The concurrent presence of lupus anticoagulant, anti-cardiolipin and anti β2-glycoprotein I antibodies (triple positive profile) identifies patients at high-risk of thromboembolic events. These patients are also positive for anti phosphatidyl-serine/prothrombin antibodies (tetra positive profile).
Understand which antibody among anti β2-glycoprotein I and anti phosphatidyl-serine/prothrombin is responsible for lupus anticoagulant activity is not defined.
Affinity purified anti β2-glycoprotein I antibodies from plasma of 14 tetra positive patients spiked into normal pooled plasma were tested.
Anti β2-glycoprotein I antibodies did not prolong the diluted Russell Viper Venom Time and Silica Clotting Time (median ratio 0.98, 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 co-eluted 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, 1.35 and that of Silica Clotting Time was 2.05, 1.5, 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.

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