The role of stress hormones in exercise-induced suppression of alveolar macrophage antiviral function

Extreme anaerobic exercise causes reduced cytotoxicity and increased cytokine production by peripheral blood lymphocytes

Exercise has many beneficial effects for our body, but can become detrimental at high intensity, especially for our immune system. Little is known about the underlying mechanism of impaired immune functionality under conditions of intense physical strain. Freedivers, people who dive to high depths on a single breath, perform extreme exercise under anaerobic conditions. In this study, we investigated the impact of freediving on the cytotoxic arm of the immune system. At rest, elite freedivers did not display changes in their immunological profile compared to non-diving controls. In contrast, after a freedive, granzyme B and IL-2 production were reduced, whereas IFNγ and TNF secretion were increased by cytotoxic immune cells. Using in vitro models mimicking freedive conditions, we could show that hypoxia in combination with stress hyperglycemia had a negative impact on Granzyme B secretion, whereas IL-2 production was inhibited by stress hormones. Our findings suggest that in response to extreme exercise, cytotoxic immune cells transiently change their functional profile to limit tissue damage.

Involvement of dopaminergic signaling in the cross talk between the renin-angiotensin system and inflammation

The renin-angiotensin system (RAS) is a fundamental regulator of blood pressure and has emerged as an important player in the control of inflammatory processes. Accordingly, imbalance on RAS components either systemically or locally might trigger the development of inflammatory disorders by affecting immune cells. At the same time, alterations in the dopaminergic system have been consistently involved in the physiopathology of inflammatory disorders. Accordingly, the interaction between the RAS and the dopaminergic system has been studied in the context of inflammation of the central nervous system (CNS), kidney, and intestine, where they exert antagonistic actions in the regulation of the immune system. In this review, we summarized, integrated, and discussed the cross talk of the dopaminergic system and the RAS in the regulation of inflammatory pathologies, including neurodegenerative disorders, such as Parkinson’s disease. We analyzed the molecular mechanisms underlying the interaction between both systems in the CNS and in systemic pathologies. Moreover, we also analyzed the impact of the commensal microbiota in the regulation of RAS and dopaminergic system and how it is involved in inflammatory disorders. Furthermore, we summarized the therapeutic approaches that have yielded positive results in preclinical or clinical studies regarding the use of drugs targeting the RAS and dopaminergic system for the treatment of inflammatory conditions. Further understanding of the molecular and cellular regulation of the RAS-dopaminergic cross talk should allow the formulation of new therapies consisting of novel drugs and/or repurposing already existing drugs, alone or in combination, for the treatment of inflammatory disorders.

The COVID-19 pandemic and physical activity

The SARS-CoV-2-caused COVID-19 pandemic has resulted in a devastating threat to human society in terms of health, economy, and lifestyle. Although the virus usually first invades and infects the lung and respiratory track tissue, in extreme cases, almost all major organs in the body are now known to be negatively impacted often leading to severe systemic failure in some people. Unfortunately, there is currently no effective treatment for this disease. Pre-existing pathological conditions or comorbidities such as age are a major reason for premature death and increased morbidity and mortality. The immobilization due to hospitalization and bed rest and the physical inactivity due to sustained quarantine and social distancing can downregulate the ability of organs systems to resist to viral infection and increase the risk of damage to the immune, respiratory, cardiovascular, musculoskeletal systems and the brain. The cellular mechanisms and danger of this "second wave" effect of COVID-19 to the human body, along with the effects of aging, proper nutrition, and regular physical activity, are reviewed in this article.

The Effect of Race Training on the Basal Gene Expression of Alveolar Macrophages Derived From Standardbred Racehorses

