THE TARGET ANTIGEN OF ANTI-TUBULAR BASEMENT-MEMBRANE ANTIBODY-MEDIATED INTERSTITIAL NEPHRITIS

Our previous studies showed that 54 kD and 48 kD tubular basement memb rane (TBM) proteins were the major form of the target antigen involved in anti-TBM antibody-mediated tubulo-interstitial nephritis in humans . In those studies, we isolated the 54 kD glycoprotein (named gp54) fr om collagenase-digested bovine TBM. NH2-terminal amino acid sequencing indicated that gp54 represented a newly defined glycoprotein. In this study, we further characterized the target antigen, using mouse monoc lonal antibodies to gp54 and polyclonal anti-gp54 peptide antibody. Tw o monoclonal antibodies (H79 and H80) were established, and they react ed, by immunofluorescence, predominantly with the proximal TBM of huma ns, rabbits, and Wistar, Sprague-Dawley, and Brown-Norway rats, but no t with that of Lewis rats. They were also fixed by blotting intensely to the 54 kD component and weakly to the 48 kD component of collagenas e-digested human TBM. In vivo transfer of H79 to Wistar rats showed ex tensive linear binding of mouse IgG to the TBM and the basal membrane of the small intestine; however, no pathologic changes were seen by li ght microscopy. The anti-gp54 peptide antibody reacted with both the 5 4 kD and 48 kD TBM components of human TBM. mRNA was prepared from rab bit kidneys, and fractionated to enrich mRNA encoding the 54 kD and 48 kD peptides. On in vitro translation experiments with the mRNA fracti on, the 54 kD and 48 kD peptides were immunoprecipitated with anti-gp5 4 antibodies. These findings indicate that the 54 kD and 48 kD compone nts are encoded with different mRNA, but that they share the same anti genic epitope. It is likely that they are structurally related and exi st as isoforms.