title: Thrombospondin promotes platelet aggregation.
abstract: Thrombospondin (TSP), isolated from human platelets, promotes aggregation of both nonstimulated platelets and platelets stimulated with thrombin or ADP. The TSP-promoted aggregation is specific since a monoclonal antibody against TSP inhibits the effect of exogenously added TSP and inhibits thrombin-induced platelet aggregation in the absence of added TSP. Several lines of evidence suggest that TSP mediates its effect on aggregation of nonstimulated and stimulated platelets through different platelet-surface receptor systems. The TSP-promoted aggregation of nonstimulated platelets was inhibited by a monoclonal antibody to platelet glycoprotein IV (GPIV), but not by a monoclonal antibody to the fibrinogen receptor, GPIIb-IIIa. In contrast, the antibody to GPIIb-IIIa totally inhibited the TSP-potentiated aggregation of thrombin-stimulated platelets, whereas the antibody to GPIV has no effect. Thus, these studies suggest that TSP promotes platelet aggregation by at least two mechanisms--one dependent on and one independent of the platelet fibrinogen receptor system.
authors.affiliation: Lankenau Medical Research Center, Philadelphia, PA 19151.
authors.forename: G P
authors.initials: GP
authors.lastname: Tuszynski
authors.forename: V L
authors.initials: VL
authors.lastname: Rothman
authors.forename: A
authors.initials: A
authors.lastname: Murphy
authors.forename: K
authors.initials: K
authors.lastname: Siegler
authors.forename: K A
authors.initials: KA
authors.lastname: Knudsen
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000502:physiology; D001792:Blood Platelets / Q000502:physiology*; D006023:Glycoproteins / Q000276:immunology / Q000502:physiology*; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects*; D013917:Thrombin / Q000494:pharmacology; D019699:Thrombospondins
chemical_list: D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D019699:Thrombospondins; D000244:Adenosine Diphosphate; D013917:Thrombin