April 20, 2024

Immunohistochemistry Essentials: A Comprehensive Guide


Immunohistochemistry (IHC) is a technique that uses the principle of antibodies binding specifically to antigens in biological tissues. By harnessing the ability of antibodies to bind only their designated antigen, immunohistochemistry allows cells and tissues to be examined with great resolution.

The History and Development of IHC
The first recorded use of IHC was in 1941 when Albert Coons used fluorescent antibodies to localize antigens in tissue sections. However, it was not until the 1970s and 1980s when more sensitive antibodies and techniques like enzyme-labeled antibodies were developed that IHC became a staple diagnostic tool in pathology labs. Since then, hundreds of antibodies have been produced against an array of molecular markers, organelles, and proteins. Advancements in microscopy and staining methods over the decades have continued to improve the specificity and sensitivity of IHC analysis.

How Does IHC Work?
In IHC, thin sections of formalin-fixed paraffin-embedded tissue are labeled with antibodies that recognize cell or tissue components. The tissue sections are first deparaffinized and pre-treated to expose the antigens. Primary antibodies selected for the target antigen are then applied to the tissue. Secondary antibodies linked to an enzyme or fluorescent dye are applied which bind to the primary antibodies. When substrate is added to the enzyme-conjugated secondary antibodies, a colored precipitate or fluorescent signal is produced which can be seen under the microscope at the site of the target antigen.

Applications of IHC
IHC has numerous clinical applications and is essential for making many diagnoses in anatomic pathology. Some key uses of IHC include:

Cancer Diagnosis and Subtyping
By detecting expression patterns of tumor markers and cellular markers, IHC allows malignant tumors to be diagnosed, classified, and determined if they originated from one type of cell over another. For example, antibodies against progesterone receptor help classify tumors as breast cancer.

Infectious Disease Diagnosis
Certain microorganisms that cause infectious diseases can be detected with IHC using antibodies specific to viral, bacterial, fungal or parasitic antigens. This aids diagnosis of infections especially in limited or ambiguous samples.

Neurological and Neuromuscular Disease Diagnosis
Antibodies against neuronal, axonal or muscle proteins help diagnosis conditions affecting the nervous system or muscles. Markers like CD3 and CD20 stain cell types involved in diseases such as multiple sclerosis.

Localization of Hormones and Receptors
Antibodies detect steroid receptors in neoplasms and localize hormone production in endocrine tissues, assisting with diagnoses and treatment decisions in diseases of the endocrine system.

Other Applications and Future Advances
Beyond diagnostics, IHC finds uses in research applications studying protein expression and distribution in normal and diseased cells. Quantitative techniques are being developed along with multiplex IHC to measure and simultaneously visualize multiple biomarkers. Automation and digital pathology also hold promise to advance IHC in the future. Molecular techniques like in situ hybridization complement IHC by localizing genetic material. Overall, immunohistochemistry remains a versatile and powerful tool for cellular and molecular pathology.

Advantages and Limitations of IHC
As a technique, IHC has key strengths in enabling visualization of molecular events directly in tissue context at the microscopic level. It is highly sensitive and specific when performed and interpreted correctly. However, limitations include the dependence on antibody specificity and tissue fixation/processing. Quantitative results also rely on experience and can vary between protocols. False negatives can occur if target antigens degrade during processing. Ongoing quality assurance measures help maximize the advantages and minimize the limitations of IHC to enhance diagnostics and research applications.

In summary, since its origins in the 1940s, immunohistochemistry has transformed into an indispensable mainstay of anatomical pathology. By leveraging highly specific antibody-antigen interactions, IHC provides crucial molecular insights into both healthy and diseased cells and tissues. Applications continue to expand across clinical diagnostics, scientific discovery and numerous other areas of biomedicine. With ongoing advancements, immunohistochemistry will assuredly retain its position as a powerful tool in the histopathologist’s diagnostic armamentarium for many years to come.

1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it