Failure of Thrombus to Resolve in Urokinase-Type Plasminogen Activator Gene–Knockout Mice

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Abstract
Background— Monocytes may have an important role in the resolution of venous thrombosis. Increased expression of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) is associated with an ingress of monocytes into the thrombus. This study was designed to evaluate the importance of these activators in thrombus resolution. Methods and Results— Inferior caval vein thrombosis was induced in cohorts of adult wild-type, uPA gene-knockout (uPA−/−), and tPA gene-knockout (tPA−/−) mice in a flow model. Thrombi were harvested from wild-type and uPA−/− mice (n=60 per group) between 1 and 60 days. Thrombi were also obtained from groups of wild-type and tPA−/− mice (n=24 per group) between 1 and 28 days. Thrombus size and macrophage content were measured by computer-assisted image analysis. Thrombus resolution was significantly impaired in the uPA−/− mice compared with wild-type controls (P<0.0001) but was unaffected in tPA−/− mice. Monocyte content in wild-type mice was highest at 14...