Potentiation of Th17 cytokines in aging process contributes to the development of colitis

Th17 cells, which produce IL-17 and IL-22, promote autoimmunity in mice and have been implicated in the pathogenesis of autoimmune/inflammatory diseases in humans. However, the Th17 immune response in the aging process is still not clear. In the present study, we found that the induction of IL-17-produing CD4⁺ T cells was significantly increased in aged individuals compared with young healthy ones. The mRNA expression of IL-17, IL-17F, IL-22, and RORC2 was also significantly increased in aged people. Similar to humans, Th17 cells as well as mRNAs encoding IL-17, IL-22 and RORγt were dramatically elevated in naïve T cells from aged mouse compared to young ones. In addition, CD44 positive IL-17-producing CD4⁺ T cells were significantly higher in aged mice, suggesting that memory T cells are an important source of IL-17 production. Furthermore, the percentage of IL-17-produing CD4⁺ T cells generated in co-culture with dendritic cells from either aged or young mice did not show significant differences, suggesting that dendritic cells do not play a primary role in the elevation of Th17 cytokines in aged mouse cells. Importantly, transfer of CD4⁺CD45Rb^hi cells from aged mice induced more severe colitis in RAG^−/− mice compared to cells from young mice, Taken together, these results suggest that Th17 immune responses are elevated in aging humans and mice and may contribute to the increased development of inflammatory disorders in the elderly.     

TLR-activated dendritic cells enhance the response of aged naive CD4 T cells via an IL-6-dependent mechanism

The most effective immunological adjuvants contain microbial products, such as TLR agonists, which bind to conserved pathogen recognition receptors. These activate dendritic cells (DCs) to become highly effective APCs. We assessed whether TLR ligand-treated DCs can enhance the otherwise defective response of aged naive CD4 T cells. In vivo administration of CpG, polyinosinic-polycytidylic acid, and Pam(3)CSK(4) in combination with Ag resulted in the increased expression of costimulatory molecules and MHC class II by DCs, increased serum levels of the inflammatory cytokines IL-6 and RANTES, and increased cognate CD4 T cell responses in young and aged mice. We show that, in vitro, preactivation of DCs by TLR ligands makes them more efficient APCs for aged naive CD4 T cells. After T-DC interaction, there are enhanced production of inflammatory cytokines, particularly IL-6, and greater expansion of the aged T cells, resulting from increased proliferation and greater effector survival with increased levels of Bcl-2. TLR preactivation of both bone marrow-derived and ex vivo DCs improved responses. IL-6 produced by the activated DCs during cognate T cell interaction was necessary for enhanced aged CD4 T cell expansion and survival. These studies suggest that some age-associated immune defects may be overcome by targeted activation of APCs by TLR ligands.     

Blocking IL-15 prevents the induction of allergen-specific T cells and allergic inflammation in vivo

IL-15 has been shown to accelerate and boost allergic sensitization in mice. Using a murine model of allergic sensitization to OVA, we present evidence that blocking endogenous IL-15 during the sensitization phase using a soluble IL-15Ralpha (sIL-15Ralpha) suppresses the induction of Ag-specific, Th2-differentiated T cells. This significantly reduces the production of OVA-specific IgE and IgG and prevents the induction of a pulmonary inflammation. Release of proinflammatory TNF-alpha, IL-1beta, IL-6, and IL-12 as well as that of Th2 cytokines IL-4, IL-5, and IL-13 into the bronchi are significantly reduced, resulting in suppressed recruitment of eosinophils and lymphocytes after allergen challenge. It is of clinical relevance that the airway hyper-responsiveness, a major symptom of human asthma bronchiale, is significantly reduced by sIL-15Ralpha treatment. Ex vivo analysis of the draining lymph nodes revealed reduced numbers of CD8, but not CD4, memory cells and the inability of T cells of sIL-15Ralpha-treated mice to proliferate and to produce Th2 cytokines after in vitro OVA restimulation. This phenomenon is not mediated by enhanced numbers of CD4(+)/CD25(+) T cells. These results show that IL-15 is important for the induction of allergen-specific, Th2-differentiated T cells and induction of allergic inflammation in vivo.     

