A major pathogenic antigen of Heymann nephritis is present exclusively in the renal proximal tubule brush border--studies with a monoclonal antibody against pronase-digested tubular antigen.

We have isolated a nephritogenic 120-kD antigen from rat renal tubule brush border that induces rat Heymann nephritis. A MoAb that recognized this antigen reacted exclusively with the brush border on indirect immunofluorescence and immunoelectron microscopy. Rabbit antiserum against this antigen also reacted exclusively with the brush border. With the injection of this antiserum, rabbit IgG became detectable along the glomerular basement membrane (GBM) after 3 days. Our 120-kD antigen was shown to have a close relationship with gp330 based on the following: (i) this antigen can induce active Heymann nephritis as gp330; (ii) our MoAb reacted with the immune deposits of nephritic kidneys induced not only by the 120-kD antigen but also by gp330, and conversely, rabbit antiserum against gp330 reacted with those induced by the 120-kD antigen as well as gp330; and (iii) by immunoblotting, polyclonal antibodies against the 120-kD antigen reacted with gp330 and polyclonal antibodies against gp330 reacted with the 120-kD antigen. These observations indicate that antigen present exclusively in the brush border can induce active Heymann nephritis, and the common antigenic determinants shared by brush border and the coated pits of glomerular epithelium may not be a prerequisite to induce nephritis. A more precise relationship between the 120-kD antigen and reported C14 fusion protein or 40-kD alpha 2MRAP remains to be established.