Rat mesangial cells express macrophage migration inhibitory factor in vitro and in vivo

Mesangial cells are thought to promote glomerular macrophage accumulation in glomerulonephritis. This may occur through the production of macrophage migration inhibitory factor (MIF), a molecule known to regulate macrophage accumulation at sites of inflammation. To study this, glomerular MIF expression and macrophage accumulation were examined in rat anti-Thy-1 disease, a model of mesangioproliferative nephritis. In situ hybridization and immunohistochemistry showed that MIF is expressed by some podocytes in normal rat glomeruli. De novo MIF expression by glomerular endothelium was seen on day 1 of anti-Thy-1 disease. On day 6, glomerular MIF mRNA and protein expression were prominent in segmental proliferative lesions, which was also the location of most infiltrating macrophages. Double-staining identified de nova MIF mRNA and protein expression by proliferating mesangial cells within these lesions. Cytokine regulation of mesangial cell MIF expression was examined in vitro. Northern blotting showed that cultured rat mesangial cells express a single 0.6-kb species of MIF mRNA, and Western blotting detected a single protein band of 12.5 kD. Six-hour stimulation of mesangial cells with interferon-gamma or platelet-derived growth factor significantly increased MIF mRNA levels. However, the addition of recombinant MIF to mesangial cells did not affect mesangial cell proliferation or constitutive transforming growth factor-beta mRNA expression, nor did MIF induce monocyte chemoattractant protein-1 mRNA expression. In conclusion, this is the first study to demonstrate that mesangial cells can produce MIF in vivo and in vitro. It is postulated that mesangial cell MIF production in response to injury acts to promote macrophage accumulation within segmental proliferative lesions in rat anti-Thy-1 nephritis.