Tissue factor-expressing monocytes inhibit fibrinolysis through a TAFI-mediated mechanism, and make clots resistant to heparins

• Published in: Haematologica (Roma) 2009-06, Vol.94 (6), p.819-826
• Main Authors: Semeraro, Fabrizio, Ammollo, Concetta T, Semeraro, Nicola, Colucci, Mario
• Format: Article
• Language: English
• Subjects: Antibodies - pharmacology; Biological and medical sciences; Carboxypeptidase B2 - metabolism; Cells, Cultured; Dose-Response Relationship, Drug; Enoxaparin - pharmacology; Fibrinolysis - drug effects; Fibrinolytic Agents - pharmacology; Hematologic and hematopoietic diseases; Heparin - pharmacology; Humans; Lipopolysaccharides - pharmacology; Medical sciences; Monocytes - cytology; Monocytes - metabolism; Original; Thrombin - metabolism; Thromboplastin - immunology; Thromboplastin - metabolism; Time Factors; Tissue Plasminogen Activator - pharmacology
• ISSN: 0390-6078; 1592-8721
• DOI: 10.3324/haematol.2008.000042

Department of Biomedical Sciences and Human Oncology, Section of General and Experimental Pathology, University of Bari, Bari, Italy Correspondence: Mario Colucci, Department of Biomedical Sciences and Human Oncology, Section of General and Experimental Pathology Policlinico, Piazza G. Cesare 11 70124 Bari, Italy. E-mail: mario.colucci{at}dimo.uniba.it Background: Thrombin is the main activator of the fibrinolysis inhibitor TAFI (thrombin activatable fibrinolysis inhibitor) and heightened clotting activation is believed to impair fibrinolysis through the increase of thrombin activatable fibrinolysis inhibitor activation. However, the enhancement of thrombin generation by soluble tissue factor was reported to have no effect on plasma fibrinolysis and it is not known whether the same is true for cell-associated tissue factor. The aim of this study was to evaluate the effect of tissue factor-expressing monocytes on plasma fibrinolysis in vitro . Design and Methods: Tissue factor expression by human blood mononuclear cells (MNC) and monocytes was induced by LPS stimulation. Fibrinolysis was spectrophotometrically evaluated by measuring the lysis time of plasma clots containing LPS-stimulated or control cells and a low concentration of exogenous tissue plasminogen activator. Results: LPS-stimulated MNC (LPS-MNC) prolonged fibrinolysis time as compared to unstimulated MNC (C-MNC) in contact-inhibited but not in normal citrated plasma. A significantly prolonged lysis time was observed using as few as 30 activated cells/µL. Fibrinolysis was also impaired when clots were generated on adherent LPS-stimulated monocytes. The antifibrinolytic effect of LPS-MNC or LPS-monocytes was abolished by an anti-tissue factor antibody, by an antibody preventing thrombin-mediated thrombin activatable fibrinolysis inhibitor activation, and by a TAFIa inhibitor (PTCI). Assays of thrombin and TAFIa in contact-inhibited plasma confirmed the greater generation of these enzymes in the presence of LPS-MNC. Finally, the profibrinolytic effect of unfractionated heparin and enoxaparin was markedly lower (~50%) in the presence of LPS-MNC than in the presence of a thromboplastin preparation displaying an identical tissue factor activity. Conclusions: Our data indicate that LPS-stimulated monocytes inhibit fibrinolysis through a tissue factor-mediated enhancement of thrombin activatable fibrinolysis inhibitor activation and make clots resistant to the profibrinolytic activity of heparins, thus