Background: The aim of this study was to determine serum lactoferrin concentrations and serum antibacterial activity before and after running exercise. Methods: Twenty-four healthy young men were randomly assigned to high, middle, or low intensity of exercise groups (5000 steps running at 180, 130, and 80 steps/min, respectively). Blood samples were collected at baseline and immediately, 1 and 4 h after exercise. Concentrations of circulating neutrophils, serum lactoferrin, iron in whole blood, and serum iron were measured. Antibacterial activity of serum was evaluated using live Micrococcus luteus. Results: The numbers of circulating neutrophils were increased by 20.0% and 15.5% 1 h after exercise in high and middle groups (both P<0.01), respectively. Serum lactoferrin concentrations were significantly increased immediately after exercise by 48.3% and 33.0% in the high and middle groups (both P<0.01), respectively. No significant changes in total iron or serum iron concentrations were observed during the study. Antibacterial activities of serum collected immediately after exercise in the high and middle groups were significantly stronger than those before exercise, by 31.2% and 25.4% (both P<0.05), respectively. Conclusions: Serum lactoferrin concentrations are increased immediately after running exercise and may play an antibacterial role in host defenses before mobilization of neutrophils into the circulating pool.
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