Sestrins induce natural killer function in senescent-like CD8+ T cells.

Aging is associated with remodeling of the immune system to enable the maintenance of life-long immunity. In the CD8+ T cell compartment, aging results in the expansion of highly differentiated cells that exhibit characteristics of cellular senescence. Here we found that CD27-CD28-CD8+ T cells lost the signaling activity of the T cell antigen receptor (TCR) and expressed a protein complex containing the agonistic natural killer (NK) receptor NKG2D and the NK adaptor molecule DAP12, which promoted cytotoxicity against cells that expressed NKG2D ligands. Immunoprecipitation and imaging cytometry indicated that the NKG2D-DAP12 complex was associated with sestrin 2. The genetic inhibition of sestrin 2 resulted in decreased expression of NKG2D and DAP12 and restored TCR signaling in senescent-like CD27-CD28-CD8+ T cells. Therefore, during aging, sestrins induce the reprogramming of non-proliferative senescent-like CD27-CD28-CD8+ T cells to acquire a broad-spectrum, innate-like killing activity.

Dietary supplementation with inulin-propionate ester or inulin improves insulin sensitivity in adults with overweight and obesity with distinct effects on the gut microbiota, plasma metabolome and systemic inflammatory responses: a randomised cross-over trial.

OBJECTIVE: To investigate the underlying mechanisms behind changes in glucose homeostasis with delivery of propionate to the human colon by comprehensive and coordinated analysis of gut bacterial composition, plasma metabolome and immune responses. DESIGN: Twelve non-diabetic adults with overweight and obesity received 20 g/day of inulin-propionate ester (IPE), designed to selectively deliver propionate to the colon, a high-fermentable fibre control (inulin) and a low-fermentable fibre control (cellulose) in a randomised, double-blind, placebo-controlled, cross-over design. Outcome measurements of metabolic responses, inflammatory markers and gut bacterial composition were analysed at the end of each 42-day supplementation period. RESULTS: Both IPE and inulin supplementation improved insulin resistance compared with cellulose supplementation, measured by homeostatic model assessment 2 (mean±SEM 1.23±0.17 IPE vs 1.59±0.17 cellulose, p=0.001; 1.17±0.15 inulin vs 1.59±0.17 cellulose, p=0.009), with no differences between IPE and inulin (p=0.272). Fasting insulin was only associated positively with plasma tyrosine and negatively with plasma glycine following inulin supplementation. IPE supplementation decreased proinflammatory interleukin-8 levels compared with cellulose, while inulin had no impact on the systemic inflammatory markers studied. Inulin promoted changes in gut bacterial populations at the class level (increased Actinobacteria and decreased Clostridia) and order level (decreased Clostridiales) compared with cellulose, with small differences at the species level observed between IPE and cellulose. CONCLUSION: These data demonstrate a distinctive physiological impact of raising colonic propionate delivery in humans, as improvements in insulin sensitivity promoted by IPE and inulin were accompanied with different effects on the plasma metabolome, gut bacterial populations and markers of systemic inflammation.

The effects of dietary supplementation with inulin and inulin-propionate ester on hepatic steatosis in adults with non-alcoholic fatty liver disease.

The short chain fatty acid (SCFA) propionate, produced through fermentation of dietary fibre by the gut microbiota, has been shown to alter hepatic metabolic processes that reduce lipid storage. We aimed to investigate the impact of raising colonic propionate production on hepatic steatosis in adults with non-alcoholic fatty liver disease (NAFLD). Eighteen adults were randomized to receive 20 g/d of an inulin-propionate ester (IPE), designed to deliver propionate to the colon, or an inulin control for 42 days in a parallel design. The change in intrahepatocellular lipid (IHCL) following the supplementation period was not different between the groups (P = 0.082), however, IHCL significantly increased within the inulin-control group (20.9% ± 2.9% to 26.8% ± 3.9%; P = 0.012; n = 9), which was not observed within the IPE group (22.6% ± 6.9% to 23.5% ± 6.8%; P = 0.635; n = 9). The predominant SCFA from colonic fermentation of inulin is acetate, which, in a background of NAFLD and a hepatic metabolic profile that promotes fat accretion, may provide surplus lipogenic substrate to the liver. The increased colonic delivery of propionate from IPE appears to attenuate this acetate-mediated increase in IHCL.

