Antineutrophil cytoplasmic antibodies in synovial fluid and in serum of patients with rheumatoid arthritis and other types of synovitis

OBJECTIVE: Antineutrophil cytoplasmic antibodies (ANCA) are present in several vasculitides and in other immunomediated diseases. The reported prevalence of ANCA in rheumatoid arthritis (RA) is variable. In addition, the presence of such autoantibodies has been poorly investigated in synovial fluid (SF). The objectives of this study were (1) to investigate the presence of ANCA both in the serum and in SF from patients with RA and other forms of synovitis (OS); (2) to analyze the reactivity of ANCA against isolated antigens proteinase 3 (PR3), myeloperoxidase (MPO) and lactoferrin (LF); and (3) to evaluate the clinical relevance of these autoantibodies. METHODS: Twenty-eight patients with RA, 13 with OS, and 17 with osteoarthritis (OA) of the knee joint were studied. No patient had clinical manifestations of vasculitis. SF and serum samples were investigated for the presence of ANCA by indirect immunofluorescence (IIF); the reactivity against PR3, MPO and LF was assessed by ELISA. RESULTS: ANCA were detected by IIF in SF of 39.3% patients with RA, 38.5% with OS, and 5.9% with OA. With 2 exceptions, patients who had ANCA in SF showed positivity also in serum. The presence of both anti-MPO and anti-LF antibodies was found in 3 patients with RA and 1 with OA; a patient with RA showed antibodies only against LF and another one with RA only against MPO. No reactivity was found against PR3. In patients with RA ANCA were not associated with disease activity. CONCLUSION: We found an increased incidence of ANCA both in SF and serum from patients with RA and OS. The pathogenic role and the clinical relevance of such autoantibodies in these diseases remain to be established.