The effect of age on the expression of interleukin-2

Suppression of autophagy induces senescence in the heart

Aging is a critical risk factor for heart disease, including ischemic heart disease and heart failure. Cellular senescence, characterized by DNA damage, resistance to apoptosis and the senescence-associated secretory phenotype (SASP), occurs in many cell types, including cardiomyocytes. Senescence precipitates the aging process in surrounding cells and the organ through paracrine mechanisms. Generalized autophagy, which degrades cytosolic materials in a non-selective manner, is decreased during aging in the heart. This decrease causes deterioration of cellular quality control mechanisms, facilitates aging and negatively affects lifespan in animals, including mice. Although suppression of generalized autophagy could promote senescence, it remains unclear whether the suppression of autophagy directly stimulates senescence in cardiomyocytes, which, in turn, promotes myocardial dysfunction in the heart. We addressed this question using mouse models with a loss of autophagy function. Suppression of general autophagy in cardiac-specific Atg7 knockout (Atg7cKO) mice caused accumulation of senescent cardiomyocytes. Induction of senescence via downregulation of Atg7 was also observed in chimeric Atg7 cardiac-specific KO mice and cultured cardiomyocytes in vitro, suggesting that the effect of autophagy suppression upon induction of senescence is cell autonomous. ABT-263, a senolytic agent, reduced the number of senescent myocytes and improved cardiac function in Atg7cKO mice. Suppression of autophagy and induction of senescence were also observed in doxorubicin-treated hearts, where reactivation of autophagy alleviated senescence in cardiomyocytes and cardiac dysfunction. These results suggest that suppression of general autophagy directly induces senescence in cardiomyocytes, which in turn promotes cardiac dysfunction.

mTORC2: A neglected player in aging regulation

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a pivotal role in various biological processes, through integrating external and internal signals, facilitating gene transcription and protein translation, as well as by regulating mitochondria and autophagy functions. mTOR kinase operates within two distinct protein complexes known as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which engage separate downstream signaling pathways impacting diverse cellular processes. Although mTORC1 has been extensively studied as a pro-proliferative factor and a pro-aging hub if activated aberrantly, mTORC2 received less attention, particularly regarding its implication in aging regulation. However, recent studies brought increasing evidence or clues for us, which implies the associations of mTORC2 with aging, as the genetic elimination of unique subunits of mTORC2, such as RICTOR, has been shown to alleviate aging progression in comparison to mTORC1 inhibition. In this review, we first summarized the basic characteristics of mTORC2, including its protein architecture and signaling network. We then focused on reviewing the molecular signaling regulation of mTORC2 in cellular senescence and organismal aging, and proposed the multifaceted regulatory characteristics under senescent and nonsenescent contexts. Next, we outlined the research progress of mTOR inhibitors in the field of antiaging and discussed future prospects and challenges. It is our pleasure if this review article could provide meaningful information for our readers and call forth more investigations working on this topic.

Translational Frontiers and Clinical Opportunities of Immunologically Fitted Radiotherapy

Ionizing radiation can have a wide range of impacts on tumor-immune interactions, which are being studied with the greatest interest and at an accelerating pace by the medical community. Despite its undeniable immunostimulatory potential, it clearly appears that radiotherapy as it is prescribed and delivered nowadays often alters the host's immunity toward a suboptimal state. This may impair the full recovery of a sustained and efficient antitumor immunosurveillance posttreatment. An emerging concept is arising from this awareness and consists of reconsidering the way of designing radiation treatment planning, notably by taking into account the individualized risks of deleterious radio-induced immune alteration that can be deciphered from the planned beam trajectory through lymphocyte-rich organs. In this review, we critically appraise key aspects to consider while planning immunologically fitted radiotherapy, including the challenges linked to the identification of new dose constraints to immune-rich structures. We also discuss how pharmacologic immunomodulation could be advantageously used in combination with radiotherapy to compensate for the radio-induced loss, for example, with (i) agonists of interleukin (IL)2, IL4, IL7, IL9, IL15, or IL21, similarly to G-CSF being used for the prophylaxis of severe chemo-induced neutropenia, or with (ii) myeloid-derived suppressive cell blockers.

The companion dog as a model for inflammaging: a cross-sectional pilot study

Inflammaging, the chronic, progressive proinflammatory state associated with aging, has been associated with multiple negative health outcomes in humans. The pathophysiology of inflammaging is complex; however, it is often characterized by high serum concentrations of inflammatory mediators such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, and C-reactive protein (CRP). Few studies have evaluated the effects of age on inflammatory cytokines in companion dogs, and most of these studies included dogs of a single breed. In this cross-sectional study, we measured multiple circulating inflammatory markers and hematological parameters in banked serum samples from 47 healthy companion dogs of various breeds enrolled in the Dog Aging Project. Using univariate linear models, we investigated the association of each of these markers with age, sex, body weight, and body condition score (BCS), a measure of obesity in the dog. Serum IL-6, IL-8, and TNF-α concentrations were all positively associated with age. Lymphocyte count was negatively associated with age. Platelet count had a negative association with body weight. IL-2, albumin, cholesterol, triglyceride, bilirubin, S100A12, and NMH concentrations were not associated with age, weight, BCS, or sex after adjustment for multiple comparisons. Our findings replicate previous findings in humans, including increases in IL-6 and TNF-α with age, giving more evidence to the strength of the companion dog as a model for human aging.

Suppression of autophagy induces senescence in the heart

Aging is a critical risk factor for heart disease, including ischemic heart disease and heart failure. Cellular senescence, characterized by DNA damage, resistance to apoptosis and the senescence-associated secretory phenotype (SASP), occurs in many cell types, including cardiomyocytes. Senescence precipitates the aging process in surrounding cells and the organ through paracrine mechanisms. Generalized autophagy, which degrades cytosolic materials in a non-selective manner, is decreased during aging in the heart. This decrease causes deterioration of cellular quality control mechanisms, facilitates aging and negatively affects lifespan in animals, including mice. Although suppression of generalized autophagy could promote senescence, it remains unclear whether the suppression of autophagy directly stimulates senescence in cardiomyocytes, which, in turn, promotes myocardial dysfunction in the heart. We addressed this question using mouse models with a loss of autophagy function. Suppression of general autophagy in cardiac-specific Atg7 knockout ( Atg7 cKO) mice caused accumulation of senescent cardiomyocytes. Induction of senescence via downregulation of Atg7 was also observed in chimeric Atg7 cardiac-specific KO mice and cultured cardiomyocytes in vitro , suggesting that the effect of autophagy suppression upon induction of senescence is cell autonomous. ABT-263, a senolytic agent, reduced the number of senescent myocytes and improved cardiac function in Atg7 cKO mice. Suppression of autophagy and induction of senescence were also observed in doxorubicin-treated hearts, where activation of autophagy alleviated senescence in cardiomyocytes and cardiac dysfunction. These results suggest that suppression of general autophagy directly induces senescence in cardiomyocytes, which in turn promotes cardiac dysfunction.

Extracellular Delivery of Functional Mitochondria Rescues the Dysfunction of CD4+ T Cells in Aging

Mitochondrial dysfunction alters cellular metabolism, increases tissue oxidative stress, and may be principal to the dysregulated signaling and function of CD4+ T lymphocytes in the elderly. In this proof of principle study, it is investigated whether the transfer of functional mitochondria into CD4+ T cells that are isolated from old mice (aged CD4+ T cells), can abrogate aging-associated mitochondrial dysfunction, and improve the aged CD4+ T cell functionality. The results show that the delivery of exogenous mitochondria to aged non-activated CD4+ T cells led to significant mitochondrial proteome alterations highlighted by improved aerobic metabolism and decreased cellular mitoROS. Additionally, mito-transferred aged CD4+ T cells showed improvements in activation-induced TCR-signaling kinetics displaying markers of activation (CD25), increased IL-2 production, enhanced proliferation ex vivo. Importantly, immune deficient mouse models (RAG-KO) showed that adoptive transfer of mito-transferred naive aged CD4+ T cells, protected recipient mice from influenza A and Mycobacterium tuberculosis infections. These findings support mitochondria as targets of therapeutic intervention in aging.

