, and the expression of CD28 and CD95 were evaluated in T lymphocytes from beta-thalassemia major patients. The ex vivo spontaneous apoptosis in CD4(+) or CD8(+) T cells from patients and healthy subjects was assessed by an in situ TdT mediated dUTP-biotin nick end labelling (TUNEL) assay after 24h incubation in medium. Flow cytometric data revealed that lymphocytes from beta-thalassemia patients were resistant to spontaneous apoptosis compared to the normal lymphocytes. Moreover, the percentages of TUNEL(+)CD4(+) or TUNEL(+)CD8(+) T cells from patients were significantly lower than those control cells. Quantitative determination of telomerase activity in resting and activated T cells was performed using the Telomeric Repeat Amplification Protocol (TRAP). The results showed a decreased telomerase activity of activated T cells in patients with thalassemia major compared to that in healthy controls. However, the percentages of CD8(+)CD28(-) and CD3(+)CD95(+) T lymphocytes were significantly higher in thalassemia patients, indicating the phenotypes associated with senescent T lymphocytes. These data provide evidences for the occurrence of accelerated aging of T cells in beta-thalassemia major; possibly result in abnormal T cell function leading to suppressed cell mediated immunity.

Does senescence give rise to disease?

The distinctions between senescence and disease are blurred in the literature of evolutionary biology, biodemography, biogerontology and medicine. Theories of senescence that have emerged over the past several decades are based on the concepts that organisms are a byproduct of imperfect structural designs built with imperfect materials and maintained by imperfect processes. Senescence is a complex mixture of processes rather than a monolithic process. Senescence and disease have overlapping biological consequences. Senescence gives rise to disease, but disease does not give rise to senescence. Current data indicate that treatment of disease can delay the age of death but there are no convincing data that these interventions alter senescence. An understanding of these basic tenets suggests that there are biological limits to duration of life and the life expectancy of populations and reveal biological domains where the development of interventions and/or treatments may modulate senescence.

Optimal window of caloric restriction onset limits its beneficial impact on T-cell senescence in primates

We have recently shown in non-human primates that caloric restriction (CR) initiated during adulthood can delay T-cell aging and preserve naïve CD8 and CD4 T cells into advanced age. An important question is whether CR can be initiated at any time in life, and whether age at the time of onset would modulate the beneficial effects of CR. In the current study, we evaluated the impact of CR started before puberty or during advanced age on T-cell senescence and compared it to the effects of CR started in early adulthood. Our data demonstrate that the beneficial effects of adult-onset CR on T-cell aging were lost by both early and late CR onset. In fact, some of our results suggest that inappropriate initiation of CR may be harmful to the maintenance of T-cell function. This suggests that there may be an optimal window during adulthood where CR can delay immune senescence and improve correlates of immunity in primates.

Current status and future prospects in the search for protein biomarkers of immunosenescence

Complex adaptations including changes in cellular redox status, the production of high levels of pro-inflammatory cytokines and alterations in immunity occur as the result of aging of the immune system (immunosenescence). These events are thought to underlie the progression of chronic degenerative diseases of aging, such as atherosclerosis, Type 2 diabetes and Alzheimer's disease. It is envisaged that identifying early biomarkers of immune aging would aid in identifying individuals at risk of age-related disease and would allow the discovery of novel intervention strategies. Proteomics has emerged as a rapidly expanding and innovative field, investigating protein expression, interaction and function at a global level. Several proteomic strategies, including use of mass spectrometry and non-mass spectrometry-based detection systems (including secondary antibody labeling with fluorescent tags) may be particularly advantageous in identifying biomarkers of immune health. Application of these approaches may identify factors that both contribute to (and define) age-dependent deregulation of the immune system.

Antigen-independent generation of a unique CD4 T cell-subset with aging and its persistent unresponsiveness

Aging leads to a decline in the reactivity of CD4 T cells, in humans and mice. However, we have reported that not all CD4 T cells in aged mice were hyporesponsive, that is, a particular subset maintained the ability to mount a normal response. In this study, we examined the possibility of recalling reactivity in the hyporesponsive CD4 T cell-subset in aged mice. In vivo experiments revealed the changes in CD4 T cell-subsets in aged mice to be antigen-independent and aging-dependent. Once the CD4 T cells became hyporesponsive, they persistently exhibited a weak response. Furthermore, immunization with a co-stimulatory antibody had no effect on T cell-responses in aged mice, although it had a significant effect in young mice. As this hyporesponsive subset accounts for the majority of CD4 T cells in aged mice, it is important to elucidate the cause of the hyporesponsiveness.

