Elevated levels of synovial fluid antibodies reactive with the small proteoglycans biglycan and decorin in patients with rheumatoid arthritis or other joint diseases.

OBJECTIVES To determine whether patients with rheumatoid arthritis (RA) express humoral immunity to the small proteoglycans biglycan and decorin and to compare the response to that of patients suffering from other joint diseases. METHODS Serum and synovial fluid IgG and IgM antibody levels were determined by enzyme-linked immunosorbent assay. Antibodies to biglycan and decorin as well as to other known and extensively investigated cartilage matrix components such as type II collagen, aggrecan and fibronectin were investigated. Patients suffering from RA, osteoarthritis (OA), psoriatic arthritis and other seronegative spondylarthropathies were included in the study. Correlation between antibody levels and clinical/laboratory parameters was determined. RESULTS Patients with RA expressed an increased humoral immunity to biglycan, while patients with seronegative spondylarthropathies displayed elevated decorin-specific synovial antibody levels compared with OA patients. CONCLUSION These results indicate a significantly higher immunity to small proteoglycans in RA and seronegative spondylarthropathies than in OA suggesting a possible involvement in the pathogenesis of inflammatory rheumatic diseases.