Analysis of the impact of handling and culture on the expansion and functionality of NK cells

Natural killer (NK) cells are lymphocytes of the innate immune system that play a key role in the elimination of tumor and virus-infected cells. Unlike T cells, NK cell activation is governed by their direct interaction with target cells via the inhibitory and activating receptors present on their cytoplasmic membrane. The simplicity of this activation mechanism has allowed the development of immunotherapies based on the transduction of NK cells with CAR (chimeric antigen receptor) constructs for the treatment of cancer. Despite the advantages of CAR-NK therapy over CAR-T, including their inability to cause graft-versus-host disease in allogenic therapies, a deeper understanding of the impact of their handling is needed in order to increase their functionality and applicability. With that in mind, the present work critically examines the steps required for NK cell isolation, expansion and storage, and analyze the response of the NK cells to these manipulations. The results show that magnetic-assisted cell sorting, traditionally used for NK isolation, increases the CD16+ population of NK cultures only if the protocol includes both, antibody incubation and passage through the isolation column. Furthermore, based on the importance of surface potential on cellular responses, the influence of surfaces with different net surface charge on NK cells has been evaluated, showing that NK cells displayed higher proliferation rates on charged surfaces than on non-charged ones. The present work highlights the relevance of NK cells manipulation for improving the applicability and effectiveness of NK cell-based therapies.

Aging of the Immune System: Focus on Natural Killer Cells Phenotype and Functions

Aging is the greatest risk factor for nearly all major chronic diseases, including cardiovascular diseases, cancer, Alzheimer’s and other neurodegenerative diseases of aging. Age-related impairment of immune function (immunosenescence) is one important cause of age-related morbidity and mortality, which may extend beyond its role in infectious disease. One aspect of immunosenescence that has received less attention is age-related natural killer (NK) cell dysfunction, characterized by reduced cytokine secretion and decreased target cell cytotoxicity, accompanied by and despite an increase in NK cell numbers with age. Moreover, recent studies have revealed that NK cells are the central actors in the immunosurveillance of senescent cells, whose age-related accumulation is itself a probable contributor to the chronic sterile low-grade inflammation developed with aging (“inflammaging”). NK cell dysfunction is therefore implicated in the increasing burden of infection, malignancy, inflammatory disorders, and senescent cells with age. This review will focus on recent advances and open questions in understanding the interplay between systemic inflammation, senescence burden, and NK cell dysfunction in the context of aging. Understanding the factors driving and enforcing NK cell aging may potentially lead to therapies countering age-related diseases and underlying drivers of the biological aging process itself.

Cytoplasmic DNA sensing by KU complex in aged CD4+ T cell potentiates T cell activation and aging-related autoimmune inflammation

Aging is associated with DNA accumulation and increased homeostatic proliferation of circulating T cells. Although these attributes are associated with aging-related autoimmunity, their direct contributions remain unclear. Conventionally, KU complex, the regulatory subunit of DNA-dependent protein kinase (DNA-PK), together with the catalytic subunit of DNA-PK (DNA-PKcs), mediates DNA damage repair in the nucleus. Here, we found KU complex abundantly expressed in the cytoplasm, where it recognized accumulated cytoplasmic DNA in aged human and mouse CD4⁺ T cells. This process enhanced T cell activation and pathology of experimental autoimmune encephalomyelitis (EAE) in aged mice. Mechanistically, KU-mediated DNA sensing facilitated DNA-PKcs recruitment and phosphorylation of the kinase ZAK. This activated AKT and mTOR pathways, promoting CD4⁺ T cell proliferation and activation. We developed a specific ZAK inhibitor, which dampened EAE pathology in aged mice. Overall, these findings demonstrate a KU-mediated cytoplasmic DNA-sensing pathway in CD4⁺ T cells that potentiates aging-related autoimmunity.

The Neuroimmunology of Guillain-Barré Syndrome and the Potential Role of an Aging Immune System

Guillain-Barré syndrome (GBS) is a paralyzing autoimmune condition affecting the peripheral nervous system (PNS). Within GBS there are several variants affecting different aspects of the peripheral nerve. In general, there appears to be a role for T cells, macrophages, B cells, and complement in initiating and perpetuating attacks on gangliosides of Schwann cells and axons. Of note, GBS has an increased prevalence and severity with increasing age. In addition, there are alterations in immune cell functioning that may play a role in differences in GBS with age alongside general age-related declines in reparative processes (e.g., delayed de-differentiation of Schwann cells and decline in phagocytic ability of macrophages). The present review will explore the immune response in GBS as well as in animal models of several variants of the disorder. In addition, the potential involvement of an aging immune system in contributing to the increased prevalence and severity of GBS with age will be theorized.

Fructus Ligustri Lucidi preserves bone quality through the regulation of gut microbiota diversity, oxidative stress, TMAO and Sirt6 levels in aging mice

Gut dysbiosis and oxidative stress may trigger senile osteoporosis. Fructus Ligustri Lucidi (FLL) has bone-preserving properties and affects the intestinal microecology. However, the mechanism of the anti-osteoporotic effect of FLL and its link to the gut microbiota remains to be elucidated. Here, we demonstrated that sustained exposure of ICR mice to D-galactose / sodium nitrite for 90 days causes aging-related osteoporosis and reduced cognitive performance. The aging phenotype is also characterized by increased oxidative stress in serum. This is likely triggered by abnormal changes in the gut microbiota population of Bifidobacterium and the ratio of Firmicutes/ Bacteroidetes that resulted in increased levels of flavin-containing monooxygenase-3 and trimethylamine-N-oxide (TMAO). Moreover, the increased oxidative stress further accelerated aging by increasing tumor necrosis factor-α levels in serum and reducing Sirtuin 6 (Sirt6) expression in long bones, which prompted nuclear factor kappa-B acetylation as well as over-expression and activation of cathepsin K. FLL-treated aging mice revealed a non-osteoporotic bone phenotype and an improvement on the cognitive function. The mechanism underlying these effects may be linked to the regulation of gut microbiota diversity, antioxidant activity, and the levels of TMAO and Sirt6. FLL may represent a potential source for identifying anti-senile osteoporotic drug candidates.

An evaluation of multiplex bead-based analysis of cytokines and soluble proteins in archived lithium heparin plasma, EDTA plasma and serum samples

OBJECTIVE

To assess the usability of archived plasma and serum by multiplex (Luminex) analysis of circulating proteins (analytes) by evaluating the day to day variation, the effect of several freeze-thaw cycles, and the influence of the media and choice of anticoagulant.

METHODS

Nineteen analytes in plasma and serum from 86 head and neck cancer patients and 33 controls were evaluated: EGFR, leptin, OPN, VEGFR-1, VEGFR-2, IL-2, IL-13, PDGF-bb, TNF, PAI-1, SDF-1a, IL-4, IL-6, IL-8, eotaxin, G-CSF, VEGF, GRO-a, and HGF.

RESULTS

The correlation between measurements of the same samples analyzed on different dates was reasonable. However, samples run on different dates could exhibit different absolute values. The 75th percentile of the fold differences for samples run on different dates was 2.2. No significant difference was found between one and four freeze-thaw cycles (except for HGF), and the correlation was high. We found significant differences in mean concentrations of the majority of analytes in different media and with different anticoagulants. Only the following analytes did not show difference in mean concentrations: EDTA plasma vs. serum: leptin and VEGFR-2, LH plasma vs. serum: IL-2, IL-13, and VEGF, LH plasma levels vs. EDTA plasma: IL-2 and IL-4.

CONCLUSION

Stored serum, LH plasma, and EDTA plasma from clinical trials can be used for analysis of circulating cytokines and proteins. Variations in measurements occur, but are within reasonable ranges. The optimal type of media depends on the analytes, as different analytes have low number of measurements below the lower limit of quantification and higher dynamic ranges in different media.

