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CMV and Aging, Immunosenescence, NK Cell Activator, Nicotinamide Riboside and A4M

January 2015

By Life Extension

Cytomegalovirus infection is associated with increased mortality in the older population.

Cytomegalovirus (CMV) is a common herpesvirus infection and stimulates the expansion of very large numbers of CMV-specific T cells that reduce the CD4/CD8 ratio and suppress the number of naïve T cells. CMV infection has been associated with frailty and impaired survival. We investigated the correlates of CMV and the impact of the CMV infection on mortality within a cohort of 511 individuals aged at least 65 years who were followed up for 18 years. The mean age of the participants was 74 years of which 70% were CMV-seropositive. CMV was strongly linked to socio-economic status, and CMV infection increased the annual mortality rate by 42% (Hazard ratio = 1.42, 95% CI: 1.11-1.76 after adjusting for age, sex and baseline socio-economic and health variables) corresponding to 3.7 years lower life expectancy from age 65. Infection was associated with a near doubling of cardiovascular deaths, whereas there was no increase in mortality from other causes. These results show that CMV infection markedly increases the mortality rate in healthy older individuals due to an excess of vascular deaths. These findings may have significant implications for the study of immune senescence and if confirmed more generally could have important implications for measures to optimize the health of the elderly.

Aging Cell . 2013 Jun;12(3):381-7

Cytomegalovirus infection and risk of alzheimer disease in older black and white Individuals.

BACKGROUND: Human cytomegalovirus (CMV) is prevalent in older adults and has been implicated in many chronic diseases of aging. This study investigated the relation between CMV and the risk of Alzheimer disease (AD). METHODS: Data come from 3 cohort studies that included 849 participants (mean age [±SD], 78.6 ± 7.2 years; mean education duration [±SD], 15.4 ± 3.3 years; 25% black). RESULTS: A solid-phase enzyme-linked immunosorbent assay was used for detecting type-specific immunoglobulin G antibody responses to CMV and herpes simplex virus type 1 (HSV-1) measured in archived serum samples. Of 849 participants, 73.4% had serologic evidence of exposure to CMV (89.0% black and 68.2% white; P < .001). During an average of 5.0 years of follow-up, 93 persons developed AD. CMV seropositivity was associated with an increased risk of AD (relative risk, 2.15; 95% confidence interval, 1.42-3.27) and a faster rate of decline in global cognition (estimate [±standard error], -0.02 ± 0.01; P = .03) in models that controlled for age, sex, education duration, race, vascular risk factors, vascular diseases, and apolipoprotein e4 level. Results were similar in black and white individuals for both incident AD and change in cognitive function and were independent of HSV-1 status. CONCLUSIONS:  These results suggest that CMV infection is associated with anincreased risk of AD and a faster rate of cognitive decline in older diverse populations.

J Infect Dis. 2014 Aug 8

The impact of ageing on natural killer cell function and potential consequences for health in older adults.

Forming the first line of defence against virally infected and malignant cells, natural killer (NK) cells are critical effector cells of the innate immune system. With age, significant impairments have been reported in the two main mechanisms by which NK cells confer host protection: direct cytotoxicity and the secretion of immunoregulatory cytokines and chemokines. In elderly subjects, decreased NK cell activity has been shown to be associated with an increased incidence and severity of viral infection, highlighting the clinical implications that age-associated changes in NK cell biology have on the health of older adults. However, is an increased susceptibility to viral infection the only consequence of these age-related changes in NK cell function? Recently, evidence has emerged that has shown that in addition to eliminating transformed cells, NK cells are involved in many other biological processes such as immune regulation, anti-microbial immune responses and the recognition and elimination of senescent cells, novel functions that involve NK-mediated cytotoxicity and/or cytokine production. Thus, the decrease in NK cell function that accompanies physiological ageing is likely to have wider implications for the health of older adults than originally thought. Here, we give a detailed description of the changes in NK cell biology that accompany human ageing and propose that certain features of the ageing process such as: (i) the increased reactivation rates of latent Mycobacterium tuberculosis, (ii) the slower resolution of inflammatory responses and (iii) the increased incidence of bacterial and fungal infection are attributable in part to an age-associated decline in NK cell function.

Ageing Res Rev. 2013 Sep;12(4):1069-78

Cytomegalovirus is associated with reduced telomerase activity in the Whitehall II cohort.

