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

Abstract

BackgroundThe concurrent presence of lupus anticoagulant, anticardiolipin, 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). ObjectiveUnderstand which antibody among anti‐β2‐glycoprotein I and anti‐phosphatidyl‐serine/prothrombin is responsible for lupus anticoagulant activity. Patients/MethodsAffinity purified anti‐β2‐glycoprotein I antibodies from plasma of 14 tetra‐positive patients spiked into normal pooled plasma were tested. Results and ConclusionsAnti‐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.