ROLE OF MAC-1 AND ICAM-1 IN ISCHEMIA-REPERFUSION INJURY IN A MICROCIRCULATION MODEL OF BALB/C MICE

The leukocyte beta(2)-integrin Mac-1 (CD11b/CD18) and its endothelial ligand intercellular adhesion molecule 1 (ICAM-1) are involved in leukocyte adhesion to and macromolecular leakage from postcapillary venules during inflammatory reactions. Both events are also encountered after ischemia-reperfusion of striated muscle, suggesting a central role of both adhesion proteins in reperfusion injury. Using intravital fluorescence microscopy and a microcirculation model in awake BALB/C mice, we investigated the effects of monoclonal antibodies (MAb) and Fab fragments to Mac-1 and MAb to ICAM-1 on leukocyte-endothelium interaction and macromolecular leakage of fluorescein isothiocyanate-dextran (1.5 x 10(5) mol wt) in striated skin muscle after 3 h of ischemia followed by reperfusion. We demonstrate that administration of MAb and Fab to Mac-1 before reperfusion was as effective as administration of MAb to ICAM-1, which was found to be significantly upregulated in the postischemic tissue by immunohistochemical analysis, in preventing postischemic leukocyte adhesion to and macromolecular leakage from postcapillary venules, whereas postischemic leukocyte rolling was not affected after MAb administration. Postischemic capillary perfusion was efficiently preserved in animals treated with anti-Mac-1 and anti-ICAM-1 MAb compared with animals receiving the isotype-matched control antibodies. Likewise, delayed infusion of anti-Mac-1 or anti-ICAM-1 MAb at 0.5 h of reperfusion effectively prevented the further increase of postischemic leukocyte adhesion and macromolecular leakage compared with controls. Transmission electron-microscopic analysis of the postischemic tissue revealed marked endothelial cell swelling in control animals, which was absent in animals treated with anti-Mac-1 or anti-ICAM-1 MAb before onset of reperfusion. These results demonstrate the pathophysiological role of Mac-1/ICAM-1-mediated leukocyte adhesion in the development of postischemic reperfusion injury of striated muscle in vivo and indicate the therapeutic relevance of antiadhesive strategies against these adhesion molecules before and after onset of reperfusion.