In Vivo Role of Neutrophil Extracellular Traps in Antiphospholipid Antibody-Mediated Venous Thrombosis

Objective: Antiphospholipid syndrome (APS) is a leading acquired cause of thrombotic events. While antiphospholipid antibodies have been shown to promote thrombosis in mice, the role of neutrophils has not been explicitly studied. Here, we characterized neutrophils in the context of a new model of antiphospholipid antibody-mediated venous thrombosis. Methods: Mice were administered IgG fractions prepared from patients with APS. At the same time, flow through the inferior vena cava was reduced by a standard stenosis. Resulting thrombi were characterized for size and neutrophil content. Circulating factors and the vessel wall were also assessed. Results: As measured by both thrombus weight and thrombosis frequency, mice treated with IgG from patients with APS demonstrated exaggerated thrombosis as compared with controls. APS thrombi were enriched for citrullinated histone H3 (a marker of neutrophil extracellular traps/NETs). APS mice also demonstrated elevated levels of circulating cell-free DNA and human IgG bound to the neutrophil surface. In contrast, circulating neutrophil numbers and markers of vessel wall activation were not appreciably different between APS and control mice. Regarding therapy, treatment with either deoxyribonuclease (which dissolves NETs) or a neutrophil-depleting antibody reduced thrombosis in APS mice to the level seen in controls. Conclusion: These data support a mechanism whereby circulating neutrophils are primed by antiphospholipid antibodies to accelerate thrombosis. This line of investigation suggests new, immunomodulatory approaches for the treatment of APS. This article is protected by copyright. All rights reserved.