Impact of heat exposure and moderate, intermittent exercise on cytolytic cells

The Effect of Acute Physical Exercise on NK-Cell Cytolytic Activity: A Systematic Review and Meta-Analysis

Background

Data on changes in natural killer cell cytolytic activity (NKCA) in response to acute physical exercise are contradictory.

Objective

The aim of this systematic review, meta-analysis and meta-regression is to (1) examine the effect of acute physical exercise on NKCA, (2) shed more light on the moderating factors, and (3) test the assumption of NKCA suppression subsequent to performing sports.

Methods

Two comparisons of NKCA were performed: (1) pre- versus post-exercise and (2) pre-exercise versus recovery. Data were acquired through a systematic search of MEDLINE (via PubMed), Scopus, and SportDiscus. Studies were eligible for inclusion if the effect of acute physical exercise was assessed including a passive control group and reporting NKCA prior to and immediately after the trial, and during the first 2 h of recovery. To better explain between-study heterogeneity, a moderator analysis was conducted.

Results

Pooled estimate from 12 studies reporting 18 effect sizes show that NKCA is largely elevated by acute physical exercise (Hedges’ g = 1.02, 95% CI 0.59–1.46, p < 0.01). Meta-regressions reveal that this effect is larger for endurance versus resistance exercise and increases with the intensity of exercise (both p < 0.01), whereas the blood material used in the assay (p = 0.71), and the quantitative change in NK-cell count (R² = 0%, p = 0.55) do not play a significant role. Physical exercise does not affect the level of NKCA after the recovery period (g = 0.06, 95% CI − 0.37 to 0.50, p < 0.76).

Conclusions

This work provides solid evidence for elevated NKCA through performing sports which returns to baseline during the first 1–2 h of recovery, but not below the pre-exercise values providing counterevidence to the assumption of temporarily reduced NKCA. Remarkably, the functional change in NKCA exists independently from the quantitative change in NK-cell count.

PROSPERO registration number: CRD42020134257.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-020-01402-9.

Heat, Athletes, and Immunity

During exercise, body temperature rises as a result of increased energy metabolism and heat absorbed from the environment. In response to this rise in body temperature, blood flow increases and stress hormones are released. Together, blood flow and stress hormones stimulate increases in the number of circulating leukocytes and alterations in various aspects of immune function, including cytokine production. The extent of changes in leukocyte numbers, cytokine concentrations, and immune cell function depends on how high body temperature rises and the intensity and duration of exercise. In general, increases in body temperature of ≤ 1.8° F (1° C) induce mild changes in immune function, and such changes are unlikely to increase the risk of illness in athletes, firefighters, and military personnel who regularly exercise in hot conditions. More severe immune disturbances during exercise in extreme heat (≥ 106° F or 41° C) may contribute to classical symptoms of heatstroke.

Acute Effect of Qi-Training on Natural Killer Cell Subsets and Cytotoxic Activity

This study assesses the effects of Qi-training on natural killer cell cytotoxicity. Nine experimental subjects did 1 h of Qi-training, and 9 control subjects relaxed during the same time. Natural killer cell cytotoxicity increased 60% immediately after Qi-training (p<.01) and returned to the basal level within 2 h after training. Natural killer cell subset number did not change after Qi-training. Natural killer cell cytotoxicity and cell number were not significantly correlated. These data suggest that Qi-training has an acute stimulatory effect on natural killer cell activity, but has no effect on phenotypical changes in the natural killer cell subset.

The effects of chronic aerobic and anaerobic exercises n lymphocyte subgroups

Exercise is the strongest stress to which the body is ever exposed. The body responds to this stress through a set of physiological changes in its metabolic, hormonal and immunological systems. In this study, responses of the immune system to the long-term aerobic and anaerobic exercises have been investigated. Twenty-four sedentary male university students and officers participated in this study. Subjects were divided into two groups, each consisting of twelve people. Group-1 (age: 25.67 +/- 3.79 years, height: 174.83 +/- 5.15 cm, body mass: 72.17 +/- 8.05 kg) and Group-2 (age: 24.83 +/- 2.89 years, height: 175.3 +/- 6.68 cm, body mass: 70.67 +/- 6.15 kg). After physical examinations of the two groups, resting ECG, respiratory function tests and metabolic tests with the use of the breath by breath method were completed, and anerobic heart rates at the threshold level were determined. The first group was subjected to exercise using Monark ergometry cycles at a heart rate 10% below the threshold level for 8 weeks, 3 days a week, 30 min a day. The second group exercised at a heart rate 10% above the threshold level for 8 weeks, 3 days a week, 20 min a day. Heart rates were checked with the Polar Test during exercises. Pre-exercise (Ep) venous blood samples were taken from each group before their 1st and 24th exercises. Hb (gr), Hct (%), erythrocyte (x10(6)/microl), leukocyte (x10(6)/microl), leukocyte subpopulations (neutrophil, lymphocyte, monocyte, eosinophil, basophil %) and thrombocyte (x10(6)/microl) values were determined. CD3, CD4, CD8, CD19 and CD56 values were determined by Flow Cytometry method using monoclonal antibodies. The chronic effects of exercise were examined through a comparison of Ep blood samples at the 1st exercise with Ep blood samples at the 24th exercise. While the increase in the total leukocyte number was significant (p<0.05) in the first group, increase in the second group was found to be non-significant. When percentiles of leukocyte subpopulations were taken into consideration, changes in the first and second group were found to be non-significant. When lymphocyte subgroups were examined; in the first group a decrease in CD3 and CD4 percentiles to 7% and 12%, respectively (p<0.05) and a 65% increase (p<0.01) in the CD56 value were observed. In the second group a decrease in CD3 and CD4 percentiles to 13% and 17%, respectively (p<0.05) and a 73% increase (p<0.01) in the CD56 value were observed. The Sample-t Test and The Wilcoxon Test were used for statistical analysis.

