Reduced tissue factor (thromboplastin) activity in von Willebrand's disease

Atherosclerosis and coronary bypass surgery in hereditary factor VII deficiency

A 66-year-old man with homozygous deficiency of factor VII (less activity than 4 percent of normal) had a minimal hemorrhagic tendency and severe coronary atherosclerosis, and underwent aortocoronary saphenous vein bypass surgery. Although plasma factor VII coagulant activity and cross-reacting material were markedly reduced, comparable amounts of factor VII antigen were detected in peripheral blood mononuclear cells of both the patient and of a normal subject by Western blotting techniques. Accelerated coagulation was observed following brief exposure of the patient's phytohemagglutinin-stimulated peripheral blood mononuclear cells to low concentrations of ambient factor VII in vitro. Evidence indicates that factor VII plays a role in vivo in both hemostasis and atherogenesis and it might be assumed that factor VII deficiency would both predispose to excessive bleeding and forestall atherosclerosis. However, these observations suggest that factor VII-mediated thrombin generation may proceed by partitioning of small amounts of factor VII on tissue factor-expressing cells and that factor VII contained within monocytes may facilitate tissue factor-induced coagulation by these cells. These features may provide efficient coagulation activation despite a deficiency of the plasma coagulant protein. The current results may explain, at least in part, the minimal bleeding tendency, and also the occurrence of thrombosis and atherosclerosis in certain persons with factor VII deficiency.

In vitro stimulation of monocyte tissue factor activity by autologous platelets

Washed human platelets were found to enhance phytohemagglutinin (PHA)-stimulated tissue factor (TF) synthesis when incubated with autologous mononuclear cell cultures. Furthermore, platelets increased TF synthesis even when no other stimulator was present during the incubation. Experiments utilizing similar cultures derived from blood of patients with Glanzmann's disease, von Willebrand's disease, and platelet storage pool disease indicated that platelets with each of these genetic defects possessed the capacity to enhance the synthesis of this initiator of coagulation by unstimulated cells as did normal platelets. The degree of platelet enhancement varied between individuals, but for any given donor, the extent of the effect depended on the concentration of platelets used. The effect was demonstrable at platelet/monocyte ratios ranging from a low of approximately 15 to the highest ratio used, about 300. For comparison the ratio of these two cellular elements in normal human blood is estimated to be approximately 1,000. These findings may reflect a relationship between these two cell types that can occur in vivo.

Monocyte tissue factor activity in anticoagulant-treated patients

The tissue factor coagulant activity of peripheral blood monocytes was measured in 20 patients on long-term anticoagulant treatment with warfarin and in 21 healthy individuals. Contrary to expectations, tissue factor activity was not reduced in the warfarin-treated group and was, in fact, elevated in several patients. No relationship existed between the daily warfarin dose or the degree of prolongation of the prothrombin time and the monocyte tissue factor activity. These results indicate that monocyte tissue factor activity is not necessarily reduced to below normal levels with warfarin treatment.

[The importance of the plasmatic blood clotting system in the early stages of arterial thrombogenesis (author's transl)]

Apart from today's concept of arterial thrombogenesis, a mechanism of the early events in arterial thrombus formation is proposed, which also includes recent insight into the nature of the blood vessel wall and its interaction with the plasmatic blood clotting system. Observations have accumulated indicating that at the site of lesions of the interior vessel lining thromboplastic activity does appear to induce local thrombin formation. Under conditions of high arterial blood flow thrombin interacts with platelets culminating in the formation of a white thrombus. Based on these considerations, which in part may still be speculative, the possibility may evolve to develop a new highly specific prophylaxis and therapy of arterial thrombosis.