The effect of exercise on secretory and natural immunity

Physical exercise in kidney disease: A commonly undervalued treatment modality

BACKGROUND

Physical inactivity has been identified as a risk factor for multiple disorders and a strong association exists between chronic kidney disease (CKD) and a sedentary lifestyle. Even though physical activity is crucial in the development and progression of disease, the general focus of the current medical practice is the pharmacological perspective of diseases with inadequate emphasis on lifestyle intervention.

METHODS

In this narrative review we explain the pathophysiological mechanisms underlying the beneficial effects of physical exercise on CKD in addition to discussing the clinical studies and trials centred on physical exercise in patients with CKD.

RESULTS

Physical activity influences several pathophysiological mechanisms including inflammation, oxidative stress, vascular function, immune response and macromolecular metabolism. While exercise can initially induce stress responses like inflammation and oxidative stress, long-term physical activity leads to protective countermeasures and overall improved health. Trials in pre-dialysis CKD patients show that exercise can lead to reductions in body weight, inflammation markers and fasting plasma glucose. Furthermore, it improves patients' functional capacity, cardiorespiratory fitness and quality of life. The effects of exercise on kidney function have been inconsistent in these trials. In haemodialysis, peritoneal dialysis and kidney transplant patients exercise interventions improve cardiorespiratory fitness, walking capacity and quality of life. Combined training shows the best performance to increase peak oxygen uptake in haemodialysis patients. In kidney transplant recipients, exercise improves walking performance, quality of life and potentially arterial stiffness. However, exercise does not affect glucose metabolism, serum cholesterol and inflammation biomarkers. Long-term, adequately powered trials are needed to determine the long-term feasibility, and effects on quality of life and major clinical outcomes, including mortality and cardiovascular risk, in all CKD stages and particularly in kidney transplant patients, a scarcely investigated population.

CONCLUSION

Physical exercise plays a crucial role in ameliorating inflammation, oxidative stress, vascular function, immune response and macromolecular metabolism, and contributes significantly to the quality of life for patients with CKD, irrespective of the treatment and stage. Its direct impact on kidney function remains uncertain. Further extensive, long-term trials to conclusively determine the effect of exercise on major clinical outcomes such as mortality and cardiovascular risk remain a research priority.

Effect of Acute High-Intensity Interval Training on Immune Function and Oxidative Stress in Canoe/Kayak Athletes

The aim of this study was to investigate the effects of acute high-intensity interval training (HIIT) on immune function and oxidative stress in male canoe/kayak athletes who were well trained. A total of 22 participants were voluntarily recruited with an age range of 15.9 ± 2.3 years, height of 172.2 ± 5.5 cm, body mass of 63.30 ± 6.95 kg, and body fat of 13.77 ± 3.76%. The modified Wingate kayaking test on a kayak ergometer was performed by all participants. Blood samples were collected at three different time points: before the test (Pre-T), immediately after (Post-T), and 3 h post-test (Post-3 h). Saliva samples were collected at two different time points: before the test (Pre-T) and 3 h after the test (Post-3 h). Results indicated that acute canoe/kayak ergometry HIIT had significant effects on the percentages and counts of leukocytes, neutrophils, lymphocytes, and lymphocyte subsets. Additionally, it resulted in increased total LPS-stimulated neutrophil elastase release and alterations in plasma concentrations of superoxide dismutase, catalase, and TBARS. These findings suggest that conventional kayak HIIT regimens can have short-term effects on immune function and induce oxidative stress in athletes.

Vitamin D, exercise, and immune health in athletes: A narrative review

Vitamin D exerts important extra-skeletal effects, exhibiting an exquisite immune regulatory ability, affecting both innate and adaptive immune responses through the modulation of immunocyte function and signaling. Remarkably, the immune function of working skeletal muscle, which is fully recognized to behave as a secretory organ with immune capacity, is under the tight control of vitamin D as well. Vitamin D status, meaning hormone sufficiency or insufficiency, can push toward strengthening/stabilization or decline of immune surveillance, with important consequences for health. This aspect is particularly relevant when considering the athletic population: while exercising is, nowadays, the recommended approach to maintain health and counteract inflammatory processes, “too much” exercise, often experienced by athletes, can increase inflammation, decrease immune surveillance, and expose them to a higher risk of diseases. When overexercise intersects with hypovitaminosis D, the overall effects on the immune system might converge into immune depression and higher vulnerability to diseases. This paper aims to provide an overview of how vitamin D shapes human immune responses, acting on the immune system and skeletal muscle cells; some aspects of exercise-related immune modifications are addressed, focusing on athletes. The crossroad where vitamin D and exercise meet can profile whole-body immune response and health.

Resistance training and clinical status in patients with postdischarge symptoms after COVID-19: protocol for a randomized controlled crossover trial "The EXER-COVID Crossover Study"

BACKGROUND

Physical exercise induces a coordinated response of multiple organ systems, including the immune system. In fact, it has been proposed that physical exercise may modulate the immune system. However, the potential effect of an exercise program on COVID-19 survivors has not been investigated. Thus, the aim of this study is to evaluate the modifications in immunological parameters, physical condition, inflammatory profile, and perceived persistent symptoms after 6 weeks of supervised resistance training (RT), in addition to the standard care on the clinical status of patients with persistent COVID-19 symptoms. The objective of this protocol is to describe the scientific rationale in detail and to provide information about the study procedures.

METHODS/DESIGN

A total of 100 patients with postdischarge symptoms after COVID-19 will be randomly allocated into either a group receiving standard care (control group) or a group performing a multicomponent exercise program two times a week over a period of 6 weeks. The main hypothesis is that a 6-week multicomponent exercise program (EXER-COVID Crossover Study) will improve the immunological and inflammatory profile, physical condition, and persistent perceived symptoms (fatigue/tiredness, musculoskeletal pain, and shortness of breath) in patients with postdischarge symptoms after COVID-19.

DISCUSSION

Our results will provide insights into the effects of a multicomponent exercise program on immunological parameters, physical condition, inflammatory profile, and persistent perceived symptoms in patients with postdischarge symptoms after COVID-19. Information obtained by this study will inform future guidelines on the exercise training rehabilitation of patients with postdischarge symptoms after COVID-19.

