As reported previously (21, 22), mean levels of SAA were found to be much greater (50.3-fold) in the synovial fluids of patients with RA than in those of patients with osteoarthritis (OA), a noninflammatory control (Figure 1I, mean level: 3.1 ± 1.7 versus 0.1 ± 0.2 μg/mL, P < 0.001). Here, SAA2 is linked to osteoarthritis.