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.

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Mesangial cells are thought to be important mediators of glomerular inflammation and fibrosis. Studies have established a direct role for nitric oxide (NO) in the regulation of gene expression in mesangial cells. Representational difference analysis was used to investigate changes in gene expression elicited by the treatment of S-nitroso-L-glutathione in rat mesangial cells. Seven upregulated and 11 downregulated genes were identified. Four out of 11 downregulated genes (connective tissue growth factor, thrombospondin-1, collagen type I a1 and collagen type I a2) are known to be linked to inflammation and fibrosis. Results were verified across species in mesangial cells treated with a series of NO donors using Northern blot analysis, quantitative real-time PCR and protein analysis methods. Induction of endogenous NO production by cytokine stimulation also triggered regulation of the genes. One example gene, connective tissue growth factor, was studied at the promoter level. Promoter-reporter gene studies in mesangial cells demonstrated that NO acts at the transcriptional level to suppress gene expression. Our results reveal a complex role of NO in regulating gene expression in mesangial cells and suggest an antifibrotic potential for NO.

We conclude that the transcription factor Egr-1 plays a critical role for mesangial cell proliferation in vivo. Interfering with the induction of Egr-1 or with its target genes could give rise to novel therapeutic principles in mesangioproliferative glomerulonephritis.

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