Tetra positive thrombotic antiphospholipid syndrome: Major contribution of anti-phosphatidyl-serine/prothrombin antibodies to lupus anticoagulant activity.

Anti-β2-glycoprotein I antibodies did not prolong the diluted Russell viper venom time and silica clotting time (median ratio 0.98, interquartile ratio [IQR] 0.9-1.06; and 1.0, IQR 0.91-1.03, respectively). Anticoagulant activity remained in the flow-through that was deprived of anti-β2 glycoprotein I antibodies (median ratio 1.88, IQR 1.58-2.77; and 1.75, IQR 1.17-2.9, respectively). This material was loaded on size-exclusion chromatography Sephacryl S-300 column and showed that anticoagulant activity and anti-phosphatidyl-serine/prothrombin antibodies coeluted in the same fractions. Besides, the flow through was poured into a prothrombin affinity column. Protein yield in three patients ranged from 54 to 91 μg/mL and showed strong positivity in phosphatidyl-serine/prothrombin ELISA. The affinity purified material prolonged the coagulation time of normal pooled plasma: the diluted Russell viper venom ratio in the three patients was 2.09, 1.21, and 1.35; that of silica clotting time was 2.05, 1.5, and 2.13. In conclusion, under the assay conditions used, anticoagulant activity in tetra-positive antiphospholipid syndrome patients may largely be attributable to anti-phosphatidyl-serine/prothrombin antibodies.