High expression of macrophage migration inhibitory factor in the synovial tissues of rheumatoid joints

Macrophage migration inhibitory factor (MIF) plays an important role in inf lammation and immunity via autocrine/paracrine and endocrine routes. We exa mined the presence of MIF in the synovial fluids of rheumatoid arthritis (R A) patients. The content of MIF in the synovial fluid was quantitated by en zyme-linked immunosorbent assay which revealed that the concentration of MI F for RA patients was 85.7 +/- 35.2 ng/ml (mean +/- SD) (n = 25). In compar ison, the concentrations for osteoarthritis patients and normal volunteers were 19.5 +/- 5.3 ng/ml (n = 12) and 10.4 +/- 1.1 ng/ml (n = 5), respective ly. The expression of MIF mRNA and presence of MIF protein in the synovial tissues of RA were demonstrated by Northern blot and Western blot analyses, respectively. Immunohistochemical analysis revealed that positive staining was largely observed in the cytoplasm of infiltrating T lymphocytes, which might be the major source of MIF detected in the synovial fluids. The path ophysiological role of MIF in RA remains to be elucidated; however, the pre sent results for the first time suggest the possibility that MIF is involve d in the potentiation of inflammatory and immunological responses in rheuma toid joints. (C) 1999 Academic Press.