Oral administration with papillomavirus pseudovirus encoding IL-2 fully restores mucosal and systemic immune responses to vaccinations in aged mice

Infectious diseases are one of the major threats for the elderly because their immune system is often compromised, and vaccinations to prevent these infections are not effective. A major defect in their immune system seems to be the inability of T cells to produce IL-2. We used papillomavirus (PV) pseudoviruses (PSVs) as a model vaccine and a gene delivery vector to address how to enhance immune responses to vaccinations. We found that oral immunization with PV PSV induced minimal mucosal and systemic Abs and CTLs specific for the PSVs in aged mice compared with young adult mice. In addition, fewer specific Th cells were generated in the aged mice. When aged mice were immunized with PV PSVs encoding human IL-2, specific Th cells were generated, producing murine IL-2, IL-4, and IFN-gamma. Further, specific Abs and CTLs were induced, resulting in protection against mucosal viral challenge. Thus, this study provided a basis for clinical trials using PV PSVs encoding IL-2 for vaccination of the elderly.     

Inhibition of NF-kappa B activity in T and NK cells results in defective effector cell expansion and production of IFN-gamma required for resistance to Toxoplasma gondii

To define the role of NF-kappa B in the development of T cell responses required for resistance to Toxoplasma gondii, mice in which T cells are transgenic for a degradation-resistant (Delta N) form of I kappa B alpha, an inhibitor of NF-kappa B, were challenged with T. gondii and their response to infection compared with control mice. I kappa B alpha(Delta N)-transgenic (Tg) mice succumbed to T. gondii infection between days 12 and 35, and death was associated with an increased parasite burden compared with wild-type (Wt) controls. Analysis of the responses of infected mice revealed that IL-12 responses were comparable between strains, but Tg mice had a marked reduction in systemic levels of IFN-gamma, the major mediator of resistance to T. gondii. In addition, the infection-induced increase in NK cell activity observed in Wt mice was absent from Tg mice and this correlated with NK cell expression of the transgene. Infection-induced activation of CD4(+) T cells was similar in Wt and Tg mice, but expansion of activated CD4(+)T cells was markedly reduced in the Tg mice. This difference in T cell numbers correlated with a reduced capacity of these cells to proliferate after stimulation and was associated with a major defect in the ability of CD4(+) T cells from infected mice to produce IFN-gamma. Together, these studies reveal that inhibition of NF-kappa B activity in T and NK cells results in defective effector cell expansion and production of IFN-gamma required for resistance to T. gondii.     

Cytokine deprivation of naive CD8+ T cells promotes minimal cell cycling but maximal cytokine synthesis and autonomous proliferation subsequently: a mechanism of self-regulation.

Naive CD8+ T cells differentiate into effectors secreting various cytokines that aid their function. IL-2, but not IL-15, promoted this differentiation of naive CD8+ T cells into effectors. However, the amount of IL-2 present during differentiation had a dichotomous effect on their subsequent function. High concentrations of IL-2 enhanced proliferation and cell cycling initially, but the effectors subsequently failed to produce cytokines and proliferate autonomously, although CD28 expression was maintained. In contrast, suboptimal amounts of IL-2 during priming promoted apoptosis, little proliferation and cell cycling, yet the CD8+ effectors generated produced high levels of cytokines and proliferated autonomously. Interestingly, the effects of IL-2 on naive CD8+ T cells were totally opposite those on naive CD4+ T cells. Although IL-2 impaired cytokine synthesis by CD8+ T cells, the expression of LFA1 and CD44 as well as Fas-dependent cytotoxicity were enhanced. However, loss of cytokine synthesis was not due to increased cytotoxicity, as inhibition occurred even in the absence of perforin/FasL. Interestingly, CD8+ effectors secreting reduced amounts of cytokines exhibited enhanced IL-2Ralpha, but reduced IL-2Rbeta, expression. Furthermore, sorted CD8+ IL-2Ralphahigh cells secreted less cytokines than IL-2Ralphalow cells. These results suggest that the presence of excessive IL-2 during the activation of naive CD8+ T cells, while promoting cell cycling initially, may compromise long-term immunity.     

