Interleukin-1 synthesis and activity in aged mice

Aging-associated immunosenescence via alterations in splenic immune cell populations in rat

AIM

Immunosenescence is the decline of the host immune system due to aging, resulting in various complications. The splenic lymphoid nodule is the pivotal compartment involved in immunosenescence. In this study, we investigated the important changes in the splenic immune cell populations of aged rats (18-24 months) in comparison with young rats (3-5 months).

MATERIALS AND METHODS

We, also, studied the effects of aging on the activities of total superoxide dismutase (T-SOD) and malondialdehyde (MDA) levels in spleen of both groups, besides the changes of the splenic architecture. Furthermore, immunohistochemical staining was performed to detect the aging effects in T cells, B cells, macrophages, granulocytes, mast cells, proliferating cells, apoptotic cells, and cells positive for interleukin-1β (IL-1β), interleukin-6 (IL-6), and Toll-like receptor 4 (TLR4).

KEY FINDINGS

The aged rats had significantly lower spleen/body weight ratios and smaller splenic nodules, indicating a decline in general immunity in them. With aging, T-SOD activities were decreased, while MDA levels were increased, exhibiting that oxidative stress increases in spleens. In addition, the aged group also had significantly fewer T and B cells, macrophages, granulocytes, IL-6 and TLR4 immuno-positive cells, and proliferating cells in the periarterial lymphatic sheaths, marginal zone, and lymphoid follicles compared with the young group. On the other hand, the number of mast cells and apoptotic cells was significantly increased with age. Therefore, we can conclude that cellular immunity and humoral immunity were crumpled with age.

Xiaoyaosan Improves Depressive-Like Behaviors in Mice through Regulating Apelin-APJ System in Hypothalamus

Background: The apelin-APJ system has been considered to play a crucial role in HPA axis function, and how the traditional Chinese compound prescription Xiaoyaosan regulates the apelin-APJ system as a supplement to treat depressive disorders. Objective: To investigate the depression-like behaviors and expression of apelin and APJ in hypothalamus of chronic unpredictable mild stress (CUMS) mice and study whether these changes related to the regulation of Xiaoyaosan. Methods: 60 adult C57BL/6J mice were randomly divided into four groups, including control group, CUMS group, Xiaoyaosan treatment group and fluoxetine treatment group. Mice in the control group and CUMS group received 0.5 mL physiological saline once a day by intragastric administration. Mice in two treatment groups received Xiaoyaosan (0.25 g/kg/d) and fluoxetine (2.6 mg/kg/d), respectively. After 21 days of modeling with CUMS, the expression of apelin and APJ in hypothalamus were measured by real-time fluorescence quantitative PCR, western blot and immunohistochemical staining. The physical condition, body weight, food intake and behavior tests such as open field test, sucrose preference test and force swimming test were measured to evaluate depressive-like behaviors. Results: In this study, significant behavioral changes were found in CUMS-induced mice, meanwhile the expressions of apelin and APJ in the hypothalamus were changed after modeling. The body weight, food-intake and depressive-like behaviors in CUMS-induced mice could be improved by Xiaoyaosan treatment which is similar with the efficacy of fluoxetine, while the expressions of apelin and APJ in hypothalamus were modified by Xiaoyaosan. Conclusions: The data suggest that apelin-APJ system changes in the hypothalamus may be a target of depressive disorders, and the beneficial effects of Chinese compound prescription Xiaoyaosan on depressive-like behaviors may be mediated by the apelin-APJ system.

Toll-like Receptor function of murine macrophages, probed by cytokine induction, is biphasic and is not impaired globally with age

Aging is associated with a waning of normal immune function. This "immunosenescence" is characterized by a diverse repertoire of seemingly discreet and unbalanced immune alterations. A number of studies have suggested that aging-associated alterations in innate immune responsiveness, especially responsiveness dependent on Toll-like Receptor (TLR) engagement, are causally involved. We find, however, that the magnitude and dose-dependency of responsiveness to TLR engagement (assessed with respect to cytokine production) in distinct populations of murine macrophages are not altered generally with animal age or as a consequence of immunosenescence. Responses elicited with a wide array of TLR agonists were examined by extensive functional analyses, principally on the level of the individual cell. These studies reveal an intriguing "all-or-nothing" response behavior of macrophages, independent of animal age. Although reports to the contrary have been cited widely, aging-associated immune decline cannot be attributed to widespread alterations in the extents of TLR-dependent innate immune macrophage responses.

Septic shock in older people: a prospective cohort study

Background

Septic shock is the first cause of death in Intensive Care Units. Despite experimental data showing increased inflammatory response of aged animals following infection, the current accepted hypothesis claims that aged patients are immunocompromised, when compared to young individuals.

Results

Here, we describe a prospective cohort study designed to analyze the immune profile of this population.

Conclusion

Older people are as immunocompetent as the young individual, regarding the cytokines, chemokines and growth factors response to devastating infection.

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.

