The pathogenic antigen of Heymann nephritis is a membrane glycoprotein of the renal proximal tubule brush border.

Purified brush border fractions prepared from rat kidneys were solubilized in detergent, iodinated, and subjected to immunoprecipitation to identify the pathogenic antigen present in brush border membranes that is responsible for the production of Heymann nephritis (HN). Purified IgG prepared from the sera of rabbits or rats immunized with a crude cortical preparation, known as Fx1A, precipitated multiple peptides, whereas IgG eluted from glomeruli of rats with active or passive HN specifically immunoprecipitated a single large glycoprotein (Mr = 330,000). This protein (gp330) was subsequently purified by gel filtration and lentil lectin affinity chromatography from detergent-solubilized brush border membranes. When rats were immunized with purified gp330, they developed anti-brush border antibodies and active HN. IgG prepared from the serum of rats with active HN caused passive HN when injected into normal recipients. Rats immunized against brush border membrane proteins depleted of gp330 developed anti-brush border antibodies but did not develop HN. Further analysis of gp330 indicated that it is solubilized by detergent treatment of isolated brush border microvilli, and its antigenic component is released from intact microvilli by trypsin. By immunoperoxidase staining it was localized to the luminal side of the brush border membranes. These results indicate that (i) gp330 is the pathogenic antigen of HN; (ii) the antigen is a glycoprotein of the brush border membrane; and (iii) it is disposed with its pathogenic domain(s) facing the tubule lumen.