title: Identification of thrombin activatable fibrinolysis inhibitor (TAFI) in human platelets.
abstract: Thrombin activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like proenzyme that after activation down-regulates fibrinolysis. Platelets are known to contain antifibrinolytic factors that are secreted during platelet activation. Therefore, the presence of TAFI in platelets was analyzed. TAFI was identified in platelets in a concentration of about 50 ng/1 x 109 platelets and was secreted on platelet activation. Thrombin-mediated activation of platelet-derived TAFI resembled that of plasma-derived TAFI with respect to stimulation by thrombomodulin and spontaneous loss of activity at 37 degrees C. The different glycosylation of platelet-derived TAFI compared with plasma-derived TAFI suggests that platelet-derived TAFI is synthesized in the megakaryocyte. This suggestion was substantiated by the detection of mRNA in the megakaryocytic cell lines DAMI and CHRF, representing the intermediate and late stages of megakaryocyte development. These results establish the presence of TAFI in platelets and suggest a role for platelet-derived TAFI in the protection of the clot against fibrinolysis.
authors.affiliation: Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center Utrecht, The Netherlands. lmosnier@scripps.edu
authors.forename: Laurent O
authors.initials: LO
authors.lastname: Mosnier
authors.forename: Paula
authors.initials: P
authors.lastname: Buijtenhuijs
authors.forename: Pauline F
authors.initials: PF
authors.lastname: Marx
authors.forename: Joost C M
authors.initials: JC
authors.lastname: Meijers
authors.forename: Bonno N
authors.initials: BN
authors.lastname: Bouma
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D025901:Carboxypeptidase B2 / Q000097:blood* / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D005455:Fluorescent Antibody Technique; D006031:Glycosylation; D006801:Humans; D008533:Megakaryocytes / Q000201:enzymology; D008856:Microscopy, Fluorescence; D015539:Platelet Activation; D012333:RNA, Messenger / Q000032:analysis; D013917:Thrombin / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D025901:Carboxypeptidase B2; D013917:Thrombin