A single-chain Fv reactive with the Goodpasture antigen

Goodpasture's disease is defined by the presence of autoantibodies to the glomerular basement membrane and characterized clinically by rapidly progressive glomerulonephritis and pulmonary hemorrhage. P1, a murine monoclonal antibody to the Goodpasture antigen (the noncollagenous domain of the a3 chain of type IV collagen, α3(IV)NC1), has been a valuable reagent in investigating the pathogenesis of this disorder. The purpose of this study was to generate and characterize a recombinant form of P1 as a single-chain Fv (scFv). First strand cDNA was made from RNA extracted from the P1 hybridoma cell line, and DNA encoding the antibody light and heavy chain variable domains was amplified by polymerase chain reaction, using universal oligonucleotides. The purified products were ligated sequentially into an expression plasmid separated by a sequence encoding a 15 amino acid flexible oligopeptide linker. The resulting scFv was expressed in E. coli. Functional scFv, designated HBR-3, was obtained by denaturing and refolding the expressed product. HBR-3 was shown by ELISA, immunoblotting, and immunohistologic techniques, to have the same specificity for α3(IV)NC1 as P1 and autoantibodies from patients with Goodpasture's disease. HBR-3 and P1 were shown to have similar affinity for their mutual ligand. On sections of normal human kidney, the scFv bound only to glomerular basement membrane and distal tubular basement membrane. It did not bind to the glomerular basement membrane of patients with Alport's syndrome, in whom the Goodpasture antigen is often not expressed in an antigenic form. We have, therefore, generated a scFv which reproduces the specific binding properties of the parent monoclonal antibody, P1. The potential of HBR-3 as a diagnostic reagent in Alport's syndrome has been demonstrated. The development of this recombinant molecule should permit new approaches to the investigation of Goodpasture's disease.