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Beta2-glycoprotein I binding to platelet microparticle membrane specifically reduces immunoreactivity of
L Vallar1, V Regnault, V Latger-Cannard
1Laboratoire Franco-Luxembourgeois de Recherche Biomédicale (CNRS and CRP-Santé), Center Universitaire, Luxembourg.
Abstract:
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.
Insights
Beta2-glycoprotein I (beta2GPI) binds to platelet-derived microparticles (PMP), potentially modulating their functions. This binding specifically affects GPIIb/IIIa immunoreactivity, suggesting a regulatory role for beta2GPI in platelet-related processes.
Area of Science:
- Immunology
- Hematology
- Biochemistry
Background:
- Platelet-derived microparticles (PMP) are released from activated platelets and carry surface proteins.
- Beta2-glycoprotein I (beta2GPI) is an autoantigen implicated in autoimmune diseases.
- The interaction between beta2GPI and PMP, and its functional consequences, require further investigation.
Purpose of the Study:
- To investigate the binding of beta2GPI to PMP.
- To determine the effect of beta2GPI binding on the immunoreactivity of GPIIb/IIIa on PMP.
- To explore the potential functional modulation of PMP by beta2GPI.
Main Methods:
- Isolation of PMP from human platelets stimulated with A23187.
- Surface plasmon resonance spectroscopy to analyze beta2GPI binding kinetics and affinity.
- Flow cytometry to assess the impact of beta2GPI on antibody binding to PMP surface markers.
Main Results:
- Beta2GPI, activated protein C (APC), and annexin V bound to immobilized PMP, indicating exposed anionic phospholipids.
- Beta2GPI binding to PMP was calcium-dependent and occurred with a dissociation constant (KD) of 1.7 x 10(-7) M.
- Beta2GPI, but not APC or annexin V, reduced the binding of certain anti-GPIIb/IIIa monoclonal antibodies (mAbs) to PMP, while other markers remained unaffected.
Conclusions:
- Beta2GPI specifically interacts with PMP and influences GPIIb/IIIa immunoreactivity.
- Beta2GPI may act as a modulator of GPIIb/IIIa-dependent functions associated with PMP.
- These findings highlight a novel role for beta2GPI in platelet microparticle biology.