ANTIMITOCHONDRIAL M5 TYPE ANTIBODY REPRESENTS ONE OF THE SEROLOGICAL MARKERS FOR ANTIPHOSPHOLIPID SYNDROME DISTINCT FROM ANTICARDIOLIPIN AND ANTI-BETA(2)-GLYCOPROTEIN-I ANTIBODIES

The aim of this study was to characterize the antigen specificity and to evaluate the diagnostic and prognostic value of anti-mitochondrial M5 type antibodies (AMA M5). Fifty-eight patients selected on the basi s of their AMA M5 positivity were investigated in relationship to thei r clinical and serological profile. Cross-absorption studies, Western blotting and immunoprecipitation analysis were carried out for AMA M5 antigen specificity characterization. Most patients had a diagnosis of systemic lupus erythematosus (SLE) (65.5%) or of primary anti-phospho lipid syndrome (PAPS) (24%); all the patients were positive for IgG or IgM anti-cardiolipin (anti-CL) antibodies and 49% of them also displa yed lupus anticoagulant (LA) activity. Anti-beta(2)-glycoprotein I (be ta(2)-GPI) IgG were detectable in 30/38 sera(78.9%) and IgM in 34/38 ( 89.4%). While anti-CL and anti-beta(2)-GPI IgG antibodies were signifi cantly associated with history of thrombosis and fetal loss, AMA M5 di splayed a statistical association only for thrombocytopenia and recurr ent fetal loss. Absorption with human beta(2)-GPI both in free solutio n or in solid phase as well as with CL liposomes or CL/beta(2)-GPI lip osome complexes did not affect AMA M5 fluorescence. While AMA M5 activ ity is absorbed by whole mitochondrial preparations, no specific react ivities against several human, bovine and rat mitochondrial proteins c ould be detected in Western blotting and immunoprecipitation studies. AMA M5 appear to be detectable in both primary and secondary APS, disp laying a strong association with the presence of thrombocytopenia and fetal loss. Although strictly related to anti-phospholipid antibodies, AMA M5, anti-CL and anti-beta(2)-GPI antibodies represent distinct se rological markers of the APS.