Signal transduction changes in granulocytes and lymphocytes with ageing

Ontogeny of immunity and potential implications for co-infection

Immunity changes through ontogeny and can mediate facilitative and inhibitory interactions among co-infecting parasite species. In amphibians, most immune memory is not carried through metamorphosis, leading to variation in the complexity of immune responses across life stages. To test if the ontogeny of host immunity might drive interactions among co-infecting parasites, we simultaneously exposed Cuban treefrogs (Osteopilus septentrionalis) to a fungus (Batrachochytrium dendrobaditis, Bd) and a nematode (Aplectana hamatospicula) at tadpole, metamorphic and post-metamorphic life stages. We measured metrics of host immunity, host health and parasite abundance. We predicted facilitative interactions between co-infecting parasites as the different immune responses hosts mount to combat these infectious are energetically challenging to mount simultaneously. We found ontogenetic differences in IgY levels and cellular immunity but no evidence that metamorphic frogs were more immunosuppressed than tadpoles. There was also little evidence that these parasites facilitated one another and no evidence that A. hamatospicula infection altered host immunity or health. However, Bd, which is known to be immunosuppressive, decreased immunity in metamorphic frogs. This made metamorphic frogs both less resistant and less tolerant of Bd infection than the other life stages. These findings indicate that changes in immunity altered host responses to parasite exposures throughout ontogeny. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.

Immune system aging and the aging-related diseases in the COVIID-19 era

The interest in the process of aging, and specifically in how aging affects the working of our immune system, has recently enormously grown among both specialists (immunologists and gerontologists) and representatives of other disciplines of health sciences. An obvious reason for this interest is the current pandemics of COVID-19, known to affect the elderly more than younger people. In this paper current knowledge about mechanisms and complex facets of human immune system aging is presented, stemming from the knowledge about the working of various parts of the immune system, and leading to understanding of immunological mechanisms of chronic, inflammatory, aging-related diseases and of COVID-19.

Endocrine-Disrupting Chemicals' (EDCs) Effects on Tumour Microenvironment and Cancer Progression: Emerging Contribution of RACK1

Endocrine disruptors (EDCs) can display estrogenic and androgenic effects, and their exposure has been linked to increased cancer risk. EDCs have been shown to directly affect cancer cell regulation and progression, but their influence on tumour microenvironment is still not completely elucidated. In this context, the signalling hub protein RACK1 (Receptor for Activated C Kinase 1) could represent a nexus between cancer and the immune system due to its roles in cancer progression and innate immune activation. Since RACK1 is a relevant EDCs target that responds to steroid-active compounds, it could be considered a molecular bridge between the endocrine-regulated tumour microenvironment and the innate immune system. We provide an analysis of immunomodulatory and cancer-promoting effects of different EDCs in shaping tumour microenvironment, with a final focus on the scaffold protein RACK1 as a pivotal molecular player due to its dual role in immune and cancer contexts.

Should we Try to Alleviate Immunosenescence and Inflammaging - Why, How and to What Extent?

With advancing age, immune responses of human beings to external pathogens, i.e., bacteria, viruses, fungi and parasites, and to internal pathogens - malignant neoplasm cells - become less effective. Two major features in the process of aging of the human immune system are immunosenescence and inflammaging. The immune systems of our predecessors co-evolved with pathogens, which led to the occurrence of effective immunity. However, the otherwise beneficial activity may pose problems to the organism of the host and so it has builtin brakes (regulatory immune cells) and - with age - it undergoes adaptations and modifications, examples of which are the mentioned inflammaging and immunosenescence. Here we describe the mechanisms that first created our immune systems, then the consequences of their changes associated with aging, and the mechanisms of inflammaging and immunosenescence. Finally, we discuss to what extent both processes are detrimental and to what extent they might be beneficial and propose some therapeutic approaches for their wise control.

Influence of fish oil supplementation and strength training on some functional aspects of immune cells in healthy elderly women

Immune function changes with ageing and is influenced by physical activity (strength training, ST) and diet (fish oil, FO). The present study investigated the effect of FO and ST on the immune system of elderly women. Forty-five women (64 (sd 1·4) years) were assigned to ST for 90 d (ST; n 15), ST plus 2 g/d FO for 90 d (ST90; n 15) or 2 g/d FO for 60 d followed by ST plus FO for 90 d (ST150; n 15). Training was performed three times per week, for 12 weeks. A number of innate (zymosan phagocytosis, lysosomal volume, superoxide anion, peroxide of hydrogen) and adaptive (cluster of differentiation 4 (CD4), CD8, TNF-α, interferon-γ (IFN-γ), IL-2, IL-6 and IL-10 produced by lymphocytes) immune parameters were assessed before supplementation (base), before (pre-) and after (post-) training. ST induced no immune changes. FO supplementation caused increased phagocytosis (48 %), lysosomal volume (100 %) and the production of superoxide anion (32 %) and H2O2 (70 %) in the ST90. Additional FO supplementation (ST150) caused no additive influence on the immune system, as ST150 and ST90 did not differ, but caused greater changes when compared to the ST (P< 0·05). FO increased CD4+ and CD8+ lymphocytes in the ST150, which remained unchanged when training was introduced. The combination of ST and FO reduced TNF-α in the ST150 from base to post-test. FO supplementation (ST150, base–pre) when combined with exercise (ST150, pre–post) increased IFN-γ, IL-2, IL-6 and IL-10 production. The immune parameters improved in response to FO supplementation; however, ST alone did not enhance the immune system.

