Increased severity of glomerulonephritis in C-C chemokine receptor 2 knockout mice

Background The C-C chemokine receptor 2 (CCR2) is expressed on monocytes an d facilitates monocyte migration. CCR2 is a prominent receptor for monocyte chemoattractant protein-1 (MCP-1). This chemokine recruits monocytes to si tes of inflammation. It has been suggested that CCR2 and its ligand, MCP-1, play a role in the pathogenesis of glomerulonephritis. The goal of this st udy was to determine the contribution of CCR2 in a murine model of accelera ted nephrotoxic nephritis. We measured the extent of development of renal d isease in CCR2 wild-type and knockout mice after the administration of anti glomerular basement membrane antibody. Methods. Eight groups of animals were treated (N = 10 per group). Four days after IgG immunization, CCR2 wild-type and knockout mice received control serum or nephrotoxic serum. The urinary protein/creatinine ratio was measur ed on days 1 and 3; plasma and kidneys were collected on days 4 and 7. Kidn eys were evaluated by light microscopy, immunohistochemistry, and immunoflu orescence. The genotype of mice was confirmed by tissue analysis. Results. Protective effects of CCR2 knockout on the urinary protein/creatin ine ratio were observed on day 1, as values for this parameter were signifi cantly lower (35 +/- 3.6) than in nephritic wild-type mice (50 +/- 6.8). Th ere was a marked increase in proteinuria in nephritic wild-type mice on day 1 compared with vehicle-treated, wild-type animals (5 +/- 1.0). On day 3, the ameliorative effects of CCR2 knockout were not observed; the increase i n the urinary protein/creatinine ratio was similar in nephritic CCR2 wild-t ype (92 +/- 11.2) and knockout mice (102 +/- 9.2). Plasma markers of diseas e were evaluated on days 4 and 7. At these time points, there were no benef icial effects of CCR2 receptor knockout on plasma levels of urea nitrogen, creatinine, albumin, or cholesterol. On day 7, blood urea nitrogen (248 +/- 19.9 mg/dL) and plasma cholesterol were higher in nephritic CCR2 knockout mice than in wild-type mice (142 +/- 41.7 mg/dL) that received nephrotoxic serum. Histopathologic injury was more severe in nephritic CCR2 knockout mi ce than nephritic wild-type mice on day 4 (3.1 +/- 0.3 vs. 2.0 +/- 0.3) and day 7 (3.6 +/- 0.2 vs. 2.9 +/-. 0.3). By immunohistochemical analysis at d ay 4, there were significantly fewer mac-2-positive cells, representative o f macrophages in the,glomeruli of nephritic CCR2 knockout (2.1 +/- 0.6) mic e than nephritic wild-type (3.9 +/- 0.5) animals. By indirect immunofluores cence, there was a moderate, diffuse linear IgG deposition of equivalent se verity present in glomeruli of both wild-type and CCR2 knockout nephritic m ice. Conclusion. These results suggest that our strategy was successful in reduc ing macrophage infiltration, but this model of glomerulonephritis is not so lely dependent on the presence of CCR2 for progression of disease. After a transient ameliorative effect on proteinuria, CCR2 knockout led to more sev ere injury in nephritic mice. This raises the intriguing possibility that a CCR2 gene product ameliorates glomerulonephritis in this murine model. Alt hough effects that occur in chemokine knockout mice are not equivalent to t hose expected with prolonged use of a chemokine antagonist, this study may nevertheless have implications for consideration of long-term use of chemok ine antagonists in renal disease.