TRIAL REGISTRATION

NCT04797871 , Version 2. Registered on March 15, 2021.

Influence of Nutritional Status and Physical Exercise on Immune Response in Metabolic Syndrome

Metabolic Syndrome (MetS) is a cluster of metabolic alterations mostly related to visceral adiposity, which in turn promotes glucose intolerance and a chronic systemic inflammatory state, characterized by immune cell infiltration. Such immune system activation increases the risk of severe disease subsequent to viral infections. Strong correlations between elevated body mass index (BMI), type-2-diabetes and increased risk of hospitalization after pandemic influenza H1N1 infection have been described. Similarly, a correlation between elevated blood glucose level and SARS-CoV-2 infection severity and mortality has been described, indicating MetS as an important predictor of clinical outcomes in patients with COVID-19. Adipose secretome, including two of the most abundant and well-studied adipokines, leptin and interleukin-6, is involved in the regulation of energy metabolism and obesity-related low-grade inflammation. Similarly, skeletal muscle hormones—called myokines—released in response to physical exercise affect both metabolic homeostasis and immune system function. Of note, several circulating hormones originate from both adipose tissue and skeletal muscle and display different functions, depending on the metabolic context. This review aims to summarize recent data in the field of exercise immunology, investigating the acute and chronic effects of exercise on myokines release and immune system function.

WAS POSTPONING THE TOKYO 2020 OLYMPIC AND PARALYMPIC GAMES A CORRECT DECISION?

ABSTRACT In December 2019, Wuhan, in China, attracted international attention due to a pneumonia outbreak caused by the new coronavirus (2019-nCoV). Infection by 2019-nCoV is more likely in elderly people with comorbidities or with associated chronic diseases. Due to the high transmission rate among humans, this disease is rapidly disseminated, which led to several events being canceled, including the Tokyo 2020 Olympic and Paralympic Games. The aim of this article is to discuss the risk factors for Olympic and Paralympic athletes, as well as for spectators, that justify the decision to postpone the Tokyo Games 2020. Regular physical exercise is associated with health and the prevention of chronic diseases. Although athletes generally appear to be healthy and physically fit, this may not be true. The immune system, which protects the organism from invasive microorganisms, can be affected by the duration and quality of sleep, as well as by physical exercise which influences the quality of the immune response. High volumes of high-intensity physical exercise, as well as changes in sleep patterns during the pre-competition period and the impacts of jet lag on athletes traveling for the Tokyo Games in 2020 may lead to immune system suppression, making these groups more vulnerable to infection by 2019-nCoV. Moreover, during the period planned for the games in 2020 the pandemic may be subsiding in some countries and increasing in others, and this was also taken into consideration as a risk factor. Hence, the decision taken to postpone the Tokyo 2020 Olympic and Paralympic Games until 2021 due to the 2019-nCoV was the correct one, and was extremely important to protect the health of Olympic and Paralympic athletes, as well as spectators. Level of evidence V; expert opinion .

Exercise reduces inflammatory cell production and cardiovascular inflammation via instruction of hematopoietic progenitor cells

A sedentary lifestyle, chronic inflammation and leukocytosis increase atherosclerosis; however, it remains unclear whether regular physical activity influences leukocyte production. Here we show that voluntary running decreases hematopoietic activity in mice. Exercise protects mice and humans with atherosclerosis from chronic leukocytosis but does not compromise emergency hematopoiesis in mice. Mechanistically, exercise diminishes leptin production in adipose tissue, augmenting quiescence-promoting hematopoietic niche factors in leptin-receptor-positive stromal bone marrow cells. Induced deletion of the leptin receptor in Prrx1-creER^T2; Lepr^fl/fl mice reveals that leptin's effect on bone marrow niche cells regulates hematopoietic stem and progenitor cell (HSPC) proliferation and leukocyte production, as well as cardiovascular inflammation and outcomes. Whereas running wheel withdrawal quickly reverses leptin levels, the impact of exercise on leukocyte production and on the HSPC epigenome and transcriptome persists for several weeks. Together, these data show that physical activity alters HSPCs via modulation of their niche, reducing hematopoietic output of inflammatory leukocytes.

The compelling link between physical activity and the body's defense system

This review summarizes research discoveries within 4 areas of exercise immunology that have received the most attention from investigators: (1) acute and chronic effects of exercise on the immune system, (2) clinical benefits of the exercise-immune relationship, (3) nutritional influences on the immune response to exercise, and (4) the effect of exercise on immunosenescence. These scientific discoveries can be organized into distinctive time periods: 1900-1979, which focused on exercise-induced changes in basic immune cell counts and function; 1980-1989, during which seminal papers were published with evidence that heavy exertion was associated with transient immune dysfunction, elevated inflammatory biomarkers, and increased risk of upper respiratory tract infections; 1990-2009, when additional focus areas were added to the field of exercise immunology including the interactive effect of nutrition, effects on the aging immune system, and inflammatory cytokines; and 2010 to the present, when technological advances in mass spectrometry allowed system biology approaches (i.e., metabolomics, proteomics, lipidomics, and microbiome characterization) to be applied to exercise immunology studies. The future of exercise immunology will take advantage of these technologies to provide new insights on the interactions between exercise, nutrition, and immune function, with application down to the personalized level. Additionally, these methodologies will improve mechanistic understanding of how exercise-induced immune perturbations reduce the risk of common chronic diseases.

Realising the Potential of Urine and Saliva as Diagnostic Tools in Sport and Exercise Medicine

Accurate monitoring of homeostatic perturbations following various psychophysiological stressors is essential in sports and exercise medicine. Various biomarkers are routinely used as monitoring tools in both clinical and elite sport settings. Blood collection and muscle biopsies, both invasive in nature, are considered the gold standard for the analysis of these biomarkers in exercise science. Exploring non-invasive methods of collecting and analysing biomarkers that are capable of providing accurate information regarding exercise-induced physiological and psychological stress is of obvious practical importance. This review describes the potential benefits, and the limitations, of using saliva and urine to ascertain biomarkers capable of identifying important stressors that are routinely encountered before, during, or after intense or unaccustomed exercise, competition, over-training, and inappropriate recovery. In particular, we focus on urinary and saliva biomarkers that have previously been used to monitor muscle damage, inflammation, cardiovascular stress, oxidative stress, hydration status, and brain distress. Evidence is provided from a range of empirical studies suggesting that urine and saliva are both capable of identifying various stressors. Although additional research regarding the efficacy of using urine and/or saliva to indicate the severity of exercise-induced psychophysiological stress is required, it is likely that these non-invasive biomarkers will represent "the future" in sports and exercise medicine.

