The effects of tissue factor pathway inhibitor and anti-beta-2-glycoprotein-I IgG on thrombin generation

BACKGROUND AND OBJECTIVES: Recent evidence suggests that autoantibodies to tissue factor pathway inhibitor (TFPI) and/or antiphospholipid antibodies (aPL) may contribute to upregulation of the tissue factor (TF) pathway of blood coagulation and the development of thrombotic complications in the antiphospholipid syndrome (aPS). The aim of this study was to determine the influence of aPL e.g. anti-beta-2-glycoprotein-I (anti-beta2GPI) and anti-prothrombin, on in vitro TF-induced thrombin generation in the presence and absence of TFPI. DESIGN-AND-METHODS: IgG fractions were collected from subjects with aPL (n=21) and normal controls (n=36). Anti-TFPI activity was determined after incubation of IgG isolated from control or subject plasma with pooled normal plasma using an amidolytic assay for TFPI. The influence of IgG fractions and purified aPL (anti-beta2GPI and anti-prothrombin) on TF-induced in vitro thrombin generation was determined using a chromogenic assay of thrombin activity. RESULTS: Patients with aPL had significantly elevated thrombin generation (median [interquartile range]) compared to normal controls (112.0 [104.0-124.0]% vs 89.9 [85.7-100.9]%, respectively; p