What is immunohistochemistry?
Immunohistochemistry (IHC) is considered to be an advanced form of histopathology. It is not usually used initially, but rather added when routine/regular histological testing cannot provide the answers which clinicians need to form a diagnosis – and thus a plan of care.
IHC uses primary antibodies to label a protein, then follows this up with a secondary antibody which is bound to the primary one. In immunoperoxidase staining, an antibody is joined to a enzyme, peroxidase, that catalyses a reaction in which the protein is specifically stained brown. IHC can also involve fluorescently labelled antibody, so that when viewed under a light microscope, a certain pattern will be observed from the emitted fluorescence.
The IHC pattern is considered diagnostic. This is why IHC is often used in situations where a presence or absence of certain proteins can form a basis for a diagnosis. It can also be used to distinguish between two different disease processes that may otherwise appear similar to the pathologist.
How is an immunohistochemistry assay performed?
The most common process of preparing immunohistochemical slides is as follows:
- Fixation of the tissue (in general, IHC stains are fixed with formalin)
- Embedding of the tissue (in paraffin)
- Sectioning of the tissues
- Retrieval (done with application of heat or proteolytic enzymes)
- Mounting and dehydration
- Clearing and observation of the slides.
What are some examples of immunohistochemistry stains?
A wide variety of immunohistochemical stains is used to identify different tumours and other neoplasms. Some of the most common are listed in the table below.
What are the advantages and disadvantages of immunohistochemistry?
The advantages of IHC include:
- It is possible to use fresh or frozen tissue samples for IHC.
- IHC is well-established and readily available.
- The cost of IHC is relatively low
- It has a fast turn-around time.
- Because there are no infectious agents involved in the study, the risk to human health is minimal.
The disadvantages of IHC are as follows:
- IHC stains are not standardised worldwide.
- While the cost of the procedure is relatively inexpensive, the equipment needed to perform IHC is costly.
- Quantifying results is difficult.
- IHC is subject to human error. Well-trained personnel are paramount.