Intravascular adhesion of leucocytes plays a role in the pathogenesis of acute and chronic vascular disease. Regular aerobic exercise seems to protect against vascular disease. Since leucocyte adhesion is mediated by integrins, we tested the hypothesis that surface expression of the integrin adhesive receptors LFA-1 (cd11a/cd18), MAC-1 (cd11b/cd18), gp 150/95 (cd11c/cd18), and VLA-4 (cd29/cd49) is decreased by moderate endurance exercise. Surface expression of integrins was measured by FACS analysis in 19 healthy subjects (16 males, 3 females, 36.6 +/- 8.7 years, 177.1 +/- 7.5 cm, 70.3 +/- 8.1 kg) before and after submaximal exercise (3 h run) using monoclonal antibodies against cd11a, cd11b, cd11c, cd18, cd29 and cd49. In addition, we compared resting integrin expression in this group with a group of sedentary subjects (19 males, 6 females, 29.3 +/- 5.3 years). White blood cell count increased from 5300 ml(-1) to 9740 ml(-1) during exercise (P < 0.001). Nevertheless, the expression (indicated by the mean log fluorescence) of cd11a (94 +/- 24 vs. 78 +/- 14) and cd18 (128 +/- 31 vs. 102 +/- 21) on lymphocytes and of cd11a (104 +/- 25 vs. 85 +/- 16), cd11c (497 +/- 171 vs. 408 +/- 126) cd29 (109 +/- 16 vs. 89 +/- 16), cd49 (69 +/- 8 vs. 54 +/- 11) on monocytes was decreased after exercise (all P < 0.05). In contrast, integrin expression on granulocytes was not altered by exercise. Comparison of exercising and sedentary subjects showed a significantly decreased expression of integrins in exercising subjects. Our results demonstrate that moderate exercise leads to decreased expression of integrin receptors on leucocytes. This decreased expression of adhesion molecules may result in decreased adhesion and infiltration of leucocytes into the vessel wall. This phenomenon may play a role in the beneficial effect of moderate exercise in prevention of acute and chronic vascular disease.