MONOCYTE VESICULATION IS A POSSIBLE MECHANISM FOR DISSEMINATION OF MEMBRANE-ASSOCIATED PROCOAGULANT ACTIVITIES AND ADHESION MOLECULES AFTERSTIMULATION BY LIPOPOLYSACCHARIDE

Endotoxin-stimulated monocytes can elicit a dual procoagulant response . They express tissue factor and expose phosphatidylserine in the oute r leaflet of the plasma membrane. Tissue factor, a membrane glycoprote in, is the cellular trigger of blood coagulation reactions. Phosphatid ylserine is an essential anionic phospholipid for surface amplificatio n of thrombin generation. in this study the distribution of these two procoagulant entities between activated monocytes and derived micropar ticles was assessed after stimulation by LPS. The presence of CD14, CD 11a, and CD18, and possible associated adhesion potential were examine d, particularly on microparticles. Tissue factor was evidenced by usin g a specific functional assay and flow cytometry. Phosphatidylserine e xposure was monitored through its catalytic activity in a thrombin gen eration assay and by flow cytometry with the use of FITC-conjugated an nexin V, a protein probe of anionic phospholipids. CD14, CD11a, and CD 18 were detected by flow cytometry. The interaction of microparticle C D11a/CD18 with intracellular adhesion molecule-1 was demonstrated by u sing immobilized recombinant intracellular adhesion molecule-1 fusion protein. The major part of tissue factor and phosphatidylserine-depend ent procoagulant activity was associated with microparticles after LPS stimulation. This was confirmed by flow cytometry. The presence of fu nctional CD1la/CD18, and CD14 on microparticles testifies to an associ ated adhesion potential. These results show that membrane vesiculation could be responsible for dissemination of inducible monocyte procoagu lant activities and suggest that derived microparticles could also par ticipate in endothelium stimulation. This emphasizes the role of monoc yte as a central element in the coupling between inflammation/infectio n and thrombosis.