Reduced thymus activity and infection prematurely age the immune system

Changes observed in the thymus and lymph nodes 14 days after exposure to BVDV field strains of enhanced or typical virulence in neonatal calves

Clinical presentation following uncomplicated acute infection with bovine viral diarrhea viruses (BVDV) ranges from clinically unapparent to severe (including hemorrhagic disease and death) depending on the strain virulence. Regardless of clinical presentation, BVDV infection of cattle results in a generalized immunosuppression. BVDV immunosuppression is characterized by a reduction of circulating white blood cells (WBC) that is typically evident by day 3 post infection (PI). In infections with typical BVDV field strains WBC counts decrease until days 6-9 PI and then return to baseline values. In infections with enhanced virulence BVDV, WBC counts may continue to decline through day 14. In this study, the lymph nodes and thymus of non-infected neonatal calves and neonatal calves infected 14 days previously with either a BVDV of typical virulence or one of enhanced virulence were compared. It was found that while calves, infected with the typical virulence BVDV, had cleared BVDV, and WBC counts had returned to near baseline, the number of B-B7(+) cells in lymph nodes were reduced whereas numbers of CD4(+) cells were increased as compared to control calves. In contrast, calves infected with the high virulence strain, had not cleared the virus by day 14 and WBC counts had not returned to pre-exposure levels. Furthermore, these calves had more substantial deficits of B-B7(+) and CD4(+) cell subpopulations, compared to calves infected with a typical virulence strain. There were also an increased number of macrophages observed in both lymphoid tissues examined. The thymuses from both groups of BVDV-infected calves were significantly smaller than non-infected age matched calves. The reduction in size was accompanied by a significant depletion of the thymic cortex. These results indicate that regardless of the virulence of the infecting BVDV, infection leaves neonatal calves with deficits in specific lymphocyte subsets and lymphoid tissues that could have long-term immunosuppressive implications.

Reduced thymic output in elite athletes

Athletes undergoing intensive training schedules have chronic exposure to stress-induced hormones such as cortisol that can depress immune function. We compared the circulating levels of T cell receptor excision circles (TREC), a marker of recent thymic emigrants, as well as the levels of naïve and memory subsets in a group of elite endurance athletes and in controls. The athletes showed a reduction in absolute numbers of naïve T cells, particularly in CD4 T cells. In contrast, memory cells were increased. TREC levels in the athletes were significantly reduced compared to age-matched controls. Such changes resemble premature ageing of the T cell component of the immune system. Since thymic production of T cells naturally decline with age, these results raise the concern that prolonging high intensity exercise into the 4th decade of life may have deleterious consequences for athletes' health.

Naïve and memory CD8 T cell pool homeostasis in advanced aging: impact of age and of antigen-specific responses to cytomegalovirus

Alterations in the circulating CD8+ T cell pool, with a loss of naïve and accumulation of effector/effector memory cells, are pronounced in older adults. However, homeostatic forces that dictate such changes remain incompletely understood. This observational cross-sectional study explored the basis for variability of CD8+ T cell number and composition of its main subsets: naïve, central memory and effector memory T cells, in 131 cytomegalovirus (CMV) seropositive subjects aged over 60 years. We found great heterogeneity of CD8+ T cell numbers, which was mainly due to variability of the CD8 + CD28- T cell subset regardless of age. Analysis, by multiple regression, of distinct factors revealed that age was a predictor for the loss in absolute number of naïve T cells, but was not associated with changes in central or effector memory CD8+ T cell subsets. By contrast, the size of CD8+ T cells specific to pp65 and IE-1 antigens of CMV, predicted CD28 - CD8+ T cell, antigen-experienced CD8+ T cell, and even total CD8+ T cell numbers, but not naïve CD8+ T cell loss. These results indicate a clear dichotomy between the homeostasis of naïve and antigen-experienced subsets of CD8+ T cells which are independently affected, in human later life, by age and antigen-specific responses to CMV, respectively.

CD8 T-cell activation is associated with lipodystrophy and visceral fat accumulation in antiretroviral therapy-treated virologically suppressed HIV-infected patients

OBJECTIVE

HIV-infected patients receiving antiretroviral treatment frequently accumulate fat at the abdominal level. It is unknown whether T-cell activation and immune phenotypes are associated with fat accumulation. Thus, the aim of the study was to search for an association between the presence of clinical lipodystrophy (LD), visceral and subcutaneous abdominal adipose tissue amount (VAT and SAT), and peripheral T-cell immune phenotypes.

DESIGN

Cross-sectional study including 87 HIV-infected antiretroviral therapy-treated virologically suppressed and immune-reconstituted patients.