Telomere length and telomerase activity have received increased attention as markers of cellular aging, but the determinants of inter-individual variation in these markers are incompletely understood. Cytomegalovirus (CMV) infection may be particularly important for telomere and telomerase dynamics due to its dramatic impact on peripheral blood lymphocyte composition, i.e., increasing the number and proportions of highly differentiated T cells that are characterized by shorter telomere length (TL) and lowered telomerase activity (TA). However, the possible relationship between CMV infection and leukocyte TL and TA has not been well-examined in vivo. This study examined the associations of CMV seropositivity and CMV IgG antibodies with leukocyte (TL) and (TA) in a sample of 434 healthy individuals (ages 53-76) from the Whitehall II cohort. Positive CMV serostatus was significantly associated with lower TA among women, and higher CMV IgG antibody levels were associated with lower TA in the overall sample. However, neither CMV seropositivity nor CMV IgG antibody levels (reflecting subclinical reactivation) among the seropositive were significantly associated with TL. These associations were robust to adjustment for age, employment grade, BMI, and smoking status. The results demonstrate that CMV seropositivity and subclinical reactivation predict lower TA. Future longitudinal studies should test whether the association of CMV with lower TA contributes to accelerated telomere shortening over time.

Exp Gerontol. 2013 Apr;48(4):385-90

Cytomegalovirus contributes partly to uraemia-associated premature immunological ageing of the T cell compartment.

Cytomegalovirus (CMV) infection has been implicated in accelerated T cell ageing. End-stage renal disease (ESRD) patients have a severely immunologically aged T cell compartment but also a high prevalence of CMV infection. We investigated whether CMV infection contributes to T cell ageing in ESRD patients. We determined the thymic output by the T cell receptor excision circle (TREC) content and percentage of CD31+ naïve T cells. The proliferative history of the T cell compartment by determination of the relative telomere length (RTL) and the T cell differentiation status was determined by immunophenotyping. It appeared that CMV infection did not affect thymic output but reduced RTL of CD8+ T cells in ESRD patients. Moreover, increased T cell differentiation was observed with higher percentages of CD57+ and CD28null CD4+ and CD8+ memory T cells. These CD28null T cells had significantly shorter telomeres compared to CD28+ T cells. Therefore we concluded that CMV infection does not affect the decreased thymic output but increases T cell differentiation as observed in ESRD-related premature T cell ageing.

Clin Exp Immunol. 2013 Dec;174(3):424-32

Immune senescence: relative contributions of age and cytomegalovirus infection.

Immune senescence, defined as the age-associated dysregulation and dysfunction of the immune system, is characterised by impaired protective immunity and decreased efficacy of vaccines. Recent clinical, epidemiological and immunological studies suggest that Cytomegalovirus (CMV) infection may be associated with accelerated immune senescence, possibly by restricting the naïve T cell repertoire. However, direct evidence whether and how CMV-infection is implicated in immune senescence is still lacking. In this study, we have investigated whether latent mouse CMV (MCMV) infection with or without thymectomy (Tx) alters antiviral immunity of young and aged mice. After infection with lymphocytic choriomeningitis virus (LCMV) or Vaccinia virus, specific antiviral T cell responses were significantly reduced in old, old MCMV-infected and/or Tx mice compared to young mice. Importantly, control of LCMV replication was more profoundly impaired in aged MCMV-infected mice compared to age-matched MCMV-naïve or young mice. In addition, latent MCMV infection was associated with slightly reduced vaccination efficacy in old Tx mice. In contrast to the prevailing hypothesis of a CMV-mediated restriction of the naïve T cell repertoire, we found similar naïve T cell numbers in MCMV-infected and non-infected mice, whereas ageing and Tx clearly reduced the naïve T cell pool. Instead, MCMV-infection expanded the total CD8(+) T cell pool by a massive accumulation of effector memory T cells. Based on these results, we propose a new model of increased competition between CMV-specific memory T cells and any ‘de novo’ immune response in aged individuals. In summary, our results directly demonstrate in a mouse model that latent CMV-infection impairs immunity in old age and propagates immune senescence.

PLoS Pathog. 2012;8(8):e1002850

Human cytomegalovirus infection levels in glioblastoma multiforme are of prognostic value for survival.

BACKGROUND: Patients with glioblastoma multiforme (GBM) generally live 12-15 months after diagnosis, despite maximal surgical resection, adjuvant radiotherapy, and chemotherapy. HCMV has been detected in 90-100% of GBMs. We recently found that low grade HCMV infection in GBM tumours was highly associated with survival over 18 months (case-control study). Here, we sought to determine whether low-grade HCMV infection in GBMs is associated with prolonged survival in a consecutive patient cohort, analysed retrospectively. STUDY DESIGN: Tumour samples from 75 consecutive GBM patients treated surgically at Karolinska University Hospital in 2004-2005 were examined by immunohistochemistry (IHC) and in situ hybridization for HCMV proteins and DNA, respectively. Tumours were graded 1-4, depending on the percentage of positive cells by IHC. Low-grade HCMV was defined as grade 1 (< 25% of HCMV infected tumour cells). Time to tumour progression (TTP) and survival data were analysed with Cox regression and Kaplan-Meier models. RESULTS: HCMV infection was detected in 74 of 75 tumours (99%). In patients with low-grade HCMV infection, median survival was 20 months longer than in patients with high-grade infections (P = 0.036, HR: 2.2), and TTP was 8 months longer (P = 0.1, HR: 1.8). Two-year survival was much higher in patients with low-grade HCMV infection (63.6% vs. 17.2%, P = 0.003). CONCLUSION: The longer survival in patients whose tumours had low-grade HCMV infection suggests that the level of HCMV infection in GBMs has a prognostic value and that HCMV may contribute to the pathogenesis of GBM.