Menstrual cycle and reproductive aging alters immune reactivity, NGF expression, antioxidant enzyme activities, and intracellular signaling pathways in the peripheral blood mononuclear cells of healthy women

Reproductive senescence in women is a process that begins with regular menstrual cycles and culminates in menopause followed by gradual development of diseases such as autoimmune diseases, osteoporosis, neurodegenerative diseases, and hormone-dependent cancers. The age-associated impairment in the functions of neuroendocrine system and immune system results in menopause which contributes to subsequent development of diseases and cancer. The aim of this study is to characterize the alterations in immune responses, compensatory factors such as nerve growth factor (NGF) and antioxidant enzyme activities, and the molecular mechanisms of actions in the peripheral blood mononuclear cells (PBMCs) of young (follicular and luteal phases), middle-aged, and old healthy women. Peripheral blood mononuclear cells were isolated from young women in follicular and luteal phases of the menstrual cycle (n=20; 22.6±2.9 yrs), middle-aged women (n=19; 47.1±3.8 yrs; perimenopausal) and old (n=16; 63.2±4.7 yrs; post-menopausal) women and analyzed for Concanavalin (Con A)-induced proliferation of lymphocytes and cytokine (IL-2 and IFN-γ) production, expression of NGF, p-NF-κB, p-ERK, p-CREB, and p-Akt, antioxidant enzymes [superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), glutathione-S-transferase (GST)], extent of lipid peroxidation, and nitric oxide (NO) production. Serum gonadal hormones (17β-estradiol and progesterone) were also measured. A characteristic age- and menstrual cycle-related change was observed in the serum gonadal hormone secretion (estrogen and progesterone), T lymphocyte proliferation and IFN-γ production. Salient features include the age-related decline observed in target-derived growth factors (lymphocyte NGF expression), signaling molecules (p-ERK/ERK and p-CREB/CREB ratios) and compensatory factors such as the activities of plasma and PBMC antioxidant enzymes (SOD and catalase) and NO production. Further, an age-associated increase in p-NF-κB expression and lipid peroxidation was observed. Also, serum 17β-estradiol levels were positively correlated with IFN-γ production, SOD activity and NGF expression in the PBMCs. These results suggest that alterations in the levels of gonadal hormones are associated with immunosenescence characterized by decreased IFN-γ production and proliferation of T lymphocytes, decline in NGF expression, SOD and catalase activities, NO production, and signaling mechanisms and thus, may increase the incidence of diseases and cancer in women.

Diminished cytokines gene expression in lymphoid organs of healthy aged rats

Immunuosenescence-related dysregulation of cytokine production is not fully understood and the roles of cytokines in organ aging have been insufficiently studied. This work aimed to compare the expression of interleukin-2 (IL-2), IL-4, IL-6, interferon-gamma (IFNγ), and transforming growth factor-beta (TGFβ) in lymphoid organs of young (3 months; n = 10), adult (1 year; n = 10), and aged (2 years; n = 7) rats under healthy, steady-state conditions. Cytokine mRNA levels were determined with TaqMan real-time PCR. In the spleen, all cytokine expression gradually declined with age (for representative cytokine IL-2 averages dCt in spleens of 3 months, 1 year and 2 years rats were 13,645, 13,19 and 15,470, respectively). In lymph nodes, all cytokines except TGF-β showed markedly upregulated expression in adult compared to young rats, but all were expressed at very low levels in aged rats. In bone marrow, adult animals showed enhanced IL-2, IFNγ, and TGFβ expression, but similar IL-4 and IL-6 expression, compared to young rats. Bone marrow of aged rats showed very low expression of all the measured cytokines. Our results demonstrated that changes occurred unevenly with aging in different immune system compartments.

Influence of age on behavioral, immune and endocrine responses to the T-cell superantigen staphylococcal enterotoxin A

Aged subjects are more vulnerable to administration of the endotoxin lipopolysaccharide, but research on age-associated sensitivity to other immune stimulants has been limited. The current study examined the effects of administering the superantigen, staphylococcal enterotoxin A (SEA), to young (4-month-old) and aged (20-month-old) male C57BL/6J mice on consumption of a novel liquid, cytokine production, corticosterone levels, and expression of central mRNA levels of cytokines and corticotropin-releasing hormone. SEA produced exaggerated hypophagia in aged mice, as they showed decreased consumption that persisted for 24 h. SEA increased hypothalamic mRNA levels of interleukin-1beta in the aged, but not the young, mice 2 h after administration. No differences in cytokine expression were observed 24 h after SEA. Both age groups showed increased plasma corticosterone levels 2 h after SEA administration. However, 24 h after SEA exposure the aged, but not the young, mice showed an augmented corticosterone response to the consumption test. Collectively, these data show that aging may exacerbate the behavioral and neuroinflammatory response to superantigen exposure. Further, the present study suggests that immune activation may result in delayed alterations in stress-induced corticosterone production in aged subjects.

Aging reduces the primary humoral response and the in vitro cytokine production in mice

Aging is accompanied by a decrease in several physiological functions that make older individuals less responsive to environmental challenges. In the present study, we analyzed the immune response of female BALB/c mice (N = 6) of different ages (from 2 to 96 weeks) and identified significant age-related alterations. Immunization with hapten-protein (trinitrophenyl-bovine serum albumin) conjugates resulted in lower antibody levels in the primary and secondary responses of old mice (72 weeks old). Moreover, young mice (2, 16, and 32 weeks old) maintained specific antibodies in their sera for longer periods after primary immunization than did old mice. However, a secondary challenge efficiently induced memory in old mice, as shown by the increased antibody levels in their sera. The number of CD4+ and CD8+ T cells in the spleen increased until 8 weeks of age but there was no change in the CD4+/CD8+ ratio with aging. Splenic T cells from old mice that had or had not been immunized were less responsive to concanavalin-A and showed reduced cytokine production compared to young mice (IL-2: 57-127 vs 367-1104 pg/mL, IFN-gamma: 2344-12,836 vs 752-23,106 pg/mL and IL-10: 393-2172 vs 105-2869 pg/mL in old and young mice, respectively). These data suggest that there are significant changes in the organization of the immune system throughout life. However, the relevance of these alterations for the functioning of the immune system is unknown.

Changes with ageing in several leukocyte functions of male and female rats

The impairment of the immune system with aging, or 'immunosenescence', appears to contribute to the increased morbidity and mortality of aged subjects. T cell functions and Natural Killer activity seem to be the immune responses most affected by ageing. Since the immune system works more efficiently in females than in males, we have studied the changes of several immune functions with age in rats of both sexes. In addition, we have investigated if ovariectomy, a model of menopause in rats, produces a loss of this gender-related advantage. In the present work, the changes with age (2, 6, 12, 14, 18, 22 and 24 months old) in lymphocyte chemotaxis, T lymphoproliferative response to the mitogen ConA, IL-2 release and Natural Killer activity of cells from axillary nodes and spleen of male and female rats as well as of females ovariectomized at 12 months of age have been studied. An age-related decrease was found in all investigated functions, with a slightly different evolution depending on the immune organ and gender considered. In general, the data obtained show that a certain degree of immunosenescence takes place with age in rats, with males being less immunocompetent than intact age-matched females, but showing an immune response similar to that of ovariectomized animals.

Influence of age and physical activity on the primary in vivo antibody and T cell-mediated responses in men

The aging immune system is characterized by the progressive decline in the antibody and T cell-mediated responses to antigen. Little is known, however, about the benefits of exercise in aging on the generation of a primary immune response to antigen and the subsequent antibody and memory T cell-mediated response. Most in vivo immune research to date has utilized vaccines or recall antigens to elicit an immune response. Therefore, the purpose of this experiment was to examine the association of aging and physical activity on the primary antibody and T cell response to the novel protein antigen keyhole-limpet hemocyanin (KLH). Forty-six physically active and sedentary, young (20-35 yr) and older (60-79 yr) men were recruited. Subjects were intramuscularly immunized with 100 microg of KLH, and blood samples were collected at days 0, 7, 14, 21, and 28. Samples were measured for anti-KLH IgM, IgG, IgG1, and IgG2 by ELISA. On day 21 after intramuscular KLH administration, subjects received an intradermal injection with 1 microg of KLH of inflammation recorded at 24, 48, 72, 96, and 120 h to assess anti-KLH delayed-type hypersensitivity response. There was a significant reduction in all anti-KLH measures with aging except for anti-KLH IgG2. The physically active older group had significantly higher anti-KLH IgM, IgG, IgG1, and delayed-type hypersensitivity responses, but not IgG2 compared with the sedentary older group. In conclusion, regular physical activity in older men is associated with a more robust immune response to novel antigenic challenge.

