Immunoperoxidase stains are used in the microscopic examination of tissues. These stains are based on antibodies which will bind to specific antigens, usually of protein or glycoprotein origin: hence the presence or distribution of particular molecules in the sample can be studied. Once all antibodies were polyclonal (raised by normal antibody reactions in animals such as horses or rabbits) but now many are monoclonal (produced in tissue culture). Monoclonal antibodies, consisting of only one type of antibody tend to be more narrowly focused and are easier to get in consistent supply.

The binding of the antibody to a specific antigen in the sample is the first important part: showing where it has attached is done by various methods. There are various ways in which the attachment of antibodies is made visible for the pathologist: the antibody can be tagged with a fluorescent marker, or attached to colloidal gold particles, or a chemical reaction used to produce a specific colour where the antibody has bound (eg. urease, peroxidase).

Optimal staining depends on a number of factors including dilution, batch of stain, preparation of tissue, timing of staining process, pH etc. These tend to be determined by trial and error. While the process is becoming more repeatable there is considerable variability.

The most common use is to sub-classify tumours. They are used to help diagnose skin conditions, glomerulonephritis, sub classify amyloid deposits etc. Related techniques are also useful in sub-typing lymphocytes which all look quite similar on light microscopy.

One of the problems is the naming of stains. Polyclonal stains may not be repeatable and monoclonal antibodies can have a bewildering range of similar subtypes. The CK (cytokeratin) and CD (for lymphoid and haematological markers) are attempts to systematise nomenclature. Tables of synonyms are useful.

http:www.immunoquery.com is a very useful online reference resource.

Common immunoperoxidase stains:

S100, HMB45 , Vimentin, LCA, EMA , CAM5.1 , WSK , CK7 , CK20 , Estrogen receptor, Progesterone receptor , CEA, AFP, BHCG, CD3, CD20 , CD10 , CD34 , CD68 , CD99 , CD5 etc GH, PRO, ACTH, TSH, tau, chromogranin , NSE, GFA,C3, ..., ..., Ca125 , Ca19.9