Blockade of PD-1 or p38 MAP kinase signaling enhances senescent human CD8(+) T-cell proliferation by distinct pathways.

Immune enhancement is desirable in situations where decreased immunity results in increased morbidity. We investigated whether blocking the surface inhibitory receptor PD-1 and/or p38 MAP kinase could enhance the proliferation of the effector memory CD8(+) T-cell subset that re-expresses CD45RA (EMRA) and exhibits characteristics of senescence, which include decreased proliferation and telomerase activity but increased expression of the DNA damage response related protein γH2AX. Blocking of both PD-1 and p38 MAPK signaling in these cells enhanced proliferation and the increase was additive when both pathways were inhibited simultaneously in both young and old human subjects. In contrast, telomerase activity in EMRA CD8(+) T cells was only enhanced by blocking the p38 but not the PD-1 signaling pathway, further indicating that nonoverlapping signaling pathways were involved. Although blocking p38 MAPK inhibits TNF-α secretion in the EMRA population, this decrease was counteracted by the simultaneous inhibition of PD-1 signaling in these cells. Therefore, end-stage characteristics of EMRA CD8(+) T cells are stringently controlled by distinct and reversible cell signaling events. In addition, the inhibition of PD-1 and p38 signaling pathways together may enable the enhancement of proliferation of EMRA CD8(+) T cells without compromising their capacity for cytokine secretion.

Multifunctional cytomegalovirus (CMV)-specific CD8(+) T cells are not restricted by telomere-related senescence in young or old adults.

Antigen-specific multifunctional T cells that secrete interferon-γ, interleukin-2 and tumour necrosis factor-α simultaneously after activation are important for the control of many infections. It is unclear if these CD8(+) T cells are at an early or late stage of differentiation and whether telomere erosion restricts their replicative capacity. We developed a multi-parameter flow cytometric method for investigating the relationship between differentiation (CD45RA and CD27 surface phenotype), function (cytokine production) and replicative capacity (telomere length) in individual cytomegalovirus (CMV) antigen-specific CD8(+) T cells. This involves surface and intracellular cell staining coupled to fluorescence in situ hybridization to detect telomeres (flow-FISH). The end-stage/senescent CD8(+)  CD45RA(+)  CD27(-) T-cell subset increases significantly during ageing and this is exaggerated in CMV immune-responsive subjects. However, these end-stage cells do not have the shortest telomeres, implicating additional non-telomere-related mechanisms in inducing their senescence. The telomere lengths in total and CMV (NLV)-specific CD8(+) T cells in all four subsets defined by CD45RA and CD27 expression were significantly shorter in old compared with young individuals in both a Caucasian and an Asian cohort. Following stimulation by anti-CD3 or NLV peptide, similar proportions of triple-cytokine-producing cells are found in CD8(+) T cells at all stages of differentiation in both age groups. Furthermore, these multi-functional cells had intermediate telomere lengths compared with cells producing only one or two cytokines after activation. Therefore, global and CMV (NLV)-specific CD8(+) T cells that secrete interferon-γ, interleukin-2 and tumour necrosis factor-α are at an intermediate stage of differentiation and are not restricted by excessive telomere erosion.

Progenitor cells are mobilized by acute psychological stress but not beta-adrenergic receptor agonist infusion.

