Treatment with antibody 7E3 decreases platelet spreading and development of a sheetlike mass.

Human platelets were anticoagulated with ACD, gel-filtered, and untreated or treated with 7E3 (10 μg/mL) for 15 minutes at 22°C. Platelets (120 000 μL; 50 μL) were added to the collagen-coated microtiter wells and incubated for 1 hour, and then the specimens were prepared for scanning electron microscopy. High-power (A) and low-power (B) views of untreated human platelets show extensive platelet spreading and additional layers of platelets on top of the spread platelets. High-power (C) and low-power (D) views show that 7E3-treated platelets extend filopodia and spread variably but do not form a sheetlike surface; they also retain their granulomeres to a greater extent than do the platelets making up the initial layer of untreated platelets.