An Investigation of the Antigenic Characteristics of the Renal Glomerulus in the Rat

The finding of a granular deposition of immunoglobulin in the kidney in experimental animal models of glomerulonephritis has been been interpreted as resulting from the random deposition of immune complexes in the glomeruli. Recent data suggests that although immune complex deposition may be an important factor in some forms of glomerulonephritis, the in situ formation of immune complexes between circulating anti-kidney antibodies and fixed glomerular capillary wall antigens may also be a significant factor in the pathogenesis of some animal models of glomerulonephritis. To examine the characteristics of discontinuously represented glomerular capillary wall antigens in the rat, monoclonal antibodies were generated against a glomerular plasma membrane fraction, depleted of glomerular basement membrane, prepared from isolated Lewis rat glomeruli. A total of 17 hybridomas, generated from the fusion of splenocytes obtained from mice immunised with the glomerular membrane fraction produced monoclonal antibodies which reacted with discontinuously represented antigens in the glomerulus and renal tubules. One further hybridoma secreted a monoclonal antibody which reacted with an antigen present on glomerular and tubular nuclear membranes. No hybridomas were produced which secreted a monoclonal antibody which reacted with linearly arrayed glomerular basement membrane antigens. Two of these monoclonal antibodies, both of the IgM subclass and code-named PH7 and SC5, produced a heavy granular glomerular staining pattern when examined by indirect immunofluorescence microscopy. Neither monoclonal antibody was kidney specific, with reactivity being demonstrated with a number of non-renal tissues. When administered intravenously to normal Lewis rats both SC5 and PH7 induced a mild proteinuric lesion. The proteinuria was not associated with histopathological changes at the light or electron microscope level. Immunoblotting experiments revealed that SC5 reacted predominantly with a protein band of 96 kDa present in detergent extracts of isolated glomeruli and glomerular plasma membranes. PH7 was shown to react with three low molecular weight proteins of 14, 13 and 11 kDa The findings of this study demonstrate the potential for a nephritogenic response to occur following the in situ formation of immune complexes between circulating anti-kidney antibodies and discontinuously arrayed non-glomerular, basement membrane glomerular capillary wall antigens characterised by granular immunofluorescence patterns,in animal models of glomerulonephritis.