Mild-to-moderate equine asthma is prevalent in young racehorses, particularly early in their training period. Although the precise etiopathogenesis remains undetermined, it is possible that the susceptibility of this population might partly reflect an exercise-associated immune derangement at the level of the airway. We performed a genome-wide basal gene expression scan on alveolar macrophages (AMs) isolated from Standardbred racehorses before and after commencement of competition race training with a view to identifying any exercise-associated gene expression modulation consistent with functional alterations, which might reflect training-associated immunological derangement. Microarray technology was used to analyze the basal gene expression profiles of bronchoalveolar fluid-derived AMs, harvested from six systemically healthy Standardbred racehorses before (T0) and after (T1) entry into training. In addition, AM lipopolysaccharide (LPS)-induced TNF-α and IL-10 release at T0 and T1 was assessed. Although the data revealed significant interhorse heterogeneity in relation to the magnitude of individual gene expression at each timepoint, within each horse, several inflammatory-related genes [e.g., chemokine ligands, interferons, and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB)] declined in expression from T0 to T1. Entry into training did not significantly alter AM LPS-induced TNF-α or IL-10 release. The data support a direct effect of training on AM basal gene expression, particularly with respect to immune-related genes. The pattern of training-associated differential gene expression may indicate relative downregulation of inflammatory-related genes, consistent with an immunosuppressive effect of training and an increased susceptibility to opportunistic pathogens.

Physical Activity and Gastric Cancer Risk in Patients with and without Helicobacter pylori Infection in A Korean Population: A Hospital-Based Case-Control Study

Although physical activity (PA) is beneficial for prolonging lifespan, evidence for the protective role of PA against the development of gastric cancer (GC) is not yet well established. This study assessed the association between PA and GC risk in patients with and without Helicobacter pylori (H. pylori) infection in a Korean population. In total, 415 GC patients and 830 controls were enrolled at the National Cancer Center, Korea. The International Physical Activity Questionnaire-Short Form was used to collect PA data. The odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression models. In the H. pylori-positive group, subjects who engaged in regular exercise showed a significantly reduced risk of GC in the entire population (OR = 0.52, 95% CI = 0.38⁻0.70) and in females (OR = 0.60, 95% CI = 0.21⁻0.64). Subjects who engaged in a high level of total PA showed a significantly reduced risk of GC relative to subjects in the lowest tertile in the fully adjusted model (OR = 0.46, 95% CI = 0.32⁻0.65, p-trend < 0.001). There was an inverse association between PA and GC risk in the entire population, and in the H. pylori-positive subgroup. Our data indicate the need for the promotion of all domains of PA, especially for Korean populations.

The exercise-glucocorticoid paradox: How exercise is beneficial to cognition, mood, and the brain while increasing glucocorticoid levels

Exercise is known to have beneficial effects on cognition, mood, and the brain. However, exercise also activates the hypothalamic-pituitary-adrenal axis and increases levels of the glucocorticoid cortisol (CORT). CORT, also known as the "stress hormone," is considered a mediator between chronic stress and depression and to link various cognitive deficits. Here, we review the evidence that shows that while both chronic stress and exercise elevate basal CORT levels leading to increased secretion of CORT, the former is detrimental to cognition/memory, mood/stress coping, and brain plasticity, while the latter is beneficial. We propose three preliminary answers to the exercise-CORT paradox. Importantly, the elevated CORT, through glucocorticoid receptors, functions to elevate dopamine in the medial prefrontal cortex under chronic exercise but not chronic stress, and the medial prefrontal dopamine is essential for active coping. Future inquiries may provide further insights to promote our understanding of this paradox.

Benefits of oat β-glucan and sucrose feedings on infection and macrophage antiviral resistance following exercise stress

Oat β-glucan can counteract the exercise-induced increased risk for upper respiratory tract infection (URTI) in mice, which is at least partly mediated by its effects on lung macrophages. Substantial evidence in humans indicates that carbohydrate-containing sports drinks can offset the decreased immune function associated with stressful exercise. However, no studies in animals or humans have directly examined their effects on URTI using a controlled virus-challenge model. We examined the effects of sucrose feedings alone and in combination with oat β-glucan on susceptibility to infection and on macrophage antiviral resistance in mice following stressful exercise. These effects were also examined in rested, nonimmunocompromised control mice. Mice were assigned to one of four groups: H2O (water), sucrose (S), oat β-glucan (OβG), and sucrose + oat β-glucan (S+OβG). OβG and S treatments consisted of a solution of 50% OβG and 6% sucrose, respectively, and were administered in drinking water for 10 consecutive days. Exercise consisted of a treadmill run to fatigue performed on three consecutive days. Mice were then intranasally inoculated with a standardized dose of herpes simplex virus 1 (HSV-1) and monitored for morbidity and mortality for 21 days. Additional mice were used to determine macrophage antiviral resistance. In the exercise experiment, S, OβG, and S+OβG all reduced morbidity ( P < 0.05), while only S+OβG reduced mortality ( P < 0.05). Macrophage antiviral resistance was also increased in S, OβG, and S+OβG treatments ( P < 0.05). In resting controls, S and S+OβG reduced morbidity and mortality ( P < 0.05) and showed a trend toward increased macrophage antiviral resistance. There was no significant additive effect of S and OβG in either control or exercised animals. These data extend our previous work on the benefits of oat β-glucan to show that sucrose feedings have similar effects on susceptibility to respiratory infection and macrophage antiviral resistance in both resting controls and following exercise stress.

