The total patient population consisted of 32 patients with RA (25 women and seven men; mean ± standard deviation age, 52.8 ± 12.4 years) diagnosed according to the revised 1987 criteria of the American College of Rheumatology (formally, the American Rheumatism Association) [25]. All patients were receiving prednisolone (≤ 7.5 mg/day) and disease-modifying antirheumatic drugs. Clinical parameters in the study patients were as follows (mean ± standard deviation): erythrocyte sedimentation rate, 55.9 ± 35.4 mm/hour; serum C-reactive protein (CRP) level, 32.0 ± 32.0 mg/l; and IgM class rheumatoid factor titer, 142 ± 158 U/ml. Patients were divided into two groups: 24 patients with active disease, who had multiple tender and/or swollen joints and elevated serum CRP level (≥ 10 mg/l); and eight patients with inactive disease, who satisfied the American College of Rheumatology preliminary criteria for clinical remission [26]. Sixteen healthy volunteers (11 women and five men; age, 45.8 ± 11.2 years) served as controls. ST samples were obtained from three RA patients undergoing total knee replacement. All patients gave informed consent.