Beta2-glycoprotein I: target antigen for 'antiphospholipid' antibodies. Immunological and molecular aspects.

It has become clear that beta2-glycoprotein I (beta2GPI) is the most common and best-characterised antigenic target for 'antiphospholipid' (aPL) autoantibodies. These antibodies preferentially bind beta2GPI that has been immobilised on anionic phospholipid membranes or certain synthetic surfaces. These surfaces appear to act by increasing antigen density to allow binding of intrinsically low-affinity anti-beta2GPI autoantibodies. Binding of beta2GPI in fluid phase is weak and requires high concentrations of beta2GPI. Our understanding of the pathophysiology of the 'Antiphospholipid' Syndrome (APS) has increased exponentially with the number of studies into the interactions of aPL antibodies and beta2GPI.