Age-related inflammatory cytokines and disease

Aging is associated with chronic low-grade increases in circulating levels of inflammatory markers. A wide range of environmental factors, including smoking, infections, and obesity, genetic factors, and the declining function of sex hormones may contribute to systemic low-grade inflammatory activity in older individuals. Age-associated disease may exacerbate this phenomenon. The multifunctional cytokines TNF-alpha and IL-6 have been associated with morbidity and mortality in the elderly. Evidence supports the direct role of TNF-alpha in the pathogeneses of atherosclerosis, type 2 DM, and AD in older individuals. Age-related increases in systemic levels of TNF-alpha could provide a unifying basis for these disorders. Furthermore, TNF-alpha induces a catabolic state that causes frailty. Circulating levels of IL-6 seem to be a strong risk factor for frailty in the elderly, which could reflect its association with increased production of TNF-alpha. IL-6 also may be a risk factor for thromboembolic complications. In healthy, elderly populations, high circulating levels of TNF-alpha and IL-6 predict mortality, independent of comorbidity, indicating that TNF-alpha and IL-6 cause morbidity and mortality. In cohorts of frail, older individuals, TNF-alpha and IL-6 also act as disease markers. Circulating levels of TNF-alpha seem to be the best predictor of mortality in frail, elderly populations with a high mortality rate, whereas IL-6 seems to be the strongest risk marker in healthy, elderly populations. This finding could reflect that in relatively healthy old populations the increase in circulating levels of IL-6 represent a systemic response to local proinflammatory activities; however, when age-related inflammatory diseases progress, levels of TNF-alpha increase in the circulation and become gradually a stronger risk marker than IL-6. In conclusion low-grade elevations in levels of circulating cytokines are strong independent risk factors of morbidity and mortality in the elderly, and lifestyle factors and comorbidities may modulate these levels. Exercise and dietary interventions may be possible strategies to decrease inflammatory activity and improve the health status of the elderly.

Impaired production of proinflammatory cytokines in response to lipopolysaccharide (LPS) stimulation in elderly humans

Ageing is associated with decreased resistance to bacterial infections and concomitant increased circulating levels of inflammatory cytokines. The purpose of the present study was to research age-related changes in levels of early mediators of the acute-phase response in whole blood supernatants following LPS stimulation, representing an ex vivo model of sepsis. Levels of tumour necrosis factor-alpha (TNF-alpha), IL-1beta and IL-6 in whole blood supernatants were measured after in vitro LPS stimulation for 24 h in 168 elderly humans aged 81 years from the 1914 cohort in Glostrup, Denmark and in 91 young controls aged 19-31 years. Levels of TNF-alpha and IL-1beta were significantly lower in elderly humans compared with young controls, whereas no difference was detected with regard to IL-6. Elderly humans with low body mass index had the lowest levels of IL-1beta. Young women had lower levels of proinflammatory cytokines compared with young men, but this difference was blurred by ageing. No relation was found between circulating plasma levels of TNF-alpha and levels after in vitro LPS stimulation. In conclusion, decreased production of TNF-alpha and IL-1beta after exposure to LPS may reflect impaired host defence against infections in the elderly and be of importance in elderly humans with underlying health disorders. However, the clinical relevance is questionable in healthy elderly people because decreased levels were found compared with young men but not compared with young women.

Chronic exercise increases macrophage-mediated tumor cytolysis in young and old mice

In this study, we determined the effects of age and chronic treadmill running (16 wk; 5 days/wk; 45 min/day; 18-22 m/min) on resident peritoneal macrophage responsiveness to interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) in young (6 mo) and aged (22 mo) male BALB/cByJ mice by measuring cytolytic ability and production of reactive nitrogen products. Macrophages (>90% Mac-3(+)) were incubated with various concentrations of IFN-gamma and LPS for 24 h. After washing, P815 tumor cells were utilized as targets in a 16-h 51Cr release assay. We found that aging resulted in a significant reduction in the ability of macrophages to respond to the highest doses of IFN-gamma and LPS and kill P815 cells (46 +/- 4 vs. 34 +/- 2% in young and old mice, respectively). Exercise training significantly increased macrophage cytolysis in both age groups (66 + 7 vs. 44 + 2% in young and old mice, respectively); this effect was larger in the young mice. Macrophages from young exercised mice also produced significantly (50-60%) more NO-2; there was a tendency for higher NO-2 in old exercisers. The inducible nitric oxide synthase (iNOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) significantly reduced macrophage cytolysis and NO-2 production and completely abrogated exercise-induced increases in these measures. RT-PCR analysis revealed significantly higher iNOS mRNA levels in macrophages obtained from the exercise-trained mice and significantly lower iNOS mRNA in old compared with young mice. We conclude that aging reduces and exercise training increases the capacity of resident peritoneal macrophages to respond to IFN-gamma and LPS with increased tumor cytolysis. Enhanced iNOS gene expression and NO-2 production are likely the contributing mechanisms of the exercise-induced enhancement of cytolysis in young mice. While L-NMMA did block the exercise-induced increase in cytolysis, exercise did not increase NO-2 or iNOS gene expression in the old mice, indicating perhaps the contribution of other cytolytic mechanisms in old mice.

