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 (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 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-alpha, interleukin-1 alpha, 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 VT resolution similar to that of WT. However, inhibition of the NOTCH ligand delta-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. (Arterioscler Thromb Vasc Biol. 2011; 31: 43-49.)