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MACKINNON, L. T. and D. G. JENKINS. Decreased salivary immunoglobulins after intense interval exercise before and after training. Med. Sci. Sports Exerc., Vol. 25, No. 6, pp. 678–683, 1993. Endurance athletes have been shown to suffer a high incidence of upper respiratory tract infection (URTI). Previous studies have shown that concentration and flow rate of secretory immunoglobulin A (IgA), the major effector of host resistance to URTI, decrease after intense endurance exercise. The purpose of this study was to determine whether salivary IgA concentration and flow rate decrease after brief intense interval exercise, and whether the response to exercise changes with training. Twelve male subjects performed five 60-s bouts of supramaximal interval exercise at 0.075 g.kg-1 body mass on a cycle ergometer; each bout was separated by 5-min rest. Subjects then trained for 8 wk by performing the same interval exercise protocol three times per week. Timed, whole unstimulated saliva samples were obtained before and after the interval exercise protocol, before and after training. Salivary IgA, IgG, and IgM concentrations were measured by ELISA and flow rates calculated. IgA and IgM concentrations relative to total protein decreased after each exercise session; IgG concentration relative to total protein did not change after exercise. IgA, IgM, and IgG flow rates decreased 50–65% after interval exercise. There was no effect of training on any immune parameter measured, although total work performed in the five 60-s bouts increased after training. These data show that the output of salivary IgA and IgM decrease after brief supramaximal interval exercise, and that the decreased output is due, at least partially, to the decrease in saliva flow. In addition, there appears to be a specific effect of intense exercise on IgA concentration greater than that due to decreased saliva flow alone. These data suggest that decreases in secretory IgA output after repeated bouts of supramaximal exercise may be one mechanism contributing to the high incidence of upper respiratory tract infection among athletes.