Insight into the hypercoagulable state of high-risk thrombotic APS patients: Contribution of aβ2GPI and aPS/PT antibodies

Objective Most high-risk thrombotic antiphospholipid syndrome (APS) patients test positive for anti-beta 2-glycoprotein I (a beta 2GPI) and anti-phosphatidylserine/prothrombin (aPS/PT) antibodies. Information on the influence of these antibodies on thrombin generation and activated protein C resistance (aPCr) is still sparse and contradictory. Methods Plasma of 16 patients poured into a beta 2GPI affinity column allowed the perfect separation of a beta 2GPI and aPS/PT antibodies. aPS/PT antibodies were further purified through a prothrombin affinity column. Obtained material was spiked into normal pooled plasma (NPP) and tested in the thrombin generation assay in the absence or presence of aPC. Results aPS/PT antibodies showed a marked anticoagulant effect. Affinity purified aPS/PT and a beta 2GPI antibodies from five patients were compared. aPS/PT antibodies showed significantly prolonged lag time and time to peak (5.0 minutes [interquartile range (IQR)3.5-6.1] versus 2.7 minutes [IQR2.2-3.5], P = .03 and 8.7 minutes [IQR6.7-10.3] versus 5.7 minutes [IQR4.5-6.2], P = .05, respectively) and significantly lower peak and velocity index (143 nmol/L [IQR131-163] versus 171 nmol/L [IQR157-182], P = .03 and 35 nmol/L/min [IQR32-59] versus 72 nmol/L/min [IQR54-77], P = .03, respectively). When aPC was added to the system, aPCr was significantly increased compared to controls for both a beta 2GPI and aPS/PT antibodies. However, it was significantly stronger using aPS/PT antibodies. Median inhibition of endogenous thrombin potential was 22% (IQR16-33) with aPS/PT compared to 52% (IQR46-56) with a beta 2GPI antibodies (P = .002). Conclusions A beta 2GPI antibodies show a mild anticoagulant and moderate procoagulant effect in thrombin generation and moderate aPC resistance. Conversely, aPS/PT antibodies show a strong anticoagulant effect and a strong aPCr.

Automated summary

This study indicates that aPS/PT antibodies have a strong anticoagulant effect, while a β2GPI antibodies exhibit mild anticoagulant and moderate procoagulant effects in thrombin generation and moderate aPC resistance.