Xiong, Jing

Cell membrane‐derived microvesicles (MV) are shed into the circulation and reflect cell‐cell interaction, intravascular and intercellular signaling process. Infection increases risk for thrombosis and LPS signaling through toll‐like receptor 4 (TLR 4 ) may activate cells to generate procoagulant (phosphatidylserine surface) MV. This study was designed to investigate MV production from leukocytes and platelets exposed to LPS in vitro . Blood from wild type (WT) and TLR 4 gene deleted (dTLR 4 ) mice was incubated with LPS (500ng/ml or 5ug/ml) for 6 hours. Flow cytometer was used to quantify MV using fluorophore conjugated cell specific antibodies plus annexin‐V. Leukocyte‐ and platelet‐derived MV showed a concentration dependent increase in the blood from WT mice; whereas in dTLR 4 mice increased counts of leukocyte‐ and platelet‐derived MV were observed only at the higher concentration of LPS. At the higher concentration of LPS, numbers of leukocyte‐derived MV increased significantly and the mean number of platelet‐derived MV was two fold greater than under control conditions. These results indicate that low concentrations of LPS act through TLR 4 but higher concentrations of LPS act through other receptors in addition to TLR 4 to increase production of leukocyte‐ and platelet‐derived MV which could account in part for increased thrombotic risk with infection. Supported by AHA‐SDG 30503Z and Mayo Foundation.