Expression of calpain-calpastatin system (CCS) member proteins in human lymphocytes of young and elderly individuals; pilot baseline data for the CALPACENT project

BACKGROUND

Ubiquitous system of regulatory, calcium-dependent, cytoplasmic proteases - calpains - and their endogenous inhibitor - calpastatin - is implicated in the proteolytic regulation of activation, proliferation, and apoptosis of many cell types. However, it has not been thoroughly studied in resting and activated human lymphocytes yet, especially in relation to the subjects' ageing process. The CALPACENT project is an international (Polish-Italian) project aiming at verifying the hypothesis of the role of calpains in the function of peripheral blood immune cells of Polish (Pomeranian) and Italian (Sicilian) centenarians, apparently relatively preserved in comparison to the general elderly population. In this preliminary report we aimed at establishing and comparing the baseline levels of expression of μ- and m-calpain and calpastatin in various, phenotypically defined, populations of human peripheral blood lymphocytes for healthy elderly Sicilians and Poles, as compared to these values observed in young cohort.

RESULTS

We have found significant differences in the expression of both μ- and m-calpain as well as calpastatin between various populations of peripheral blood lymphocytes (CD4+, CD8+ and CD19+), both between the age groups compared and within them. Interestingly, significantly higher amounts of μ- and m-calpains but not of calpastatin could be demonstrated in the CD4+CD28- and CD8+CD28- lymphocytes of old subjects (but not in the cells of young individuals), as compared to their CD28+ counterparts. Finally, decreased expression of both calpains in the elderly T cells is not related to the accumulation of effector/memory (CD45RO+) cells in the latter, as the expression of both calpains does not differ significantly between the naïve and memory T cells, while is significantly lower for elderly lymphocytes if both populations are taken separately.

CONCLUSIONS

Observed differences in the amounts of CCS member proteins between various populations of lymphocytes of young and elderly subjects may participate in the impaired proliferative activity of these cells in the elderly.

Opposing effects of cortisol and dehydroepiandrosterone on the expression of the receptor for Activated C Kinase 1: implications in immunosenescence

Aging is associated to a decline in immune functions that are in part related to a defective protein kinase C dependent signal transduction machinery. RACK-1 (Receptor for Activated C Kinase 1) is a scaffold protein for different kinases and membrane receptors. We have previously demonstrated, in the elderly, a defective PCKβII (Protein Kinase C βII) translocation related to a decrease in RACK-1 protein expression, which is correlated to the age-associated decline in DHEA (dehydroepiandrosterone) levels. As a consequence of this signal transduction impairment, a significant decrease in immune cells functionality was observed. Furthermore, we could demonstrate that in vivo and in vitro DHEA administration restored RACK-1 level and immune functions, indicating that this hormone behaved as a positive RACK-1 regulator. We have most recently characterized the human GNB2L1 promoter region, coding for RACK-1 protein. Although no direct DHEA responsive elements were found, a glucocorticoid responsive element (GRE) was identified. The purpose of this work was to investigate, in the human pro-myelocytic cell line THP-1, whether physiological cortisol concentrations were able to modulate GNB2L1 promoter activity, RACK-1 transcription as well as cytokine production. As DHEA is endowed of anti-glucocorticoid properties in several cellular systems, and as cortisol:DHEA ratio imbalance is relevant in aging, we also investigated their possible interaction at the RACK-1 expression level. We could demonstrate that cortisol acted in a dose-related manner as a GNB2L1 promoter repressor, reducing RACK-1 mRNA expression and protein level. Probably by interfering with glucocorticoid receptor binding to GRE sequence, prolonged DHEA exposure counteracted cortisol effects, restoring RACK-1 levels and cytokine production, as assessed by LPS-induced TNF-α release.

Defective B cell ontogeny and humoral immune response in mice prematurely expressing human complement receptor 2 (CR2, CD21) is similar to that seen in aging wild type mice

Mice prematurely expressing human CR2 (hCR2) in the B cell lineage have a defective B cell ontogeny and humoral immune response. We have previously determined altered tyrosine phosphorylation patterns within hCR2 transgenic mice, suggesting that irreversible changes in B cell signaling pathways had occurred, which could explain the B cell unresponsiveness associated with hCR2 transgene expression. In support of that assertion, we found that increasing antigen dose or addition of adjuvant had a minimal impact on the ability of B cells to respond to antigen. However, analysis of aged hCR2^high mice (1 year plus) revealed that both B cell numbers, B cell sub-population distribution including expansion of a newly described B regulatory cell subset, and immune responses were comparable with age-matched hCR2 negative mice. Finally, we established that B cell unresponsiveness to antigen in aging wild type mice (1 year plus) was equivalent to that noted in 3-month-old hCR2^high mice. This data provides evidence that 3-month-old hCR2^high mice have a humoral immune system resembling aged mice and suggests that further examination of the precise molecular and cellular parallells between aged wild type mice and 3-month-old hCR2^high mice could provide an important insight into the mechanisms which lead to B cell unresponsiveness in the aging immune system.

Role of inositol 1,4,5-triphosphate and p38 mitogen-activated protein kinase in reactive oxygen species generation by granulocytes in a cyclic AMP-dependent manner: an age-related phenomenon

BACKGROUND

It is generally agreed that elderly subjects undergo progressive deterioration of their immune responsiveness, which leads to an increased susceptibility to autoimmune processes, neoplasm and inflammation. Thus there is a general consensus that regulation of inflammation results from a balance between pro-inflammatory and anti-inflammatory pathways.

OBJECTIVE

The present study aimed to investigate the possible alterations of cyclic AMP/protein kinase A (cAMP/PKA) and p38 mitogen-activated protein kinase (p38 MAPK) pathway signaling (reactive oxygen species (ROS) generation) and inositol 1,4,5-triphosphate (InsP3) production by neutrophils during the aging process.

METHODS

Age-induced ROS generation and InsP3 production were studied in healthy subjects ranging in age from 20 to 80 years. The subjects were divided into six age groups: (I) 20-29, (II) 30-39, (III) 40-49, (IV) 50-59, (V) 60-69, and (VI) 70-80 years old. The effect of cAMP, H89 (inhibitor PKA), and PD169316 (inhibitor p38 MAPK) on ROS production was quantified in a luminol-dependent chemiluminescence assay (relative light units/min) and by InsP3 release (cpm).

