Intraglomerular leukocyte recruitment during nephrotoxic serum nephritis in rats

Macrophage depletion ameliorates nephritis induced by pathogenic antibodies

Kidney involvement affects 40-60% of patients with lupus, and is responsible for significant morbidity and mortality. Using depletion approaches, several studies have suggested that macrophages may play a key role in the pathogenesis of lupus nephritis. However, "off target" effects of macrophage depletion, such as altered hematopoiesis or enhanced autoantibody production, impeded the determination of a conclusive relationship. In this study, we investigated the role of macrophages in mice receiving rabbit anti-glomerular antibodies, or nephrotoxic serum (NTS), an experimental model which closely mimics the immune complex mediated disease seen in murine and human lupus nephritis. GW2580, a selective inhibitor of the colony stimulating factor-1 (CSF-1) receptor kinase, was used for macrophage depletion. We found that GW2580-treated, NTS challenged mice did not develop the increased levels of proteinuria, serum creatinine, and BUN seen in control-treated, NTS challenged mice. NTS challenged mice exhibited significantly increased kidney expression of inflammatory cytokines including RANTES, IP-10, VCAM-1 and iNOS, whereas GW2580-treated mice were protected from the robust expression of these inflammatory cytokines that are associated with lupus nephritis. Quantification of macrophage related gene expression, flow cytometry analysis of kidney single cell suspensions, and immunofluorescence staining confirmed the depletion of macrophages in GW2580-treated mice, specifically within renal glomeruli. Our results strongly implicate a specific and necessary role for macrophages in the development of immune glomerulonephritis mediated by pathogenic antibodies, and support the development of macrophage targeting approaches for the treatment of lupus nephritis.

Podocytes regulate neutrophil recruitment by glomerular endothelial cells via IL-6-mediated crosstalk

Stromal cells actively modulate the inflammatory process, in part by influencing the ability of neighboring endothelial cells to support the recruitment of circulating leukocytes. We hypothesized that podocytes influence the ability of glomerular endothelial cells (GEnCs) to recruit neutrophils during inflammation. To address this, human podocytes and human GEnCs were cultured on opposite sides of porous inserts and then treated with or without increasing concentrations of TNF-α prior to addition of neutrophils. The presence of podocytes significantly reduced neutrophil recruitment to GEnCs by up to 50% when cultures were treated with high-dose TNF-α (100 U/ml), when compared with GEnC monocultures. Importantly, this phenomenon was dependent on paracrine actions of soluble IL-6, predominantly released by podocytes. A similar response was absent when HUVECs were cocultured with podocytes, indicating a tissue-specific phenomenon. Suppressor of cytokine signaling 3 elicited the immunosuppressive actions of IL-6 in a process that disrupted the presentation of chemokines on GEnCs by altering the expression of the duffy Ag receptor for chemokines. Interestingly, suppressor of cytokine signaling 3 knockdown in GEnCs upregulated duffy Ag receptor for chemokines and CXCL5 expression, thereby restoring the neutrophil recruitment. In summary, these studies reveal that podocytes can negatively regulate neutrophil recruitment to inflamed GEnCs by modulating IL-6 signaling, identifying a potential novel anti-inflammatory role of IL-6 in renal glomeruli.

The lupus-susceptibility gene kallikrein downmodulates antibody-mediated glomerulonephritis

Sle3 is a NZM2410/NZW-derived lupus-susceptibility interval on murine chromosome 7, which is associated with spontaneous lupus nephritis (SLN), and also anti-GBM-induced glomerulonephritis (GN). The tissue kallikrein gene cluster is located within the Sle3 interval and constitutes potential candidate genes for this locus. We have recently reported that renal kallikrein expression was upregulated by anti-GBM antibody challenge in a strain-specific manner and that it was significantly underexpressed in the anti-GBM-sensitive strains, including B6.Sle3. Further sequencing and functional studies reported earlier provided evidence that kallikreins could constitute disease genes in lupus. In this report, we have used an adenoviral vector to deliver the klk1 gene to B6.Sle3 congenics to directly test if kallikreins might have a protective effect against anti-GBM-induced nephritis. Our data show that klk1 gene delivery ameliorated anti-GBM-induced nephritis in B6.Sle3 congenics. Taken together with earlier studies, these findings indicate that kallikreins play an important protective role in autoantibody-initiated GN and could constitute potential candidate genes for anti-GBM-induced GN and SLN.