SIgA and Upper Respiratory Syndrome During a College Cross Country Season

We examined the changes in salivary immunoglobulin A (SIgA) and the incidence of upper respiratory syndrome (URS) throughout a college cross-country season as well as the acute effect of a VO _2max test on SIgA. Subjects were 22 cross country athletes (XC) (20.7±0.3 years) and 23 matched controls (C) (20.4±0.2 years). Saliva samples were collected pre and post VO2max and at four training time points (August – November). Weekly logs indicating S&S of URS from which a total symptom score (TSS) was calculated were collected. There was a significant decrease in SIgA F(1,43)=10.742, p<0.001 and the secretion rate of SIgA F(1,43)=15.617, p<0.001 for XC at time points two through four. XC was also significantly lower than controls in those two variables across those time points. The secretion rate of SIgA and URS were negatively correlated at time point four R2=0.443, F(4,22)=26.9, p=0.001. There was a significant acute post exercise decrease in the secretion rate of SIgA, pre (M=21.44, SEM=3.95) and post (M=14.5, SEM=3.0), t(1,21)=2.185, p=0.039. Prolonged training resulted in decreased mucosal SIgA.

Probiotic strain Bacillus subtilis CU1 stimulates immune system of elderly during common infectious disease period: a randomized, double-blind placebo-controlled study

Background

Bacillus probiotics health benefits have been until now quite poorly studied in the elderly population. This study aimed to assess the effects of Bacillus subtilis CU1 consumption on immune stimulation and resistance to common infectious disease (CID) episodes in healthy free-living seniors.

Results

One hundred subjects aged 60–74 were included in this randomized, double-blind, placebo-controlled, parallel-arms study. Subjects consumed either the placebo or the probiotic (2.10⁹B. subtilis CU1 spores daily) by short periodical courses of 10 days intermittently, alternating 18-day course of break. This scheme was repeated 4 times during the study. Symptoms of gastrointestinal and upper/lower respiratory tract infections were recorded daily by the subjects throughout the study (4 months). Blood, saliva and stool samples were collected in a predefined subset of the first forty-four subjects enrolled in the study. B. subtilis CU1 supplementation did not statistically significantly decrease the mean number of days of reported CID symptoms over the 4-month of study (probiotic group: 5.1 (7.0) d, placebo group: 6.6 (7.3) d, P = 0.2015). However, in the subset of forty-four randomized subjects providing biological samples, we showed that consumption of B. subtilis CU1 significantly increased fecal and salivary secretory IgA concentrations compared to the placebo. A post-hoc analysis on this subset showed a decreased frequency of respiratory infections in the probiotc group compared to the placebo group.

Conclusion

Taken together, our study provides evidence that B. subtilis CU1 supplementation during the winter period may be a safe effective way to stimulate immune responses in elderly subjects.

Preventing or reversing immunosenescence: can exercise be an immunotherapy?

There is now a strong body of evidence demonstrating that aging is accompanied by severe alterations in the immune system, a process known as immunosenescence. Among these changes are alterations in T-cell subpopulation size, cytokine secretion pattern, cell replicative capacity and antibody production, all of which culminate in a proinflammatory state called 'inflammaging' and a diminished capacity to respond to new antigens. These alterations are closely related to the increased mortality and morbidity rates observed in this population. However, the role of exercise on the prevention or treatment of immunosenescence is virtually unknown. Data gathered from the literature regarding the effects of physical activity on immune system aging are still limited and conflicting, with existing reports either advocating benefits or asserting a lack of evidence. Exercise as part of a healthy lifestyle has already been shown to provide long-term benefits with regard to cardiovascular, cognitive, psychosocial and other aspects of the elderly. If positive effects are also observed for immunosenescence, exercise could be a highly cost-effective measure to improve human quality of life compared with other strategies currently being pursued.

Dehydration decreases saliva antimicrobial proteins important for mucosal immunity

The aim of the study was to investigate the effect of exercise-induced dehydration and subsequent overnight fluid restriction on saliva antimicrobial proteins important for host defence (secretory IgA (SIgA), α-amylase, and lysozyme). On two randomized occasions, 13 participants exercised in the heat, either without fluid intake to evoke progressive body mass losses (BML) of 1%, 2%, and 3% with subsequent overnight fluid restriction until 0800 h in the following morning (DEH) or with fluids to offset losses (CON). Participants in the DEH trial rehydrated from 0800 h until 1100 h on day 2. BML, plasma osmolality (Posm), and urine specific gravity (USG) were assessed as hydration indices. Unstimulated saliva samples were assessed for flow rate (SFR), SIgA, α-amylase, and lysozyme concentrations. Posm and USG increased during dehydration and remained elevated after overnight fluid restriction (BML = 3.5% ± 0.3%, Posm = 297 ± 6 mosmol·kg–1, and USG = 1.026 ± 0.002; P < 0.001). Dehydration decreased SFR (67% at 3% BML, 70% at 0800 h; P < 0.01) and increased SIgA concentration, with no effect on SIgA secretion rate. SFR and SIgA responses remained unchanged in the CON trial. Dehydration did not affect α-amylase or lysozyme concentration but decreased secretion rates of α-amylase (44% at 3% BML, 78% at 0800 h; P < 0.01) and lysozyme (46% at 3% BML, 61% at 0800 h; P < 0.01), which were lower than in CON at these time points (P < 0.05). Rehydration returned all saliva variables to baseline. In conclusion, modest dehydration (~3% BML) decreased SFR, α-amylase, and lysozyme secretion rates. Whether the observed magnitude of decrease in saliva AMPs during dehydration compromises host defence remains to be shown.

