Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
Immunohistological staining procedures with enzymes as markers make use of enzyme substrate reactions which convert colorless chromogens into colored and insoluble end products. Enzyme labels offer the advantage of instant visualization and great sensitivity. Furthermore, enzyme markers may be utilized for both light and electron microscopic studies. Generally, either direct or indirect labeling techniques can be employed. Regardless of whether a direct or an indirect immunohistological method will be used, the choice of of the label is often a crucial decision. The most employed enzymes, their advantages, disadvantages as well as the various chromogens and substrates are described.