OBJECTIVES: Stimuli that activate the sympathetic nervous system, such as acute psychological stress, rapidly invoke a robust mobilization of lymphocytes into the circulation. Experimental animal studies suggest that bone marrow-derived progenitor cells (PCs) also mobilize in response to sympathetic stimulation. Here we tested the effects of acute psychological stress and brief pharmacological ß-adrenergic (ßAR) stimulation on peripheral PC numbers in humans. METHODS: In two studies, we investigated PC mobilization in response to an acute speech task (n=26) and ßAR-agonist (isoproterenol) infusion (n=20). A subset of 8 participants also underwent the infusion protocol with concomitant administration of the ßAR-antagonist propranolol. Flow cytometry was used to enumerate lymphocyte subsets, total progenitor cells, total haematopoietic stem cells (HSC), early HSC (multi-lineage potential), late HSC (lineage committed), and endothelial PCs (EPCs). RESULTS: Both psychological stress and ßAR-agonist infusion caused the expected mobilization of total monocytes and lymphocytes and CD8(+) T lymphocytes. Psychological stress also induced a modest, but significant, increase in total PCs, HSCs, and EPC numbers in peripheral blood. However, infusion of a ßAR-agonist did not result in a significant change in circulating PCs. CONCLUSION: PCs are rapidly mobilized by psychological stress via mechanisms independent of ßAR-stimulation, although the findings do not exclude ßAR-stimulation as a possible cofactor. Considering the clinical and physiological relevance, further research into the mechanisms involved in stress-induced PC mobilization seems warranted.

Age-associated increase of low-avidity cytomegalovirus-specific CD8+ T cells that re-express CD45RA.

The mechanisms regulating memory CD8(+) T cell function and homeostasis during aging are unclear. CD8(+) effector memory T cells that re-express CD45RA increase considerably in older humans and both aging and persistent CMV infection are independent factors in this process. We used MHC class I tetrameric complexes that were mutated in the CD8 binding domain to identify CMV-specific CD8(+) T cells with high Ag-binding avidity. In individuals who were HLA-A*0201, CD8(+) T cells that expressed CD45RA and were specific for the pp65 protein (NLVPMVATV epitope) had lower avidity than those that expressed CD45RO and demonstrated decreased cytokine secretion and cytolytic potential after specific activation. Furthermore, low avidity NLVPMVATV-specific CD8(+) T cells were significantly increased in older individuals. The stimulation of blood leukocytes with CMV lysate induced high levels of IFN-α that in turn induced IL-15 production. Moreover, the addition of IL-15 to CD45RA(-)CD45RO(+) CMV-specific CD8(+) T cells induced CD45RA expression while Ag activated cells remained CD45RO(+). This raises the possibility that non-specific cytokine-driven accumulation of CMV-specific CD8(+)CD45RA(+) T cells with lower Ag-binding avidity may exacerbate the effects of viral reactivation on skewing the T cell repertoire in CMV-infected individuals during aging.

Varicella zoster-specific CD4+Foxp3+ T cells accumulate after cutaneous antigen challenge in humans.

We investigated the relationship between varicella zoster virus (VZV)-specific memory CD4(+) T cells and CD4(+)Foxp3(+) regulatory T cells (Tregs) that accumulate after intradermal challenge with a VZV skin test Ag. VZV-specific CD4(+) T cells were identified with a MHC class II tetramer or by intracellular staining for either IFN-γ or IL-2 after Ag rechallenge in vitro. VZV-specific T cells, mainly of a central memory (CD45RA(-)CD27(+)) phenotype, accumulate at the site of skin challenge compared with the blood of the same individuals. This resulted in part from local proliferation because >50% of tetramer defined Ag-specific CD4(+) T cells in the skin expressed the cell cycle marker Ki67. CD4(+)Foxp3(+) T cells had the characteristic phenotype of Tregs, namely CD25(hi)CD127(lo)CD39(hi) in both unchallenged and VZV challenged skin and did not secrete IFN-γ or IL-2 after antigenic restimulation. The CD4(+)Foxp3(+) T cells from unchallenged skin had suppressive activity, because their removal led to an increase in cytokine secretion after activation. After VZV Ag injection, Foxp3(+)CD25(hi)CD127(lo)CD39(hi) T cells were also found within the VZV tetramer population. Their suppressive activity could not be directly assessed by CD25 depletion because activated T cells in the skin were also CD25(+). Nevertheless, there was an inverse correlation between decreased VZV skin responses and proportion of CD4(+)Foxp3(+) T cells present, indicating indirectly their inhibitory activity in vivo. These results suggest a linkage between the expansion of Ag-specific CD4(+) T cells and CD4(+) Tregs that may provide controlled responsiveness during Ag-specific stimulation in tissues.

