Neutrophils and NETs have recently been associated with crosstalk between inflammation and thrombosis. Besides playing a role in innate immunity, neutrophils are involved in thrombosis by releasing procoagulant and anticoagulant mediators. Neutrophil Extracellular Traps (NETs), which are extruded from neutrophils on activation by inflammatory stimuli, have been shown to provide a “scaffold” for thrombosis and to increase the resistance of clots to fibrinolysis. However, the exact cellular and biochemical mechanisms behind some of these reactions are not yet fully understood.
This thesis describes the use of human neutrophils and a neutrophil-like cell model (PLB-985 cell line) to investigate the role of neutrophils/NETs in blood coagulation, fibrin formation, clot stability and clot porosity. Specifically, the experiments were aimed at investigating the effects of neutrophils on fibrinopeptide A and B release and comparing the effects of neutrophil-like cells, human neutrophils and their NETs on the structure of fibrin fibres amongst other investigations, in order to decipher how neutrophils/NETs interact with the fibrin network.
Results using coagulation factor-specific deficient plasmas showed that NETs promoted clotting independently of FXII, FXI and FVII, and contributed to the formation of a denser clot architecture that is more resistant to lysis. Neutrophils induced blood clotting in a different manner than NETs, more specifically mediated by FXI. Both neutrophils and NETs also delayed clot lysis in plasma. Neutrophil-like cells, PLB-985 NETs and human NETs induced the formation of a fibrin fibre network structure, and significantly increased the diameter of fibrin fibres. Human neutrophils increased the release of fibrinopeptide B in plasma, but human neutrophil-induced clots lack a substantial fibrin scaffold and form only short and thin fibrin fibres. This study shows a distinctive role for neutrophils and NETs in coagulation and contributes to a better understanding of their mechanisms.
