Adhesion Molecule Mediated Endothelial Cell Injury Elicited by Activated Leukocytes a

To clarify the mechanism of vascular endothelial cell injury induced by activated leukocytes, we examined the effects of antibodies against adhesion molecules on the injury and on the intracellular peroxide level in endothelial cells. Treatment of leukocytes with phorbol myristate acetate (PMA) caused significant increases in the expression of adhesion molecules, CD11a, CD11b, CD11c, and CD18, on the surface of the leukocytes. Monoclonal antibodies against CD11a, CD11b and CD18, and ICAM-1, an adhesion molecule in the side of endothelial cells, abolished significantly the endothelial cell injury induced by PMA-stimulated leukocytes. These antibodies affected neither the production of active oxygen species by the leukocytes nor the rate of adhesion of leukocytes to endothelial cells. These data indicated that adhesion through CD11/CD18-ICAM-1 is necessary for leukocytes to induce endothelial cell injury. To investigate the phenomenon that occurred after the specific adhesion, the change in the intracellular peroxide level was measured using fluorescence of 2,7-dichlorofluorescein diacetate. The fluorescence intensity of the endothelial cells exposed to PMA-stimulated leukocytes increased with time up to 15 minutes, although neither PMA alone nor unstimulated leukocytes alone showed such activity at all. The monoclonal antibodies against CD11a, CD11b, CD18, and ICAM-1 also showed inhibitory effects on the increase in intracellular fluorescence intensity of the endothelial cells exposed to PMA-stimulated leukocytes. In contrast, CD11c could block neither the cell injury nor the increase in intracellular fluorescence in endothelial cells exposed to PMA-stimulated leukocytes. Thus, the addition of PMA-stimulated leukocytes to an endothelial cell monolayer caused a significant increase in the intracellular peroxide level in the endothelial cells after 15 minutes and severe endothelial cell injury after 5 hours. Both the early increase in peroxide production and late cell lysis were abolished by specific antibodies against CD11a, CD11b, CD18, and ICAM-1, but not CD11c. There seems to be a close relationship between the early and late events. Both events were only partially blocked by catalase (approximately 40%), but almost completely abolished by deferoxamine, a chelator of ferrous ions, suggesting that hydroxyl radicals produced in endothelial cells themselves from xanthine oxidase may injure the cells from their inside. Therefore, the effect of allopurinol, a specific inhibitor of xanthine oxidase, was examined. Pretreatment of endothelial cells with allopurinol caused significant but not complete inhibition (approximately 60%) of both the early and the late events, suggesting that influx of hydrogen peroxide may also be important.(ABSTRACT TRUNCATED AT 400 WORDS)