title: Alpha-granule pool of glycoprotein IIb-IIIa in normal and pathologic platelets and megakaryocytes.
abstract: Using an immunogold staining technique and electron microscopy, we investigated the localization of the alpha-granule pool of glycoprotein (GP) IIb-IIIa in normal platelets and maturing megakaryocytes (MK), in pathologic platelets from a patient with type I Glanzmann's thrombasthenia (GT), and from three patients with the gray platelet syndrome (GPS). In normal resting platelets, GPIIb-IIIa was observed on the plasmatic side of the plasma membrane, the open canicular system (OCS) membranes, and along the internal face of the alpha-granule membrane. This location was found with three monospecific polyclonal antibodies: one anti-GPIIb-IIIa antibody, the second specific for GPIIb, and the third specific for GPIIIa. After thrombin stimulation, the alpha-granule labeling disappeared whereas membrane labeling increased. Platelets from GT did not display labeling on plasma membranes, OCS membranes, or alpha-granule membranes. Platelets from the three patients with GPS displayed intense labeling of the plasma membrane and the OCS membrane, as well as the abnormal small alpha-granules and along the inside of large vacuoles (which contain the granule membrane protein [GMP]-140). In cultured immature MK from normal progenitors, both peptide components of GPIIb-IIIa appeared in the Golgi saccules and vesicles, and in the small precursors of alpha-granules, labeling both their membranes and their matrix. It was then observed only on the membrane of the mature MK alpha-granules, although labeling was less consistent than on the platelet granules. The MK plasma membrane and demarcation membrane system also displayed GPIIb-IIIa labeling. In conclusion, this study demonstrates that GPIIb-IIIa is present on the internal face of the alpha-granule membranes of platelets (where it appears early during MK maturation) as well as in the abnormal alpha-granules of gray platelets; it is absent from GT type I platelets.
authors.affiliation: Départment d'Angio-hématologie and INSERM U.150, Hôpital Lariboisière, Paris, France.
authors.forename: E M
authors.initials: EM
authors.lastname: Cramer
authors.forename: G F
authors.initials: GF
authors.lastname: Savidge
authors.forename: W
authors.initials: W
authors.lastname: Vainchenker
authors.forename: M C
authors.initials: MC
authors.lastname: Berndt
authors.forename: D
authors.initials: D
authors.lastname: Pidard
authors.forename: J P
authors.initials: JP
authors.lastname: Caen
authors.forename: J M
authors.initials: JM
authors.lastname: Massé
authors.forename: J
authors.initials: J
authors.lastname: Breton-Gorius
mesh_terms: D000918:Antibody Specificity; D001791:Blood Platelet Disorders / Q000378:metabolism / Q000473:pathology; D001792:Blood Platelets / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D015550:Cell Degranulation / Q000502:physiology; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism* / Q000648:ultrastructure; D005340:Fibrinogen / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008533:Megakaryocytes / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000379:methods; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism* / Q000502:physiology; D013577:Syndrome; D013915:Thrombasthenia / Q000378:metabolism / Q000473:pathology; D013917:Thrombin / Q000494:pharmacology
chemical_list: D010980:Platelet Membrane Glycoproteins; D005340:Fibrinogen; D013917:Thrombin