Antineutrophil cytoplasmic antibodies in Bulgarian patients with rheumatoid arthritis: characterization and clinical associations

The aim of this study was to study the prevalence, subspecificities, and immunoglobulin (Ig)G subclass distribution of antineutrophil cytoplasmic antibodies (ANCA) in 90 Bulgarian patients with rheumatoid arthritis (RA) and to investigate the clinical associations of ANCA in these patients. The ANCA were detected by indirect immunofluorescence, while antigen specificities were determined by enzyme-linked immunosorbent assay (ELISA) directed against myeloperoxidase (MPO), proteinase 3 (PR3), bactericidal/permeability-increasing protein (BPI), lactoferrin (LF), leukocyte elastase (LE), and cathepsin G (CG). The IgG subclass reactivity of antibodies to BPI and LF was measured. Antineutrophil cytoplasmic antibodies were found in 18 RA patients. Only a P-ANCA fluorescence pattern was seen. Six sera reacted to BPI, five to LF, one to MPO, one to PR3, and one to CG by ELISA testing. Immunoglobulin-G1 was the predominant subclass for LF-ANCA, whereas IgG1/3 contributed mainly to BPI-ANCA. Compared to P-ANCA-negative RA patients, the P-ANCA-positive patients exhibited significantly higher inflammatory activity, as estimated by disease activity score, C-reactive protein, erythrocyte sedimentation rate, and higher levels of IgM rheumatoid factor. Twenty percent of Bulgarian patients with RA have P-ANCA in their sera. These antibodies are directed against variable antigen specificities, while ANCA positivity in RA reflects disease and inflammatory activity.