Macrophage migration inhibitory factor (MIF) is a widely-expressed and versatile cytokine that plays key roles in several pain [1, 2] and inflammatory diseases [3, 4], including neuropathic pain, rheumatoid arthritis, atherosclerosis, asthma, sepsis, and bladder inflammation [1, 2, 5–10]. Here, MIF is linked to rheumatoid arthritis.