Characterization of Immunoglobulin G Anti-Glomerular Basement Membrane Antibodies Eluted from Kidneys of Patients with Glomerulonephritis

Direct immunofluorescence microscopy was performed on sections of kidney from 22 patients with anti-glomerular basement membrane (anti-GBM) antibody-mediated nephritis proved by in vitro elution techniques. Although immunoglobulin G (IgG) was fixed to glomeruli of all native or transplanted kidneys, the third component of complement (C3) was bound at the site of IgG fixation in slightly more than half (10 of 17). Immunoglobulin subtyping of eluted IgG anti-GBM antibodies, performed by an indirect immunofluorescence technique, indicated the presence of IgG subtypes 1, 2 and 3 in the eluates. Although eluted IgG anti-GBM antibodies failed to fix human C3 on normal homologous kidney sections, IgG anti-GBM antibodies isolated from serum of nephritic patients did so. Failure to visualize C3 by immuno-fluorescence examination of nephritic human kidneys was usually not due to an anomaly of IgG subtype participation or to lack of intrinsic ability of IgG anti-GBM antibodies to bind C3 in vitro.