Beneficial effects of the Nishino breathing method on immune activity and stress level

OBJECTIVES

Immunologic activity and stress level in practitioners of the Nishino breathing method were assayed before and after 90 minutes of an exercise class, in order to assess the value of the method.

BACKGROUND

The Nishino Breathing Method was developed by Kozo Nishino, a former ballet choreographer and a master of martial arts, in the 1970s in an attempt to develop Ki (an internal life energy or a spiritual energy). Although he developed his method independently of the Chinese qigong practice, there are certain similarities between them, in that both involve visualization of internal energy flow, slow body movements, and the emission of life energy from one's hand.

METHODS

Twenty one (21) practitioners were tested. Their blood was withdrawn before and after a class, and the activity of natural killer (NK) cells and their cell numbers were assayed. The level of stress was also measured using the Lorish face scale method. The heart rate was also monitored.

RESULTS

The NK cell activity of 17 of 21 (76%) subjects increased after attending a class. The mean NK cell activity of the whole group of subjects increased after the practice (p < 0.03). The mean stress level was significantly reduced after the class (p < 0.001).

CONCLUSIONS

These results demonstrated that the Nishino Breathing Method can effectively enhance the immunoregulatory system and reduce stress even after one class. This indicates that the method would help improve the health of its practitioners if they continue to practice it.

Natural killer cell lytic activity and CD56dim and CD56bright cell distributions during and after intensive training

The purpose of this study was to examine the impact of intensive training for competitive sports on natural killer (NK) cell lytic activity and subset distribution. Eight female college-level volleyball players undertook 1 mo of heavy preseason training. Volleyball drills were performed 5 h/day, 6 days/wk. Morning resting blood samples were collected before training (Pre), on the 10th day of training (During), 1 day before the end of training (End), and 1 wk after intensive training had ceased (Post). CD3-CD16brightCD56dim (CD56dim NK), CD3-CD16dim/-CD56bright NK (CD56bright NK), and CD3+CD16-CD56dim (CD56dim T) cells in peripheral blood were determined by flow cytometry. The circulating count of CD56dim NK cells (the predominant population, with a high cytotoxicity) did not change, nor did the counts for other leukocyte subsets. However, counts for CD56bright NK and CD56dim T cells (subsets with a lower cytotoxicity) increased significantly ( P < 0.01) in response to the heavy training. Overall NK cell cytotoxicity decreased from Pre to End ( P = 0.002), with a return to initial values at Post. Lytic units per NK cell followed a similar pattern ( P = 0.008). Circulating levels of interleukin-6, interferon-γ, and tumor necrosis factor-α remained unchanged. These results suggest that heavy training can decrease total NK cell cytotoxicity as well as lytic units per NK cell. Such effects may reflect in part an increase in the proportion of circulating NK cells with a low cytotoxicity.

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.

Sepsis and mechanisms of inflammatory response: is exercise a good model?

OBJECTIVES

The immune changes induced by a bout of prolonged and vigorous exercise have been suggested to be a useful experimental model of sepsis and the inflammatory response. Available literature was reviewed to evaluate this hypothesis.

METHODS

Literature describing the immune response to various patterns of exercise was compared with data on the immune changes observed during sepsis and inflammation.

RESULTS

Although there are qualitative similarities between the immune responses to exercise and sepsis, the magnitude of the changes induced by most forms of exercise remains much smaller than in a typical inflammatory response. Indeed, the exercise induced changes in some key elements such as plasma cytokine concentrations are too small to be detected reliably by current technology.

CONCLUSIONS

If exercise is to provide a valid model of sepsis and the inflammatory response, it will be necessary to focus on subjects who are willing to exercise extremely hard, to use the pattern of exercise that has the greatest effect on the immune system, and to combine this stimulus with other psychological, environmental, or nutritional stressors.

