Avidity of anti-beta-2-glycoprotein I antibodies

The terms affinity and avidity are often used indiscriminately, despite clearly differing. Since affinity refers to monovalent binding of antibodies to a monovalent epitope, the majority of data on the binding of anti-beta 2-glycoprotein I antibodies (anti-beta 2-GPI) characterized their avidity rather than affinity. Anti-beta 2-GPI were generally believed to be of low avidity, but heterogeneous avidity of patients' IgG anti-beta 2-GPI has been demonstrated. High avidity anti-beta 2-GPI monoclonals were reported to possess higher pathogenicity than low avidity anti-beta 2-GPI. Polyclonal high avidity anti-beta 2-GPI were found to be more common in patients with antiphospholipid syndrome (APS) and associated with thrombosis. Some conformational changes of beta 2-GPI are required for the binding of polyclonal anti-beta 2-GPI to the antigen: neither high density of the antigen nor high avidity of the anti-beta 2-GPI alone is sufficient for the recognition. Avidity of anti-beta 2GPI should be considered in any attempt of inter-laboratory standardisation and/or evaluation of anti-beta 2-GPI enzyme-linked immunosorbent assay (ELISA). (c) 2005 Elsevier B.V. All rights reserved.