Strategies for reconstituting and boosting T cell-based immunity following haematopoietic stem cell transplantation: pre-clinical and clinical approaches

Poor immune recovery is characteristic of bone marrow transplantation and leads to high levels of morbidity and mortality. The primary underlying cause is a compromised thymic function, resulting from age-induced atrophy and further compounded by the damaging effects of cytoablative conditioning regimes on thymic epithelial cells (TEC). Several strategies have been proposed to enhance T cell reconstitution. Some, such as the use of single biological agents, are currently being tested in clinical trials. However, a more rational approach to immune restoration will be to leverage the evolving repertoire of new technologies. Specifically, the combined targeting of TEC, thymocytes and peripheral T cells, together with the bone marrow niches, promises a more strategic clinical therapeutic platform.

Composition and function of haemolymphatic tissues in the European common shrew

BACKGROUND

Studies of wild animals responding to their native parasites are essential if we are to understand how the immune system functions in the natural environment. While immune defence may bring increased survival, this may come at a resource cost to other physiological traits, including reproduction. Here, we tested the hypothesis that wild common shrews (Sorex araneus), which produce large numbers of offspring during the one breeding season of their short life span, forgo investment in immunity and immune system maintenance, as increased longevity is unlikely to bring further opportunities for mating. In particular, we predicted that adult shrews, with shorter expected lifespans, would not respond as effectively as young animals to infection.

METHODOLOGY/PRINCIPAL FINDINGS

We examined haemolymphatic tissues from wild-caught common shrews using light and transmission electron microscopy, applied in conjunction with immunohistology. We compared composition and function of these tissues in shrews of different ages, and the extent and type of inflammatory reactions observed in response to natural parasitic infections. All ages seemed able to mount systemic, specific immune responses, but adult shrews showed some signs of lymphatic tissue exhaustion: lymphatic follicles in adults (n = 21) were both smaller than those in sub-adults (n = 18; Wald = 11.1, p<0.05) and exhibited greater levels of depletion (Wald = 13.3, p<0.05).

CONCLUSIONS/SIGNIFICANCE

Contrary to our expectations, shrews respond effectively to their natural parasites, and show little indication of immunosenescence as adults. The pancreas of Aselli, a unique lymphoid organ, may aid in providing efficient immune responses through the storage of large numbers of plasma cells. This may allow older animals to react effectively to previously encountered parasites, but infection by novel agents, and eventual depletion of plasma cell reserves, could both still be factors in the near-synchronous mortality of adult shrews observed shortly after breeding.

Age-related changes in the human thymus studied with scanning electron microscopy

This investigation describes some morphological, age-related changes in different compartments and cells of the human thymus. Scanning electron microscopic observations were done on human thymus samples obtained from four young and eight elderly patients during thoracic surgery and/or diagnostic biopsy of the thymus, after receiving authorization from the Ethical Committee of our university. The morphological data were submitted to quantitative image analysis so as to obtain quantitative results. Subsequently, the related values were used for statistical analysis. Our findings demonstrate that (1) all thymus compartments (subcapsular spaces, cortical, medullar, thymus microenvironment) contain numerous thymocytes even after the thymus has aged. (2) In older humans, residual thymus lymphoid islets contain, in addition to fatty cells and/or fibrous cells, also the same types of resident and nonresident cells (permanent and moving cells) that are found in young and adult subjects. (3) Endothelial cells of thymus microvessels contain numerous gaps. These gaps are tight in young subjects and become loose with age. (4) Thymocytes, in older subjects, are always found near these loose endothelial gaps of thymus microvessels. (5) While thymus cortical microvessels are provided with pericytes and/or periarteriolar spaces, microvessels of the thymus medullar are free of such spaces. Our morphological and quantitative results lead us to consider the possibility that the thymus fraction of resident and permanent cells (including thymocytes and reticular epithelial cells) is larger in younger subjects compared with older ones. The endothelial loose gaps of thymus microvessels, in older subjects, can allow the bidirectional transit of thymocytes through the wall of the said microvessels.