Oxygen supply modulates MCP-1 release in monocytes from young and aged rats: decrease of MCP-1 transcription and translation is age-related

Hyper or hypoxia may affect the immune system's chemokine production. Monocyte chemotactic protein-1 (MCP-1), an important chemotactic cytokine can be activated by active oxygen species. Groups of rats were exposed to hypoxic and hyperoxic environmental conditions for 60 h and MCP-1 was determined in their peripheral blood mononuclear cells by Elisa and Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). In this study we evaluated if the ability of monocytes to produce MCP-1 under basal conditions or after stimulation with lipopolysaccharide (LPS) or phytohaemagglutinin (PHA) was differently affected by exposure to hyper or hypoxic conditions in young and aged rats. MCP-1 expression and production in monocyte/macrophages from rats at normoxic conditions was reduced in aged subjects. However, spontaneous, LPS or PHA-induced MCP-1 production was up-regulated by exposure to hyperoxic conditions in both young (62 +/- 8, 99 +/- 7, 102 +/- 8 pg/ml, respectively) and aged rats (79 +/- 4, 112 +/- 9, 117 +/- 10 pg/ ml, respectively). We conclude that hyperoxia is an important regulator of MCP-1 release and support the hypothesis that increased % of O2 may serve to initiate MCP-1 production which then serves to recruit and regulate the distribution of mononuclear cells to the sites of inflammation.

Effects of sphingomyelin on aberrant colonic crypt foci development, colon crypt cell proliferation and immune function in an aging rat tumor model

Sphingomyelin (SPM) was assessed in older rats for in vivo effects on multiple immune responses and the development of colon preneoplastic lesions. Fifty-four-week-old rats were injected with 10 mg/kg body weight of the carcinogen azoxymethane (AOM), and then treated with 35 mg/kg body weight SPM orally for 6 weeks beginning 6 weeks after AOM treatment. None of the immune functions tested (antibody formation, delayed-type hypersensitivity or natural killer cell cytotoxicity) were significantly affected by SPM treatment. Natural killer (NK) cell activity was, however, decreased in all rats that were treated with AOM. There was a tendency for decreased aberrant crypt foci (ACF) numbers in the SPM-treated rats but this reduction was only significant for the largest lesions (> nine crypts per foci). The decreased ACF numbers were most evident in the proximal end of the colon. Colonic crypt cell proliferation was also decreased in SPM treated rats. This reduction was primarily in the base of the crypt column. Also, low numbers of ACF developed spontaneously in rats not treated with AOM, but no ACF were present in non-AOM rats that also received SPM. It appears that SPM may have effects on the post-initiation development of preneoplastic lesions in the rat colon but not on the immune functions assessed in this study.

Effects of N-acetylcysteine on macrophage and lymphocyte functions in a mouse model of premature ageing

In previous studies, we have observed that mice of the same strain and age show striking interindividual differences in behavior when exposed to a T-maze test. The animals that take longer to explore a T-shaped maze ("slow" animals) show high levels of emotionality/anxiety in other standard behavioral tests, prematurely aged immune functions, and a shorter life span, in comparison to "fast" mice. In these slow mice, which are a model of premature immunosenescence, the immune functions were improved after the ingestion of the thiolic antioxidant thioproline in the diet. In the present work, we studied the effects in vivo (0.1% w/w, for 4 weeks) and in vitro (0.001, 0.01, 0.1, 1, and 2.5 mM) of the thiolic antioxidant N-acetylcysteine (NAC) on different functions of peritoneal macrophages and lymphocytes from slow and fast adult Swiss mice. The results showed an improvement of all the functions studied, namely adherence to substrate, directed migration or chemotaxis, phagocytosis, and reactive oxygen species (ROS) production, after in vivo and in vitro treatment with NAC. The effect of this antioxidant was stronger in the cells from the slow than in those from the fast mice.

A diet supplemented with thiolic anti-oxidants improves leucocyte function in two strains of prematurely ageing mice

1. According to previous studies, Swiss mice of the same age showed striking interindividual differences in behaviour when exposed to a T-maze test, with a slow performance being linked to an impaired immune function, hyperemotional response to stress and a shorter life span compared with mice that quickly explore the maze. These facts led us to propose the slow mice as a model of prematurely ageing mice (PAM). 2. In the present study, we investigated whether this prematurely ageing model could be found in other strains of mice, such as BALB/c mice, by analysing several lymphocytes functions, such as adherence, chemotaxis, proliferative response to the mitogen concanavalin A (Con A), interleukin (IL)-2 release and natural killer (NK) activity. In addition, we tested the probable beneficial effects on these functions of dietary supplementation with thioproline (TP) plus N-acetylcysteine (NAC; 0.1% w/w of each anti-oxidant) in female Swiss and BALB/c mice. 3. Our model of premature ageing, previously reported in Swiss mice, has also been reproduced in the inbred BALB/c mouse strain, in which PAM showing an immunosenescence in several lymphocyte functions, such as lower chemotaxis, proliferative response to Con A, IL-2 release and NK activity, as well as higher adherence, were observed. A short-term (5 week) ingestion of TP + NAC by female Swiss and BALB/c mice improved leucocyte function, increasing chemotaxis, the proliferative response to Con A, IL-2 release and NK activity and decreasing the adherence of lymphocytes. These effects are greatest in cells from PAM of both strains. 4. In conclusion, our model of premature ageing has been reproduced in an inbred strain. In addition, the ingestion of a diet supplemented with two thiolic anti-oxidants, such as NAC and TP, has been shown to be beneficial to the immune response in PAM.

Glutamine protects activated human T cells from apoptosis by up-regulating glutathione and Bcl-2 levels

Glutamine is the most abundant amino acid in the body. A decrease of plasma glutamine concentrations is found in catabolic stress and is related to susceptibility to infections. Glutamine is known to modulate lymphocyte activation; however, little is known about glutamine modulation of cell death of activated human T cells. Using Jurkat T cells, we investigated glutamine modulation of T-cell apoptosis activated by PMA plus ionomycin. We found that glutamine at various concentrations significantly enhanced IL-2 production, cell proliferation, and cell viability of Jurkat T cells. Glutamine also decreased the number of apoptotic cells stimulated with PMA plus ionomycin as demonstrated by flow cytometry. Meanwhile, glutamine down-regulated CD95 and CD95L expression, but up-regulated CD45RO and Bcl-2 expression in activated T cells. Further investigation of CD95-mediated caspase activities revealed that supplementation of glutamine significantly decreased caspase-3 and caspase-8 activities in activated T cells. Since oxidative stress is closely associated with induction of lymphocyte apoptosis, we found that glutamine significantly increased glutathione (GSH), but decreased reactive oxygen species levels in activated T cells. Blockade of intracellular GSH formation enhanced, but exogenous GSH supplementation decreased, activated T-cell apoptosis. Studying normal peripheral lymphoproliferation, we also found that the presence of glutamine increased lymphoproliferation as well as Bcl-2 and CD95 expression; but decreased CD95L and activation-induced T-cell death. Taken together, glutamine appeared to augment lymphoproliferation but suppressed activation-induced T-cell death in both Jurkat T cells and human peripheral T lymphocytes.

Immunological memory and late onset autoimmunity

This review will address a paradox that has long fascinated scientists studying the effects of aging on the immune system. Although it has been clearly documented that B and T lymphocytes lose the ability to respond to antigenic or mitogenic stimulation with age, it has nonetheless been noted that the frequency of autoreactive antibodies is higher in older individuals. Given that the majority of the age-associated defects in immune regulation target the naïve T and B lymphocyte subsets, it has been presumed that this increase in antibodies specific for self antigens was due to changes in the B cell repertoire and/or to differences in the mechanisms responsible for generating immune tolerance in primary responses. However, in this review, we will address an alternative possibility that memory immune responses, first generated when the individual was young, may play a critical role in the appearance of serum autoantibodies by reactivation later in life (recall memory). It has recently been shown, in several different systems, that memory immunity can be maintained over the lifetime of the animal. Thus, memory B cells which are self-reactive may be harbored within an organism as it ages and the potential exists that they become re-activated at a later time, resulting in a vigorous autoreactive recall response. This may occur preferentially in older individuals due to several factors, including deficiencies in immune tolerance with age, progressive age-associated loss of tissue integrity yielding neo-self antigens, and possible re-exposure to an infectious agent which induces an autoimmune memory response through molecular mimicry. Thus, we propose that some of the autoantibodies seen in elderly patients and in older animals may have been produced by memory lymphocytes originally generated against antigens encountered during one's youth, but maintained in a tolerant (non reactive) state until a subsequent triggering event occurs. Possible implications of this model will be discussed.

