Von Willebrand factor in the vessel wall mediates platelet adherence

A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.

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Von Willebrand factor in the vessel wall mediates platelet adherence

Blood ◽

10.1182/blood.v65.1.85.85 ◽

1985 ◽

Vol 65 (1) ◽

pp. 85-90 ◽

Cited By ~ 126

Author(s):

HV Stel ◽

KS Sakariassen ◽

PG de Groot ◽

JA van Mourik ◽

JJ Sixma

Keyword(s):

Monoclonal Antibody ◽

Shear Rate ◽

Von Willebrand Factor ◽

Vessel Wall ◽

Human Artery ◽

Shear Rates ◽

Platelet Adherence ◽

Wall Shear ◽

Von Willebrand ◽

Willebrand Factor

Abstract A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.

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Glycoprotein Ib, von Willebrand factor, and glycoprotein IIb:IIIa are all involved in platelet adhesion to fibrin in flowing whole blood

Blood ◽

10.1182/blood.v76.2.345.bloodjournal762345 ◽

1990 ◽

Vol 76 (2) ◽

pp. 345-353 ◽

Cited By ~ 1

Author(s):

RR Hantgan ◽

G Hindriks ◽

RG Taylor ◽

JJ Sixma ◽

PG de Groot

Keyword(s):

Platelet Aggregation ◽

Shear Rate ◽

Von Willebrand Factor ◽

Whole Blood ◽

Platelet Adhesion ◽

Thrombus Formation ◽

Shear Rates ◽

Wall Shear ◽

Von Willebrand ◽

Willebrand Factor

We have investigated the molecular basis of thrombus formation by measuring the extent of platelet deposition from flowing whole blood onto fibrin-coated glass coverslips under well-defined shear conditions in a rectangular perfusion chamber. Platelets readily and specifically adhered to fibrin-coated coverslips in 5 minute perfusion experiments done at either low (300 s-1) or high (1,300 s-1) wall shear rates. Scanning electron microscopic examination of fibrin-coated coverslips after perfusions showed surface coverage by a monolayer of adherent, partly spread platelets. Platelet adhesion to fibrin was effectively inhibited by a monoclonal antibody (MoAb) specific for glycoprotein (GP) IIb:IIIa. The dose-response curve for inhibition of adhesion by anti-GPIIb:IIIa at both shear rates paralleled that for inhibition of platelet aggregation. Platelet aggregation and adhesion to fibrin were also blocked by low concentrations of prostacyclin. In contrast, anti- GPIb reduced adhesion by 40% at 300 s-1 and by 70% at 1,300 s-1. A similar pattern of shear rate-dependent, incomplete inhibition resulted with a MoAb specific for the GPIb-recognition region of von Willebrand factor (vWF). Platelets from an individual with severe von Willebrand's disease, whose plasma and platelets contained essentially no vWF, exhibited defective adhesion to fibrin, especially at the higher shear rate. Addition of purified vWF restored adhesion to normal values. These results are consistent with a two-site model for platelet adhesion to fibrin, in which the GPIIb:IIIa complex is the primary receptor, with GPIb:vWF providing a secondary adhesion pathway that is especially important at high wall shear rates.

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Glycoprotein Ib, von Willebrand factor, and glycoprotein IIb:IIIa are all involved in platelet adhesion to fibrin in flowing whole blood

Blood ◽

10.1182/blood.v76.2.345.345 ◽

1990 ◽

Vol 76 (2) ◽

pp. 345-353 ◽

Cited By ~ 80

Author(s):

RR Hantgan ◽

G Hindriks ◽

RG Taylor ◽

JJ Sixma ◽

PG de Groot

Keyword(s):

