SPECIFICITIES AND CHARACTERISTICS OF BETA-2 GLYCOPROTEIN I-INDUCED ANTIPHOSPHOLIPID ANTIBODIES

Autoimmune antiphospholipid antibodies are associated with thrombosis, thrombocytopenia, and recurrent fetal death. These antibodies are tho ught to be directed against an epitope formed by phospholipids complex ed with beta(2) glycoprotein I (beta,GPI), a plasma protein with affin ity for phospholipids. By immunizing mice and rabbits with heterologou s beta(2),GPI, we produced antibodies that bind strongly to acidic pho spholipids in addition to binding to beta(2)GPI, To evaluate the speci ficities of these antibodies, we passed the serum of a rabbit immunize d with beta(2)GPI through a cardiolipin (CL) affinity column and studi ed the bound and fall-through antibodies for binding to CL and beta(2) GPI by ELISA. The results demonstrated the presence of two populations of antibodies, one with specificity for beta(2)GPI alone without bind ing to phospholipids and the other with specificities for both CL and beta(2),GPI, These dual-specificity antibodies are similar to the anti phospholipid antibodies present in autoimmune diseases because they bi nd to other acidic phospholipids in addition to CL and because their b inding to phospholipids is enhanced by beta(2)GPI and blocked by place ntal anticoagulant protein I (annexin V).