Introduction: Immunoglobulin A (IgA) is the major class of immunoglobulin in mucosal secretions. The level of IgA in mucosal fluids is more closely correlated with resistance to upper respiratory tract infections (URTI) than serum antibodies. The purpose of this paper was to investigate the sIgA response to exercise under various conditions. Findings will attempt to determine whether there is a relationship between salivary sIgA and the incidence of URTI. Methods Study 1: 11 male university students (age: 19.2±1.1ys; height: 171.3±6.3cm; weight: 57.8±5.3kg) were recruited. The subjects ran on a treadmill for 1 hour at 40%VO2max, 60%VO2max and 80%VO2max. Saliva sIgA pre-exercise, post-exercise and 3, 6 and 24 hours post-exercise were determined. Study 2: The study was conducted with the informed consent of the Hiroshima University rowing team, which consisted of 5males (age: 20.2±0.6yr, height: 172.4±5.2cm, weight: 67.0±8.9kg) and 3 female rowers (age: 19.8±0.5yr, height: 161.0±8.7cm, weight: 57.7±4.9kg). The rowers undertook about 10h/wk of rowing, rowing distances of 60~80km. The rowers were followed for 8 weeks over the training season, with saliva collected every training day in the first week, one day in the second, third, fourth and the eighth week. Measurement of sIgA: One minute of saliva was collected with salivette (German). sIgA was measured by ELISA. URTI was defined as symptoms of sore throat, cough, runny nose or fever, and a clinical diagnosis by the physician. Results Study 1: The results showed that both saliva sIgA concentration ( g/ml) and sIgA secretion rate ( g/min) increased after exercise at 60%VO2max, and sIgA concentration increased significantly (p<0.05). Study 2:Taken together each bout of exercise during 8-weeks of training, sIgA concentration ( g/ml) and sIgA secretion rate ( g/min) post-exercise increased significantly in comparison to pre-exercise (p<0.01). Over the 8-week training season, there were significant decreases in the concentration and secretion rate of sIgA in the second, third and fourth week (p<0.05) (there was a competition in the third week).The sIgA concentration and the secretion rate of the rowers with URTI were significantly lower than that of the non-infected ones (p<0.05). Logistic analysis showed that the risk of URTI with sIgA concentration below 85 g/ml is 3.07 times significantly higher than above 85 g/ml (p<0.05). Discussion / Conclusions This data suggests that sIgA increases after a bout of moderate intensity exercise. Intense daily exercise appears to have a cumulative effect on mucosal immunity and monitoring salivary sIgA and may foresee the onset of URTI.
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