Detection of anionic sites and immunoglobulin A deposits in the glomerular capillary walls from patients with IgA nephropathy

A study of anionic sites in the glomerular basement membrane (GBM) from patients with immunoglobulin A (IgA) nephropathy is described. The relationship between the deposition of IgA and the detection of glomerular extracellular components, i.e., noncollagenous (NC-1) domain of Type IV collagen, in the glomerular capillary walls was examined by double immunofluorescence. Renal biopsy specimens from patients with IgA nephropathy were immersed in polyethyleneimine (PEI) as a cationic probe and then examined by electron microscopy. Renal specimens were also incubated with mouse monoclonal anti-NC-1 domain of Type IV collagen and then stained with fluorescein isothiocyanate (FITC)-labelled goat antimouse Ig antiserum. After these reactions, sections were stained with rhodamine-labelled rabbit antihuman IgA antiserum. GBM subepithelial anionic sites marked by PEI were altered by the deposition of electron-dense deposits (EDD) in patients with IgA nephropathy and there was a significant correlation between the levels of proteinuria and the incidence of EDD in the GBM in such patients. Marked proteinuria was observed in patients who showed loss of anionic sites in the GBM by electron microscopy. By double immunofluorescence, IgA was shown to be focally deposited outside the NC-1 domain of Type IV collagen-detected regions in the same patients. The authors concluded that high levels of proteinuria might be due to alterations of the size barrier and/or anionic sites of GBM in the moderate stage of IgA nephropathy.