Protective effect of ligustrazine on accelerated anti-glomerular basement membrane antibody nephritis in rats is based on its antioxidant properties

Ligustrazine has a renoprotective effect against nephritis. In this study, we further characterized the renoprotective properties of ligustrazine in an experimental model using accelerated anti-glomerular basement membrane antibody (AGBM-Ab). Ligustrazine was given i.p. once daily at 50, 100 mg/kg for 15 days after singly giving i.v. of rabbit anti-rat glomerular basement membrane serum, and showed dose-dependent inhibition the elevation of urinary protein, serum creatinine and blood urea nitrogen as well as the development of glomerular histological changes. Ligustrazine (50 mg/kg) had no affect on glutathione (GSH) content, glutathione peroxidase and catalase activities, but decreased the malondialdehyde (MDA) content and increased superoxide dismutase (SOD) activity in nephritis induced by AGBM-Ab. Ligustrazine (100 mg/kg) significantly decreased MDA content while significantly increased GSH content and SOD, glutathione peroxidase, catalase activities of kidney tissues in the rats treated with AGBM-Ab alone. In conclusion, our results show that ligustrazine has protective activity against accelerated AGBM-Ab nephritis, and its renoprotective effect may be due to its antioxidant properties and inhibition reactive oxygen species (ROS).

Histologic analysis of renal leukocyte infiltration in antineutrophil cytoplasmic antibody-associated vasculitis: importance of monocyte and neutrophil infiltration in tissue damage

OBJECTIVE

The histopathologic lesions in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) have been studied extensively, but the exact composition of the cellular infiltrate is unclear. We undertook this study to analyze renal leukocyte infiltration and the cellular distribution within glomeruli and interstitium in 65 renal biopsy samples obtained from patients newly diagnosed as having AAV.

METHODS

Renal cellular tissue infiltration was assessed with an immunoperoxidase method. Furthermore, the infiltrating cell types were correlated with clinical and histopathologic data.

RESULTS

The predominant interstitial infiltrating cells were T lymphocytes, while monocytes and, to a lesser extent, granulocytes constituted the dominant infiltrating cell types in glomeruli. Interestingly, lymphocyte infiltration was predominantly periglomerular, especially around glomeruli with sclerosis or heavy crescent formation, while interstitial monocyte and neutrophil infiltration was diffusely distributed over the interstitial tissue. A significant correlation was found for the glomerular infiltration of CD68-positive macrophages with the presence of glomerular necrosis as well as with the number of glomeruli with crescents (P < 0.0001 and P = 0.005, respectively). No correlation was found for interstitial fibrosis with the infiltration of any leukocyte subset. Furthermore, a significant correlation was found for the interstitial as well as for the glomerular infiltration of CD68-positive macrophages with serum creatinine concentration at the time of biopsy (P = 0.001 and P = 0.006, respectively).

CONCLUSION

These data underscore a major role of monocytes in addition to neutrophils in the tissue damage of AAV.

Rapid and diverse changes of gene expression in the kidneys of protein-overload proteinuria mice detected by microarray analysis

BACKGROUND

Microarray is a method that allows the analysis of a large number of genes at the same time. We applied this method to show the difference of gene expression in the kidney caused by proteinuria.

METHODS

An experimental mouse model of protein overload was prepared by bovine serum albumin injection. The mRNAs of kidneys isolated after 0, 1, 2, 3 and 4 weeks loading were analysed by Northern blotting. We analysed about 18000 genes by microarray. The expression patterns of the microarray were displayed on control, 1 and 3 weeks of protein overload using the clustering procedure. A clone showing the greatest changes of up-regulation in the kidney was cloned and analysed by in situ hybridization and immunohistochemistry.