Platelet Aggregation ◽

Shear Rate ◽

Von Willebrand Factor ◽

Whole Blood ◽

Platelet Adhesion ◽

Thrombus Formation ◽

Shear Rates ◽

Wall Shear ◽

Von Willebrand ◽

Willebrand Factor

Abstract We have investigated the molecular basis of thrombus formation by measuring the extent of platelet deposition from flowing whole blood onto fibrin-coated glass coverslips under well-defined shear conditions in a rectangular perfusion chamber. Platelets readily and specifically adhered to fibrin-coated coverslips in 5 minute perfusion experiments done at either low (300 s-1) or high (1,300 s-1) wall shear rates. Scanning electron microscopic examination of fibrin-coated coverslips after perfusions showed surface coverage by a monolayer of adherent, partly spread platelets. Platelet adhesion to fibrin was effectively inhibited by a monoclonal antibody (MoAb) specific for glycoprotein (GP) IIb:IIIa. The dose-response curve for inhibition of adhesion by anti-GPIIb:IIIa at both shear rates paralleled that for inhibition of platelet aggregation. Platelet aggregation and adhesion to fibrin were also blocked by low concentrations of prostacyclin. In contrast, anti- GPIb reduced adhesion by 40% at 300 s-1 and by 70% at 1,300 s-1. A similar pattern of shear rate-dependent, incomplete inhibition resulted with a MoAb specific for the GPIb-recognition region of von Willebrand factor (vWF). Platelets from an individual with severe von Willebrand's disease, whose plasma and platelets contained essentially no vWF, exhibited defective adhesion to fibrin, especially at the higher shear rate. Addition of purified vWF restored adhesion to normal values. These results are consistent with a two-site model for platelet adhesion to fibrin, in which the GPIIb:IIIa complex is the primary receptor, with GPIb:vWF providing a secondary adhesion pathway that is especially important at high wall shear rates.

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Platelet von Willebrand factor: evidence for its involvement in platelet adhesion to collagen

Blood ◽

10.1182/blood.v70.4.1214.bloodjournal7041214 ◽

1987 ◽

Vol 70 (4) ◽

pp. 1214-1217

Author(s):

E Fressinaud ◽

D Baruch ◽

C Rothschild ◽

HR Baumgartner ◽

D Meyer

Keyword(s):

Shear Rate ◽

Von Willebrand Factor ◽

Platelet Adhesion ◽

Von Willebrand Disease ◽

High Shear ◽

Shear Rates ◽

High Shear Rates ◽

Von Willebrand ◽

Willebrand Factor

Although it is well established that plasma von Willebrand Factor (vWF) is essential to platelet adhesion to subendothelium at high shear rates, the role of platelet vWF is less clear. We studied the respective role of both plasma and platelet vWF in mediating platelet adhesion to fibrillar collagen in a parallel-plate perfusion chamber. Reconstituted blood containing RBCs, various mixtures of labeled washed platelets and plasma from controls or five patients with severe von Willebrand disease (vWD), was perfused through the chamber for five minutes at a shear rate of 1,600 s-1. Platelet-collagen interactions were estimated by counting the radioactivity in deposited platelets and by quantitative morphometry. When the perfusate consisted of normal platelets suspended in normal plasma, platelet deposition on the collagen was 24.7 +/- 3.6 X 10(6)/cm2 (mean +/- SEM, n = 6). Significantly less deposition (16 +/- 2.3) was observed when vWD platelets were substituted for normal platelets. In mixtures containing vWD plasma, significantly greater deposition (9 +/- 2.2) was obtained with normal than with vWD platelets (1 +/- 0.4) demonstrating a role for platelet vWF in mediating the deposition of platelets on collagen. Morphometric analysis confirmed these data. Our findings indicate that platelet, as well as plasma, vWF mediates platelet-collagen interactions at a high shear rate.

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Asialo-von Willebrand factor inhibits platelet adherence to human arterial subendothelium: discrepancy between ristocetin cofactor activity and primary hemostatic function

Blood ◽

10.1182/blood.v70.4.1084.1084 ◽

1987 ◽

Vol 70 (4) ◽

pp. 1084-1089 ◽

Cited By ~ 6

Author(s):

JB Lawrence ◽

HR Gralnick

Keyword(s):

Von Willebrand Factor ◽

Whole Blood ◽

Specific Activity ◽

Human Platelets ◽

Primary Hemostasis ◽

Platelet Adherence ◽

Wall Shear ◽

Von Willebrand ◽

Willebrand Factor ◽

Ristocetin Cofactor

Abstract Platelet adherence at high wall shear rates requires plasma von Willebrand factor (vWF). Clinically, the ristocetin cofactor (RCof) activity is the only widely available assay for vWF function. When purified vWF is treated with neuraminidase to yield asialo-vWF (AS- vWF), its RCof activity is increased by 20% to 40%. AS-vWF binds to normal human platelets independently of ristocetin and induces platelet aggregation in the presence of fibrinogen. To determine whether AS-vWF also shows an enhanced capacity to support platelet adherence to subendothelium, we used the Baumgartner technique. Intact vWF, AS-vWF, or AS-vWF treated with beta-galactosidase (asialo, agalacto-vWF; AS,AG- vWF) was added to normal citrated whole blood before perfusion over human umbilical artery segments (wall shear rate, 2,600 sec-1). Four micrograms per milliliter AS-vWF caused a 69% reduction in total platelet adherence compared with citrated whole blood (P less than .001), and 4 micrograms/mL AS,AG-vWF led to a 48% reduction (P less than .005). With 4 micrograms/mL intact vWF, the platelet adherence values were not significantly different from the controls. No significant differences in subendothelial platelet thrombi or postperfusion platelet counts were evident among any of the groups. In reconstituted afibrinogenemic perfusates, 4 micrograms/mL AS-vWF caused a 42% reduction in platelet adherence (P less than .05). Thus, AS-vWF is a potent inhibitor of platelet adherence, despite its enhanced RCof specific activity. Abnormalities in vWF carbohydrate may play a role in impaired primary hemostasis in some patients with von Willebrand's disease.