The effects of single and repeated bouts of soccer-specific exercise on salivary IgA

OBJECTIVE

Athletes frequently train with a short time recovery between sessions. The present aim was to establish how salivary IgA is altered following two soccer-specific intermittent exercise bouts performed on the same day.

DESIGN

Ten males participated in two experimental trials (single session, double session) 1 week apart, in a counterbalanced design. One trial entailed afternoon exercise only (PMEX), in which participants completed soccer-specific intermittent exercise starting at 14:30h. On the other occasion, participants performed two bouts of exercise [starting at 10:30h (AMEX(1)) and at 14:30h (PMEX(2))]. Timed unstimulated saliva samples were collected before and immediately after exercise.

RESULTS

Mean salivary IgA levels increased significantly immediately post-exercise in the single afternoon trial (PMEX). Performance of a second soccer-specific exercise bout in 1 day elicited an increase in heart rate and perceived exertion, compared with the single session, but did not appear to suppress salivary IgA outcomes. Performing soccer-specific exercise at these different times of day did not affect the salivary IgA concentration and secretion rate or salivary cortisol in the short term.

CONCLUSIONS

These findings suggest that, two 90-min exercise sessions performed at a moderate intensity with a 2.25h rest in between do not necessarily have adverse effects on salivary IgA levels.

Mucosal IgA and URTI in American college football players: a year longitudinal study

PURPOSE

The purpose of this study was: (a) to evaluate secretory immunoglobulin A (s-IgA) over a 12-month time period in college football players, and (b) to assess which of the commonly used standard methods of reporting s-IgA, either alone or in combination, serves as the best predictor of incidence of upper respiratory tract infection (URTI).

METHODS

One hundred college-aged males (75 varsity college football athletes, 25 nonfootball controls) were studied at eight points over a 12-month period. Resting mucosal IgA, protein and osmolality levels were determined from saliva using established procedures. In addition, incidence of URTI over the 12-month study duration was calculated from completed standard research logs. Repeated-measures ANOVA were conducted on the dependent variables and eight separate stepwise multiple regression analyses were conducted to predict the dependent variable "number of colds" by the independent variables, s-IgA, saliva flow rate, secretion rate of s-IgA, protein, s-IgA:protein, osmolality and s-IgA:osmolality at each data collection point.

RESULTS

There was a significant main effect for group, time, and the group x time interaction for s-IgA, the secretion rate of s-IgA, and the number of colds. In the regression model, the only variable that made a significant contribution to the variance at all time points was the secretion rate of s-IgA.

CONCLUSION

These findings suggest that a season of training in American football results in a significant decrease in both s-IgA and the secretion rate of s-IgA as well as an increase in the incidence of URTI. Among the various methods commonly employed to express s- IgA levels, the secretion rate of s-IgA may be the most useful clinical biomarker to predict the incidence of URTI.

Suppression of viral specific primary T-cell response following intense physical exercise in young but not old mice

Intense exercise to exhaustion leads to increased susceptibility and severity of infections. T cells play an essential role in control of viral infections. Whereas immune suppression is considered as a likely mechanism for exhaustive exercise-induced susceptibility to infection, we know little about viral-specific T-cell response following exhaustive exercise in young or old mice. In this study, one group of female young (10–12 wk) and old (22–24 mo) C57BL/6 mice was exposed to a single bout of intense exercise to exhaustion and immediately infected with lymphocytic choriomeningitis virus (LCMV). Eight days later, at the peak of expansion phase of T-cell response, we used tetramers of MHC class I molecules containing viral peptides to directly visualize antigen-specific CD8 T cells and a sensitive functional assay measuring interferon-γ production at the single-cell level to quantitate the CD8 and CD4 T-cell response. To evaluate the impact of intense exercise during both the initiation and evolution of the expansion phase of the T-cell response, a second group of young and old mice continued their daily bouts of intense exercise to exhaustion over the next 8 days. Our data show that, in young mice, LCMV infection following exhaustive exercise leads to suppression of LCMV-specific CD8 and CD4 T-cell responses, and this suppression effect occurs at the initiation of the expansion phase of viral-specific T cells. However, in old mice, unlike young mice, exhaustive exercise does not cause suppression of LCMV-specific T-cell responses.

Salivary IgA response to prolonged exercise in a hot environment in trained cyclists

The aim of this study was to determine the effects of prolonged exercise in hot conditions on saliva IgA (s-IgA) responses in trained cyclists. On two occasions, in random order and separated by 1 week, 12 male cyclists cycled for 2 h on a stationary ergometer at 62 (3)% V(.)O(2 max) [194 (4) W; mean (SEM)], on one occasion (HOT: 30.3 degrees C, 76% RH) and on another occasion (

CONTROL

20.4 degrees C, 60% RH). Water was available ad-libitum. Venous blood samples and 2-min whole unstimulated saliva samples were collected at pre, post and 2 h post-exercise. The s-IgA concentration was determined using a sandwich-type ELISA. Exercising heart rate, rating of perceived exertion, rectal temperature, corrected body mass loss (P<0.01) and plasma cortisol (P<0.05) were greater during HOT. The decrease in plasma volume post-exercise was similar on both trials [HOT: -6.7 (1.1) and

CONTROL

-6.6 (1.3)%; P<0.01]. Saliva flow rate decreased post-exercise by 43% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. Saliva IgA concentration increased post-exercise (P<0.05) with no difference between trials. Saliva IgA secretion rate decreased post-exercise by 34% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. These data show that a prolonged bout of exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in the heat, with ad libitum water intake, does not influence s-IgA responses to prolonged exercise.

Lymphocyte responses to maximal exercise: a physiological perspective

Exercise affects lymphocytes as reflected in total blood counts and the lymphocyte proliferative response. In addition, the production of immunoglobulins is impaired and during exercise the natural killer cell activity increases followed by suppression in the recovery period. Cardiopulmonary adjustments play a major role in lymphocyte response to physical activity. During intense exercise, the activated sympathetic nervous system increases blood flow to muscle as blood flow to splanchnic organs decreases. After exercise, sympathetic tone and blood pressure becomes reduced. The spleen contains lymphocytes and blood resides in gut vessels. A change in blood flow to these organs could affect the number of circulating lymphocytes. Reduced production of immunoglobulins results from suppressed B-cell function and, in response to exercise, mucosal immunity appears to decrease. Pulmonary hyperventilation and enhanced pressure in pulmonary vessels induce increased permeability of airway epithelium and stress failure of the alveolar-capillary membrane during intense exercise. A physiological perspective is of importance for evaluation of the exercise-induced change in lymphocyte function and, in turn, to post-exercise increased susceptibility to infections.

