ISOLATION AND CHARACTERIZATION OF TUBULAR BASEMENT-MEMBRANE ANTIGEN COMMON TO HUMANS AND RATS

Using Brown Norway (BN) rats, we isolated and characterized the tubula r basement membrane (TBM) antigens that are immunologically common to humans. The renal basement membrane (RBM) of BN rat, as an antigen sou rce, was solubilized with 8 M urea instead of collagenase followed by extraction with 0.5 M NaCl. On frozen section-immunohistochemistry, th e autoantibody obtained from BN rats, which had been immunized with hu man RBM and showed tubulointerstitial nephritis, bound to the TBM, the basement membrane of the Bowman's capsule, and the brush border of th e proximal tubules, but not to the GEM of the normal BN rat kidney. Ne phritogenic antigens were isolated by immunoaffinity chromatography us ing Sepharose-bound purified autoantibody. By Western blot analysis of the eluate, bands with molecular weight of 200 kDa and 180 kDa were p ositively reacted to anti-FX1A (brush border antigen) antibody and wer e apparently different from the major bands with molecular weight of 1 45 kDa and 130 kDa. The bands with molecular weight of 145 and 130 kDa showed major cross reactivity with antibodies to fibronectin and lami nin. In contrast with these high molecular weight (HMW) bands, the maj or 60 kDa band with three minor bands showed no reactivity with any ty pe of antibody tested. These results indicated that the non-enzymatic solubilization of RBM is one of the possible procedures for isolating the HMW form of antigens. These antigens may be epitopically modified pre-existing constitutions of the basement membrane and may play a rol e in the induction of tubulo-interstitial nephritis.