Application of electron microscopic immunocytochemistry to the human kidney: Distribution of type IV and type VI collagen in normal human kidney

We used immunogold electron microscopic (IEM) techniques with periodate- lysine-paraformaldehyde-fixed and Lowicryl-embedded or cryopreserved tissues to study the distribution of α1(IV) and α3(IV) chains of Types IV and VI collagen in glomerular basement membrane (GBM) and mesangial matrix of glomeruli in normal human kidneys. Monoclonal antibodies to α1(IV) and α3(IV) collagen chains and Type VI collagen could be detected only with cryoultramicrotomy, whereas polyclonal anti-Type IV collagen antibody was detectable in Lowicryl-embedded tissue. Ultrastructural detail was better preserved in the Lowicryl-embedded tissue. IEM labeling provided more detailed information as to the site-specific array of these extracellular matrix molecules in glomeruli than did immunofluorescent microscopy. The labeling of α1(IV) collagen chain was distributed mainly along the endothelial side of glomerular basement membrane and the mesangial matrix. Mesangial GBM was relatively poorly labeled compared with that of mesangial matrix. In contrast, the α3(IV) chain was detected throughout the thickness of the GBM, but there was no labeling of mesangial matrix. Type IV collagen distribution was identical to that of the α1(IV) chain within the glomerulus but was also associated with interstitial collagen fibrils. This study documents and details the heterogeneous distribution of Type IV and VI collagen chains within the normal human glomerulus and provides the framework for the study of these matrix components in human glomerular diseases.