J Clin Virol. 2013 May;57(1):36-42

Increased risk of serious non-AIDS-related events in HIV-infected subjects on antiretroviral therapy associated with a low CD4/CD8 ratio.

BACKGROUND: A low CD4/CD8 ratio has been identified in the general population as a hallmark of inmmunosenescence and a surrogate of all-cause mortality. We aimed to investigate in treated HIV-infected individuals the relationship between the CD4/CD8 ratio and serious non-AIDS events. METHODS: Case-control study within a prospective hospital-based cohort of HIV-infected subjects during at least one year of ART-mediated viral suppression. Cases were patients with serious non-AIDS events (non-AIDS malignancies, cardiovascular disease, and end-stage kidney disease), and controls individuals who did not developed non-AIDS events during follow-up. Data were analyzed using ROC analysis and multivariate logistic regression. Conditional logistic regression was performed in 200 cases/controls matched by age, sex, nadir CD4 and proximal CD4 counts. RESULTS: We analyzed 407 subjects (109 cases, 298 controls). The CD4/CD8 ratio was lower in cases (0.44 vs. 0.70, P<0.0001), with higher discriminatory ability for the detection of non-AIDS events than the CD4 count, CD8 count and nadir CD4. Multivariate analyses (adjusted for age, sex, nadir CD4, proximal CD4 count, year of ART initiation and ART duration) confirmed the independent association of a low CD4/CD8 ratio with the risk of non-AIDS morbidity (per CD4/CD8 ratio quartile decrease, OR, 2.9; 95% CI, 1.3-6.2) and non-AIDS mortality (OR, 2.8; 95% CI, 1.5-5.3). CONCLUSIONS: The CD4/CD8 ratio provides additional information to the CD4 counts and nadir CD4 in treated HIV-infected individuals, since it is independently associated with the risk of non-AIDS-related morbidity and mortality. This association is robust and maintained within different subgroups of patients.

PLoS One. 2014 Jan 30;9(1):e85798

The impact of aging on regulatory T-cells.

Age-related deviations of the immune system contribute to a higher likelihood of infections, cancer, and autoimmunity in the elderly. Senescence of T-lymphocytes is characterized by phenotypical and functional changes including the loss of characteristic T-cell surface markers, while an increase of stimulatory receptors, cytotoxicity as well as resistance against apoptosis is observed. One of the key mediators of immune regulation are naturally occurring regulatory T-cells (Tregs). Tregs express high levels of CD25 and the intracellular protein forkhead box P3; they exert their suppressive functions in contact-dependent as well as contact-independent manners. Quantitative and qualitative defects of Tregs were observed in patients with autoimmune diseases. Increased Treg activity was shown to suppress anti-tumor and anti-infection immunity. The effect of aging on Tregs, and the possible contribution of age-related changes of the Treg pool to the pathophysiology of diseases in the elderly are still poorly understood. Treg homeostasis depends on an intact thymic function and current data suggest that conversion of non-regulatory T-cells into Tregs as well as peripheral expansion of existing Tregs compensates for thymic involution after puberty to maintain constant Treg numbers. In the conventional T-cell subset, peripheral proliferation of T-cells is associated with replicative senescence leading to phenotypical and functional changes. For Tregs, different developmental stages were also described; however, replicative senescence of Tregs has not been observed yet.

Front Immunol. 2013 Aug 6;4:231

Cytomegalovirus infection is associated with increased mortality in the older population.

Cytomegalovirus (CMV) is a common herpesvirus infection and stimulates the expansion of very large numbers of CMV-specific T cells that reduce the CD4/CD8 ratio and suppress the number of naïve T cells. CMV infection has been associated with frailty and impaired survival. We investigated the correlates of CMV and the impact of the CMV infection on mortality within a cohort of 511 individuals aged at least 65 years who were followed up for 18 years. The mean age of the participants was 74 years of which 70% were CMV-seropositive. CMV was strongly linked to socio-economic status, and CMV infection increased the annual mortality rate by 42% (Hazard ratio = 1.42, 95% CI: 1.11-1.76 after adjusting for age, sex and baseline socio-economic and health variables) corresponding to 3.7 years lower life expectancy from age 65. Infection was associated with a near doubling of cardiovascular deaths, whereas there was no increase in mortality from other causes. These results show that CMV infection markedly increases the mortality rate in healthy older individuals due to an excess of vascular deaths. These findings may have significant implications for the study of immune senescence and if confirmed more generally could have important implications for measures to optimize the health of the elderly.

Aging Cell. 2013 Jun;12(3):381-7