Abstract 32: Ly6C Lo Monocyte/Macrophages Are Essential for Thrombus Resolution in a Murine Model of Venous Thrombosis

Abstract

Venous thrombosis (VT) results in vein wall injury by promoting inflammation and fibrosis leading to venous reflux, swelling, pain, and potentially, recurrent thrombosis. While prior work has shown that infiltrating leukocytes are important for VT resolution, as of yet, the precise roles of different leukocyte subsets are not well understood. Monocyte/macrophages (Mo/MΦs) are essential for the repair and resolution of tissue injury in other models, and come in inflammatory (Ly6C Hi ) or pro-resolution (Ly6C Lo ) subtypes. We hypothesized that infiltrating Mo/MΦs would be critical to VT resolution. In order to study this in vivo , we utilized a conditional macrophage depletion technique, using CD11b-DTR mice, to examine the effects of Mo/MΦs in a murine model of stasis VT by inferior vena cava ligation. Administration of 10ng/g diphtheria toxoid (DTx) every 48 hours by intra-peritoneal injection in CD11b-DTR mice resulted in an 89% and 55% decrease in circulating monocytes at 24hrs and 48hrs, respectively. When compared to saline controls, DTx injection had no effects on thrombogenic response or IVC thrombus cell populations in C57BL/6 control mice. At 8 days’ post-ligation, DTx treated CD11b-DTR mice had preferentially decreased vein wall-thrombus Ly6C Lo Mo/MΦs as compared with controls. DTx treated mice had significantly larger thrombi (1.7-fold) and less TGF-β, FSP-1, and plasminogen by western immunoblotting (all P-values ≤ 0.01). Consistent with a reduction in Ly6C Lo Mo/MΦs was a significant decrease in cellular TGF-β by intra-cellular flow cytometry. These findings suggest that Ly6C Lo Mo/MΦs are essential for normal VT resolution and may promote thrombus resolution via a plasminogen-mediated mechanism.