Utilization of Dilute Russell’s Viper Venom Time to Detect Autoantibodies against β2-Glycoprotein I which Express Anticoagulant Activity in the Presence but not in the Absence of Exogenous Phospholipids

Abstract

SummaryLupus 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 # 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 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.

Incidence of a first thromboembolic event in carriers of isolated lupus anticoagulant

“…In most cases aCL antibodies are also positive (same isotype) supporting the presence in plasma of anti-Domain I antibodies as they also preferentially bind the amino terminal part of β2-glycoprotein I [21]. Thus, when LAC is positive and ELISA for abeta2GPI and aCL antibodies are also positive (triple positivity), these tests probably recognize the same antibody directed against Domain I of β2-glycoprotein I [22,23]. This study enrolled carriers of LAC with negative aβ2GPI and aCL ELISA (isolated LAC positivity) and shows that thromboembolic events in the follow up period are few and occur in subjects with other important risk factors for thrombosis.…”

The Diagnosis of the Antiphospholipid Syndrome

“…For the time being it is essential that all the three tests (LAC, aCL and aβ2GPI be carried out if information useful for the discrimination between low and high risk patients is to be obtained. In those presenting triple positivity the risk of thromboembolic events or obstetric complications is very high and aβ2GPI antibodies might represent the common denominator since normal plasma spiked with affinity-purified aβ2GPI antibodies expresses both LA and aCL activity (35,36). The new classification of APS according to the Sydney criteria correctly allocates patients in class I when more than one laboratory criteria is present.…”

Which are the Best Biological Markers of the Antiphospholipid Syndrome?

“…Moreover, Kandiah et al [101] have shown that clotting activities in dRVVT and KCT could be separated by polyacrylamide-immobilized PS but not by CL liposomes. In addition, Pengo et al [102] have demonstrated that purified anti-2-GPI display LA activity prolonging dRVVT only in the presence of PLs, and they proposed to perform dRVVT with and without PLs to identify specific antibodies populations with LA activity. On the other hand, it has been shown that purified anti-II from different patients show different reactivity on dRVVT or KCT: some anti-II prolong mainly dRVVT and some anti-2-GPI KCT [103].…”