Establishment of a novel assay method for anticardiolipin antibodies.

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An autoimmune disease, "antiphospholipid syndrome (APS) ", with appearance of antiphospholipid antibodies such as anticardiolipin antibodies (aCL) and lupus anticoagulants is thought to be based on these antibodies mediated-procoagulant features. Various aCL-immunoassays (ELISA and RIA) using cardiolipin (CL) -coated plates have been used for aCL detection, however, we learned that they have some technical difficulties and produce false-positive results.In the present study, we investigated the specificity of aCL from patients with APS and obtained following results. We also established a novel and accurate assay (ELISA) method for aCL using polyoxygenated polystirene plates coated with beta2-glycoprotein I (beta2-GPI), instead of CL-coated plates.1) aCL from patients with APS recognized an cryptic epitope appearing on the beta2-GPI structure when beta2-GPI interacts with polyoxygenated polystirene plates as well as with lipid membranes composed of negatively-charged phospholipids such as cardiolipin and phosphatidylserine.2) There was a good correlation between the antibody titers obtained in the conventional aCL-ELISA and in the improved ELISA using polyoxygenated plates coated with beta2-GPI.However, antibodies non-specifically bound to negatively charged molecules were negligible only in the improved aCL-ELISA.3) There was good correlation between the appearance of antibodies detected in the improved ELISA and thrombosis and also between the appearance and lupus anticoagulants or biological false positive for the test of syphilis.4) aCL from APS-patients could be detected in the improved ELISA using not only the polyoxygenated but also the non-treated polystirene plates coated with the beta2-GPI mutant protein lacking its domain V.