Microparticle formation after exposure of blood to activated endothelium under flow.

Increased numbers of circulating microparticles (MPs) are indicative of poor clinical outcome in a number of inflammatory disorders, including atherosclerosis. Platelets and megakaryocytes are a major source of MP and are identified by presence of CD42b on the MP surface. MP shed from activated platelets can be identified by presence of P-selectin (CD62P). Tissue factor (TF) is the principal initiator of blood coagulation and its activity has been identified in MPs derived from patient plasma, which may contribute to thrombosis. Here, we have investigated by flow cytometry the expression of TF and CD62P on MP after exposure of diluted whole blood to TNF-activated endothelial cells (EC) both under static conditions and in our newly established model of flow. MPs were significantly increased in blood subjected to flow and this was further enhanced after exposure of blood to TNF-activated EC. MP surface expression of CD62P or TF was upregulated following exposure to TNF-activated EC under flow compared with flow with nonactivated EC or after static coculture with and without prior EC activation. These data strongly suggest that interactions of blood with inflamed EC can modulate production of CD62P and TF bearing MP under flow conditions, and thus may contribute to a prothrombotic environment.