Calorie restriction and susceptibility to intact pathogens

Long-term calorie restriction (CR) causes numerous physiological changes that ultimately increase mean and maximum lifespan of most species examined to date. One physiological change that occurs with CR is enhanced immune function, as tested using antigens and mitogens to stimulate an immune response. Fewer studies have used intact pathogen exposure to test whether the enhanced capacity of the immune response during CR actually decreases susceptibility of hosts to their pathogens. So far, studies using intact bacteria, virus, and helminth worm exposure indicate that, despite similar or enhanced immune system function, CR hosts are more susceptible to infection by intact pathogens than their fully fed counterparts. Long-term CR studies that examine susceptibility to a variety of parasite taxa will help determine if direct CR or CR mimetics will be beneficial to people living in pathogen-rich environments.

Age-associated T-cell Clonal Expansions (TCE) in vivo—Implications for Pathogen Resistance

Age-related T-cell clonal expansions (TCE) are an incompletely understood disturbance in T-cell homeostasis found frequently in old humans and experimental animals. These accumulations of CD8 T-cells have the potential to distort T-cell population balance and reduce T-cell repertoire diversity above and beyond the changes seen in the aging of T-cell pool in the absence of TCE. This chapter discusses our current knowledge of the role of these expansions in health and disease, with a special focus on their influence upon immune defense against infectious diseases.

An exploration of the association between frailty and muscle fatigue

Frailty is increasingly recognized as a geriatric syndrome that shares common biomedical determinants with rapid muscle fatigue: aging, disease, inflammation, physical inactivity, malnutrition, hormone deficiencies, subjective fatigue, and changes in neuromuscular function and structure. In addition, there is an established relationship between muscle fatigue and core elements of the cycle of frailty as proposed by Fried and colleagues (sarcopenia, neuroendocrine dysregulation and immunologic dysfunction, muscle weakness, subjective fatigue, reduced physical activity, low gait speed, and weight loss). These relationships suggest that frailty and muscle fatigue are closely related and that low tolerance for muscular work may be an indicator of frailty phenotype.

Multiparameter flow cytometric analysis of CD4 and CD8 T cell subsets in young and old people

Background

T cell-mediated immunity in elderly people is compromised in ways reflected in the composition of the peripheral T cell pool. The advent of polychromatic flow cytometry has made analysis of cell subsets feasible in unprecedented detail.

Results

Here we document shifts in subset distribution within naïve (N), central memory (CM) and effector memory (EM) cells defined by CD45RA and CCR7 expression in the elderly, additionally using the costimulatory receptors CD27 and CD28, as well as the coinhibitory receptors CD57 and KLRG-1, to further dissect these. Although differences between young and old were more marked in CD8 than in CD4 cells, a similar overall pattern prevailed in both. Thus, the use of all these markers together, and inclusion of assays of proliferation and cytokine secretion, may enable the construction of a differentiation scheme applicable to CD4 as well as CD8 cells, with the model (based on Romero et al.) suggesting the progression N→CM→EM1→EM2→pE1→pE2→EM4→EM3→E end-stage non-proliferative effector cells.

Conclusion

Overall, the results suggest that both differences in subset distribution and differences between subsets are responsible for age-related changes in CD8 cells but that differences within rather than between subsets are more prominent for CD4 cells.

Ageing and life-long maintenance of T-cell subsets in the face of latent persistent infections

A decline in T-cell immunity is one of the most consistent and most profound deficiencies of the elderly. Therapeutic correction of this decline often restores immune responsiveness and immune defence.

T-cell immune decline in the elderly has at least two underpinnings: a drop in the responsiveness of naive T cells to stimulation (cell-autonomous defects) and a reduction in naive T-cell numbers and diversity that leads to a dominant memory T-cell pool (T-cell population imbalance).

This article discusses two key causes of age-related T-cell population imbalance: homeostatic cycling or proliferative expansion in the peripheral T-cell pool, and latent persistent infections, which repeatedly stimulate the T-cell pool over the lifetime of the individual.

The reduction in production of naive T cells by the thymus forces the ageing organism to rely on compensatory homeostatic mechanisms to maintain the balance between naive and memory T-cell pools. Although this may be initially successful, recent evidence suggests that late in life these mechanisms exhaust their usefulness and actually contribute to a further demise of the remaining naive T cells.

Latent persistent infections, particularly with herpesviruses, lead to life-long periodic restimulation of the immune system, here, evidence is presented for the role of viral reactivation in this restimulation using a mouse model of herpesvirus infection and ageing.

