Characterization of COX-2 expression and activity in platelets from ET patients. (A) Western blot analysis of platelet protein extracts for COX-1 and COX-2 in 4 patients and 1 healthy subject. Proteins were extracted from washed platelets and electrophoresed in 10% SDS polyacrylamide gel under reducing conditions. Gels were blotted onto nitrocellulose membranes, which were incubated with monoclonal antibodies against COX-1 or COX-2. Positivity was revealed by anti–mouse horseradish peroxidase–conjugated antibodies and ECL detection reagent. Protein bands were visualized using Kodak Biomax light film. (B) Correlation between COX-2 expression in platelets, expressed as ΔMFI, and the percentage of TO-positive platelets in 16 patients (●) and 14 healthy subjects (○). (C) Box-whisker plots representing whole blood TXB₂ production in vitro, as reflected by serum TXB₂, in samples from 41 ET patients incubated with vehicle (open box) or NS-398 (striped box) added in vitro, at V0. *P < .001 versus vehicle.