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 twofold 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. Following exercise, increased production of interleukin 1 (IL-1) and interleukin 6 (IL-6) were found, whereas we were unable to show any exercise-induced changes in the production of the tumour necrosis factor (TNF), interleukin 2 (IL-2) or interferon-gamma (IFN-gamma). Using a reverse plaque forming cell (PFC) assay, it was shown that exercise induced significantly decreased numbers of IgG-, IgA- and IgM-secreting blood mononuclear cells. Purified B cells produced plaques only after EBV stimulation and in these cultures no exercise-induced suppression was found. The suppression of the PFC response was shown to be mediated by monocytes. The NK cell activity and the production of IL-1 have been shown to be elevated in trained versus untrained, whereas the concentration of secretory IgA was lower in the trained. In this review, the possible role of different stress hormones is discussed. Results are presented showing that selective administration of epinephrine to obtain plasma concentrations identical with those seen during exercise mimicked the exercise-induced effects of NK activity, lymphocyte proliferative response and blood mononuclear cell subsets, but not totally the effect on neutrophils. It is concluded that exercise-induced immunomodulation occurs due to altered composition of immunocompetent cells as well as due to activation of the immune system; furthermore, that during severe as well as moderate exercise, the immune system is enhanced, whereas severe exercise only causes post-exercise immunodepression.