Severe exercise enhances phagocytosis by murine bronchoalveolar macrophages

Because physical activity affects the immune competency of individuals by an unknown mechanism, we investigated the effect of acute exercise on phagocytosis of bronchoalveolar macrophages (BAMs). Male BALB/c mice, 7-9 weeks old, ran on a treadmill to exhaustion (severe exercise, SE) or at a final speed of 17 m/min for 30 min (moderate exercise, ME). Although both exercise protocols induced differential leukocytosis, 95% leukocytes from lung lavages of both groups were BAMs. The BAM phagocytic capacity of nonopsonized beads increased immediately after SE but not after ME, gradually returning to the basal level after 4 h. SE upregulates the macrophage scavenger receptors (SR-A type I/II and MARCO), CR3, and ICAM-1, but not Fc gammaR. Although the blocking effect of MARCO antibody was most pronounced, that of ICAM-1 antibody was totally reversed by cross-linking CR3. Our results showed that SE, but not ME, activated BAMs and that the enhanced nonopsonized phagocytosis was mainly mediated by scavenger receptors and ICAM-1/CR3.