Early activation defects in T lymphocytes from aged mice

The MAPK dual specific phosphatase (DUSP) proteins: A versatile wrestler in T cell functionality

The functional state of T cells is diverse and under dynamic control for adapting to the changes of microenvironment. Reversible protein phosphorylation represents an important post-translational modification that not only involves in the immediate early response of T cells, but also affects their functionality in the long run. Perturbation of global phosphorylation profile and/or phosphorylation of specific signaling nodes result in aberrant T cell activity. Dual specific phosphatases (DUSPs), which target MAPKs and beyond, have increasingly been emerged as a versatile regulator in T cell biology. Herein in this mini review, we sought to summarize and discuss the impact of DUSP proteins on the regulation of effector T cell activity, T cell polarization, regulatory T cell development and T cell senescence/exhaustion. Given the distinctive engagement of each DUSP member under various disease settings such as chronic infection, autoimmune disorders, cancer and age-related diseases, DUSP proteins likely hold the promise to become a druggable target other than the existing therapeutics that are predominantly by manipulating protein kinase activity.

T-cell Subset Profile in Kidney Recipients of Extended or Standard Donors

INTRODUCTION

The usage of extended-criteria donors (ECD) became a routinely accepted manner in the last decade. ECD is a potential risk factor for antibody-mediated rejection. Analysis of lymphocyte subsets might be a complementary diagnostic toolkit because there is limited knowledge about this term.

METHOD

Between May 12, 2016, and September 4, 2019, a total of 130 patients who had undergone kidney transplant were investigated. Patients were divided in ECD and standard criteria donor (SCD) groups. Blood samples were collected before the operation, then in the first week and after 30, 60, 180, and 365 days. Besides routine laboratory tests, multicolor flow cytometry was performed for lymphocyte subsets.

RESULTS

ECD grafts were transplanted to older recipients. The number of CD4+ cells increased in the SCDs from the first week to until the end of first month, and then decreased. The number of CD4+ cells decreased from the beginning of the study until the end of first year to 66% of its original value in ECDs. At the first month, the number of CD19+ cells was higher in SCD compared with ECD cases; the number then decreased in both groups. T-regulatory cells had a drop at the first week that lasted until the first month. A bigger increase in SCD and a moderate increase in ECD group were then observed. The kinetics of CD19+ and CD19+ naive cells are similar in the ECD and SCD groups. In the SCD group, cell count decreased in both CD19+ (13%) and CD19+ naive (12%) between third and sixth month. The count of CD19+ cells decreased by 9%, but the count of CD19+ naive cells increased by 11% between the sixth month and first year.

DISCUSSION

The prolonged postoperative uremic state caused by the poorer initial function, together with an aging immune system, explains the weaker immune response in ECD patients, which may be the cause of the decreased number of memory and regulatory T cells. Older patients with an ECD graft need a tailored, personalized, and less aggressive immunosuppressive treatment.

Proteodynamics and aging of eukaryotic cells

All aspects of each protein existence in the eukaryotic cells, starting from the pre-translation events, through translation, multiple different post-translational modifications, functional life and eventual proteostatic removal after loss of functionality and changes in physico-chemical properties, can be collectively called the proteodynamics. With aging, passing of time as well as accumulating effects of exposures, interactions and wearing-off lead to problems at each of the above mentioned stages, eventually leading to general malfunction of the proteome. This work briefly reviews and summarizes current knowledge concerning this important topic.

Age-related Autoimmune Changes in Lacrimal Glands

Aging is a complex process associated with dysregulation of the immune system and low levels of inflammation, often associated with the onset of many pathologies. The lacrimal gland (LG) plays a vital role in the maintenance of ocular physiology and changes related to aging directly affect eye diseases. The dysregulation of the immune system in aging leads to quantitative and qualitative changes in antibodies and cytokines. While there is a gradual decline of the immune system, there is an increase in autoimmunity, with a reciprocal pathway between low levels of inflammation and aging mechanisms. Elderly C57BL/6J mice spontaneously show LGs infiltration that is characterized by Th1 but not Th17 cells. The aging of the LG is related to functional alterations, reduced innervation and decreased secretory activities. Lymphocytic infiltration, destruction, and atrophy of glandular parenchyma, ductal dilatation, and secretion of inflammatory mediators modify the volume and composition of tears. Oxidative stress, the capacity to metabolize and eliminate toxic substances decreased in aging, is also associated with the reduction of LG functionality and the pathogenesis of autoimmune diseases. Although further studies are required for a better understanding of autoimmunity and aging of the LG, we described anatomic and immunology aspects that have been described so far.

Proteodynamics in aging human T cells - The need for its comprehensive study to understand the fine regulation of T lymphocyte functions

Cellular life depends mostly on the creation, modification, interactions and destruction of proteins. This is true for every cell, including human T lymphocytes. One way these cells can ascertain the fidelity and at least partial functionality of their proteomes under constant attack of irreversible modulations (e.g., ROS- or glycation-dependent) is proteostasis. However, with cellular aging proteostasis progressively fails and proteostenosis (decreased amounts and functionalities of remaining proteins) occurs. There are several mechanisms involved in the modulation and protection of the proteome in the T cells which include mainly multiple layers of vesicle-bound and cytoplasmic proteases (e.g., lysosomal and proteasomal ones) acting mostly by degradation of obsolete and age-modified proteins. Recently it was shown that another not yet so widely known system consisting of obligatorily calcium-dependent cysteine proteases, the calpains and their inhibitor, the calpastatin serves in T cells as a dual switch, either activating or inactivating different proteins depending on intracellular conditions. Thus the proteolytic elimination of altered proteins as well as modulation of activity of those remaining leads to dynamic change of proteome composition and function (proteodynamics) in aging lymphocytes, so far in an almost unknown way. Aging T cell proteodynamics requires further comprehensive analysis of the resulting lysoproteomic patterns and their changes.

