PB0863 - Anti-beta2-glycoprotein I antibodies mediate increased procoagulant platelet and thrombus formation in an ex vivo model of antiphospholipid syndrome

Background: Antiphospholipid syndrome (APS) is an autoantibody-mediated prothrombotic disease that is characterized by an increased risk for recurrent thrombosis and pregnancy loss. Circulating anti-beta2-glycoprotein-I APS antibodies (anti-beta(2)GPI Abs) are increasingly recognized to harbor high prothrombotic potential as they were identified to elicit multicellular prothrombotic effector mechanisms. However, the impact of anti-beta(2)GPI Ab-mediated interactions with platelets (PLTs) and subsequent relevance on thrombus formation are not well understood.

Aims: This study aims to investigate the potential impact of human anti-beta(2)GPI APS Abs on procoagulant PLT and thrombus formation ex vivo.

Methods: For the investigation of anti-beta(2)GPI Ab-induced procoagulant PLT formation, a flow cytometry (FC)-based assay that utilizes CD62p/Annexin-V double staining was employed. To analyze the impact of anti-beta(2)GPI APS Ab-induced PLT alterations on thrombus formation, an ex vivo model of Ab-mediated thrombosis was utilized.

Results: FC analysis revealed that human anti-beta(2)GPI APS Abs have the potential to induce increased formation of procoagulant (CD62p and PS double positive) PLTs (p-value 0.0026). Anti-beta(2)GPI-Ab-induced formation of procoagulant was detected to be PLT Fc-gamma-RIIA (FcyRIIA)-dependent as specific PLT FcyRIIA blockade resulted in a nearly complete inhibition of Ab-induced procoagulant PLT formation in vitro (p=0.0161).
Of note, anti-beta(2)GPI Ab-induced prothrombotic PLT changes were not only phenotypical but also showed high prothrombotic potential as reconstitution of anti-beta(2)GPI Ab-induced procoagulant PLTs into healthy whole blood resulted in a dramatic multicellular thrombus formation ex vivo (p=0.0004). Interestingly, APS Ab-induced thrombus formation was neraly completely prevented when PLTs were pretreated with therapeutic doses of intravenous immunoglobulin G (IVIG) prior to Ab incubation (p=0.0018).

Conclusion(s): Our findings indicate a high potential of human anti-beta(2)GPI APS Abs to induce procoagulant PLT and increased thrombus formation ex vivo. The observation that IVIG treatment could prevent from anti-beta(2)GPI Ab-induced procoagulant PLT-mediated thrombus formation direct towards a therapeutic potential of IVIG in the prothrombotic condition often observed in patients with APS.