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Immunohistochemistry is a method used to determine in which cells and in which parts of cells a particular protein or other macromolecule is located. These stains are based on using antibodies to bind to specific antigens, usually of protein or glycoprotein origin. For detection, an enzyme known as a peroxidase is used to catalyze a chemical reaction to produce a coloured product.
Simply, a very thin slice of tissue is fixed onto glass, incubated with antibody or a series of antibodies, the last of which is chemically linked to the peroxidase enzyme. After developing the stain by adding the chemical substrate, the distribution of the stain can be examined by microscopy.
Additional recommended knowledge
Types of antibodies
Originally all antibodies produced for immunostaining were polyclonal, i.e. raised by normal antibody reactions in animals such as horses or rabbits. Now, many are monoclonal, i.e. produced in tissue culture. Monoclonal antibodies that consist of only one type of antibody tend to provide greater antigen specificity, and also tend to be more consistent between batches.
Methods for immunoperoxidase staining
The first step in immunoperoxidase staining is the binding of the specific (primary) antibody to the cell or tissue sample. The detection of the primary antibody can be then accomplished directly (example 1) or indirectly (examples 2 & 3).
Optimal staining depends on a number of factors including the antibody dilution, the staining chemicals, the preparation and/or fixation of the cells/tissue, and length of incubation with antibody/staining reagents. These are often determined by trial and error rather than any sort of systematic approach.
Alternatives to peroxidase stains
Other catalytic enzymes such as alkaline phosphatase can be used instead of peroxidases for both direct and indirect staining methods. Alternatively, the primary antibody can be detected using fluorescent label (immunofluorescence), or be attached to colloidal gold particles for electron microscopy.
Uses of immunoperoxidase staining
Immunoperoxidase staining is used in clinical diagnostics and in laboratory research.
In clinical diagnostics, immunostaining can be used on tissue biopsies for more detailed histopathological study. In the case of cancer, it can aid in sub-classifying tumours. Immunostaining can also be used to help diagnose skin conditions, glomerulonephritis and to sub classify amyloid deposits. Related techniques are also useful in sub-typing lymphocytes which all look quite similar on light microscopy.
In laboratory research, antibodies against specific markers of cellular differentiation can be used to label individual cell types. This can enable a better understanding of mechanistic changes to specific cell lineages resulting from a particular experimental intervention.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Immunoperoxidase". A list of authors is available in Wikipedia.|