A crucial role of the PD-1H coinhibitory receptor in suppressing experimental asthma

Programmed death one homolog (PD-1H) is a cell surface molecule of the B7/CD28 immune modulatory gene family. Although PD-1H has been shown to function as a coinhibitory receptor on T cells to limit naive T-cell activation and proliferation, its role in the regulation of the T-cell response to allergens is unknown. We report here that genetic ablation or blockade of PD-1H drastically promotes pulmonary inflammation with massive accumulation of eosinophils in a mouse model of experimental asthma, indicating a suppressive function of PD-1H in allergic inflammation. The loss of PD-1H led to elevated production of both innate cytokines (IL-6, MCP-1 and TNFα) and Th2 cytokines (IL-5 and IL-13) in the lung, indicating a critical role of PD-1H in suppressing the production of airway inflammatory cytokines. In addition, the loss of PD-1H also impaired the expansion of systemic and pulmonary regulatory T cells during asthma induction. These findings support a critical role of intrinsic PD-1H in the regulation of inflammatory responses to allergens. Finally, we showed that treatment with a PD-1H agonistic monoclonal antibody reduced the severity of asthma, which was accompanied by suppressed lung inflammation. Our findings support PD-1H as a potential target and suggest a possible strategy for the treatment of allergic asthma in humans.

Nutritional modulation of age-related changes in the immune system and risk of infection

The immune system undergoes some adverse alterations during aging, many of which have been implicated in the increased morbidity and mortality associated with infection in the elderly. In addition to intrinsic changes to the immune system with aging, the elderly are more likely to have poor nutritional status, which further impacts the already impaired immune function. Although the elderly often have low zinc serum levels, several manifestations commonly observed during zinc deficiency are similar to the changes in immune function with aging. In the case of vitamin E, although its deficiency is rare, the intake above recommended levels is shown to enhance immune functions in the elderly and to reduce the risk of acquiring upper respiratory infections in nursing home residents. Vitamin D is a critical vitamin in bone metabolism, and its deficiency is far more common, which has been linked to increased risk of infection as demonstrated in a number of observational studies including those in the elderly. In this review, we focus on zinc, vitamin E, and vitamin D, the 3 nutrients which are relatively well documented for their roles in impacting immune function and infection in the elderly, to discuss the findings in this context reported in both the observational studies and interventional clinical trials. A perspective will be provided based on the analysis of information under review.

Differential effect of HLA class-I versus class-II transgenes on human T and B cell reconstitution and function in NRG mice

Humanized mice expressing Human Leukocyte Antigen (HLA) class I or II transgenes have been generated, but the role of class I vs class II on human T and B cell reconstitution and function has not been investigated in detail. Herein we show that NRG (NOD.RagKO.IL2RγcKO) mice expressing HLA-DR4 molecules (DRAG mice) and those co-expressing HLA-DR4 and HLA-A2 molecules (DRAGA mice) did not differ in their ability to develop human T and B cells, to reconstitute cytokine-secreting CD4 T and CD8 T cells, or to undergo immunoglobulin class switching. In contrast, NRG mice expressing only HLA-A2 molecules (A2 mice) reconstituted lower numbers of CD4 T cells but similar numbers of CD8 T cells. The T cells from A2 mice were deficient at secreting cytokines, and their B cells could not undergo immunoglobulin class switching. The inability of A2 mice to undergo immunoglobulin class switching is due to deficient CD4 helper T cell function. Upon immunization, the frequency and cytotoxicity of antigen-specific CD8 T cells in DRAGA mice was significantly higher than in A2 mice. The results indicated a multifactorial effect of the HLA-DR4 transgene on development and function of human CD4 T cells, antigen-specific human CD8 T cells, and immunoglobulin class switching.

Renal transplantation with expanded criteria donors: Which is the optimal immunosuppression?

The growing gap between demand and supply for kidney transplants has led to renewed interest in the use of expanded criteria donor (ECD) kidneys in an effort to increase the donor pool. Although most studies of ECD kidney transplantation confirm lower allograft survival rates and, generally, worse outcomes than standard criteria donor kidneys, recipients of ECD kidneys generally have improved survival compared with wait-listed dialysis patients, thus encouraging the pursuit of this type of kidney transplantation. The relative benefits of transplantation using kidneys from ECDs are dependent on patient characteristics and the waiting time on dialysis. Because of the increased risk of poor graft function, calcineurin inhibitor (CNI)-induced nephrotoxicity, increased incidence of infections, cardiovascular risk, and malignancies, elderly recipients of an ECD kidney transplant are a special population that requires a tailored immunosuppressive regimen. Recipients of ECD kidneys often are excluded from transplant trials and, therefore, the optimal induction and maintenance immunosuppressive regimen for them is not known. Approaches are largely center specific and based upon expert opinion. Some data suggest that antithymocyte globulin might be the preferred induction agent for elderly recipients of ECD kidneys. Maintenance regimens that spare CNIs have been advocated, especially for older recipients of ECD kidneys. CNI-free regimens are not universally accepted due to occasionally high rejection rates. However, reduced CNI exposure and CNI-free regimens based on mammalian target of rapamycin inhibitors have shown acceptable outcomes in appropriately selected ECD transplant recipients.

IL-6 and ICOS Antagonize Bim and Promote Regulatory T Cell Accrual with Age

Regulatory T cells (Tregs), a subset of CD4(+) T cells, dramatically accumulate with age in humans and mice and contribute to age-related immune suppression. Recently, we showed that a majority of accumulating Tregs in aged mice expressed low levels of CD25, and their accrual is associated with declining levels of IL-2 in aged mice. In this study, we further investigated the origin of CD25(lo) Tregs in aged mice. First, aged Tregs had high expression of neuropilin-1 and Helios, and had a broad Vβ repertoire. Next, we analyzed the gene expression profile of Tregs, naive T cells, and memory T cells in aged mice. We found that the gene expression profile of aged CD25(lo) Tregs were more related to young CD25(lo) Tregs than to either naive or memory T cells. Further, the gene expression profile of aged Tregs was consistent with recently described "effector" Tregs (eTregs). Additional analysis revealed that nearly all Tregs in aged mice were of an effector phenotype (CD44(hi)CD62L(lo)) and could be further characterized by high levels of ICOS and CD69. ICOS contributed to Treg maintenance in aged mice, because in vivo Ab blockade of ICOSL led to a loss of eTregs, and this loss was rescued in Bim-deficient mice. Further, serum levels of IL-6 increased with age and contributed to elevated expression of ICOS on aged Tregs. Finally, Treg accrual was significantly blunted in aged IL-6-deficient mice. Together, our data show a role for IL-6 in promoting eTreg accrual with age likely through maintenance of ICOS expression.

