Characterization of naïve, memory and effector CD8+ T cells: effect of age

Aging is associated with progressive decline in T cell functions and increased frequency of infections, autoimmune phenomenon, and cancer. Memory T cells rapidly acquire effector functions to kill infected and malignant cells and/or inhibit their replication. Recently, memory T cells have been further classified into central and effector memory T cells (and early and intermediate T cells by some investigators). In aging, memory T cells are accumulated; however, these subpopulations of memory and effector T cells have not been fully characterized and changes in central memory and effector memory T cells in aged humans have not been described. In this article, we have further defined na?ve, central memory, effector memory, and effector CD8+ T cells in humans and their changes in aged humans.     

The dominant human conjunctival epithelial CD8αβ+ T cell population is maintained with age but the number of CD4+ T cells increases

The conjunctiva is a highly specialized ocular mucosal surface that, like other mucosa, houses a number of leukocyte populations. These leukocytes have been implicated in age-related inflammatory diseases such as dry-eye, but their phenotypic characteristics remain largely undetermined. Existing literature provides rudimentary data from predominantly immunohistochemical analyses of tissue sections, prohibiting detailed and longitudinal examination of these cells in health and disease. Using recovered cells from ocular surface impression cytology and flow cytometry, we examined the frequency of leukocyte subsets in human conjunctival epithelium and how this alters with age. Of the total CD45+ leukocyte population within the conjunctival epithelium, 87% [32–99] (median) [range] comprised lymphocytes, with 69% [47–90] identified as CD3 + CD56- T cells. In contrast to peripheral blood, the dominant conjunctival epithelial population was TCRαβ + CD8αβ + (80% [37–100]) with only 10% [0-56%] CD4+ cells. Whilst a significant increase in the CD4+ population was seen with age (r = 0.5; p < 0.01) the CD8+ population remained unchanged, resulting in an increase in the CD4:CD8 ratio (r = 0.5;p < 0.01). IFNγ expression was detectable in 18% [14–48] of conjunctival CD4+ T cells and this was significantly higher among older individuals (<35 years, 7[4–39] vs. >65 years, 43[20–145]; p < 0.05). The elevation of CD4+ cells highlights a potentially important age-related alteration in the conjunctival intra-epithelial leukocyte population, which may account for the vulnerability of the aging ocular surface to disease.     

CD95-mediated apoptosis in naïve, central and effector memory subsets of CD4+ and CD8+ T cells in aged humans

Aging is associated with a decrease in naïve (T_N) and central memory (T_CM), and an accumulation of effector memory (T_EM and T_EMRA) T cell subsets. Previously, we have demonstrated an increased sensitivity of T_N and T_CM CD4+ and CD8+ T cells in aging to TNF-α-induced apoptosis. In this investigation, we examined whether similar differential sensitivity is applicable to CD95-mediated apoptosis. We show that T_N and T_CM CD4+ and CD8+ T cells from aged subjects are significantly more sensitive to CD95-mediated apoptosis. Increased apoptosis is associated with increased activation of caspase-8 and caspase-3. Both caspase-8 and caspase-3 inhibitors blocked CD95-mediated apoptosis and activation of caspase-8 and caspase-3 in T_N and T_CM CD4+ and CD8+ T cells. No significant difference was observed in apoptosis or in activation of caspase-8 and caspase-3 in T_EM and T_EMRA CD4+ and CD8+ T cells between young and aged subjects; both populations were relatively and comparably resistant to CD95-mediated apoptosis and caspase activation. No correlation was observed between the sensitivity/resistance of any of the subsets of CD4+ or CD8+T cells to CD95-mediated apoptosis and the expression of CD95. Our data suggest that increased CD95-mediated apoptosis of T_N and T_CM CD8+ and CD4+ T cells may play a role in their decline in human aging.     

