Role of Anti-beta2 Glycoprotein I Antibodies in Antiphospholipid Syndrome: In Vitro and In Vivo Studies.

Antiphospholipid syndrome (APS) is characterized by the presence of recurrent venous/ arterial thrombosis and fetal losses associated with a family of auto-antibodies directed against phospholipid (PL)-binding proteins. Among them, β2 glycoprotein I (β2GPI) is the most important. As a plasma cationic protein, β2GPI binds to anionic PLs involved in several fluid-phase coagulation steps, and more importantly, it can be expressed on the surface of different cell types. Anti-β2GPI antibodies recognize the molecule expressed on endothelial cells, platelets, monocytes, and trophoblast cells. Once bound, the antibodies trigger in vitro cell signaling that modulates biological responses potentially responsible for pathogenic mechanisms. Experimental animal models have supported the in vivo pathogenic role of anti-β2GPI antibodies in both thrombosis and fetal loss models.