Inhibition of adenylyl cyclase type 5 increases longevity and healthful aging through oxidative stress protection

Mice with disruption of adenylyl cyclase type 5 (AC5 knockout, KO) live a third longer than littermates. The mechanism, in part, involves the MEK/ERK pathway, which in turn is related to protection against oxidative stress. The AC5 KO model also protects against diabetes, obesity, and the cardiomyopathy induced by aging, diabetes, and cardiac stress and also demonstrates improved exercise capacity. All of these salutary features are also mediated, in part, by oxidative stress protection. For example, chronic beta adrenergic receptor stimulation induced cardiomyopathy was rescued by AC5 KO. Conversely, in AC5 transgenic (Tg) mice, where AC5 is overexpressed in the heart, the cardiomyopathy was exacerbated and was rescued by enhancing oxidative stress resistance. Thus, the AC5 KO model, which resists oxidative stress, is uniquely designed for clinical translation, since it not only increases longevity and exercise, but also protects against diabetes, obesity, and cardiomyopathy. Importantly, inhibition of AC5's action to prolong longevity and enhance healthful aging, as well as its mechanism through resistance to oxidative stress, is unique among all of the nine AC isoforms.

Zinc homeostasis and immunosenescence

For more than 50 years, zinc is known to be an essential trace element, having a regulatory role in the immune system. Deficiency in zinc thus compromises proper immune function, like it is observed in the elderly population. Here mild zinc deficiency is a common condition, documented by a decline of serum or plasma zinc levels with age. This leads to a dysregulation mainly in the adaptive immunity that can result in an increased production of pro-inflammatory cytokines, known as a status called inflamm-aging. T cell activation as well as polarization of T helper (Th) cells into their different subpopulations (Th1, Th2, Th17, regulatory T cells (Treg)) is highly influenced by zinc homeostasis. In the elderly a shift of the Th cell balance towards Th2 response is observed, a non-specific pre-activation of T cells is displayed, as well as a decreased response to vaccination is seen. Moreover, an impaired function of innate immune cells indicate a predominance of zinc deficiency in the elderly that may contribute to immunosenescence. This review summarizes current findings about zinc deficiency and supplementation in elderly individuals.

Peripheral residence of naïve CD4 T cells induces MHC class II-dependent alterations in phenotype and function

BACKGROUND

As individual naïve CD4 T lymphocytes circulate in the body after emerging from the thymus, they are likely to have individually varying microenvironmental interactions even in the absence of stimulation via specific target recognition. It is not clear if these interactions result in alterations in their activation, survival and effector programming. Naïve CD4 T cells show unimodal distribution for many phenotypic properties, suggesting that the variation is caused by intrinsic stochasticity, although underlying variation due to subsets created by different histories of microenvironmental interactions remains possible. To explore this possibility, we began examining the phenotype and functionality of naïve CD4 T cells differing in a basic unimodally distributed property, the CD4 levels, as well as the causal origin of these differences.

RESULTS

We examined separated CD4hi and CD4lo subsets of mouse naïve CD4 cells. CD4lo cells were smaller with higher CD5 levels and lower levels of the dual-specific phosphatase (DUSP)6-suppressing micro-RNA miR181a, and responded poorly with more Th2-skewed outcomes. Human naïve CD4lo and CD4hi cells showed similar differences. Naïve CD4lo and CD4hi subsets of thymic single-positive CD4 T cells did not show differences whereas peripheral naïve CD4lo and CD4hi subsets of T cell receptor (TCR)-transgenic T cells did. Adoptive transfer-mediated parking of naïve CD4 cells in vivo lowered CD4 levels, increased CD5 and reactive oxygen species (ROS) levels and induced hyporesponsiveness in them, dependent, at least in part, on availability of major histocompatibility complex class II (MHCII) molecules. ROS scavenging or DUSP inhibition ameliorated hyporesponsiveness. Naïve CD4 cells from aged mice showed lower CD4 levels and cell sizes, higher CD5 levels, and hyporesponsiveness and Th2-skewing reversed by DUSP inhibition.

CONCLUSIONS

Our data show that, underlying a unimodally distributed property, the CD4 level, there are subsets of naïve CD4 cells that vary in the time spent in the periphery receiving MHCII-mediated signals and show resultant alteration of phenotype and functionality via ROS and DUSP activity. Our findings also suggest the feasibility of potential pharmacological interventions for improved CD4 T cell responses during vaccination of older people via either anti-oxidant or DUSP inhibitor small molecules.

Allergen-specific immunotherapy in patients 55 years and older: results and review of literature

Introduction Over the years the immune system suffers many morphologic and functional alterations, which result in a peak of function in puberty and a gradual decrease in the elderly. Aim Treat patients 55 years or older with allergic rhinitis with immunotherapy and then analyze the response to allergens. Materials and Methods From June 2009 to July 2010, 104 charts of patients 55 years or older with allergic complaints were evaluated. The patients were selected by anamnesis, physical examination, and otorhinolaryngologic exam. The patients had cutaneous test for mites before and after 1 year of sublingual specific immunotherapy. The cutaneous response was classified as negative (absent), light, moderate, or severe. Results Before vaccination, 42 (40.4%) patients were classified as having a severe form of allergy and 62 (59.6%) as having a moderate allergy. After the specific therapy, 40 (38.4%) patients were classified as negative (absent), 37 (35.6%) as light, 19 (18.3%) as moderate, and 8 (7.7%) as severe responses. Conclusion Immunotherapy, a desensitization technique, is indicated in cases which patients cannot avoid the exposure to allergens and in situations where pharmacologic therapy is not ideal. Specific immunotherapy to treat the allergic rhinitis in elderly patients was efficient and had no collateral effects, and in addition to the clinical benefit, improvement in the cutaneous test could also be observed.

IL-15 Fosters Age-Driven Regulatory T Cell Accrual in the Face of Declining IL-2 Levels

We and others have shown that regulatory T cells (Treg) accumulate dramatically with age in both humans and mice. Such Treg accrual contributes to age-related immunosenescence as they reduce the response to tumors and parasite infection. While we reported earlier that aged Treg have decreased expression of the pro-apoptotic molecule Bim and germline deletion of Bim promoted earlier accumulation of Treg, it remains unclear whether the effects of Bim are: (i) Treg intrinsic and (ii) dominant to other BH3-only pro-apoptotic molecules. Further, the mechanism(s) controlling Bim expression in aged Treg remain unclear. Here we show that Treg-specific loss of Bim is sufficient to drive Treg accrual with age and that additional loss of the downstream apoptotic effectors Bax and Bak did not exacerbate Treg accumulation. Further, our results demonstrate that a subpopulation of Treg expands with age and is characterized by lower expression of CD25 (IL-2Rα) and Bim. Mechanistically, we found that IL-2 levels decline with age and likely explain the emergence of CD25(lo)Bim(lo) Treg because Treg in IL-2(-/-) mice are almost entirely comprised of CD25(lo)Bim(lo) cells, and IL-2 neutralization increases CD25(lo)Bim(lo) Treg in both young and middle-aged mice. Interestingly, the Treg population in aged mice had increased expression of CD122 (IL-2/IL-15Rβ) and neutralization or genetic loss of IL-15 led to less Treg accrual with age. Further, the decreased Treg accrual in middle-aged IL-15(-/-) mice was restored by the additional loss of Bim (IL-15(-/-)Bim(-/-)). Together, our data show that aging favors the accrual of CD25(lo) Treg whose homeostasis is supported by IL-15 as IL-2 levels become limiting. These data have implications for manipulating Treg to improve immune responses in the elderly.