Similar responses by macrophages from young and old mice infected with Mycobacterium tuberculosis

The growth of four isolates of Mycobacterium tuberculosis was compared in cultures of bone marrow-derived macrophages generated from young (3 months) and old (24 months) female C57BL/6 mice. In all four cases, no differences were seen in the course of the in vitro infection over a 10-day culture period. Macrophages from both young and old mice secreted similar levels of nitric oxide if treated with interferon gamma (IFN) 24 h prior to infection. Expression of mRNA encoding an array of early response genes in the two sets of cultures was also generally similar. These data indicate that the capacity of macrophages to respond to infection with a virulent intracellular bacterial infection does not seem to be influenced by the increasing age of the host.

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.

Lipopolysaccharide-induced lethality and cytokine production in aged mice

This study was designed to define the lipopolysaccharide (LPS) sensitivity of aged mice in terms of lethality and cytokine production and to determine down-regulating responses of corticosterone and interleukin 10 (IL-10). The 50% lethal doses of LPS in young (6- to 7-week-old) and aged (98- to 102-week-old) mice were 601 and 93 microg per mouse (25.6 and 1.6 mg per kg of body weight), respectively. Aged mice were approximately 6.5-fold more sensitive to the lethal toxicity of LPS in micrograms per mouse (16-fold more sensitive in milligrams per kilogram) than young mice. Levels in sera of tumor necrosis factor-alpha (TNF-alpha) IL-1alpha, and IL-6 after intraperitoneal injection of 100 microg of LPS peaked at 1.5, 3, and 3 h, respectively, and declined thereafter in both groups of mice. However, the peak values of these cytokines were significantly higher in aged than in young mice (P < 0.05). Gamma interferon (IFN-gamma) was detectable at 3 h, and sustained high levels were still detected after 12 h in both age groups. Although there were no significant differences in levels of IFN-gamma in sera from both groups, aged mice showed higher IFN-gamma levels throughout the 3- to 12-h study period. Administration of increasing doses of LPS revealed that aged mice had a lower threshold to IL-1alpha production than young mice. In addition, aged mice were approximately 4-fold more sensitive to the lethal toxicity of exogenous TNF in units per mouse (10-fold more sensitive in units per kilogram) than young mice. With regard to down-regulating factors, corticosterone amounts were similar at basal levels and no differences in kinetics after the LPS challenge were observed, whereas IL-10 levels in sera were significantly higher in aged mice at 1.5 and 3 h than in young mice (P < 0.01). These results indicate that aged mice are more sensitive to the lethal toxicities of LPS and TNF than young mice. We conclude that a relatively activated, or primed, state for LPS-induced cytokine production, in spite of full down-regulating responses by corticosterone and IL- 10, may explain at least in part LPS sensitivity in aged mice.

Interrelationship of fever, immune response and aging in mice

Fever is the cardinal manifestation of infection and may be blunted in certain infected elderly individuals. It is known that elevated body temperature enhances both the inflammation response and immune function, resulting in increased host resistance to infection. Recently, it has been suggested that the elevation of body temperature and the activation of lymphocytes by IL-1 are interrelated host effects. However, the question of whether fever response in vivo is closely correlated to cell-mediated immune parameters is unknown. In this study, a well-defined murine model was used to study the relationships between aging, fever and cell-mediated immune response. Thus, measurements of rectal temperature changes were made in individual young (4-6 months) and old (26-27 months) BALB/c mice to determine their ability to respond to endogenous pyrogen (recombinant IL-1). Splenic cells from these animals were used to assess T- and B-cell proliferation, production of interleukin 1 (IL-1) and IL-2. The results revealed that the proliferative capacity and the IL-1 and IL-2 producing capacity of splenic cells from old mice were markedly decreased. However, aging did not significantly affect the mean febrile responses in old mice following rIL-1 injections. Finally, there was no significant correlation between in vivo fever responses and the immune parameters measured in vitro in both young and old mice.

Decreases in macrophage mediated antitumor activity with aging

We have demonstrated that immunotherapy of young (6-10 weeks old), and aged, (greater than 24 months old), tumor bearing mice with biological response modifiers enhanced survival and inhibited tumor growth, while treatment of aged mice had little or no effect. We hypothesized that the antitumor activity in young mice was principally mediated by activated macrophages (M phi) and predicted that the change in aged mice was caused by an intrinsic M phi defect which develops with advancing age. To directly test our hypothesis, we examined the antitumor activity of resident peritoneal M phi, purified and activated in vitro with IFN gamma plus LPS. Paralleling the results seen in vivo, M phi from aged mice exhibited reduced antitumor activity in comparison with M phi from younger mice. Moreover, there was reduced capacity of in vitro activated M phi from aged mice to produce TNF, IL-1 and nitric oxide, which are critical monokines and effector molecules that have been established to either directly inhibit tumor growth or cause tumor cell destruction. These studies establish that peritoneal M phi from aged mice have an intrinsic defect which prevents them from fully expressing their antitumor potential.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Increased release of tumor necrosis factor-alpha into the cerebrospinal fluid and peripheral circulation of aged rats

BACKGROUND AND PURPOSE

We earlier reported that risk factors for stroke prepare brain stem tissue for a modified Shwartzman reaction, including the development of ischemia and hemorrhage and the production of tumor necrosis factor-alpha, after a provocative dose of lipopolysaccharide. In the present study, we sought to determine whether blood and central nervous system cells of rats with the stroke risk factor of advanced age produce more proinflammatory and prothrombotic mediators than do those of young rats of the same strain.

