Immunohistochemical and double-immunofluorescent stainings were performed to detect the expression of 78-kDa glucose-regulated protein (GRP78), a marker of activation of the UPR, in infiltrating plasma cells of synovium, and flow cytometry and immunoblotting analyses were performed to quantify GRP78 in plasma cells of synovial fluid in inflamed peripheral joints of RA. The gene discussed is HSPA5; the disease is rheumatoid arthritis.