HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Lupus Anticoagulants Form Immune Complexes With Prothrombin and Phospholipid That Can Augment Thrombin Production in Flow

are performed. In contrast, thrombus formation occurs in flowing blood. We reasoned that the effects of LA IgGs on coagulation might be different when examined under flow conditions, which is more representative of the in vivo situation. We hypothesized that enhanced binding of prothrombin to phospholipid in the presence of LA IgG would result in increased thrombin production by prothrombinase when reactions are performed in flow. We now report that a murine monoclonal antiprothrombin antibody and 7 of 7 LA IgGs tested enhanced binding of prothrombin to phospholipid vesicles and that the monoclonal antibody (MoAb) and 4 of 6 LA IgGs from patients with a history of thrombosis augmented thrombin production by purified prothrombinase components in flow. These observations suggest that LA might propagate coagulation in flowing blood by facilitating prothrombin interaction with the damaged blood vessel wall.