RESULTS

Our results demonstrated a lack of dibutyryl cAMP inhibitory effects on ROS generation and InsP3 production by granulocytes from PKA-dependent 50-year-olds. However, the inhibitory effect of cAMP is restored in neutrophils after the age of 50 years when p38 MAPK signaling is inhibited.

CONCLUSIONS

The present study may be important towards a better understanding of the high susceptibility to infections and age-related inflammatory and deregulation diseases. The alteration of cAMP/PKA and p38 MAPK signaling pathways enhances the inflammatory process.

GM-CSF activates the Jak/STAT pathway to rescue polymorphonuclear neutrophils from spontaneous apoptosis in young but not elderly individuals

Polymorphonuclear neutrophils (PMN) are the first cells to be recruited to the site of tissular aggression. They have a short-life span and die by spontaneous apoptosis. However, their life span and functional activities can be extended in vitro by a number of proinflammatory cytokines, including the granulocyte-macrophage colony stimulating factor (GM-CSF). We have reported that the protective effect of GM-CSF did not occur in PMN of elderly subjects. Data reported here showed that this difference was not due to a change in the expression of the GM-CSF receptor in the PMN of elderly individuals compared to young subjects. Furthermore, we showed here that GM-CSF activated the Janus kinase/signal transducer and activator of transcription (Jak/STAT) pathway and this activation appeared to be maintained for an extended period of time (18 h) playing an important role in the GM-CSF induced delayed PMN apoptosis. In marked contrast, GM-CSF had no effects on Jak2 activation in PMN of elderly individuals. We found that an inhibitor of Jak2 activation (AG490) abolished the protective effect of GM-CSF in PMN from young donors, however had no effect in PMN of elderly subjects. GM-CSF induced a transient activation of STAT3 and STAT5 in PMN of young donors but failed to activate to the same extent these signal transducers in PMN of elderly donors. The levels of proCaspase-3 were reduced in PMN of young donors treated with GM-CSF for 18 h but remained unchanged in PMN of elderly subjects treated under the same conditions compared to the untreated PMN. Our data are consistent with the interpretation that, at least in part (1) the protective effect of GM-CSF against apoptosis results from the activation of the Jak/STAT pathway and (2) decreased rescue from apoptosis in PMN of elderly is related to a failure of GM-CSF to activate this pathway in these cells.

Signal transduction and functional changes in neutrophils with aging

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first-line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor-driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.

Tyrosine phosphorylation signalling dependent on 1α,25(OH)2-vitamin D3 in rat intestinal cells: effect of ageing

In intestinal cells, as in other target cells, 1alpha,25(OH)(2)D(3) elicits long-term and short-term responses which involve genomic and non-genomic mode of actions, respectively. There is evidence indicating that activation of tyrosine phosphorylation pathways may participate in the responses induced by 1alpha,25(OH)(2)D(3) through its non-genomic mechanism. In this study we have evaluated the involvement of 1alpha,25(OH)(2)D(3) in the tyrosine phosphorylation of PLCgamma and MAPK (ERK1/2) in enterocytes from young (3 months) and aged (24 months) rats. Immunochemical analysis revealed that the hormone stimulates PLCgamma tyrosine phosphorylation in young rat enterocytes. Hormone effect on PLCgamma is rapid, peaking at 2 min (+100%), is dose-dependent (10(-10) to 10(-8)M) and decreases with ageing. 1alpha,25(OH)(2)D(3) also induces the phosphorylation and activation of the mitogen-activated-protein kinases ERK1 and ERK2, effect which was evident at 1 min (three-fold) and reached a maximum at 2 min (six-fold). Hormone-dependent ERK1 and ERK2 phosphorylation and activity is greatly reduced in enterocytes from old rats. In both, young and aged animals, 1alpha,25(OH)(2)D(3)-induced PLCgamma and ERK1/2 phosphorylation was effectively suppressed by the tyrosine kinase inhibitor genistein (100 uM) and suppressed to a great extent by PP1, an inhibitor of c-Src kinases. LY294002, a specific inhibitor of PI3 kinase (PI3K), enzyme with an important role in mitogenesis, did not affect hormone-dependent ERK1/2 phosphorylation, indicating that PI3K is not involved in 1alpha,25(OH)(2)D(3)-induced MAPK activation. In agreement with this data, enzyme activity assays and tyrosine phosphorylation of the regulatory subunit (p85) of PI3K showed that the hormone has no effect on the enzyme activity in rat enterocytes. Taken together, the present study suggest that in intestinal cells, tyrosine phosphorylation is an important mechanism of 1alpha,25(OH)(2)D(3) involved in PLCgamma and MAPK regulation and that this mechanism is impair with ageing.

Ageing, autoimmunity and arthritis: Perturbations of TCR signal transduction pathways with ageing - a biochemical paradigm for the ageing immune system

It is widely accepted that cell-mediated immune functions decline with age, rendering an individual more susceptible to infection and possibly cancer, as well as to age-associated autoimmune diseases. The exact causes of T-cell functional decline are not known. One possible cause could be the development of defects in the transduction of mitogenic signals following TCR stimulation. This T-cell hyporesponsiveness due to defects of signalling through the TCR either from healthy elderly subjects or from individuals with autoimmune diseases such as rheumatoid arthritis or systemic lupus erythematosus results in an impaired ability to mount efficient immune responses and to maintain responsiveness to foreign antigens. This implies that a high proportion of autoreactive T cells might accumulate either intrathymically or in the periphery. T-cell anergy and differential TCR signalling could thus also be key players in the disruption of tolerance and the onset of autoimmune diseases. The increasing number of the elderly may lead to an increase of clinically important autoimmune diseases. We will review the signal transduction changes through the TCR-CD3 complex in T lymphocytes from healthy elderly subjects, which result in a modification of the activation of transcription factors involved in IL-2 gene expression leading to decreased IL-2 production. The putative contribution of altered T-cell signalling with ageing in the development of autoimmune diseases will be also discussed.