METHODS

The patients were evaluated for clinical LD, VAT, SAT, homeostasis model of insulin resistance, and coronary artery calcium score (>10). T-cell activation (CD8/CD38), differentiation (CD4/CD8/CCR7/CD45RA), and expression/activation of the interleukin-7 (IL-7)/IL-7R system (CD4/CD8/CD127, IL-7, and CD4/CD8/pStat-5) were assessed by cytometry.

RESULTS

In multivariable analyses, CD8 T-cell activation (CD38) was associated with lipoatrophy and central fat accumulation (respectively, β = 5.63, P = 0.005, and β = 4.19, P = 0.020). This was also the case for IL-7R expressing CD8⁺ T cells (CD127⁺) for lipoatrophy β = 12.8, P = 0.003, and for central fat accumulation β = 9.45, P = 0.016. CD8⁺ T-cell activation was also associated with VAT/total adipose tissue (β = 0.01, P = 0.002) and SAT/VAT ratios (β = -0.014, P = 0.015). As expected, VAT/total adipose tissue was an independent risk factor for homeostasis model of insulin resistance (r = 0.364, P = 0.028) and cardiovascular risk (coronary artery calcium, r = 0.406, P = 0.002).

CONCLUSIONS

CD8⁺ T-cell activation was associated with LD and the relative amount of VAT in antiretroviral therapy-controlled, virologically suppressed, HIV-infected patients. We propose that CD8 activation may be involved in the accumulation of central fat frequently observed in these patients, with resulting increased cardiometabolic risk.

REGγ deficiency promotes premature aging via the casein kinase 1 pathway

Our recent studies suggest a role for the proteasome activator REG (11S regulatory particles, 28-kDa proteasome activator)γ in the regulation of tumor protein 53 (p53). However, the molecular details and in vivo biological significance of REGγ-p53 interplay remain elusive. Here, we demonstrate that REGγ-deficient mice develop premature aging phenotypes that are associated with abnormal accumulation of casein kinase (CK) 1δ and p53. Antibody array analysis led us to identify CK1δ as a direct target of REGγ. Silencing CK1δ or inhibition of CK1δ activity prevented decay of murine double minute (Mdm)2. Interestingly, a massive increase of p53 in REGγ(-/-) tissues is associated with reduced Mdm2 protein levels despite that Mdm2 transcription is enhanced. Allelic p53 haplodeficiency in REGγ-deficient mice attenuated premature aging features. Furthermore, introducing exogenous Mdm2 to REGγ(-/-) MEFs significantly rescues the phenotype of cellular senescence, thereby establishing a REGγ-CK1-Mdm2-p53 regulatory pathway. Given the conflicting evidence regarding the "antiaging" and "proaging" effects of p53, our results indicate a key role for CK1δ-Mdm2-p53 regulation in the cellular aging process. These findings reveal a unique model that mimics acquired aging in mammals and indicates that modulating the activity of the REGγ-proteasome may be an approach for intervention in aging-associated disorders.

Feline degenerative joint disease: a genomic and proteomic approach

The underlying disease mechanisms for feline degenerative joint disease (DJD) are mostly unidentified. Today, most of what is published on mammalian arthritis is based on human clinical findings or on mammalian models of human arthritis. However, DJD is a common occurrence in the millions of domestic felines worldwide. To get a better understanding of the changes in biological pathways that are associated with feline DJD, this study employed a custom-designed feline GeneChip, and the institution's unique access to large sample populations to investigate genes and proteins from whole blood and serum that may be up- or down-regulated in DJD cats. The GeneChip results centered around three main pathways that were affected in DJD cats: immune function, apoptosis and oxidative phosphorylation. By identifying these key disease-associated pathways it will then be possible to better understand disease pathogenesis and diagnose it more easily, and to better target it with pharmaceutical and nutritional intervention.

Screening NK-, B- and T-cell phenotype and function in patients suffering from Chronic Fatigue Syndrome

BACKGROUND

Chronic Fatigue Syndrome (CFS) is a debilitating neuro-immune disorder of unknown etiology diagnosed by an array of clinical manifestations. Although several immunological abnormalities have been described in CFS, their heterogeneity has limited diagnostic applicability.

METHODS

Immunological features of CFS were screened in 22 CFS diagnosed individuals fulfilling Fukuda criteria and 30 control healthy individuals. Peripheral blood T, B and NK cell function and phenotype were analyzed by flow cytometry in both groups.

RESULTS

CFS diagnosed individuals showed similar absolute numbers of T, B and NK cells, with minor differences in the percentage of CD4+ and CD8+ T cells. B cells showed similar subset frequencies and proliferative responses between groups. Conversely, significant differences were observed in T cell subsets. CFS individuals showed increased levels of T regulatory cells (CD25+/FOXP3+) CD4 T cells, and lower proliferative responses in vitro and in vivo. Moreover, CD8 T cells from the CFS group showed significantly lower activation and frequency of effector memory cells. No clear signs of T-cell immunosenescence were observed. NK cells from CFS individuals displayed higher expression of NKp46 and CD69 but lower expression of CD25 in all NK subsets defined. Overall, T cell and NK cell features clearly clustered CFS individuals.

