PLATELET-LEUKOCYTE INTERACTIONS

Platelet-leukocyte interactions may contribute to the development of s everal pathological conditions, including myocardial ischemic disorder s. Using an in vitro system that simulates vascular flow conditions, w e investigated platelet-neutrophil adhesion. Collagen-adherent platele ts were shown to express P-selectin and were able to mediate the bindi ng of flowing neutrophils. Some of the adherent neutrophils displayed signs of cellular activation. Flow cytometric analyses revealed that a ctivation induced a rapid and marked reduction of the P-selectin ligan d, with levels decreased by 71% after 15 minutes of stimulation. Using a visual assay of platelet-neutrophil resetting, we showed that the P -selectin ligand was translocated and clustered at the uropod of neutr ophils after the shape changes and polarization induced by stimulation . Activated neutrophils that were bound to surface-adherent platelets also displayed the clustering of P-selectin ligand at the uropod, and these neutrophils detached from the platelets when a shear stress was applied through the adhesion chamber. These results indicate that stim ulation of neutrophils induces changes in the surface expression and d istribution of the ligand for P-selectin, and that these changes might influence the adhesive interactions occurring between neutrophils and activated platelets.