Antigenic specificity of anti-neutrophil cytoplasmic antibody

Purpose: To deter-mine the antigens recognized by sera containing classic a ntineutrophil cytoplasmic antibodies (c-ANCAs) and perinuclear anti-neutrop hil cytoplasmic antibodies (p-ANCAs). Methods: A total of 160 serum samples (all from a reference laboratory) tha t were originally collected from different clinics for ANCA tests were exam ined for c-ANCA and p-ANCA by indirect immunofluoresrence (IIF). All positi ve sera were further tested for reactivity; to proteinase 3 (PR3), melopero xidase (MPO), lactoferrin (LF), and lysozyme (LZ) by enzyme-linked immunoso rbent assay (ELISA). In addition, sera from 110 patients with systemic lupu s erythematosus (SLE), 51 patients with rheumatoid arthritis (RA), and 40 h ealthy subjects were also tested for reactivity to these antigens. Results: IIF detected ANCA in 81 (51%) of the 160 clinical serum samples, O f these 81 serum samples, 21 (26%) contained c-ANCA and 60 (74%) contained p-ANCA. P-ANCA was more commonly found in antinuclear antibody (ANA)-positi ve sera than in ANA-negative sera (p < 0.01). Of the 21 serum samples posit ive for c-ANCA. 12 (57%) reacted to PR3, four (19%) to LF, four (19%) to LZ . and three (14%) to MPO on ELISA. By contrast, of the 60 sera positive for p-ANCA. 15 (25%) reacted to MPO, 13 (22%) to PR3, eight (13%) to LF, and f our (7%) to LZ. The prevalence of ANCA specificities in serum samples from SLE patients were as follows: anti-PR3, 0%; anti-MPO, 1%; anti-LF, 27%: and anti-LZ. 29%. The prevalence of ANCA specificities in serum samples from R A patients were as follows: anti-PR3, 6%: anti-MPO, 2%; anti-LF, 8%; anti-L Z, 3%. Conclusion: Sera positive for c-ANCA and p-ANCA reacted to diverse cytoplas mic antigens from neutrophils. P-ANCA was found in 55% of ANA-positive seru m samples. LF and LZ were most commonly found in serum samples from patient s with SLE.