Characterization of the NC1 domain of collagen type IV in glomerular basement membranes (GBM) and of antibodies to GBM in a patient with anti-GBM nephritis.

Anti-glomerular basement membrane (GBM) nephritis is associated with production of antibodies to the Goodpasture antigen (GPA) component of the NC1 domain of collagen type IV. We studied a patient with anti-GBM nephritis with regard to 1) reactivity of the anti-GBM antibodies in his serum, plasmapheresis fluid (PPF), and an eluate prepared from GBM of his nephrectomy specimen, and 2) electrophoretic and immunologic properties of the NC1 domain extracted by collagenase digestion from GBM of his nephrectomy specimen. Antibodies to different NC1 determinants in serum, PPF and eluate were detected by immunofluorescence of glomerular capillaries of normal kidney. In addition, the antibody in PPF, but not in the eluate, reacted strongly in a plate-binding radioimmunoassay with NC1 domain extracted from normal human GBM, and bound by Western blotting to both dimer (46 kD and 49 kD) and monomer (24 kD, 26 kD and 28 kD) components of the NC1 domain. Analysis of the NC1 domain in the patient's GBM by SDS-PAGE showed a number of abnormalities, including an absence of monomer bands. Moreover, there was diminished reactivity of the patient's NC1 domain by the radioimmunoassay and Western blotting, using his PPF and a rabbit anti-NC1 antiserum. These findings indicated that there were different types of antibodies to NC1 domain in PPF and eluate, associated with an abnormal NC1 domain in GBM. These results have allowed us to speculate on the pathogenesis of anti-GBM nephritis in this patient.