Relative roles and the interplay between the homeostatic and viral factors are discussed, with the former having a surprisingly prominent role. Finally, modes of immune rejuvenation and anti-ageing intervention are debated in light of these advances in our knowledge.

A decline in T-cell immunity is a major cause of morbidity and mortality from infectious diseases in the elderly. Janko Nikolich-Žugich weighs up the relative roles of and the interplay between homeostatic factors and persistent viruses in immune senescence.

A diverse and well-balanced repertoire of T cells is thought to be crucial for the efficacious defence against infection with new or re-emerging pathogens throughout life. In the last third of the mammalian lifespan, the maintenance of a balanced T-cell repertoire becomes highly challenging because of the changes in T-cell production and consumption. In this Review, I question whether latent persistent pathogens might be key factors that drive this imbalance and whether they determine the extent of age-associated immune deficiency.

Age-associated changes in immune and inflammatory responses: impact of vitamin E intervention

Aging is associated with dysregulated immune and inflammatory responses. Declining T cell function is the most significant and best-characterized feature of immunosenescence. Intrinsic changes within T cells and extrinsic factors contribute to the age-associated decline in T cell function. T cell defect seen in aging involves multiple stages from early receptor activation events to clonal expansion. Among extrinsic factors, increased production of T cell-suppressive factor PGE(2) by macrophages (Mphi) is most recognized. Vitamin E reverses an age-associated defect in T cells, particularly naïve T cells. This effect of vitamin E is also reflected in a reduced rate of upper respiratory tract infection in the elderly and enhanced clearance of influenza infection in a rodent model. The T cell-enhancing effect of vitamin E is accomplished via its direct effect on T cells and indirectly by inhibiting PGE(2) production in Mphi. Up-regulated inflammation with aging has attracted increasing attention as a result of its implications in the pathogenesis of diseases. Increased PGE(2) production in old Mphi is a result of increased cyclooxygenase 2 (COX-2) expression, leading to higher COX enzyme activity, which in turn, is associated with the ceramide-induced up-regulation of NF-kappaB. Similar to Mphi, adipocytes from old mice have a higher expression of COX-2 as well as inflammatory cytokines IL-1beta, IL-6, and TNF-alpha, which might also be related to elevated levels of ceramide and NF-kappaB activation. This review will discuss the above age-related immune and inflammatory changes and the effect of vitamin E as nutritional intervention with a focus on the work conducted in our laboratory.

Ageing in a eusocial insect: molecular and physiological characteristics of life span plasticity in the honey bee

Commonly held views assume that ageing, or senescence, represents an inevitable, passive, and random decline in function that is strongly linked to chronological age. In recent years, genetic intervention of life span regulating pathways, for example, in Drosophila as well as case studies in non-classical animal models, have provided compelling evidence to challenge these views.Rather than comprehensively revisiting studies on the established genetic model systems of ageing, we here focus on an alternative model organism with a wild type (unselected genotype) characterized by a unique diversity in longevity - the honey bee.Honey bee (Apis mellifera) life span varies from a few weeks to more than 2 years. This plasticity is largely controlled by environmental factors. Thereby, although individuals are closely related genetically, distinct life histories can emerge as a function of social environmental change.Another remarkable feature of the honey bee is the occurrence of reverted behavioural ontogeny in the worker (female helper) caste. This behavioural peculiarity is associated with alterations in somatic maintenance functions that are indicative of reverted senescence. Thus, although intraspecific variation in organismal life span is not uncommon, the honey bee holds great promise for gaining insights into regulatory pathways that can shape the time-course of ageing by delaying, halting or even reversing processes of senescence. These aspects provide the setting of our review.We will highlight comparative findings from Drosophila melanogaster and Caenorhabditis elegans in particular, and focus on knowledge spanning from molecular- to behavioural-senescence to elucidate how the honey bee can contribute to novel insights into regulatory mechanisms that underlie plasticity and robustness or irreversibility in ageing.