Influence of vitamin C supplementation on oxidative and salivary IgA changes following an ultramarathon

This randomized study measured the influence of vitamin C ( N=15) compared to placebo ( N=13) supplementation on oxidative and salivary immunoglobulin A (sIgA) changes in runners competing in an ultramarathon race. Seven days prior to the race, subjects ingested in randomized, double-blind fashion three 500-mg tablets of vitamin C or placebo each day. On race day, blood and saliva samples were collected 1 h pre-race, after 32 km of running, and then again immediately post-race. During the race, runners received 1 l/h carbohydrate beverages (60 g/l) with vitamin C (150 mg/l) or without in a double-blinded fashion. The runners also ingested two to three carbohydrate gel packs per hour (25 g each). Subjects in both groups ran a mean of 69 km (range 48-80 km) in 9.8 h (range 5-12 h) and maintained an intensity of approximately 75% maximal heart rate (HR(max)) throughout the ultramarathon race. Plasma ascorbic acid was higher in the vitamin C compared to placebo group pre-race, and increased significantly in the vitamin C group during the race [post-race, 3.21 (0.29) and 1.28 (0.12) microg/100 microl, respectively, P<0.001]. No significant group or interaction effects were measured for lipid hydroperoxide and F(2)-isoprostane, but both oxidative measures rose significantly during the ultramarathon race. Saliva volume, sIgA concentration, sIgA secretion and sIgA:saliva protein ratio all decreased significantly (P<0.001) during the race, but the pattern of change in all saliva measures did not differ significantly between groups. No significant correlations were found between post-race plasma vitamin C, oxidative, and saliva measures, except for a positive correlation between post-race serum cortisol and serum vitamin C (r=0.50, P=0.006). These data indicate that vitamin C supplementation in carbohydrate-fed runners does not serve as a countermeasure to oxidative and sIgA changes during or following a competitive ultramarathon race.

Salivary IgA response to prolonged exercise in a cold environment in trained cyclists

PURPOSE

The purpose of the present study was to determine the effect of a prolonged bout of exercise in freezing cold conditions on saliva immunoglobulin A (s-IgA) responses in endurance-trained males.

METHODS

Using a randomized cross-over design, 15 trained male cyclists cycled for 2 h on a stationary ergometer at 70% VO(2max) in an environmental chamber on one occasion at a temperature of -6.4 +/- 0.1 degrees C (cold) and on another occasion at a temperature of 19.8 +/- 0.2 degrees C (control). Trials began at 12:30 h to avoid the fall in s-IgA concentration that occurs during the morning hours. Unstimulated whole-saliva samples were collected over a 2-min period at preexercise, postexercise, and 2-h postexercise. The s-IgA concentration was determined using a sandwich-type ELISA method.

RESULTS

Saliva flow rate decreased postexercise by 31%, returning to preexercise levels by the 2-h postexercise collection (main effect of time: < 0.01). The decrease in saliva flow rate postexercise in the control trial (39% compared with 22% on cold trial) approached significance (interaction: = 0.08) and may have accounted for the corresponding increase in s-IgA concentration postexercise in the control trial (s-IgA concentration: control preexercise; 91 +/- 12; postexercise; 110 +/- 13 mg x L(-1); < 0.05). Saliva IgA secretion rate decreased postexercise by 19.5% returning to preexercise levels by 2-h postexercise measure (main effect of time: < 0.05).

CONCLUSIONS

These data show that performing a bout of prolonged exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in freezing cold conditions does not influence saliva flow rate or s-IgA secretion rate responses to prolonged exercise.

Exercise-induced immunodepression- plasma glutamine is not the link

The amino acid glutamine is known to be important for the function of some immune cells in vitro. It has been proposed that the decrease in plasma glutamine concentration in relation to catabolic conditions, including prolonged, exhaustive exercise, results in a lack of glutamine for these cells and may be responsible for the transient immunodepression commonly observed after acute, exhaustive exercise. It has been unclear, however, whether the magnitude of the observed decrease in plasma glutamine concentration would be great enough to compromise the function of immune cells. In fact, intracellular glutamine concentration may not be compromised when plasma levels are decreased postexercise. In addition, a number of recent intervention studies with glutamine feeding demonstrate that, although the plasma concentration of glutamine is kept constant during and after acute, strenuous exercise, glutamine supplementation does not abolish the postexercise decrease in in vitro cellular immunity, including low lymphocyte number, impaired lymphocyte proliferation, impaired natural killer and lymphokine-activated killer cell activity, as well as low production rate and concentration of salivary IgA. It is concluded that, although the glutamine hypothesis may explain immunodepression related to other stressful conditions such as trauma and burn, plasma glutamine concentration is not likely to play a mechanistic role in exercise-induced immunodepression.

Influências do exercício na resposta imune

RESUMO O estudo da relação entre o exercício e a resposta imune teve grande impulso a partir da metade da década de 70, tendo como principais áreas de interesse o estudo da infecção de vias aéreas superiores em atletas submetidos a grandes esforços, o exercício como modelo de estresse e a resposta do treinamento como resposta adaptativa frente a situações de estresse. A descrição da interação entre os sistemas imune e neuroendócrino foi de importância capital no desenvolvimento desses estudos. O exercício gerando um desvio da homeostase orgânica leva à reorganização das respostas de diversos sistemas, entre eles o sistema imune. É adequado dividir a resposta ao exercício em resposta aguda, resposta transitória ao estresse e resposta de adaptação crônica, na qual o treinamento capacita o organismo a lidar com o estímulo estressante de maneira mais adequada. Ambas as respostas afetam os diversos componentes do sistema imune, tanto a resposta inata em seu componente celular compreendendo neutrófilos, macrófagos e células natural killer, como em seu componente humoral, proteínas de fase aguda, sistema do complemento e enzimas, como o sistema imune adaptativo, em seu componente celular (linfócitos T e B), como no componente humoral (anticorpos e citocinas). Apesar das incorreções que cometemos quando das generalizações, podemos dizer que, de modo geral, o exercício de intensidade moderada, praticado com regularidade, melhora a capacidade de resposta do sistema imune, enquanto o exercício de alta intensidade praticado sob condições estressantes provoca um estado transitório de imunodepressão.

