The protein A-gold technique. Use in the immunoelectron microscopic study of the teleost growth hormone

By the application of the protein A-gold technique for immunocytochemistry of the tilapia pituitary growth hormone (GH), our electron micrographs revealed that the antigenicity of tilapia GH and the cytoplasmic structure were well preserved in the tissues fixed with periodate-lysine-paraformaldehyde followed by osmium tetroxide postfixation. Using the specific antiserum against tilapia GH, the immunoreactive gold particles of 20-40 nm in size were located on secretory granules (200-300 nm in diameter) exclusively of one cell type in the proximal pars distalis identified as GH cells on the basis of their ultrastructural characteristics. This technique is considered to be fairly efficient for the detection of intracellular antigenic sites on ultrathin sections.