RESULTS

Over 1600 kinds of gene expression were confirmed in control kidneys. Proteinuria caused systematic changes of gene expression demonstrated by the cluster analysis. The up-regulation of osteopontin mRNA was shown and confirmed by Northern blot analysis. One of the clones showing the largest changes, AA275245, was isolated and characterized. It revealed that AA275245 was an unreported 3' non-coding region of vinculin mRNA which was associated with cytoskeleton proteins (e.g. alpha-actinin, talin, F-actin). Immunohistochemistry and in situ hybridization showed that this clone was identified in glomeruli as a mesangial pattern. The detected signal intensity using both methods, however, was virtually identical in control and disease kidney models. All data including images and analysed signal intensities are accessible on the web site.

CONCLUSION

The microarray analysis revealed that the renal gene expression pattern was changed dynamically in mice with experimentally induced proteinuria within a few weeks.

Infiltration patterns of macrophages and lymphocytes in chronically rejecting rat kidney allografts

The migration of circulating leukocytes to sites of inflammation or antigen is based, at least in part, on the activities of adhesion molecules. In the context of organ transplantation, some of these have been shown to be upregulated during acute allograft rejection. As their role during chronic rejection has not been examined, we have used an established rat model to compare sequentially the presence of host cells within the grafts, as defined immunohistologically, with patterns of in vitro leukocyte binding and their dependence upon particular adhesion molecules. Various donor populations of peripheral blood lymphocytes (PBL), lymph node lymphocytes (LNL), and splenic monocytes were interacted with snap-frozen sections of allografted, isografted, and native kidneys at serial intervals up to 24 weeks after transplantation. Monocyte binding in the allografts rose at 8 weeks and peaked at 12 weeks, a period preceding the maximum numbers of macrophages noted immunohistologically in the chronically rejecting grafts at 16 weeks. Lymphocyte binding and infiltration patterns were similar, remaining stable throughout the follow-up period and consistently greater than those noted in isografts. In vitro binding of the monocytes was inhibited by mAbs against ICAM-1, LFA-1, CD18, and MAC-1; MAC-1 did not influence lymphocyte binding, although the other mAbs were effective. We conclude that adhesion molecules are responsible, at least in part, for patterns of cell populations infiltrating chronically rejecting renal allografts.

Glomerular macrophage phagocytic activity in experimental immune complex nephritis

In rats with the proliferative immune complex glomerulonephritis of chronic serum sickness, kidney function deteriorates in three clearly distinguishable and discrete stages: mild, moderate and severe. The macrophage component of glomerular inflammation in each stage is also quantitatively and qualitatively distinct, with abnormal phenotypic markers appearing in the moderate stage and increasing in the severe stage. To determine whether there were distinct functional differences among macrophages from the three stages, Fc gamma receptor-mediated phagocytic capacity was measured. The phagocytic capacity of glomerular macrophages increased significantly in the moderate stage, then significantly decreased, as rats progressed to severe chronic serum sickness. This decline in phagocytic function was not associated with a decrease in the expression of Fc gamma receptors on the glomerular macrophage cell surface. Furthermore, the phagocytic function of peritoneal macrophages from rats with severe chronic serum sickness was not impaired. Whether or not this attenuation of glomerular macrophage phagocytic capacity is the cause, or result, of renal disease progression remains unclear. It may indicate a potentially protective role for intraglomerular macrophages, and can serve as an additional functional marker of disease progression.

Depletion of CD8 positive cells in nephrotoxic serum nephritis of WKY rats

Following a small dose of nephrotoxic serum (NTS) WKY rats demonstrated crescentic glomerulonephritis, which was characterized by the early infiltration of CD8 positive cells in glomeruli. In vivo depletion of CD8 positive cells from WKY rats completely prevented proteinuria (4.6 +/- 4.8 mg/day vs. 105.3 +/- 11.6 mg/day on day 10; N = 19, P less than 0.001) and crescent formation (2.7 +/- 2.9% vs. 94.3 +/- 2.6%; P less than 0.001). Immunofluorescence revealed complete inhibition of the influx of CD8 positive cells and subsequent reduction of the infiltration of macrophages in the glomeruli. Glomerular binding of 125I-anti-rat glomerular basement membrane antibodies, host anti-rabbit IgG production and the C3 level in the circulation were the same as in the control. These data indicate that CD8 positive cells play a key role in glomerular injury and crescent formation. This model provides a useful system for studying the cellular mechanisms that lead to glomerular injury and subsequent crescent formation.