Anticardiolipin Antibodies Recognize β(2)-Glycoprotein I Structure Altered by Interacting with an Oxygen Modified Solid Phase Surface

Anticardiolipin antibodies (aCL) derived from the sera of individuals exhibiting the antiphospholipid syndrome (APS) directly bind to beta(2)-glycoprotein I (beta(2)-GPI), which is adsorbed to an oxidized polystyrene surface. Oxygen atoms were introduced on a polystyrene surface by irradiation with electron or gamma-ray radiation. X-ray photoelectron spectroscopy revealed the irradiated surfaces were oxidized to generate C-O and C=O moieties. aCL derived from either APS patients or (NZW x BXSB)F-1 mice bound to beta(2)-GPI coated on the irradiated plates, depending on the radiation dose. Antibody binding to beta(2)-GPI on the irradiated plates was competitively inhibited by simultaneous addition of cardiolipin (CL)-coated latex beads mixed together with beta(2)-GPI but were unaffected by addition of excess beta(2)-GPI, CL micelles, or CL-coated latex beads alone. There was a high correlation between binding values of aCL in sera from 40 APS patients obtained by the anti-beta(2)-GPI enzyme-linked immunosorbent assay (ELISA) using the irradiated plates and those by the beta(2)-GPI-dependent aCL ELISA. Therefore, aCL have specificity for an epitope on beta(2)-GPI. This epitope is expressed by a conformational change occurring when beta(2)-GPI interacts with an oxygen-substituted solid phase surface.