MIF and rheumatoid arthritis: Besides the induction of MMPs, MIF participates indirectly in joint destruction by promoting angiogenesis in RA synovial fibroblasts [8] and inducing many osteoclast (OC)-inducing molecules such as TNF-α, IL-1, IL-6, and prostaglandin E2 (PGE2) [1,2,9,10].