Exercise stress increases susceptibility to influenza infection

Exercise stress is associated with an increased risk for upper respiratory tract infection (URTI) while moderate exercise has been associated with a decreased risk. We have shown that exercise stress can increase susceptibility (morbidity, symptom severity and mortality) to HSV-1 respiratory infection, but there is little evidence on the effects of stressful exercise on susceptibility to the principal etiological agents of human respiratory infections, including influenza viruses. This study examined the effects of stressful exercise on susceptibility to influenza virus (A/Puerto Rico/8/34 (H1N1)). Mice were assigned to one of two groups: exercise (Ex) or control (Con). Exercise consisted of a treadmill run to volitional fatigue ( approximately 120 min) performed on three consecutive days. Fifteen minutes after the last bout of exercise or rest, mice (n=20-21/group) were intranasally inoculated with a standardized dose of influenza virus (0.25 HAU). Mice were monitored daily for morbidity (time to sickness), symptom severity and mortality (time to death) for 21 days. Exercise stress was associated with an increase in susceptibility to infection (morbidity, mortality and symptom severity on days 6 and 7; P<0.05). These data from a controlled influenza virus challenge model add significantly to the growing body of evidence that severe exercise can increase susceptibility to URTI.

Benefits of oat beta-glucan on respiratory infection following exercise stress: role of lung macrophages

Exercise stress is associated with an increased risk for upper respiratory tract infection (URTI). We have shown that consumption of the soluble oat fiber beta-glucan (ObetaG) can offset the increased risk for infection and decreased macrophage antiviral resistance following stressful exercise; however, the direct role of macrophages is unknown. This study examined the effect of macrophage depletion on the benefits of orally administered ObetaG on susceptibility to infection (morbidity, symptom severity, and mortality) following exercise stress. CL(2)MDP (Ex- H(2)O-CL(2)MDP, Ex-ObetaG-CL(2)MDP, Con-H(2)O-CL(2)MDP, Con-ObetaG-CL(2)MDP)-encapsulated liposomes were administered intranasally to deplete macrophages, and PBS (Ex-H(2)O-PBS, Ex-ObetaG-PBS, Con-H(2)O-PBS, Con-ObetaG-PBS)-encapsulated liposomes were given to macrophage-intact groups. Ex mice ran to volitional fatigue on a treadmill for 3 consecutive days, and ObetaG mice were fed a solution of 50% ObetaG in their drinking water for 10 consecutive days before infection. Fifteen minutes following the final bout of Ex or rest, mice were intranasally inoculated with 50 microl of a standardized dose of herpes simplex virus-1. Ex increased morbidity (P < 0.001) and symptom severity (P < 0.05) but not mortality (P = 0.09). The increase in morbidity and symptom severity was blocked by ObetaG consumption for 10 consecutive days before exercise and infection [morbidity (P < 0.001) and symptom severity (P < 0.05)]. Depletion of macrophages negated the beneficial effects of ObetaG on reducing susceptibility to infection following exercise stress, as evidenced by an increase in morbidity (P < 0.01) and symptom severity (P < 0.05). Results indicate that lung macrophages are at least partially responsible for mediating the beneficial effects of ObetaG on susceptibility to respiratory infection following exercise stress.

Neuroimmunomodulation during exercise: role of catecholamines as 'stress mediator' and/or 'danger signal' for the innate immune response

Exercise-induced neuroimmunomodulation is clearly accepted today. The present article reviews the main literature concerning the immunomodulatory capacity of catecholamines on the innate immune response during physical exercise, and presents our laboratory's latest results on this topic. It is well known that the effects of exercise on the immune system are mediated by the 'stress hormones and mediators'. Although catecholamines have usually been regarded as immunosuppressors, they may stimulate innate immune response mechanisms (such as phagocytic function) during exercise-induced stress, even without previous antigenic stimulation. The exercise-induced stimulation of the phagocytic response in particular and the innate responses in general have been considered as a prevention strategy of the athlete's organism in order to prevent the entry and/or maintenance of antigens in a situation where the adaptive immune response seems to be depressed, and thus it has been suggested that catecholamines participate as a 'stress mediator' of these effects. Given this hypothesis, it is also suggested here that catecholamines may be the first 'danger signal' to the immune system during exercise-induced stress.

