Special feature for the Olympics: effects of exercise on the immune system: exercise-induced modulation of macrophage function

Macrophages are important effector cells involved in phagocytosis, microbial killing and antitumour activity. Macrophages also display accessory cell function, in that they can present antigen to foster the development of T lymphocyte-mediated immunity. Recent work, including studies from this group, has demonstrated that acute and chronic exercise can affect many facets of macrophage biology. Manifestation of these effects depends on exercise intensity and duration, the function measured, the timing of measurement in relation to exercise and the concentration of the macrophage-activating stimulus. Exercise has potent stimulatory effects on phagocytosis, antitumour activity, reactive oxygen and nitrogen metabolism, and chemotaxis. Indeed, it has been shown that exercise training can increase macrophage antitumour activity in mice of different ages. However, not all functions are enhanced by exercise. Exercise-induced reductions in macrophage MHC II expression and antigen-presentation capacity have been documented. These findings bring up the possibility that exercise, and perhaps other stressors, activate macrophages for effector functions while downregulating accessory cell functions. To a large extent, the mechanisms responsible for the exercise-induced changes in macrophage function remain unknown, but may depend on exercise-induced changes in neuroendocrine factors. Future studies need to explore the effects in a mechanistic way and provide documentation as to their physiological significance.