Role of membrane glycoproteins in the interaction of blood platelets with the vessel wall--the study on platelet adhesion to in vitro cultured subendothelial matrix.

Adhesion of platelets to the subendothelium is an essential step in hemostasis and thrombosis. Several receptors for adhesive macromolecules have been identified on platelets and are included in the integrin family. To clarify the role of platelet membrane glycoproteins in the interaction of platelets with the subendothelium, 51Cr-labeled platelet adhesion assay and antibody-blocking experiments were performed by using in vitro cultured subendothelium under the static condition. The platelet adhesion in this assay was inhibited by anti-GPIa (VLA-2), GPIc (VLA-5) and -GPIc'-(VLA-6) antibodies, while anti-GPIb and -GPIIb/IIIa antibodies had no effect. Platelets from the patients with Glanzmann's thrombasthenia could also attach to the subendothelium, whereas those from a patient whose platelets lacked GPIa failed to attach to the extracellular matrix (ECM). The monoclonal antibodies against fibronectin and laminin which recognized the cell binding domain of these molecules inhibited the platelet adhesion when they were pre-treated with ECM. Furthermore, antibody-blocking experiments revealed that the percent inhibition by the combination of anti-GPIa, -GPIc and -GPIc' antibodies used herein was approximately 75%. They did not completely inhibit the attachment. These results suggest that the interactions of collagen, fibronectin and laminin with their receptors on platelets are involved in the mechanism of platelet adhesion to subendothelium.