Which statement best describes a characteristic of the PAP method?

• A. Higher sensitivity due to more peroxidase molecules to bind to chromogen DAB + hydrogen peroxide
• B. Lower sensitivity compared to indirect methods
• C. Requires fluorescent detection
• D. It does not involve peroxidase

Answer: (D)

PAP uses a peroxidase enzyme in its detection step, making it a peroxidase-based chromogenic method. After the primary antibody binds the antigen, a secondary antibody binds to it, and a peroxidase-labeled anti-peroxidase antibody then attaches, forming a complex that brings peroxidase to the site of the antigen. In the presence of hydrogen peroxide, the peroxidase catalyzes the oxidation of DAB to a brown insoluble product, giving a visible signal at the antigen location. Because the signal comes from this enzymatic color reaction, PAP is a colorimetric method rather than a fluorescent one. Therefore, saying it does not involve peroxidase contradicts how PAP works.