Histochemical and molecular overview of the thymus as site for T-cells development

The thymus represents the primary site for T cell lymphopoiesis, providing a coordinated set for critical factors to induce and support lineage commitment, differentiation and survival of thymus-seeding cells. One irrefutable fact is that the presence of non-lymphoid cells through the thymic parenchyma serves to provide coordinated migration and differentiation of T lymphocytes. Moreover, the link between foetal development and normal anatomy has been stressed in this review. Regarding thymic embryology, its epithelium is derived from the embryonic endodermal layer, with possible contributions from the ectoderm. A series of differentiating steps is essential, each of which must be completed in order to provide the optimum environment for thymic development and function. The second part of this article is focused on thymic T-cell development and differentiation, which is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. It depends strongly on the thymic microenvironment, a cellular network formed by epithelial cells, macrophages, dendritic cells and fibroblasts, that provide the combination of cellular interactions, cytokines and chemokines to induce thymocyte precursors for the generation of functional T cells. The mediators of this process are not well defined but it has been demonstrated that some interactions are under neuroendocrine control. Moreover, some studies pointed out that reciprocal signals from developing T cells also are essential for establishment and maintenance of the thymic microenvironment. Finally, we have also highlighted the heterogeneity of the lymphoid, non-lymphoid components and the multi-phasic steps of thymic differentiation. In conclusion, this review contributes to an understanding of the complex mechanisms in which the foetal and postnatal thymus is involved. This could be a prerequisite for developing new therapies specifically aimed to overcome immunological defects, linked or not-linked to aging.

The double-edged sword of statin immunomodulation

Statin drugs are widely prescribed to achieve aggressive low-density lipoprotein lowering in order to decrease cardiovascular disease. Although some of the immunomodulatory effects of statins may stabilize atherosclerotic plaque, they may be harmful in certain segments of the population. Recently, statins have been shown to increase the concentration of regulatory T cells (Tregs), in vivo. There is evidence that this increases the risk of many cancers, particularly in the elderly. Furthermore, a statin induced increase in Tregs may be detrimental in neurodegenerative disorders, such as amyotrophic lateral sclerosis; and a myriad of infectious diseases. These include, but are not limited to, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and varicella zoster virus. These issues need our attention, and call for a heightened state of vigilance among those prescribing statins.

Stem cells and aging in the hematopoietic system

The effector cells of the blood have limited lifetimes and must be replenished continuously throughout life from a small reserve of hematopoietic stem cells (HSCs) in the bone marrow. Although serial bone marrow transplantation experiments in mice suggest that the replicative potential of HSCs is finite, there is little evidence that replicative senescence causes depletion of the stem cell pool during the normal lifespan of either mouse or man. Studies conducted in murine genetic models defective in DNA repair, intracellular ROS management, and telomere maintenance indicate that all these pathways are critical to the longevity and stress response of the stem cell pool. With age, HSCs show an increased propensity to differentiate towards myeloid rather than lymphoid lineages, which may contribute to the decline in lymphopoiesis that attends aging. Challenges for the future include assessing the significance of 'lineage skewing' to immune dysfunction, and investigating the role of epigenetic dysregulation in HSC aging.

High titers of mucosal and systemic anti-PrP antibodies abrogate oral prion infection in mucosal-vaccinated mice

Significant outbreaks of prion disease linked to oral exposure of the prion agent have occurred in animal and human populations. These disorders are associated with a conformational change of a normal protein, PrP(C) (C for cellular), to a toxic and infectious form, PrP(Sc) (Sc for scrapie). None of the prionoses currently have an effective treatment. Some forms of prion disease are thought to be spread by oral ingestion of PrP(Sc), such as chronic wasting disease and variant Creutzfeldt-Jakob disease. Attempts to obtain an active immunization in wild-type animals have been hampered by auto-tolerance to PrP and potential toxicity. Previously, we demonstrated that it is possible to overcome tolerance and obtain a specific anti-PrP antibody response by oral inoculation of the PrP protein expressed in an attenuated Salmonella vector. This past study showed that 30% of vaccinated animals were free of disease more than 350 days post-challenge. In the current study we have both optimized the vaccination protocol and divided the vaccinated mice into low and high immune responder groups prior to oral challenge with PrP(Sc) scrapie strain 139A. These methodological refinements led to a significantly improved therapeutic response. 100% of mice with a high mucosal anti-PrP titer immunoglobulin (Ig) A and a high systemic IgG titer, prior to challenge, remained without symptoms of PrP infection at 400 days (log-rank test P<0.0001 versus sham controls). The brains from these surviving clinically asymptomatic mice were free of PrP(Sc) infection by Western blot and histological examination. These promising findings suggest that effective mucosal vaccination is a feasible and useful method for overcoming tolerance to PrP and preventing prion infection via an oral route.