Specific immunotherapy of cancer in elderly patients

The concept of immunotherapy of cancer is more than a century old, but only recently have molecularly defined therapeutic approaches been developed. In this review, we focus on the most promising approach, active therapeutic vaccination. The identification of tumour antigens can now be accelerated by methods allowing the amplification of gene products selectively or preferentially transcribed in the tumour. However, determining the potential immunogenicity of such gene products remains a demanding task, since major histocompatibility complex (MHC) restriction of T cells implies that for any newly defined antigen, immunogenicity will have to be defined for any individual MHC haplotype. Tumour-derived peptides eluted from MHC molecules of tumour tissue are also a promising source of antigen. Tumour antigens are mostly of weak immunogenicity, because the vast majority are tumour-associated differentiation antigens already 'seen' by the patient's immune system. Effective therapeutic vaccination will thus require adjuvant support, possibly by new approaches to immunomodulation such as bispecific antibodies or antibody-cytokine fusion proteins. Tumour-specific antigens, which could be a more potent target for immunotherapy, mostly arise by point mutations and have the disadvantage of being not only tumour-specific, but also individual-specific. Therapeutic vaccination will probably focus on defined antigens offered as protein, peptide or nucleic acid. Irrespective of the form in which the antigen is applied, emphasis will be given to the activation of dendritic cells as professional antigen presenters. Dendritic cells may be loaded in vitro with antigen, or, alternatively, initiation of an immune response may be approached in vivo by vaccination with RNA or DNA, given as such or packed into attenuated bacteria. The importance of activation of T helper cells has only recently been taken into account in cancer vaccination. Activation of cytotoxic T cells is facilitated by the provision of T helper cell-derived cytokines. T helper cell-dependent recruitment of elements of non-adaptive defence, such as leucocytes, natural killer cells and monocytes, is of particular importance when the tumour has lost MHC class I expression. Barriers to successful therapeutic vaccination include: (i) the escape mechanisms developed by tumour cells in response to immune attack; (ii) tolerance or anergy of the evoked immune response; (iii) the theoretical possibility of provoking an autoimmune reaction by vaccination against tumour-associated antigens; and (iv) the advanced age of many patients, implying reduced responsiveness of the senescent immune system.

Defect in ERK2 and p54(JNK) activation in aging mouse splenocytes

We have previously reported on a defect in both extracellular signal-regulated protein kinase (ERK) and c-jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) activation in splenocytes obtained from old rats. In order to investigate whether these effects are conserved across species, we have now used mouse splenocytes to measure the effect of aging on the activation of the same two MAPK families: ERK and JNK. Our results demonstrate that, as in rats, both MAPK signal transduction pathways are affected by aging in mice, indicating the existence of a further defect located downstream of the receptor-proximal events. Whereas ERK1 and p46(JNK) activation were not significantly modified, the kinetics of both ERK2 and p54(JNK) activation and inactivation were affected in splenocytes from old animals. Specifically, by analyzing the kinetics of activation and inactivation of these enzymes, we found a nearly 50% decrease in the fold of activation of both ERK2 and p54(JNK). These defects result in an overall diminution of enzyme activities without changes in the steady-state levels of relevant proteins. The impaired activity of these two MAPK pathways is likely to play a role in the reduced expression of interleukin-2 and diminished lymphoproliferation observed in old animals.

Leukocyte function and life span in a murine model of premature immunosenescence

Aging associates with a decline of physiological functions, including the function of the nervous and the immune system. These aged-related changes occur in various degrees in different members of a mouse outbred population. Accordingly, we have proposed a model of premature immunosenescence in mice, based on the demonstration of premature decline in the behavioral response in a simple T-maze and in several immune functions in Swiss outbred mice. Those mice with a worst (slow) performance in this test (linked to a higher emotional response to stress) show a shorter life span and a decreased immune function when compared to fast mice. In order to provide biomarkers of "biological aging" related to health and survival, the present longitudinal study includes the analysis of several immunological parameters such as, proliferative response to mitogen Con A, NK activity and cytokine (TNFalpha, IL-1beta and IL-2) release by peritoneal leukocytes from female Swiss mice. Slow mice showed a lower proliferative response to Con A, IL-2 and IL-1beta release, an impaired NK activity and an increased TNFalpha production as compared to fast mice. Moreover, the age-associated decline of these functions is more strikingly slow than in fast mice. In summary, we propose the above immunological parameters, that change with aging at a different rate in members of a same population, as useful biomarkers to asses the rate of biological aging in mice.

The role of immunity in susceptibility to respiratory infection in the aging lung

Respiratory tract infections, particularly pneumonia, are a leading cause of death in persons 65 years or older in both developed and developing countries. Because many attributes of immunity wane with advancing age, the elderly may be more susceptible to respiratory infections, even if they appear to be in good health. A decline in the ability of lymphoid tissues to mount an antigen-specific response (adaptive immunity) to specific microorganisms such as influenza virus or Streptococcus pneumoniae is thought to be an important factor in increasing susceptibility to respiratory tract infection with advancing age. However, abnormalities in innate immunity may also contribute to increased susceptibility to respiratory infections and have been poorly characterized in the elderly. Although changes in immune parameters such as T cell subsets and immunoglobulin concentrations have been observed in respiratory secretions from older healthy individuals compared to younger subjects, the significance of these changes for protective immunity in the lung is unknown. The incidence of pneumonia may be lessened by measures such as optimizing treatment of comorbid conditions, optimizing nutrition, and addressing swallowing disorders. The use of vaccines directed against the influenza virus and S. pneumoniae appears to have made an impact on the degree of morbidity and mortality, and perhaps, the incidence, of community-acquired pneumonia. However, better stimulation of specific immune responses with improved vaccines and more widespread use of these vaccines for protection of elderly individuals are needed.

Interleukin-2 involvement in early acute respiratory distress syndrome: relationship with polymorphonuclear neutrophil apoptosis and patient survival

OBJECTIVE

To determine blood and lung alveolar concentrations of interleukin (IL)-2 in acute respiratory distress syndrome (ARDS) and their relationship with polymorphonuclear neutrophil (PMN) apoptosis and patient survival.

DESIGN

Prospective cohort study.

SETTING

Medical and surgical intensive care units (ICUs; Canada) and the intensive care department (Belgium).

PATIENTS

Nineteen consecutive patients with ARDS, 14 non-ARDS ICU patients, and 20 healthy volunteers.

INTERVENTIONS

Blood samples and bronchoalveolar lavages (BAL) obtained via venous puncture and by fiberoptic bronchoscopy in the first 72 hrs after the onset of ARDS.

MEASUREMENTS AND MAIN RESULTS

One early point concentration of IL-2 was measured in both blood and BAL fluids of the three groups. In vivo alveolar PMN apoptotic index in BAL fluids and the influence of BAL fluid exposure on normal blood PMN spontaneous apoptosis in vitro were evaluated. Blood IL-2 was significantly lower in patients with ARDS compared with non-ARDS ICU patients and controls. In contrast, IL-2 in BAL fluids of patients with ARDS was dramatically elevated compared with non-ARDS ICU patients and controls. ARDS survivors exhibited lower early IL-2 blood levels than nonsurvivors and generally had a higher IL-2 lung content Lung alveolar PMN apoptosis in vivo was lower in patients with ARDS in comparison with controls. This apoptotic index was correlated with corresponding IL-2 alveolar levels in patients with ARDS. Exposure of normal blood PMN to BAL fluids from patients with ARDS delayed apoptosis in vitro. Immunodepletions of IL-2, granulocyte-macrophage colony stimulating factor, and a combination of both cytokines from BAL fluids of ARDS patients significantly restored PMN apoptosis. The recovery of PMN apoptosis was more effective when IL-2 was depleted in BAL fluids from ARDS survivors compared with nonsurvivors.

CONCLUSIONS

Opposite and disproportional concentrations of IL-2 are observed in blood and lung fluids of patients with early ARDS. IL-2 significantly contributes (with granulocyte-macrophage colony stimulating factor) to the inhibition of PMN apoptosis in BAL fluids of patients with ARDS. Early low blood IL-2 and high IL-2-driven inhibition of PMN apoptosis are beneficial to survivors. Thus, IL-2 is a new candidate for monitoring in early ARDS and an interesting indicator of prognosis.

