Quantitation of macrophage migration inhibitory factor (MIF) using the one-step sandwich enzyme immunosorbent assay: Elevated serum MIF concentrations in patients with autoimmune diseases and identification of MIF in erythrocytes

We raised monoclonal antibodies against human macrophage migration inhibito ry factor (MIF) and developed a one-step sandwich enzyme-linked immunosorbe nt assay (ELISA) method highly specific for human MIF. The ELISA system uti lizes a solid phase monoclonal antibody as a capture antibody and a horsera dish peroxidase-conjugated monoclonal antibody as a detector antibody. We u sed this ELISA method to evaluate the serum level of MIF in 240 healthy vol unteers (140 males and 100 females). We found no significant difference in MIF concentration with respect to age. A significant difference was found w ith respect to sex, with the mean value (+/- SD) for male subjects of 5.3+/ -2.3, and that for female subjects of 4.6+/-2.3 ng/ml (p<0.05). We next mea sured the serum MIF contents of patients with autoimmune diseases, and foun d that MIF levels were significantly elevated in patients with systemic lup us erythematosus and rheumatoid arthritis, 20.0+/-11.0 ng/ml and 21.7+/-11. 2 ng/ml, respectively. Using anti-MIF antibody-immobilized sepharose column chromatography, we discovered for the first time that MIF was present in e rythrocytes. Taken together these results suggest that MIF plays a major ro le in autoimmune diseases and, moreover, potentially induces various patho- logical outcomes in cases of hemolytic disorders.