METHODS

Levels of tumor necrosis factor-alpha and platelet activating factor in the cerebrospinal fluid and tumor necrosis factor-alpha in the serum of 2-year-old and 16-week-old Sprague-Dawley rats were monitored before and after challenge with lipopolysaccharide.

RESULTS

No consistent tumor necrosis factor-alpha activity was found in the cerebrospinal fluid or blood of control animals. Intravenous administration of lipopolysaccharide (1.8 mg/kg) increased serum tumor necrosis factor-alpha levels but had no effect on tumor necrosis factor-alpha in the cerebrospinal fluid. Serum tumor necrosis factor-alpha increased much more in aged rats than in young rats. When lipopolysaccharide was injected intracerebroventricularly, tumor necrosis factor-alpha activity in cerebrospinal fluid increased significantly more in old rats than in young rats. Baseline levels of platelet activating factor in cerebrospinal fluid were significantly higher in old rats than in young rats, and the levels increased to a greater degree in aged rats on stimulation.

CONCLUSIONS

Rats with the stroke risk factor of advanced age respond to lipopolysaccharide with a more exuberant production of tumor necrosis factor-alpha and platelet activating factor than young rats of the same strain. These findings are consistent with our working hypothesis that perivascular cells are capable of exaggerated signaling of endothelium through cytokines such as tumor necrosis factor-alpha in animals with stroke risk factors. The effect of such signaling might be to prepare the endothelium of the local vascular segment for thrombosis or hemorrhage in accord with the local Shwartzman reaction paradigm.

Aging and eliciting agents: effect on murine peritoneal macrophage monokine bioactivity

Decreased responsiveness of the aged to infection may be associated with a decline in monokine production. Prior studies in macrophages have used different eliciting agents, and results have varied. We assessed the effect of age on interleukin-1 (IL-1), tumor necrosis factor (TNF), and interleukin-6 (IL-6) in unelicited, thioglycollate (TG)-elicited, and complete Freund's adjuvant (CFA)-elicited peritoneal macrophages. Resident macrophages or CFA-elicited macrophages from middle aged or aged mice produced significantly less monokine bioactivity than resident or CFA-elicited macrophages from young mice. Monokine bioactivity from TG-elicited macrophages from aged and middle aged mice was significantly increased when compared with macrophages of young mice. Eliciting agents may alter macrophage populations and interactions with other cells leading to changes in monokine bioactivity with aging.

Explanations for reduced tumor proliferative capacity with age

Tumors in general occur more frequently in older people, but many of the common tumors appear to be less malignant in older hosts. In this article mechanisms of tumor enhancement are reviewed, and those that are age-sensitive are emphasized. In this regard, our earlier experimental work suggested that age-associated immune change (immune senescence) is most important in explaining reduced tumor growth. We have found that unstimulated spleen cells in culture produce a tumor-enhancing factor (TEF) that enhances B16 murine melanoma cell proliferation. TEF, and others, such as lymphocyte-induced angiogenesis factor (LIA) and various other autocrine growth factors, may stimulate malignant cells in cancer-bearing hosts. An age-associated reduction in those factors could account for the observed reduced tumor growth and spread in hosts of advanced age.

Splenic and inguinal lymph node T cells of aged mice respond differently to polyclonal and antigen-specific stimuli

Numerous changes have been reported to occur in T cell responsiveness of mice with increasing age. However, most of these studies have examined polyclonal stimulation of spleen cells from a limited number of mouse strains. This study investigated the influence of genetic background, source of lymphocytes, and type of stimulus on age-associated changes in T cells response. Con A-induced proliferation and IL-2 and IFN-gamma production by splenic lymphocytes (SL) was significantly greater in CBA/Ca mice compared to C57BL/6 mice, regardless of age. SL of both strains exhibited the predicted age-dependent decline in proliferative response and an increase in IFN-gamma production in response to Con A. In contrast, however, only SL from C57BL/6 mice demonstrated the predicted age-dependent decline in Con A-induced IL-2 production; Con A-induced SL of young and aged CBA/Ca mice produced comparable amounts of IL-2. Differences in age-associated responses to Con A were also observed between SL and inguinal lymph node (ILN) cells of CBA/Ca mice. In contrast to SL, ILN cells demonstrated an increased proliferative response to Con A. However, lymphokine production by Con A-stimulated ILN cells from aged CBA/Ca mice was similar to that of Con A-stimulated SL from aged CBA/Ca mice. To determine if aged ILN T cells respond similarly to polyclonal and antigen-specific stimuli, keyhole limpet hemocyanin (KLH) responses of T cells isolated from ILN of aged and young CBA/Ca mice were examined. KLH-specific T cells from aged mice cultured with KLH-pulsed macrophages (M phi) from aged mice were significantly reduced in their ability to proliferate compared to KLH-specific T cells of young mice cultured with young KLH-pulsed M phi. In contrast to the expected results, the defect was not at the level of the T cells; proliferation of young T cells cultured with aged KLH-pulsed M phi was equivalent to the proliferation of aged T cells cultured with aged M phi. These results suggest that aging has differential effects on polyclonal and antigen-specific T cell proliferation and on polyclonal stimulation of T cells isolated from different lymphoid organs and from different strains of mice.

