Immunohistochemical detection of uPA, tPA, and PAI-1 in a stasis-induced deep vein thrombosis model and its application to thrombus age estimation

We immunohistochemically examined the expression of urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (tPA), and plasminogen-activator inhibitor type-1 (PAI-1) using venous thrombi developed by ligation of the inferior vena cava (IVC) in mice. The uPA-, tPA- and PAI-1-positive cells could be firstly detected 5, 7, and 3 days, respectively, after IVC ligation. Morphometrically, the number of PAI-1-positive cells was significantly higher than those of uPA- and tPA-positive cells at later than 7 days. In all of the thrombus samples aged 10–21 days, the uPA/PAI-1 and tPA/PAI-1 ratios were >0.1 and >0.2, respectively. In contrast, all of the thrombus samples aged 1–7 days had uPA/PAI-1 of <0.1 and tPA/PAI-1 ratios of <0.2. These findings implied that uPA/PAI-1 of >0.1 and tPA/PAI-1 of >0.2 indicated an age of 10 days or more. Moreover, in four of five samples aged 10 days, uPA/PAI-1 ratios were <0.3, and the remaining one had uPA/PAI-1 of 0.32. All thrombi aged 14–21 days showed values greater than 0.3. Thus, uPA/PAI-1 ratios, markedly exceeding 0.3, strongly indicated an age of more than 14 days. The present study demonstrated that the immunohistochemical detection of uPA, tPA, and PAI-1 was suitable to estimate the age of venous thrombi.