S100A8 and rheumatoid arthritis: The levels of S100A8, S100A9, and S100A8/A9 in serum and SF were all significantly increased in patients with RA (20.4 ± 7.8 ng/ml, 2.9 ± 0.3 ng/ml, and 38.9 ± 6.0 mg/ml in serum and 65.3 ± 23.4 ng/ml, 27.9 ± 4.5 ng/ml, and 54.8 ± 7.2 μg/ml in SF, respectively) as compared with patients with OA (7.0 ± 3.0 ng/ml, 0.9 ± 0.1 ng/ml, and 16.8 ± 4.8 μg/ml in serum and 5.1 ± 2.2 ng/ml, 3.6 ± 0.4 ng/ml, and 7.3 ± 4.5 μg/ml in SF, respectively) (Figure 1).