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.

Kidney transplantation and the ageing immune system

The world population is rapidly growing and ageing at a pace that is projected to continue for at least three decades. This shift towards an older populace has invariably increased the number of individuals with diseases related to ageing, such as chronic kidney disease. The increase in chronic kidney disease is associated with a growing number of elderly patients receiving kidney transplants. Understanding how the immune system changes with increasing age will help to define the risks of rejection and infection in the elderly population and will focus attention on the need for individualized immunosuppression for patients in this age group. This Review addresses what is currently known about ageing and the immune system, highlighting age-related changes that affect the outcome of transplantation in elderly individuals. The need for new strategies to improve outcomes in this growing population of elderly renal transplant recipients is also emphasized.

Ex vivo enzymatic treatment of aged CD4 T cells restores cognate T cell helper function and enhances antibody production in mice

Previous in vitro studies showed that CD4 T cells from old mice have defects in TCR signaling, immune synapse formation, activation, and proliferation. We reported that removing a specific set of surface glycoproteins by ex vivo treatment with O-sialoglycoprotein endopeptidase (OSGE) can reverse many aspects of the age-related decline in CD4 T cell function. However, the specific mechanism by which this process occurs remains unclear, and it is unknown whether this enzymatic treatment can also restore important aspects of adaptive immunity in vivo. By using an in vivo model of the immune response based on adoptive transfer of CD4 T cells from pigeon cytochrome C-specific transgenic H-2(k/k) TCR-Vα(11)Vβ(3) CD4(+) mice to syngeneic hosts, we demonstrate that aging diminishes CD28 costimulatory signals in CD4 T cells. These age-associated defects include changes in phosphorylation of AKT and expression of glucose transporter type I, inducible T cell costimulatory molecule, and CD40L, suggesting that the lack of CD28 costimulation contributes to age-dependent loss of CD4 function. All of these deficits can be reversed by ex vivo OSGE treatment. Blocking B7-CD28 interactions on T cells prevents OSGE-mediated restoration of T cell function, suggesting that changes in surface glycosylation, including CD28, may be responsible for the age-related costimulation decline. Finally, we show that the age-related decline in CD4 cognate helper function for IgG production and long-term humoral immunity can also be restored by OSGE treatment of CD4 T cells prior to adoptive transfer.

Aged-related shifts in T cell homeostasis lead to intrinsic T cell defects

Our recent studies indicate that the longer peripheral persistence of naïve CD4 T cells that occurs with age is necessary for the development of the key aging defects that lead to compromised responses to vaccination and to new pathogens or new strains of circulating infectious agents. This longer persistence is in turn is linked to the decrease in development of new thymic emigrants and thymic involution that occur at adolescence. Therefore the process of development of naïve CD4 aging defects, is closely tied to the homeostasis of T cells and the shifts that occur in their homeostasis with age. Here we review this connection between age-related changes in T cell homeostasis and the development of T cell defects and discuss the implication for approaches to better vaccinating the elderly.

Decline in miR-181a expression with age impairs T cell receptor sensitivity by increasing DUSP6 activity

The ability of the human immune system to respond to vaccination declines with age. We identified an age-associated defect in T cell receptor (TCR)-induced extracellular signal-regulated kinase (ERK) phosphorylation in naive CD4(+) T cells, whereas other signals, such as ζ chain-associated protein kinase 70 (ZAP70) and phospholipase C-γ1 phosphorylation, were not impaired. The defective ERK signaling was caused by the dual specific phosphatase 6 (DUSP6), whose protein expression increased with age due to a decline in repression by miR-181a. Reconstitution of miR-181a lowered DUSP6 expression in naive CD4(+) T cells in elderly individuals. DUSP6 repression using miR-181a or specific siRNA and DUSP6 inhibition by the allosteric inhibitor (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one improved CD4(+) T cell responses, as seen by increased expression of activation markers, improved proliferation and supported preferential T helper type 1 cell differentiation. DUSP6 is a potential intervention target for restoring T cell responses in the elderly, which may augment the effectiveness of vaccination.

Signaling pathways in aged T cells - a reflection of T cell differentiation, cell senescence and host environment

With increasing age, the ability of the immune system to protect against new antigenic challenges or to control chronic infections erodes. Decline in thymic function and cumulating antigenic experiences of acute and chronic infections threaten T cell homeostasis, but insufficiently explain the failing immune competence and the increased susceptibility for autoimmunity. Alterations in signaling pathways in the aging T cells account for many of the age-related defects. Signaling threshold calibrations seen with aging frequently built on mechanisms that are operational in T cell development and T cell differentiation or are adaptations to the changing environment in the aging host. Age-related changes in transcription of receptors and signaling molecules shift the balance towards inhibitory pathways, most dominantly seen in CD8 T cells and to a lesser degree in CD4 T cells. Prominent examples are the expression of negative regulatory receptors of the CD28 and the TNF receptor superfamilies as well the expression of various cytoplasmic and nuclear dual-specific phosphatases.

Age-related accumulation of T cells with markers of relatively stronger autoreactivity leads to functional erosion of T cells

Background

Thymic involution is a prominent characteristic of an aging immune system. When thymic function is reduced/absent, the peripheral T cell pool is subject to the laws of peripheral T cell homeostasis that favor survival/expansion of T cell receptors with relatively higher functional avidity for self-peptide/MHC complexes. Due to difficulties in assessing the TCR avidity in polyclonal population of T cells, it is currently not known whether high avidity T cells preferentially survive in aging individuals, and what impact this might have on the function of the immune system and development of autoimmune diseases.