Anti-tumor effect of L-deprenyl is associated with enhanced central and peripheral neurotransmission and immune reactivity in rats with carcinogen-induced mammary tumors

L-Deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, has previously been shown to improve immune responses and restore noradrenergic (NA) nerve fibers in the spleen of old rats. In tumor-bearing rats, L-deprenyl inhibited tumor incidence and enhanced tuberoinfundibular dopaminergic (TIDA) neurotransmission in the hypothalamus. The aim of the present study was to investigate whether alterations in sympathetic NA activity and cellular immune responses in the spleen, and TIDA activity in the hypothalamus, accompany deprenyl-induced regression of 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced mammary tumors. Rats with DMBA-induced mammary tumors were treated with 0, 2.5 mg, or 5.0 mg/kg body weight of deprenyl daily for 13 weeks. Saline-treated tumor-bearing rats exhibited reduced splenic IL-2 and IFN-gamma levels, and lowered splenic norepinephrine (NE) concentration and hypothalamic dopaminergic activity, compared to rats without tumors. In contrast, treatment with 2.5 mg/kg and 5.0 mg/kg of deprenyl reduced the number and size of mammary tumors. Deprenyl-induced tumor regression was accompanied by increased immune measures in the spleen, including enhanced IL-2 and IFN-gamma production, and NK cell activity. Neural measures enhanced by deprenyl included NE concentration in the spleen and TIDA neuronal activity in the hypothalamus. These results suggest that (1) mammary tumorigenesis is associated with the inhibition of sympathetic NA activity in the spleen, TIDA activity in the hypothalamus, and cell-mediated immunity, and (2) reversal of the inhibition of catecholaminergic neuronal activities of the central nervous system and peripheral nervous system by deprenyl may enhance anti-tumor immunity.

Age-related changes in the neuropeptide Y effects on murine lymphoproliferation and interleukin-2 production

Neuropeptide Y (NPY) modulates several aspects of the immune response but it is not known whether NPY responsiveness is altered with aging. In this work, the in vitro effect of NPY at concentrations ranging from 10(-)(14) M to 10(-)(7) M on lymphoproliferation has been studied in spleen, axillary node and thymus leukocytes from young, adult, mature and old BALB/c mice. The spontaneous proliferation of spleen lymphocytes from young mice was significantly stimulated by NPY. In response to the mitogen Con A, lymphoproliferation and IL-2 release by lymphocytes were inhibited significantly by NPY, these effects disappearing with aging. The results show that NPY is a modulator of lymphoproliferation and that this effect disappears progressively with age. Moreover, this regulatory role of NPY may be carried out through a decrease in IL-2 production.

The effect of a ceramide analog, N-acetylsphingosine on the induction of proliferation and IL-2 synthesis in T cells from young and old F344 rats

Ceramide is a physiological mediator of extracellular signals that control various cellular functions, including proliferation and apoptosis. In the present study, we examined the effects of cell-permeable ceramide analog, N-acetyl-sphingosine (C(2)-ceramide) on the induction of proliferation and interleukin-2 (IL-2) synthesis in T cells from young and old rats. Splenic T cells from 6- and 24-month-old Fischer 344 rats were treated with C(2)-ceramide and then incubated with anti-CD3 antibody for 24 or 48 h. The induction of proliferation and IL-2 production by anti-CD3 was significantly (P<0.001) lower in T cells from old rats compared to T cells from young rats. C(2)-ceramide treatment resulted in suppression of proliferation and IL-2 production in a concentration-dependent manner. The suppressive effect of C(2)-ceramide on proliferation and IL-2 production was greater in T cells from old rats than T cells from young rats. We investigated whether this decreased responsiveness was due to induction of program cell death (apoptosis) and found that there was a significant increase in DNA fragmentation in C(2)-ceramide treated and anti-CD3 stimulated T cells from both young and old rats. The increase in DNA fragmentation was paralleled with an increase in caspase-3 activation. C(2)-ceramide-induced caspase-3 activation and DNA fragmentation was significantly (P<0.5) higher in stimulated T cells from old rats compared to stimulated T cells from young rats. These results suggest that the sphingomyelin-ceramide signaling pathway may play an important regulatory role in the well-documented age-related decline in immune function.

Microbial risk assessment: dose-response relations and risk characterization

Characterizations of the risks associated with foodborne pathogens are dependent on the availability of information on the population's exposure to the biological agents. However, by itself, exposure data are insufficient to assess the public health impact of pathogenic microorganisms. This requires the availability of effective dose-response models. Successful development of models that describe dose-response relations for enteric pathogens is dependent on a sound understanding of the mechanisms of pathogenicity associated with individual pathogens. This includes knowledge of how the various pathogen, host, and food matrix factors influence pathogenicity. Currently, a group of sigmoidal mathematical equations are used to empirically describe dose-response relations. While these have proven to be highly useful, advances in microbial food safety risk assessment will likely require the development of mechanistic models that more effectively consider the range of factors that influence the frequency and severity of foodborne infections in a population.

Efficacy of cancer gene therapy in aging: adenocarcinoma cells engineered to release IL-2 are rejected but do not induce tumor specific immune memory in old mice

Numerous studies have demonstrated the efficacy of cytokine gene-engineered tumor cells to induce tumor rejection and specific memory acquisition into syngeneic immunocompetent mice by activation of host-dependent antitumor responses. A progressive immune dysfunction, mainly involving thymus-dependent specific immunity, occurs during aging. In this study we evaluated whether the injection of IL-2 gene-transfected tumor cells in old mice causes an immune activation which results in tumor rejection and induction of specific immune memory as occurs in young animals. Young and old mice were inoculated with syngeneic parental mammary adenocarcinoma cells (TS/A p.c.) or with TS/A cells engineered to release IL-2 (TS/A-IL2). Three clones of TS/A-IL-2 cells were used producing low (30 U, B1.30), intermediate (3600 U, B6.3600), or high (6000 U, B4.6000) IL-2. While the B1.30 clone grew in 100% of mice, the B6.3600 and B4.6000 clones were promptly rejected in both young and old animals. In young mice, rejection was associated with a large neutrophil and macrophage infiltration, with a minor number of CD4+ and CD8+ lymphocytes. In old mice, neutrophils and macrophages were the main cells involved in tumor rejection whereas both CD4+ and CD8+ lymphocytes were scarcely present in tumoral infiltrate. A lower number of apoptotic tumor cells was found in TS/A-IL2-challenged old mice in comparison with young animals. To test whether the injection of TS/A-IL2 cells induced a specific immune memory, mice with no tumors after the challenge with B6.3600 and B4.6000 clones received a lethal challenge of TS/A p.c. 90% and 30% of young mice previously injected with B4.6000 or B6.3600 clones, respectively, rejected TS/A p.c. In old mice, B4.6000 cells did not confer protection, whereas only 10% of mice which received B6.3600 cells were able to reject TS/A p.c. Neither the graft of a young thymus or the adoptive transfer of young T lymphocytes to old mice induced specific immune memory for TS/A p.c. in old animals. These data suggest the necessity to refine antitumor vaccination procedures in aging.

Measurement of cytokines in clinical samples using immunoassays: problems and pitfalls

With the explosion in interest in cytokines and an increasing understanding of their possible involvement in the pathogenesis of many diseases, the number of studies measuring cytokines in body fluids has increased markedly over the last 5 to 10 years. However, it is readily apparent from the literature that the level of awareness of the many factors that can potentially influence the results obtained is very low. Such factors are likely to contribute considerably to the disparities seen among similar types of study. These include assay properties such as standardization and specificity, type of sample and sample handling, and many biological influences such as age, sex, ethnic background, and diurnal rhythmicity. Clearly, it is not possible to control for all these factors, but a minimum evaluation of assays should be carried out as described, including recovery and parallelity studies using relevant samples and the establishment of reproducibility and normal healthy population levels. An awareness of these factors, which is the purpose of this review, may hopefully lead to an improvement in the quality of studies incorporating the measurement of cytokines in clinical samples and should aid in the interpretation of the data.

