Lupus Anticoagulant Activity Is Frequently Dependent on the Presence of β₂-Glycoprotein I

Summary

Antiphospholipid antibodies (aPL) are defined by anticardioli-pin antibody (aCL) ELISA and prolongation of phospholipid dependent coagulation assays (lupus anticoagulant; LAC). For the binding of aCL to cardiolipin a cofactor, β₂-glycoprotein I (β₂-GPI), is necessary. We have investigated whether the same cofactor is essential for LAC activity. Plasma from 6 LAC positive patients and 3 controls was depleted from β₂-GPI by means of affinity chromatography. From the 6 LAC positive plasmas, 4 became LAC negative (tested with dRWT) when β₂-GPI was depleted and became positive again when purified β₂-GPI (200 μg/ml) was added. A dose response curve showed that addition of 50 μg/ml β₂-GPI to β₂-GPI deficient patient plasma, led to a positive dRWT. Depletion of, and addition of β₂-GPI to plasma from controls had no effect on the dRWT. Measurement of β₂-GPI plasma levels in 19 LAC positive patients, 40 LAC negative patients and 15 controls showed no difference in β₂-GPI levels.

These results show that a combination of aPL and β₂-GPI is essential not only for binding to cardiolipin, but also for LAC activity and imply that low β₂-GPI levels (<50 μg/ml) can lead to false negative LAC tests. These observations may lead to new insights in the pathophysiological complications associated with aPL.

• References

• 1 Derksen RHWM, Hasselaar P, Oosting JD, De Groot PG. The antiphospholipid antibody dilemma. Clin Rheumatol 1990; 9 (No. 1 Suppl. No. 1) 39-44
• 2 McNeil HP, Simpson RJ, Chesterman CN, Krilis SA. Anti-phospholipid antibodies are directed against a complex antigen that induces a lipid-binding inhibitor of coagulation: p₂-glycoprotein I (apolipoprotein H). Proc Natl Acad Sci 1990; 87: 4120-4124
• 3 Galli M, Comfurius P, Maassen C, Hemker HC, DeBaets MH, Breda-Vriesman van PJC, Barbui T, Zwaal RFA, Bevers EM. Anticardiolipin antibodies (ACA) directed not to cardiolipin but to a plasma protein cofactor. Lancet 1990; 335: 1544-1547
• 4 Tan EM, Cohen AS, Fries JF. The 1982 revised criteria for the classification of SLE. Arthritis Rheum 1982; 25: 1271-1277
• 5 Thiagarajan P, Pengo V, Shapiro SS. The use of the dilute Russell viper venom time for the diagnosis of lupus anticoagulants. Blood 1986; 68: 869-874
• 6 Out HJ, Van Vliet M, De Groot PG, Derksen RHWM. A prospective study on fluctuations of lupus anticoagulant activity and anticardiolipin antibody titre in patients with systemic lupus erythematosus. Ann Rheum Dis. 1992 (in press)
• 7 Derksen RHWM, Hasselaar P, Blokzijl L, Gmelig Meyling FHJ, De Groot PG. Coagulation screen is more specific than the anticardiolipin antibody ELISA in defining a thrombotic subset of lupus patients. Ann Rheum Dis 1988; 47: 364-371
• 8 Harris EN. The second international anti-cardiolipin standardization workshop/The Kingston anti-phospholipid antibody study (KAPS) group. Am J Clin Pathol 1990; 94: 476-484
• 9 Oosting JD, Derksen RHWM, Hackeng TM, Van Vliet M, Preissner KT, Bouma BN, De Groot PG. In vitro studies of antiphospholipid antibodies and its cofactor, p₂-glycoprotein I, show negligible effects on endothelial cell mediated protein C activation. Thromb Haemostas 1991; 66: 666-671
• 10 Haupt H, Schwick HG, Storiko K. Uber einen erblichen p₂-Glycopro-tein-I-Mangel. Humangenetik 1968; 5: 291-293
• 11 Schousboe I. Addition of deoxycholate in electroimmunoassay and crossed immunofocusing for quantification of p₂-glycoprotein I and its subfractions. J Biochem Biophys Methods 1982; 6: 105-114
• 12 Bevers EM, Galli M, Barbui T, Comfurius P, Zwaal RFA. Lupus anticoagulant IgG’s (LA) are not directed to phospholipids only, but to a complex of lipid bound human prothrombin. Thromb Haemostas 1991; 66: 629-632