Effect of glutamine and protein supplementation on exercise-induced decreases in salivary IgA

Postexercise immune impairment has been linked to exercise-induced decrease in plasma glutamine concentration. This study examined the possibility of abolishing the exercise-induced decrease in salivary IgA through glutamine supplementation during and after intense exercise. Eleven athletes performed cycle ergometer exercise for 2 h at 75% of maximal oxygen uptake on 3 separate days. Glutamine (a total of 17.5 g), protein (a total of 68.5 g/6.2 g protein-bound glutamine), and placebo supplements were given during and up to 2 h after exercise. Unstimulated, timed saliva samples were obtained before exercise and 20 min, 140 min, 4 h, and 22 h postexercise. The exercise protocol induced a decrease in salivary IgA (IgA concentration, IgA output, and IgA relative to total protein). The plasma concentration of glutamine was decreased by 15% 2 h postexercise in the placebo group, whereas this decline was abolished by both glutamine and protein supplements. None of the supplements, however, was able to abolish the decline in salivary IgA. This study does not support that postexercise decrease in salivary IgA is related to plasma glutamine concentrations.

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 effects on mucosal immunity

The present review examines the effects of exercise on mucosal immunity in recreational and elite athletes and the role of mucosal immunity in respiratory illness. Habitual exercise at an intense level can cause suppression of mucosal immune parameters, while moderate exercise may have positive effects. Saliva is the most commonly used secretion for measurement of secretory antibodies in the assessment of mucosal immune status. Salivary IgA and IgM concentrations decline immediately after a bout of intense exercise, but usually recover within 24 h. Training at an intense level over many years can result in a chronic suppression of salivary immunoglobulin levels. The degree of immune suppression and the recovery rates after exercise are associated with the intensity of exercise and the duration or volume of the training. Low levels of salivary IgM and IgA, particularly the IgA1 subclass, are associated with an increased risk of respiratory illness in athletes. Monitoring mucosal immune parameters during critical periods of training provides an assessment of the upper respiratory tract illness risk status of an individual athlete. The mechanisms underlying the mucosal immune suppression are unknown.

Exercise and the immune system: regulation, integration, and adaptation

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It is suggested that exercise can be employed as a model of temporary immunosuppression that occurs after severe physical stress. The exercise-stress model can be easily manipulated experimentally and allows for the study of interactions between the nervous, the endocrine, and the immune systems. This review focuses on mechanisms underlying exercise-induced immune changes such as neuroendocrinological factors including catecholamines, growth hormone, cortisol, beta-endorphin, and sex steroids. The contribution of a metabolic link between skeletal muscles and the lymphoid system is also reviewed. The mechanisms of exercise-associated muscle damage and the initiation of the inflammatory cytokine cascade are discussed. Given that exercise modulates the immune system in healthy individuals, considerations of the clinical ramifications of exercise in the prevention of diseases for which the immune system has a role is of importance. Accordingly, drawing on the experimental, clinical, and epidemiological literature, we address the interactions between exercise and infectious diseases as well as exercise and neoplasia within the context of both aging and nutrition.

Effects of exercise and training on natural killer cell counts and cytolytic activity: a meta-analysis

Meta-analysis techniques have been used to accumulate data from 94 studies describing the natural killer (NK) cell response of some 900 volunteers to acute and chronic exercise. NK cell numbers have been indicated in terms of CD3-CD16+CD56+, CD16+ or CD56+ phenotypes, and cytolytic activity has been expressed per 10,000 peripheral blood mononuclear cells or in terms of lytic units. Acute exercise has been categorised as sustained moderate (50 to 65% of aerobic power), sustained vigorous (>75% of aerobic power), brief maximal or 'supramaximal', prolonged, eccentric or resistance, and repeated exercise. In general, there was a marked increase in NK cell count at the end of exercise, probably attributable to a catecholamine-mediated demargination of cells. Following exercise, cell counts dropped to less than half of normal levels for a couple of hours but, except in unusual circumstances (e.g. prolonged, intense and stressful exercise), normal resting values are restored within 24 hours. If activity is both prolonged and vigorous, the decrease in NK cell counts and cytolytic activity may begin during the exercise session. Although the usual depression of NK cell count seems too brief to have major practical importance for health, there could be a cumulative adverse effect on immunosurveillance and health experience in athletes who induce such changes several times per week. There is a weak suggestion of an offsetting increase in resting NK cell counts and cytolytic action in trained individuals, and this merits further exploration in studies where effects of recent training sessions are carefully controlled.

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.

Salivary IgA levels and infection risk in elite swimmers

The effects of exercise on the immune system has been shown to be dependent on the level of fitness of the subjects, the degree of intensity, and the duration of the exercise. A reduction in salivary IgA levels occurs after individual sessions of exercise.

PURPOSE

The purpose of this study was to assess the relationship between changes in salivary IgA and training volume, psychological stress, and infection rates in a cohort of 26 elite swimmers over a 7-month training period and to compare the changes with a group of 12 moderately exercising controls.

METHODS

Salivary IgA concentrations were measured by an electroimmunodiffusion. Exercise gradings were assessed by a standardized aerobic-anaerobic rating system. Psychological stress/anxiety was evaluated by the Spielberger State-Trait Anxiety Inventory. Infections were physician-verified.

RESULTS

Salivary IgA levels showed an inverse correlation with the number of infections in both elite swimmers and moderately exercising control subjects. The pretraining salivary IgA levels in swimmers were 4.1% lower for each additional month of training and 5.8% lower for each additional infection. The posttraining salivary IgA levels in swimmers were not significantly correlated with infection rates but were 8.5% lower for each additional 1 km swum in a training session and 7.0% lower for each additional month of training. The number of infections observed in the elite swimmers was predicted from regression models by the preseason (P = 0.05) and the mean pretraining salivary IgA levels (P = 0.006). The trends in pretraining salivary IgA levels over the 7-month season, calculated as individual slopes of pretraining IgA levels over time, were also predictive of the number of infections (P = 0.03) in the swimmers.

