Prothrombin antibodies, also known as antithrombin antibodies, are autoantibodies targeting prothrombin (Factor II), a key glycoprotein in the blood coagulation cascade. Prothrombin is synthesized in the liver and converted to thrombin during clot formation. These antibodies are primarily associated with autoimmune disorders, notably antiphospholipid syndrome (APS), where they often coexist with other antiphospholipid antibodies like anticardiolipin antibodies and lupus anticoagulants.
Two main subtypes exist: IgG and IgM. They may interfere with prothrombin’s activation to thrombin or form immune complexes that enhance thrombosis risk by disrupting anticoagulant pathways. While their exact pathogenic role remains debated, their presence is linked to thrombotic events (arterial/venous) and obstetric complications like recurrent miscarriages.
Detection typically involves enzyme-linked immunosorbent assays (ELISA), though interpretation requires caution due to potential cross-reactivity with phospholipid-binding proteins like β?-glycoprotein I. Notably, some prothrombin antibodies recognize cryptic epitopes exposed when prothrombin binds phosphatidylserine on cell membranes, influencing thrombin generation assays.
Clinically, they contribute to APS diagnosis alongside clinical criteria, but their isolated presence without other antiphospholipid markers may have uncertain significance. Research continues to clarify their mechanisms and refine their prognostic value in thrombotic and autoimmune contexts.