A Fifty Percent Reduction of Platelet Surface Glycoprotein Ib Does Not Affect Platelet Adhesion Under Flow Conditions

Abstract

Glycoprotein (GP) Ib is an adhesion receptor on the platelet surface that binds to von Willebrand Factor (vWF). vWF becomes attached to collagens and other adhesive proteins that become exposed when the vessel wall is damaged. Several investigators have shown that during cardiopulmonary bypass (CPB) surgery and also during platelet activation in vitro by thrombin or thrombin receptor activating peptide (TRAP) GPIb disappears from the platelet surface. Such a disappearance is presumed to lead to a decreased adhesive capacity. In the present study, we show that a 65% decrease in platelet surface expression of GPIb, due to stimulation of platelets in Orgaran anticoagulated whole blood with 15 μmol/L TRAP, had no effect on platelet adhesion to both collagen type III and the extracellular matrix (ECM) of human umbilical vein endothelial cells under flow conditions in a single-pass perfusion system. In contrast to adhesion, ristocetin-induced platelet agglutination was highly dependent on the presence of GPIb. Immunoelectron microscopic studies showed that GPIb almost immediately returned to the platelet surface once platelets had attached to collagen. In a subsequent series of experiments, we showed that when less than 50% of GPIb was blocked by an inhibitory monoclonal antibody against GPIb (6D1), platelet adhesion under flow conditions remained unaffected.

In vitro function of platelet concentrates prepared after filtration of whole blood or buffy coat pools

“…A strong correlation between the percentage of platelets able to bind antibodies that recognize the N‐terminal of CD42b and in vivo recovery has been reported; however, levels observed here (> 88% at day 7) are higher than those associated with poor in vivo recovery [27]. Poor expression of CD42b might result in reduced platelet function; however, blockade of 50% of CD42b sites on platelets does not affect platelet adhesion under flow conditions in vitro [28]. Furthermore, heterozygote carriers for Bernard–Soulier syndrome (who also have 50% of CD42b) are not prone to bleeding episodes [29].…”

A comparison of haematopoietic stem cells from umbilical cord blood and peripheral blood for platelet production in a microfluidic device

“…This was caused by ectodomain shedding and could be prevented by co‐incubation with a metalloproteinase inhibitor. Importantly, GPIbα levels were not decreased to levels relevant to impede haemostasis . Contrary to GPIbα, an increase in integrin β 3 expression was found.…”

In vitro properties of platelets stored in a small container for pediatric transfusion

“…We found that GPIb remained unchanged on PLTs during storage in the test container. GPIb decreased when storing ¼ of a unit in the reference container but the decrease was less than what has been shown to affect PLT adhesion …”