Using a perfusion chamber and confocal
laser scanning microscopy, we analyzed the interplay of
von Willebrand factor (VWF) and
fibrinogen during
thrombus growth on a
collagen surface under physiologic high shear rate conditions. During initial thrombogenesis, platelet thrombi were constructed totally by VWF, not by
fibrinogen.
Fibrinogen accumulated predominantly inside the growing thrombi as a function of time, whereas the
thrombus surfaces directly exposed to flow were occupied constantly by VWF throughout the observation period. In perfusion of
afibrinogenemia (AF) blood lacking both plasma and platelet
fibrinogen, the final height and volume of thrombi were significantly reduced compared with controls, albeit the area of surface coverage was normal. The impaired
thrombus growth in AF was only partially corrected by the addition of purified
fibrinogen to AF blood, whereas the addition of purified VWF to blood of severe
von Willebrand disease (VWD) completely normalized the defective
thrombus growth in this disease. Thus, the initial 2-dimensional
thrombus expansion involves only VWF, whereas the time-dependent accumulation of
fibrinogen, released from activated platelets, acts as a core adhesive
ligand, increasing
thrombus strength and height and resulting in 3-dimensional
thrombus development against rapid blood flow.