Reversible senescence in human CD4+CD45RA+CD27- memory T cells.

Persistent viral infections and inflammatory syndromes induce the accumulation of T cells with characteristics of terminal differentiation or senescence. However, the mechanism that regulates the end-stage differentiation of these cells is unclear. Human CD4(+) effector memory (EM) T cells (CD27(-)CD45RA(-)) and also EM T cells that re-express CD45RA (CD27(-)CD45RA(+); EMRA) have many characteristics of end-stage differentiation. These include the expression of surface KLRG1 and CD57, reduced replicative capacity, decreased survival, and high expression of nuclear γH2AX after TCR activation. A paradoxical observation was that although CD4(+) EMRA T cells exhibit defective telomerase activity after activation, they have significantly longer telomeres than central memory (CM)-like (CD27(+)CD45RA(-)) and EM (CD27(-)CD45RA(-)) CD4(+) T cells. This suggested that telomerase activity was actively inhibited in this population. Because proinflammatory cytokines such as TNF-α inhibited telomerase activity in T cells via a p38 MAPK pathway, we investigated the involvement of p38 signaling in CD4(+) EMRA T cells. We found that the expression of both total and phosphorylated p38 was highest in the EM and EMRA compared with that of other CD4(+) T cell subsets. Furthermore, the inhibition of p38 signaling, especially in CD4(+) EMRA T cells, significantly enhanced their telomerase activity and survival after TCR activation. Thus, activation of the p38 MAPK pathway is directly involved in certain senescence characteristics of highly differentiated CD4(+) T cells. In particular, CD4(+) EMRA T cells have features of telomere-independent senescence that are regulated by active cell signaling pathways that are reversible.

A multiplex PCR assay for the differentiation of Mycobacterium tuberculosis complex reveals high rates of mixed-lineage tuberculosis infections among patients in Ghana.

In low-resource settings with high tuberculosis (TB) burdens, lack of rapid diagnostic methods for detection and differentiation of Mycobacterium tuberculosis complex (MTBC) is a major challenge affecting TB management. This study utilized comparative genomic analyses of MTBC lineages; M. tuberculosis, M. africanum Lineages 5/6 and M. bovis to identify lineage-specific genes. Primers were designed for the development of a Multiplex PCR assay which was successful in differentiating the MTBC lineages. There was no cross-reaction with other respiratory pathogens tested. Validation of the assay using clinical samples was performed with sputum DNA extracts from 341 clinically confirmed active TB patients. It was observed that 24.9% of cases were caused by M. tuberculosis, while M. africanum L5 & L6 reported 9.0% and 14.4%, respectively. M. bovis infection was the least frequently detected lineage with 1.8%. Also, 27.0% and 17.0% of the cases were PCR negative and unspeciated, respectively. However, mixed-lineage TB infections were recorded at a surprising 5.9%. This multiplex PCR assay will allow speciation of MTBC lineages in low-resource regions, providing rapid differentiation of TB infections to select appropriate medication at the earliest possible time point. It will also be useful in epidemiological surveillance studies providing reliable information on the prevalence of TB lineages as well as identifying difficult to treat cases of mixed-lineage tuberculosis infections.

CMV and Immunosenescence: from basics to clinics.

