Beta2-glycoprotein I binding to platelet microparticle membrane specifically reduces immunoreactivity of glycoproteins IIb/IIIa.
We have investigated beta2-glycoprotein I (beta2GPI) binding to platelet-derived microparticles (PMP) and its effect on GPIIb/IIIa. PMP were isolated from washed human platelets after stimulation with A23187, and analyzed by surface plasmon resonance spectroscopy. Beta2GPI as well as activated protein C (APC) or annexin V bound to PMP-coated sensorchips, demonstrating exposure of anionic phospholipids on immobilized PMP. Beta2GPI binding was impaired by calcium and occurred in a concentration-dependent manner with apparent k(on) = 2.6 x 10(4) M(-1) s(-1) and k(off) = 4.4 x 10(-3) s(-1), corresponding to a KD value of 1.7 x 10(-7) M. When analyzed by flow cytometry, the binding of certain mAbs specific for GPIIb and/or GPIIIa was reduced in the presence of beta2GPI but not of APC or annexin V, whereas the binding of anti-GPIb or anti-P-selectin mAbs, or of soluble fibrinogen remained unchanged. These results suggest a broad but specific influence of beta2GPI on GPIIb/IIIa immunoreactivity, and indicate that beta2GPI may act as a modulator of GPIIb/IIIa-dependent functions of PMP.
Laboratoire Franco-Luxembourgeois de Recherche Biomédicale (CNRS and CRP-Santé), Center Universitaire, Luxembourg.
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Vallar
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Regnault
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Latger-Cannard
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Lecompte
D000911:Antibodies, Monoclonal / Q000378:metabolism; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects / Q000648:ultrastructure*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D005340:Fibrinogen / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism* / Q000494:pharmacology*; D006801:Humans; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D020349:Surface Plasmon Resonance; D053482:beta 2-Glycoprotein I
D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D053482:beta 2-Glycoprotein I; D000001:Calcimycin; D005340:Fibrinogen; D002118:Calcium