Electron micrographs of α-granules (A) from control (a, c, and e) and patient (III-1; b, d, and f ) platelets. (a) The ultrastructure of normal α-granules is composed of a dense nucleoid and an eccentric zone in which the von Willebrand factor tubules (arrowheads) are located. (b) The patient's α-granule ultrastructure is well preserved and von Willebrand factor tubules (arrowheads) are present but are less abundant than in control platelets. (c) Immunolabeling for von Willebrand factor is found in normal α-granules in a zone of lower density (arrowheads). (d) In the patient's α-granules, immunolabeling for von Willebrand factor (arrowheads) is less abundant. (e) Fibrinogen immunolabeling (arrowheads) is prominent and is scattered throughout the matrix of normal α-granules. (f ) Immunolabeling for fibrinogen (arrowheads) is decreased in this patient's α-granules. (Original magnification × 60,000 for [a] through [f].)