Generation of Tissue factor-rich microparticles in an ex vivo whole blood model

Abstract

The aim of this study was to investigate the role of blood cells in the expression of tissue factor (TF) and P-selectin in platelets and microparticles from blood stimulated with lipopolysaccharide (LPS), with or without the further addition of phorbol myristyl acetate (PMA). TF activity was found to be associated with platelets after 2 h incubation of whole blood with LPS or LPS + PMA, while no TF activity was detected in microparticles from blood subjected to such stimulation. In blood stimulated for 6 and 24 h, addition of PMA to the samples led to a substantial increase in TF activity associated with microparticles, compared with stimulation with LPS alone. Addition of PMA to blood samples also led to a three-fold increase in the amount of P-selectin found in the isolated microparticle fraction, and a 50% reduction in P-selectin measured in platelets, compared with LPS alone used for stimulation. In a different experiment, TF-rich microparticles were shown to be absorbed very efficiently by neutrophils in a calcium-independent reaction. Our results imply that LPS stimulation of whole blood is associated with a direct transfer of TF from monocytes to platelets in the absence of free TF-rich microparticles, which probably is accounted for by the fusion of TF-rich microparticles with activated platelets exposing P-selectin. Further addition of PMA to samples generates both free TF-rich microparticles as well as enhanced transfer of TF from monocytes to platelets.

Platelet-Derived Microparticles and Platelet Count in Preterm Newborns

“…The calculated r value seems to indicate that the platelet count has no relation to the percentage of PDMP. PDMP not only play an important role in the coagulation system as a major source of PF3 [19] but also cooperate with neutrophils [10,20] . They are closely associated at sites of hemorrhage and thrombosis [21] .…”

Procoagulant Microparticles

“…Multiple fusions and exchanges between monocyte, endothelial, and platelet plasma or MP membranes have been considered. [17][18][19] Polynuclear leukocytes constitute another controversial source of blood-borne TF evidenced by MP labeling, which does not exclude fusion or phagocytosis events between cell lineages. 20,21 The contribution of endothelial-derived MPs (EMPs) to blood-borne TF appears limited in the absence of stimulation, its importance being evoked under circumstances of drastic endothelial activation.…”

Tissue Factor Structure and Function

“…However, due to the controversy related to the presence of TF on some cell types and platelets, the presence of TF on microparticles shed by those cells remains a subject of the discussion. For example, while the role of lipopolysaccharide-stimulated monocytes as a source of microparticles containing active TF has been established [98, 110–112], that of platelets and granulocytes remains questionable [110, 113–115]. Despite the controversies related to sources of TF-bearing microparticles, there has been a growing body of evidence that this form of TF is associated with pathologic conditions, such as pulmonary embolism [116], venous thromboembolism [117], and disseminated intravascular coagulation [118], particularly in patients with various types of malignancy [118–122].…”