XO INCREASES NEUTROPHIL ADHERENCE TO ENDOTHELIAL-CELLS BY A DUAL ICAM-1 AND P-SELECTIN-MEDIATED MECHANISM

Circulating xanthine oxidase (XO) can modify adhesive interactions bet ween neutrophils and the vascular endothelium, although the mechanisms underlying this effect are not clear. We found that treatment with XO of bovine pulmonary artery endothelial cells (EC), but not neutrophil s or plasma, increased adherence, suggesting that XO had its primary e ffect on EC. The mechanism by which XO increased neutrophil adherence to EC involved binding of XO to EC and production of H2O2. XO also inc reased platelet-activating factor production by EC by a H2O2-dependent mechanism. Similarly the platelet-activating factor-receptor antagoni st WEB-2086 completely blocked XO-mediated neutrophil EC adherence. In addition, neutrophil adherence was dependent on the beta(2)-integrin Mac-1 (CD11b/CD18) but not on leukocyte functional antigen-1 (CD11a/CD 18). Treatment of EC with XO for 30 min did not alter intercellular ad hesion molecule-1 surface expression but increased expression of P-sel ectin and release of von Willibrand factor. Antibodies against P-selec tin (CD62) did not affect XO-mediated neutrophil adherence under stati c conditions but decreased both rolling and firm adhesive interactions under conditions of shear. We conclude that extracellular XO associat es with the endothelium and promotes neutrophil-endothelial cell inter actions through dual intercellular adhesion molecule-1 and P-selectin ligation, by a mechanism that involves platelet-activating factor and H2O2 as intermediates.