Figure 5. Real-time immunofluorescence study of P-selectin surface expression on platelets adhered to VWF and stimulated by thrombin.

Human blood platelets were perfused on human VWF at 1800 s⁻¹ for 20 minutes and activated with thrombin as described in Materials and Methods. Then an Alexa fluor 488 conjugated antibody to P-selectin was perfused in the flow channels. Phase-contrast images are shown for non-stimulated platelets (Panel A) and stimulated platelets (Panel B). Following immunofluorescent labeling, thrombin-activated platelets displayed positive P-selectin staining (Panel D), whereas unactivated platelets remained negative (Panel C). Images were recorded using a Qimaging Rolera camera. Bar = 20 µm.