Alone among herpesviruses, persistent Cytomegalovirus (CMV) markedly alters the numbers and proportions of peripheral immune cells in infected-vs-uninfected people. Because the rate of CMV infection increases with age in most countries, it has been suggested that it drives or at least exacerbates "immunosenescence". This contention remains controversial and was the primary subject of the Third International Workshop on CMV & Immunosenescence which was held in Cordoba, Spain, 15-16th March, 2012. Discussions focused on several main themes including the effects of CMV on adaptive immunity and immunosenescence, characterization of CMV-specific T cells, impact of CMV infection and ageing on innate immunity, and finally, most important, the clinical implications of immunosenescence and CMV infection. Here we summarize the major findings of this workshop.

Sleep disturbances in HIV infection and their biological basis.

Antiretroviral therapy has significantly reduced morbidity and mortality in people living with HIV (PLWH). However, a direct consequence of higher survival is the development of ageing-related co-morbidities that have considerable potential to affect quality of life. Sleep disturbances in PLWH are a significant source of morbidity. A meta-analysis has estimated the prevalence of self-reported sleep disturbances in PLWH to be 58%, with commonly identified disturbances including insomnia, obstructive sleep apnoea and poor sleep quality. Not only do sleep disturbances impair daytime functioning, but chronic sleep disruption also associates with metabolic dysregulation and cardiometabolic disease. Therefore, an understanding of the pathogenesis of sleep disturbances in PLWH is important for reducing morbidity and improving quality of life. Several pathophysiological processes in HIV infection may cause sleep-wake dysregulation. In early infection stages, immunological changes such as expression of sleep-promoting cytokines could mediate sleep disturbances. Long term, chronic immune activation, in addition to side effects of antiretroviral therapy, may impact sleep homeostasis more severely, for example through increasing the risk of obstructive sleep apnoea. These sleep disturbances may further contribute to an inflammatory state, due to the bi-directional relationship between sleep and immunity. In summary, further elucidating the link between HIV, immune activation, and sleep is an underexplored avenue for minimising population morbidity and mortality.

Report from the second cytomegalovirus and immunosenescence workshop.

The Second International Workshop on CMV & Immunosenescence was held in Cambridge, UK, 2-4th December, 2010. The presentations covered four separate sessions: cytomegalovirus and T cell phenotypes; T cell memory frequency, inflation and immunosenescence; cytomegalovirus in aging, mortality and disease states; and the immunobiology of cytomegalovirus-specific T cells and effects of the virus on vaccination. This commentary summarizes the major findings of these presentations and references subsequently published work from the presenter laboratory where appropriate and draws together major themes that were subsequently discussed along with new areas of interest that were highlighted by this discussion.

The association between loneliness, social isolation and inflammation: A systematic review and meta-analysis.

The review synthesised evidence examining the association between a. loneliness with inflammation and b. social isolation with inflammation in adults aged 16 or older from the general population. From an initial 7,400 articles we identified 14 papers that examined loneliness, and 16 that examined social isolation. Qualitative syntheses indicated mixed results, variable study quality, and methodological heterogeneity. Most studies provided associations for C-reactive protein CRP, fibrinogen and Interleukin-6 IL-6, and these results were synthesised using random-effects meta-analyses. There was no association between loneliness with CRP or fibrinogen, but there was a significant association between loneliness and IL-6 for most-adjusted but not least-adjusted analyses. There was also a significant least-adjusted association between social isolation with CRP and fibrinogen, which remained significant for fibrinogen in most-adjusted analyses. There was no association between social isolation with IL-6. Sensitivity analyses indicated that methodological heterogeneity impacted on results. Results indicate that social isolation and loneliness could be linked with systemic inflammation, but more robust methodology is needed to confirm these associations and unpack mechanisms.

Mobilization of gammadelta T lymphocytes in response to psychological stress, exercise, and beta-agonist infusion.