Identification of non-naïve CD4+CD45RA+ T cell subsets in adult allogeneic haematopoietic cell transplant recipients

The study of thymic-dependent pathways of T cell reconstitution in T cell replete haematopoietic cell transplant (HCT) recipients in previous studies was complicated by the transfer of na?ve CD4(+)CD45RA(+) T cells with the stem cell graft. However, direct quantification of thymic output has been enabled by measurement of T cell receptor excision circles (TREC). We analysed T cell reconstitution using T cell phenotyping and TREC quantification in 12 T cell-replete HCT recipients 6-53 years of age during the first 12 months post transplant. We have identified a novel subpopulation of CD4(+)CD45RA(+) T cells in the peripheral blood of these HCT recipients with expansions of this subset being more pronounced in older recipients. The recovery of classical na?ve CD4(+)CD45RA(+) T cells was dependent on thymic output whereas this novel CD4(+)CD45RA(+) subpopulation arose independently of thymic output and displayed effector function and phenotype. These results suggest that CD4(+)CD45RA(+) effector populations exist, similar to the CD8(+)CD45RA(+) effector subset, and that the CD45RA antigen should not be used alone to define na?ve CD4(+) T cells when monitoring T cell reconstitution in T cell replete HCT recipients. Furthermore, these results raise important questions regarding the role of the thymus in regulating T cell homeostasis in older HCT recipients and normal individuals.     

Increased CD4+CD16+ and CD4+CD56+ T cell subsets in Behçet's disease

Behçet's disease is a systemic vasculitis of unknown etiology. Various immune abnormalities have previously been shown in Behçet's disease. We investigated T lymphocyte subsets associated with cytotoxic activity and natural killer (NK) cells by flow cytometry in 37 patients with Behçet's disease, 38 healthy controls, and 17 diseased control patients. Compared to the healthy controls, CD4⁺CD16⁺ and CD4⁺CD56⁺ subsets were found to be higher in the Behçet's disease group as well as in the disease control group (CD4⁺CD16⁺: BD=5?±?3, DC=14?±?14, HC= 3?±?2, P=0.001; CD4⁺CD56⁺: BD=11?±?5, DC= 18?±?17, HC=8?±?6, P=0.01). CD8⁺CD16⁺ and CD8⁺CD56⁺ T cell subsets were at normal levels in Behçet's disease but found to be elevated in disease controls. Similarly, NK cells (CD16⁺CD56⁺) were high only in the disease control group. Significant increases in CD4⁺CD16⁺ and CD4⁺CD56⁺ cell subsets in Behçet's patients and disease controls suggest that T cell activation patterns of these subsets in Behçet's disease are similar to those in other inflammatory disorders.     

CD8+T细胞与重症哮喘

近几十年来,尽管对哮喘发病机制的研究和治疗不断取得进步,但在美国哮喘的死亡率还是从20年前的0.8人/10万人增加到现在的2.0人/10万人[1]。与哮喘死亡有关的社会经济因素和心理因素已有大量的文献报道[2],然而对于致死性重症哮喘的气道病理变化至今还没有深入研究。大量临床和流行病学研究表明,呼吸道病毒感染对于哮喘病情的急性加重起着重要作用。成人和儿童呼吸道病毒感染与哮喘入院治疗密切相关并有相似的季节性特征[3]。Teichtahl等在1年内需要入院治疗的80%成人急性哮喘患者中分离到病毒[4]。在一项为期11个月对31例急性哮喘患者的前…     

Cross-dressed CD8α+/CD103+ dendritic cells prime CD8+ T cells following vaccination

