Increased expression levels of key ER stress markers, such as glucose-regulated protein of 78 (GRP78), IRE1, the spliced form of X-box-binding protein 1 (XBP1s), ATF6, and eukaryotic translation initiation factor 2a (eIF2a), have been reported in macrophages and synovial tissues of patients with RA (10, 11). This evidence concerns the gene XBP1 and rheumatoid arthritis.