Results

The phenotype of T cells from aged mice (18-24 months) indicating functional TCR avidity (CD3 and CD5 expression) correlates with the level of preserved thymic function. In mice with moderate thymic output (> 30% of peripheral CD62L^hi T cells), T cells displayed CD3^lowCD5^hi phenotype characteristic for high functional avidity. In old mice with drastically low numbers of CD62L^hi T cells reduced CD5 levels were found. After adult thymectomy, T cells of young mice developed CD3^lowCD5^hi phenotype, followed by a CD3^lowCD5^low phenotype. Spleens of old mice with the CD3^low/CD5^hi T cell phenotype displayed increased levels of IL-10 mRNA, and their T cells could be induced to secrete IL-10 in vitro. In contrast, downmodulation of CD5 was accompanied with reduced IL-10 expression and impaired anti-CD3 induced proliferation. Irrespective of the CD3/CD5 phenotype, reduced severity of experimental allergic myelitis occurred in old mice. In MTB TCRβ transgenic mice that display globally elevated TCR avidity for self peptide/MHC, identical change patterns occurred, only at an accelerated pace.

Conclusions

These findings suggest that age-associated dysfunctions of the immune system could in part be due to functional erosion of T cells devised to protect the hosts from the prolonged exposure to T cells with high-avidity for self.

Vitamin E, signalosomes and gene expression in T cells

CD4+T cells from aged humans or mice show significant reductions in IL-2 production upon activation. The resulting decreased proliferation is linked to higher risks of infection in the elderly. Several lines of evidence indicate that intrinsic defects preferentially affecting the naïve subset of CD4+T cells contribute to this reduced IL-2 production. Comparison of the biochemical pathways that transduce activation signals from the T cell receptor to the IL-2 promoter in young and old CD4+T cells has demonstrated age-related impairments at initial molecular events, in particular the phosphorylation of kinases and adapter proteins involved in the formation of signalosomes - complex multiprotein assemblies that provide the framework for effective signal transduction. Confocal microscopy has demonstrated a series of age-related impairments in effective immune synapse formation. Vitamin E can reverse many of these CD4+T cell age-associated defects, including reduced levels of phosphorylation of critical signaling/adapter proteins as well as defective immune synapse formation. Vitamin E also enhances IL-2 production, expression of several cell cycle control proteins, and proliferation. Although the precise mechanisms underlying this effect are not understood, it is possible that this antioxidant lipophilic vitamin can prevent the propagation of polyunsaturated fatty acid peroxidation in the cell membrane, influence the biochemical characteristics of specific lipid bilayer microdomains involved in signal transduction, modulate the activity of kinases/phosphatases, or interact with intracellular receptors.

Expression of HLA class II molecules in humanized NOD.Rag1KO.IL2RgcKO mice is critical for development and function of human T and B cells

BACKGROUND

Humanized mice able to reconstitute a surrogate human immune system (HIS) can be used for studies on human immunology and may provide a predictive preclinical model for human vaccines prior to clinical trials. However, current humanized mouse models show sub-optimal human T cell reconstitution and limited ability to support immunoglobulin class switching by human B cells. This limitation has been attributed to the lack of expression of Human Leukocyte Antigens (HLA) molecules in mouse lymphoid organs. Recently, humanized mice expressing HLA class I molecules have been generated but showed little improvement in human T cell reconstitution and function of T and B cells.

METHODS

We have generated NOD.Rag1KO.IL2RγcKO mice expressing HLA class II (HLA-DR4) molecules under the I-E(d) promoter that were infused as adults with HLA-DR-matched human hematopoietic stem cells (HSC). Littermates lacking expression of HLA-DR4 molecules were used as control.

RESULTS

HSC-infused HLA-DR4.NOD.Rag1KO.IL-2RγcKO mice developed a very high reconstitution rate (>90%) with long-lived and functional human T and B cells. Unlike previous humanized mouse models reported in the literature and our control mice, the HLA-DR4 expressing mice reconstituted serum levels (natural antibodies) of human IgM, IgG (all four subclasses), IgA, and IgE comparable to humans, and elicited high titers of specific human IgG antibodies upon tetanus toxoid vaccination.

CONCLUSIONS

Our study demonstrates the critical role of HLA class II molecules for development of functional human T cells able to support immunoglobulin class switching and efficiently respond to vaccination.

Increased sensitivity to antigen in high avidity CD8(+) T cells results from augmented membrane proximal T-cell receptor signal transduction

The functional avidity of a cytotoxic T lymphocyte (CTL) is known to be a critical determinant of the efficacy with which it clears pathogens. High avidity cells, which are by definition highly sensitive to peptide antigen, are superior for elimination of viruses and tumours. Our studies have established the ability of T cells to undergo avidity modulation as a result of antigen encounter. High and low avidity cells established in this manner exhibit significant differences in the amount of peptide required to elicit effector function. However, how signalling is regulated in these cells as it relates to the control of peptide sensitivity remains to be defined. To address this question, we compared T-cell receptor (TCR) signal transduction events in high and low avidity CTL generated from OT-I(rag2-) TCR transgenic mice. Our data suggest that divergent signalling is initiated at the TCR-associated CD3ζ, with low avidity CTL requiring higher amounts of pMHC to achieve threshold levels of phosphorylated CD3ζ compared with high avidity CTL. Further, this difference is transduced further downstream to mitogen-activated protein kinase and Ca(2+) signalling pathways. These results suggest that regulated control of the initiation of TCR signalling in high versus low avidity cells determines the amount of peptide required for T-cell activation.

Gain and loss of T cell subsets in old age--age-related reshaping of the T cell repertoire

The immune system is affected by the aging process and undergoes significant age-related changes, termed immunosenescence. Different T cell subsets are affected by this process. Alterations within the bone marrow and thymus lead to a shift in the composition of the T cell repertoire from naïve to antigen-experienced T cells, thereby compromising the diversity of the T cell pool. Additional infection with latent pathogens such as cytomegalovirus aggravates this process. In this review, we focus on the major age-related changes that occur in the naïve and the antigen-experienced T cell population. We discuss the mechanisms responsible for the generation and maintenance of these subsets and how age-related changes can be delayed or prevented by clinical interventions.

