A double labeling system was used to test the resolution of the indirect immunoperoxidase procedure in the localization of extracellular matrix components. A recognizable antigen, cationized ferritin, was first implanted at specific anionic sites (approximately 60 nm periodicity) in the lamina rara interna and externa of the glomerular basement membrane (GBM) and subsequently localized by immunoperoxidase. The coincidence between the location of reaction product and the ferritin clusters was assessed. When the amount of immunoadsorbed peroxidase and time of exposure to the 3,3'-diaminobenzidine (DAB)-containing medium were limited, discrete deposits of reaction product were observed around individual ferritin clusters. When immunolabeling was increased, the whole GBM was stained, and DAB staining was also found along the endothelial plasmalemma and the epithelial plasmalemma at the base of the foot processes at some distance (greater than 100 nm) from the ferritin clusters in the laminae rarae. These findings indicate that oxidized DAB reaction product can diffuse over long distances and be reabsorbed onto cell membranes. Even under limited incubation conditions some diffusion of DAB reaction product was encountered. The value and limitations of the DAB-peroxidase procedures are discussed.
Recovery of Anionic Sites of the Glomerular Basement Membrane after Their Disappearance by the Cationic Probe Molecule