ADAMTS13 deficiency in mice results in increased leukocyte rolling per minute in unstimulated mesenteric veins. (A) Leukocyte rolling on the vessel wall was recorded in two to three unstimulated veins (200–300 μm diameter) per mouse. There was an ∼2.5-fold increase in leukocyte rolling per minute on the endothelium in Adamts13^−/− compared with Adamts13^+/+ mice, suggesting endothelial activation. The absence of ADAMTS13 activity on a VWF-deficient background did not increase leukocyte rolling, indicating that the increased leukocyte rolling observed in Adamts13^−/− mice is dependent on the presence of VWF. Data represent the mean ± SEM. (B) P-selectin–dependent rolling in Adamts13^−/− mice. The unstimulated veins of Adamts13^−/− mice were infused with either control Ig or anti–P-selectin Ig (n = 6 veins from three mice of each group). Endogenous leukocytes and platelets were labeled with Rhodamine 6G. Representative photographs are shown. Lines delineate the blood vessel. The white arrow indicates a labeled leukocyte. Bars, 50 μm. Video 1 is available.