Epitope studies with anti-beta(2)-glycoprotein I antibodies from autoantibody and immunized sources

This paper examines the methodology of anti-beta(2)-glycoprotein I (beta(2) -GPI) epitope determination and provides further epitope studies using huma n sera containing anti-beta(2)-GPI autoantibodies. Studies in this field ma y be misleading as the antigen coating density using mutant forms of beta(2 )-GPI may be below the threshold required for monogamous divalent binding b y low affinity anti-beta(2)-GPI autoantibodies, while being easily detected by high affinity anti-beta(2)-GPI from immunized animals. The antigen dens ity threshold effect is found in anti-beta(2)-GPT autoantibodies from human s and from monoclonal anti-beta(2)-GPI derived from mice with models of aut oimmune disease. Anti-beta(2)-GPI from an autoimmune mouse and from 18/21 h uman sera did not bind above background levels to a domain-I-deleted mutant . In addition, single point mutations in domain I result in dramatic change s in the binding of many human sera containing anti-beta(2)-GPI. These find ings support a conclusion that domain I of beta(2)-GPI contains significant epitopes for the anti-beta(2)-GPI antibodies found in the antiphospholipid syndrome. (C) 2000 Academic Press.