The role of macrophage migration inhibitory factor in the inflammatory immune response and rheumatoid arthritis

Rheumatoid arthritis (RA) is a debilitating disease of unknown etiology. Although the pathogenesis of RA is multifactorial, the contribution of cytokines is undoubtedly pivotal in the progression of the inflammatory process. One cytokine gaining recognition for its importance in inflammation is macrophage migration inhibitory factor (MIF). Initially described as a biological activity, a broad range of functions of MIF has emerged including induction of proinflammatory mediators as well as demonstrated roles in both innate and adaptive immunity. In RA, increased MIF levels have been demonstrated in serum, synovial fluid and tissue with the latter correlating with disease activity. In vitro, MIF induces production of key proinflammatory genes operative in arthritis, including IL-1, TNF, IL-6, IL-8, COX-2, PLA2, and MMPs. In addition, MIF regulates proliferation and apoptosis via direct effects on the tumor suppressor protein p53 implicating a role for MIF in synovial hyperplasia. In vivo, MIF antagonism or MIF deficiency result in decreased disease severity in animal models of RA further confirming a role for MIF in joint inflammation. Interestingly, MIF is induced by glucocorticoids and MIF in turn antagonises glucocorticoid effects. This unique relationship presents antagonism of MIF as a potentially effective steroid-sparing therapy.