CONCLUSIONS

These results indicate that measurement of salivary IgA levels over a training season may be predictive for athletes at risk of infection.

Saliva composition and exercise

Little attention has been directed toward identifying the changes which occur in salivary composition in response to exercise. To address this, our article first refers to the main aspects of salivary gland physiology. A knowledge of the neural control of salivary secretion is especially important for the understanding of the effects of exertion on salivary secretion. Both salivary output and composition depend on the activity of the autonomic nervous system and any modification of this activity can be observed indirectly by alternations in the salivary excretion. The effects of physical activity (with reference to factors such as exercise intensity and duration, or type of exercise protocol) on salivary composition are then considered. Exercise might indeed induce changes in several salivary components such as immunoglobulins, hormones, lactate, proteins and electrolytes. Saliva composition might therefore be used as an alternative noninvasive indicator of the response of the different body tissues and systems to physical exertion. In this respect, the response of salivary amylase and salivary electrolytes to incremental levels of exercise is of particular interest. Beyond a certain intensity of exercise, and coinciding with the accumulation of blood lactate (anaerobic threshold or AT), a 'saliva threshold' (Tsa) does indeed exist. Tsa is the point during exercise at which the levels of salivary alpha-amylase and electrolytes (especially Na+) also begin to rise above baseline levels. The occurrence of the 2 thresholds (AT and Tsa) might, in turn, be attributable to the same underlying mechanism, that of increased adrenal sympathetic activity at high exercise intensities.

Recovery of the immune system after exercise

In the recovery phase after intense exercise is found suppressed blood concentration of lymphocytes, suppressed natural immunity of blood lymphocytes, decreased concentration of secretory IgA in mucosa, but increased blood concentration of neutrophils and increased levels in the blood of inflammatory cytokines. Thus, after intense long-term exercise, the immune system is characterized by concomitant inflammation and temporary suppression of the cellular immune system, the most pronounced findings being 2-4 h after the exercise. The underlying mechanisms are multifactorial and include neuroendocrinological and metabolic factors. High levels of cytokines, especially interleukin-6, are found in the recovery period after eccentric exercise, and it has been demonstrated that a close association exists between muscle damage and increased levels of interleukin-6.

Effect of exercise on milk immunoglobulin A

The major immunoglobulin (Ig) in human secretions is IgA. The immune properties of breast milk are well documented; however, the immunological influence of maximal exercise has not been established. The objective of this study was to investigate the role that exercise has on breast milk IgA and IgA subclasses. Breast milk was collected from 17 lactating women (4.6 +/- 2.3 months postpartum) before and after randomized exercise and control periods. The exercise treatment was a maximal graded treadmill test (VO2max = 30.3 +/- 5.7 mL x min-1 x kg-1). Milk was collected at rest, the breasts were emptied, and samples obtained 10, 30, and 60 min following either exercise or 30-min control rest periods. IgA concentrations were established by enzyme-linked immunosorbent assay. The results indicated that samples taken 10 and 30 min after the exercise period had significantly lower (P < or = 0.05) milk IgA concentrations (21.0 +/- 1.8 and 21.8 +/- 1.4 microg x mL-1, respectively) than the corresponding control resting samples (52.8 +/- 3.5 and 79.3 +/- 7.7 microg x mL-1). The exercise samples were similar to the control samples at 60 min (134.0 +/- 24.6 and 116.0 +/- 15.4 microg x mL-1, respectively), indicating that by 1 h, milk IgA production had recovered. The IgA1 data showed a similar significant decrease (P < or = 0.05) at 10 min postexercise, which also returned to control concentrations by the 30- and 60-min collection intervals. There was no significant change in the milk IgA2 concentrations at any of the time points studied. Milk IgA concentrations increased significantly in both exercise and resting control groups after the breasts were emptied, suggesting that breast emptying stimulated milk IgA synthesis. The results provide evidence that exercise alters milk IgA and IgA1 concentrations for 10-30 min after exhaustive exercise, but recovers by 1 h, and provide additional support for exercise effects on the mucosal immune system.

In vivo cell-mediated immunity and vaccination response following prolonged, intense exercise

Epidemiological and experimental studies have shown increased frequency and severity of infections after intense, long-term exercise. This study examines whether an in vivo impairment of the cell-mediated immunity and antibody production can be demonstrated after intense, long-term exercise. Twenty-two male triathletes performed one-half an ironman (group A). Vaccinations with tetanus and diphtheritis toxoid and purified pneumococcal polysaccharide were given after the exercise. Furthermore, a skin test with seven different antigens was applied on the forearm. Antibody titers were measured before and 2 wk after the exercise. The skin test was read 48 h after the application. Eleven non-exercising triathletes (group B) and 22 moderately trained men (group C) were used as control groups. Group A revealed a significantly lower skin test response to the tetanus antigen than both groups B and C. In group A, a smaller cumulative response (sum of the diameters of indurations and number of positive skin test spots) was found than in both groups B and C. No differences in antibody titers were found among the three groups. Thus, the in vivo cell-mediated immunity was impaired in the first days after prolonged, high intensity exercise, whereas there was no impairment of the in vivo antibody production measured 2 wk after vaccination.

Saliva and marathon running

The aim of this study was to follow changes in saliva and serum after strenous prolonged exercise. Twenty individuals, three women and 17 men, 24-62 years old, well-trained but not at elite level, participating in the Stockholm Marathon, were selected for the study. Two of the subjects broke the race after 20 km. Three samples of saliva were collected, i.e. (i) just before the race, (ii) directly after the race, and (iii) 1 h after the race. Paraffin-stimulated whole saliva, resting non-stimulated whole saliva and citric acid-stimulated parotid saliva were investigated. In all three types of saliva, there was a decrease in secretion rate and only 14 of the 18 participants could produce resting non-stimulated whole saliva directly after the race. The salivary concentration of chloride, phosphate, potassium, amylase, hexosamine, sialic acid and salivary peroxidase were significantly higher after than before the race. There were no significant changes in salivary pH and buffer capacity. The total protein concentration was increased in all types of saliva after the race. To conclude, there were several changes in the saliva composition just after the marathon, but most of the values were back to baseline after 1 h of rest. However, the values for sodium, calcium, phosphate, salivary peroxidase, amylase and salivary IgA were still elevated 1 h after the race.

