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.

Objective-Toll-like receptors (TLR) bridge innate immunity and host responses, including inflammation. Sterile inflammation such as a venous thrombus (VT) may involve TLR signaling, including TLR9. Methods and Results-TLR9 signaling on thrombus resolution was investigated using a mouse model of stasis VT. VT were significantly larger in TLR9Ϫ/Ϫ mice compared with wild-type (WT) at 2 and 8 days, despite a 2-fold increase in thrombus polymorphonucleic neutrophils at 2 days and monocytes at 8 days, whereas thrombus collagen and neovascularization was 55% and 37% less, respectively, at 8 days. Coincidently, decreased fibrinogen and increased thrombin-antithrombin complex were observed in TLR9Ϫ/Ϫ mouse thrombi. Vein wall interferon-␣, interleukin-1␣, and interleukin-2 were significantly reduced in TLR9Ϫ/Ϫ mice compared with WT. Thrombus cell death pathway markers were not significantly altered at 2 days, but caspase-1 was reduced in TLR9Ϫ/Ϫ thrombi at 8 days. MyD88 confers TLR9 intracellular signaling, but MyD88Ϫ/Ϫ mice had VT resolution similar to that of WT. However, inhibition of the NOTCH ligand ␦-like 4 was associated with larger VT. Finally, stimulation with a TLR9 agonist was associated with smaller VT. Conclusion-TLR9 signaling is integral for early and mid-VT resolution through modulation of sterile inflammation, maintaining a TH1 milieu, and effects on the thrombosis pathway.

Background Post-thrombotic syndrome (PTS) is characterized by a fibrotic vein injury following deep vein thrombosis (DVT). We sought to quantify the change in vein wall thickness in patients who fail to resolve DVT by 6 months and whether there were differences in blood or plasma levels of inflammatory proteins associated with venous remodeling. Methods Patients presenting with confirmed lower extremity DVT were prospectively recruited for this study. Duplex imaging of the lower extremity venous system was performed, and blood was collected at entrance and repeat evaluation with blood draw and ultrasound imaging at 1 and 6 months. DVT resolution and thickness of the vein wall was quantified by ultrasound imaging in each segment affected by thrombus, and a contralateral, unaffected vein wall served as a control. Gene and protein expression of inflammatory markers were examined from leukocytes and serum, respectively. ANOVA or Student’s t-tests were used, and a P <.05 was significant. N = 10 – 12 for all analyses. Results 32 patients (12 patients with DVT resolution at 6 months, 10 patients with persistent thrombus at 6 months, and 10 healthy controls) were compared. Both resolving and non-resolving DVT were associated with 1.5 – 1.8 fold increased vein wall thickness at 6 months (P = .008) as compared with non affected vein wall segments. However, the thickness of the affected segments was 1.4 fold greater in patients who had total resolution of the DVT by 6 months than in patients who had persistent chronic thrombus 6 months after presentation (P = .01). There was a 4 – 5 fold increased level of matrix metalloproteinase-9 (MMP9) in thrombosed patients compared with non-thrombosed patient controls (P <.05), while Toll like receptor-9 (TLR-9) expression was 3 fold less than controls (P <.05) at enrollment. D-dimer and P-selectin were higher in thrombosed as compared to controls at diagnosis, but not at 6 months. Both TLR4 (marker of inflammation) and P-selectin gene expression were higher in leukocytes from patients with chronic DVT compared to those who resolved at one month after diagnosis (P <.05). Conclusions This preliminary study suggests ongoing vein wall remodeling after DVT, measurable by ultrasound and associated with certain biomarkers. At 6 months, the vein wall is markedly thickened, and directly correlates with resolution. This suggests that the vein wall response is initiated early following thrombus formation, and persists even in the presence of total resolution.

OBJECTIVE Deep vein thrombosis (DVT) resolution instigates an inflammatory response, resulting in vessel wall damage and scarring. Urokinase-plasminogen activator (uPA) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), are integral components of the fibrinolytic system, essential for VT resolution. This study determined the vein wall response when exposed to increased and decreased plasmin activity. Methods A mouse inferior vena cava (IVC) ligation model in uPA −/− or PAI-1 −/− and their genetic wild types (B6/SvEv and C57/BL6, respectively) was used to create stasis thrombi, with tissue harvest at either 8 or 21d. Tissue analysis included gene expression of vascular smooth muscle cells (alpha SMA [αSMA], SM22) and endothelial marker (CD31), by real time PCR, ELISA, matrix metalloproteinase (MMP) -2 and 9 activity by zymography and vein wall collagen by picrosirius red histological analysis. A P < .05 was considered significant. RESULTS Thrombi were significantly larger in both 8d and 21d uPA −/− as compared to WT, and were significantly smaller in both 8 and 21d PAI-1 −/− as compared to WT. Correspondingly, 8d plasmin levels were reduced in half in uPA −/− and increased 3 fold in PAI-1 −/− when compared to respective WT thrombi (P < .05, N = 5 – 6). The endothelial marker CD31 was elevated 2 fold in PAI-1 −/− mice at 8d, but reduced 2.5 fold at 21d in uPA −/− as compared with WT (P = .02, N = 5 – 6), suggesting less endothelial preservation. Vein wall VSMC gene expression showed that 8d and 21d PAI-1 −/− mice had 2.3 and 3.8 fold more SM22 and 1.8 and 2.3 fold more αSMA expression than respective WT (P < .05, N = 5 – 7), as well as 1.8 fold increased αSMA (+) cells (N = 3 – 5, P ≤ .05). No significant difference in MMP2 or 9 activity was found in the PAI-1 −/− mice compared with WT, while 5.4 fold more MMP9 was present in 21d WT than 21d uPA −/− (P = .03, N = 5). Lastly, collagen was ~2 fold greater at 8d in PAI-1 −/− IVC as compared to WT (P = .03, N = 6) with no differences observed in uPA −/− mice. CONCLUSIONS In stasis DVT, plasmin activity is critical for thrombus resolution. Divergent vein wall responses occur with gain or loss of plasmin activity, and despite smaller VT, greater vein wall fibrosis was associated with lack of PAI-1.

PE is associated with an early influx of polymorphonuclears and macrophages and monocyte chemoattractant protein-1 elevation within the PA wall. These are temporally associated with thrombus resolution and intimal hyperplasia. These factors may mediate these two processes after PE. This offers targets for further study with the hopes of minimizing the pathophysiologic response to PE.