Neutrophils can promote clotting via FXI and impact clot structure via neutrophil extracellular traps in a distinctive manner in vitro

Abstract

Neutrophils and neutrophil extracellular traps (NETs) have been shown to be involved in coagulation. However, the interactions between neutrophils or NETs and fibrin(ogen) in clots, and the mechanisms behind these interactions are not yet fully understood. In this in vitro study, the role of neutrophils or NETs on clot structure, formation and dissolution was studied with a combination of confocal microscopy, turbidity and permeation experiments. Factor (F)XII, FXI and FVII-deficient plasmas were used to investigate which factors may be involved in the procoagulant effects. We found both neutrophils and NETs promote clotting in plasma without the addition of other coagulation triggers, but not in purified fibrinogen, indicating that other factors mediate the interaction. The procoagulant effects of neutrophils and NETs were also observed in FXII- and FVII-deficient plasma. In FXI-deficient plasma, only the procoagulant effects of NETs were observed, but not of neutrophils. NETs increased the density of clots, particularly in the vicinity of the NETs, while neutrophils-induced clots were less stable and more porous. In conclusion, NETs accelerate clotting and contribute to the formation of a denser, more lysis resistant clot architecture. Neutrophils, or their released mediators, may induce clotting in a different manner to NETs, mediated by FXI.

Pathogenic Basis of Thromboinflammation and Endothelial Injury in COVID-19: Current Findings and Therapeutic Implications

“…Activated macrophages express a cell surface glycoprotein, tissue factor, to initiate the blood coagulation cascades and the generation of thrombin. Activated neutrophils produce a variety of toxic substances, including reactive oxygen species, and NETs, which enhance the coagulation pathways [ 66 , 70 , 71 ]. Collectively, hyperactivation of the innate immune system might contribute to thromboinflammation in severe COVID-19 patients.…”

Coagulation and complement: Key innate defense participants in a seamless web

“…Since NETs comprise multiple constituents, including DNA, histones, various proteolytic enzymes, complement factors C3 and FB, lipids and other associated proteins ( 87 , 92 ), they convey a myriad of properties that bridge coagulation and complement ( Figure 3 ). The negatively charged NET components provide surfaces for activation of the contact pathway of coagulation, resulting in generation of FXIa, FXIIa and kallikrein (PKa) ( 93 ). NETs also release or expose functionally active TF and release TF positive extracellular vesicles that participate in the local amplification of thrombin generation.…”

Neutrophil Extracellular Traps (NETs) im Gefäßsystem

“…Der Begriff Immunthrombose wurde geprägt, um den Einfluss des zellulären angeborenen Immunsystems auf das Hämostasesystem zu beschreiben. Die Interaktionen von aktivierten NG sowie NETs mit klassischen Akteuren der Gerinnungskaskade sind zahlreich [ 13 ]. Sie erfolgen über direkte Zell-Zell-Interaktionen mit Thrombozyten, Modulation des Komplementsystems und Aktivierung der intrinsischen sowie extrinsischen Gerinnungskaskade.…”