Lymphocyte subset responses to exercise and glucocorticoid suppression in healthy men

Dexamethasone Release from Within Engineered Cartilage as a Chondroprotective Strategy Against Interleukin-1α

While significant progress has been made toward engineering functional cartilage constructs with mechanical properties suitable for in vivo loading, the impact on these grafts of inflammatory cytokines, chemical factors that are elevated with trauma or osteoarthritis, is poorly understood. Previous work has shown dexamethasone to be a critical compound for cultivating cartilage with functional properties, while also providing chondroprotection from proinflammatory cytokines. This study tested the hypothesis that the incorporation of poly(lactic-co-glycolic acid) (PLGA) (75:25) microspheres that release dexamethasone from within chondrocyte-seeded agarose hydrogel constructs would promote development of constructs with functional properties and protect constructs from the deleterious effects of interleukin-1α (IL-1α). After 28 days of growth culture, experimental groups were treated with IL-1α (10 ng/mL) for 7 days. Reaching native equilibrium moduli and proteoglycan levels, dexamethasone-loaded microsphere constructs exhibited tissue properties similar to microsphere-free control constructs cultured in dexamethasone-supplemented culture media and were insensitive to IL-1α exposure. These findings are in stark contrast to constructs containing dexamethasone-free microspheres or no microspheres, cultured without dexamethasone, where IL-1α exposure led to significant tissue degradation. These results support the use of dexamethasone delivery from within engineered cartilage, through biodegradable microspheres, as a strategy to produce mechanically functional tissues that can also combat the deleterious effects of local proinflammatory cytokine exposure.

Biological mechanisms underlying the role of physical fitness in health and resilience

Physical fitness, achieved through regular exercise and/or spontaneous physical activity, confers resilience by inducing positive psychological and physiological benefits, blunting stress reactivity, protecting against potentially adverse behavioural and metabolic consequences of stressful events and preventing many chronic diseases. In this review, we discuss the biological mechanisms underlying the beneficial effects of physical fitness on mental and physical health. Physical fitness appears to buffer against stress-related disease owing to its blunting/optimizing effects on hormonal stress responsive systems, such as the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. This blunting appears to contribute to reduced emotional, physiological and metabolic reactivity as well as increased positive mood and well-being. Another mechanism whereby regular exercise and/or physical fitness may confer resilience is through minimizing excessive inflammation. Chronic psychological stress, physical inactivity and abdominal adiposity have been associated with persistent, systemic, low-grade inflammation and exert adverse effects on mental and physical health. The anti-inflammatory effects of regular exercise/activity can promote behavioural and metabolic resilience, and protect against various chronic diseases associated with systemic inflammation. Moreover, exercise may benefit the brain by enhancing growth factor expression and neural plasticity, thereby contributing to improved mood and cognition. In summary, the mechanisms whereby physical fitness promotes increased resilience and well-being and positive psychological and physical health are diverse and complex.

Posttraumatic stress and immune dissonance

Stress or neuroendocrine response usually occurs soon after trauma, which is central to the maintenance of post-traumatic homeostasis. Immune inflammatory response has been recognized to be a key element both in the pathogenesis of post-traumatic complications and in tissue repair. Despite the existence of multiple and intricate interconnected neuroendocrine pathways, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system have been considered to be the most important in trauma. Although the short-term and appropriate activation of these stress responses is vital to the host's adaptation, prolonged duration and exaggerative magnitude of their activity leads to deleterious effects on immune function in trauma, causing immune dissonance. The overall appropriate and controlled activation and termination of the neuroendocrine responses that mediate the necessary physiological functions involved in maintaining and restoring homeostasis in the event of trauma are of critical importance. This review will describe the effects of some important neuroendocrine responses on immune system. Present evidences indicate that the neuroendocrine and immune systems form a cohesive and integrated early host response to trauma, and identify areas for further research to fully elucidate the regulatory role of neuroendocrine system in trauma.

Effect of acute maximal exercise on lymphocyte subgroups in type 1 diabetes

The essential therapy of diabetes mellitus includes medical nutrition therapy (MNT), exercise and medical therapy. Exercise, besides its metabolic effects, has positive influence on the immune system, but some forms of exercise may cause trauma for muscle and skeletal systems, they may also support negative effects on the immune system. Nineteen type 1 diabetic patients (mean age 22.1 +/- 2.8 yrs), followed by Diabetes Outpatient Clinic and twenty age matched male control subjects were included into the study, to demonstrate the effects of maximal, acute exercise on the immune system. The exercise test was performed according to Bruce protocol on treadmill. In diabetic subjects, increased CD19 and CD23 expressions were observed before exercise. In both groups (diabetic/control) CD3, CD4 expressions and CD4/CD8 ratio were decreased following the exercise, however expression of natural killer (NK) cells increased. Compared to type 1 diabetic patients healthy subjects had longer acute exercise that caused the increased level of CD8 expression, however type 1 diabetic patients did not show any difference. These results indicate that submaximal aerobic exercise might be recommended for type 1 diabetics without any complications because of its positive reflection on metabolic control and no negative effects on the immune system.

