Immunohistochemistry (IHC) is a method for detecting antigens or haptens in cells of a tissue section by exploiting the principle of antibodies binding specifically to antigens in biological tissues. The antibody-antigen binding can be visualized in different manners. Enzymes, such as Horseradish Peroxidase (HRP) or Alkaline Phosphatase (AP), are commonly used to catalyze a color-producing reaction.
Immunohistochemical (IHC) or immunoperoxidase stains are another very useful category of special tests. The basic principle of this method is that an immune protein called an antibody will attach itself to certain substances, called antigens, that are on or in the cell. Each type of antibody recognizes and attaches to antigens that fit it exactly. Certain types of normal cells and cancer cells have unique antigens. If cells have a specific antigen, they will attract the antibody that fits the antigen. To find out if the antibodies have been attracted to the cells, chemicals are added that make the cells change color only if a certain antibody (and, therefore, the antigen) is present.