Difference in antigenic determinant profiles between human and rat myeloperoxidase.

We tested whether rat and human MPO have similar antigenic determinants using 36 human MPO-ANCA positive sera, one mouse anti-rat MPO and four mouse anti-human MPO monoclonal reagents. Purified rat and human MPO were used in ELISA, with or without crossinhibition by preincubation with human MPO or irrelevant antigen in the liquid phase. Only one human MPO ANCA positive serum exhibited significant binding in rat MPO ELISA. This binding was poorly inhibited by preincubation with human MPO in the liquid phase, but was conserved after adsorption of non specific anti-rat activity in a chromatography column. Three mouse anti-human MPO IgG monoclonal antibodies did not recognize rat MPO. Only one mouse anti-human MPO IgA monoclonal antibody bound to rat MPO. This binding was poorly inhibited by preincubation with human MPO (35% at 2 micro g/ml). Conversely, the mouse anti-rat MPO monoclonal did not bind human MPO. We have concluded that: (1) Most human MPO-ANCA recognize antigenic determinants on human MPO which are absent on rat MPO. Therefore, human auto-antibodies bind to epitopes which recently appeared after species evolution; (2) Inversely, the mouse anti-rat MPO monoclonal do not bind human MPO. Therefore, rat MPO epitopes have been altered during species evolution; (3) Mice injected with human MPO preferentially develop antibodies against xeno-epitopes which are not present in rodents. Therefore, human MPO may not be the best antigen to raise ANCA in animal models and (4) A comparison of the amino acid sequences of rat and human MPO may help elucidate the major antigenic epitopes.

Value of autoantibodies to beta(2)-glycoprotein 1 in the diagnosis of antiphospholipid syndrome.

OBJECTIVES: To define the specificity and positive predictive value of anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) antibodies for the diagnosis of antiphospholipid syndrome (APS). METHODS: We determined the presence of anticardiolipin (aCL) antibodies and anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) immunoglobulin (Ig) G and IgM in 191 consecutive sera from 191 patients and reviewed clinical data separately. aCL IgG and IgM were detected separately using commercial ELISA kits. Anti-beta(2)GP1 antibodies were detected with an in-house ELISA using beta(2)GP1. RESULTS: Seven patients were diagnosed as having APS and 184 as having other diseases. Thirty-six patients were aCL-positive and 12 were anti-beta(2)GP1-positive, seven of these 12 were APS patients. The specificity for anti-beta(2)GP1 in our population was 97%, with a positive predictive value (PPV) of 58%. Among the aCL-positive patients, specificity was 90% and PPV 70-87%. CONCLUSIONS: This study shows that anti-beta(2)GP1 antibodies have a higher specificity and PPV than aCL for APS. The PPV of anti-beta(2)GP1 was greater in aCL-positive than in all patients. We conclude that screening for anti-beta(2)GP1 antibodies in aCL-positive patients increases the specificity and the PPV of aCL testing. In addition, we show that there is no need to screen for anti-beta(2)GP1 antibodies in the absence of aCL antibodies and in the absence of strong clinical suspicion of APS.