The Peroxidase-Antiperoxidase (PAP) Method and Other All-Immunologic Detection Methods

These methods have, as an underlying unification, the sole use of antibody-antigen interaction to provide the binding of reagents, ultimately leading to the localization of enzyme at the site of cellular antigen. The earlier direct and indirect techniques, while still used today, were found to be less sensitive than the later-used peroxidase-antiperoxidase (PAP) techniques. The newer immune complex polymer type of detection system (Envision™ Dako Corporation, Santa Barbara, CA) increases the amplification with an indirect style of reaction while still keeping the binding entirely immunologic. These techniques have been supplanted mostly by the avidin-biotin binding schema (see Chapter 25). However, there are still times when a non-avidin-biotin system is preferred. The following procedure highlights the PAP type of reaction, the most commonly used immunologic reaction method, and additional versions— direct, indirect and polymer types of procedures—are discussed at the end of the chapter.