Endogenous alkaline phosphatase activity is often found in lymphoid tissue, intestinal tissue, and placenta. These endogenous enzymes can react with the substrate-chromogen used in the IHC staining procedure to produce a false-positive result. This is common with horseradish peroxidase (HRP) and alkaline phosphatase (AP) staining applications. To quench endogenous alkaline phosphatase activity, a 1mM concentration of levamisole can be added to the chromogen substrate solution.