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Modulation of von Willebrand Factor A1 Domain-Mediated Platelet Aggregation/Agglutination by α-Thrombin.

Blood ◽

10.1182/blood.v104.11.628.628 ◽

2004 ◽

Vol 104 (11) ◽

pp. 628-628

Author(s):

Grazia Loredana Mendolicchio ◽

Reha Celikel ◽

Kottayil I. Varughese ◽

Brian Savage ◽

Zaverio M. Ruggeri

Keyword(s):

Platelet Aggregation ◽

Shear Rate ◽

Von Willebrand Factor ◽

Platelet Glycoprotein ◽

Shear Rates ◽

Amino Terminal ◽

Low Responder ◽

A1 Domain ◽

Von Willebrand ◽

Willebrand Factor

Abstract Evaluation of the crystal structures of the amino terminal domain of platelet glycoprotein (GP) Ibα bound to the von Willebrand factor A1 domain (VWFA1) or to α-thrombin indicate the absence of significant steric hindrance in a putative triple complex of the two ligands interacting with the same receptor molecule. Superposition of the models reveals that intermolecular contacts may be established between VWFA1 and α-thrombin concurrently bound to GP Ibα, and suggests that these additional interactions could stabilize the intrinsically low affinity binding of the VWF A1 domain. To verify the predictions of the model, we used gel electrophoresis under native conditions and purified components in solution to demonstrate directly the formation of a triple complex. We then sought to evaluate whether α-thrombin could influence the functional effects of the VWF-GP Ibα interaction. For this purpose, we established a model of platelet agglutination/aggregation dependent on the interaction between recombinant dimeric VWFA1 domain, purified from the culture medium of stably transfected D. melanogaster cell lines, and GP Ibα. In this assay, platelet rich plasma prepared from individual donor blood collected with the thrombin inhibitor D-phenyl alanyl-L-prolyl-L-arginine chloromethyl ketone dihydrochloride (PPACK) as an anticoagulant (80 μM) was mixed with varying concentrations of dimeric VWFA1 (0.5-10 μg/ml) and exposed to variable shear rate levels in a cone-and-plate viscometer. Platelet aggregation was observed at shear rates between 6 and 108 dyn/cm2. The response in different normal controls was reproducible but variable in extent, and individuals could be assigned to one of two categories, low responder and high responder. An agglutination response was observed after platelets were treated with 10 μM prostaglandin E1 to block activation, and the distinction between low and high responders remained true under these conditions. For simplicity, agglutinated platelets were still defined as “aggregates”. With activation blocked platelets, aggregates were stable up to a shear rate of 30 dyn/cm2, but began to dissipate at higher levels. The addition of α-thrombin with the active site irreversibly blocked by PPACK at concentrations between 5 and 10 μg/ml substantially increased the extent of the platelet response. This was demonstrated by a faster rate of platelet agglutination/aggregation, a greater stability of aggregates at higher shear rates, and an overall increase in the size of aggregates formed. To demonstrate the latter, samples were exposed to shear stress under selected conditions and immediately fixed with 1% glutaraldehyde for quantitative image analysis. Maximum aggregate size was increased several fold in the presence of α-thrombin, and the difference was particularly evident in low responder individuals in whom dimeric VWFA1 alone caused the formation of small and unstable aggregates. PPACK-blocked thrombin by itself had no effect on platelet aggregate formation at any shear rate tested. Our findings delineate a mechanism through which α-thrombin may stabilize platelet-platelet contacts by mediating a tighter association between VWF A1 domain and GP Ibα receptor. Such a function, independent of proteolytic activity, may enhance platelet deposition at sites of vascular injury.