Gender Differences in Macrophage Antiviral Function following Exercise Stress

INTRODUCTION

In male mice, exhaustive exercise increases susceptibility to respiratory infection following intranasal inoculation with herpes simplex virus-1 (HSV-1), whereas moderate exercise decreases the risk of infection. These responses have been linked with altered macrophage antiviral resistance, among other immune mechanisms. Female mice appear to be better protected from death than male mice following HSV-1 infection, although their response to exercise stress is similar. The possible immune mechanisms, however, have not been explored.

PURPOSE

This study was conducted to examine gender differences in macrophage antiviral resistance following repeated moderate and exhaustive treadmill exercise.

METHODS

Male (M, N = 36) and female (F, N = 36) CD-1 mice were randomly assigned to moderate exercise (Mod), exhaustive exercise (Exh), or control (C) groups. Exercise was done daily for 3 d; moderate exercise consisted of treadmill running for 90 min, whereas exhaustive exercise consisted of running to volitional fatigue (approximately 50 min).

RESULTS

Females had greater macrophage antiviral resistance to HSV-1 than males in C and Mod (P < 0.05), but not Exh; Mod increased resistance, whereas Exh decreased resistance similarly in both genders (P < 0.001).

CONCLUSIONS

These data suggest that altered macrophage antiviral resistance to HSV-1 may contribute to gender differences in in vivo resistance to HSV-1 respiratory infection at rest, as well as following moderate and exhaustive exercise.

Glucocorticoids produced during exercise may be necessary for optimal virus-induced IL-2 and cell proliferation whereas both catecholamines and glucocorticoids may be required for adequate immune defense to viral infection

Prolonged, exhaustive exercise has been associated with impaired immune responsiveness and increased susceptibility to infection. We have shown that one bout of exercise to fatigue followed by viral challenge increases mortality. Stress hormones such as corticosteroids and catecholamines have been suggested as potential mediators of exhaustive exercise-induced immunosuppression. The purpose of this study was to determine whether the administration of pharmacological agents to block the effect of catecholamines or corticosteroids would minimize the immunosuppression associated with this type of exercise. Mice either exercised to fatigue or were exposed to control conditions, and mice received an i.p. injection of either nadolol (beta-adrenergic receptor antagonist), RU486 (glucocorticoid type II receptor antagonist), or vehicle. Fifteen minutes post-exercise, mice were exposed to viral infection (Herpes simplex virus; HSV) via an intranasal route, and cells were collected 3 days post-infection. The results showed that exercise suppressed HSV-specific cell proliferation, HSV-specific IL-2, and IFN-gamma, but did not alter these same immune parameters when the mitogen ConA was used to stimulate cells. In addition, exercise reduced NK cell cytotoxicity, alveolar cell TNFalpha, and peritoneal IL-1beta, but did not affect IL-10. The pharmacological blockade did not attenuate the exercise-associated immunosuppression. In fact, RU486 treatment exacerbated the exercise-induced decline in HSV-induced IL-2 production and cell proliferation. RU486 and nadolol treatment also tended to decrease IL-10, IFN-gamma, TNFalpha (nadolol only), and IL-1beta (RU486 only) in both exercise and control mice, suggesting that stress hormones may be necessary during infection for optimal responsiveness. These findings suggest that suppression of immune defenses during viral infection persists for at least 3 days post-exercise, and stress hormones may be essential for optimal immune defense to viral challenge, rather than detrimental.

