====== Immunohistochemistry ======

Immunohistochemistry is the process of detection of proteins expressed in [[tissue]] using [[antigen|antigens]]/[[antibody|antibodies]] interaction to visualize localization of expressed proteins. The antibodies, raised to a specific protein antigen can be [[polyclonal]], antibodies raised in non-related animal species, or [[monoclonal]], raised in the species of interest, and then purified. Immunohistochemistry is widely used for diagnosis of [[cancer|cancers]]. Specific markers are known for various cancers.

    * Carcino-embryonic antigen (CEA): used for colon cancer
    * CD15 and CD30 : used for Hodgkin's disease
    * Alpha fetoprotein: for yolk sac tumors and hepatocellular carcinoma
    * CD117: for gastrointestinal stromal tumors (GIST)



===== METHODS =====

There are basically two methods for immmunohistochemical demonstration of [[antigen|antigens]] in the [[tissue]], the direct and the indirect method.

The "direct method" is a one-step staining method, and involves a labeled [[antibody]] (e.g. FITC conjugated antiserum) reacting directly with the [[antigen]] in [[tissue]] sections. This technique utilizes only one antibody and the procedure is therefore short and quick. However, it is insensitive due to little signal amplification and rarely used since the introduction of indirect method.

The "indirect method" involves an unlabeled primary antibody (first layer) which reacts with tissue antigen, and a labeled secondary antibody (second layer) reacts with primary antibody. (The secondary antibody must be against the [[IgG]] of the animal species in which the primary antibody has been raised.) This method is more sensitive due to signal amplification through several secondary antibody reactions with different antigenic sites on the primary antibody. The second layer antibody can be labeled with a fluorescent dye such as [[FITC]], [[rhodamine]] or [[Texas red]], and this is called indirect immunofluorescence method. The second layer antibody may be labeled with an [[enzyme]] such as [[peroxidase]], [[alkaline phosphatase]] or [[glucose oxidase]], and this is called indirect immunoenzyme method. Offering a substrate to these enzymes will demonstrate presence of the enzyme (and hence the antibody) in a quantifiable fashion.


=====External links=====

[[http://www.immunoportal.com/modules.php?name=Recipes|Immunohistochemical Staining Protocols]]
[[http://www.immunoportal.com/modules.php?name=gallery2|Immunohistochemistry Image Gallery]]