A major role for Bim in regulatory T cell homeostasis

We have previously shown that regulatory T cells (Treg) accumulate dramatically in aged animals and negatively impact the ability to control persistent infection. However, the mechanisms underlying the age-dependent accrual of Treg remain unclear. In this study, we show that Treg accumulation with age is progressive and likely not the result of increased thymic output, increased peripheral proliferation, or from enhanced peripheral conversion. Instead, we found that Treg from aged mice are more resistant to apoptosis than Treg from young mice. Although Treg from aged mice had increased expression of functional IL-7Rα, we found that IL-7R signaling was not required for maintenance of Treg in vivo. Notably, aged Treg exhibit decreased expression of the proapoptotic molecule Bim compared with Treg from young mice. Furthermore, in the absence of Bim, Treg accumulate rapidly, accounting for >25% of the CD4(+) T cell compartment by 6 mo of age. Additionally, accumulation of Treg in Bim-deficient mice occurred after the cells left the transitional recent thymic emigrant compartment. Mechanistically, we show that IL-2 drives preferential proliferation and accumulation of Bim(lo) Treg. Collectively, our data suggest that chronic stimulation by IL-2 leads to preferential expansion of Treg having low expression of Bim, which favors their survival and accumulation in aged hosts.

Age-related defects in the cytoskeleton signaling pathways of CD4 T cells

It has been postulated that the cytoskeleton controls many aspects of T cell function, including activation, proliferation and apoptosis. Recent advances in our understanding of F-actin polymerization and the Ezrin-Radixin-Moesin (ERM) family of cytoskeleton signal proteins have provided new insights into immunological synapse formation during T cell activation. During aging there is a significant decline of T cell function largely attributable to declines in activation of CD4 T cells and defects in the formation of the immunological synapse. Here we discuss recent progress in the understanding of how aging alters F-actin and ERM proteins in mouse CD4 T cells, and the implications of these changes for the T cell activation process.

Aging and HIV infection

INTRODUCTION

Population aging has become a global phenomenon, and HIV infection among older individuals is also increasing. Because age can affect the progression of HIV infection, we aimed to evaluate the present knowledge on HIV infection in older patients.

METHODS

Literature review of the last 20 years.

RESULTS

Older HIV-infected patients have lower CD4(+) T cell counts, higher viral load and are more frequently symptomatic at diagnosis. The infection progresses more rapidly, with higher morbidity and lethality rates. However, older patients are more compliant to antiretroviral treatment; they experience a better virologic response, and treatment represents a positive clinical impact. Aging affects the complex interaction between HIV infection and the immune system. Both conditions contribute to the dysfunction of immune cells, including a decrease in the phagocytes' microbicidal capability, natural killer cells' cytolytic function, expression of toll-like receptors and production of interleukin-12. Chronic immune activation responsible for the depletion of CD4(+) and CD8(+) T cells in HIV infection appears to worsen with senescence. Older patients also exhibit a less robust humoral response, with the production of less avid and specific antibodies.

CONCLUSION

Both HIV and aging contribute to immune dysfunction, morbidity and mortality. However, highly active antiretroviral therapy (HAART) is beneficial for older patients, and treatment of older patients should not be discouraged.

Predicting cytotoxic T-cell age from multivariate analysis of static and dynamic biomarkers

Adoptive T-cell transfer therapy relies upon in vitro expansion of autologous cytotoxic T cells that are capable of tumor recognition. The success of this cell-based therapy depends on the specificity and responsiveness of the T cell clones before transfer. During ex vivo expansion, CD8+ T cells present signs of replicative senescence and loss of function. The transfer of nonresponsive senescent T cells is a major bottleneck for the success of adoptive T-cell transfer therapy. Quantitative methods for assessing cellular age and responsiveness will facilitate the development of appropriate cell expansion and selection protocols. Although several biomarkers of lymphocyte senescence have been identified, these proteins in isolation are not sufficient to determine the age-dependent responsiveness of T cells. We have developed a multivariate model capable of extracting combinations of markers that are the most informative to predict cellular age. To acquire signaling information with high temporal resolution, we designed a microfluidic chip enabling parallel lysis and fixation of stimulated cell samples on-chip. The acquisition of 25 static biomarkers and 48 dynamic signaling measurements at different days in culture, integrating single-cell and population based information, allowed the multivariate regression model to accurately predict CD8+ T-cell age. From surface marker expression and early phosphorylation events following T-cell receptor stimulation, the model successfully predicts days in culture and number of population doublings with R2=0.91 and 0.98, respectively. Furthermore, we found that impairment of early signaling events following T cell receptor stimulation because of long term culture allows prediction of costimulatory molecules CD28 and CD27 expression levels and the number of population divisions in culture from a limited subset of signaling proteins. The multivariate analysis highlights the information content of both averaged biomarker values and heterogeneity metrics for prediction of cellular age within a T cell population.

Cytomegalovirus infection- and age-dependent changes in human CD8+ T-cell cytokine expression patterns

T cells are strongly affected by immune aging, a phenomenon that leads to increased susceptibility to infections and decreased vaccination efficacy in elderly individuals. Cytomegalovirus (CMV) infection induces vigorous T-cell immune responses in humans and is thought to be a driving force of immune aging. In the present study we analyzed CMV-induced quantitative and qualitative differences in the cytokine-expressing T-cell repertoire from individuals of different age groups after in vitro stimulation. The CMV pp65 peptide pool and the superantigen Staphylococcus enterotoxin B (SEB) induced higher proportions of CD8+ effector T cells expressing gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and granulocyte-macrophage colony-stimulating factor in the oldest study group, while only SEB induced increased responses in the middle-aged study group. Notably, CMV-specific multiple cytokine expression patterns revealed higher proportions of IFN-gamma- and TNF-alpha-coexpressing CD8+ T cells exclusively in the oldest study group. These qualitative differences were absent in SEB-induced CD8+ effector T cells, although quantitative differences were detected. We report age-dependent qualitative changes in CMV-specific CD8+ T-cell cytokine patterns which are biocandidate markers of immune exhaustion in elderly individuals.

