Analysis of CD41⁺ microparticles from human plasma demonstrates that the majority are CD62P⁻ and contain full-length filamin A. (A) Microparticles were isolated from human plasma, platelets activated with thrombin and collagen, or platelets activated by Ca²⁺-ionophore A23187 and analyzed for CD62P expression by flow cytometry. The percentage of CD62P⁺ (□) and CD62P⁻ (■) microparticles is indicated. Error bars indicate the standard deviation of 4 independent assays. (B) Filamin A was assayed by immunoblot analysis in resting human platelets, human platelets exposed to thrombin and collagen, microparticles isolated from platelet-free plasma, or microparticles isolated from activated platelets.