Thymectomy at weaning. An accelerated aging model for the mouse immune system

Mouse thymectomy at weaning induces a long lasting immunodepression which can be measured by in vivo and in vitro experiments. Lymphocyte proliferation and IL2 production in response to a T cell mitogen are greatly diminished during the whole life of the animals, on the contrary B cell proliferation in the presence of lipopolysaccharide is not modified. The lack of effect of surgery on the in vitro T cytotoxic activity compared to the total abolition of in vivo graft versus host reaction shows that these two phenomena are under the control of different immunocompetent cell subsets. Thymectomy induces a stabilization of natural killer cell activity, while during normal aging, this parameter decreases regularly. Surprisingly, the thy 1+ cell level is normal 8-10 months after thymectomy compared to sham operated animals showing that phenotypically normal cells can be dysfunctional. Macrophage activity is not modified either by aging or by thymectomy. So, thymectomized mice can be used after less than 1 year to study immunopharmacology of aging.

Immunotoxicity of alcohol in young and old mice. II. Impaired T cell proliferation and T cell-dependent antibody responses of young and old mice fed ethanol-containing liquid diet

The effect of extended ethanol consumption of young and old BALB/c mice on the proliferative response to Concanavalin A (Con A) and T cell-dependent antibody response of their spleen cells to sheep red blood cell (RBC) stimulation was determined. Splenic cells of young (3 months) and old (25 months) BALB/c mice, fed with one of three different diets (ethanol, maltose-substitute and standard mouse chow), were first cultured with Con A to assess T cell proliferation and production of interleukin 2 (IL2). Then, Con A-activated T blast cells from young and old mice were assessed for their proliferative responding capacity to exogenous human recombinant IL2 and crude rat IL2 supernatant. Finally, splenic cells of young and old mice were assessed for their ability to generate plaque-forming cells in response to sheep RBC. The results revealed that both T cell mitogenesis and IL2-dependent proliferation of T blast cells from young and old ethanol diet-fed mice were remarkably diminished as compared to that of young and old maltose-substituted diet (isocaloric control) fed mice, respectively. The ability of T cells from both young and old ethanol diet-fed mice to produce IL2, however, was not affected. Finally, the ability of young and old ethanol diet-fed mice to mount a primary antibody response to SRBC was also significantly reduced. These results taken together demonstrate for the first time that both T cell proliferative activity and T cell-dependent antibody response of young and old ethanol diet-fed mice are impaired; however, with respect to age, a differential effect of immunosuppression of ethanol was not noted.

Cellular immunosenescence: an overview

Recent studies on space flights suggest that certain T cell immunologic activities are vulnerable to microgravitation. It would be desirable to know the extent to which these changes can be prevented or reversed. Since the changes observed are analogous to the effects of aging on immunity, a brief overview is presented of our current knowledge of age-related changes in immune cells and of the various interventional methods which have been used successfully in preventing the decline with age and in elevating the levels of immune functions of old individuals.

Effects of long-term, low-dose growth hormone therapy on immune function and life expectancy of mice

We have studied effects of long-term, low-dose growth hormone therapy on the immune function and life expectancy of Balb/c mice. Sixty male Balb/c mice were aged up to the time when they started showing signs of senescence and causal death (deaths started when they became 17 months old). The aged mice were divided into two groups of 26 mice each. One group received growth hormone (30 micrograms/mouse) subcutaneously twice a week for 13 weeks. The control group received an equal volume of saline for the same period. During this treatment period, 16 control mice died (61%) whereas only 2 of the hormone-treated mice died (7%). Four mice from each group were killed and immunological functions of splenocytes were evaluated. Hormone-treated mice had higher stimulation indices for pokeweed mitogen but not for Concanavalin-A. Total IgG production was decreased but IL-1, IL-2 and TNF production was increased. After a lag period of 4 weeks, growth hormone therapy was continued for another 6 weeks. One of the growth hormone treated mice died while the control group no longer existed. Splenocyte functions of the growth hormone treated mice were compared to those of young mice. The results showed no significant difference between cytokine production (IL-1, IL-2, TNF and IgG) in the young and the hormone treated groups. Stimulation induced by concanavalin-A and pokeweed mitogen however, was higher in the young group than the old group. The mortality curve obtained suggests that long-term low-dose growth hormone treatment prolongs life expectancy.

Aging and immune function

Since it is too difficult to study aging of the organism as a whole, most investigators try to focus on a specific physiological system that exhibits age-dependent functional changes, in the hopes that elucidation (in biochemical and developmental terms) of the mechanism of senescent change will provide insight into the aging process itself. The immune system is among the most maleable of such models, in that well-defined cell types will produce well-defined molecules with predictable functions in vitro and in vivo. The increasing power of basic immunological science should, in the next decade, permit an increasingly fine appreciation of how aging leads to immune decline. This expanding conceptual framework will then suggest new ideas about the role of immunosenescence in degenerative, infectious, and neoplastic illnesses and may also generate increasingly rational strategies for therapeutic intervention.

