The beta-2-glycoprotein I and antiphospholipid antibodies

Beta₂-GPI is a single chain, 50 kd glycoprotein made up of 326 amino-acids, present in human plasma at concentrations of about 200 μg/ml. It has been shown to represent the 'serum cofactor' important in determining the binding of aCL to phospholipids both in fluid and in solid phase assays. Its cofactor activity is demonstrable for aPL antibodies from patients with autoimmune but not with infectious diseases. It is immunogenic in heterospecific models, and immunization with β₂-GPI seems to be able to induce the production not only of anti-β₂-GPI but also of aPL antibodies. Most probably its binding to GL changes the configuration of phospholipids to a more immunogenic one. The various characteristics of β₁-GPI are summarized in Table I.β₂-GPI has been recognized as a natural anticoagulant protein, but its possible role in the pathogenesis of the APLS remains to be determined.