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Direct Observation of Von Willebrand Factor Elongation and Fiber Formation On Collagen During Acute Whole Blood Exposure to Pathological Flow

Blood ◽

10.1182/blood.v120.21.1070.1070 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1070-1070

Author(s):

Thomas Vincent Colace ◽

Scott L. Diamond

Keyword(s):

Shear Rate ◽

Blood Perfusion ◽

Fiber Formation ◽

Shear Rates ◽

Wall Shear ◽

Long Fibers ◽

Von Willebrand ◽

Collagen Type 1 ◽

Willebrand Factor

Abstract Abstract 1070 Under conditions of pathological shear rate, von Willebrand Factor (vWF) undergoes conformational changes and self aggregation. We sought to visualize this phenomenon using a novel microfluidic model of stenosis and understand its role in thrombus formation in elevated shear rate environments. In severe stenosis, vWF experiences millisecond exposures to pathological wall shear rates (gw). Distinct from shear experiments that last many seconds, we deployed microfluidic devices for single-pass perfusion of whole blood or platelet free plasma (PFP) over fibrillar type 1 collagen (< 50 msec transit time) at pathological gw or spatial wall shear rate gradient (grad gw). Using fluorescent anti-vWF, long thick vWF fibers (>20 mm) bound to collagen were visualized at constant gw > 30,000 s−1 during perfusion of PFP, a process enhanced by EDTA. Rapid acceleration or deceleration of EDTA-PFP at grad gw = ± 5.5 × 105 to 4.3 × 107 s−1/cm did not promote vWF deposition when gw < 30,000. At 19,400 s−1, EDTA-blood perfusion resulted in rolling vWF-platelet nets, while blood perfusion (normal Ca2+) generated large vWF/platelet deposits that repeatedly embolized and were blocked by anti-GP1b or the aIIbβ3 inhibitor GR144053 and did not require shear gradients. Blood perfusion at venous shear rate (200 s−1) produced a stable platelet deposit that was a substrate for massive but unstable vWF-platelet aggregates when flow was increased to 7800 s−1. Supported by collagen and enhanced by platelet GP1b and aIIbβ3, vWF fiber formation occurred during acute exposures to pathological gw but did not require wall shear rate gradients. Figure 1 A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Figure 1. A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Disclosures: No relevant conflicts of interest to declare.

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Platelet von Willebrand factor: evidence for its involvement in platelet adhesion to collagen

Blood ◽

10.1182/blood.v70.4.1214.1214 ◽

1987 ◽

Vol 70 (4) ◽

pp. 1214-1217 ◽

Cited By ~ 36

Author(s):

E Fressinaud ◽

D Baruch ◽

C Rothschild ◽

HR Baumgartner ◽

D Meyer

Keyword(s):

Shear Rate ◽

Von Willebrand Factor ◽

Platelet Adhesion ◽

Von Willebrand Disease ◽

High Shear ◽

Shear Rates ◽

High Shear Rates ◽

Von Willebrand ◽

Willebrand Factor

Abstract Although it is well established that plasma von Willebrand Factor (vWF) is essential to platelet adhesion to subendothelium at high shear rates, the role of platelet vWF is less clear. We studied the respective role of both plasma and platelet vWF in mediating platelet adhesion to fibrillar collagen in a parallel-plate perfusion chamber. Reconstituted blood containing RBCs, various mixtures of labeled washed platelets and plasma from controls or five patients with severe von Willebrand disease (vWD), was perfused through the chamber for five minutes at a shear rate of 1,600 s-1. Platelet-collagen interactions were estimated by counting the radioactivity in deposited platelets and by quantitative morphometry. When the perfusate consisted of normal platelets suspended in normal plasma, platelet deposition on the collagen was 24.7 +/- 3.6 X 10(6)/cm2 (mean +/- SEM, n = 6). Significantly less deposition (16 +/- 2.3) was observed when vWD platelets were substituted for normal platelets. In mixtures containing vWD plasma, significantly greater deposition (9 +/- 2.2) was obtained with normal than with vWD platelets (1 +/- 0.4) demonstrating a role for platelet vWF in mediating the deposition of platelets on collagen. Morphometric analysis confirmed these data. Our findings indicate that platelet, as well as plasma, vWF mediates platelet-collagen interactions at a high shear rate.