Defective T cell priming associated with aging can be rescued by signaling through 4-1BB (CD137)

Aging is associated with an increased susceptibility to infectious agents and correlates with a decreased ability to mount an immune response. It has been postulated that the major defect is related to a reduced capacity of an aged T cell to proliferate and to survive after encounter with Ag. This is similar to the phenotype associated with T cell tolerance in young adults. In this study, we determined whether targeting 4-1BB (CD137), a member of the TNFR family implicated in providing expansion and survival signals to T cells, can rescue defective priming in aged and tolerized animals. Agonist Abs to 4-1BB injected in vivo were capable of preventing CD4 T cell tolerance to soluble peptide in young mice. Moreover, anti-4-1BB rescued defective priming of aged TCR transgenic CD4 T cells responding to peptide Ag in a young host, and as importantly, anti-4-1BB completely restored T cell priming to protein Ag in nontransgenic aged mice. These studies demonstrate that 4-1BB, and potentially other costimulatory members of the TNFR family, are targets for therapies aimed at augmenting weak T cell responses in elderly immunocompromised individuals.     

Vaccination without autoantigen protects against collagen II-induced arthritis via immune deviation and regulatory T cells

Anti-inflammation immunotherapy has been successfully applied for the treatment of autoimmune diseases. Mucosal vaccines against autoimmune disorders are beneficial by influencing the regulatory compartment of gut and systemic adaptive immune systems. A Salmonella vector expressing colonization factor Ag I (CFA/I), shown to behave as an anti-inflammatory vaccine, stimulates the production of CD4(+)CD25(+) T cells and regulatory cytokines. In this work, we queried whether Salmonella-CFA/I can protect DBA/1 mice from collagen-induced arthritis. The incidence of arthritis and cartilage loss in vaccinated DBA/1 mice was remarkably lower when compared with unprotected mice. Clinical findings were accompanied by the suppression of inflammatory cytokines TNF-alpha, IL-1beta, IL-6, and IL-27. Vaccination evoked a multi-tier response consisting of IL-4 producing Th2 cells, an increased production of TGF-beta by CD4(+) T cells, and suppression of collagen II-specific CD4(+) T cell proliferation. To assess the contribution of Salmonella-CFA/I-primed CD4(+) T cells, adoptive transfer studies with total CD4(+), CD4(+)CD25(-), or CD4(+)CD25(+) T cells were performed 15 days postchallenge. Mice receiving either subset showed reduced disease incidence and low clinical scores; however, mice receiving total CD4(+) T cells showed delayed disease onset by 10 days with reduced clinical scores, reduced IL-17 and IL-27, but enhanced IL-4, IL-10, IL-13, and TGF-beta. Inhibition of TGF-beta or IL-4 compromised protective immunity. These data show that Salmonella-CFA/I vaccination of DBA/1 mice protects against collagen-induced arthritis by stimulating TGF-beta- and IL-4-producing regulatory CD4(+) T cells.     

Bone marrow precursor cells from aged mice generate CD4 T cells that function well in primary and memory responses

Understanding how aging impacts the function of memory CD4 T cells is critical for designing effective vaccines. Our studies show that immunological memory generated during youth functions well into old age, whereas that generated later in life functions poorly. This is the result of declines in the function of naive CD4 T cells from aged individuals and contributes to reduced efficacy of vaccines in the elderly. To begin to identify the cause of this defect, we examined the function of memory T cells generated from bone marrow precursor cells (BMPC) from young or aged mice in young hosts. In two different models, memory cells derived from young and aged BMPC exhibit good ex vivo and in vivo function. Importantly, memory CD4 T cells generated from aged BMPC exhibit potent cognate helper function for humoral responses, which are critical for effective immunization. These results indicate that there are no apparent age-related intrinsic defects in BMPC with regards to generation of functional memory T cells.     

Impact of post-thymic cellular longevity on the development of age-associated CD4+ T cell defects

Elderly people are at higher risk for infections due to declining cellular and humoral immune responses. Central to this dysfunction is the reduced responsiveness of the naive CD4(+) T cell compartment. Previous data from our laboratory suggest that although defects in the aged naive CD4(+) T cell response are apparent in recent thymic emigrant populations, additional defects develop during extended post-thymic longevity in the periphery. To further investigate the factors that lead to aging defects, we took advantage of the OT-II TCR-transgenic (Tg) mouse model. We show that because of an apparent superantigen-mediated loss of naive Vbeta5(+) Tg CD4(+) T cells from the periphery of aging OT-II mice, this compartment becomes enriched for cells of reduced post-thymic longevity, resulting in a frequency of recent thymic emigrants in aged mice that is similar to that of young mice. Purification and functional analysis of aged OT-II cells with reduced post-thymic longevity reveal that they have an age-associated decrease in expansion and IL-2 production in response to Ag in vitro. However, the in vivo expansion, IL-2 production, and cognate B cell helper ability of these cells are similar to those of cells from young mice. In contrast, T cells from aged HNT Tg mice demonstrate extended post-thymic longevity and exhibit severe defects in the same in vitro and in vivo models. These data support a correlation between the requirement for increased post-thymic longevity and the development of the most severe naive CD4(+) T cell-aging defects.     

