Changes in the concentration and distribution of tissue factor pathway inhibitor in Behcet's disease and systemic lupus erythematosus: effect on the prethrombotic state

Background-Tissue factor pathway inhibitor (TFPI) is an anticoagulant which modulates the tissue factor (TF) dependent pathway, acting on the factor V IIa/TF complex, factor Xa, and thrombin. Although most TFPI is found in ass ociation with plasma lipoproteins and platelets, the functional pool is bou nd to vascular endothelium and is released into the circulation on stimulat ion with heparin or low molecular weight heparin (LMWH). Objective-To assess the vascular endothelial TFPI pool in patients with Beh cet's disease (BD) or systemic lupus erythernatosus (SLE). Methods-Plasma TFP1 concentrations were determined before, and 20 and 60 mi nutes after subcutaneous LMWH injection in 15 newly diagnosed patients with BD and 12 with SLE, and in 12 healthy controls. Results-Baseline median TFPI was 149.5 ng/ml in healthy subjects, and the p ercentage change in TFPI at 20 minutes (((value at 20th min - baseline valu e)/baseline value) x 100) was 575.2. TFP1 concentrations in patients with B D were initially normal at baseline (136.0 ng/ml), but the percentage chang e (44.7) was significantly lower than in the patients with SLE and the cont rols. Baseline TFPI concentrations in patients with SLE (83.0 ng/ml) were l ower than in the control group, but the TFPI response to stimulation with L MWH reached a level (626.4%) comparable to that of the controls. Conclusion-Depletion of the functional endothelial pool in BD and low circu lating concentrations of TFPI despite an intact pool in SLE may be importan t in the pathogenesis of thrombosis in these vasculitic syndromes.