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The ninth complement component in rheumatoid arthritis, Behçet's disease and other rheumatic diseases
Insights
Plasma C9 levels, a complement system component, are significantly elevated in active rheumatoid arthritis and Behçet's disease. C9 may serve as a superior indicator of disease activity compared to CRP and ESR in rheumatoid arthritis.
Area of Science:
- Immunology
- Rheumatology
- Complement System
Background:
- The complement system plays a crucial role in inflammatory and autoimmune diseases.
- Complement component 9 (C9) is the terminal component of the complement cascade.
- Understanding C9 levels in various arthritic conditions can provide insights into disease pathogenesis and activity.
Purpose of the Study:
- To measure plasma C9 levels in patients with rheumatoid arthritis and other rheumatic diseases.
- To evaluate the correlation between plasma C9 levels and disease activity.
- To compare the efficacy of C9 as a disease activity marker against C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).
Main Methods:
- An immunoradiometric assay using two monoclonal antibodies was employed to quantify plasma C9 levels.
- Plasma C9 levels were analyzed in patients diagnosed with rheumatoid arthritis, Behçet's disease, ankylosing spondylitis, psoriatic arthropathy, systemic lupus erythematosus, erosive osteoarthritis, and acute gout.
- Sequential monitoring of C9 levels was performed in four Behçet's disease patients to observe fluctuations during disease activity.
Main Results:
- Significantly elevated plasma C9 levels were observed in active rheumatoid arthritis (119.7 +/- 28.3 mg/l), Behçet's disease (177.9 +/- 26.2 mg/l), and ankylosing spondylitis (116.1 +/- 23.1 mg/l).
- In Behçet's disease, C9 levels decreased to normal ranges during disease quiescence, indicating its potential as a disease activity monitor.
- Plasma C9 elevation was more consistent in active rheumatoid arthritis than CRP or ESR, with no significant mathematical association found between these markers.
Conclusions:
- Plasma C9 is significantly elevated in active rheumatoid arthritis, Behçet's disease, and ankylosing spondylitis.
- Plasma C9 serves as a reliable indicator of disease activity, particularly in Behçet's disease, and potentially outperforms CRP and ESR in rheumatoid arthritis.
- Further investigation into C9's role in rheumatic diseases is warranted for improved diagnostic and monitoring strategies.
Abstract:
Using an immunoradiometric assay with two monoclonal antibodies plasma C9 levels were measured in 49 patients with rheumatoid arthritis, eight patients with Behçet's disease, six patients with ankylosing spondylitis, nine patients with psoriatic arthropathy, six patients with systemic lupus erythematosus, five patients with erosive osteoarthritis and four patients with acute gout. Plasma C9 levels were also followed sequentially in four patients with Behçet's disease to show fluctuation during disease activity. The upper limit of normal for plasma C9 was 90 mg/l, 2 standard deviations above the known mean value. Significantly raised levels were found in active rheumatoid arthritis (119.7 +/- 28.3), Behçet's disease (177.9 +/- 26.2) and ankylosing spondylitis (116.1 +/- 23.1). In Behçet's disease the raised C9 levels normalized during disease quiescence suggesting that C9 is a good monitor of disease activity. CRP and ESR values were also measured. In rheumatoid arthritis C9 was more consistently elevated in active disease than CRP or ESR. As there was no association between these measures on mathematical analysis it was concluded that plasma C9 is a better indicator of disease activity in rheumatoid arthritis.