Activation of naïve cluster of differentiation (CD)8⁺ cytotoxic T lymphocytes (CTLs) is a tightly regulated process, and specific dendritic cell (DC) subsets are typically required to activate naive CTLs. Potential pathways for antigen presentation leading to CD8⁺ T-cell priming include direct presentation, cross-presentation, and cross-dressing. To distinguish between these pathways, we designed single-chain trimer (SCT) peptide–MHC class I complexes that can be recognized as intact molecules but cannot deliver antigen to MHC through conventional antigen processing. We demonstrate that cross-dressing is a robust pathway of antigen presentation following vaccination, capable of efficiently activating both naïve and memory CD8⁺ T cells and requires CD8α⁺/CD103⁺ DCs. Significantly, immune responses induced exclusively by cross-dressing were as strong as those induced exclusively through cross-presentation. Thus, cross-dressing is an important pathway of antigen presentation, with important implications for the study of CD8⁺ T-cell responses to viral infection, tumors, and vaccines.Professional antigen-presenting cells (APCs) are typically required to activate naïve cluster of differentiation (CD)8⁺ T cells, either by direct priming or cross-priming. In direct priming, infected (viral infection) or directly transfected (DNA vaccination) APCs synthesize the foreign antigen and use endogenous MHC class I pathways of antigen presentation to present antigen and prime CD8⁺ T cells. In cross-priming, APCs are able to capture, process, and present exogenous antigen onto MHC class I molecules through a process known as cross-presentation (1). Cross-priming has been shown to be an essential pathway for immunity to many viral infections and tumors. Although the pathways that lead to cross-presentation remain incompletely understood, increasing evidence suggests that only certain dendritic cell (DC) subsets are efficient in this process.Cross-dressing involves the transfer of intact MHC class I/peptide complexes between cells without the requirement for further processing, representing an alternative pathway of indirect antigen presentation (2, 3). Although cross-dressed DCs can activate memory CD8⁺ T cells following viral infection in vivo (4), it remains unclear whether cross-dressing can prime naïve CD8⁺ T-cell responses, what DC subtypes are required to prime CD8⁺ T cells by cross-dressing, and how robust this pathway is compared with traditional pathways of indirect antigen presentation. These questions must be addressed before the physiologic relevance of cross-dressing can be evaluated in context.To address these questions, we have taken advantage of Batf3-deficient mice and engineered MHC class I single chain trimer (SCT) constructs. Batf3^−/− mice have a selective loss of CD8α⁺ and CD103⁺ DCs, without abnormalities in other hematopoietic cell types or architecture (5). DCs from Batf3^−/− mice are deficient in cross-presentation, and cytotoxic T lymphocyte (CTL) responses to viral infection and syngeneic tumors are impaired in Batf3^−/− mice. Thus, Batf3^−/− mice represent a valuable model system to study cross-presentation, cross-dressing, and the role of CD8α⁺/CD103⁺ DCs following DNA or cellular vaccination. We have previously engineered completely assembled MHC class I SCT whereby all three components of the complex (heavy chain, β₂m, and peptide) are attached by flexible linkers (6). Through progressive molecular engineering, even peptides with low binding affinities can be successfully anchored in the peptide binding groove by a disulfide trap between the first linker and the heavy chain (7–9). Using these experimental tools, we demonstrate that cross-dressing is a robust pathway of antigen presentation following DNA and cellular vaccination, capable of priming naïve and memory CD8⁺ T cells. In addition, we demonstrate that CD8α⁺/CD103⁺ DCs are required to prime CTLs by cross-dressing.     

Na?ve 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.

Electronic supplementary material

The online version of this article (doi:10.1007/s11357-013-9594-z) contains supplementary material, which is available to authorized users.     

TNF-alpha-induced apoptosis in human naïve and memory CD8+ T cells in aged humans

Recently, human CD8+ T cells have been divided into naïve, central memory (T_CM), and two types of effector memory cells (T_EM and T_EMRA), which are phenotypically identified by a set of cell surface molecules. In this investigation, we have compared the relative sensitivity of these subsets to TNF-α-induced apoptosis in young and aged humans. Our data show increased sensitivity of naïve and T_CM CD8+ T cells from aged humans to TNF-α-induced apoptosis as compared to young subjects. Both T_EM and T_EMRA CD8+ T cells from young and aged subjects were relatively resistant to TNF-α-induced apoptosis and no significant difference was observed between young and aged subjects. Increased apoptosis of naïve and T_CM CD8+ T cells in aged humans was associated with increased activation of caspase-8 and caspase-3 as compared to young subjects. There was no difference in the expression of TNFR-I or TNFR-II on any of the four subpopulations of CD8+ T cells between young and aged subjects. These data suggest that increased TNF-α-induced apoptosis of naïve and T_CM CD8+ T cells may play a role in the deficiency of naïve and T_CM CD8+ T cells in human aging. However, apoptosis does not appear to play a major role in increased accumulation of effector memory CD8+ T cells during human aging.     

