Flow cytometry of activated platelets. Platelets were incubated with 1 U/mL thrombin for 0, 5, 15, 30, or 60 seconds and labeled with anti-PrP^C Ab 308. Flow cytometry was used to distinguish platelets from microvesicles on the basis of their forward-scatter (FSC-H) and side-scatter (SSC-H) profiles (platelets, solid line ♦, microvesicles, broken line ▴). Fluorescence backgating determined the percentage of PrP^C-positive cells in each region. (Percentage of platelet region positive for PrP^C, ▪; percentage of microvesicle region positive for PrP^C, •).