Impaired signal transduction in mitogen activated rat splenic lymphocytes during aging

Mitogen activated protein kinases (MAPK) are activated by a wide variety of signals leading to cell proliferation and differentiation in different cell types. With aging, there is a marked decrease in proliferation of T-lymphocytes in response to a variety of mitogens. Several age-related changes in the activation of MAPK pathways in T-lymphocytes activated via the T-cell receptor (TCR) have been described in different species. This way, some TCR proximal defects in tyrosine kinase activity have been delineated. In this study, we have used rat splenic lymphocytes to measure the effect of aging on the activation of two MAP kinase families: ERK and JNK. In order to bypass the receptor-proximal age-dependent defects previously described, we used phorbol ester (PMA) and Ca2+ ionophore (A23187) as co-mitogens. Our results demonstrate that splenic lymphocytes from old rats have a disturbance in the activation of the ERK and JNK MAPK signal transduction pathways, that are located downstream of the receptor-proximal events. At least part of the age-related defect leading to decreased ERK activity appears to be located upstream of ERK itself, since activation of MEK is also impaired. On the other hand, the observed defects in MAPK activation do result in decreased activation of downstream events, such as c-Jun phosphorylation. Thus, we conclude that aging of splenic lymphocytes results in a functional decline in signal transduction, and at least some of these defects are located downstream of the receptor-proximal events previously described by others. The impaired activity of these two MAP kinase pathways is likely to play a role in the diminished lymphoproliferation observed in old individuals.

Hematopoiesis and cytokines. Relevance to cancer and aging

Impaired hematopoiesis and dysregulated cytokine expression have important implications for cancer in the elderly. In aged people, hematopoiesis is dysregulated and becomes paradoxically down-modulated under periods of increased hematopoietic demand. This down-modulation may explain, at least in part, the increased incidence of anemia in the elderly, although the cause of anemia can usually be identified in these patients and frequently reversed with targeted therapy. An age-associated decrease in the expression of interleukin-2 may contribute to impaired cellular immunity. Additionally, the increased interleukin-6 production frequently found in the elderly may participate in promoting the survival and proliferation of malignant myeloma and in inducing resistance by myeloma cells to therapies that act through apoptosis. Dysregulation of the expression of these and other cytokines may be a mechanism contributing to age-related impairment of the hematopoietic response, the genesis and therapeutic resistance of specific malignancies, and cancer cachexia.

Age-related decline in activation of calcium/calmodulin-dependent phosphatase calcineurin and kinase CaMK-IV in rat T cells

We have previously shown that the DNA binding activity of the transcription factor NFAT which plays a predominant role in IL-2 transcription decreases with age. Because the transactivation (dephosphorylation and nuclear translocation) of the NFAT-c (cytoplasmic component of the NFAT complex) is mediated by the calcium/calmodulin-dependent phosphatase, calcineurin (CaN), and because Ca2+/calmodulin-dependent kinases (CaMK-II and IV/Gr) have been shown to play a critical role in calcium signaling in T cells, it was of interest to determine what effect aging has on the activation and the levels of these calcium regulating enzymes. The induction of calcineurin phosphatase activity, and CaMK-II and IV/Gr activities, were studied in splenic T cells isolated from Fischer 344 rats at 6, 15, and 24 months of age. In addition, the changes in the protein levels of these enzymes were measured by Western blot. The calcineurin phosphatase activity and CaMK-II and IV kinase activities were at a maximum after the cells were incubated with anti-CD3 antibody for 5-10 minutes. The induction of calcineurin activity by anti-CD3 and by calcium ionophore (A23187) declined 65 and 55%, respectively, between 6 and 24 months of age. The induction of CaMK-IV activity, but not CaMK-II activity by anti-CD3, was significantly less (by 54%) in T cells from old rats compared to T cells from young rats. The decline in the activation of these enzymes with age was not associated with changes in their corresponding protein levels. These results demonstrate that alterations in calcineurin phosphatase activity and CaMK-IV activity may contribute to the well-documented age-related decline in T cell function.

The immune system in the elderly: III. Innate immunity

The capability to cope with infectious agents and cancer cells resides not only in adaptive immune responses against specific antigens, mediated by T and B lymphocytes clonally distributed, but also in natural immune reactions. These innate defence mechanisms include chemotaxis, phagocytosis, natural cytotoxicity, cell interactions, and soluble mediators or cytokines. However, specific and natural immune mechanisms are always closely linked and interconnected, providing the primary defense against pathogens. The Authors discuss the main changes observed with advancing age in granulocytes and natural killer (NK) cell activity, in the expression and function of adhesion molecules, and in the pattern of cytokine production. Since phagocytic function is the primary mechanism through which the immune system eliminates most extracellular pathogenic microorganisms, analysis of this function is of clinical importance. Neutrophils from aged subjects often exhibit a diminished phagocytic capacity, as well as a depressed respiratory burst, notwithstanding an activated state. The activity of NK cells during aging has been studied extensively and different results have been reported. The most consistent data indicate an increase in cells with high NK activity with advancing age. Cells from healthy centenarians can efficiently kill target cells. This finding seems to suggest that innate immunity and in particular NK cell activity, is not heavily deteriorated with age. Conversely, a low NK activity is a predictor of impending morbidity. Immunosenescence is associated with increased expression of several cell adhesion molecules (CAM) resulting in an augmented capacity to adhere. Finally, also the cytokine network, responsible for differentiation, proliferation, and survival of lymphoid cells, undergoes complex changes with age. The main findings are a Th1 to Th2 cytokine production shift and an increased production of proinflammatory cytokines, which could explain many aspects of age-associated pathological events, such as atherosclerosis and osteoporosis.

The immune system in the elderly: II. Specific cellular immunity

Numerous changes occur in the immune system with advancing age, probably contributing to the decreased immunoresponsiveness in the elderly. These changes are often associated with important clinical manifestations such as increased susceptibility to infection and cancer frequently observed in the elderly population. Although both cellular and humoral immune responses are modified with advancing age, much of the decrease in immunoresponsiveness seen in elderly populations is associated with changes in T cell responses. The loss of effective immune activity is largely due to alterations within the T cell compartment which occur, in part, as a result of thymic involution. Substantial changes in both the functional and phenotypic profiles of T cells have been reported with advancing age. In fact, two prominent features of immunosenescence are altered T cell phenotype and reduced T cell response. One of the most consistent changes noted in T cells with advancing age is the decrease in the proportion of naive T cells with a concomitant increase in T cells with an activated/memory phenotype. In addition, there is evidence that the T cell population from aged individuals is hyporesponsive. The observed functional changes include decreased responsiveness to T cell receptor stimulation, impaired T cell proliferative capacity, a decline in the frequency of CD4+ T cells producing IL-2 and a decreased expression in IL-2 receptors. These latter findings probably explain the loss of proliferative capability of T cells from aged individuals. There is also evidence of a decrease in the early events of signal transduction, decreased activation-induced intracellular phosphorylation, and decreased cellular proliferative response to T cell receptor stimulation. The present review analyzes the main changes of the T cell compartment characterizing immunosenescence and discusses the possible mechanisms underlying these disregulations and their clinical implications.

Immunological changes in the elderly

Immunosenescence is a complex remodelling of the immune system which may contribute significantly to morbidity and mortality in the elderly. Much evidence suggests an association between immune function and longevity. It was advanced that individuals who have survived in good health to the maximum life span are equipped with optimal cell defense mechanisms. Despite the great number of studies on the immune system in the elderly, little is known of the biological basis of immunosenescence in humans. This is partly due to the contrasting results often obtained by the various investigators. One source of discrepancy is that diseases are frequent in aging, and the alterations observed in the immune parameters of the elderly could be a cause or alternatively a consequence of the underlying pathological processes. Undoubtedly some diseases to which aged people are particularly susceptible, such as infectious, autoimmune and neoplastic pathologies, include dysregulation of several immune functions in their pathogenesis. On the other hand, recent studies in healthy centenarians suggest that the immunological changes observed during aging are consistent with a reshaping, rather than a generalized deterioration, of the main immune functions. Considering that the number of old people is dramatically increasing, and that geriatric pathology is becoming an important aspect of clinical practice, it seems particularly interesting to review the peculiar findings in the immune system of the elderly so as to better understand their susceptibility to certain diseases, and the links between health and longevity.

Age-dependent alterations in mRNA level and promoter methylation of collagen alpha1(I) gene in human periodontal ligament

In an attempt to understand the molecular mechanisms of age-dependent degenerative alteration in human periodontal tissues, we examined mRNA level and DNA methylation of collagen alpha1(I) gene. Using healthy periodontal ligament tissues from humans aged 9-76 years, we found that the collagen alpha1(I) mRNA level decreased almost linearly with age. It was observed in both Northern blot and dot blot hybridization. Examination of DNA methylation in the collagen alpha1(I) gene promoter region by its susceptibility to methylation-sensitive restriction enzyme followed by Southern blot analysis showed age-dependent increase of DNA methylation at -1705 and -80 positions located upstream of the gene. The data suggest the possible importance of alterations in collagen alpha1(I) gene expression and its DNA methylation in promoter region in age-dependent degeneration of periodontal ligament.

