title: Interaction of AP-2, a monoclonal antibody specific for the human platelet glycoprotein IIb-IIIa complex, with intact platelets.
abstract: A murine monoclonal antibody, designated AP-2, reacts specifically with the complex formed by human platelet membrane glycoproteins IIb and IIIa, but does not react at all with the individual glycoproteins. Purified AP-2 covalently coupled to Sepharose CL4B was used as an immunoadsorbent column to purify the IIb-IIIa complex from a preparation of Triton X-100-solubilized human platelet proteins. Radioiodinated AP-2 was shown to bind to a single class of sites, with 57,400 +/- 9,700 molecules bound per cell (mean +/- S.D.) at saturation and a dissociation constant (Kd) of 0.64 +/- 0.15 nM (mean +/- S.D.). Binding could not be readily reversed even after a 1-h incubation with a 100-fold excess of cold antibody. AP-2 inhibits ADP-induced binding of radiolabeled fibrinogen to gel-filtered platelets in a noncompetitive fashion, consistent with the previous observation that AP-2 also inhibits the aggregation of platelets in plasma induced by a number of physiologic agonists, including adenosine diphosphate, epinephrine, collagen, thrombin, and arachidonic acid. Using AP-2, we have obtained evidence that the IIb-IIIa complex exists in the membrane of intact nonstimulated platelets and that complex integrity is not affected by external calcium ion concentration.
mesh_terms: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D001792:Blood Platelets / Q000032:analysis*; D002462:Cell Membrane / Q000032:analysis; D002846:Chromatography, Affinity / Q000379:methods; D006023:Glycoproteins / Q000032:analysis* / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D007700:Kinetics; D008970:Molecular Weight; D010980:Platelet Membrane Glycoproteins
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D006023:Glycoproteins; D010980:Platelet Membrane Glycoproteins