Factors influencing the mucosal immune response to exercise

Despite the abundance of research conducted into the effects of exercise on mucosal immunity the results remain controversial. Much of the inconsistencies arise from the exercise protocols, the participants studied and their nutritional status, as well as methodological and analytical differences. The purpose of this thesis was to examine the influence of some of these factors, and to investigate potential means of enhancing the mucosal immune response to exercise. In study 1 (Chapter 3) it was shown that a fed or fasted state 2 h prior to exercise had no effect on the s-IgA concentration or secretion rate during prolonged exercise. However, when participants were fed during exercise (Chapter 4), the secretion rate of salivary antimicrobial proteins lysozyme and a-amylase increased, but sIgA remained unchanged. These changes were likely due to the activation of mechanical and gustatory receptors leading to a reflex stimulation of protein secretion via the autonomic nerves, rather than changes in stress hOnliones, since cortisol did not change significantly during exercise. Study 3 (Chapter 5) extended these findings where it was demonstrated that chewing flavoured gum during exercise enhanced lysozyme and a-amylase secretion but resulted in a small reduction in s-IgA secretion rate. Salivary antimicrobial proteins are affected by the exercise intensity since both s-IgA and lysozyme secretion rate increased post -exercise following an incremental test to exhaustion, but not after exercise at 50% Y02max. Moreover, lysozyme secretion rate was also elevated following exercise at 75% Y02mru<, whereas s-IgA remained unchanged. These effects are thought to be mediated by increased sympathetic nervous system activity reflected by the concomitant increases in (lamylase and chromogranin A, rather than the hypothalamic-pituitary-adrenal axis. Resting mucosal immunity exhibits significant gender differences. In study 1 (Chapter 3) s-IgA concentration, secretion rate and osmolality were found to be lower in females than in males at rest. In addition, saliva flow rate was found to be lower in females compared with males in study 5 (Chapter 7). However, these differences did not appear to influence the salivary responses to acute exercise or exercise training. Chronic exercise training in elite male and female swimmers resulted in lower levels of s-IgA secretion rate following periods of intense training prior to competition compared with post-competition (Chapter 7), but these levels were not directly associated with reported episodes of respiratory illness