Antigen retrieval for electron microscopy using a microwave technique for epithelial and basal lamina antigens

Abstract

The current study extends the principles of the antigen retrieval technique for formalin-fixed, paraffin-embedded tissues to transmission electron microscopy. Specimens prepared for both routine and immunoultrastructural studies were examined for the effects of microwave treatment on the immunolabeling of tissue antigens. Specimens of normal rat tongue mucosa and human oral mucosa were microwaved before immunogold labeling was done using six types of antibody (types I, III, IV, and VI collagen, laminin, and cytokeratin). Sections were cut from tissue blocks that had been fixed and embedded for either ultrastructural immunocytochemistry in L.R. White resin or routine electron microscopic morphology in TAAB resin. Compared with nonmicrowaved sections, microwave-treated, immunolabeled sections of both types of embedded tissues revealed markedly enhanced gold labeling for type IV collagen in the oral epithelial basal lamina. Moreover, microwave-treated L.R. White sections showed greater label density for type III and VI collagens and for cytokeratin compared with nonmicrowaved sections. There was variable gold labeling for laminin in both TAAB and L.R. White sections with or without microwave pretreatment and no improvement in type I collagen detection in microwave-treated sections. We concluded that postembedding microwave treatment of plastic ultrathin sections on sodium citrate buffer enhances some tissue antigens by increasing the likelihood of reexposing epitopes encrypted by a fixative-denaturative milieu. This microwave technique offers the potential of combining immunocytochemistry with enhanced exposure of antigenic markers of ultrastructural morphology in a number of extracellular sites.