ALL 4 PUTATIVE LIGAND-BINDING DOMAINS IN MEGALIN CONTAIN PATHOGENIC EPITOPES CAPABLE OF INDUCING PASSIVE HEYMANN NEPHRITIS

Megalin (gp330) is the main target antigen involved in the induction o f Heymann nephritis (HN), a rat model of human membranous nephropathy. Its large extracellular region contains four putative ligand-binding domains separated by spacer regions. Previously, it was reported that the second ligand-binding domain (LBD II) of megalin is involved in th e pathogenesis of passive HN because it is capable of binding antibodi es in vivo and initiating formation of immune deposits (ID). This stud y explores the possibility that pathogenic epitopes might also be pres ent in the other putative ligand-binding domains. Recombinant fragment s of ligand-binding domains (LBD)I through IV expressed in a baculovir us system were used to generate polyclonal domain-specific antibodies. Antibodies raised against each of the recombinant megalin fragments r eacted preferentially with its respective antigen and with whole megal in by immunoblotting. Each of the antibodies also gave a characteristi c brush-border staining for megalin by indirect immunofluorescence on rat kidney. When rats were injected with the domain-specific antibodie s to test their ability to produce passive HN, glomerular ID were pres ent in kidneys of all injected animals. The staining pattern in glomer uli of rats injected with LED I, III, or IV was similar to that obtain ed with antibodies to LED II. It is concluded that passive HN can be i nduced with antibodies against LED I, III, and IV, as well as LED II, and that each of the ligand-binding domains contains a pathogenic epit ope. These findings provide further evidence for the multiple epitope model of HN.