B7-H1 expression on old CD8+ T cells negatively regulates the activation of immune responses in aged animals

T cell responses are compromised in the elderly. The B7-CD28 family receptors are critical in the regulation of immune responses. We evaluated whether the B7-family and CD28-family receptors were differentially expressed in dendritic cells, macrophages, and CD4(+) and CD8(+) T cells from young and old mice, which could contribute to the immune dysfunction in the old. Although most of the receptors were equally expressed in all cells, >85% of the old naive CD8(+) T cells expressed B7-H1 compared with 25% in the young. Considering that B7-H1 negatively regulates immune responses, we hypothesized that expression of B7-H1 would downregulate the function of old CD8(+) T cells. Old CD8(+) T cells showed reduced ability to proliferate, but blockade of B7-H1 restored the proliferative capacity of old CD8(+) T cells to a level similar to young CD8(+) T cells. In vivo blockade of B7-H1 restored antitumor responses against the B7-H1(-) BM-185-enhanced GFP tumor, such that old animals responded with the same efficiency as young mice. Our data also indicate that old CD8(+) T cells express lower levels of TCR compared with young CD8(+) T cells. However, following antigenic stimulation in the presence of B7-H1 blockade, the levels of TCR expression were restored in old CD8(+) T cells, which correlated with stronger T cell activation. These studies demonstrated that expression of B7-H1 in old CD8(+) T cells impairs the proper activation of these cells and that blockade of B7-H1 could be critical to optimally stimulate a CD8 T cell response in the old.

Ex vivo enzymatic treatment of aged CD4 T cells restores antigen-driven CD69 expression and proliferation in mice

Declines in immune function have been associated with declines in the function of naïve CD4 T cells. In vitro studies of naïve CD4 T cells in TCR-specific transgenic AND mice have shown age-related defects in immunosynapse formation, activation, proliferation and cytokine production. Previous work has also documented age-related alteration in the glycosylation of surface proteins involved in TCR signaling, and shown that enzymatic treatments to remove specific surface glycoproteins can restore in vitro function in CD4 cells from aged mice. Here an adoptive transfer system shows that a large percentage of naïve CD4 T cells from old mice fail to express CD69 and expand in antigen-primed mice, but these declines in CD69 and expansion can be restored by ex vivo pretreatment of the T cells with the bacterial enzyme O-sialoglycoprotein endopeptidase (OSGE). OSGE treatment also repairs the age-dependent loss of CD69 expression after in vivo activation.

Immunological risk in recipients of kidney transplants from extended criteria donors

BACKGROUND

Determining if a kidney from a marginal donor is likely to elicit a strong and specific immune response, leading to an increased risk of acute rejection, is of importance in renal transplantation.

METHODS

In this study, we analysed the effect of extended criteria donor (ECD) on the incidence of biopsy-proven acute rejection (BPAR) and the effect of immunological risk factors on graft outcome in a large cohort of kidney transplant recipients (n = 2121 patients) grafted with ECD (n = 656 patients) or optimal donor (OD) (n = 1465 patients).

RESULTS

The incidence of BPAR was not statistically different between the ECD group recipients (105/656, 16%) and the OD group recipients (251/1465, 17%) (P = 0.52). These values remained similar after adjustment for immunological risk [defined as retransplantation and/or panel-reactive antibody (PRA) level >20%] (P = 0.92 for patients with immunological risk and P = 0.47 for patients without immunological risk). We next analysed the death-censored graft survival data for OD and ECD groups, as a function of immunological status, and found that the immunological risk factor did not affect graft survival in ECD transplant recipients (P = 0.64).

CONCLUSION

Although our groups were not homogenous, our study did not reveal an increased risk of acute rejection in recipients of ECD allograft.

Memory T cells in Rhesus macaques

The Rhesus macaque (Macaca mulatta) is one of the best studied species of Old World monkeys. DNA sequencing of the entire Rhesus macaque genome, completed in 2007, has demonstrated that humans and macaques share about 93% of their nucleotide sequence. Rhesus macaques have been widely used for medical research including drug testing, neurology, behavioral and cognitive science, reproduction, xenotransplantation and genetics. Because of the Rhesus macaque's sensitivity to bacteria, parasites and viruses that cause similar disease in humans, these animals represent an excellent model to study infectious diseases. The recent pandemic of HIV and the discovery of SIV, a lentivirus genetically related to HIV Type 1 that causes AIDS in Rhesus macaques, have prompted the development of reagents that can be used to study innate and adaptive immune responses in macaques at the single cell level. This review will focus on the distribution of memory cells in the different immunologic compartments of Rhesus macaques. In addition, the strategies available to manipulate memory cells in Rhesus macaques to understand their trafficking and function will be discussed. Emphasis is placed on studies of memory cells in macaques infected with SIV because many studies are available. Lastly, we highlight the usefulness of the Rhesus macaque model in studies related to the aging of the immune system.

Effects of aging on the adaptive immune response to respiratory virus infections

Severe acute respiratory disease caused by respiratory virus infections in individuals aged 65 years and older and in high-risk adults, such as those with chronic cardiopulmonary disorders, is associated with increased hospitalization and mortality rates. Epidemiological studies have identified influenza virus and respiratory syncytial virus as the most frequent causes of virus-induced respiratory disease in elderly and high-risk adults. Studies in both humans and animal models have established fundamental defects in cell-mediated and humoral immune responses in aged individuals. However, it is not well understood how age specifically alters the immune response to respiratory pathogens. In this review, we will focus our discussion on the major causative agents of severe respiratory virus infections in elderly and high-risk adults and the age-associated defects in the immune response that probably contribute to the increased disease severity observed in these populations.

PD-1+ memory phenotype CD4+ T cells expressing C/EBPalpha underlie T cell immunodepression in senescence and leukemia

Although altered T cell function plays a part in immunosenescence, the mechanisms remain uncertain. Here we identify a bona fide age-dependent PD-1(+) memory phenotype (MP) CD4(+) T cell subpopulation that hardly proliferates in response to T cell receptor (TCR) stimulation and produces abundant osteopontin at the cost of typical T cell lymphokines. These T cells demonstrate impaired repopulation in Rag2(-/-) mice, but a homeostatic proliferation in gamma-ray-irradiated mice. These T cells also reveal a unique molecular signature, including a strong expression of C/EBPalpha normally expressed in myeloid-lineage cells, with diminished c-Myc and cyclin D1. Transduction of Cebpa in regular CD4(+) T cells inhibited the TCR-mediated proliferation with c-Myc and cyclin D1 repression and caused a striking activation of Spp1 encoding osteopontin along with concomitant repression of T cell lymphokine genes. Although these T cells gradually increase in number with age and become predominant at the senescent stage in normal mice, the generation is robustly accelerated during leukemia. In both conditions, their predominance is associated with the diminution of specific CD4(+) T cell response. The results suggest that global T cell immunodepression in senescence and leukemia is attributable to the increase in PD-1(+) MP CD4(+) T cells expressing C/EBPalpha.

