Immunoelectron microscopy of cationized bovine serum albumin-induced glomerulonephritis in the rabbit

Immunocytochemical investigation of the in vivo endocytosis by renal tubular epithelial cells

The internalization and degradation of glomerular filtered serum proteins by the proximal tubular epithelium has been extensively studied by microperfusion methods. By using a cationic probe that easily traverses the glomerular wall into the urinary space, we have performed a morpho-cytochemical and quantitative study of the in vivo endocytotic activity of the proximal tubular epithelial cell. Bovine serum albumin (BSA) was tagged with dinitrophenol (DNP) and cationized to pI over 8. It was introduced into the circulation of normal mice for 5, 10, and 30 minutes and the distribution of the labeling was determined by protein A-gold immunocytochemistry, using specific antiDNP antibodies on tissue sections of routinely aldehyde-fixed, osmiumpostfixed, and Epon-embedded kidneys. Cationic BSA-DNP was detected at the endothelial and epithelial sides of the glomerular basement membrane, and over capillary and tubular basement membranes. In the proximal tubular epithelial cell, labeling was present over microvilli as well as over endosomal and lysosomal compartments, with labeling intensities varying from one compartment to the other. Morphometric evaluations of the labeling demonstrated a progressive incorporation of the probe from microvilli and endocytic compartments at 5 minutes to endocytic and lysosomal compartments at 10 and then 30 minutes. When considering labeling densities, no significant differences were found on microvilli and basolateral membranes between times of circulation; however, the labeling density over endosomal and lysosomal compartments was very intense at 10 minutes compared with 5 minutes, decreasing at 30 minutes. Results from this study validate the cationic albumin tagged with DNP as a tool in the study of the quantitative aspects of protein endocytosis at the ultrastructural level, in the kidney tubular epithelium.

Alterations in the glomerular charge barrier in human lupus nephritis

Renal tissue taken from ten patients with proteinuria and diagnosed as suffering from human lupus nephritis was examined by a post-embedding charge labelling method using cationic gold (CG). The method allows localization of the anionic charge in the glomerular epithelial cell coat and/or glomerular basement membrane (GBM). Our results demonstrate that in human lupus nephritis there are gaps in the charge barrier associated with immune deposits found in the lamina rara externa of the GBM. These data suggest that the loss of glomerular fixed anionic charges in the GBM may play an important role in the development of proteinuria in patients suffering from lupus nephritis.