Immune dysfunction in the elderly: effect of thymic hormone administration on several in vivo and in vitro immune function parameters

The effects of short-term thymic hormone administration on age-associated immune function were evaluated. Two groups of individuals greater than 65 years of age were treated for 30 days with thymic extracts (TP1) or placebo; before and after this treatment a panel of in vitro and in vivo parameters was determined according to a very rigorous experimental protocol. In most individuals, TP1 treatment was associated with an improvement in cutaneous delayed-type response to PPD. Moreover, an increase in a circulating T cell subpopulation bearing the CD45R surface antigen ("virgin" T cells), and in NK cell cytotoxic activity was also observed in some subjects. Finally, lymphocyte responsiveness to PHA tended to increase, while no effect on lymphocyte ability to produce IL-2 following mitogen stimulation was observed. These findings suggest that TP1 treatment may influence age-related alterations in immune function parameters in some subjects.

A decreased functional capacity of CD4+ T cells underlies the impaired DTH reactivity in old mice

The data presented in this paper show that the in vivo delayed-type-hypersensitivity (DTH) reaction to both H-2 and non-H-2 alloantigens declines with increasing age. It is also shown that cells generated in vitro are capable to transfer DTH to young naive syngeneic recipients. Using this in vitro system it could be demonstrated that cells from old CBA/Rij mice induced lower DTH responses than cells from young CBA/Rij mice. Depletion experiments with the effector T cell population showed that the DTH effector phase is mediated by CD4+ T cells. Lower responses in old mice were not due to increased CD8+ suppressor T cell activity, since after removal of the CD8+ T cells old CD4+ cells were still less effective in the generation of DTH effector T cells than young CD4+ cells. Addition of IL-2 containing supernatant to in vitro cultures did not improve the subsequent DTH response. From these data it can be concluded that the reduced DTH responses in old mice are not solely due to CD8+ suppressor cell activity and/or lack of IL-2, but that rather intrinsic defects of the CD4+ T cell population appear to play a major role in the impaired DTH reactivity during ageing.

Immunotoxicity of alcohol in young and old mice. I. In vitro suppressive effects of ethanol on the activities of T and B immune cells of aging mice

A murine aging model was employed to assess effects of ethanol exposure on the T-cell proliferative response to mitogenic stimulation and on the T cell-dependent primary antibody response to sheep red blood cells (RBC) in vitro. Splenic cells from young (3-5 months) and old (28-32 months) BALB/c mice were first assessed for their ability to produce interleukin (IL) 2 and proliferate in response to mitogenic stimulation in the presence of various doses of ethanol. Then, splenic T blast cells from young and old mice, generated by Con A-activation, were assessed for their IL2-dependent proliferative capacity in the presence of various doses of ethanol. Finally, splenic cells of young and old mice were assessed for their ability to generate plaque-forming cells (PFC) in response to sheep RBC in the presence of various doses of ethanol. The results revealed that ethanol has a much greater suppressive effect on old than young splenic T cells (10-15 times), as judged by their ability to proliferate in response to mitogenic stimulation. However, the magnitude of the difference in the suppressive effect is less when the cells are cycling (2 times). Furthermore, ethanol had only a minimal suppressive effect on IL2 production by T cells of both young and old mice, even at the concentration of 100 mM. These findings would suggest that the ethanol-mediated suppression of T cell proliferation of both young and old mice is more likely due to an impairment of metabolic event(s) associated with or subsequent to the interaction of IL2 and IL2 receptor leading to cellular replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitogen-activation of spleen cells in aged animals is potentiated by dietary restriction: a preliminary report

Dietary restriction has been reported to be associated with increased life span and increased DNA repair capacity in both male and female rats and mice. We examined dietary restriction effects on immune system function and prolongation of life span in specific pathogen free rats and mice. In this preliminary report the authors show that dietary restriction is correlated with a dramatic increase in the lifespan of both male and female rats and mice in a pathogen free environment, and in the capacity of cultured splenocytes from those animals to initiate blastogenesis in response to antigenic stimulation.

Analysis of the age-related decline in alloreactivity of CD4+ and CD8+ T cells in CBA/RIJ mice

CD4+ T cells from healthy old CBA/Rij mice were studied for their ability to respond to alloantigens by IL-2 production and proliferation. IL-2 production by these purified cells in response to BALB/c spleen cells was about 4 times lower than the IL-2 production (50 U/ml) by CD4+ T cells from young mice. After stimulation with concanavalin A only a two-fold difference in IL-2 production was found. The extent of proliferation by CD4+ T cells from old mice in response to allogeneic cells was at least 4 times lower than that by the cells from young mice. This difference was not influenced by the addition of IL-2 containing conditioned medium (CM). Proliferative responses by CD8+ T cells were only found after the addition of CM and then the response by cells from old mice was 2-10 times lower than the response by cells from young mice. Limiting dilution analysis of the separate T cell subpopulations showed that these low responses to alloantigens by cells from old mice were only in part due to a decline in the frequency of antigen-specific CD4+ or CD8+ T cells. As far as old CD8+ T cells were concerned, an additional explanation for the low responsiveness was found in a diminished expression of the IL-2 receptor (IL-2R) alpha-chain. However, CD4+ T cells from old mice expressed normal levels of IL-2R alpha-chain. The observation that proliferative responses by CD4+ T cells may be low, despite a normal frequency of antigen-specific cells, an apparently normal IL-2R expression and despite the presence of exogenous IL-2, indicates that CD4+ T cells from old mice are not only impaired in their ability to produce IL-2, but are also impaired in their ability to handle the IL-2 signal.