Role of lung macrophages on susceptibility to respiratory infection following short-term moderate exercise training

Moderate exercise training is associated with a decreased risk for upper respiratory tract infection in human and animal studies, but the mechanisms have not been elucidated. Lung macrophages play an important role in resistance to respiratory infection, and moderate exercise can enhance macrophage antiviral resistance, but no studies have directly tested the role of lung macrophages in this response. This study tested the effect of lung macrophage depletion on susceptibility to infection following short-term moderate exercise training. Mice were assigned to one of four groups: exercise (Ex) and resting controls (Con) with and without clodronate encapsulated liposomes (CL2MDP-lip). Ex mice ran for 1 h on a treadmill for 6 days at 36 m/min, 8% grade. Fifteen minutes following exercise or rest on the last day of training, mice were intranasally inoculated with a standardized dose of herpes simplex virus type 1. Clodronate (Ex-CL2MDP-lip and Con-CL2MDP-lip) or PBS liposomes (Ex-PBS-lip and Con-PBS-lip) (100 μl) were intranasally administered following exercise or rest on the 4th day of training and again on the 4th day postinfection. Morbidity, mortality, and symptom severity were monitored for 21 days. Exercise decreased morbidity by 36%, mortality by 61%, and symptom severity score on days 5–7 ( P < 0.05). Depletion of lung macrophages negated the beneficial effects of moderate exercise. This was indicated by no differences between Ex-CL2MDP-lip and Con-PBS-lip in morbidity (89 vs. 95%), mortality (79 vs. 95%), or symptom severity. Results indicate that lung macrophages play an important role in mediating the beneficial effects of moderate exercise on susceptibility to respiratory infection.

Effects of Oat ??-Glucan on Innate Immunity and Infection after Exercise Stress

PURPOSE

To test the effects of oat beta-glucan (ObetaG) on respiratory infection, macrophage antiviral resistance, and NK cytotoxicity.

METHODS

Mice were randomly assigned to one of four groups: Ex-H2O, Ex-ObetaG, Con-H2O, or Con-ObetaG. ObetaG was fed in the drinking water for 10 d before intranasal inoculation of HSV-1 or sacrifice. Exercise consisted of treadmill running to volitional fatigue (approximately 140 min) for three consecutive days. Fifteen minutes after the last bout of exercise or rest, mice (N = 24) were intranasally inoculated with a standardized dose of HSV-1. Mice were monitored twice daily for morbidity and mortality. Additional mice were sacrificed after exercise, peritoneal macrophages were obtained via i.p. lavage and assayed for antiviral resistance to HSV-1 (N = 18), and spleens were harvested and assayed for NK cell cytotoxicity (N = 12).

RESULTS

Exercise stress was associated with a 28% increase in morbidity (P = 0.036) and 18% increase in mortality (P = 0.15). Ingestion of ObetaG before infection prevented this increase in morbidity (P = 0.048) and mortality (P = 0.05). Exercise stress was associated with a decrease in macrophage antiviral resistance (P = 0.007), which was blocked by ingestion of ObetaG (P < 0.001). There were no effects of exercise or ObetaG on NK cytotoxicity.

CONCLUSION

These data suggest that daily ingestion of ObetaG may offset the increased risk of URTI associated with exercise stress, which may be mediated, at least in part, by an increase in macrophage antiviral resistance.

Exercise training-induced adaptations of immune response are mediated by β-adrenergic receptors in aged but not young mice

β-Adrenergic blockade was used to determine whether the exercise training-induced adaptations of immune response to viral infection were mediated by catecholamines in young and old mice. Young (2 mo) and older (16 mo) male BALB/c mice were randomly assigned to an exercise or control group, and half of the mice in each group received the β-adrenergic receptor antagonist nadolol. After 8 wk of moderate exercise training, mice were challenged with herpes simplex virus (HSV) 24 h postexercise. The results showed that exercise treatment increased anti-HSV IgM antibody, enhanced IL-10, and altered the kinetics of IFN-γ and IL-2 production in young and old mice. Unique to older mice, exercise decreased mitogen-induced proliferation, increased splenocytes, and tended to decrease memory cells (CD44hi+). In contrast, exercise increased mitogen-induced proliferation but decreased the number of splenic lymphocyte and CD4+ cells in young mice. β-Adrenergic blockade blunted the exercise-induced changes in anti-HSV IgM, IL-2, IFNγ, and mitogen-induced proliferation in old but not young mice. The findings suggest that some of the immunomodulatory effects of chronic exercise are mediated via β-adrenergic receptors and that the role of β-adrenergic receptors is age dependent.

