Induced Platelet Agglutination Research Articles

Molecular defect in platelets from patients with bernard-soulier syndrome

An IgG antibody isolated from the serum of a patient with the Bernard- Soulier syndrome induced platelet agglutination in the platelet-rich plasma of 50 normal subjects regardless of their ABO, KOa, KOb, HLA, or PlA1 types. This antibody was nonreactive with platelets from three other Bernard-Saulier syndrome patients. Indirect immunoprecipitation tests using this serum (or purified IgG) and soluble membrane antigens labeled with 125I that had been extracted from normal platelets by the nonionic detergent Nonidet P-40 gave a single radioactive peak at 150,000 MW in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These findings strongly suggest that the antigenic determinant reacting with this antibody is absent from platelets of Bernard-Soulier syndrome patients and that the deficient molecule is of 150,000 MW. The role of this molecule in subendothelial adhesion and macromolecular-mediated aggregations is discussed.

Studies on the mechanism of ristocetin-induced platelet agglutination. Effects of structural modification of ristocetin and vancomycin.

The mechanism by which ristocetin induces platelet agglutination in the presence of the von Willebrand factor was studied by chemically altering ristocetin and a similar antibiotic, vancomycin, by reaction with a water-soluble carbodiimide in the presence of glycine methyl ester at pH 4.75. Altering ristocetin's phenolic groups (which are thought to be important in its peptide-binding properties) resulted in a loss of both platelet-agglutinating and antibiotic activities. Restoring the phenolic groups with hydroxylamine restored both activities. Vancomycin has antibiotic and peptide-binding properties similar to ristocetin's, but differs structurally in having a free carboxyl group and thus a less positive charge at neutral pH. It does not induce platelet agglutination and actually inhibits ristocetin-induced agglutination. Reacting vancomycin with the water-soluble carbodiimide resulted in alteration of phenolic groups and permanent conversion of the carboxyl to a neutral derivative. Restoring the phenolic groups with hydroxylamine (but leaving the carboxyl neutralized) produced a compound with charge properties similar to ristocetin's which induced platelet agglutination as ristocetin does. These data suggest both a binding requirement (mediated through phenolic groups) and a strong positive charge requirement for ristocetin-induced agglutination. The data are consistent with a model wherein positively charged ristocetin binds, via its phenolic groups, to sites on the platelet surface and reduces the platelet's negative charge. This could reduce the electrostatic repulsion between platelets and/or between platelets and the negatively charged von Willebrand factor, and permit the macromolecular von Willebrand factor to cause agglutination by bridging between platelets.

Congenital Afibrinogenemia

Abstract In a study of three subjects with incoagulable blood due to congenital afibrinogenemia, information is presented regarding some basic aspects of coagulation independent, of the fibrinogen-fibrin conversion mechanism. The following facts have been established: (1) Shortly after the blood is exposed to glass, the earliest detectable changes are morphologic alteration in the platelets and their progressive agglutination and lysis. (2) Almost in parallel, plasma antihemophilic activity, originally normal, declines rapidly and practically disappears. (3) Also within minutes, SPCA evolves from its precursor in a normal manner. (4) Acglobulin is rapidly consumed. (5) These changes are well along before detectable amounts of prothrombin have disappeared. (6) Prothrombin consumption proceeds at normal velocity, or slightly faster than normal. (7) Thrombin addition to afibrinogenemic plasma induces platelet agglutination, but this does not occur when thrombin is mixed with platelets alone. (8) The "natural" antithrombic activity of afibrinogenemic plasma is normal. (9) The heparin co-factor of antithrombic activity was demonstrable. (10) Quantitative data were obtained relating the one-stage prothrombin time with the fibrinogen concentration. The theoretic and practical implications of the observations are discussed.