ABSTRACT. Glomerular epithelial cells are primary pathogenic sites in focal segmental glomerulosclerosis (FGS) lesions. Glomerular epithelial cells are regarded as terminally differentiated cells that do not proliferate. These characteristics are also noted for neurons and muscular cells, which are major sites of mitochondrial DNA (mtDNA) mutation accumulation. Screening for mtDNA mutations was performed with renal biopsy specimens from patients with primary FGS and patients with IgA nephropathy (as subjects with secondary FGS and as control subjects). mtDNA extracted from kidney biopsy specimens was amplified with appropriate primer pairs for study of the mtDNA point mutations 3243A→G, 3271T→C, 8344A→G, and 8993T→G/C, as well as the common deletion (a 4977-bp deletion spanning mtDNA nucleotide pairs 8469 to 13447). In situ amplification of both total mtDNA and the common deletion was also performed. Two patients with FGS demonstrated the 3243A→G point mutation; 12 patients with FGS and seven patients with IgA nephropathy accompanied by glomerulosclerotic lesions exhibited the common deletion in their kidney tissue. No patient demonstrated the mtDNA mutations 3271T→C, 8344A→G, or 8993T→G/C. The degree of heteroplasmy for the 3243A→G point mutation was >85%; however, the heteroplasmy for the common deletion was <1%. As determined with in situ PCR, normal mtDNA was mainly distributed in the tubular epithelium and mtDNA with the common deletion was mainly distributed among glomerular epithelial cells. In conclusion, it is suggested that mtDNA mutations are distributed in glomerular epithelial cells among some patients with primary FGS or secondary FGS with IgA nephropathy. These mutations may be related to glomerular epithelial cell damage.

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Renal involvement is a significant complication of multicentric Castleman's disease (MCD) and various glomerular involvements have been reported. A 45-year-old Japanese man presented with persistent proteinuria, with lymphadenopathy and hypergammaglobulinemia. He had been diagnosed 4 years previously with MCD. As his renal impairment had progressed to renal failure, he underwent a renal biopsy. Histology revealed diffuse and global membranous lesions with large and heterogeneous epimembranous deposits. In addition, mesangial cell proliferation and focal extracapillary lesions were found. Under immunofluorescence, granular staining for anti-IgG, IgG1, IgG2 and IgA was strongly positive in the capillary loop, and weakly positive in the mesangium. As such, there was a diversity of histological features. Our perspective with regard to pathogenesis is that the formation of the immune-complex contributed to the membranoproliferative glomerulonephritis type 3-like lesion. This histological multiform with MCD is valuable for increasing our understanding of the mechanism for onset of immune-complex glomerular deposition and cellular proliferation of glomerulonephritis.

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Staphylococcus aureus (S. aureus) is a common, normal, and pathogenic flora that colonizes on mucosal tissues. Recently, we have reported glomerulonephritis occurred during MRSA infection. These glomerulonephritis have showed elevation of polyclonal serum IgA and IgG levels and IgA, IgG, and C3 deposition in glomeruli. In order to investigate the pathogenic roles of S. aureus antigens, we measured antibodies against S. aureus and stained glomeruli with mouse monoclonal antibody against S. aureus cell membrane antigens in patients with IgArelated nephropathy.S. aureus were treated with lysostaphin and centrifuged and sonicated. After centrifugation at 100 000 g for 1 h, precipitates (membrane component) were used as antigens. These antigens were purified by Sepharose 4B columns conjugated with IgG to remove antigens reacted to protein A. Affinity columns were made by BrCN-activated Sepharose 4B conjugated with purified antigens. The sera from patients with post-MRSA glomerulonephritis were purified with this affinity column and labelled with Biotin. Western blotting analysis showed that in patients with IgA nephropathy and post-MRSA glomerulonaphritis, 35 kDa and 17 kDa bands were clearly detected, while no or only weak bands were detected in normal controls. On the other hand, mouse monoclonal antibodies against S. aureus produced by polyethylene glycol method using purified antigens.Western blotting analysis showed that the monoclonal antibody (IgG1 kappa) reacted with 35 kDa of S. aureus antigens. Histopathological examination was performed in 130 patients with IgA-related nephropathy and 108 patients with other renal diseases using antibodies originated from patients' sera and mouse monoclonal antibody against S. aureus cell membrane antigens.On ELISA for serum titres of IgA and IgG classes against S. aureus, both titres in patients with IgA nephropathy and post-MRSA glomerulonephritis were significantly higher than those in normal and patients with non-IgA deposit disease (P < 0.05). S. aureus antigens in the glomeruli were detected in 62.5% of patients with IgA nephropathy and 55.6% of patients with post-MRSA glomerulonephritis by staining with antibodies from patients' sera. However, these were not detected in patients with other glomerulopathies. On staining with the monoclonal antibody, S. aureus antigens in the glomeruli were detected in 68.1% of patients with IgA nephropathy, 75.0% of patients with post-MRSA glomerulonephritis, and 60.0% of patients with purpura nephritis. However, these were negative staining in patients with other glomerulonephritis.From the above observations, we concluded that at least the antigens containing S. aureus cell envelope antigen play immunopathogenic roles in the development of IgA-related nephropathy.