Superoxide generation by alveolar macrophages from aged rats: improvement by in vitro treatment with IFN-gamma

Redox mechanisms in age-related lung fibrosis

Redox signaling and oxidative stress are associated with tissue fibrosis and aging. Aging is recognized as a major risk factor for fibrotic diseases involving multiple organ systems, including that of the lung. A number of oxidant generating enzymes are upregulated while antioxidant defenses are deficient with aging and cellular senescence, leading to redox imbalance and oxidative stress. However, the precise mechanisms by which redox signaling and oxidative stress contribute to the pathogenesis of lung fibrosis are not well understood. Tissue repair is a highly regulated process that involves the interactions of several cell types, including epithelial cells, fibroblasts and inflammatory cells. Fibrosis may develop when these interactions are dysregulated with the acquisition of pro-fibrotic cellular phenotypes. In this review, we explore the roles of redox mechanisms that promote and perpetuate fibrosis in the context of cellular senescence and aging.

Cell Therapy Strategies to Combat Immunosenescence

Declining function of the immune system, termed "immunosenescence," leads to a higher incidence of infection, cancer, and autoimmune disease related mortalities in the elderly population. (1) Increasing interest in the field of immunosenescence is well-timed, as 20% of the United States population is expected to surpass the age of 65 by the year 2030. (2) Our current understanding of immunosenescence involves a shift in function of both adaptive and innate immune cells, leading to a reduced capacity to recognize new antigens and widespread chronic inflammation. The present review focuses on changes that occur in haematopoietic stem cells, macrophages, and T-cells using knowledge gained from both rodent and human studies. The review will discuss emerging strategies to combat immunosenescence, focusing on cellular and genetic therapies, including bone marrow transplantation and genetic reprogramming. A better understanding of the mechanisms and implications of immunosenescence will be necessary to combat age-related mortalities in the future.

IL-2/CD40-activated macrophages rescue age and tumor-induced T cell dysfunction in elderly mice

The role of macrophages and their interactions with T cells during aging is not well understood. We determined if activating elderly-derived macrophages could rescue age-related and tumor-induced T cell dysfunction. Healthy elderly (18-24 months) Balb/c contained significantly more splenic IL-10-secreting M2-macrophages and myeloid-derived suppressor cells than young (6-8 weeks) mice. Exposure to syngeneic mesothelioma or lung carcinoma-conditioned media polarized peritoneal macrophages into suppressive M2-macrophages regardless of age. Tumor-exposed, elderly, but not young-derived, macrophages produced high levels of IL-4 and could not induce T cell IFN-γ production. We attempted to rescue tumor-exposed macrophages with LPS/IFN-γ (M1 stimulus) or IL-2/agonist anti-CD40 antibody. Tumor-exposed, M1-stimulated macrophages retained high CD40 expression, yet TNF-α and IFN-γ production were diminished relative to non-tumor-exposed, M1-stimulated controls. These macrophages induced young and elderly-derived T cell proliferation however, T cells did not secrete IFN-γ. In contrast, tumor-exposed, IL-2/CD40-stimulated macrophages rescued elderly-derived T cell IFN-γ production, suggesting that IL-2/CD40-activated macrophages could rescue T cell immunity in aging hosts.

Dahi containing Lactobacillus acidophilus and Bifidobacterium bifidum improves phagocytic potential of macrophages in aged mice

The present study investigated the effect of Dahi containing potential probiotic bacterial strains on macrophage functions in ageing mice. Probiotic Dahi was prepared by co-culturing Dahi bacteria (Lactococcus lactis ssp. cremoris and Lactococcus lactis ssp. lactis biovar diacetylactis) along with Lactobacillus acidophilus LaVK2 (La-Dahi) or combined L. acidophilus LaVK2 and Bifidobacterium bifidum BbVK3 (LaBb-Dahi) in buffalo milk. The effect of ageing on phagocytic function was evaluated on 4 mo, 12 mo and 16 mo old mice. The effect of probiotic Dahi was evaluated for macrophage functions in ageing mice (12 mo old) fed La-Dahi or LaBb-Dahi supplements for 4 months. The production of extracellular superoxide and H2O2 declined in peritoneal macrophages but enhanced in splenic macrophages, while intracellular superoxide declined in both peritoneal and splenic macrophages with ageing in mice. A decline in phagocytic activity of peritoneal macrophages was also observed in aged mice. Supplementation of diet with La-Dahi or LaBb-Dahi for 4 months improved production of reactive oxygen species and phagocytic and adherence indices of peritoneal macrophages in aged mice. These results suggest that oral administration of La-Dahi or LaBb-Dahi has potential to improve immune functions in ageing individuals.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

Age effects on macrophage function vary by tissue site, nature of stimulant, and exercise behavior

