DIFFERENT TARGET SPECIFICITIES OF PHOSPHOLIPID-DEPENDENT ANTIBODIES

Phospholipid dependent antibodies are usually measured with assays for antiphosholipid/anticardiolipin antibodies (aPLA) or for lupus antico agulant (LA) activity. Most of them are targeted to complexes of beta( 2)-glycoprotein I (beta(2)-GPI) and anionic phospholipds (PLP) or to p rothrombin for some LA. New understandings allow a better standardisat ion and optimisation of assays' reactivity. Antigenic targets of phosp holipid dependent antibodies were studied on plasmas from 38 patients with the antiphospholipid syndrome (APS) and presenting aPLA and/or LA . Using human beta(2)-GPI-PLP complexes as solid phase antigen offers the highest sensitivity for measuring aPLA. Many aPLA, but not all, al so react with beta(2)-GPI coated on solid phase, however there is no e vidence until now that this latter reactivity shows a closest associat ion with the clinical context. Most of the patients with LA present an immunological reactivity to beta(2)-GPI alone or to prothrombin, when these proteins are coated on solid phase. In two cases there was a re activity to only beta(2)-GPI-PLP complexes. For the various immunoassa ys, using NUNC type I plates offers a good binding capacity For coatin g antigens. They are then present at enough density on solid phase for insuring an efficient binding of autoantibodies. This is an important factor for assay sensitivity and reproducibility. Interestingly, in 1 case with LA, autoantibodies were reactive with coated beta(2)-GPI al one but not with its PLP-complexes. In another case reactivity to beta (2)-GPI was much higher than that to beta(2)-GPI-PLP.