“…6 MIF was originally described over 30 years ago as a Tlymphocyte-derived factor that inhibited the migration of peritoneal macrophages, 7 but it is now known that several other cell types, including macrophages themselves, are important sources of MIF. 8 MIF levels are elevated in the serum and synovial fluid of patients with rhemuatoid arthritis, 2,9 and within the synovial joint MIF immunostaining can be localized to the synovial lining CD14 + macrophages and fibroblast-like synoviocytes. 2 Upon release MIF is directly pro-inflammatory by activating or promoting cytokine expression (TNF␣, 8,10 IL-1, IL-2, 11 IL-6, 8,12 IL-8 13 and IFN␥, 11,14 ), nitric oxide release, 15 matrix metalloproteinase (MMP) expression, 16,17 and induction of the cyclooxygenase-2 (Cox-2) pathway.…”