We explored the effects of aging on macrophage function in male BALB/c mice from three age groups: young (2 months), middle-aged (12 months), and old (21 months). Macrophages were collected from alveoli, peritonea, and spleens of each age group. Cells were cultured in vitro with LPS or LPS+IFN-gamma and assayed for production of IL-1, IL-12, NO, and TNF-alpha. Using herpes simplex virus-1, age-related changes in intrinsic antiviral resistance (plaque assay) and extrinsic antiviral resistance (NO and TNF-alpha production) were determined in alveolar and/or peritoneal macrophages. Effects of chronic exercise on age-related macrophage changes were examined. In vitro, macrophages from the alveoli and spleen of older mice generally produced more cytokine and NO compared to younger counterparts. Conversely, macrophages from the peritonea of older mice generally produced less cytokine and NO in vitro compared to younger counterparts. Alveolar macrophages from both old and young mice showed higher intrinsic antiviral resistance to HSV-1 compared to middle-aged mice, while peritoneal macrophages from young mice showed reduced intrinsic resistance compared to those from both middle-aged and old mice. When challenged with HSV-1, a trend towards decreased peritoneal macrophage production of TNF-alpha and decreased alveolar macrophage production of IL-12 with advancing age was found. Chronic moderate exercise tended to reverse age-associated changes in macrophage function in old mice.

Aging and innate immune cells

The innate immune system serves an important role in preventing microbial invasion. However, it experiences significant changes with advancing age. Among the age-associated changes are: Aged macrophages and neutrophils have impaired respiratory burst and reactive nitrogen intermediates as a result of altered intracellular signaling, rendering them less able to destroy bacteria. Aged neutrophils are also less able to respond to rescue from apoptosis. Aged dendritic cells (DC) are less able to stimulate T and B cells. The altered T cell stimulation is a result of changes in human leukocyte antigen expression and cytokine production, and lower B cell stimulation is a result of changes in DC immune complex binding. Natural killer (NK) cells from the elderly are less capable of destroying tumor cells. NK T cells increase in number and have greater interleukin-4 production with age. Levels of various complement components are also altered with advancing age.

Evaluation of phagocytosis and arachidonate metabolism by alveolar macrophages and recruited neutrophils from F344xBN rats of different ages

The incidence of infectious respiratory diseases increases with aging. Resident alveolar macrophages (AMs) and recruited leukocytes (PMNL) mediate cellular defense against bacterial infections in the lung, and phagocytosis and lipid mediator synthesis are important components of their antimicrobial capacity. The objective of this study was to determine if either phagocytic capacity or lipid mediator generation declines with normal aging, in either AMs or PMNL recruited to a site of inflammation. The F344xBN rat hybrid has a lower incidence of pathologies associated with aging, particularly up to 20 months; animals aged 6,12 and 18 months were chosen to evaluate changes associated with normal aging. As previously reported for peripheral blood leukocytes, phagocytosis by recruited PMNL declined with aging: recruited PMNL from 18 months rats showed a significantly decreased capacity to phagocytose live Klebsiella pneumoniae bacteria, compared to PMNL from 6 months rats. Surprisingly, however, the phagocytic capacity of AMs increased with aging: the phagocytic index of AMs from 18 months rats was more than three times that of AMs from 6 months rats. The capacity of AMs and recruited PMNL to release arachidonic acid or synthesize leukotrienes or prostaglandins did not change with aging. This study demonstrates that, although phagocytosis by recruited PMNL declines with aging, other aspects of immune function do not decline, and may actually increase, with normal aging. These results suggest that impaired phagocytosis by recruited PMNL may be an important component of the increased susceptibility to infectious respiratory diseases during normal aging.

Age-related alterations in inflammatory response during experimental autoimmune prostatitis

Experimental autoimmune prostatitis (EAP) is an experimental model of autoimmune disease, developed in Wistar rats against prostatic components. The 12-and 18-month-old rats with EAP show a higher cellular autoimmune response and lower humoral autoimmune response compared to 3-month-old rats. The analysis of NO(.) and O(2)(-) production by peritoneal exudate cells (PECs) resulted in a higher NO(.) and O(2)(-) production in EAP rats at all ages, compared to control animals. PECs from 12- and 18-month-old rats produced more NO(.) and less O(2)(-) than PECs from 3-month-old rats. However, lipopolysacharide (LPS) did not stimulate PECs from aged rats for NO(.) production as much as in 3-month-old rats and thus, turning out in a lower index of LPS-stimulation of PECs from aged rats, compared to 3-month-old rats. Furthermore, the mast cells number in prostates of EAP rats, especially the number of degranulated cells, was higher than in control animals, but no significant differences were found between 3- and 12-month-old control rats. In conclusion, these results show that aging affects differentially the inflammation mediators during EAP.

