We have recently demonstrated in Schistosoma mansoni infection that rat and human platelets could very efficiently kill parasite larvae, both in vivo and in vitro. The study of this IgE-dependent platelet effector function has led us to several subsequent findings. They concern: (1) the existence of a specific receptor for IgE on the platelet surface; (2) its close association with a platelet membrane glycoprotein of essential functional importance, the GPIIb-IIIa complex; (3) the observation, in extrinsic allergic asthma, of an allergen-specific IgE-dependent platelet activation; (4) the identification, in aspirin-sensitive asthma, of a similar, but non-IgE-dependent, platelet activation selectively induced by cyclo-oxygenase inhibitors, and prevented by salicylate. Beyond their implication in anti-parasite immunity, these findings provide a basis for new insights on the participation of platelets in disease.

The ultrastructure and cytochemistry of megakaryocytes from two patients with a familial gray platelet syndrome are described. Although the Golgi zones appeared normally developed, the megakaryocytes lacked alpha-granules. Catalase-containing particles were normal in number. In immature megakaryocytes, granules measuring from 0.05-0.1 mu and having an electron-dense core occurred in the Golgi area. These granules, which are considered as the precursors of alpha-granules in normal megakaryocytes, appeared unable to mature, and their number decreased with the megakaryocyte maturation. The presence of dense material in distended demarcation membranes and/or vacuoles suggested that their content was discharged. It is suggested that myelofibrosis present in the bone marrow from these two patients may be related to the possible excretion of a polypeptide growth factor normally contained in the alpha-granules. Megakaryocytes grown by the plasma clot procedure from blood precursors isolated from the two patients also did not exhibit alpha-granules, which were replaced by vacuoles. Our findings suggest that the lack of alpha-granules in gray platelets may be related to a defective megakaryocyte-committed cell, and evidence is presented which suggests that the precursors of alpha-granules are produced but that their contents are then lost.

Crossed immunoelectrophoresis of Triton X-100 solubilized proteins from normal and abnormal platelets was performed with rabbit antibodies raised against normal platelets. In Bernard-Soulier platelets protein 13 was not detected, and neither the amphiphilic (probably GP Ib) nor the hydrophilic (glycocalicin) glycocalicin-related proteins were seen when monospecific antiglycocalicin antiserum was used. The most prominent precipitate, 16, and platelet fibrinogen, 24 were not detected in platelets of two patients with type I thrombasthenia, whereas in one patient with type II thrombasthenia fibrinogen was clearly detected, but the amount of protein 16 remained severely reduced. Protein 16 was heavily labeled after lactoperoxidase-catalyzed (125)I iodination of normal platelets, and was precipitated by IgG-L, an alloantibody from a polytransfused thrombasthenic patient. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or protein 16 cut out from immunoplates showed two (125)I-labeled glycoprotein bands, which migrate as GP IIb and GP IIIa. SDS-PAGE of (125)I-labeled type I thrombasthenic platelets showed no periodic acid-Schiff bands or peaks of radioactivity in the GP IIb and GP IIIa regions, whereas in the GP I region both the periodic acid-Schiff band intensity and the radiolabeling were within the normal range. Autoradiography after crossed immunoelectrophoresis of iodinated thrombasthenic platelets showed that the bulk of radioactivity was bound to protein 17. This glycoprotein, which was also present in normal and Bernard-Soulier platelets, migrates in the GP I region on SDS-PAGE. Thus, the bulk of radioactivity observed in the GP I region after SDS-PAGE is associated with protein 17 and not with glycocalicin.

Using peroxidase coupled antibodies to human factor VIII, factor VIII related antigen (F VIIIRA) was localized in platelets and megakaryocytes of normal and Von Willebrand’s patients. Megakaryocytes and washed platelets were fixed either in glutaraldehyde alone or in a mixture of tannic acid, paraformaldehyde and glutaraldehyde and then incubated with the peroxidase coupled antibodies. In normal platelets, the peroxidase was found in two locations, on the plasma membrane and surface connecting system (S.C.S.) and in the cytoplasm associated with the membrane complex and dense tubular system. The plasma membrane of the megakaryocyte and the demarcating membrane system were not labelled. Antigen was localized in the perinuclear space, in smooth reticulum and clear vesicles, known to be the future platelet S. C.S. In homozygotes with severe forms of Von Willebrand’s disease (VWd) no F VIIIRA was detected around or in the platelete either before of after transfusion of normal cryo or after incubation of their washed platelets in normal plasma. In less severe forms, with detectable F VIIIRA in the plasma there is no such clear correlation between plasma and platelet F VIIIRA. Some have antigen in all platelets with a low plasma level. Others have two populations of platelets some with and others totally lacking antigen. In genetic variants of the disease all the platelets are normally labelled.

A new technique for platelet isolation from five ml of total blood on metrizamide gradients has been applied to the study of platelet coagulant activities.” Assay methods have been described : contact product forming activity (CPFA), collagen induced coagulant activity (CICA) and platelet factor three (PF3) have been measured in the metrizamide gradient platelets (MGP) and found similar to that of platelets in platelet richplasma (PRP). Platelet coagulant activities of the MGP have been measured in patients with hemorragie tendencies like Bernard-Soulier (B-S) patients or those with thrombotic tendencies including diabetics with or without vascular complications or patients with transient ischemic attacks (TIA). CICA was not found in. all the 3 patients with B-S syndrome. 3 of the 10 diabetics showed an increased CPFA activity while 5 showed an increased CICA activity contrasting with the normal activities found in diabetics without vascular complications ; PF3 activity is increased in the two groups of diabetics. 3 patients of the 7 with TIA had an increased CPFA as well CICA. The results suggest that these activities may play some role in diabetics with vascular complications and in some cases with TIA.