PPARγ agonists block the thrombin-induced increase in platelet surface CD40L expression. Purified human platelets were exposed to 20 μM 15d-PGJ₂ or rosiglitazone for 15 minutes and were then stimulated with 0.8 U/mL thrombin for 60 minutes. The platelets were then stained and prepared for flow cytometry with a monoclonal antihuman CD40L antibody or with control isotype antibody. The graph shows a representative experiment with the results presented as the percent of surface CD40L⁺ platelets.