T-cell immunosenescence: lessons learned from mouse models of aging

It is well established that increasing age is associated with a decreased capacity of the immune system to mediate effective immune responses to vaccination and invading pathogens. Because of the inherent limitations of conducting experiments in humans, much of what we have learned is owed to the utility of experimental mouse models of aging. Recent studies performed in the mouse have demonstrated mechanisms responsible for age-related declines in the function of CD4(+) and CD8(+) cells. This review describes key findings regarding age-related defects in T-cell function and discusses the impact these defects have on vaccine efficacy and immunity.

Decreased DNA methyltransferase levels contribute to abnormal gene expression in "senescent" CD4(+)CD28(-) T cells

A senescent CD4(+)CD28(-) T cell subset develops with aging and in chronic inflammatory diseases like rheumatoid arthritis, and is implicated in plaque rupture and myocardial infarctions. This subset is pro-inflammatory, cytotoxic for endothelial cells, and aberrantly expresses genes like CD70, perforin and killer cell immunoglobulin-like receptor (KIR) genes. Why CD4(+)CD28(-) cells overexpress these genes is unclear. We found that the CD70, perforin and KIR2DL4 promoters are demethylated in CD4(+)CD28(-) T cells, and that DNA methyltransferase 1 (Dnmt1) and Dnmt3a levels are decreased in this subset. siRNA "knockdown" of Dnmt1, but not Dnmt3a, in CD4(+)CD28(+) T cells caused similar demethylation and overexpression of KIR2DL4, perforin and CD70, while simultaneous knockdown of Dnmt1 and Dnmt3a caused greater demethylation and overexpression of these genes than Dnmt1 alone. We conclude that decreased Dnmt1 and Dnmt3a cause demethylation and overexpression of these and perhaps other genes in CD4(+)CD28(-) cells, potentially contributing to pathologic functions by this subset.

Alterations of T cell activation signalling and cytokine production by postmenopausal estrogen levels

Background

Immunosenescence is an age-associated disorder occurring primarily in T cell compartments, including altered subset composition, functions, and activation. In women, evidence implicates diminished estrogen in the postmenopausal period as a contributing factor to diminished T cell responsiveness. Since hypoestrogenism is present in postmenopausal women, our objective focused on whether T cell activation, defined as signalling molecule expressions and activation, and function, identified as IL-2 production, were affected by low estrogen.

Methods

Using Jurkat 6.1 T cells, consequences of 4 pg/ml (corresponding to postmenopausal levels) or 40 pg/ml (premenopausal levels) of estradiol (E₂) were analyzed on signalling proteins, CD3-zeta, JAK2, and JAK3, determined by Western immunoblotting. These consequences were correlated with corresponding gene expressions, quantified by real time-polymerase chain reaction. Tyrosine phosphorylation of CD3-zeta was defined by immunoprecipitation and western immunoblotting following activation by T cell receptor (TcR) cross-linking. CD3-zeta expression and modulation was also confirmed in T cells from pre- and postmenopausal women. To assess functional consequences, IL-2 production, induced by PMA and ionomycin, was determined using enzyme-linked immunosorbent spot assay (ELISpot).

Results

At 40 pg/ml E₂, the level of signalling protein CD3-zeta was elevated 1.57-fold, compared with cells exposed to 4 pg/ml E₂. The CD3-zeta proteins also exhibited altered levels of activation-induced phosphorylation in the presence of 40 pg/ml E₂ versus 4 pg/ml: 23 kD phosphorylated form increased 2.64-fold and the 21 kD form was elevated 2.95-fold. Examination of kinases associated with activation signalling also demonstrated that, in the presence of 40 pg/ml E₂, JAK2 protein expression was increased 1.64-fold (p < 0.001) and JAK3 enhanced 1.79-fold (p < 0.001) compared to 4 pg/ml. mRNA levels for CD3-zeta, JAK2, and JAK3 were significantly increased following exposure to 40 pg/ml E₂ (2.39, 2.01, and 2.21 fold, respectively) versus 4 pg/ml. These findings were confirmed in vivo, since T cells from postmenopausal women exhibited 7.2-fold diminished CD3-zeta expression, compared to pre-menopausal controls and this expression was elevated 3.8-fold by addition of 40 pg/ml E₂. Functionally, Jurkat cells exposed to 40 pg/ml E₂ and activated exhibited significantly elevated numbers of IL-2 producing colonies compared to 4 pg/ml (75.3 ± 2.2 versus 55.7 ± 2.1 colonies, p < 0.0001).

Conclusion

Jurkat T cells exposed to 4 pg/ml E₂ expressed significantly diminished activation signalling proteins, correlating with reduced IL-2 production. Lower signalling protein levels appear to result from decreased CD3-zeta, JAK2, and JAK3 gene expressions. These findings may provide a molecular basis for immunosenescence associated with the postmenopausal state.

Aging augments IL-17 T-cell alloimmune responses

As increasing numbers of elderly patients require solid organ transplantation, the need to better understand how aging modifies alloimmune responses increases. Here, we examined whether aged mice exhibit augmented, donor-specific memory responses prior to transplantation. We found that elevated donor-specific IL-17, but not IFN-gamma, responses were observed in aged mice compared to young mice prior to transplantation. Further characterization of the heightened IL-17 alloimmune response with aging demonstrated that memory CD4(+) T cells were required. Reduced IL-2 alloimmune responses with age contributed to the elevated IL-17 phenotype in vitro, and treatment with an anti-IL-17 antibody delayed the onset of acute allograft rejection. In conclusion, aging leads to augmented, donor-specific IL-17 immune responses that are important for the timing of acute allograft rejection in aged recipients. IL-17 targeting therapies may be useful for averting transplant rejection responses in older transplant recipients.

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.

The effect of age and telomere length on immune function in the horse

Telomeres, specialized structures present at the ends of linear eukaryotic chromosomes, function to maintain chromosome stability and integrity. Telomeres shorten with each cell division eventually leading to replicative senescence, a process thought to be associated with age-related decline in immune function. We hypothesized that shortened PBMC telomere length is a factor contributing to immunosenescence of the aged horse. Telomere length was assessed in 19 horses ranging in age from 1 to 25 years. Mitogen-induced 3H-thymidine incorporation, total serum IgG, and pro-inflammatory cytokine expression was also determined for each horse. Relative telomere length (RTL) was highly correlated with overall age. RTL was positively correlated with 3H-thymidine incorporation and total IgG. Expression of pro-inflammatory cytokines was negatively correlated with RTL. These measures were also correlated with age, as expected. However, RTL was not correlated with immunosenescence and inflammaging in the oldest horse.

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.