JunD regulates lymphocyte proliferation and T helper cell cytokine expression

Transgenic mice broadly expressing JunD (Ubi-junD(m)) appear phenotypically normal, but have strongly reduced numbers of peripheral lymphocytes. JunD overexpression in lymphocytes does not protect from numerous apoptotic insults; however, transgenic T cells proliferate poorly and exhibit impaired activation due to reduced levels of IL-4, CD25 and CD69. Consistently, in the absence of JunD (junD(-/-)) T cells hyperproliferate following mitogen induction. Moreover, transgenic T helper (Th) 2 cells have decreased IL-4 and IL-10 expression, whereas junD(-/-) Th2 cells secrete higher amounts of both Th2 cytokines. Th1-polarized junD(-/-) CD4(+) T cells display enhanced IFN-gamma cytokine production associated with upregulated T-bet expression and downregulated expression of suppressor of cytokine signaling-1. These novel findings demonstrate a regulatory role of JunD in T lymphocyte proliferation and Th cell differentiation.     

The aged microenvironment contributes to the age-related functional defects of CD4 T cells in mice

CD4 T cells, and especially T follicular helper cells, are critical for the generation of a robust humoral response to an infection or vaccination. Importantly, immunosenescence affects CD4 T‐cell function, and the accumulation of intrinsic defects decreases the cognate helper functions of these cells. However, much less is known about the contribution of the aged microenvironment to this impaired CD4 T‐cell response. In this study, we have employed a preclinical model to determine whether the aged environment contributes to the defects in CD4 T‐cell functions with aging. Using an adoptive transfer model in mice, we demonstrate for the first time that the aged microenvironment negatively impacts at least three steps of the CD4 T‐cell response to antigenic stimulation. First, the recruitment of CD4 T cells to the spleen is reduced in aged compared to young hosts, which correlates with dysregulated chemokine expression in the aged organ. Second, the priming of CD4 T cells by DCs is reduced in aged compared to young mice. Finally, naïve CD4 T cells show a reduced transition to a T follicular helper cell phenotype in the aged environment, which impairs the subsequent generation of germinal centers. These studies have provided new insights into how aging impacts the immune system and how these changes influence the development of immunity to infections or vaccinations.     

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.     

Aging up-regulates expression of inflammatory mediators in mouse adipose tissue

Obesity is a leading risk factor for type 2 diabetes (T2D). Aging is associated with an increase in T2D incidence, which is not totally explained by the much lower prevalence of obesity in the elderly. Low-grade inflammation in adipose tissue (AT) contributes to insulin resistance and T2D. Thus, we determined whether inflammatory responses are up-regulated with age in AT. The results showed that visceral AT from old C57BL mice had significantly higher mRNA expression of the proinflammatory cytokines IL-1beta, IL-6, TNF-alpha, and COX-2 and lower expression of anti-inflammatory PPAR-gamma than those of young mice. We further showed that adipocytes (AD) and not stromal vascular cells including macrophages (Mphi) were the cells responsible for this higher inflammatory state of the aged AT, suggesting that the age-associated increase in AT inflammation is distinguished from that seen in obesity, in which Mphi are the main contributors. However, peritoneal Mphi of either age (young or old) produced more TNF-alpha and IL-6 after incubation in old AD-conditioned medium compared with young AD-conditioned medium. This suggests that in addition to producing more inflammatory cytokines, AD from old mice induce a higher inflammatory response in other cells. Sphingolipid ceramide was higher in old compared with young AD. Reducing ceramide levels or inhibiting NF-kappaB activation decreased cytokine production, whereas the addition of ceramide increased cytokine production in young AD to a level comparable to that seen in old AD, suggesting that ceramide-induced activation of NF-kappaB plays a key role in AT inflammation.     

