Immunoelectron microscopy of resting platelets. Frozen sections of resting platelets were incubated with Abs to PrP^C (FL253) and fibrinogen, followed by incubation in protein G conjugated to 5 or 10 nm gold. Normal resting platelets showing alpha granule (α) and open canalicular system (OCS) (A). PrP^C (10 nm gold, arrows) is seen in alpha granule and the open canalicular system (B-C). Alpha granules are identified by the presence of fibrinogen (5 nm gold, arrows; D). Double labeling with Abs to PrP^C (5 nm gold, black arrows) and fibrinogen (10 nm gold, white arrows) localized both proteins to the same granules (E-F).