Neutrophil immunity of the elderly

Due to age-related changes of the immune system, elderly people are more susceptible to microbial infections than the young. Most research concerning immune senescence has been done on T and B cells, yet the first cells to migrate into microbe-infected tissue are neutrophils, which phagocytose and kill the pathogens. Long regarded as mere phagocytes, the neutrophils' importance for the immune response has been recognized in current publications, which acknowledge them an active participation in the cytokine network. Similarities in the symptoms of patients with genetical neutrophil deficiencies and those of the elderly indicate a leading role of neutrophils in the effects of immune senescence. While the number of circulating neutrophils remains unaltered in the elderly compared with young controls, phagocytosis and intracellular killing have been reported impaired. Oddly enough, the results for various stimuli differed: while some showed a decrease in neutrophil activation, the response to others remained unaltered. More research needs to be done on this, preferably using preparations of high purity to exclude monocytic interventions. Elucidation of immune deficiencies caused by neutrophil senescence can be an important contribution to a healthier elderly population.

Altered signal pathway in angiotensin II-stimulated neutrophils of patients with hypercholesterolaemia

Angiotensin II (AII) in 1-10 nM concentrations has an in vivo immunostimulating effect on human neutrophils. The release of superoxide anions and leukotrienes (LTs) is significantly increased by 10 nM AII-stimulated neutrophils of patients with hypercholesterolaemia (HCH). These oxidizing agents may be involved in the damage of vessel walls, i.e., in atherosclerotic plaque formation. To clarify the receptor types and signal pathways in neutrophils of healthy controls and patients, inositol trisphosphate (IP(3)) production and Ca(2+) signalling were studied. Neutrophils were pretreated before AII stimulation with different inhibitory drugs. In control cells, the stimulation occurred predominantly through pertussis toxin-sensitive, type angiotensin 1 receptors. This induced IP(3) production and Ca(2+) signalling from intracellular pools. In neutrophils of hypercholesterolaemic patients, the enhanced release of oxidizing agents was dependent more on type angiotensin 2 than type angiotensin 1 receptors. After stimulation, there was no IP(3) production detected. The Ca(2+) signalling was lower than in control cells and was dependent on extracellular Ca(2+).

Drug-induced and postnatal hypothyroidism impairs the accumulation of diacylglycerol in liver and liver cell plasma membranes

BACKGROUND

Thyroid hormones are well known modulators of signal transduction. The effect of hyper- and hypo-thyroidism on diacylglycerol/protein kinase C (DAG/PKC) signaling in cardiomiocytes has been determined. Triiodothyronine (T3) has been shown to prevent the alpha1-adrenoreceptor-mediated activation of PKC but does not alter the stimulation of enzyme and hepatic metabolism by phorbol ethers. It has been suggested that the elevation of endogenous DAG in senescent or hypothyroid cells changes the PKC-dependent response of cells to phorbol esters and hormones. In the present study, was examined the formation of DAG and activation of PKC in liver cells from rats of different thyroid status.

RESULTS

The results obtained provide the first demonstration of DAG accumulation in liver and cell plasma membranes at age- and drug-dependent thyroid gland malfunction. The experiments were performed in either the [14C]CH3COOH-labeled rat liver, liver slices or hepatocytes labeled by [14C] oleic acid and [3H]arachidonic acid or [14C]palmitic acid as well as in the isolated liver cell plasma membranes of 90- and 720-day-old rats of different thyroid status. The decrease of T4 and T3 levels in blood serum of 720-day-old rats and mercazolil-treated animals was associated with increases of both the DAG mass in liver and liver cell plasma membranes and newly synthesized [14C]DAG level in liver and isolated hepatocytes. Hypothyroidism decreased PKC activity in both membrane and cytosol as well as phospholipid and triacylglycerol synthesis in liver. These hypothyroidism effects were restored in liver by injection of T4. T4 administration to the intact animals of different ages decreased the DAG level in liver and isolated plasma membranes and the content of newly synthesized DAG in liver. The reduction of DAG level in liver was not associated with increasing free fatty acid level. DAG labeling ratio 14C/3H in liver slices of rats of different thyroid state sharply differed from PL. DAG was relatively enriched in [14C]oleic acid whereas PL were enriched in [3H]arachidonic acid.

CONCLUSIONS

The above data have indicated that thyroid hormones are important physiological modulators of DAG level in rat liver and cell plasma membranes. Age- and drug-induced malfunction of thyroid gland resulted in a prominent decrease of glycerolipid synthesis which may promote DAG accumulation in liver.

Modulation of human lymphocyte proliferative response with aging

Previously, we have demonstrated age-associated alterations in transmembrane signaling. One of the most reproducible alterations found in the immune response with aging is the decrease of lymphocyte proliferation on stimulation with various different mitogens. Here, we confirm that proliferative responses to stimulation with phytohaemagglutin (PHA), recombinant human IL-2, or anti-CD3 monoclonal antibody are all greater in the young (20-25 years) than old (60-87 years) population. We attempted to modulate the proliferative response using various agents acting at different levels of transmembrane signaling (pertussis toxin, cholera toxin, isoproterenol, PMA, Ca ionophore A23187), as well as at the level of the lymphocyte plasma membrane (methyl-beta-cyclodextrin, MBCD), or by using antioxidant vitamins (Vitamin E or C). None of these agents was able to restore effectively the proliferative response of lymphocytes from the aged to the level of young subjects. Even the combination of A23187 and PMA acting directly on calcium metabolism and protein kinase C activity was insufficient to restore the decreased mitogenic capacity of T cells from elderly subjects. Cyclodextrin, which decreases the cholesterol content of the membrane, increased the proliferative response of lymphocytes of elderly subjects, but not to the level of the young. Vitamin E had a very strong inhibitory effect on lymphocyte stimulation in both the age groups, except in combination with MBCD in T cells of the elderly, while Vitamin C had no significant modulatory effect. MAPK ERK and p38 activation was found to be decreased with aging in T cells after anti-CD3 mAb stimulation. Vitamin E but not Vitamin C strongly inhibited MAPK ERK or p38 activation. The direct activation of certain molecules or the modulation of the cholesterol content of the membrane seems to be effective immunomodulatory interventions with aging.

