A study by immunofluorescence microscopy of the NC1 domain of collagen type IV in glomerular basement membranes of two patients with hereditary nephritis.

The NC1 domain of the collagen type IV molecule, the major component of glomerular basement membranes (GBM), consists of dimers and 24 kilodalton (K), 26 K and 28 K monomers in man, and contains the Goodpasture antigen. Serum obtained from patients with Goodpasture's syndrome has been reported not to stain GBM of most male and some female patients with hereditary nephritis (HN) by immunofluorescence (IF) microscopy. In the present study, GBM seen on the renal biopsies of 2 patients (one male and one female) with HN were examined by IF to ascertain whether NC1 monomers were detectable. Three reagents were used: a plasmapheresis fluid (PPF) obtained from a patient who was treated for anti-GBM nephritis (human anti-GBM PPF); a commercial rabbit antibody against human NC1; and a rabbit antibody raised by us against dog NC1, which cross-reacted with human NC1. All 3 reagents detected NC1 determinants in GBM of normal human kidney by IF and reacted with human NC1 by a plate-binding radioimmunoassay (RIA). The human anti-GBM PPF bound to 28 K and 26 K monomer components of NC1 by Western blotting, the rabbit anti-human NC1 antibody bound to 26 K and 24 K monomers, while the rabbit anti-dog NC1 antibody bound only to the 26 K monomer. By IF, the human anti-GBM PPF did not stain GBM of the male patient with HN, but produced segmental staining of GBM (i.e., some GBM stained, while others did not) of the female patient. In contrast, the rabbit anti-NC1 antibodies produced global staining by IF of GBM of both patients. The absence of staining (i.e., global or segmental) seen with the human anti-GBM PPF implied that the 26 K and 28 K monomers of NC1 were either absent from GBM, or were present but altered structurally, leading to a diminution in their immunological reactivity. However, the positive staining observed with the rabbit anti-NC1 antibodies implied that the 26 K monomer was actually present in GBM. Hence, we postulate that the 26 K monomer of NC1 in GBM was structurally altered, and that the 28 K monomer was either absent, or present but altered. These findings suggest that there is an abnormality of more than one monomer of NC1 in GBM of patients with HN.