CONCLUSIONS

Our findings suggest that alterations in T-cell phenotype and proliferative response along with the specific signature of NK cell phenotype may be useful to identify CFS individuals. The striking down modulation of T cell mediated immunity may help to understand intercurrent viral infections in CFS.

Impact of age on markers of HIV-1 disease

Aging is a complicated process characterized by a progressive loss of homeostasis, which results in an increased vulnerability to multiple diseases. HIV-1-infected patients demonstrate a premature aging phenotype and develop certain age-related diseases earlier in their lifespan than what is seen in the general population. Age-related comorbidities may include the development of bone disease, metabolic disorders, neurologic impairment and immunosenescence. Age also appears to have an effect on traditional markers of HIV-1 disease progression, including CD4+ T-cell count and viral load. These effects are not only a consequence of HIV-1 infection, but in many cases, are also linked to antiretroviral therapy. This review summarizes the complex interplay between HIV-1 infection and aging, and the impact that aging has on markers of HIV-1 disease.

Diabetes and Hypertension among Patients Receiving Antiretroviral Treatment Since 1998 in Senegal: Prevalence and Associated Factors

Cardiovascular risk factors in people on antiretroviral treatment (ART) are poorly documented in resource-constrained settings. A cross-sectional study was conducted in 2009 to assess prevalence of diabetes and hypertension in a sample of 242 HIV-infected patients who had initiated ART between 1998 and 2002 in Dakar, Senegal (ANRS 1215 observational cohort). World Health Organization (WHO) criteria were applied to diagnose diabetes and hypertension. Multiple logistic regressions were used to identify factors associated with diabetes and hypertension. Patients had a median age of 46 years and had received ART for a median duration of about 9 years. 14.5% had diabetes and 28.1% had hypertension. Long duration of ART (≥119 months), older age, higher body mass index (BMI), and higher levels of total cholesterol were associated with higher risks of diabetes. Older age, higher BMI at ART initiation, and higher levels of triglycerides were associated with higher risk of hypertension. This study shows that diabetes and hypertension were frequent in these Senegalese HIV patients on ART. It confirms the association between duration of ART and diabetes and highlights the need to implement programs for prevention of cardiovascular risk factors in HIV patients from resource-constrained settings.

Immune modulation during latent herpesvirus infection

Nearly all human beings, by the time they reach adolescence, are infected with multiple herpesviruses. At any given time, this family of viruses accounts for 35-40 billion human infections worldwide, making herpesviruses among the most prevalent pathogens known to exist. Compared to most other viruses, herpesviruses are also unique in that infection lasts the life of the host. Remarkably, despite their prevalence and persistence, little is known about how these viruses interact with their hosts, especially during the clinically asymptomatic phase of infection referred to as latency. This review explores data in human and animal systems that reveal the ability of latent herpesviruses to modulate the immune response to self and environmental antigens. From the perspective of the host, there are both potentially detrimental and surprisingly beneficial effects of this lifelong interaction. The realization that latent herpesvirus infection modulates immune responses in asymptomatic hosts forces us to reconsider what constitutes a 'normal' immune system in a healthy individual.

Premature age-related comorbidities among HIV-infected persons compared with the general population

BACKGROUND

Human immunodeficiency virus (HIV)-infected patients may have a greater risk of noninfectious comorbidities (NICMs) compared with the general population. We assessed the prevalence and risk factors for NICMs in a large cohort of HIV-infected adults and compared these findings with data from matched control subjects.

METHODS

We performed a case-control study involving antiretroviral therapy (ART)-experienced HIV-infected patients treated at Modena University, Italy, from 2002 through 2009. These patients were compared with age-, sex-, and race-matched adults (control subjects) from the general population included in the CINECA ARNO database. NICMs included cardiovascular disease, hypertension, diabetes mellitus, bone fractures, and renal failure. Polypathology (Pp) was defined as the concurrent presence of ≥2 NICMs. Logistic regression models were constructed to evaluate associated predictors of NICMs and Pp.

RESULTS

There were 2854 patients and 8562 control subjects. The mean age was 46 years, and 37% were women. Individual NICM and Pp prevalences in each age stratum were higher among patients than among controls (all P <.001). Pp prevalence among patients aged 41-50 years was similar to that among controls aged 51-60 years (P value was not statistically significant); diabetes mellitus, cardiovascular disease, bone fractures, and renal failure were statistically independent after adjustment for sex, age, and hypertension. Logistic regression models showed that independent predictors of Pp in the overall cohort were (all P < .001) age (odds ratio [OR], 1.11), male sex (OR, 1.77), nadir CD4 cell count <200 cells/μL (OR, 4.46), and ART exposure (OR, 1.01).

