SAA concentrations were found to be significantly higher in the sera than in the synovial fluids of patients with RA (mean levels: 3.6 ± 2.1 and 2.3 ± 1.4 μg/mL, P < 0.01, Figure 8A), suggesting that chronic arthritis stimulates production of SAA from extraarticular sources such as the liver, thus contributing to the higher level of SAA in sera. Here, SAA1 is linked to rheumatoid arthritis.