Toll-Like Receptor 9 Signaling Is Critical for Early Experimental Deep Vein Thrombosis Resolution

Objective— Toll-like receptors (TLR) bridge innate immunity and host responses, including inflammation. Sterile inflammation such as a venous thrombus (V t ) may involve TLR signaling, including TLR9. Methods and Results— TLR9 signaling on thrombus resolution was investigated using a mouse model of stasis V t . V t were significantly larger in TLR9−/− 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 TLR9−/− mouse thrombi. Vein wall interferon-α, interleukin-1α, and interleukin-2 were significantly reduced in TLR9−/− mice compared with WT. Thrombus cell death pathway markers were not significantly altered at 2 days, but caspase-1 was reduced in TLR9−/− thrombi at 8 days. MyD88 confers TLR9 intracellular signaling, but MyD88−/− mice had V t resolution similar to that of WT. However, inhibition of the NOTCH ligand δ-like 4 was associated with larger V t . Finally, stimulation with a TLR9 agonist was associated with smaller V t . Conclusion— TLR9 signaling is integral for early and mid-V t resolution through modulation of sterile inflammation, maintaining a TH1 milieu, and effects on the thrombosis pathway.