A POSSIBLE MECHANISM FOR VASCULAR ENDOTHELIAL-CELL INJURY ELICITED BYACTIVATED LEUKOCYTES - A SIGNIFICANT INVOLVEMENT OF ADHESION MOLECULES, CD11 CD18, AND ICAM-1/

To clarify the mechanism of vascular endothelial cell injury induced b y activated leukocytes, we investigated the intracellular peroxide lev el in endothelial cells and the effect of antibodies against adhesion molecules on it. The change in the intracellular peroxide level was me asured using the fluorescence of 2,7-dichlorofluorescein diacetate. Th e fluorescence intensity of the endothelial cells exposed to PMA-stimu lated leukocytes increased with time up to 15 min, although neither PM A alone nor unstimulated leukocytes alone showed such increase at all. When catalase, which degrades hydrogen peroxide produced by leukocyte s, was added to this system, the peroxide level in endothelial cells d ecreased significantly. On the other hand, pretreatment of endothelial cells with allopurinol, a specific inhibitor of xanthine oxidase, als o caused significant inhibition of the increase in peroxide level in t he endothelial cells. The monoclonal antibodies against CD11a, CD11b, CD18, and ICAM-1 showed almost complete inhibition of the increase in intracellular peroxide levels of the endothelial cells exposed to PMA- stimulated leukocytes. In contrast, the anti-CD11c antibody could not block the increase in fluorescence intensity due to peroxides. The end othelial injury elicited by activated leukocytes was partially inhibit ed by catalase alone (approximately 40%) and allopurinol alone (approx imately 60%), but it was completely inhibited by the concomitant treat ment of endothelial cells with catalase and allopurinol. The specific antibodies against such adhesion molecules as ICAM-1 and CD11/CD18 exc ept CD11c/CD18 also blocked the endothelial cell injury significantly. These data suggest that there is a good correlation between the early increase in intracellular peroxides and endothelial cell injury elici ted by PMA-stimulated leukocytes and that the adhesion of activated le ukocytes to endothelial cells via CD11a/CD18-ICAM-1 must be deeply inv olved in these phenomena. (C) 1994 Academic Press, Inc.