Neuropeptide Y effects on murine natural killer activity: changes with ageing and cAMP involvement

Changes in the bidirectional interaction between the nervous and the immune systems have been proposed as a cause of ageing. Neuropeptides, such as neuropeptide Y (NPY), could show different effects on immune function with age. In the present work, we have studied the in vitro action of a wide range of NPY concentrations, i.e. from 10(-13) to 10(-7) M, on natural killer (NK) activity, a function which decreases with age. Spleen, axillary nodes, thymus and peritoneum leukocytes from mice of different ages: young (12+/-2 weeks), adult (24+/-2 weeks), mature (50+/-2 weeks) and old (72+/-2 weeks) were used. Stimulation by NPY of NK activity was observed in adult and mature animals in axillary nodes and thymus, and an inhibition in the spleen from young mice. The specificity of the NPY effect on cytotoxic activity was confirmed using a C-terminal fragment of NPY. Furthermore, cAMP levels in leukocytes were found to be decreased by NPY in adult mice, suggesting an involvement of this messenger system in the NK modulation by this neuropeptide.

Cyclodextrin modulation of T lymphocyte signal transduction with aging

There is an alteration of the immune response in aging that leads to the increased incidence of infections, cancers and autoimmune disorders. The aim of the present study was to investigate whether there exists changes in signal transduction under the IL-2 receptor stimulation and the role of plasma membrane cholesterol in the activation of T cells with aging. We report age-related changes in the JAK-STAT signalling pathway that results in decreased tyrosine phosphorylation of STAT5. We present evidence for the importance of cholesterol content in regulating signalling pathways in T cells and in modulating their proliferation by using the plasma membrane cholesterol-depleting agent methyl-beta-cyclodexrin (MBCD). MBCD treatment (0.5 mM) induced a significant decrease in the cholesterol content of T cells of elderly subjects whereas it was increased in T cells of young subjects. MBCD induced changes in the phosphorylation of p56(lck), especially in T cells of elderly subjects. The proliferation of MBCD-treated T cells decreased in lymphocytes of young subjects but did not change in T cells of elderly subjects. These results suggest a role for plasma membrane cholesterol in the regulation of the TcR signalling pathways with differential effects related to aging. However, the data suggest that modulation of the plasma membrane cholesterol content alone may not be enough to restore signal transduction changes with aging.

Age-related changes in membrane lipid composition, fluidity and respiratory burst in rat peritoneal neutrophils

The O2*(-) production has been studied in rat peritoneal neutrophils of different age (3, 12 and 24 months), in order to analyse whether the neutrophil respiratory burst is modified with increasing age. To stimulate NADPH oxidase, the enzyme responsible for the respiratory burst, two stimuli that act in different way have been used: phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (N-FMLP). Production of O2*(-) decreased with age in neutrophils stimulated with N-FMLP (about 40%), but not in the stimulated with PMA. No difference in NADPH oxidase activity was found with age. The NADPH is supplied to the respiratory burst mainly by the pentose phosphate shunt. A progressive and significant decrease in the two most important enzymes of this route, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, was detected as a function of age; in spite of this reduction, the NADPH produced by cells from old animals seems not limiting for the O2*(-) production. The N-FMLP-induced decrease in the O2*(-) production may be related to the age-dependent increase in the membrane fluidity observed. A decline in the cholesterol/phospholipid ratio and a rise in the total polyunsaturated fatty acids content were found, that correlated well with the increase in the membrane fluidity. The decrease (50%) of phosphatidylinositols in the 24-month-old animals may be also related to the age-impairment in the respiratory burst found after stimulation with N-FMLP. These studies suggest that the age-related alterations in neutrophil may result in diminished neutrophil function and increased susceptibility to infection in the ageing.

Age-related alterations in the signal transduction pathways of the elastin-laminin receptor

With aging we assist to alterations in the vascular structure and function. One important factor in these vascular wall changes is the degradation of the elastin fibre major protein: elastin. Elastin peptides derived from the degradation are present in human sera. Elastin peptides induce on fibroblasts, phagocytic cells, lymphocytes, smooth muscle cells and endothelial cells, a variety of biological effects mediated by the elastin-laminin receptor which has been demonstrated to be present on the membrane of these cells. The transduction pathway of the ELR receptor involves the activation of phospholipase C (PLC) by a pertussis toxin sensitive G-protein. PLC induces the production of inositol trisphosphate (IP3) leading to the increase of the intracellular free calcium on one hand, and of diacylglycerol (DAG) which stimulates the translocation to the membrane of PKC leading to the phosphorylation of members of the MAPK family, such as p42/p44 MAPK. A progressive age dependent uncoupling of the elastin-laminin receptor occurs impairing its transduction pathway and which results in alteration of the calcium signaling and loss in calcium homeostasis of the cells. These alterations in the signal transduction of the elastin-laminin receptor result in modified activities of parenchymal and phagocytic cells with aging, such as free radical production and elastase release. Thus, these age-related alterations in the elastin-laminin receptor signal transduction may be involved in the atherogenesis.

