HSPA5 and rheumatoid arthritis: The existing research on the potential clinical biomarker GRP78/Bip in RA has primarily been limited to isolated examinations of either synovium [23,36,37,38,39,40], blood [14,36,39,40,42,43,44,45,46,47,48,49,50,51], or SF [42,44,52,53,54].