Ab1804

Anti-cardiolipin antibody from a patient with antiphospholipid syndrome (APS) recognizes only an epitope expressed by cardiolipin/b₂-glycoprotein-I (b₂GPI) complex and induces APS

Y. Levy¹, Y. Sherer¹, A. Mathieu², A. Cauli², G. Passiu², G. Sanna², Z. Janackovic¹, M. Blank¹, Y. Shoenfeld¹

¹Department of Medicine `B' and Research Unit of Autoimmune Diseases, Sheba Medical Center, Tel-Hashomer, and Sackler Faculty of Medicine, Tel-Aviv University, Israel; ²Cagliari University, Institute of Clinical Medicine, Cattedra of Rheumatology, Cagliari, Italy.

ABSTRACT
Objective
As the antiphospholipid syndrome (APS) is characterized by antibodies which bind negatively charged phospholipids either directly or mainly through different target epitopes located on the beta-2-glycoprotein-I (b₂GPI) molecule, the aim of this study is to describe an additional target epitope for anti-cardiolipin binding.

Methods
The binding characteristics of affinity purified anti-cardiolipin antibodies from a patient with monoclonal gammopathy associated with clinically overt APS were studied; inhibition studies were also carried out. These antibodies were used for the active induction of experimental APS.

Results
The affinity purified anti-cardiolipin antibodies were found to bind a target epitope created by the complex of cardiolipin/b₂GPI, while not reacting with a complex composed by another phospholipid (phosphatidylserine/b₂GPI), as confirmed by direct binding and competition assays. Immunization of naive mice with this unique affinity purified anti-cardiolipin antibody resulted in the induction of experimental APS (thrombocytopenia, prolonged coagulation timed and fetal resorptions). The anti-cardiolipin/b₂GPI injected mice developed high titers of mouse anti-cardiolipin/b₂GPI antibodies with the same binding characteristics as the human antibody which was used for disease induction.

Conclusion
APS is a unique syndrome that is characterized by a diversity of pathogenic anti-phospholipid antibodies which may explain the diversity of clinical manifestations reported in patients.

Key words
Anticardiolipin antibody, antiphospholipid syndrome, beta-2-glycoprotein I, monoclonal gammopathy, thromboembolism.

This work was supported by the Ministry of Health Chief Scientist.

Please address correspondence and reprint requests to: Yehuda Shoenfeld, MD, Department of Medicine `B', Tel-Hashomer 52621, Israel.
E-mail: Shoenfel@post.tau.ac.il