Immunohistochemistry and Immunofluorescence.

Immunohistochemistry (IHC) is one of the most widely used protein detection techniques. The principle of this technique is based on the binding of a specific antibody to a matching specific antigen in tissue. The bound antigen-antibody complex then is visualized using a range of detection techniques. IHC uses a number of different enzymatic labels, such as peroxidase and alkaline phosphatase, for the detection of the antigens of interest whereas immunofluorescence (IF) uses a fluorescent signal. In this chapter, IHC will be described using the peroxidase label. Both IHC and IF can be used on formalin-fixed paraffin-embedded (FFPE) or appropriately processed fresh tissues. IHC/IF can be multiplexed to detect more than one antigen at a time, or may be sequentially stained to detect multiple targets. These techniques are routinely used in diagnostic pathology laboratories, not just for diagnostic purposes but many biomarkers are used for patient staging, treatment allocation, and prognostication. Immunofluorescence is routinely used for the detection of antibodies and antigens in freshly biopsied tissues, particularly for immune-mediated and vesiculobullous lesions. In this chapter, the principles of IHC are reviewed followed by examples of IHC and IF staining using readily available antibodies. Steps and processes involved in IHC/IF double staining are also described.