Effects of moderate exercise and oat β-glucan on innate immune function and susceptibility to respiratory infection

Both moderate exercise and the soluble oat fiber β-glucan can increase immune function and decrease risk of infection, but no information exists on their possible combined effects. This study tested the effects of moderate exercise and oat β-glucan on respiratory infection, macrophage antiviral resistance, and natural killer (NK) cell cytotoxicity. Mice were assigned to four groups: exercise and water, exercise and oat β-glucan, control water, or control oat β-glucan. Oat β-glucan was fed in the drinking water for 10 days before intranasal inoculation of herpes simplex virus type 1 (HSV-1) or euthanasia. Exercise consisted of treadmill running (1 h/day) for 6 days. Macrophage resistance to HSV-1 was increased with both exercise and oat β-glucan, whereas NK cell cytotoxicity was only increased with exercise. Exercise was also associated with a 45 and 38% decrease in morbidity and mortality, respectively. Mortality was also decreased with oat β-glucan, but this effect did not reach statistical significance. No additive effects of exercise and oat β-glucan were found. These data confirm a positive effect of both moderate exercise and oat β-glucan on immune function, but only moderate exercise was associated with a significant reduction in the risk of upper respiratory tract infection in this model.

Chemical sympathectomy increases numbers of inflammatory cells in the peritoneum early in murine listeriosis

Here, we investigated the effects of sympathectomy on systemic bacterial loads following infection with Listeria monocytogenes, and on innate and specific immune responses in the peritoneum. Sympathectomy decreased systemic bacterial loads, and increased the number of peritoneal leukocytes and the percentage of peritoneal macrophages three days postinfection. This suggests that sympathectomy-induced decreases systemic bacterial loads are associated with increased recruitment of inflammatory cells into tissues during the innate immune response.

Prevalence and mechanisms of development of asthma and airway hyperresponsiveness in athletes

A high prevalence of asthma and airway hyperresponsiveness (AHR) has been reported in the athlete population. Factors potentially predisposing athletes to these conditions have not been clearly identified. Although moderate exercise has been shown to be beneficial in patients with asthma, repeated high-intensity exercise could possibly contribute to the development of asthma and AHR. This report provides an overview of the prevalence and possible mechanisms of development of asthma and AHR in the athlete population. The prevalence of asthma and AHR are higher in athletes than in the general population, particularly in swimmers and athletes performing sports in cold air environments. Possible mechanisms involved in the development of asthma in athletes are still uncertain; however, the content and physical characteristics of the inhaled air seem to be important factors, while immune and neurohumoral influences could play a modulatory role. This report stresses the need for further studies to better define the aetiologic factors and mechanisms involved in the development of asthma and AHR in athletes, and proposes relevant preventive and therapeutic measures.

Moderate exercise is associated with enhanced antigen-specific cytokine, but not IgM antibody production in aged mice

It has been suggested that moderate exercise may modulate the immune response in the elderly. We investigated whether moderate exercise had an effect on the immune response to viral infection in both young (2-4 months) and older (16-18 months) male BALB/cJ mice. Exercised (EX) mice ran on a treadmill for 8 weeks at a gradually increasing speed and duration whereas control (CON) mice were only handled briefly during each exercise session and then returned to their cages. Mice were infected with herpes simplex virus type 1 (HSV-1) 24 h post-exercise. Serum IgM anti-HSV antibody, HSV-1 specific Th1/Th2 cytokine production by spleen cells, and cytokine production by alveolar cells were measured 7 days post-infection. In the aged mice, exercise was associated with an enhanced production of the HSV-1 specific Th1-associated cytokines, interleukin (IL)-2 and interferon (IFN)-gamma, but had no effect on the Th2-associated cytokine IL-10 or IgM antibody. No effect of exercise was observed in young mice. IL-12 production was not altered by exercise, but aging was associated with altered IL-12 production in a tissue-specific manner. In conclusion, moderate exercise was associated with increased antigen-specific IL-2 and IFN-gamma production in response to viral challenge in older mice.

