Platelets adhere to vWF released from activated endothelial cells in venules through the GPIbα receptor.

(A) Incubation of washed platelets with antibodies directed against PECAM-1 (○) or PSGL-1 () did not affect their adhesion on mesenteric venules superfused withA23187. Similarly, β3−/− platelets transfused into β3−/− recipient mice adhered normally (▪). (B) Fluorescent P−/− platelets adhered to the activated vessel wall of GPIbα-deficient mice (▴), as did platelets with human GPIbα onto P−/− venules (○). Mocarhagin treatment of mGPIb−/−;TghGPIb platelets (), but not WT platelets (■), prevented the adhesion process. Values are expressed as number of adherent fluorescent platelets/mm²·frame (see “Materials and methods”).