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Defective adhesion of blood platelets to vascular microfibrils in the Bernard-Soulier syndrome
F Fauvel-Lafève1, V Tabaka, J P Caen
1Unité 353 Inserm, Hôpital Saint Louis, Paris, France.
Abstract:
Bernard-Soulier syndrome (BSS) platelets, which lack the membrane glycoprotein complex Ib-IX, do not adhere to subendothelium. The adhesion of platelets from two patients with BSS to subendothelial microfibrils (MFs) and type I collagen was compared in an in vitro assay adapted to patients with low platelet count. With both patients, platelet adhesion to MFs was strongly defective, whereas the adhesion to collagen was normal. The involvement of GPIb in the MFs-induced platelet adhesion was confirmed by the inhibitory effect of a MoAb (AN51) to the von Willebrand (vWF) factor binding domain of GPIb. The adhesion of platelets to MFs thus requires GPIb-IX and an axis MFs-vWF-GPIb-IX seems therefore to be prevalent in the reactivity of platelets with subendothelium.
Insights
Bernard-Soulier syndrome (BSS) platelets lack the essential glycoprotein complex Ib-IX, impairing their adhesion to microfibrils. This study confirms the critical role of the microfibril-von Willebrand factor-glycoprotein Ib-IX axis in platelet reactivity.
Area of Science:
- Hematology
- Platelet Biology
- Vascular Biology
Background:
- Bernard-Soulier syndrome (BSS) is characterized by defective platelet adhesion.
- Platelets in BSS lack the glycoprotein complex Ib-IX, crucial for interacting with the subendothelium.
- Understanding the specific adhesion defects in BSS is vital for diagnosing and managing bleeding disorders.
Purpose of the Study:
- To investigate the adhesion properties of BSS platelets to subendothelial microfibrils (MFs) and type I collagen.
- To elucidate the role of glycoprotein Ib (GPIb) in platelet adhesion to MFs.
- To confirm the importance of the microfibril-von Willebrand factor-GPIb-IX pathway in platelet-subendothelium interactions.
Main Methods:
- An in vitro adhesion assay was adapted for patients with low platelet counts.
- Adhesion of platelets from two BSS patients to MFs and collagen was assessed.
- The effect of a monoclonal antibody (MoAb AN51) targeting the GPIb von Willebrand factor binding domain was evaluated.
Main Results:
- Platelet adhesion to MFs was significantly defective in both BSS patients.
- Platelet adhesion to type I collagen was normal in both patients.
- The MoAb AN51 inhibited MFs-induced platelet adhesion, confirming GPIb involvement.
Conclusions:
- Platelet adhesion to subendothelial microfibrils critically requires the GPIb-IX complex.
- The MFs-von Willebrand factor-GPIb-IX axis is a primary pathway for platelet adhesion to the subendothelium.
- These findings highlight the specific adhesion defect in Bernard-Soulier syndrome.