Prolonged exercise suppresses antigen-specific cytokine response to upper respiratory infection

Fatiguing exercise has been associated with an increased susceptibility to infection. This study examined the antigen-specific T-helper (Th) type 1 and Th type 2 cytokine response to herpes simplex virus (HSV) infection after an acute bout of fatiguing exercise. Male BALB/cJ mice ran on a treadmill (Ex) until voluntary fatigue (approximately 2.5 h), and control mice were handled and remained next to the treadmill. Mice were infected with HSV 20 min after exercise. Mice were killed 2 or 7 days postinfection, and sera and spleens were taken for the determination of HSV-specific serum IgM, splenocyte cytokine production during culture with HSV, and splenocyte natural killer cell cytotoxicity. Both Th type 1 [interleukin (IL)-2, interferon-gamma, IL-12] and Th type 2 (IL-10) cytokine production in spleen cell cultures, as well as natural killer cell cytotoxicity, decreased in Ex on day 2 postinfection. On day 7 postinfection, there was no difference in HSV-specific serum IgM or cytokine production by cells from control and Ex mice, with the exception of decreased IL-12 in Ex mice. These findings suggest that fatiguing exercise may alter the kinetics of antigen-specific cytokine production.

Special feature for the Olympics: effects of exercise on the immune system: exercise-induced modulation of macrophage function

Macrophages are important effector cells involved in phagocytosis, microbial killing and antitumour activity. Macrophages also display accessory cell function, in that they can present antigen to foster the development of T lymphocyte-mediated immunity. Recent work, including studies from this group, has demonstrated that acute and chronic exercise can affect many facets of macrophage biology. Manifestation of these effects depends on exercise intensity and duration, the function measured, the timing of measurement in relation to exercise and the concentration of the macrophage-activating stimulus. Exercise has potent stimulatory effects on phagocytosis, antitumour activity, reactive oxygen and nitrogen metabolism, and chemotaxis. Indeed, it has been shown that exercise training can increase macrophage antitumour activity in mice of different ages. However, not all functions are enhanced by exercise. Exercise-induced reductions in macrophage MHC II expression and antigen-presentation capacity have been documented. These findings bring up the possibility that exercise, and perhaps other stressors, activate macrophages for effector functions while downregulating accessory cell functions. To a large extent, the mechanisms responsible for the exercise-induced changes in macrophage function remain unknown, but may depend on exercise-induced changes in neuroendocrine factors. Future studies need to explore the effects in a mechanistic way and provide documentation as to their physiological significance.

Catecholamines inhibit microglial nitric oxide production

Viral infection in the central nervous system can induce nitric oxide production, which serves as a major host defense against viral infection. Under stress, catecholamine secretion is enhanced and immune responses are diminished in animals. Using N9 microglial cells, this study tested the effect of catecholamines on microglial nitric oxide production. Results indicated that each member of the catecholamine family (dopamine, norepinephrine and epinephrine) was a potent inhibitor of the microglial nitric oxide production. In contrast, dopa, the immediate precursor of the catecholamine biosynthesis pathway, was a weak inhibitor, except at very high concentrations. The inhibitory effect of catecholamines was mimicked by an alpha-adrenergic receptor agonist (phenylephrine) and by a beta-adrenergic receptor agonist (isoproterenol), but not by forskolin or analogs of cyclic adenosine monophosphate. Western blot analysis indicated that catecholamines caused a slight decrease in the formation of inducible nitric oxide synthase. These results suggest that catecholamines have the ability to block nitric oxide production by microglia, which could partially explain the impaired immune protection against viral infection in the central nervous system in stressed animals.

Inhibition of microglial nitric oxide production by hydrocortisone and glucocorticoid precursors

Viral and bacterial infection in the central nervous system can induce nitric oxide production, which serves as a major host defense against invading microorganisms. Glucocorticoids secretion is enhanced and immune responses are diminished in stressed animals or in patients suffering depression. Using N9 microglial cells, this study tested the hypothesis that glucocorticoids and their precursors caused an impaired immune defense in animals because these compounds could inhibit microglial nitric oxide production. Results indicated that both hydrocortisone and the synthetic glucocorticoid, dexamethasone, were potent inhibitors of the microglial nitric oxide production. While glucocorticoid precursors were not as potent as hydrocortisone, the potency of these precursors increased linearly as they advanced on the biosynthesis pathway. Northern and Western blot analyses indicated that hydrocortisone and dexamethasone might interfere with the inducible nitric oxide synthase at either the transcription or at the post-translational level, depending on the concentrations used. These results suggest that glucocorticoids have the ability to block nitric oxide production by microgila, which could partially explain the impaired immune protection against infection in the central nervous system in stressed animals.

