The accuracy of an Immunohistochemistry procedure depends fundamentally on the quality and function of its Detection Reagents, a critical component segment. The core of the technique involves a primary antibody that binds specifically to the target antigen in the tissue. This binding is subsequently visualized, most commonly using an indirect method where a labeled secondary antibody attaches to the primary antibody, greatly amplifying the signal intensity.

The label is typically an enzyme, such as Horseradish Peroxidase (HRP) or Alkaline Phosphatase (AP), which catalyzes a reaction with a chromogen. The chromogen, such as Diaminobenzidine (DAB), forms an insoluble colored precipitate directly at the site of the antigen. This colored precipitate—usually brown or red—allows the pathologist to visualize the precise location and distribution of the target protein under a standard bright-field microscope, enabling clear and objective analysis.

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