ENDOTHELIAL-BORNE PLATELET-ACTIVATING-FACTOR AND INTERLEUKIN-8 RAPIDLY IMMOBILIZE ROLLING NEUTROPHILS

The kinetics of the response of integrins to activating signal(s) must be rapid to ensure that rolling neutrophils are localized at the site s of inflammation. From video records, we analyzed the adhesion of ind ividual neutrophils in a flow-based in vitro model of endothelial hypo xia and reoxygenation. There were numerous rolling interactions betwee n flowing neutrophils and P-selectin an human umbilical vein endotheli al cells after hypoxia, but 90% lasted for <1 s, with similar to 30% c onverted to stationary attachment via beta(2)-integrin(s). Interleukin -8 (IL-8) and platelet-activating factor (PAF) were responsible for ne utrophil activation in this model [G. E. Rainger, A. Fisher, C. Shearm an, and G. B. Nash. Am. J. Physiol. 269 (Heart Circ. Physiol. 38): H13 98-H1406, 1995]. In the presence of a PAF-receptor antagonist, IL-8 ac ting alone induced conversion of rolling to stationary adhesion in as Little as 80 ms after the initial attachment of a neutrophil, with a m edian response time of 240 ms. In the presence of a monoclonal antibod y that neutralized IL-8 activity, PAF acting alone required a minimum duration of rolling of 560 ms to promote stationary adhesion, with a s ignificantly longer median duration of 720 ms. In a reconstituted mode l, treatment of endothelial cells with hydrogen peroxide induced short -lived foiling of neutrophils supported by P-selectin. Exogenously add ed IL-8 and/or PAF bound to the endothelial surface and successfully i nduced the immobilization of neutrophils. Rapid and distinct kinetics of the conversion to stationary adhesion were observed again for IL-8 or PAF. Thus although endothelial-presented signals differed in their rate of action, neutrophils could be localized within one or two endot helial cell diameters of their initial adhesive contact point.