We found that IL-20RA, RANKL, and CD55 were abundantly expressed in RA-FLSs but negligibly expressed in OA-FLSs and that dual-immunofluorescent labeling of IL-20RA and RANKL revealed consistent overlaps between RANKL, IL-20RA, and CD55 (Fig. 1a–c). This evidence concerns the gene CD55 and rheumatoid arthritis.