Enzyme-antienzyme method for immunohistochemistry

Immunohistochemical stains use antibodies to identify specific constituents in tissue sections. In order to detect the site of reaction, the antibody is labeled with an enzyme that can be reacted with a suitable substrate to give a colored product. The alternative is to use a fluorescent label. The advantage of an enzyme label is that the nuclei can be counterstained, thereby revealing the tissue architecture, and that the stain fades slowly, if at all, with time, allowing the slides to be stored.