Antigen Specificity and Clinical Relevance of Antiphospholipid Syndrome- Related Autoantibodies

The presence of antiphospholipid antibodies (aPL) combined with venous or arterial thrombosis, and/or obstetric complications defines the antiphospholipid syndrome (APS). Lupus anticoagulants (LA) and anticardiolipin antibodies (aCL) were the first described aPL. It has been shown that aPL, despite their name, are not directed against anionic phospholipids, as had previously thought, but are a part of a large family of autoantibodies against phospholipid-binding plasma proteins. The most important and relevant antigenic targets involved in APS are β2 glycoprotein I (β2GPI) and prothrombin. However, an increasing number of other phospholipid-binding proteins with crucial functions in the regulation of blood coagulation and fibrinolysis are also targeted by APS-related autoantibodies. For clinical purposes, it is important to find which aPL markers has the best prognostic value. While it has been clearly demonstrated that LA and, to a lesser extent, aCL represent a risk for thrombosis, the role of antibodies directed against β2GPI, prothrombin as well as other targets is still uncertain and controversial. Data from a prospective study showed the presence of antibodies to prothrombin and/or β2GPI is a predictor of first or recurrent thromboembolic events in patients with LA and/or aCL. This review intends to highlight the antigen specificity and clinical relevance of APSrelated aPL.