CONCLUSIONS

Specific age-related NICMs and Pp were more common among HIV-infected patients than in the general population. The prevalence of Pp in HIV-infected persons anticipated Pp prevalence observed in the general population among persons who were 10 years older, and HIV-specific cofactors (lower nadir CD4 cell count and more prolonged ART exposure) were identified as risk factors. These data support the need for earlier screening for NICMs in HIV-infected patients.

Age-related deregulation of naive T cell homeostasis in elderly humans

Immunosenescence is characterized by phenotypic and functional changes of effector memory T cells. In spite of the well-described senescent defects of these experienced T cells, immune responses to new pathogens are also deeply affected in elderly humans, suggesting that naive T cells could also show age-related defects. It has been reported in both, animal models and humans, alterations of the naive T cell turnover associated to advanced age or low thymic function. However, as far as we know, homeostatic mechanisms involved in the deregulation of naive T cell peripheral dynamics and their consequences are still not well understood. Thus, the aim of our study was to analyze homeostatic parameters of peripheral naive T cells and their relationship with thymic function in young and elderly humans. Our results show that lower naive T cell numbers were associated with a lower thymic function and higher activation and proliferating naive T cell levels. We then analyzed sjTREC numbers and relative telomere length from sorted naive T cells. Our results show that the aberrant activation and proliferation status was related to lower sjTREC numbers (a peripheral proliferation marker) and both, higher CD57 expression levels and shortened telomeres (replicative senescence-related markers). Elderly individuals show a greater contraction of the CD8 naive T cell numbers and all homeostatic alterations were more severe in this compartment. In addition, we found that low functional thymus show a CD4-biased thymocyte production. Taken together, our results suggest a homeostatic deregulation, affecting mostly the naive CD8 T cell subset, leading to the accumulation of age-associated defects in, otherwise, phenotypically naive T cells.

Aging and immune function: molecular mechanisms to interventions

Abstract The immune system of an organism is an essential component of the defense mechanism aimed at combating pathogenic stress. Age-associated immune dysfunction, also dubbed "immune senescence," manifests as increased susceptibility to infections, increased onset and progression of autoimmune diseases, and onset of neoplasia. Over the years, extensive research has generated consensus in terms of the phenotypic and functional defects within the immune system in various organisms, including humans. Indeed, age-associated alterations such as thymic involution, T cell repertoire skewing, decreased ability to activate naïve T cells and to generate robust memory responses, have been shown to have a causative role in immune decline. Further, understanding the molecular mechanisms underlying the generation of proteotoxic stress, DNA damage response, modulation of ubiquitin proteasome pathway, and regulation of transcription factor NFκB activation, in immune decline, have paved the way to delineating signaling pathways that cross-talk and impact immune senescence. Given the role of the immune system in combating infections, its effectiveness with age may well be a marker of health and a predictor of longevity. It is therefore believed that a better understanding of the mechanisms underlying immune senescence will lead to an effective interventional strategy aimed at improving the health span of individuals. Antioxid. Redox Signal. 14, 1551-1585.

Cytomegalovirus-specific T cells persist at very high levels during long-term antiretroviral treatment of HIV disease

Background

In healthy, HIV seronegative, CMV seropositive adults, a large proportion of T cells are CMV-specific. High-level CMV-specific T cell responses are associated with accelerated immunologic aging (“immunosenesence”) in the elderly population. The impact of untreated and treated HIV infection on the frequency of these cells remains undefined.

Methodology/Principal Findings

We measured the proportion of CD4+ and CD8+ T cells responding to CMV pp65 and IE proteins was measured using flow cytometry in 685 unique HIV seronegative and seropositive individuals. The proportion of CMV-specific CD8+ T cells was consistently higher in the HIV-seropositive subjects compared to the HIV-seronegative subjects. This HIV effect was observed even in patients who lacked measurable immunodeficiency. Among the HIV-seropositive subjects, CMV-specific CD8+ T cell responses were proportionately lower during recent infection, higher during chronic untreated infection and higher still during long-term antiretroviral treated infection. The CD8+ T cell response to just two CMV proteins (pp65 and IE) was approximately 6% during long-term therapy, which was over twice that seen in HIV-seronegative persons. CMV-specific CD4+ T cell responses followed the same trends, but the magnitude of the effect was smaller.

Conclusions/Significance

Long-term successfully treated HIV infected patients have remarkably high levels of CMV-specific effector cells. These levels are similar to that observed in the elderly, but occur at much younger ages. Future studies should focus on defining the potential role of the CMV-specific inflammatory response in non-AIDS morbidity and mortality, including immunosenescence.