Immune response to heavy exertion

Epidemiological data suggest that endurance athletes are at increased risk for upper respiratory tract infection during periods of heavy training and the 1- to 2-wk period following race events. There is growing evidence that, for several hours subsequent to heavy exertion, several components of both the innate (e.g., natural killer cell activity and neutrophil oxidative burst activity) and adaptive (e.g., T and B cell function) immune system exhibit suppressed function. At the same time, plasma pro- and anti-inflammatory cytokines are elevated, in particular interleukin-6- and interleukin-1-receptor antagonist. Various mechanisms explaining the altered immunity have been explored, including hormone-induced trafficking of immune cells and the direct influence of stress hormones, prostaglandin-E2, cytokines, and other factors. The immune response to heavy exertion is transient, and further research on the mechanisms underlying the immune response to prolonged and intensive endurance exercise is necessary before meaningful clinical applications can be drawn. Some attempts have been made through chemical or nutritional means (e.g., indomethacin, glutamine, vitamin C, and carbohydrate supplementation) to attenuate immune changes following intensive exercise.

Lymphocyte redistribution in connection with physical activity in the rat

Previous studies have demonstrated numerous immunobiological changes in connection with exercise. A decrease in peripheral blood mononuclear white cells (PBMC) 2 h after intense exercise has been shown. This lymphocytopenia in humans after exercise is thought to be of great importance regarding the morbidity to viral infection. We constructed an animal experimental set-up, previously published, to investigate the exercise-induced lymphocyte redistribution. The experimental set-up allowed us to draw blood from catheters implanted in the right carotid artery in rats. PBMC were isolated and labelled with In111 and reinfused before the exercise run on a treadmill to exhaustion. The runner and control rats were killed and dissection performed 1 h after the exercise. Tissue samples were weighed and measured in a gamma counter. Furthermore, blind microscopic examinations of selected tissues were performed to study a hypothesized accumulation of blood mononuclear cells in relation to muscle fibre lesions. We found that the total number of PBMC in the running rats was decreased (P = 0.018) and granulocytes increased, 1 h after the exercise (P = 0.028). Similar findings in humans in connection with physical activity have been observed. The percentage of total injected counts per minute per gram tissue (% c.p.m. g-1) showed significantly lower values in the liver and kidney from runners than from controls (P = 0.032 and P = 0.028). These findings might be the result of a visceral hypoflow in connection with exercise. Furthermore, a tendency to decreased % c.p.m. g-1 in the lungs were seen in the exercised rats (P = 0.083) indicating a possible redistribution from the lungs during the run. Light microscopy demonstrated an accumulation of PBMC around muscle fibre lesions, but there was no significant difference between runners and controls. Furthermore, no significant difference in % c.p.m. g-1 was found between working muscle groups in runner and control rats. In conclusion, the demonstration of the redistribution of PBMC from the liver and kidney in the exercised rats and the absence of any significant accumulation of PBMC in working muscles or other organs, do not explain the lymphocytopenia demonstrated here.

The effect on immunity of long-term intensive training in elite swimmers

The impact of long-term training on systemic and mucosal immunity was assessed prospectively in a cohort of elite swimmers over a 7-month training season in preparation for national championships. The results indicated significant suppression (P < 0.05) of serum IgA, IgG and IgM and salivary IgA concentration in athletes associated with long-term training at an intensive level. There was also a trend towards lower IgG2 subclass levels in serum in athletes compared with controls (P = 0.07). There were no significant changes in numbers or percentages of B or T cell subsets, but there was a significant fall in natural killer (NK) cell numbers and percentages in athletes over the training season (P < 0.05). After individual training sessions there was a significant decrease in salivary IgA levels for athletes compared with controls (P = 0.002). In athletes there was a downward trend in salivary IgA levels over the 7-month training period in both the pre-exercise (P = 0.06) and post-exercise samples (P = 0.04). There were no significant trends in salivary IgG levels over the study period in either athletes or controls. The only significant change in salivary IgM levels was an increase in detection rate in the pre-competition phase in athletes (P = 0.03). The study suggests that training of elite athletes at an intensive level over both short- and long-time frames suppresses both systemic and mucosal immunity. Protracted immune suppression linked with prolonged training may determine susceptibility to infection, particularly at times of major competitions.

How physical exercise influences the establishment of infections

During exercise, leucocytes are recruited to the blood, and if muscle damage occurs the cytokine level is enhanced. After prolonged, intense exercise the number of lymphocytes in the blood is reduced, and the function of natural killer cells is suppressed; furthermore, secretory immunity is impaired. During this time of immunodepression, often referred to as 'the open window', the host may be more susceptible to micro-organisms bypassing the first line of defence. This is of interest to top athletes who perform frequent severe exercise. Clinical observations regarding an increased risk of infections in top athletes are compatible with this model. However, in those performing regular moderate exercise the immune system will often be temporarily enhanced and this will protect these individuals from infections.

Potential impact of physical activity and sport on the immune system--a brief review

Description is given of methods that can evaluate the main functional elements of the immune system. Acute responses to exercise depend on the intensity and duration of the required activity relative to the individual's fitness level. Moderate endurance exercise causes either no change or an enhancement of such indices as total leucocyte count, granulocyte, monocyte, lymphocyte and natural killer cell count, total T cell count, helper:suppressor cell ratio, cell proliferation in response to mitogens, serum immunoglobulin levels, and in vitro immunoglobulin production. However, exhausting exercise tends to produce adverse changes in these same indices, particularly if the physical activity is accompanied by environmental or competitive stress. Moderate, appropriately graded training reduces reactions to any given absolute intensity of exercise. When pursuing a more demanding training regimen, it is important that the exerciser optimize immune responses. If athletic preparation is pursued to the level of staleness and/or muscle damage, it can have substantial negative implications for many aspects of immune function, including resistance to acute infections, HIV infections, ageing, cancer and other conditions influenced by the immune system.