Abstract
Macrophages have been implicated in causing renal injury in both human and experimental kidney disease. The aim of the current study was to determine whether modulating the state of macrophage activation directly affects the capacity of these cells to cause renal injury. This was investigated using an adoptive transfer model in which macrophage activation can be manipulated in vitro, using interferon-gamma (IFN-gamma) or dexamethasone (Dex), and then macrophage-mediated renal injury determined in vivo. In this model, rats were made leukopenic by administration of cyclophosphamide (CyPh). Two days later (day 0), animals were injected with sheep anti-GBM serum followed by a single injection of rat NR8383 macrophages on day 1 and then killed 3 or 24 h after cell transfer. NR8383 macrophages were incubated IFN-gamma and/or Dex before adoptive transfer into animals. Induction of proteinuria and glomerular cell proliferation (PCNA+ cells) in this model was dependent on transfer of NR8383 macrophages. Exposure of macrophages to IFN-gamma for 18 h (but not 3 h) before transfer caused a twofold increase in the degree of proteinuria and glomerular cell proliferation compared with unstimulated cells (Nil versus IFN-gamma; P < 0.001). This was due to an increase in the number of transferred macrophages within the glomerulus and a significant increase in degree of renal injury per transferred glomerular macrophage. IFN-gamma increased iNOS and PDGF-B gene expression and upregulated adhesion molecule expression in NR8383 macrophages. In contrast, exposure of NR8383 cells to Dex for 18 h (but not 1 h) abrogated renal injury due to a failure of transferred macrophages to accumulate within the glomerulus. In addition, Dex abrogated renal injury caused by IFN-gamma-stimulated macrophages. In conclusion, activation of macrophages by IFN-gamma, independent of any effect on other leukocytes or renal cells, can substantially augment macrophage-mediated renal injury. This IFN-gamma augmentation of renal injury is sensitive to the action of glucocorticoids, which act directly on macrophages to prevent their recruitment to the inflamed glomerulus. This study provides the first evidence that it is possible to directly modulate macrophage-mediated renal injury.
Highlights
Macrophage accumulation is a common feature in most types of human glomerulonephritis [1]
Administration of anti-GBM serum to rats induced glomerulonephritis characterized by glomerular accumulation of ED1ϩ macrophages, proteinuria, and glomerular cell proliferation (Figure 1, a through c)
Adoptive transfer of 6 ϫ 107 NR8383 macrophages per animal into cyclophosphamide-treated rats given anti-GBM serum resulted in significant glomerular macrophage accumulation, causing significant proteinuria and glomerular cell proliferation (Figure 1, a through c)
Summary
Macrophage accumulation is a common feature in most types of human glomerulonephritis [1]. A number of macrophage activating cytokines, such as IFN-␥, macrophage migration inhibitory factor, interleukin-1, and tumor necrosis factor-␣, are produced within the inflamed kidney, and blockade of these cytokines inhibits macrophage accumulation and renal injury in experimental glomerulonephritis (8 –14). These studies suggest that modulation of macrophage activation may be an important therapeutic goal in the treatment of glomerulonephritis. To investigate the importance of macrophage activation in the mediation of renal injury, it is necessary to manipulate macrophage activation independently of all other cells within the kidney We addressed this question by using an adoptive transfer model of macrophage-mediated renal injury.
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