Since it has been reported that RA synovial fibroblasts are relatively resistant to ER stress [8,9] and TNFα-induced reactive oxygen species accumulation has been shown to stimulate the UPR in murine fibrosarcoma L929 cells [19], we asked whether TNFα modulated the UPR of RA synovial fibroblasts. Here, TNF is linked to rheumatoid arthritis.