PAF MEDIATES NEUTROPHIL ADHESION TO THROMBIN OR TNF-STIMULATED ENDOTHELIAL-CELLS UNDER SHEAR-STRESS

Platelet-activating factor (PAF) is known to modulate polymorphonuclea r leukocyte (PMN) adhesion to endothelial cells cultured under static conditions and activated by thrombin. In contrast, there are no data o n the role of PAF in PMN adhesion to cells exposed to flow conditions and activated by stimuli other than thrombin. Here we used the PAF rec eptor antagonist L-659,989 to evaluate PMN adhesion to human umbilical vein endothelial cells (HUVEC) in basal conditions or upon challenge with thrombin or tumor necrosis factor-alpha (TNF-alpha). Experiments were performed under dynamic flow using a parallel-plate flow chamber and a computer-based image analysis system. Rolling and adhesion of PM Ns to endothelial cells significantly increased upon stimulation with thrombin. Thrombin-stimulated HUVEC also synthesized higher amounts of PAF than untreated cells. Pretreatment of PMNs with L-659,989 signifi cantly reduced their rolling and adhesion to thrombin-activated HUVEC. Stimulation of HUVEC with TNF-alpha significantly increased the numbe r of rolling and adherent PMNs as compared with untreated cells. Adhes ion of PMNs to and migration across TNF-alpha-stimulated HUVEC were re duced by L-659,989, whereas cell rolling was unchanged. We conclude th at PAF mediates leukocyte interaction under flow conditions with HUVEC activated by inflammatory stimuli.