Effect of long-term voluntary exercise wheel running on susceptibility to bacterial pulmonary infections in a mouse model

Regular moderate exercise has been suggested to exert anti-inflammatory effects and improve immune effector functions, resulting in reduced disease incidence and viral infection susceptibility. Whether regular exercise also affects bacterial infection susceptibility is unknown. The aim of this study was to investigate whether regular voluntary exercise wheel running prior to a pulmonary infection with bacteria (P. aeruginosa) affects lung bacteriology, sickness severity and phagocyte immune function in mice. Balb/c mice were randomly placed in a cage with or without a running wheel. After 28 days, mice were intranasally infected with P. aeruginosa. Our study showed that regular exercise resulted in a higher sickness severity score and bacterial (P. aeruginosa) loads in the lungs. The phagocytic capacity of monocytes and neutrophils from spleen and lungs was not affected. Although regular moderate exercise has many health benefits, healthy mice showed increased bacterial (P. aeruginosa) load and symptoms, after regular voluntary exercise, with perseverance of the phagocytic capacity of monocytes and neutrophils. Whether patients, suffering from bacterial infectious diseases, should be encouraged to engage in exercise and physical activities with caution requires further research

Schematic representation of the study procedure.

<p>Schematic representation of the study procedure.</p

Effect of exercise on symptom severity score and bacterial load in the lung following intranasal inoculation with <i>P. aeruginosa.</i>

<p>Each dot represents one mouse. <b>A.</b> Symptom severity score (Mean ± SEM) 16 hours following intranasal inoculation with P. aeruginosa (n = 20 per group). <b>B</b>. Amount of colony forming units per lung (Median ± IR) following intranasal inoculation with P. aeruginosa (n = 14 per group). Inoculation doses was 5×10⁶ CFUs/50 μL.</p

Effectiveness of voluntary exercise wheel running.

<p>Each dot represents one mouse. <b>A</b>. Mean ± SEM running distance per day per study week (n = 20). <b>B</b>. Effect of exercise wheel running on HK II and COX I protein levels in the white part of the m. quadriceps and m. gastrocnemius (n = 20 per group). Protein contents were expressed relative to the “no running wheel group” (Mean ± SEM). <b>C</b>. Effect of exercise wheel running on lung function (Mean ± SEM): tidal volume (ml), breathing frequency (breaths/min) and minute volume (ml/min) (n = 20 per group).</p

Symptom severity scoring system.

<p>Symptom severity scoring system was adapted from Murphy et al.¹¹. Animals were scored twice post-infection. Cumulative score may range from 0 to 10, indicating no to severe illness.</p

Effect of exercise on capacity of phagocytes to take up <i>P. aeruginosa.</i>

<p><b>A.</b> Monocytes and neutrophils were gated by forward and side scatter (left panel). Representative dotplots of monocytes (left panel) and neutrophils (right panel) incubated with (lower panel) or without (upper panel) EGFP-labeled P. aeruginosa and selection of EGFP-positive cells. Bacteria were opsonized with 4% mouse serum. <b>B.</b> Phagocytic capacity of neutrophils and monocytes (Mean ± SEM) isolated from the spleen (n = 6 per group) and lungs (n = 10 per group). Each dot represents one mouse.</p