Utilization of dilute Russell's viper venom time to detect autoantibodies against beta 2-glycoprotein I which express anticoagulant activity in the presence but not in the absence of exogenous phospholipids.

Lupus anticoagulant (LA) is a general term to define immunoglobulins interfering with phospholipid-dependent coagulation tests. It is now clear that the phospholipid-dependence of some LA is related to the presence of the phospholipid-binding plasma protein β2-glycoprotein I (β2-GPI) and that autoantibodies to β2-GPI might represent a specific category of LA. To verify this hypothesis we have purified IgG autoantibodies to β2-GPI from plasma of 6 patients with antiphospholipid antibody syndrome, by means of agarose-immobilized human β2-GPI. All 6 preparations tested positive in anti-β2-GPI IgG antibody ELISA and showed a marked LA activity by prolonging dilute Russell Viper Venom Time (dRVVT) from a minimum of 5.3 s in patient no. 1 to a maximum of 41.1 s in patient no. 3. These IgG preparations behaved as typical LA, with this activity tending to disappear in the presence of increasing phospholipid (PL) concentrations. Moreover, the LA activity of the IgG preparations was not detectable in the absence of PL, in which case the ratio between dRVVT obtained in the presence and absence of IgG autoantibodies to β2-GPI was close to 1. This pattern was confirmed by using plasma from patients with antiphospholipid antibody syndrome testing positive for anti-β2-GPI IgG antibodies. These findings suggest that dRVVT performed both in the presence and absence of PL might constitute a sensitive screening test to detect specific antibodies with LA activity.