Complex Interaction of Platelets, von Willebrand Factor and Leukocytes, in Whole Blood at High Shear Rates Is Mediated by Platelet GPIIb/IIIa Receptor.

We studied the contribution of von Willebrand factor (vWF) into blood cell adhesion to collagen-coated surfaces in whole blood of healthy volunteers. Adhesion of blood cells to collagen I was measured at shear rate of 2300 sec-1. The interaction of platelet GPIIb/IIIa receptor with vWF was blocked with monoclonal anti-GPIIb/IIIa antibodies. The degree of cell adhesion was quantified by measuring the intensity of scattered light after 15-min perfusion: in samples with blocked GPIIb/IIIa it decreased to 0.39±0.13 V vs 0.06±0.03 V in control samples (p=0.002). Under a fluorescence microscope, intensively stained structures consisting of vWF, platelets, and leukocytes attached to the collagen surface were observed. After blockade of GPIIb/IIIa, these structures were absent. Leukocyte recruitment at high shear rates is a time-dependent process sensitive to complex interaction of vWF, leukocytes, and platelets, in which the platelet GPIIb/IIIa receptor is essential.

Kinetics of Platelet Adhesion to Protein-Coated Surface in Whole Blood Samples at High Flow Rates.

We studied platelet adhesion to fibrinogen-coated surface in whole blood samples under conditions of high flow rates. The degree of platelet adhesion was evaluated by the intensity of laser light scattered from protein-coated optical surface with adhered platelets. The intensity of adhesion in whole blood samples at high flow rates was by 2.7 (2.4; 4.1) times higher than in platelet-rich plasma samples. Among the factors intensifying platelet adhesion in the whole blood at high flow rates, von Willebrand factor is of utmost importance. At low flow rates, platelet adhesion almost totally depends on platelet-fibrinogen interaction. At high flow rates, the interactions of platelets with both fibrinogen and von Willebrand factor become equally important.

Real-Time Recording of Platelet Adhesion to Fibrinogen-Coated Surface under Flow Conditions.

We present a testing system allowing real-time recording of the kinetics of platelet adhesion to fibrinogen-coated surface under flow conditions. The system consists of an optical flow chamber, semiconductor laser, two photodetectors, analog-to-digital converter, computer, and peristaltic pump. Platelet adhesion to fibrinogen-coated surface is recorded with two photodetectors and analyzed by the intensity of total internal reflection and scattered laser radiation at the boundary of the blood sample and fibrinogen-coated optical surface. Kinetics of platelet adhesion was studied as a function of shear rate and platelet concentration. The specificity of platelet adhesion with proteins on the surface of the flow chamber was verified by blocking IIb/IIIa glycoprotein complex on platelets with Fab2 fragments of monoclonal antibodies.

Relationship between the Level of Circulating CD45+ Platelets and Development of Restenosis after Implantation of Drug-Eluting Stents to Patients with Coronary Heart Disease.

The study was carried out in 126 patients with stable angina pectoris, who underwent elective coronary artery stenting with drug-eluting stents and follow-up angiography within 6-12 months thereafter. Five significant risk factors of restenosis were identified by binary comparisons of different variables. The logistic regression equation that included the level of CD45-positive platelets, diabetes, small vessel stenting, number of simultaneously implanted stents in one patient, and lesion length demonstrates the highest level of prediction of in-stent restenosis (OR=22.8; p<0.001). ROC-analysis demonstrated high prognostic value of the logit model (area under ROC curve 0.87, p<0.001). The data suggest that a close relationship exists between the development of restenosis and the level of circulating CD45+ platelets.