Native and recombinant proteins to analyze auto-antibodies to myeloperoxidase in pauci-immune crescentic glomerulonephritis

The prevalence of Anti-Neutrophil Cytoplasmic Antibodies (ANCA) directed ag ainst myeloperoxidase (MPO) in pauci-immune necrotizing crescentic glomerul onephritis (NCGN) is dependent on the assay(s) used, We investigated the fr equency of MPO-ANCA as detected by different assays for MPO-ANCA in a large cohort of patients with biopsy-proven pauci-immune NCGN. Sera from 121 con secutive untreated patients presenting with pauci-immune NCGN were tested f or ANCA directed to proteinase-3 (PR3) at diagnosis. PR3-ANCA negative sera were tested by direct ELISA using recombinant or native MPO and by capture ELISA using two different specific monoclonal antibodies directed to MPO a nd three different antigenic sources. Sera from 80 relevant disease control s were tested to explore the specificity of the different assays. Thirty-ei ght out of 121 patients (31%) with pauci-immune NCGN did not have PR3-ANCA. Sufficient amounts of serum from 30 of these 38 PR3-ANCA negative patients were available for further testing, Recombinant and native MPO were recogn ized by similar numbers of sera in a direct ELISA (recombinant MPO: 93%. na tive MPO: 93%) and a capture ELISA (recombinant MPO: 77-87%. native MPO: 93 %). Sera of patients with PR3-ANCA positive pauci-immune NCGN and disease c ontrols were less frequently positive for MPO-ANCA in a capture ELISA (reco mbinant MPO: 3-7%, native MPO: 6-7%) than in a direct ELISA (recombinant MP O: 25%, native MPO: 13%). Both direct and capture ELISA assays using either native or recombinant MPO are sensitive techniques to detect MPO-ANCA in p atients with pauci-immune NCGN. A capture ELISA performs better than a dire ct ELISA because it combines a higher specificity with a comparable sensiti vity. Recombinant MPO is a good alternative for native MPO when used as ant igen in a capture ELISA, but not when used in a direct ELISA because of low er specificity in this latter assay. (C) 2001 Elsevier Science B.V. All rig hts reserved.