Platelet tissue factor is not expressed transiently after platelet activation

摘要

Blood coagulation is initiated by the binding of plasma factor Vll/VIIa to cell surface-expressed tissue factor (TF). Normally, TF expression is confined to subendothelial tissues like fibroblasts1 and pericytes2 to limit blood coagulation to sites of vascular injury. Consistent with this notion, our laboratory demonstrated previously that platelets do not express active TF constitutively,3'4 or as a result of de novo synthesis, transfer from monocytes, or a-granule release.5 Recently, Camera et al suggested that expression of TF by platelets occurs rapidly after activation, and is transient,6 explaining our inability to observe detectable TF antigen and activity after a 2-hour platelet stimulation.5 In that study,6 3 different anti-TF antibodies (2 obtained from commercial sources and another obtained from Dr Y. Nemerson, Mt Sinai School of Medicine, New York, NY [deceased]) were used and TF antigen was detected on the platelet surface after activation with a 6-amino acid protease activated receptor-1 (PAR1) agonist peptide for 15 minutes. Using a commercially available antibody (American Diagnostica; 45-07CJ), an ~ 50% increase in the mean fluorescence intensity (MFI) of the immunostained, activated platelets was observed when compared with unactivated platelets, or when activated platelets were stained with an isotype-matched control antibody.