Aging and resistance to Trichinella spiralis infection following xenobiotic exposure

Aging is accompanied by well-documented physiological changes, including alterations in the immune system that can lead to reduced resistance to a variety of infectious agents. We tested the hypothesis that immunosenescence exacerbates the immunosuppressive effect of xenobiotics. If proven true, a given dose of an immunosuppressive xenobiotic would cause greater suppression of host resistance in an aged population.

Review article: ageing and the neutrophil: no appetite for killing?

In the armoury of the immune system developed to combat the various micro-organisms that could invade the host, the neutrophil forms the first line of defence against rapidly dividing bacteria and fungi. However, as humans age they become more susceptible to infection with these microbes and this has been ascribed to a decline in immune status, termed immune senescence. Here we summarize the literature specifically concerning the attenuation of neutrophil function with age and the possible mechanisms underlying their reduced response to infectious agents.

Biogerontological research in Canada

There is an ever increasing interest in the study of the aging process. This review is aimed to make an overview of the biological aging research in Canada. I will summarize, to the best of my knowledge, the biological aging research undertaken actually in Canadian institutions dealing with various aspects of this research using many different experimental approaches, models from animals to humans and a huge array of techniques. The biological aging research is developing continuously in Canada, however, it is very important that we assist in a near future to its huge explosion if we would respond to the needs of an ever increasing aging population. Initiatives recently proposed by the Canadian government concerning the creation of Canadian Institutes on Health Research will provide good opportunities to establish a performant, cost-effective, and innovative biological aging research.

A Defective Protein Kinase C Anchoring System Underlying Age-Associated Impairment in TNF-α Production in Rat Macrophages

The ability of macrophages to secrete cytokines is important in host responses to infections inflammatory stimuli, both of which are altered with aging. In this study, age-associated changes in the release of TNF-α from LPS-stimulated rat alveolar macrophages were determined and correlated with a decrease in the level of RACK1, the anchoring protein involved in protein kinase C translocation and activation. Macrophages from aged rats produced ∼50% less TNF-α than those from young rats. This effect was observed independently from the concentration of LPS used and the time considered. The decrease observed was associated with a defective PKC translocation, due to a reduction in the expression of RACK1, whereas no differences were detected in the expression of LPS receptor (CD14) or total PKC isoforms (α and βΙΙ) in old and young rats. Use of RACK1 antisense oligonucleotide reduced the ability of young macrophages to respond to LPS, further supporting the idea that a deficit in RACK1 contributes to the functional impairment in aged macrophages and that age-induced macrophage immunodeficiencies are associated with alteration in signal transduction pathways.

Effects of aging on resistance to Trichinella spiralis infection in rodents exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Immune function, including resistance to infection, decreases as humans and rodents age. We have shown that preinfection exposure of young (9-11 weeks) mice or rats to TCDD decreased resistance to Trichinella spiralis (Ts) infection, expressed as delayed onset or completion of parasite elimination and as increased muscle burdens of larvae. It has also been shown that aged mice express lower constitutive levels of resistance to Ts infection, compared to young adult animals. This study tested the hypothesis that the age-related decrease in constitutive levels of resistance to Ts infection exacerbates the decreased resistance to infection that follows TCDD exposure. This hypothesis addresses the concern that TCDD may pose a greater threat to the elderly than to the population at large. Animals were given a single oral dose of 1, 10, or 30 microg TCDD/kg, 7 days before infection. Eleven days later, young (approximately 10 weeks) control rodents had eliminated a greater proportion of the original parasite burden from the intestine than aged control animals. Nevertheless, parasite elimination was decreased by TCDD exposure only in young rodents. The effect of TCDD exposure on numbers of encysted larvae was evaluated only in rats. Increased larvae burdens occurred in young rats at 30 microg TCDD/kg and at 10 or 30 microg TCDD/kg in aged rats. Parasite-specific splenocyte and lymph node cell proliferation was suppressed following dioxin exposure in young mice; cells from aged mice were markedly less responsive to stimulation, yet less sensitive to TCDD exposure. The response to parasite antigens was not affected in aged rats exposed to TCDD, although elevated mitogen-driven B-cell proliferation was observed. These results indicate that age-related constitutive immunosuppression did not exacerbate TCDD-induced suppression of T-cell mediated adult parasite expulsion; rather, advanced age provided some degree of protection. On the other hand, a lower dose of TCDD was required in aged rats to suppress the combined humoral and cellular responses that limit the burden of encysted larvae, compared to young rats. These model-dependent results preclude acceptance or rejection of the tested hypothesis.

Effect of 50- and 100-mg vitamin E supplements on cellular immune function in noninstitutionalized elderly persons

BACKGROUND

It has been suggested that vitamin E can counteract the age-associated decline in cellular immune responsiveness (CIR). Particularly, T helper cell type 1 (Th1) activity, ie, interferon (IFN) gamma-producing Th1 activity and, hence, delayed-type hypersensitivity (DTH) would be enhanced by vitamin E supplementation.

OBJECTIVE

Our aim was to study the effects of 6 mo supplementation with 50 and 100 mg vitamin E on CIR in the elderly.

DESIGN

A double-blind, placebo-controlled trial was conducted in 161 healthy elderly subjects aged 65-80 y. CIR was measured in vivo by means of DTH skin tests and in vitro by assessing the production of interleukin (IL) 2, IFN-gamma (a typical Th1 cytokine), and IL-4 (a typical Th2 cytokine) by peripheral blood mononuclear cells after stimulation with phytohemagglutinin.

RESULTS

Both DTH and IL-2 production showed a trend toward increased responsiveness with increasing dose of vitamin E. However, IFN-gamma production decreased whereas IL-4 production increased in the groups receiving vitamin E. Only the change in the number of positive DTH reactions was borderline significantly larger in the 100-mg vitamin E group than in the placebo group (P = 0.06, Bonferroni adjusted). Subjects receiving 100 mg vitamin E with low baseline DTH reactivity or who were physically less active had a significantly larger increase in the cumulative diameter of the skin induration resulting from the DTH test than did the placebo group (P = 0.03), although this difference was not significant after Bonferroni correction (P = 0.07).