健康傣族人CD3+ CD4+和CD8+ T淋巴细胞绝对数正常值调查

目的了解德宏州健康傣族人群外周静脉血CD3 、CD4 、CD8 T淋巴细胞绝对数和CD4 /CD8 比值的正常值范围。方法应用流式细胞仪(FACSCount)检测253例健康傣族人的CD3 、CD4 、CD8 T淋巴细胞绝对数和CD4 /CD8 比值,并观察以上数值在性别和年龄上的差异。结果CD3 、CD4 、CD8 和CD4 /CD8 的正常值参考范围分别为(1 543±443)个/μl(、849±261)个/μl(、567±225)个/μl和1.63±0.55。CD3 、CD4 在性别和年龄组别间的差异均无统计学意义,而CD8 和CD4 /CD8 在年龄组别间的差异有统计学意义。结论初步建立了健康傣族人群CD3 、CD4 、CD8 和CD4 /CD8 的正常值参考范围,对于指导德宏州艾滋病的诊断及治疗工作有重要意义。     

健康傣族人CD3+ CD4+和CD8+ T淋巴细胞绝对数正常值调查

目的 了解德宏州健康傣族人群外周静脉血CD3^＋、CD4^＋、CD8^＋T淋巴细胞绝对数和CD4^＋／CD8^＋比值的正常值范围。方法应用流式细胞仪（FAcscount）检测253例健康傣族人的CD3^＋、CD4^＋、CD8^＋T淋巴细胞绝对数和CD4^＋／CD8^＋比值，并观察以上数值在性别和年龄上的差异。结果 CD3^＋、CD4^＋、CD8^＋和CD4^＋／CD8^＋的正常值参考范围分别为（1543±443）个/μl、（849±261）个/μl、（567±225）个/μl和1．63±0．55。CD3^＋、CD4^＋在性别和年龄组别间的差异均无统计学意义，而CD8^＋和CD4^＋／CD8^＋在年龄组别间的差异有统计学意义。结论 初步建立了健康傣族人群CD3^＋、CD4^＋、CD8^＋和CD4^＋／CD8^＋的正常值参考范围，对于指导德宏州艾滋病的诊断及治疗工作有重要意义。     

CD4+CD25+调节性T细胞对慢性丙型肝炎患者病毒特异性CD8+T细胞的抑制作用

HCV感染是严重危害人民健康的传染病，易发展成慢性丙型肝炎、肝硬化，且与原发性肝癌密切相关。HCV持续感染的一个重要原因是HCV特异性CD8^＋T细胞数量及功能缺陷，表现在体外增殖能力下降和IFN-γ分泌水平降低。CD4^＋CD25^＋调节性T细胞（T regulatory cells，Treg）主要在机体免疫系统中发挥负向调节作用，在移植物抗宿主病、自身免疫病、过敏性疾病等的发病机制和临床治疗中有潜在应用价值。已有研究表明，     

Comparative analysis of naïve and memory CD4+ and CD8+ T-cell subsets in bone marrow and G-CSF-mobilized peripheral blood stem cell allografts: impact of donor characteristics

OBJECTIVE: Donor T cells expressing lymph node homing receptors are the foremost initiators of acute graft-vs-host disease (aGVHD), and a high proportion of CD4(+)CCR7(+) T cells in human leukocyte antigen-matched allografts has been shown to confer a high risk of aGVHD without interfering in other outcomes. METHODS: Na?ve, central memory (T(CM)), effector memory (T(EM)), and terminally differentiated effector memory (T(TD)) subsets, further subdivided by CD28 expression, were compared in 52 bone marrow and 37 granulocyte colony-stimulating factor-mobilized peripheral blood harvests. RESULTS: CCR7(+) cells (na?ve and T(CM)) predominated in the CD4(+) population, whereas CD8(+) memory cells were chiefly CCR7(neg) in the grafts. Donor age, antecedent of chronic infections, and graft type were independent factors influencing graft composition. CD8(+) na?ve cells negatively correlated and CD8(+) T(EM) positively correlated with age. Cytomegalovirus seropositivity was associated with more CD8(+) T(TD) and diminished CD28 expression. Toxoplasmosis seropositivity was associated with more CD4(+) T(CM) (p = 0.021). Marrow grafts comprised more CD28(+) cells within CD8(+) T(TD), but the percentage of CD4(+)CCR7(+) cells did not differ significantly between the two graft sources. Each of the four CD4(+) subsets and the percentage of CD4(+)CCR7(+) cells (p < 0.001) were correlated between graft and venous blood analyzed in 42 donors before harvest procedures. CONCLUSION: This study provides reference values for CD4(+) and CD8(+) na?ve and memory subsets within allografts applicable to the healthy donor population and indicates that beforehand analysis of a whole-blood sample can help evaluating the risk of aGVHD conferred by each donor and, when possible, choosing the one conferring the lowest risk.     

