Biotinyl-tyramide: a novel approach for electron microscopic immunocytochemistry.

The biotinyl-tyramide protocol recently introduced for sensitive light microscopic immunocytochemistry was applied to electron microscopy and revealed various tissue antigens with high resolution. The protocol consists of an indirect method in which thin tissue sections are incubated successively within a specific primary antibody, followed by a biotinylated secondary antibody, streptavidin-HRP, and then finally with biotinyl-tyramide. The reaction product appears as a dense filamentous material that is deposited over particular cellular compartments. The labeling obtained for the antigens tested, amylase and heat-shock protein 70 in pancreatic acinar cells, insulin in pancreatic beta-cells, and carbamoyl phosphate synthetase and catalase in liver tissue, was found to be highly specific, with the labeling for each antigen confined to its particular cellular compartment. Background levels and nonspecific deposition of the staining were negligible. The use of biotinyl-tyramide therefore appears to be an alternative sensitive technique for immunoelectron microscopy.