CONCLUSION

Possible beneficial effects of 100-mg vitamin E supplementation may be more pronounced in particular subgroups of elderly subjects.

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.

Age-related impairment of p56lck and ZAP-70 activities in human T lymphocytes activated through the TcR/CD3 complex

Cellular immune responses decrease with aging. Lymphocytes of aged individuals do not perform as well as cells from young subjects in a number of in vitro assays including cell proliferation, cytokine production, and protection against apoptosis. Here, we have tested the hypothesis that a decrease in T cell responses in tymphocytes from elderly subjects could parallel a decrease in the activity of protein tyrosine kinases (PTK) associated with signal transduction in T lymphocytes. We report that anti-CD3-triggered T lymphocyte proliferation was significantly decreased in T lymphocytes from elderly subjects, but the decrease was not due to an alteration of the percentage or mean fluorescence intensities of CD3, CD4, and CD45. Of significance, the activities of p56lck and ZAP-70 in vitro were significantly decreased in T lymphocytes from elderly subjects compared to young individuals. However, the level of expression of the two kinases did not change with aging. The activity of p59fyn did not show changes with aging, suggesting that p59fyn did not compensate for the decreased activity of p56lck. We also found that the extent of tyrosine phosphorylation of the adaptor protein p95vav was similar in activated T lymphocytes from elderly and young subjects. Our results suggest that the altered cellular immune responses observed in T lymphocytes with aging may be the result, at least in part, of an alteration in early events associated with signal transduction through the TcR/CD3 complex that translates into decreased activities of p56lck and ZAP-70. Impairment in the activities of these twokey components of T cell signaling may contribute to reduced immune functions associated with aging.

Effect of age on mitogen induced protein tyrosine phosphorylation in human T cell and its subsets: down-regulation of tyrosine phosphorylation of ZAP-70

Several events of T cell activation have been reported to decline in humans with age. Since protein tyrosine phosphorylation is an early critical event of T cell activation, we performed a systematic analysis of the age-associated changes in the mitogen induced protein tyrosine phosphorylation of human T lymphocytes using SDS-PAGE and Western blotting techniques. Following stimulation with Con A and PHA, an identical pattern of protein tyrosine phosphorylation was observed in the lysates of T cells prepared from seven healthy young adults and eight healthy elderly human subjects. Five different high molecular mass proteins (75, 115, 120, 140 and 170 kDa) were consistently tyrosine phosphorylated in all of the donors from both age groups and peaked between 3 and 10 min. Tyrosine phosphorylation of the above substrates was observed in both CD4 and CD8 subsets. When compared for individual donors from both age groups, variations in the T cell response with regard to net tyrosine phosphorylation for all the substrates was observed. However, the mitogen induced level of tyrosine phosphorylation of only p75 was found to be significantly lower in unfractionated T cells as well as CD4 and CD8 subsets of older subjects than that of young subjects. Using immunoblotting, p75 was identified as ZAP-70, a member of the syk family of protein tyrosine kinases. Understanding of the biochemical basis of the reduced level of tyrosine phosphorylation of ZAP-70 will be helpful in delineating the molecular basis of age-associated impairment of T cell activation.

Signal transduction in LPS-activated aged and young monocytes

Aged monocytes, that is, monocytes purified from the blood of donors > or =65 years of age, when compared with young monocytes, that is, monocytes purified from the blood of young donors 25 years of age, display a decrease in interleukin-6 (IL-6) and tumor necrosis factor (TNF) production after activation by lipopolysaccharide (LPS). The LPS concentration required to obtain IL-6 and TNF production is much higher for aged monocytes than for young monocytes. Furthermore, the intensity of TNF and IL-6 production was much weaker for LPS-activated aged monocytes than for LPS-activated young monocytes. In addition, deficient protein kinase C (PKC)-alpha, PKC-/betaI, and PKC-betaII activation, deficient mitogen-activated protein kinase (MAP-Kinase) activation, and deficient expression of c-Fos and c-Jun was observed in LPS-activated aged monocytes when compared with LPS-activated young monocytes. These data suggest that age induces human monocyte immune deficiencies that could be observed not only at the functional level but also in the signal transduction pathways.

Changes in the amount and level of phosphorylation of p56(lck) in PBL from aging humans

The effects of aging on the activation of the cytoplasmic tyrosine protein kinase p56(lck) have been investigated in PBL from adult and elderly subjects upon activation with mitogens or different co-stimuli. Results show that the amount and phosphorylation of p56(lck) are reduced in PBL from elderly as compared to adult subjects. This finding suggests that alterations in p56(lck) may contribute to the age-associated loss of some T cell functions, such as proliferation and IL-2 production, which are found decreased in PBL from old individuals. However, p56(lck) seems irrelevant to the production of IFN-gamma and IL-4 which were both found increased in the PBL from old subjects, as expected from the relative expansion of memory versus naive T cell subpopulations in aging.

Genes, immunity, and senescence: looking for a link

Aging is under the control of a small number of regulatory genes. Mice genetically selected for high immune responses, in most cases, exhibit longer life span and lower lymphoma incidence than do mice selected for low responses. The link between immunity and aging is further evidenced by the age-related alterations of the immune system, mostly of the T-cell population, in terms of replacement of virgin by memory cells, accumulation of cells with signal transduction defects, and changes in the profile of Th1 and Th2 type cytokines. Also, B cells exhibit intrinsic defects, and natural killer (NK) cell activity is profoundly depressed by aging. In vitro experiments indicate that IL-2, IFN-gamma, and IL-4 production by mouse spleen cells changes with aging and may be upregulated by recombinant cytokines. These findings suggest possible cytokine interventions to prevent or treat age-related immune disorders, as they may affect the duration and the biological quality of life.

