A nephritogenic peptide induces intermolecular epitope spreading on collagen IV in experimental autoimmune glomerulonephritis

Abstract

This group previously identified a peptide p13 of α3(IV)NC1 domain of type IV collagen that induces experimental autoimmune glomerulonephritis (EAG) in rats with generation of antibodies to sites on α3(IV)NC1 external to the peptide as a result of intramolecular epitope spreading. It was hypothesized that intermolecular epitope spreading to other collagen IV chains also was induced. Rats were immunized with nephritogenic peptide that was derived from the amino terminal part of rat α3(IV)NC1 domain, and serum and kidney eluate were examined for antibodies to both native and recombinant NC1 domains of collagen IV. Peptide induced EAG with proteinuria and decreased renal function and glomerular basement membrane IgG deposits. Sera from these rats were examined by ELISA, which revealed reactivity not only to immunizing peptide but also to human and rat α3(IV)NC1 and to human α4(IV)NC1 domains. Kidney eluate that was depleted of α3(IV)NC1 antibodies still reacted to α4(IV)NC1, and α3(IV)NC1 column-bound antibody reacted with α3(IV)NC1. There was minimal reactivity to other collagen chains. Eluate that was adsorbed to NC1 hexamer from rat glomerular basement membrane lost all reactivity to glomerular constituents, and the eluted antibodies reacted to α3(IV)NC1 and α4(IV)NC1 domains. These studies show that a T cell epitope of α3(IV)NC1 induces EAG, intramolecular epitope spreading along α3(IV)NC1, and intermolecular epitope spreading to α4(IV)NC1 domain with minimal or no reactivity to other collagen chains or glomerular constituents. This is the first demonstration in EAG of intermolecular epitope spreading and identification of the spread epitopes. Copyright © 2006 by the American Society of Nephrology.