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Some patients with von Willebrand's disease do not respond to stimuli such as venous occlusion and infusion of a vasopressin analogue DDAVP. In these patients, fibrinolytic activity is not enhanced and von Willebrand's factor is not released into the blood. Skin biopsies and cryostat sections were used to study the fibrinolytic activity of skin vessels and localization of tissue plasminogen activator (t-PA) in three patients with severe form of von Willebrand's disease. On fibrin films, no fibrinolysis developed around the skin vessels of the patients; however, using specific polyclonal and monoclonal antibodies to t-PA, and peroxidase coupled specific IgG, presence of t-PA antigen was demonstrated in endothelial cells (EC) of all of them. In plasma no t-PA activity was detected either before or after venous occlusion although t-PA inhibitor activity was in a normal range. Small amounts of t-PA antigen was measured in blood by ELISA. From these results, it is concluded that in patients with severe forms of von Willebrand's disease, t-PA present in EC is not functional and can not transform plasminogen into plasmin.

It was previously demonstrated that insoluble sulphonated polystyrene resins possessed an anticoagulant heparin-like activity in the presence of plasma. The antithrombic activity is dependent on the surface density of the sulphonated groups and involves plasmatic anti T-III. This anticoagulant activity makes this material interesting for blood compatibility concerning its effect on the coagulation system. As these anticoagulant biomaterials may be used “in vivo”, their compatibility with endothelial cells (EC) is of great interest. In the present study, EC from human umbilical cord vein were cultured in 96 well plates in presence and absence of cryoprecipitate considered as the reference culture surfaces, and in wells covered with sulphonated polystyrene beads (SPB). Cell growth in this various conditions was observed and the following parameters were compared : rate of growth of EC, presence of Von Willebrand factor (VWF) by immunofluorescence, release and synthesis of EC specific antigens : VWF, tissue plasminogen activator (T-PA) and tissue plasminogen activator inhibitor (PAI). On SPB, cellular growth was found to be in a normal range but cell morphology was somewhat different. VWF antigen was identified in cells grown either on SPB or on reference wells. Non stimulated cells, incubated in serum free medium released a basic level of VWF in the supernatant. Thrombin enhanced the release of VWF from cells cultured on coated or uncoated dishes and from cells cultured on wells covered with SPB as well. In paralell, VWF in cell extracts decreased after thrombin stimulation and no difference was observed with cells cultured in presence or in absence of SPB. Without stimulation a small amount of t-PA was only observed in the supernatant 24 H samples. Thrombin stimulation induced a comparable release of t-PA from cells cultured either on SPB or reference surfaces. t-PA synthesis, measured in cell extracts did not show significant differences. In contrast, SPB inhibited the release of PAI from EC stimulated or not stimulated by thrombin. Studies are in progress to determine whether PAI is released and absorbed by SPB or absent from the cells.