Background: Platelets are classically described to play an important role in the generation of fibrin at the site of injury by supporting the generation of thrombin. Indeed, in vitro, thrombin and collagen are both needed to induce the expression of negative phospholipids at the surface of (COATED) platelets. However, in the in vivo laser-induced injury model, thrombus formation and fibrin generation are independent of platelet-collagen interactions (Dubois et al., Blood, 2006). Neutrophils were described to be the first cells recruited at the site of injury. The presence and role of procoagulant platelets in this model is to date unknown.

Aims: The goal of our study was to investigate the role of endothelial cells, neutrophils and platelets on the activation of the blood coagulation cascade.

Methods: In vivo, the contribution of endothelial cells and platelets was determined using intravital confocal microscopy. Negative phospholipids signal was detected using fluorescent Annexin-V. In vitro, both static and flow endothelial cell culture (IBIDI system) were studied.

Results: In vivo, following a laser-induced injury, fibrin was colocalized with endothelial cells and neutrophils but not with platelets. Depletion of platelets did not affect the generation of fibrin. The presence of negative phospholipids was detected on the endothelial cells and neutrophils but not on platelets. The interaction of neutrophils with activated endothelial cells is sufficient enough to activate the coagulation cascade. Interestingly, whereas the platelet thrombus reaches a maximal size 80 to 120 sec post-injury, fibrin generation constantly increases for 6h following the laser injury surrounding the vessel wall.

Conclusions: We conclude that endothelial cells and neutrophils but not platelets are implicated in the activation of the blood coagulation cascade leading to thrombus formation following a laser induced injury in living mice. Moreover, in vitro experiments confirm that activated endothelial cell express negative phospholipids.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/endothelial-cell-and-neutrophil-interactions-are-required-for-the-activation-of-the-blood-coagulation-cascade-leading-to-thrombus-formation-following-a-laser-induced-injury/