Influence of physical activity on the cellular immune system: mechanisms of action.

This review deals with the effect of acute physical exercise and training status on different components of the immune system. Predominantly studies in humans are mentioned. In relation to acute physical exercise (75% of VO2max, 1 hour) the leukocyte concentration increased; following exercise the neutrophils increased fourfold. The lymhphocyte concentration increased during and decreased following exercise. The percentage of CD3+ cells (pan T cells) declined during exercise, mainly due to a fall in the %CD4+ cells. The %CD16+ cells (NK cells) increased two-fold and returned to prevalue two hours after exercise. The %CD20+ cells (B cells) did not change in relation to exercise, whereas the %CD14+ cells (monocytes) increased two to threefold following exercise. The NK cell activity increased during but decreased following exercise. These increases were due to recruitment of NK cells with a high IL-2 response capacity, whereas the decreased NK activity post-exercise was due to downregulation by prostaglandins released by the elevated concentration of monocytes. During severe, moderate as well as light exercise, the NK cell activity increased, but the post-exercise suppression of the NK cell function was found only following severe exercise, and not after moderate or light exercise, furthermore, only following severe exercise, an increased monocyte concentration was demonstrated. The IL-2-stimulated lymphocyte proliferative response increased due to stimulation of CD16+ cells and did not reflect expression of IL-2 receptors.