Immunoelectron microscopic localization of immune deposits in IgA glomerulonephritis

Renal biopsy specimens obtained from twelve patients with IgA glomerulonephritis (IgA GN) were studied by immunoelectron microscopy (IEM) concomitantly with light microscopy (LM), immunofluorescence microscopy (IF), and electron microscopy (EM). For IEM, we used horseradish peroxidase (HRP)-conjugated antisera to human immunoglobulins (Ig) and to the complement component C3, and a diffusion technique with periodate-lysine-paraformaldehyde (PLP)-fixed tissue-chopper or cryostat sections. Due to well-preserved ultrastructure and good penetration of the antisera in the tissue-chopper sections, a detailed analysis of the distribution of immune material in the glomeruli was possible. In cryostat sections, ice crystal artifacts could not be avoided. The typical features of IgA GN could be reliably confirmed by IEM. Furthermore, IEM revealed the presence of Ig's and C3 in mesangial channels, in the intracellular vacuoles of glomerular cells, and in the electron-lucent areas along the glomerular basement membranes (GBMs). Staining of the mesangial channels indicates that they represent a route for the immune material gaining access into the mesangium. Intracellular vacuoles suggest that the deposited immune material can be partly eliminated through endocytosis by glomerular cells. The presence of Ig's and C3 in the electron-lucent areas supplies an explanation to the discrepancy sometimes observed between a positive finding in IF and a lack of deposits in EM.