Staphylococcus aureus cell‐envelope antigens are localized in glomeruli from patients with IgA‐related nephropathy

Abstract

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.