Leukocyte counts and lymphocyte responsiveness associated with repeated bouts of strenuous endurance exercise

This study compared leukocyte counts and lymphocyte responsiveness during and after a second bout of high-intensity endurance exercise on the same day with the response to a similar but single bout of exercise. Nine athletes participated in three 24-h trials: 1) rest in bed (Rest); 2) one bout of exercise (One); and 3) two bouts of exercise (Two). All bouts consisted of 75 min at approximately 75% of maximal O(2) uptake on a cycle ergometer. Lymphocytes in whole blood were stimulated with monoclonal antibodies against CD2 and assessed by flow cytometry for expression of the early activation molecule CD69. The second bout of exercise in the Two trial was associated with significantly increased concentrations of total leukocytes, neutrophils, lymphocytes, CD4(+), CD8(+), and CD56(+) cells and a significantly decreased percentage of CD56(+) cells expressing CD69 compared with a single bout. Additionally, there was a significantly decreased CD69 fluorescence in CD56(+) cells postexercise. These differences suggest a "carry-over" effect in the immune system from a first to a second bout of exercise on the same day.

Mobilization of NK cells by exercise: downmodulation of adhesion molecules on NK cells by catecholamines

The change of plasma catecholamine concentration correlates with the change of natural killer (NK) activity and NK cell number in peripheral blood mononuclear cells (PBMC) during and after moderate exercise. We studied the causal relation between exercise-induced catecholamine and expression of adhesion molecules on NK cells during and after exercise. The expression of CD44 and CD18 on CD3(-)CD56(+) NK cells was significantly reduced during exercise (P < 0.01). When PBMC were stimulated with 10(-8)M norepinephrine in vitro, the expression of these adhesion molecules on CD3(-)CD56(+) NK cells was downmodulated within 30 min. The binding capacity of NK cells to a CD44 ligand, hyaluronate, was reduced by the stimulation with norepinephrine (P < 0.01). The intravenous injection of norepinephrine in mice decreased the expression of CD44 and CD18 on CD3(-)NK1.1(+) cells (P < 0.01) and increased the number of CD3(-)NK1.1(+) cells in PBMC (P < 0.01). These findings suggest that exercise-induced catecholamines modulate the expression of adhesion molecules on NK cells, resulting in the mobilization of NK cells into the circulation.

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.

beta-Endorphin and natural killer cell cytolytic activity during prolonged exercise. is there a connection?

This study was designed to test whether a single 50-mg dose of the opioid antagonist naltrexone hydrochloride, ingested 60 min before 2 h of moderate-intensity exercise (i.e., 65% peak O2 consumption), influenced the exercise-induced augmentation of peripheral blood natural killer cell cytolytic activity (NKCA). Ten healthy male subjects were tested on four occasions separated by intervals of at least 14 days. A rested-state control trial was followed by three double-blind exercise trials [placebo (P), naltrexone (N), and indomethacin] arranged according to a random block design. The indomethacin exercise trial is discussed elsewhere (S. G. Rhind, G. A. Gannon, P. N. Shek, and R. J. Shepherd. Med. Sci. Sports Exerc. 30: S20, 1998). For both the P and N trials, plasma levels of beta-endorphin were increased (P < 0.05) at 90 and 120 min of exercise but returned to resting (preexercise) levels 2 h postexercise. CD3(-)CD16(+)CD56(+) NK cell counts and NKCA were significantly (P < 0.05) elevated at each 30-min interval of exercise compared with correspondingly timed resting control values. However, there were no differences in NK cell counts or NKCA between P and N trials at any time point during the two trials. Changes in NKCA reflected mainly changes in NK cell count (r = 0.72; P < 0.001). The results do not support the hypothesis that the enhancement of NKCA during prolonged submaximal aerobic exercise is mediated by beta-endorphin.

Impact of physical activity and sport on the immune system

This review describes how exercise and physical training affect the immune system. Although many immune functions are stimulated by moderate physical activity, more vigorous effort and periods of heavy training suppress various immune response parameters. Experimental studies from our own laboratories and elsewhere illustrate that cellular infiltration of the active muscle is accompanied by phagocyte activation, suppressed NK-cell function, impaired lymphocyte proliferation, decreased in-vitro immunoglobulin production, pro-inflammatory eicosanoid release, cytokine cascade activation, and altered expression of cytokine receptors. Examples cover deliberate heavy training; single bouts of fatiguing, submaximal work; repeated bouts of exercise; and ultra-long distance athletic events. In young adults, age, environment, and light physical training do not change immune-response parameters. Parallels between immune impairment after vigorous exercise and reactions to surgical sepsis are noted. Vigorous exercise probably induces subclinical muscle injury and an associated inflammatory response. Heavy exercise may be a useful experimental model for developing more effective treatments for sepsis. For protection average athletes may take the anti-oxidant vitamins C and E and non-steroidal inflammatory drugs, if the muscles show signs of an inflammatory reaction. Top-level athletes have received immunoglobulin preparations.