Immunohistochemical Detection of Angiotensin II Receptor

This chapter deals with immunohistochemical detection of low copy molecules in tissue. We will focus on peptide receptors, but the same principles apply to hormones, autacoid substances, enzymes, and signaling molecules. Several approaches are currently available to characterize receptor distribution in tissue: (1) radioligand binding autoradiography, (2) immunohistochemistry (IHC), and (3) in situ hybridization (ISH). Each method yields different types of information. ISH identifies cells that express a specific mRNA and, therefore, are likely to express the protein of interest. However, the site of mRNA transcript expression for a receptor may be different from the site of receptor binding or protein expression. Although radioligand binding autoradiography provides a good measure of functional receptor expression, precise subcellular localization of receptor expression is not possible. Moreover, pharmacological ligands specific for a single-receptor subtype are not always available. IHC is necessary for cell-specific localization of receptor expression within tissue. The resolution and sensitivity achieved with IHC is far greater than that obtained with classic autoradiography techniques although antireceptor antibody