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Asialo-von Willebrand factor inhibits platelet adherence to human arterial subendothelium: discrepancy between ristocetin cofactor activity and primary hemostatic function

Blood ◽

10.1182/blood.v70.4.1084.bloodjournal7041084 ◽

1987 ◽

Vol 70 (4) ◽

pp. 1084-1089

Author(s):

JB Lawrence ◽

HR Gralnick

Keyword(s):

Von Willebrand Factor ◽

Whole Blood ◽

Specific Activity ◽

Human Platelets ◽

Primary Hemostasis ◽

Platelet Adherence ◽

Wall Shear ◽

Von Willebrand ◽

Willebrand Factor ◽

Ristocetin Cofactor

Platelet adherence at high wall shear rates requires plasma von Willebrand factor (vWF). Clinically, the ristocetin cofactor (RCof) activity is the only widely available assay for vWF function. When purified vWF is treated with neuraminidase to yield asialo-vWF (AS- vWF), its RCof activity is increased by 20% to 40%. AS-vWF binds to normal human platelets independently of ristocetin and induces platelet aggregation in the presence of fibrinogen. To determine whether AS-vWF also shows an enhanced capacity to support platelet adherence to subendothelium, we used the Baumgartner technique. Intact vWF, AS-vWF, or AS-vWF treated with beta-galactosidase (asialo, agalacto-vWF; AS,AG- vWF) was added to normal citrated whole blood before perfusion over human umbilical artery segments (wall shear rate, 2,600 sec-1). Four micrograms per milliliter AS-vWF caused a 69% reduction in total platelet adherence compared with citrated whole blood (P less than .001), and 4 micrograms/mL AS,AG-vWF led to a 48% reduction (P less than .005). With 4 micrograms/mL intact vWF, the platelet adherence values were not significantly different from the controls. No significant differences in subendothelial platelet thrombi or postperfusion platelet counts were evident among any of the groups. In reconstituted afibrinogenemic perfusates, 4 micrograms/mL AS-vWF caused a 42% reduction in platelet adherence (P less than .05). Thus, AS-vWF is a potent inhibitor of platelet adherence, despite its enhanced RCof specific activity. Abnormalities in vWF carbohydrate may play a role in impaired primary hemostasis in some patients with von Willebrand's disease.

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Shear Induced Reversible Conglomerates of Von Willebrand Factor Networks with Aggregates of Inactivated Platelets - a Fast Switchable Plugging Mechanism

Blood ◽

10.1182/blood.v116.21.2104.2104 ◽

2010 ◽

Vol 116 (21) ◽

pp. 2104-2104

Author(s):

Armin J. Reininger ◽

Marina Napoleone ◽

Jennifer Angerer ◽

Babak Falah ◽

Reinhard Schneppenheim ◽

...

Keyword(s):

Shear Rate ◽

Von Willebrand Factor ◽

Conflicts Of Interest ◽

Arterial Stenosis ◽

Critical Threshold ◽

Simultaneous Formation ◽

Shear Rates ◽

Platelet Aggregates ◽

Von Willebrand ◽

Willebrand Factor

Abstract Abstract 2104 Thrombus growth rate has been reported to be a linear function of very high shear rates beyond 40,000 s-1 (Ku DN, Bioreology. 2007;44(4):273-84), which are thought to occur in severe arterial stenosis. We therefore applied shear rates continuously increasing from 2,000 s-1 to 40,000 s-1 and examined platelet and von Willebrand factor (VWF) interaction in a parallel plate flow chamber under direct visualization. Above a critical threshold of 10,000 to 15,000 s-1 aggregates of inactivated platelets formed when VWF was present in solution and immobilized on the perfused surface (Ruggeri, … Reininger; Blood, 108: 1903–1910, 2006). A new finding was the shear dependent simultaneous formation of VWF strands in and around those platelet aggregates, growing to strands up to several microns thick and up to several tens of microns long, thus forming large VWF networks. Platelets appeared to be enmeshed in the VWF networks but were nevertheless a prerequsite for their formation, mutually fostering each other. Platelet-VWF conglomerates formed at the perfused VWF surface, were constantly rolling in the flow direction, grew in size with increasing shear rate, and were completely reversible below the critical shear rate threshold of 10,000 s-1. VWF networks assembled in whole blood as well as in washed blood cell suspensions reconstituted with VWF. Recombinant full length VWF generated larger VWF networks than a commercial VWF preparation from pooled human plasma. Perfusion of collagen coated surfaces caused assembly of VWF networks anchored to the collagen fibrils and capture of activation-blocked platelets within them at shear rates of 2,000 s-1, leading to residence times of platelet-VWF conglomerates of more than a minute. Newly formed platelet conglomerates could be visualized rolling on the surfaces of already attached conglomerates. When we used a gain of function mutation of VWF, rolling platelet aggregates could be detected at a shear rate as low as 1,500 s-1. We conclude that shear rate activation of VWF leads to reversible platelet-VWF network generation, which may be a crucial mechanism of fast platelet accrual and prolonged arrest times at sites of thrombosis as well as physiological hemostasis. Disclosures: No relevant conflicts of interest to declare.

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