Beta2-glycoprotein I in thrombosis: evidence for a role as a natural anticoagulant

Although the physiological role of beta₂-glycoprotein I (B₂GPI) is unknown, in vitro evidence indicates that B₂GPI may be a natural anticoagulant. In this study we have examined whether fluctuations of plasma B₂GPI occur in in vivo coagulation. Serial measurements of B₂GPI and other anticoagulant proteins were performed in 51 patients with thrombotic (group 1: six patients with disseminated intravascular coagulation (DIC), group 2: venous ( n =4) or arterial ( n =17) thrombosis) and non-thrombotic disease (group 3: 24 patients undergoing elective surgery). Reductions in plasma B₂GPI levels were seen in most patients which were roughly proportional to the severity of their illness. Particularly striking reductions of B₂GPI, protein C (PC) and antithrombin III (AT-III) (mean ± 95% CI: 42.7 ± 8.6%, 42.1 ± 14.8%, 39.1 ± 28.4% respectively) were seen in group 1. The reductions in plasma B₂GPI were significantly greater in group 1 than in the other groups. Dilutional factors explain most of the reductions in B₂GPI, PC and AT-III in groups 2 and 3, but contribute little to group 1. In conclusion, although B₂GPI behaves as a 'negative acute phase reactant', the magnitude of reduction of plasma B₂GPI levels, accompanied by reductions in other anticoagulant proteins in patients with DIC, suggests specific consumption of B₂GPI in in vivo coagulation. This study provides further evidence that B₂GPI is an anticoagulant of physiological importance.