Intracellular mechanisms responsible for exercise-induced suppression of macrophage antigen presentation

In a previous study, we demonstrated that exhaustive exercise suppressed peritoneal macrophage antigen presentation (AP). In this study, we explored the intracellular mechanism(s) responsible for this suppression. Pathogen-free male BALB/c mice (8 +/- 2 wk) were randomly assigned to either home cage control (HCC) or exhaustive exercise stress (Exh, 18-30 m/min for 3 h/day) treatment groups. The mice underwent treatments for a period of 4 days during induced peritoneal thioglycollate inflammation. Elicited macrophages were harvested, purified, and incubated with chicken ovalbumin (C-Ova, 2. 5 and 10 mg/ml) for 18 h. After macrophages were washed, they were cocultured with C-Ova-specific T cells for 48 h at which time the supernates were harvested and analyzed via ELISA for interleukin (IL)-2 as an indication of macrophage AP. There was no significant (P > 0.05) difference in macrophage AP between cells fixed with paraformaldehyde vs. those that remained unfixed, suggesting that Exh did not affect production of soluble factors influencing macrophage AP (i.e., IL-1, IL-4, PGE(2)). The ability of macrophages to generate C-Ova immunogenic peptides was analyzed using FITC-labeled C-Ova, which shows fluorescence only when degraded intracellularly. There was a significant ( approximately 20%, P < 0. 05) suppression in fluorescence in the Exh compared with HCC, indicating a possible defect in the ability of macrophages from Exh to degrade C-Ova into immunogenic peptides. Macrophages were also incubated with C-Ova immunogenic peptide in a manner identical to that for native C-Ova. We found a similar suppression ( approximately 22-38%, P < 0.05) in macrophage AP using a C-Ova peptide when compared with native C-Ova in the Exh group, indicating reduced major histocompatibility complex (MHC) II loading and/or C-Ova-MHC II complex cell surface expression. In conclusion, these data indicate an intracellular defect in the macrophage antigen processing pathway induced by Exh.

Exercise and cellular innate immune function

Epidemiological evidence suggests a link between the intensity of exercise and infectious and neoplastic disease. One likely way by which exercise exerts its effect on cancer and infection is by altering the function of the immune system. Cells of the innate immune system (i.e., macrophage [Mphi], natural killer [NK] cell, and polymorphonuclear neutrophils [PMN]) are first-line defenders against cancer and infectious disease by nature of their phagocytic, cytolytic, and antimicrobial properties. The purpose of this review is to define the role of cells of the innate immune system (i.e., Mphi, PMN, and NK cells) in infection and cancer, present current information regarding the effects of acute and chronic exercise on the quantification and functional activities of these cells, and briefly to discuss potential mechanisms as to how exercise affects these cells and describe how these changes may potentially affect susceptibility to infection and cancer. The effects of exercise on the number, functions, and characteristics of cells of the innate immune system are complex and are dependent several factors, including 1) the cell function or characteristic being analyzed; 2) the intensity, duration and chronicity of exercise; 3) the timing of measurement in relation to the exercise bout; 4) the dose and type of immunomodulator used to stimulate the cell in vitro or in vivo; and 5) the site of cellular origin. Further studies are needed to determine whether the exercise-induced changes in immune function alter incidence or progression of disease. Likewise, the mechanisms as to how exercise alters innate immune function are as yet unresolved.

Exercise effects on IFN-beta expression and viral replication in lung macrophages after HSV-1 infection

Mice exercised to fatigue and exposed to herpes simplex virus type 1 (HSV-1) exhibit greater mortality than control mice. In this study, we examined lung macrophage resistance to HSV-1 after exercise in terms of both viral replication and interferon (IFN)-beta production. We utilized the reverse transcriptase-rapid polymerase chain reaction to measure the IFN-beta mRNA content in alveolar macrophages. IFN release was measured with a bioassay, and viral replication within the macrophage was assessed by plaque titration. Exercised (Ex) mice ran on a treadmill until fatigue while control (Con) mice remained in lanes above the treadmill. After exercise, alveolar macrophages were removed and incubated with HSV-1. Alveolar macrophage IFN-beta mRNA was greater in Ex than in Con mice. Culture supernatant from infected macrophages showed a higher degree of IFN release and a higher number of infectious viral particles in Ex vs. Con mice. It is likely that the increase in IFN-beta mRNA occurs in response to a higher degree of viral replication. These results suggest that macrophages from Ex mice are less resistant to infection with HSV-1.