The nephritis-associated plasmin receptor is a recently identified nephritogenic antigen associated with acute poststreptococcal glomerulonephritis and proposed to play a pathogenic role, but its precise glomerular localization in acute poststreptococcal glomerulonephritis has not been elucidated. We therefore analyzed renal biopsy sections from 10 acute poststreptococcal glomerulonephritis patients by using immunofluorescence staining with anti-nephritis-associated plasmin receptor antibody and various markers of glomerular components. Nephritis-associated plasmin receptor was detected in the glomeruli of all patients, and double staining for nephritis-associated plasmin receptor and collagen IV showed nephritis-associated plasmin receptor to be predominantly on the inner side of the glomerular tufts. Nephritis-associated plasmin receptor-positive areas within glomerular tufts were further characterized with markers for neutrophils, mesangial cells, endothelial cells, and macrophages. In 6 of the patients, nephritis-associated plasmin receptor staining was seen mainly in neutrophils and to a lesser degree in mesangial and endothelial cells. In the other 4 patients, nephritis-associated plasmin receptor staining was seen mainly in mesangial cells and to a lesser degree in neutrophils and endothelial cells. In all patients, macrophages showed little staining. Elevated plasmin activity in glomerular neutrophils was identified by combining in situ zymography staining for plasmin activity and immunofluorescence staining for neutrophils. The glomerular localizations of nephritis-associated plasmin receptor and another nephritogenic antigen, streptococcal pyrogenic exotoxin B, were compared by double immunofluorescence staining and found to be similar. These findings indicate the nephritogenic potential of nephritis-associated plasmin receptor and offer valuable information with respect to the pathogenic mechanism of acute poststreptococcal glomerulonephritis.
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