Immunopharmacological actions of an extract isolated from inflamed skin of rabbits inoculated with Vaccinia virus (Neurotropin)--II. Restorative effect on immune responses through the recovery of IL-2 production in aging mice

To examine the immunopharmacological actions of an extract isolated from inflamed skin of rabbits inoculated with Vaccinia virus (Neurotropin), its effect on the immune responses in aging BALB/c mice was examined. Neurotropin clearly restored the decreasing T-cell-dependent immune responses such as delayed-type hypersensitivity (DTH) response and plaque-forming cells (PFC) response to sheep red blood cells (SRBC) when administered i.p. from 13 months old (mo) to 16 mo. However, Neurotropin administration from 2 to 5 mo had no effect on the immune responses of young animals. Neurotropin administration from 13 to 16 mo restored not only the T-cell proliferation of spleen cells induced by concanavalin A (Con A) and phytohemagglutinin (PHA), but also the interleukin-2 (IL-2) production by spleen cells activated with Con A. However, Neurotropin did not affect the responsiveness of Con A-activated spleen cells to exogenous recombinant IL-2. An absence of suppressor cells capable of inhibiting the IL-2 production in the spleens was confirmed in the 16 mo mice. Neurotropin administration also restored IL-1 production by peritoneal macrophages stimulated with lipopolysaccharide (LPS). These results suggest that long-term administration of Neurotropin restores the decreasing T-cell-dependent immune responses through the recovery of IL-2 and in part IL-1 production, but not the responsiveness to IL-2 in aging BALB/c mice.

Decline in the production of interleukin-3 with age in mice

Previously, we and others have found that the ability to produce interleukin-1 (IL-1) and interleukin-2 (IL-2) declines with age in mice. The purpose of this study was to determine the influence of age on the capacity of mice to produce interleukin-3 (IL-3). Splenic cells (5 X 10(6)/ml) from young (3-4 months) and old (24-32 months) C57BL/6 mice were first assessed for their IL-3-producing capacities in response to varying doses of concanavalin A (Con A; 2-20 micrograms/ml) in a time-dependent manner. The results showed that the production of IL-3 by both young and old C57BL/6 mice was maximal on Days 3 and 4 in response to 20 micrograms/ml of Con A, and that of IL-2 was minimal (activity was less than 0.1 unit) on Day 4. Consequently, Day 4, was selected to assess the effect of age on IL-3 production by splenic cells. The results showed a twofold reduction in IL-3 production with age (P less than 0.05). Young-old splenic cell mixture experiments at ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 indicated that the decrease in IL-3 production with age was not due to an increase in suppressor cell activity. Experiments based on mixtures of nylon wool-enriched splenic T-cell and adherent cells and on anti-MAC-1 plus complement-treated spleen cells indicated that (a) adherent cells are not required for T-cell production of IL-3, unlike IL-2 production, and (b) the decrease in IL-3 production with age is due solely to alteration in IL-3-producing T cells. Finally, a strong correlation was demonstrated between the production of IL-2 and IL-3 by spleen cells of individual young and old mice (r = 0.92, P less than 0.01). That production of both IL-2 and IL-3 is affected in a similar manner by age would suggest that a single class of helper T cells may be responsible for production of both lymphokines.

The age-related decline in interleukin-3 expression in mice

Spleen lymphocytes form 5- to 37-month-old C57BL/6J mice were stimulated by concanavalin A (con A) in vitro, and the interleukin-3 (IL-3) expression was assessed by measuring the IL-3 activity in culture supernatants and the cytoplasmic IL-3 mRNA levels. The activity and mRNA level of IL-3 was maximum at 20 hr after culturing in the presence of con A. The IL-3 activity in the culture supernatants and the IL-3 mRNA level in lymphocytes declined 70% to 80% between 5 and 37 months of age. Northern blot analysis revealed no change in the size of IL-3 mRNA between young and old mice. When the expression of IL-3 and interleukin-2 (IL-2) by con A-stimulated lymphocytes was compared, both interleukins showed a similar declined with age.

Deterioration of cellular immunity during aging. The relationship between age-dependent impairment of delayed-type hypersensitivity reactivity, interleukin-2 production capacity, and frequency of Thy-1+,Lyt-2- cells in C57BL/Ka and CBA/Rij mice

The effect of aging on the delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) in vivo and the interleukin-2 (IL-2) production capacity in vitro by spleen cells from young (17 weeks) and old (125 weeks) CBA/Rij and C57BL/Ka mice were investigated. For both CBA/Rij and C57BL/Ka mice an age-related decline in the DTH response to SRBC and the IL-2 production capacity was observed. Both parameters are mediated by Thy-1+,Lyt-2- spleen cells. For both mouse strains the proportion of Thy-1+,Lyt-2- spleen cells declined less strongly with aging than the DTH reactivity and the IL-2 production capacity. From this it was concluded that not only a quantitative but also a qualitative decrease of T-cell function occurs during senescence. It was also investigated whether the proportion of Thy-1+,Lyt-2- peripheral blood lymphocytes can be used as a predictive value with regard to the decline of DTH with aging of the corresponding mouse. This was indeed found to be the case in CBA/Rij mice, but not in C57BL mice.

