ANTIPHOSPHOLIPID ANTIBODIES ARE DIRECTED AGAINST EPITOPES OF OXIDIZEDPHOSPHOLIPIDS - RECOGNITION OF CARDIOLIPIN BY MONOCLONAL-ANTIBODIES TO EPITOPES OF OXIDIZED LOW-DENSITY-LIPOPROTEIN

The optimal clinical management of patients with antiphospholipid anti body syndrome (APS) is uncertain because of a lack of an underlying hy pothesis to explain why antiphospholipid autoantibodies (aPL) form to such ubiquitous compounds as phospholipids (PL). In this paper, we dem onstrate that many, if not most, aPL are actually directed at neoepito pes of oxidized FL, or neoepitopes generated by adduct formation betwe en breakdown products of oxidized PL and associated proteins. Each car diolipin (CL) molecule contains four unsaturated fatty acids and is hi ghly susceptible to oxidation, particularly upon exposure to air. Yet, standard anticardiolipin antibodies (aCL) immunoassays routinely bind CL to microtiter wells by evaporation of the ethanol solvent overnigh t at 4 degrees C. Using a variety of techniques, we demonstrated that rapid oxidation occurs when CL is plated and exposed to air. Sera from apo E-deficient mice, which have high autoantibody titers to oxidized low density lipoprotein, showed a striking time-dependent increase in binding to CL that was exposed to air for increasing periods of time. Monoclonal antibodies to oxidized LDL, cloned from the apo E-deficien t mice, also bound to oxidized CL. Both sera and affinity-purified aCL -IgG from APS patients bound to CL progressively as it was oxidized. H owever, the monoclonal antibodies from apo E-deficient mice, or sera o r aCL-IgG from APS patients did not bind to a reduced CL analog that w as unable to undergo peroxidation. These data demonstrate that many aP L are directed at neoepitopes of oxidized phospholipids, and suggest t hat oxidative events may be important in the pathophysiology of APS. I n turn, this suggests new therapeutic strategies, possibly including i ntensive antioxidant therapy.