The roles of exercise-induced immune system disturbances in the pathology of heat stroke : the dual pathway model of heat stroke

Heat stroke is a life-threatening condition that can be fatal if not appropriately managed. Although heat stroke has been recognised as a medical condition for centuries, a universally accepted definition of heat stroke is lacking and the pathology of heat stroke is not fully understood. Information derived from autopsy reports and the clinical presentation of patients with heat stroke indicates that hyperthermia, septicaemia, central nervous system impairment and cardiovascular failure play important roles in the pathology of heat stroke. The current models of heat stroke advocate that heat stroke is triggered by hyperthermia but is driven by endotoxaemia. Endotoxaemia triggers the systemic inflammatory response, which can lead to systemic coagulation and haemorrhage, necrosis, cell death and multi-organ failure. However, the current heat stroke models cannot fully explain the discrepancies in high core temperature (Tc) as a trigger of heat stroke within and between individuals. Research on the concept of critical Tc as a limitation to endurance exercise implies that a high Tc may function as a signal to trigger the protective mechanisms against heat stroke. Athletes undergoing a period of intense training are subjected to a variety of immune and gastrointestinal (GI) disturbances. The immune disturbances include the suppression of immune cells and their functions, suppression of cell-mediated immunity, translocation of lipopolysaccharide (LPS), suppression of anti-LPS antibodies, increased macrophage activity due to muscle tissue damage, and increased concentration of circulating inflammatory and pyrogenic cytokines. Common symptoms of exercise-induced GI disturbances include diarrhoea, vomiting, gastrointestinal bleeding, and cramps, which may increase gut-related LPS translocation. This article discusses the current evidence that supports the argument that these exercise-induced immune and GI disturbances may contribute to the development of endotoxaemia and heat stroke. When endotoxaemia can be tolerated or prevented, continuing exercise and heat exposure will elevate Tc to a higher level (>42 degrees C), where heat stroke may occur through the direct thermal effects of heat on organ tissues and cells. We also discuss the evidence suggesting that heat stroke may occur through endotoxaemia (heat sepsis), the primary pathway of heat stroke, or hyperthermia, the secondary pathway of heat stroke. The existence of these two pathways of heat stroke and the contribution of exercise-induced immune and GI disturbances in the primary pathway of heat stroke are illustrated in the dual pathway model of heat stroke. This model of heat stroke suggests that prolonged intense exercise suppresses anti-LPS mechanisms, and promotes inflammatory and pyrogenic activities in the pathway of heat stroke.

Neural regulation of innate immunity: a coordinated nonspecific host response to pathogens

The central nervous system (CNS) regulates innate immune responses through hormonal and neuronal routes. The neuroendocrine stress response and the sympathetic and parasympathetic nervous systems generally inhibit innate immune responses at systemic and regional levels, whereas the peripheral nervous system tends to amplify local innate immune responses. These systems work together to first activate and amplify local inflammatory responses that contain or eliminate invading pathogens, and subsequently to terminate inflammation and restore host homeostasis. Here, I review these regulatory mechanisms and discuss the evidence indicating that the CNS can be considered as integral to acute-phase inflammatory responses to pathogens as the innate immune system.

Neuroendocrine regulation of immunity

A reciprocal regulation exists between the central nervous and immune systems through which the CNS signals the immune system via hormonal and neuronal pathways and the immune system signals the CNS through cytokines. The primary hormonal pathway by which the CNS regulates the immune system is the hypothalamic-pituitary-adrenal axis, through the hormones of the neuroendocrine stress response. The sympathetic nervous system regulates the function of the immune system primarily via adrenergic neurotransmitters released through neuronal routes. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. Glucocorticoids are the main effector end point of this neuroendocrine system and, through the glucocorticoid receptor, have multiple effects on immune cells and molecules. This review focuses on the regulation of the immune response via the neuroendocrine system. Particular details are presented on the effects of interruptions of this regulatory loop at multiple levels in predisposition and expression of immune diseases and on mechanisms of glucocorticoid effects on immune cells and molecules.

Uptake and killing of Listeria monocytogenes by normal human peripheral blood granulocytes and monocytes as measured by flow cytometry and cell sorting

Cellular components of innate immunity (NK cells, monocytes and granulocytes) play an important role in early resistance to Listeria monocytogenes in the mouse model. Minimally invasive methods of measuring the bacteriocidal capacity of these cells may be useful as a biomarker of susceptibility in humans. A technique was developed whereby the uptake and survival of L. monocytogenes could be measured in human granulocytes and monocytes using small volumes of peripheral blood. This method used flow cytometry to detect the presence of PKH-2-labeled bacteria within these cells. Survival of bacteria was determined by sorting of infected cells based on a combination of fluorescence and light scattering properties. Considerable variation in bacterial recovery was seen between normal volunteers. There was consistently greater survival of a fully virulent strain of L. monocytogenes within monocytes and granulocytes compared with an isogenic strain lacking the hemolysin, listeriolysin O, when measured at baseline. There was no evidence of longer-term bacterial survival or growth at 2 or 24 h. This technique may be useful for assessment of both host resistance and pathogen virulence.

