Endogenous peroxidase is found in some normal and neoplastic tissues, RBCs, and leukocytes. Blocking endogenous peroxidase is necessary for 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 applying the primary antibody or after the secondary antibody incubation. Using the methanol-based H2O2 solution is harsher than using 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.
