β2 glycoprotein-I – the main antigen in antiphospholipid syndrome

The term “antiphospholipid antibodies” describing a laboratory hallmark of antiphospholipid syndrome (APS) is a misnomer. It suggests that antibodies are directed against phospholipids. Meanwhile the specific antigens are in fact proteins demonstrating an affinity to phospholipids. In APS antibodies directed against a serum protein, β2 glycoprotein-I, play most probably a pathogenic role and are strongly associated with clinical symptoms of the syndrome. Putative mechanisms of action of anti-β2 glycoprotein-I antibodies are discussed.