Clinical relevance of age-related immune dysfunction

Immunosenescence is the state of dysregulated immune function that contributes to the increased susceptibility to infection of the elderly. Extensive studies of inbred laboratory animals and very healthy elderly humans have identified changes in immunity; these studies have identified limited phenotypic and functional changes in the T cell component of adaptive immunity. However, no compelling scientific evidence has shown that these changes have direct relevance to the common infections seen in the aged population. This perspective will attempt to shed light on this dilemma. First, it will review clinically relevant infections in the elderly, focusing on influenza and influenza virus vaccination and how chronic illness contributes to increased risk and severity of infection and/or failed vaccine response. Second, key changes in immunity will be reviewed, keeping a perspective of the impact of confounding variables in addition to age but focusing on age-related changes in the interaction of the innate and acquired components of immunity. If the goal is to prevent serious infections in the elderly, it appears that the field of geriatric immunology and/or infectious diseases is faced with the tremendous challenge of studying a very diverse population, including mildly immunocompromised/chronically ill individuals and very healthy elderly.

Decreased Expression of Th2 Type Cytokine mRNA Contributes to the Lack of Allergic Bronchial Inflammation in Aged Rats

Sensitized Brown Norway rats are known to develop eosinophilic bronchial inflammation and airway hyperresponsiveness after Ag exposure. However, we have previously observed that sensitized aged rats of the same strain failed to develop such allergic inflammation. In the present study, we investigated age-associated changes of cytokine mRNA expression in bronchoalveolar lavage (BAL) cells. Both young (8- to 10-wk-old) and aged (100- to 120-wk-old) Brown Norway rats were sensitized with OVA, and BAL was performed 24 h after OVA inhalation challenge. Semiquantitative RT-PCR analysis of BAL cells showed that the cells from aged rats preferentially expressed Th1 type cytokine (IFN-γ) mRNA, whereas cells from young animals expressed more Th2 type cytokine mRNAs including those for IL-4 and IL-5. Decreased expression of Th2 type cytokine transcripts in aged animals was further confirmed by quantitative analysis, competitive RT-PCR of BAL cells, and in situ hybridization. The age-associated changes of cytokine profile were not restricted to BAL cells but were a general feature of lymphocytes, as shown by examination of popliteal lymph nodes draining the site of sensitization. These findings suggest that decreased allergic inflammation in aged animals is attributable to age-dependent impairment of Th2 generation in response to Ag.

Detection of active oxygen species in biological systems

1. Cypridina luciferin analogues, 2-methyl-6-(p-methoxyphenyl)-3,7- dihydroimidazo[1,2-a]pyrazin-3-one (MCLD) and 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one(CLA ), react with O2- or 1O2 to emit light in visible region. Such chemiluminescences were used for the detection of O2- or 1O2 in activated leukocyte systems and myeloperoxidase (granulocyte-extract) + Br- + H2O2 systems in vitro. 2. The mechanisms of MCLA (CLA)-dependent luminescence is described in detail. Superoxide generated from sinusoidal cells in acute ethanol intoxication of rats was detected by MCLA-dependent luminescence from the surface of perfused rat liver (organ luminescence). 3. Furthermore, with alive animals, O2- generated in the lung of rats with necrotized pancreatitis and that in the stomach of rats after ischemia/reperfusion were detected by their organ luminescences.

Effect of age and dietary restriction on expression of heat shock protein 70 in rat alveolar macrophages

Dietary restriction (DR) is the only effective experimental manipulation known to retard aging in rodents, and this manipulation has been shown to alter a variety of processes that change with age. However, there is no information on the effect of DR on macrophage Function. In the present study, the effect of aging and DR on the ability of alveolar macrophages (AMs) to express the heat shock gene, hsp70 was studied. AMs were isolated by lavage from the lungs of young (4-6 months) and old (24-26 months) rats fed either ad libitum (AL) or a restricted diet (60% of AL). There was no age-related change in the number of cells recovered from young and old rats fed AL. However, the number of cells recovered from the lungs of the DR rats was reduced, and this decrease was statistically significant in young rats. The expression of heat shock protein 70 (hsp70) was measured by the level of the hsp70 mRNA transcript in total RNA isolated from AMs cultured under two conditions: in suspension and after adherence to plastic. When AMs were incubated at 37 degrees C in suspension, no detectable hsp70 expression was observed; however, hsp70 expression was induced at 37 degrees C when the AMs adhered to the plastic culture dishes. Hsp70 mRNA levels were rapidly induced by heat shock (43 degrees C, 1 h) in AMs cultured both in suspension and on plastic. The induction of hsp70 expression did not change significantly with either age or DR in AMs cultured in suspension. In contrast, the induction of hsp70 mRNA levels by AMs adherent to plastic culture plates decreased approximately 70% with age, and hsp70 induction was greater in AMs isolated from DR rats; this difference was statistically significant in young rats. The induction of hsp70 by heat shock (43 degrees C, 1 h) also decreased with age in the adherent AMs, and DR increased the induction of hsp70 expression three- to fourfold in adherent AMs from both young and old rats.