Hypothesis: A recurrent, moderate activation fosters systemic autoimmunity--the apoptotic roles of TCR, IL-2 and Fas ligand

Studies of several gene knockout mice suggest an interesting association of a moderate T cell response with systemic autoimmune diseases. In addition, CD95 ligand (FasL) expression in some strains of these mice is impaired. Because FasL is critically involved in regulating peripheral tolerance, there may be a link between autoimmune diseases and a moderate T cell response that cannot activate the FasL gene. Here, we propose that there are two thresholds of T cell activation. When moderately stimulated, T cells can be activated to the low (1st) threshold, which permits the induction of CD40L, IL-2, IL-4, and other components that help the immune response. The high (2nd) activation threshold can only be achieved by a strong and concurrent stimulation through TCR and IL-2R. Once the high threshold is reached, FasL is produced to induce apoptosis of the activated T and B cells. In the absence of the FasL-mediated downregulation, the activated B cells become efficient antigen-presenting cells for self-antigens and excellent responders for T cell help. Such an exacerbating condition, induced by recurrent and moderate activation, favors the development of autoreactive T cells and autoantibody production. Evidence supporting this hypothesis and some predictions that can be tested are described.

Age-related defects in Th1 and Th2 cytokine production by human T cells can be dissociated from altered frequencies of CD45RA+ and CD45RO+ T cell subsets

The present study investigated whether age-related changes in the production of Th1 and Th2 cytokines by human T cells might be linked to altered frequencies of naive (CD45RA+) and memory (CD45RO+) T cell subsets. T cells from healthy elderly humans (n = 32) stimulated with anti-CD3epsilon monoclonal antibody OKT3 plus PMA produced significantly lower levels of IL-2 and IFNgamma (Th1 type) and of IL-4 (Th2 type) cytokines compared with T cells from young subjects. Although considerable heterogeneity was observed in the levels of cytokines produced by activated T cells from elderly individuals, linear regression analysis failed to demonstrate any significant shift in Th1 to Th2 type cytokine profiles of human T cells during aging. Sufficient T cells were available from eighteen elderly subjects to quantitate the levels of cytokine production in parallel with flow cytometry analysis of the frequencies of CD45RA+ naive and CD45RO+ memory T cells. Compared with the group of young subjects, the elderly group exhibited significant decreases in the frequencies of naive T cells with reciprocal increases in memory T cells. However, defects in Th1 and Th2 cytokine production were not significantly correlated with altered frequencies of naive/memory T cells among elderly individuals. In addition, those elderly individuals with normal frequencies of naive/memory T cells exhibited decreases in cytokine production comparable to the reductions observed for elderly donors with alterations in the frequencies of naive/memory T cells. These findings suggest that age-related defects in Th1 and Th2 cytokine production cannot be attributed entirely to alterations in the frequencies of naive/memory T cell subsets and point toward intrinsic aberrancies within human T cell cytokine networks during aging.

Tuberculosis II: the failure of the BCG vaccine

BCG (bacille Calmette-Guerin) is an attenuated pathogen characterized by its capacity to induce cellular and humoral immune responses primarily against a nonpeptidic antigen, lipoarabinomannan. Immune responses against this substance contribute to the immunoprotection of the patient if the production of IL-2 and INF-gamma is not impaired. The most adequate production of INF-gamma and IL-2 is obtained by immunoreactivity against proteinic antigens. The formation of IgG-type antibodies and of cellular immunity against mycobacterial peptidic and proteinic antigens is an additional immunological response essential for a good protection. This is achieved by the BCG vaccine in only a small proportion of the vaccinees. A vaccine adjuvant that also finds application as an immunotherapeutic agent is composed of proteinic antigens such as sonicates of Mycobacterium vaccae and antigen 60 of Mycobacterium bovis. These enhance the beneficial Th1-pole of the immune response. In addition, A60 induces the formation of antibodies against species-specific proteinic antigens. Despite the questioning of its innocuousness and efficacy, the BCG vaccine was imposed worldwide in 1950 by medical and political organizations that showed no concern for these questions. The contemporary structures of research administration in this area make it unlikely that the efficacious means recently developed to complement the action of the vaccine and of chemotherapies to face the surge of tuberculosis (TB) will be readily adopted.

Tuberculosis I: a conceptual frame for the immunopathology of the disease

An analysis of the cellular and humoral immune responses after bacille Calmette-Guerin (BCG) vaccination and during tuberculosis treatment favors the hypothesis of an immune defence developed in four overlapping successive stages. The initial immune response is innate. The following two intermingle innate and specific responses against low molecular weight oligopeptidic and nonpeptidic antigens, as muramyldipeptide and trehalose dimycolate, and large molecular weight nonpeptidic antigens such as lipoarabinomannan. The ultimate specific response is directed against protein antigens as Antigen 60. BCG and primary tuberculosis (TB) infections induce cellular and humoral immune responses essentially against oligopeptidic and small and large molecular weight nonpeptidic antigens. Immune responses against non-peptidic substances contribute to the immunoprotection of the infected person who develops a primary infection. Some infected people allow the expression of the immunosuppressive activity of the pathogen. This results in the synthesis of interleukin-10 (IL-10), which suppresses the formation of interferon-gamma (INF-gamma) and IL-2, and of IL-6, which suppresses T-cell responses. These patients have a skewed immune response against non-peptidic antigens and present with symptoms. They will not recover unless responses directed against proteinic antigens occur, which restore INF-gamma and IL-2 production. The formation of immumoglobulin-G (IgG)-type antibodies and of a cellular immunity against mycobacterial peptidic antigens is essential for a good protection against a post-primary infection.

Aging and T-cell-mediated immunity

Changes in the T-lymphocyte compartment represent the most critical component of immunological aging. Recent studies have demonstrated that the age-related decline in T-cell-mediated immunity is a multifactorial phenomenon affecting T-cell subset composition as well as several proximal events such as protein tyrosine phosphorylation, generation of second messengers, calcium mobilization and translocation of protein kinase C, and distal events such as lymphocyte proliferation and cytokine production of the T-cell activation pathway. Age-related T-cell immune deficiency is preceded by thymic involution and is influenced by several intrinsic as well as extrinsic factors. Further, the role of monocytes and macrophages in T-cell activation changes with advancing age. This brief review will summarize the current knowledge of the cellular as well as molecular aspects of immunodeficiency of T cells due to aging, some of the paradoxes of aging as related to T-cell-mediated immunity, and possible factors which contribute to this paradox. Finally, experimental approaches will be suggested that might resolve these controversies and that might provide insights into the diverse and complex mechanisms that contribute to immunodeficiency of T cells. Ultimately these studies may suggest possible therapeutic interventions to enhance immune function in the elderly.

Effects of L-deprenyl treatment on noradrenergic innervation and immune reactivity in lymphoid organs of young F344 rats

Sympathetic noradrenergic (NA) neuronal activities in the thymus, spleen and mesenteric lymph nodes (MLN) and immune responses in the spleen were examined in young male F344 rats treated daily with 0, 0.25 mg, or 2.5 mg/kg body weight of L-deprenyl, an irreversible monoamine oxidase-B (MAO-B) inhibitor. Rats were treated daily for 1, 15, or 30 days, and sacrificed 7 days after the last deprenyl treatment. Deprenyl treatment increased norepinephrine (NE) content in the spleen without modifying the pattern and density of NA innervation in the splenic white pulp. The concentration of NE was unaltered in the thymus, but it was increased in the MLN of deprenyl-treated rats. One day of treatment with deprenyl decreased splenic NK cell activity while 15 days of deprenyl treatment enhanced splenic NK cell activity. Deprenyl elevated Con A-induced T lymphocyte proliferation following 30 days of treatment, but did not alter spleen cell Con A-induced IL-2 production or the percentage of CD5 + T cells in the spleen. A moderate decrease in the percentage of sIgM + B cells was observed in the spleens of 15- and 30-day deprenyl-treated rats. These results suggest that deprenyl has sympathomimetic action on sympathetic NA nerve fibers in the spleen; the enhancement of NA neuronal activity may contribute to the modulation of immune responses in the spleen.