High-sensitivity Detection of Autoantibodies Against Proteinase-3 by a Novel Third-generation Enzyme-linked Immunosorbent Assay

The aim of this study was to evaluate a novel third-generation enzyme-linked immunosorbent assay (ELISA) for the high-sensitivity detection of autoantibodies to proteinase-3 (PR3) in patients with Wegener's granulomatosis (WG). First- and second-generation ELISA for the detection of antineutrophil cytoplasmic antibodies (ANCA) frequently demonstrate insufficient sensitivity due to inadequate presentation of autoantigenic epitopes. Human PR3 was immobilized on the solid phase of ELISA plates by anchoring technique. Anti-PR3 reactivity was measured in 34 C-ANCA positive patients with WG, 11 MPO-ANCA-positive patients with other autoimmune vasculitides, 65 patients with systemic lupus erythematosus (SLE), and 137 healthy blood donors. Thirty-three of 34 patients with WG (97.1%) showed positive anti-PR3 IgG antibody reactivity. None of 11 MPO-ANCA positive vasculitis patients, none of 137 blood donors, and 3 of 65 SLE patients expressed elevated IgG reactivity to PR3 (specificity: 98.4%). Comparison with another third-generation ELISA did not reveal different qualitative results. However, there was no significant correlation between quantitative results of both assays. Receiver operating characteristic (ROC) curve analysis revealed a significantly better assay performance compared with first (direct)- and second (capture)-generation assays (P = 0.011 and P = 0.001, respectively). Third-generation (anchor) anti-PR3 ELISA exhibit significantly higher sensitivity than previous generation assays. Anchoring of PR3 renders the granulocyte protein more autoantigenic compared with direct or capture immobilization.