Immunoelectron microscopic study of glomerular lesions using a postembedding method with a protein A-gold complex

Immuno and lectin histochemistry for renal electron microscopy

The combination of histochemical techniques and electron microscopy is a powerful tool to study the mechanisms and pathology of renal disease. Through the use of electron-dense markers such as colloidal gold, biologists are able to localize immune deposits, cellular receptors, and extracellular proteins, amongst others. In this chapter, the protocols for making colloidal gold, conjugating colloidal gold to protein A, and post-embedding labeling with a protein A-gold complex are described. Finally, a parallel technique for histochemical labeling with lectin-gold complexes is provided.

Immunoelectron microscopic diagnosis in nephropathology

An immunogold postembedding method for the ultrastructural localization of immunoglobulin G (IgG), IgA, IgM, C3, fibrinogen, and kappa and lambda immunoglobulin light chains was established. The method was performed on surplus tissue from renal biopsies fixed in 2% glutaraldehyde and embedded in acrylic LR White resin. Fifteen cases were studied and the localization of antigen in the dense deposits in glomeruli compared with the immunofluorescence (IF) findings on the same cases. The results obtained by IF and immunoelectron microscopy (IEM) were comparable for IgG and IgA. In most instances, IgM and C3 were more intensely labeled by IF than IEM. Some discrepancies were noted for fibrinogen. It is postulated that these differences are related to a partial loss of antigenicity due to fixation or chemical reaction with the embedding medium. The advantage of IEM resides in localizing antigens in very small deposits seen in early stages of glomerulonephritis. The method can supplement IF in diagnostically difficult cases or be substituted for it when material for IF is not available.

Processing of colloidal gold particles in the glomerular mesangium and macula densa of the duck kidney

Bovine-serum-albumin coated colloidal gold particles were injected intravenously into healthy, adult domestic ducks. The fate of these tracer particles was followed in a time-sequence up to 4.5 days in the renal glomerular mesangium--distal tubule macula densa junction with transmission electron microscopy. The bulk of particle aggregates is 'trapped' in the mesangial channel system, phagocyted by mesangial cells, exocyted back into the mesangial channels, transported extracellularily towards the vascular hilus, rephagocyted by macula densa cells and expelled into the tubular lumen. This process requires about nineteen hours in the experimental model chosen, although it continues to take place to a much lower extent even 4.5 days after administration of the tracer. This mode of macromolecular excretion may be of interest in connection with the pathogenesis of several forms of glomerulonephritis.