A DNA vaccine encoding multiple HIV CD4 epitopes elicits vigorous polyfunctional, long-lived CD4+ and CD8+ T cell responses

T-cell based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. Moreover, polyfunctional and long-lived specific memory T cells have been associated to vaccine-induced protection. CD4(+) T cells are important for the generation and maintenance of functional CD8(+) cytotoxic T cells. We have recently developed a DNA vaccine encoding 18 conserved multiple HLA-DR-binding HIV-1 CD4 epitopes (HIVBr18), capable of eliciting broad CD4(+) T cell responses in multiple HLA class II transgenic mice. Here, we evaluated the breadth and functional profile of HIVBr18-induced immune responses in BALB/c mice. Immunized mice displayed high-magnitude, broad CD4(+)/CD8(+) T cell responses, and 8/18 vaccine-encoded peptides were recognized. In addition, HIVBr18 immunization was able to induce polyfunctional CD4(+) and CD8(+) T cells that proliferate and produce any two cytokines (IFNγ/TNFα, IFNγ/IL-2 or TNFα/IL-2) simultaneously in response to HIV-1 peptides. For CD4(+) T cells exclusively, we also detected cells that proliferate and produce all three tested cytokines simultaneously (IFNγ/TNFα/IL-2). The vaccine also generated long-lived central and effector memory CD4(+) T cells, a desirable feature for T-cell based vaccines. By virtue of inducing broad, polyfunctional and long-lived T cell responses against conserved CD4(+) T cell epitopes, combined administration of this vaccine concept may provide sustained help for CD8(+) T cells and antibody responses- elicited by other HIV immunogens.     

CD4+CD25+ regulatory T cells control innate immune reactivity after injury

Major injury initiates a systemic inflammatory response that can be detrimental to the host. We have recently reported that burn injury primes innate immune cells for a progressive increase in TLR4 and TLR2 agonist-induced proinflammatory cytokine production and that this inflammatory phenotype is exaggerated in adaptive immune system-deficient (Rag1(-/-)) mice. The present study uses a series of adoptive transfer experiments to determine which adaptive immune cell type(s) has the capacity to control innate inflammatory responses after injury. We first compared the relative changes in TLR4- and TLR2-induced TNF-alpha, IL-1beta, and IL-6 production by spleen cell populations prepared from wild-type (WT), Rag1(-/-), CD4(-/-), or CD8(-/-) mice 7 days after sham or burn injury. Our findings indicated that splenocytes prepared from burn-injured CD8(-/-) mice displayed TLR-induced cytokine production levels similar to those in WT mice. In contrast, spleen cells from burn-injured CD4(-/-) mice produced cytokines at significantly higher levels, equivalent to those in Rag1(-/-) mice. Moreover, reconstitution of Rag1(-/-) or CD4(-/-) mice with WT CD4(+) T cells reduced postinjury cytokine production to WT levels. Additional separation of CD4(+) T cells into CD4(+)CD25(+) and CD4(+)CD25(-) subpopulations before their adoptive transfer into Rag1(-/-) mice showed that CD4(+)CD25(+) T cells were capable of reducing TLR-stimulated cytokine production levels to WT levels, whereas CD4(+)CD25(-) T cells had no regulatory effect. These findings suggest a previously unsuspected role for CD4(+)CD25(+) T regulatory cells in controlling host inflammatory responses after injury.     

Age-associated changes in interferon-γ and interleukin-4 secretion by purified human CD4+ and CD8+ T cells

Aging is associated with a decline in immune function. Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), two important immune deviation-related cytokines, are mainly produced by type 1 and type 2 T cells, respectively. To investigate the age-associated changes in the secretion of these two cytokines, 20 elderly and 20 young subjects fulfilling the SENIEUR protocol were enrolled. The ratios of CD4+ to CD8+ T cells were not different between the two age groups. The CD4+ and CD8+ T cells were purified by a magnetic cell sorting system, and then activated by concurrent anti-CD3 and anti-CD28 stimulation. The released cytokines were determined by ELISA. Both the CD4+ and the CD8+ T cells of the elderly individuals secreted a significantly larger amount of IFN-gamma after activation. Profound IL-4 production by CD8+ T cells was observed in the older subjects compared with that of the young subjects. These data suggested that age-associated decrease in immunity may be related to an imbalance in the secretion of immune deviation cytokines. The number of IL-4-secreting CD8+ T cells (T cytotoxic 2) rose significantly in the older individuals. Our design also provided a useful way to differentiate the T cell subsets secreting the same cytokine, such as IFN-gamma-producing T helper 1 and T cytotoxic 1 cells.     

