Isolation of cDNAs encoding immunogenic regions of gp330, the autoantigen involved in Heymann nephritis

Active Heymann nephritis is an organ-specific autoimmune disease of the rat kidney, characterized by the formation of immune complexes located subepithelially in the glomerulus. The T cell-mediated humoral immune response is directed to gp330, a large renal epithelial glycoprotein which is expressed both in the proximal tubule and on glomerular podocytes. In this study polyclonal rabbit antibodies raised against affinity-purified rat gp330 were used to screen a λ-gt11 expression library of the rat kidney. One cDNA clone that was recognized by the antibodies coded for a 2.7-kb protein that is not described in the sequence database of GenBank/EMBL. Two other groups of cDNA clones were identified that displayed similarity with several members of the low-density lipoprotein (LDL)-receptor gene family to which gp330 belongs. By comparison with the gp330-cDNA sequence, these two clones could be mapped to two remote areas on the extracellular domain of gp330. The antigenicity of these two areas is in accordance with their location in highly hydrophilic regions on the extracellular domain of gp330. The cDNA clones described in this study may represent two main immunodominant regions on rat gp330.