The word Immunohistochemistry derived from the words "immuno," refering to antibodies employed in the procedure, and "histo," which means tissue. It can be defined as the process of antigen or protein detection in the biological sample using antigen specific antibodies. Immunohistochemistry can be used as a diagnostic tool to assess which tumors are likely to respond to therapy, by detecting the presence or elevated levels of the molecular target. Immunohistochemical staining is widely used in the diagnosis of abnormal cells such as those found in cancerous tumors. The antigen antibody interaction can be visualised by number of ways, the foremost common one being the use of a secondary antibody that conjugates with an enzyme to produce a coloured reaction, such as peroxidise. There are two types of immunohistochemical staining: direct and indirect method. The direct method is a single step staining method and involves a labeled antibody reacting directly with the antigen in tissue sections. Since this technique utilizes only one antibody and therefore is simple and rapid. The sensitivity of this method is lower due to little signal amplification, in contrast to indirect method. In indirect method the unlabeled primary antibody (first layer) binds to the target antigen in the tissue sample and then a labelled secondary antibody (second layer) is added that reacts with the primary antibody. These secondary antibodies are raised against the IgG of the animal species in which the primary antibody has been raised. Commonly used animal model is rabbit. This method is more sensitive than direct detection strategies because of high signal amplification due to the binding of several secondary antibodies to each primary antibody. These secondary antibodies are usually conjugated with the fluorescent or enzyme reporter.
Last date updated on June, 2021