Aged Mice Exhibit a Severely Diminished CD8 T Cell Response following Respiratory Syncytial Virus Infection

Respiratory virus infections in the elderly result in increased rates of hospitalization and death. Respiratory syncytial virus (RSV) is a leading cause of severe virus-induced respiratory disease in individuals over the age of 65. CD8 T cells play a critical role in mediating RSV clearance. While it is clear that T cell immunity declines with age, it is not clear to what extent the CD8 T cell response to RSV is altered. Using aged BALB/c mice, we demonstrated that RSV-specific CD8 T cell responses were significantly reduced in the lungs of aged mice at the peak of the T cell response and that this decrease correlated with delayed viral clearance. Despite a decrease in the overall numbers of RSV-specific CD8 T cells during acute infection, their capacity to produce effector cytokines was not impaired. Following viral clearance, the RSV-specific memory CD8 T cells were similar in total number and phenotype in young and aged mice. Furthermore, following infection with a heterologous pathogen expressing an RSV epitope, RSV-specific memory CD8 T cells exhibited similar activation and ability to provide early control of the infection in young and aged mice. These data demonstrate a decrease in the capacity of aged mice to induce a high-magnitude acute CD8 T cell response, leading to prolonged viral replication, which may contribute to the increased disease severity of RSV infection observed for aged individuals.     

Impact of ageing on the response and repertoire of influenza virus-specific CD4 T cells

Background

Ageing has been shown to reduce CD8 T cell repertoire diversity and immune responses against influenza virus infection in mice. In contrast, less is known about the impact of ageing on CD4 T cell repertoire diversity and immune response to influenza virus infection.

Results

The CD4 T cell response was followed after infection of young and aged C57BL/6 mice with influenza virus using a tetramer specific for an immunodominant MHC class II epitope of the influenza virus nucleoprotein. The appearance of virus-specific CD4 T cells in the lung airways of aged mice was delayed compared to young mice, but the overall peak number and cytokine secretion profile of responding CD4 T cells was not greatly perturbed. In addition, the T cell repertoire of responding cells, determined using T cell receptor Vβ analysis, failed to show the profound effect of age we previously described for CD8 T cells. The reduced impact of age on influenza-specific CD4 T cells was consistent with a reduced effect of age on the overall CD4 compared with the CD8 T cell repertoire in specific pathogen free mice. Aged mice that were thymectomized as young adults showed an enhanced loss of the epitope-specific CD4 T cell response after influenza virus infection compared with age-matched sham-thymectomized mice, suggesting that a reduced repertoire can contribute to impaired responsiveness.

Conclusions

The diversity of the CD4 T cell repertoire and response to influenza virus is not as profoundly impaired by ageing in C57BL/6 mice as previously shown for CD8 T cells. However, adult thymectomy enhanced the impact of ageing on the response. Understanding the impact of ageing on CD4 T cell responses to influenza virus infection is an important prerequisite for developing better vaccines for the elderly.

     

Age-associated decline in effective immune synapse formation of CD4(+) T cells is reversed by vitamin E supplementation

Aging is associated with reduced IL-2 production and T cell proliferation. Vitamin E supplementation, in aged animals and humans, increases cell division and IL-2 production by naive T cells. The immune synapse forms at the site of contact between a T cell and an APC and participates in T cell activation. We evaluated whether vitamin E affects the redistribution of signaling proteins to the immune synapse. Purified CD4(+) T cells, from the spleens of young and old mice, were treated with vitamin E before stimulation with a surrogate APC expressing anti-CD3. Using confocal fluorescent microscopy, we observed that CD4(+) T cells from old mice were significantly less likely to recruit signaling proteins to the immune synapse than cells from young mice. Vitamin E increased the percentage of old CD4(+) T cells capable of forming an effective immune synapse. Similar results were found following in vivo supplementation with vitamin E. When compared with memory cells, naive T cells from aged mice were more defective in immune synapse formation and were more responsive to vitamin E supplementation. These data show, for the first time, that vitamin E significantly improves age-related early T cell signaling events in naive CD4(+) T cells.