UTILIZATION OF DILUTE RUSSELL VIPER VENOM TIME TO DETECT AUTOANTIBODIES AGAINST BETA(2)-GLYCOPROTEIN-I WHICH EXPRESS ANTICOAGULANT ACTIVITYIN THE PRESENCE BUT NOT IN THE ABSENCE OF EXOGENOUS PHOSPHOLIPIDS

Lupus anticoagulant (LA) is a general term to define immunoglobl ulins interfering with phospholipid-dependent coagulation tests. It is now clear that the phospholipid-dependence of some LA is related to the pr esence of the phospholipid-binding plasma protein beta 2-glycoprotein I (beta 2-GPI) and that autoantibodies to beta 2-GPI might represent a specific category of LA. To verify this hypothesis we have purified I gG autoantibodies to beta 2-GPI from plasma of 6 patients with antipho spholipid antibody syndrome, by means of agarose-immobilized human bet a 2-GPI. All 6 preparations tested positive in anti-beta 2-GPI IgG ant ibody ELISA and showed a marked LA activity by prolonging dilute Russe ll Viper Venom Time (dRVVT) from a minimum of 5.3 s in patient # 1 to a maximum of 41.1 s in patient # 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 activit y bf the IgG preparations was not detectable in the absence of FL, in which case the ratio between dRVVT obtained in the presence and absenc e of IgG autoantibodies to beta 2-GPI was close to 1. This pattern was confirmed by using plasma from patients with antiphospholipid antibod y syndrome testing positive for anti-beta 2-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.