When the mean plus two standard deviations of optical density (OD) of sera from healthy donors was set as the threshold [19, 25], 23.3%, 0.0%, 3.3%, 33.3%, 16.7%, 3.3%, 10.0%, and 6.7% patients with RA had autoantibodies against OPN, fibronectin, tenascin-C, α-enolase, bone sialoprotein (BSP), type II collagen, vimentin, and fibrinogen, respectively (Fig. 1A). Here, SPP1 is linked to rheumatoid arthritis.