PLAC8 and synovial sarcoma: Importantly, the PLAC8 mRNA expression levels were significantly higher in the active-AOSD patients than in the HCs or the inactive-AOSD patients, as well as than in patients with rheumatoid arthritis (RA), Sjögren syndrome (SS), systemic lupus erythematosus (SLE), or polymyositis (PM)/dermatomyositis (DM), indicating that the upregulation of PLAC8 mRNA in monocytes was specific in the patients with active-AOSD.