Inhibition of platelet activation by aspirin reduces thrombus formation in a mouse model of TTP. (A) Enzyme-linked immunosorbent assay analysis of TxA2 release from platelets. Washed platelets were treated with saline or botrocetin in the presence or absence of VWF for 7 minutes at 37°C, and released TxA2 was measured by detecting TxB2, a stable metabolite of TxA2, in the supernatant. TTP in WT mice was induced by injection of antibodies to ADAMTS13 and plasma VWF. Aspirin (5 mg/kg, body weight) was given 3 days before VWF administration through oral gavage, twice a day, until the end of the experiment. In mice without TTP, VWF was not administrated after antibody injection. At 24 hours after TTP induction with VWF, mice were euthanized and platelet count in blood and thrombus formation in lung were analyzed. (B) Aggregation of platelets from mice fed with the vehicle or aspirin. Platelet-rich plasma from mice treated with the vehicle control or aspirin was stimulated with arachidonic acids (500 μg/mL), and aggregation was monitored. Quantification of aggregation was inserted inside the figure. (C) Flow cytometry analysis of surface expression of CD61 on platelets from mice treated with the vehicle or aspirin. (D) Representative immunofluorescence images of thrombi in lungs of saline- and aspirin-treated mice with TTP. (E) Quantification of thrombus formation in lung shown in (D). Quantification of the pixels of CD41-positive areas in each field of images. (F) Platelet counts in mice with TTP. Platelet counts in mice at 7 days before experiments (basal level) and at 24 hours after induction of TTP were quantified. Each dot represented a datum from 1 mouse. The data are representative of 5 independent experiments, and data represent mean ± SD. *P < .05.