Printed in U.S.A. LIGHT AND ELECTRON MICROSCOPIC LOCALIZATION OF ANTIGENS IN TISSUES EMBEDDED IN POLYETHYLENE GLYCOL WITH A PEROXIDASE- LABELED ANTIBODY METHOD”2

Tissues embedded in polyethylene glycol (PEG) were used for the immunocytochemical localization of cellular antigens at the light and electron microscopic level. For demon-stration of the method, growth hormone and luteinizing hormone were localized in the anterior pituitary gland of the rat embedded in PEG, using peroxidase-labeled antibodies. PEG is water-soluble, has a low melting temperature yet is firm enough to be sectioned at room temperature. Preservation of cellular ultrastructu.re is good. The use of PEG-em-bedded tissue permits precise correlation of light and electron microscopic observations of the same tissue section. Conventional electron microscopic methods for the localization of enzymes or antigens uti-lize thin slices or small pieces of tissue for the initial reactions. In order to correlate electron microscopic and light microscopic observa-tions, tissues embedded in plastic are sec-tioned about 1 e in thickness for light micros-copy and adjacent ultrathin sections are exam-ined with the electron microscope. Alterna-tively, tissues are prepared separately for light and electron microscopy. With the former pro-cedure only small areas of the tissue can be examined at one time, and extensive sampling is required for an adequate survey. With the latter procedure the correlation is poor because different portions of the tissue are used. Some attempts have been made recently to solve these problems. Kobernick and Thomas (5) used tissues embedded in paraffin. After an initial light microscopic observation of the his-tologic section, areas of interest adjacent to the section were punched from the paraffin block and reembedded for electron microscopy. With this method, sampling was adequate, but cor-‘This investigation was supported in part b