The mobilization of cytotoxic lymphocytes, such Natural Killer (NK) cells and CD8(+) T cells, during stress and exercise is well documented in humans. However, humans have another cytotoxic lymphocyte subset that has not been studied in this context: the Gamma Delta (gammadelta) T lymphocyte. These cells play key roles in immune processes including the elimination of bacterial infection, wound repair and delayed-type hypersensitivity reactions. The current study investigated the effects of stress, exercise, and beta-agonist infusion on the mobilization of gammadelta T lymphocytes. Three separate studies compared lymphocytosis in response to an acute speech stress task (n=29), high (85%W(max)) and low (35%W(max)) intensity concentric exercise (n=11), and isoproterenol infusion at 20 and 40 ng/kg/min (n=12). Flow cytometric analysis was used to examine lymphocyte subsets. gammadelta T lymphocytes were mobilized in response to all three tasks in a dose-dependent manner; the extent of mobilization during the speech task correlated with concomitant cardiac activation, and was greater during higher intensity exercise and increased dose of beta-agonist infusion. The mobilization of gammadelta T lymphocytes was greater (in terms of % change from baseline) than that of CD8(+) T lymphocytes and less than NK cells. This study is the first to demonstrate that gammadelta T cells are stress-responsive lymphocytes which are mobilized during psychological stress, exercise, and beta-agonist infusion. The mobilization of these versatile cytotoxic cells may provide protection in the context of situations in which antigen exposure is more likely to occur.

Acute exercise mobilises CD8+ T lymphocytes exhibiting an effector-memory phenotype.

An acute bout of exercise evokes mobilisation of lymphocytes into the bloodstream, which can be largely attributed to increases in CD8+ T lymphocytes (CD8TLs) and natural killer (NK) cells. Evidence further suggests that, even within these lymphocyte subsets, there is preferential mobilisation of cells that share certain functional and phenotypic characteristics, such as high cytotoxicity, low proliferative ability, and high tissue-migrating potential. These features are characteristic of effector-memory CD8TL subsets. The current study therefore investigated the effect of exercise on these newly-identified subsets. Thirteen healthy and physically active males (mean+/-SD: age 20.9+/-1.5 yr) attended three sessions: a control session (no exercise); cycling at 35% Watt(max) (low intensity exercise); and 85% Watt(max) (high intensity exercise). Each bout lasted 20 min. Blood samples were obtained before exercise, during the final min of exercise, and +15, and +60 min post-exercise. CD8TLs were classified into naïve, central memory (CM), effector-memory (EM), and CD45RA+ effector-memory (RAEM) using combinations of the cell surface markers CCR7, CD27, CD62L, CD57, and CD45RA. In parallel, the phenotypically distinct CD56(bright) 'regulatory' and CD56(dim) 'cytotoxic' NK subsets were quantified. The results show a strong differential mobilisation of CD8TL subsets (RAEM>EM>CM>naïve); during high intensity exercise the greatest increase was observed for RAEM CD8Tls (+450%) and the smallest for naïve cells (+84%). Similarly, CD56(dim) NK cells (+995%) were mobilised to a greater extent than CD56(bright) (+153%) NK cells. In conclusion, memory CD8TL that exhibit a high effector and tissue-migrating potential are preferentially mobilised during exercise. This finding unifies a range of independent observations regarding exercise-induced phenotypic and functional changes in circulating lymphocytes. The selective mobilisation of cytotoxic tissue-migrating subsets, both within the NK and CD8TL population, may enhance immune-surveillance during exercise.

Quantitative Characterization of the T Cell Receptor Repertoire of Naïve and Memory Subsets Using an Integrated Experimental and Computational Pipeline Which Is Robust, Economical, and Versatile.