Is the endogenous antipyretic neuropeptide alpha-MSH responsible for reduced fever in aged rabbits?

The reduced febrile response in aged man has been noted since the beginning of clinical thermometry. Our previous research on aged rabbits and squirrel monkeys disclosed a similar reduced fever, presumably due to a decrease in central receptors for endogenous pyrogen. However, because central alpha-melanocyte stimulating hormone (MSH) appears to have a potent role in physiological control of fever, it may be that increased release of the peptide is responsible for the reduced febrile response in aged animals. To test this idea, antiserum specific to MSH was administered intracerebroventricularly to rabbits of known age. The antiserum given according to three schedules of treatment augmented fever caused by IV injections of interleukin-1 (IL-1) in young (less than 2 years) male and female rabbits. Aged female rabbits (3-5+ years) and females aged 2-3 years showed significant augmentation of fever only after pretreatment plus acute injection of antiserum. A single ICV injection of MSH (200 ng) reduced fever in all groups with the greatest antipyretic effect in the aged females. The results indicate that while aged rabbits have an increased antipyretic response to central MSH, binding of the endogenous peptide does not result in marked increases in fever in these animals. Thus, whereas a change in central MSH sensitivity may contribute to reduced fever in aged homeotherms, a reduction in central pyrogen receptors appears to be the most parsimonious explanation.

Reversal by lymphokines of the age-related hyporesponsiveness to contact sensitization and reduced Ia expression on Langerhans cells

Contact sensitivity responses were evaluated in young adult (3-5 months) and aged (16-26 months) BALB/c mice which were systemically treated with interleukin-2 (IL-2), interferon-gamma (IFN-gamma) or saline. Mice older than 16 months of age have deficient numbers of Ia+ Langerhans cells in addition to their well-known impaired T cell functions. They also have an impaired cell-mediated response to contact sensitization with 1-chloro-2,4,6-trinitrobenzene. This hyporesponsiveness in aged mice can be almost completely reversed by IL-2 and is marginally improved by IFN-gamma. Exposure of skin from aged mice to interleukin-2 or interferon-gamma, both in vivo and in vitro, causes increases in the density of Ia+ Langerhans cells to levels approximating those in young mice. Since IFN-gamma causes partial restitution while IL-2 fully restores the contact hypersensitivity in aged animals, we conclude that the hyporesponsiveness in aged mice results both from defective Ia antigen expression on the antigen-presenting Langerhans cells and from deficient T cell function.

Endogenous pyrogen/interleukin-1 production in aged rats

The effect of aging on the ability of macrophages to produce endogenous pyrogen/interleukin-1 (EP/IL-1) was tested in 13 young adult (2-3 mo) and 13 aged (24-26 mo) Fischer rats using a febrile response assay. Peritoneal macrophages from aged rats produced EP/IL-1 as well as young adult rats. Decreased production of EP/Il-1 does not appear to explain the diminished febrile response seen in the elderly.

Impaired antigen presenting function of macrophages from aged mice

Using antigen-induced proliferation assay the presence of macrophages was found to be essential for the development of the T cell response. Decreased ability of antigen presentation by macrophages from aged A/J mice was detected.

Effect of age on fever and acute-phase response of rats to endotoxin and Salmonella typhimurium

Age-related effects on endogenous pyrogen-mediated febrile and acute-phase responses to endotoxin and Salmonella typhimurium challenge were investigated in young adult and aged Fisher 344 rats. After injection of endotoxin, the febrile response over 6 h and the fall in plasma iron and zinc after 6 h were determined in 14 young adult and 14 aged rats in their thermoneutral zone (26 degrees C) and in 14 young adult and 14 aged rats maintained in a cold environment (15 degrees C). Although at 26 degrees C aged rats showed only a slightly diminished febrile response compared with that of young adult rats, at 15 degrees C they had a markedly diminished febrile response compared with that of young adult rats. At both 26 and 15 degrees C, the injection of endotoxin led to a fall in iron and zinc concentrations in the plasma of both young adult and aged rats. The intact trace metal response diminished but febrile response suggest that aged rats are able to produce endogenous pyrogen but have a reduced capacity to respond to this substance. In 22 aged and 22 young adult rats maintained at 26 degrees C and challenged with S. typhimurium, the febrile response was significantly less in the aged rats but the survival rate was virtually identical. When 10 young adult and 10 aged rats were placed at a temperature of 15 degrees C after injection with S. typhimurium, the febrile response in the aged rats was significantly lower than that in the young adult rats at only one time point, and the survival rate did not differ between the two age groups. Survival after challenge with S. typhimurium was not influenced adversely by the diminished febrile response.