Exercise, alveolar macrophage function, and susceptibility to respiratory infection

Abstract

The effects of exercise on susceptibility to respiratory infection were determined by using a murine model of intranasal challenge with herpes simplex type 1 virus (HSV-1). Two doses of treadmill exercise were assessed: moderate short-term (30 min) exercise and prolonged strenuous exercise to voluntary fatigue (2.5-3.5 h). Morbidity and mortality among exercised and control mice were compared after intranasal challenge with HSV-1. We also assessed the ability of alveolar macrophages to restrict HSV-1 viral replication (intrinsic resistance) among exercise and control groups of mice at several time points postexercise. Exercise to fatigue followed by exposure to viral infection resulted in greater morbidity and mortality than either no exercise or short-term moderate exercise. In addition, antiviral resistance of macrophages obtained from the lungs of both exercised groups was suppressed, albeit for a longer duration in the fatigued group. These data are particularly important in that they identify an exercise-induced decrease in antiviral resistance of a specific component of the immune system within the lungs, in conjunction with increased susceptibility to respiratory infection in vivo. The specific mechanism of decreased antiviral resistance of alveolar macrophages and its role in respiratory infection after exercise remains to be determined.

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

“…Data generally support the hypothesis that exercise stress can lead to immunosuppression and increased risk of infection [morbidity (time to sickness), symptom severity, and mortality (time to death)] (3,4,10,12,27,30). The mechanisms for the increased susceptibility to infection following intense exercise are thought to be mediated by alterations in the stress response.…”

“…Studies have focused on alterations in macrophage function as a mechanism for the detrimental effects of exercise on susceptibility to viral infection (10,12). Macrophages act as a first line of defense in eliminating viral pathogens by inhibiting virus growth within itself, as well as to inactivate extracellular virus, suppress virus replication in adjacent cells, and destroy infected cells (46).…”

“…Macrophages act as a first line of defense in eliminating viral pathogens by inhibiting virus growth within itself, as well as to inactivate extracellular virus, suppress virus replication in adjacent cells, and destroy infected cells (46). Alveolar and peritoneal macrophage antiviral resistance to HSV is reduced in mice following exercise to fatigue (10,12), as is macrophage antigen presentation (7). However, a direct role of macrophages on the increased susceptibility to infection following exercise stress has not been addressed.…”

“…Altered susceptibility to infection will be measured as changes in morbidity (time to sickness), symptom severity, and mortality (time to death). This was done using a murine model of exercise, respiratory infection (3,4,10,12), and in vivo lung macrophage depletion (25). The exercise protocol consisted of three consecutive days of prolonged treadmill running to fatigue designed to mimic a short period of severe exercise training.…”

Exercise-induced modulation of macrophage function

“…In contrast, exhaustive exercise decreases alveolar macrophage antiviral function, an effect that is correlated to increased susceptibility to herpes simplex virus 1 infection. [43][44][45] A follow-up experiment designed to determine the role of stress hormones in this response suggested that the reduction in alveolar macrophage antiviral resistance was likely related to increased release of adrenal catecholamines, but not corticosterone. 43 These data demonstrate that the effects of exercise on macrophage function depend on the function measured and the dose of exercise used.…”