Ultrastructural Localization of Peptides Using Immunogold Labeling
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The subcellular localization of bioactive peptides, including hormones and neurotransmitters, has immense value, not only
in understanding how cells function, but in correlating biochemical and clinical data from tissues in both normal and diseased
states. The pioneering immunocytochemical work of Coons et al. (1
) exploited the specificity of antigen-antibody interactions by using fluorescent-labeled antibodies as probes to determine
the spatial distribution of antigens. It established the principles of immunocytochemistry, and thereby revolutionized the
means of identifying peptide-containing cells by light microscopy. The application of immunocytochemistry at the ultrastructural
level combines the specificity and sensitivity it offers with the fine spatial definition of electron microscopy, providing
an exceedingly precise means of localizing the position of specific peptide antigens to a resolution of 5 nm or better. As
a technique, electron microscopic immunocytochemistry was first accomplished some 35 yr ago (2
, with the development of ferritin-antibody conjugates. Since then, the introduction of colloidal gold (3
) as a tracer in electron microscopy, and its use as a marker for antisera (4
), has established immunogold labeling as by far the most popular choice for ultrastructural localization of bioactive peptides
and most other immunogens. This is not surprising since gold spheres are easily prepared in the laboratory, and are readily
adsorbed by a variety of proteins, including immunoglobulins, with which they form simple but stable antibody-gold complexes
without involving chemical conjugation.
