PLATELET-ACTIVATING-FACTOR PROMOTES SHEAR RATE-DEPENDENT LEUKOCYTE ADHESION IN POSTCAPILLARY VENULES

Reductions in shear rate are generally associated with a recruitment o f rolling and adherent leukocytes within the microcirculation. In this study, we determined if platelet-activating factor (PAF) affects shea r rate-dependent leukocyte adhesion in cat mesenteric venules and whet her the adhesion glycoproteins CD11/CD18 and ICAM-1 contribute to this process. Shear rate was varied in postcapillary venules (25-35 mum) b y graded occlusion of the superior mesenteric artery. Vessel diameter, red blood cell velocity, leukocyte rolling velocity, and the number o f rolling and adherent leukocytes were measured at each shear rate eit her in the presence or absence of PAF superfusion. PAF superfusion res ulted in an increased number of adherent, but not rolling, leukocytes at basal and reduced venular shear rates. A monoclonal antibody (MAb) directed against CD11/CD18 prevented the PAF-induced recruitment of ad herent leukocytes, while an ICAM-1 specific MAb had no effect. These r esults indicate that PAF increases shear rate-dependent leukocyte adhe sion, presumably through activation and/or increased surface expressio n of CD11/CD18 on granulocytes.