Immunohistochemistry is a technique that involves the use of antibody-antigen interactions to identify cellular and tissue constituents. This can be achieved by labeling known antibodies with enzymes that produce a colored product after reaction, then monitoring the sample to see if a reaction has taken place. In immunohistochemistry, the preservation of antigenic determinants, also called epitopes, and binding sites is essential to ensure that an accurate result is obtained. However, tissue samples must go through various processes in a pathology laboratory before they are ready for testing and some of these processes can change the structure of epitopes. It is therefore important to take this into account when choosing reagents to reduce the risk of this happening. Tissue samples must be fixed before tests can be performed on them. This is to ensure that tissue samples are well preserved; prevent loss of molecular structure and cellular morphology, stop autolysis, and ensure the destruction of all tissue-resident pathogens. The main objective to remember when choosing a fixative is that it must maintain clear and consistent morphological characteristics in the tissues to be able to be visualized under the microscope. For this reason, the most widely used fixation method is to use 10% neutral buffered formalin, as it provides a good view of tissue morphology. Formalin is an aqueous solution that contains approximately 4% formaldehyde and the formaldehyde reacts with itself to produce polymers and methylene bridges that attach tissues by creating cross-links between tissue proteins, and other molecules, such as carbohydrates and fats, are trapped. bet...... middle of paper ...... recognition. Biotech Histochem, 84(5), pp. 223-247Pearse, AGE 1968 Histochemistry, theoretical and applied. 3rd ed. Boston, Little, Brown and CoPrento, P. Lyon H. 1997. Commercial formalin substitutes for histopathology. Biotech Histochem, 72(5), pp. 273-282. Shi et al. 1991. Antigen recovery from formalin-fixed, paraffin-embedded tissues: a method for improving immunohistochemical staining based on microwave heating of tissue sections. Journal of Histochemistry and Cytochemistry. 39(6), pp. 741-748. Snider, J. 2013. Epitope retrieval methods for IHC. [ONLINE] Available at: http://www.piercenet.com/method/paraffin-removal-antigen-retrieval [Accessed: 11/18/13] Cerio, R. Macdonald, DM 1986. Effect of routine treatment of paraffin wax on immunoreactivity of cell membranes of skin tissues. Journal of Clinical and Laboratory Immunology, 20(2), pp.. 97-100.