Endogenous peroxidase is found in some normal and neoplastic tissues, as well as RBCs and leukocytes. Blocking endogenous peroxidase is a necessary step in methods that use a peroxidase-based staining system to prevent false-positive staining reactions.
The most common method for blocking endogenous peroxidase is a 5 to 10-minute incubation with 0.3% to 3.0% hydrogen peroxide (H2O2) in phosphate buffered saline (PBS), methanol, or distilled water at room temperature. This procedure may be performed before the application of the primary antibody or after the secondary antibody incubation. Using the methanol based H2O2 solution is harsher than the other mixtures. This is commonly used with blood smears, bloody/inflamed, and/or vascular tissues. There are pre-mixed solutions available that not only block endogenous peroxidase activity but other unwanted enzymatic activity as well.