In vivo dynamics of T cell activation,proliferation, and death in HIV-1 infection: why are CD4+ but not CD8+ T cells depleted?

Deuterated glucose labeling was used to measure the in vivo turnover of T lymphocytes. A realistic T cell kinetic model, with populations of resting and activated T cells, was fitted to d-glucose labeling data from healthy and HIV-1-infected individuals before and after antiretroviral treatment. Our analysis highlights why HIV-1 infection, which increases the fraction of both CD4(+) and CD8(+) T lymphocytes that are proliferating (Ki67(+)), leads to CD4 but not CD8 depletion. We find that HIV-1 infection tends to increase the rates of death and proliferation of activated CD4(+) T cells, and to increase the rate at which resting CD4 T cells become activated, but does not increase the fraction of activated CD4(+) T cells, consistent with their preferential loss in HIV-1-infected individuals. In contrast, HIV-1 infection does not lead to an increase in proliferation or death rates of activated CD8(+) T cells, but did increase the fraction of activated CD8(+) T cells, consistent with these cells remaining in an activated state longer and undergoing more rounds of proliferation than CD4(+) T cells. Our results also explain why telomeres shorten in CD8(+) cells, but not in CD4(+) cells of HIV-1-infected patients, compared with age-matched controls.     

Dietary gluten triggers concomitant activation of CD4+ and CD8+ αβ T cells and γδ T cells in celiac disease

Celiac disease is an intestinal autoimmune disease driven by dietary gluten and gluten-specific CD4⁺ T-cell responses. In celiac patients on a gluten-free diet, exposure to gluten induces the appearance of gluten-specific CD4⁺ T cells with gut-homing potential in the peripheral blood. Here we show that gluten exposure also induces the appearance of activated, gut-homing CD8⁺ αβ and γδ T cells in the peripheral blood. Single-cell T-cell receptor sequence analysis indicates that both of these cell populations have highly focused T-cell receptor repertoires, indicating that their induction is antigen-driven. These results reveal a previously unappreciated role of antigen in the induction of CD8⁺ αβ and γδ T cells in celiac disease and demonstrate a coordinated response by all three of the major types of T cells. More broadly, these responses may parallel adaptive immune responses to viral pathogens and other systemic autoimmune diseases.     

Replicative senescence: the final stage of memory T cell differentiation?

One of the major obstacles to effective prolonged CD8 T cell control over HIV and other latent infections may be the intrinsic, genetically programmed barrier to unlimited proliferation that is characteristic of all normal human somatic cells. Replicative senescence, characterized extensively in cell culture for a variety of cell types, comprises both irreversible cell cycle arrest and striking changes in function. CD8 T cells with features similar to senescent CD8 T cell cultures (i.e., absence of CD28, inability to proliferate, telomeres in the 5-7 kb range, resistance to apoptosis) increase progressively during aging and in chronic HIV infection, suggesting that replicative senescence may be occurring in vivo, and, in fact, may constitute the final stage in the normal differentiation of human T cells. CD8 T cells with characteristics suggestive of senescence have also been implicated in modulating immune function and altering bone homeostasis. Further characterization of the underlying mechanism leading to the generation of senescent memory CD8 T cells and analysis of their functional attributes will help elucidate their role in HIV disease pathogenesis.