Exercise-induced modulation of macrophage function

Macrophages are important effector cells involved in phagocytosis, microbia l killing and antitumour activity. Macrophages also display accessory cell function, in that they can present antigen to foster the development of T l ymphocyte-mediated immunity. Recent work, including studies from this group , has demonstrated that acute and chronic exercise can affect many facets o f macrophage biology. Manifestation of these effects depends on exercise in tensity and duration, the function measured, the timing of measurement in r elation to exercise and the concentration of the macrophage-activating stim ulus. Exercise has potent stimulatory effects on phagocytosis, antitumour a ctivity, reactive oxygen and nitrogen metabolism, and chemotaxis. Indeed, i t 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 a nd antigen-presentation capacity have been documented. These findings bring up the possibility that exercise, and perhaps other stressors, activate ma crophages for effector functions while downregulating accessory cell functi ons. 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 t he effects in a mechanistic way and provide documentation as to their physi ological significance.