Macrophage infiltration at the neuromuscular junction does not contribute to AChR loss and age-related resistance to EAMG

Aged rats resistant to acetylcholine receptor loss in passive transfer experimental autoimmune myasthenia gravis (EAMG) do not reveal infiltrating macrophages at the neuromuscular junction (NMJ) as observed in susceptible rats. It was investigated whether this age-related resistance is due to impaired macrophage function in these aged rats. Reconstitution of aged rats with bone marrow from young donors did not lead to macrophage infiltration, nor did it abolish resistance to EAMG. Subsequently, it was investigated whether macrophages are a primary cause of acetylcholine receptor (AChR) loss in EAMG or are attracted to the NMJ secondary to tissue damage. In lethally irradiated young susceptible rats infiltrating macrophages were absent from the NMJ. However, similar AChR losses were observed in irradiated and non-irradiated rats. These results suggest that macrophages do not contribute to acetylcholine receptor loss in the effector phase of passive transfer EAMG and that age related resistance to passive transfer EAMG is not primarily determined by the absence of infiltrating macrophages.

Immune responses during recovery from protein-energy malnutrition

Protein-energy malnutrition (PEM) is a worldwide problem. Infants and children from developing countries and elderly people from all around the world are the two main groups suffering from PEM. PEM induces profound immunodeficiency, characterized mainly by decreased cell-mediated immunity, and also by decreased humoral and non-specific immunity. Non-specific immune deficiency is of particular importance for defences against infections and its decrease in PEM may further deteriorate nutritional and immune status, pushing patients into a vicious and dramatic circle. Refeeding such patients and the restoration of their nutritional status lead to improvement in all immune responses: a strong association between the evolution of these two responses is always observed during refeeding. The need for specific nutrients to restore immune functions during refeeding of PEM patient has been extensively studied in the past years. This review describes the pathophysiological mechanisms of immune consequences of PEM and of immune restoration with refeeding, and in addition focuses upon some nutrients of particular importance, namely glutamine, zinc and vitamin E. Particular attention is directed at the elderly patients with PEM, a growing population for which the importance of undernutrition on prognosis is not yet fully recognized.

Failure of aged rats to accumulate eosinophils in allergic inflammation of the airway

To investigate the effect of aging on the allergic airway response, we examined the bronchoconstrictive responses and cellular inflammatory changes in a rat model of bronchial asthma by evaluating young and old animals. Two different age groups of Brown-Norway rats, actively sensitized by injection of ovalbumin into the foot pads, were used: 7 to 8 weeks old (young group) and 100 to 120 weeks old (aged group). Both the aged and young rats produced on ovalbumin-specific IgE antibody and exhibited an immediate asthmatic response after exposure to ovalbumin, but the degree of specific IgE antibody was significantly higher in young rats. The young group showed a marked increase in the number of eosinophils and neutrophils in bronchoalveolar lavage fluid 2 days after exposure to ovalbumin, whereas no eosinophilia was seen in the aged group. To evaluate the mechanism of the decreased accumulation of eosinophils in aged rats, cells from popliteal lymph nodes from ovalbumin-sensitized rats were incubated with ovalbumin for 48 hours. Although eosinophil chemotactic activity, determined by a modified Boyden chamber method, was present in the supernatant of cultured lymph node cells from young rats, it was absent from those of aged rats. In vivo administration of anti-IL-5 monoclonal antibody revealed that one of the factors of eosinophil chemotactic activity was IL-5. Lymph node cells from aged rats tended to produce greater amounts of interferon-gamma than did those from young animals. Findings indicate that aged rats have a defect in eosinophil accumulation in sites exposed to antigen, probably because of an age-dependent alteration in T cells.

Heterogeneous aging of macrophage-lineage cells in the capacity for TNF production and self renewal in C57BL/6 mice

We examined age-related changes in both tumor necrosis factor-alpha (TNF) producing ability and the replicative capacity of macrophage-lineage cells from different anatomical tissues concomitantly in mice. We have previously demonstrated that alveolar macrophages of aged mice secreted decreased amounts of TNF activity compared with that of younger counterpart. In this study, it is demonstrated that peritoneal macrophages exhibited increased TNF activity with aging, while the bone marrow-derived adherent cells secreted less TNF activity. In addition, we showed that the numbers of their progenitor cells (GM-CFUs) in the bone marrow increased with age, whereas those in the spleen did not change with aging. We conclude that age associated changes in functions and proliferative capacities of macrophage-lineage cells are tissue dependent.