Changes in apoptosis of human polymorphonuclear granulocytes with aging

Many alterations with aging occur at the cellular and organic levels in the immune system ultimately leading to a decrease in the immune response. Our aim in the present work was to study apoptosis of polymorphonuclear granulocytes (PMN) with aging under various stimulations since apoptosis might play an important role in several pathologies encountered with aging. The PMN of healthy young (20-25 years) and elderly (65-85 years) subjects were examined after 24 h of sterile culture with and without stimulation. The stimulating agents included: phorbol myristate acetate (PMA), hydrogen peroxide (H2O2), N-formyl-methionyl-leucyl phenylalanine (FMLP), granulocyte-macrophage colony stimulating factor (GM-CSF), reduced glutathione (GSH), lipopolysaccharide (LPS) and interleukin 2 (IL-2). Apoptosis was assessed by traditional staining of the plates, by flow cytometric staining and DNA gel electrophoresis. It was found that without stimulation the susceptibility of PMN to apoptosis was slightly increased with aging. Under various stimulations, such as PMA. H2O2, apoptosis was almost 100%, while the treatment by FMLP, oxLDL and GSH did not change its extent in PMN obtained either from young or elderly subjects. Marked age-related changes were observed in the extent of apoptosis under stimulation with GM-CSF, IL-2 and LPS. These agents were able to significantly prevent apoptosis in PMN of young subjects, while only the GM-CSF was able to slightly modulate it in neutrophils of elderly subjects. From these results, we suggest that changes in apoptosis of PMN with aging could play a role in the increased incidence of certain immune system related pathologies of aging, such as cancer, infections and autoimmune disorders.

The dynamic interplay of malignant and benign T cells in cutaneous T-cell lymphoma

Cutaneous T-cell lymphoma is a malignancy of functional, tissue-specific T cells. Many characteristics of the disease can be explained by virtue of the ability of the malignant cell population to actively participate in the host's immunologic network. Various aspects of this dynamic interplay between malignant and benign T cells are discussed, including impact on diagnosis, staging, and therapy.

Age-dependent changes in the expression of dopamine receptor subtypes in human peripheral blood lymphocytes

The pharmacological profile and the density of dopamine D3 and D5 receptor subtypes expressed by human peripheral blood lymphocytes of subjects of different ages (ranging from 20 to 75 years) were assessed using radioligand binding techniques. Dopamine D3 receptor was assayed with [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) as a ligand. Dopamine D5 receptor was assayed using [3HIR]-(+)-(-chloro-2,3,4,5, tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate) ([3H]SCH 23390) as a ligand. The affinity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 23390 at dopamine D3 and D5 receptor, respectively, were similar in subjects of different ages. The density of dopamine D3 receptor binding sites was slightly decreased in subjects of 30-39 years in comparison with younger individuals. A remarkable loss of dopamine D3 receptor was then found between 40 and 49 years of age in comparison with younger subjects. A further slight decrease was noticeable between 50 and 59 years of age. The number of [3H]7-OH-DPAT binding sites was then stabilized after 60 years of age. The density of dopamine D5 receptor binding sites did not show age-dependent changes. The above findings indicate the occurrence of a decline in the density of lymphocyte dopamine D3 but not D5 receptor between adult and mature subjects. The possibility that dopamine D3 receptor assay in peripheral blood lymphocytes may represent a tool for investigating dopamine receptor function in aging and age-related neurological disorders is discussed.

Glutamine metabolism is changed in lymphocytes from aged rats

Changes in the protein content, maximal activity, and Km of phosphate-dependent glutaminase were measured in the lymphoid organs (thymus, spleen, and mesenteric lymph nodes) from just-weaned, mature (3 months), and aged rats (15 months). Also, [U-14C] glutamine transport and decarboxylation and the production of glutamate and aspartate from 2 and 20 mM glutamine were measured in incubated mesenteric lymph node lymphocytes. The ageing process induced a reduction in the protein content of the thymus and spleen, as well as the phosphate-dependent glutaminase activity in the thymus and isolated lymphocytes. The Km of phosphate-dependent glutaminase, however, was not affected by the process. Ageing reduced [U-14C] glutamine decarboxylation and increased glutamate and aspartate production in incubated lymphocytes. The results indicate that the ageing process does modify several aspects of glutamine metabolism in lymphocytes: reduces maximal glutaminase activity and [U-14C] glutamine decarboxylation and increases the Km for [U-14C] glutamine uptake and the production of glutamate and aspartate.

Neutrophil function in elderly persons assessed by flow cytometry

It is well known that the immune response declines with senescence and it is suggested that these changes render an individual susceptible to infection, autoimmune phenomena and cancer. Bacterial and viral infections are a major cause of illness and death amongst aged subjects, and once infection is established, the elderly also have a diminished capacity to prevent its spread (1). The cellular and molecular basis for this age-related decline in immunocompetence are still unknown and, possibly, are related to an alteration in cell transduction mechanisms (2).

Cellular distribution of protein kinase C isozymes in CD3-mediated stimulation of human T lymphocytes with aging

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL-2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we show that anti-CD3-triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti-CD3-induced T cell proliferation in a differential manner, lymphocytes of healthy young subjects being more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti-CD3 mAb stimulation using antibodies directed against PKC alpha, beta, delta, epsilon and zeta isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC-zeta. In resting lymphocytes of elderly subjects PKC-zeta and -epsilon were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC-alpha and -zeta were mainly found in the membrane fraction and PKC-beta was almost exclusively located in the cytosolic fraction. The translocation of PKC-alpha, -beta, -delta and -epsilon could be observed under anti-CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC beta isoform was translocated. Our results suggest tha the decreased availability of cytosolic PKC may contribute to the diminished PKC-dependent responses to CD3-triggered stimulation of human T lymphocytes with aging.