MIF and Arthritis: We found significantly elevated MMP-2 protein levels in knee homogenates of wild-type mice compared with MIF gene-deficient mice (wild-type, 1.3 ± 0.08 ng/mg of protein and MIF gene-deficient, 0.82 ± 0.08 ng/mg of protein; P < 0.05), pointing to an important role of MMP-2 in arthritis (Figure 3a).