The T cell receptor (TCR) repertoire can provide a personalized biomarker for infectious and non-infectious diseases. We describe a protocol for amplifying, sequencing, and analyzing TCRs which is robust, sensitive, and versatile. The key experimental step is ligation of a single-stranded oligonucleotide to the 3' end of the TCR cDNA. This allows amplification of all possible rearrangements using a single set of primers per locus. It also introduces a unique molecular identifier to label each starting cDNA molecule. This molecular identifier is used to correct for sequence errors and for effects of differential PCR amplification efficiency, thus producing more accurate measures of the true TCR frequency within the sample. This integrated experimental and computational pipeline is applied to the analysis of human memory and naive subpopulations, and results in consistent measures of diversity and inequality. After error correction, the distribution of TCR sequence abundance in all subpopulations followed a power law over a wide range of values. The power law exponent differed between naïve and memory populations, but was consistent between individuals. The integrated experimental and analysis pipeline we describe is appropriate to studies of T cell responses in a broad range of physiological and pathological contexts.

p38 signaling inhibits mTORC1-independent autophagy in senescent human CD8⁺ T cells.

T cell senescence is thought to contribute to immune function decline, but the pathways that mediate senescence in these cells are not clear. Here, we evaluated T cell populations from healthy volunteers and determined that human CD8+ effector memory T cells that reexpress the naive T cell marker CD45RA have many characteristics of cellular senescence, including decreased proliferation, defective mitochondrial function, and elevated levels of both ROS and p38 MAPK. Despite their apparent senescent state, we determined that these cells secreted high levels of both TNF-α and IFN-γ and showed potent cytotoxic activity. We found that the senescent CD45RA-expressing population engaged anaerobic glycolysis to generate energy for effector functions. Furthermore, inhibition of p38 MAPK signaling in senescent CD8+ T cells increased their proliferation, telomerase activity, mitochondrial biogenesis, and fitness; however, the extra energy required for these processes did not arise from increased glucose uptake or oxidative phosphorylation. Instead, p38 MAPK blockade in these senescent cells induced an increase in autophagy through enhanced interactions between p38 interacting protein (p38IP) and autophagy protein 9 (ATG9) in an mTOR-independent manner. Together, our findings describe fundamental metabolic requirements of senescent primary human CD8+ T cells and demonstrate that p38 MAPK blockade reverses senescence via an mTOR-independent pathway.

New advances in CMV and immunosenescence.

Immunosenescence, defined as the age-associated dysregulation and dysfunction of the immune system, is characterized by impaired protective immunity and decreased efficacy of vaccines. An increasing number of immunological, clinical and epidemiological studies suggest that persistent Cytomegalovirus (CMV) infection is associated with accelerated aging of the immune system and with several age-related diseases. However, current evidence on whether and how human CMV (HCMV) infection is implicated in immunosenescence and in age-related diseases remains incomplete and many aspects of CMV involvement in immune aging remain controversial. The attendees of the 4th International Workshop on "CMV & Immunosenescence", held in Parma, Italy, 25-27th March, 2013, presented and discussed data related to these open questions, which are reported in this commentary.

Differing HLA types influence inhibitory receptor signalling in CMV-specific CD8+ T cells.

The dysregulated immune response to CMV constitutes a major force driving T cell immunosenescence and growing evidence suggests that it is not a benign virus in old age. We show here that the PD-1/L pathway defines a reversible defect in CMV specific CD8(+) T cell proliferative responses in both young and old individuals. More specifically, highly differentiated CD45RA(+)CD27(-) CMV-specific CD8(+) T cells exhibit a proliferative deficit compared their central and effector memory counterparts, which is reversed following PD-L blockade. However, we also report that HLA-B(∗)07/TPR specific CD8(+) T cells express higher levels of PD-1 than HLA-A(∗)02/NLV specific cells and HLA-A(∗)02 individuals show a higher proliferative response to PD-L blockade, than HLA-B(∗)07 individuals, which we postulate may be due to the differing functional avidities for these two CMV-specific CD8(+) T cells populations. Nevertheless data presented here demonstrate that CMV-specific CD8(+) T cells can be functionally enhanced by perturbation of the PD-1/L signalling pathway, whose manipulation may provide a therapeutic modality to combat age-associated immune decline.