The main purpose of the blocking step with hydrogen peroxide (usually 3% H₂O₂) in an HRP-based IHC protocol is to quench endogenous peroxidase activity present in the tissue. Many tissues contain their own peroxidases, most notably in red blood cells (hemoglobin has pseudoperoxidase activity), granulocytes (myeloperoxidase), and some parenchymal cells like hepatocytes. If not inactivated, these endogenous enzymes will catalyze the same chromogen reaction (e.g., with DAB) as the HRP label added in the detection system. This would lead to non-specific, diffuse staining throughout the tissue, obscuring the specific signal and potentially causing false-positive results. Incubating the tissue with hydrogen peroxide before applying the detection system oxidizes and inactivates these endogenous enzymes. This step is typically performed after antigen retrieval and before applying the primary antibody or blocking serum.

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Zambia

• Joseph Soko – 101 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies