title: A murine antiglycoprotein Ib complex monoclonal antibody, SZ 2, inhibits platelet aggregation induced by both ristocetin and collagen.
abstract: A new monoclonal antibody (MoAb), SZ 2, reactive with the human platelet glycoprotein Ib complex has been produced by the hybridoma technique. SZ 2 immunoprecipitated the components of the glycoprotein Ib complex, glycoprotein Ib and glycoprotein IX, from Triton-X-100-solubilized, periodate-labeled platelets. Western blot analysis indicated that the epitope for SZ 2 was on the alpha-subunit of glycoprotein Ib. Scatchard analysis of SZ 2 binding to formaldehyde-fixed, washed platelets revealed a single class of binding sites with Kd = 6.6 +/- 3.3 X 10(-10) mol/L and 15,200 +/- 4,100 binding sites per platelet (mean +/- SD, n = 10). Intact antibody and its purified (Fab')2 fragments not only inhibited the ristocetin-dependent binding of von Willebrand factor to platelets and ristocetin-induced platelet agglutination but also inhibited platelet aggregation induced by Type I collagen and platelet-activating factor (PAF). SZ 2 inhibited platelet serotonin and beta-thromboglobulin release in response to these stimuli and also platelet thromboxane A2 formation in response to ristocetin and collagen. SZ 2 was without effect on platelet aggregation or release in response to other platelet stimuli such as ADP, thrombin, or arachidonic acid. The inhibition by SZ 2 of collagen- and PAF-induced platelet aggregation is surprising in that Bernard-Soulier syndrome platelets, which lack the glycoprotein Ib complex, respond normally to both these stimuli. SZ 2 was unreactive toward Bernard-Soulier syndrome platelets, as evaluated by fluorescence-associated cell sorting, and had no effect on the collagen- and PAF-induced aggregation of Bernard-Soulier syndrome platelets. The combined results suggest that the inhibition by SZ 2 of collagen- and PAF-induced aggregation of normal platelets is steric and are consistent with the glycoprotein Ib complex and the platelet collagen and PAF receptor(s) being adjacent in the human platelet plasma membrane.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D003094:Collagen / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D012310:Ristocetin / Q000037:antagonists & inhibitors*
chemical_list: D000911:Antibodies, Monoclonal; D010980:Platelet Membrane Glycoproteins; D012310:Ristocetin; D003094:Collagen