Macrophage migration inhibitory factor (MIF), a key mediator of the delayed-type hypersensitivity response, was originally thought to be produced by activated T cells. However, recent studies have found that MIF is produced in many cell types including monocytes/macrophages and anterior pituitary cells. The current study has examined MIF expression in normal and diseased kidney using in situ hybridization, immunohistochemistry, and Northern blotting. MIF mRNA and protein are constitutively expressed in normal kidney, being largely restricted to tubular epithelial cells and some glomerular visceral and parietal epithelial cells. During the development of rat anti-glomerular basement membrane glomerulonephritis, a model of macrophage-mediated renal injury, there was marked de novo expression of MIF by intrinsic kidney cells including endothelium and glomerular and tubular epithelial cells. Up-regulation of MIF expression correlated with macrophage accumulation within the glomerulus (P < 0.001) and tubulointerstitium (P < 0.001). Of significance, the accumulation of macrophages was exclusively localized to areas of strong MIF expression, contributing to focal glomerular and tubulointerstitial lesion formation. In addition, up-regulation of MIF expression by parietal epithelial cells was associated with macrophage accumulation within Bowman's space and crescent formation. Combined in situ hybridization and immunostaining also demonstrated MIF expression by macrophages, T cells, and fibroblast-like cells within renal lesions. In conclusion, these data provide the first demonstration that renal epithelial cells are a major source of MIF in both normal and diseased kidney. Furthermore, the up-regulation of MIF expression may play an important role in macrophage accumulation and progressive renal injury in rat crescentic glomerulonephritis.
Animals Disease Models, Animal