Figure 4

Decreased MMP-2 expression by synovial lining cells in zymosan-induced arthritis (ZIA) joints of MIF -/- mice. (a–c) Alkaline phosphatase staining of MMP-2 (red) was performed on frozen ZIA joint sections. MMP-2 expression was decreased in synovial lining cells, which are composed of macrophages and fibroblasts, of MIF -/- (a) compared with WT (b) mice. Irrelevant immunoglobulin G was used as the negative control (c) (400×). Black arrows indicate synovial lining cells stained for MMP-2. (d–f) The average percentage of cells stained for MMP-2. The mean percentage of MMP-2 expression ± standard error of the mean (SEM) is shown; *P < 0.05. (d) Synovial lining cells showed enhanced MMP-2 expression in WT compared with MIF -/- mice. (e) Similarly, MMP-2 was upregulated on sublining nonlymphoid mononuclear cells. (f) ECs showed a trend towards MMP-2 upregulation in WT mice ZIA joints, although the difference was not significant (n = 5, where n = number of animals in each group). EC, endothelial cell; MIF -/-, macrophage migration inhibitory factor gene-deficient; MMP, matrix metalloproteinase; WT, wild-type.