A study on antiprothrombin antibodies in antiphospholipid syndrome

In this study we investigated the frequency and the type of manifestations of antiprothrombin antibodies (aFII) in patients with antiphospholipid syndrome (APS). In 16 (84.2%) of 19 patients with lupus anticoagulant (LA) and either anticardiolipin antibodies or antiphosphatidylserine antibodies, two types of abnormal patterns were shown on a crossed immuno-electrophoresis technique using anti-human prothrombin murine IgG. The slow-moving peak of prothrombin was detected in 8 patients, while a peak in the other patients had the slow-moving shoulder. These slow-moving materials might represent prothrombin-aFII complexes. In 13 patients who were studied on Western blots, IgGs of 11 patients (84. 6%) bound to human purified prothrombin, and the IgGs of 7 (53.8%) of these patients also bound to human purified alpha-thrombin. Our results indicate that aFII detected in patients with APS may explain part of the mechanism of LA.