Circulating levels of tumor necrosis factor receptors I and II: biomarkers for ankylosing spondylitis and rheumatoid arthritis

Objective: To investigate serum concentrations of soluble tumor necrosis factor receptors I and II (TNFRI and TNFRII) in patients with ankylosing spondylitis (AS) and rheumatoid arthritis (RA) compared to healthy subjects. We further correlated the serum levels of TNFRI and TNFRII with C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) in AS and RA patients. Methods: We recruited 80 AS patients classified according to the European Spondyloarthropathy Study Group, 80 RA patients according to the American College of Rheumatology criteria, and 40 normal controls. TNFRI and TNFRII were measured by cytometric bead array. Results: Soluble TNFRI levels were higher in AS and RA patients (p ＜ 0.001) than in the controls. There were no significant differences in serum levels of TNFRII between our patients and the controls. TNFRI was correlated with high CRP and high ESR in the RA and AS patients (all p ＜ 0.001) compared with the controls. Furthermore, TNFRI was also correlated with normal CRP and ESR in the RA patients (p = 0.009 and 0.004, respectively). There were no significant differences except for the correlations found between high CRP and high ESR in the RA patients (p = 0.049 and 0.039, respectively). Conclusion: Increased levels of TNFRI were correlated with the inflammatory status in AS and RA patients, suggesting a preferable target for treatment. TNFRI but not TNFRII may be a more specific biomarker for AS and RA disease activity.