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The page below is a sample from the LabCE course Immunohistochemistry (IHC) Basics in Histology. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Enzymes such as horseradish peroxidase (HRP) and alkaline phosphatase (AP) are the most commonly used methods for antibody visualization. HRP first results in the formation of an enzyme substrate complex. As long as hydrogen peroxide (H2O2) is present the reaction continues. Once all of the H2O2 is gone, the reaction stops and a color product, chromogen, is developed. HRP is an enzyme that catalyzes the reduction of hydrogen peroxide (H202) to water and oxygen.
Commonly used chromogens with HRP include:
  • 3-amino-9-ethylcarbazole (AEC)
  • 3,3’-diaminobenzidine (DAB)