ANTI-BETA(2)-GLYCOPROTEIN-I ANTIBODIES - A MARKER OF ANTIPHOSPHOLIPIDSYNDROME

Anticardiolipin (aCL) and anti-beta(2)-glycoprotein I(anti beta 2GPI) antibodies have been shown in animal models as not cross-reacting anti body populations. This observation prompted us to prove if anti-beta 2 GPI exist in human sera by using a reliable method and then to investi gate if these are independent from aCl antibodies. We have developed a new ELISA for the detection of anti-beta 2GPI antibodies employing th e coating of the protein in carbonate buffer to irradiated microtitre plates and the filtration of serum samples, that makes irrelevant the binding to the uncoated wells. IgG F(ab)(2) fragments from IgG positiv e sera were shown bind beta 2GPI, providing that the binding was a spe cific antibody binding, mediated by the antigen binding site of the an tibody molecule; moreover the antibodies were not able to differentiat e native and delipidated beta 2GPI coated plates, making a possible ro le of a phospholipid contaminant unlikely. On the other hand, the phos phorus content of native as well as delipitated beta 2GPI was undetect able. IgG, but not IgM, anti-beta 2GPI antibodies were classically inh ibited by the addition of soluble beta 2GPI, while cardiolipin liposom es appear to modify the reaction in a completely different way, possib ly by the described interaction between cardiolipin and beta 2GPI. The application of the new ELISA to the study of patients has shown that: (Ij the presence of anti-beta 2GPI is statistically associated with t he presence of aCL antibodies (P < 0.0001), (2) anti-beta 2GPI antibod ies are related to the classical features of antiphospholipid syndrome (thrombosis: P < 0.001; fetal loss: P < 0.001) while, in this series of patients, aCl antibodies are not (thrombosis: P < 0.126; fetal loss : P < 0.061).