Expression of lymphocyte subsets after exercise and dexamethasone in high and low stress responders

PURPOSE

Recent work indicates that among the normal population, persons can be classified as low (LR) or high (HR) stress responders based on hypothalamic-pituitary-adrenal (HPA) axis responses to high-intensity exercise. We studied whether differential activation of the HPA axis affected cytokine production and expression of selected lymphocyte subsets in HR and LR in response to high-intensity exercise after placebo and dexamethasone (DEX; 4 mg).

METHODS

Healthy HR (N = 12) and LR (N = 10) underwent two exercise tests at 90% of VO2max, 8 h after placebo or DEX. Expression of lymphocyte surface markers (CD3+, CD4+, CD8+, CD56+), adhesion molecule markers (intercellular adhesion molecule-1/ICAM-1: CD54+ and L-selectin: CD62L+), and concentrations of plasma interleukin 6 (IL-6) were examined before and after exercise.

RESULTS

Baseline percentages of CD8+ and CD56+ cells were significantly higher, and concentrations of IL-6 and percentages of CD4+ cells were significantly lower in HR as compared with LR. The percentage of CD54+ and CD62L+ cells was not significantly different in HR and LR. DEX significantly reduced the percentage of CD3+ and CD4+ and increased the percentage of CD8+ and CD56+ subsets; the percent of cells expressing CD54+ increased, whereas CD62L+ decreased. Exercise-induced changes in the percentage of lymphocyte subsets were similar to those induced by DEX.

CONCLUSION

In summary, HR and LR have different baseline patterns of IL-6 and lymphocyte subsets, which may reflect differential sensitivity to endogenous glucocorticoids. However, exogenous glucocorticoids induced similar patterns of lymphocyte expression in HR and LR.

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.

Indomethacin inhibits circulating PGE2 and reverses postexercise suppression of natural killer cell activity

Natural killer (NK) cells are important in combating viral infections and cancer. NK cytolytic activity (NKCA) is often depressed during recovery from strenuous exercise. Lymphocyte subset redistribution and/or inhibition of NK cells via soluble mediators, such as prostaglandin (PG) E2 and cortisol, are suggested as mechanisms. Ten untrained (peak O2 consumption = 44.0 +/- 3.5 ml. kg-1. min-1) men completed at 2-wk intervals a resting control session and three randomized double-blind exercise trials after the oral administration of a placebo, the PG inhibitor indomethacin (75 mg/day for 5 days), or naltrexone (reported elsewhere). Circulating CD3(-)CD16(+)/56(+) NK cell counts, PGE2, cortisol, and NKCA were measured before, at 0.5-h intervals during, and at 2 and 24 h after a 2-h bout of cycle ergometer exercise (65% peak O2 consumption). During placebo and indomethacin conditions, exercise induced significant (P < 0.0001) elevations of NKCA (>100%) and circulating NK cell counts (>350%) compared with corresponding control values. With placebo treatment, total NKCA was suppressed (28%; P < 0.05) 2 h after exercise, and a postexercise elevation (36%; P = 0.02) of circulating PGE2 was negatively correlated (r = 0.475, P = 0.03) with K-562 tumor cell lysis. NK counts were unchanged in the postexercise period, but at this stage CD14(+) monocyte numbers were elevated (P < 0.0001). Indomethacin treatment eliminated the postexercise increase in PGE2 concentration and completely reversed the suppression of total and per CD16(+)56(+) NKCA 2 h after exercise. These data support the hypothesis that the postexercise reduction in NKCA reflects changes in circulating PGE2 rather than a differential lymphocyte redistribution.

Short-term attenuation of natural killer cell cytotoxic activity in wheelchair marathoners with paraplegia

OBJECTIVE

To investigate homeostasis of the immune system in athletes with spinal cord injuries during and after racing a wheelchair marathon.

DESIGN

The study examined changes in the number and function of natural killer (NK) cells in nine male wheelchair marathon athletes (spinal cord injuries between T5 and T12) who completed the 15th Oita International Wheelchair Marathon Race. Blood samples were obtained the day before, immediately after, and 1 day after the race. Blood samples were also obtained from seven age-matched control subjects with spinal cord injuries but who did not exercise regularly.

RESULTS

The number of peripheral leukocytes increased (p < .01) immediately after the race. In contrast, the number of peripheral NK cells and NK cell cytotoxic activity significantly decreased from 310+/-130/microL to 133 +/-61/microL and from 42.6%+/-3.0% to 38.2%+/-3.2%, respectively (mean+/-SD), immediately after the race. Plasma cortisol levels were increased after the race. However, all parameters returned to control levels within 24 hours. Measurements in control subjects did not change throughout the experiment.

CONCLUSION

These findings suggest that racing a marathon suppressed peripheral NK cell number as well as NK cell cytotoxic activity in wheelchair athletes and that this was probably mediated by increased postrace cortisol levels. Wheelchair marathon athletes are advised to take extra precaution to avoid infection within 24 hours after racing because of the transient suppression of NK cell cytotoxic activity during this period.