Diagnostic Pathology: Open Access
Open Access

Immunohistochemistry is a specialized laboratory technique used in pathology to detect specific antigens in tissue sections by employing antibodies that bind to them. This method combines the specificity of immunology with the detailed visualization of histology, making it a powerful tool for disease diagnosis, classification and research.

Immunohistochemistry, often abbreviated as Immunohistochemistry (IHC), allows pathologists to determine the presence, absence, or distribution of particular proteins within tissues, providing valuable insights into the biological behaviour of diseases. Its applications extend from routine cancer diagnosis to advanced biomedical research, enabling clinicians to offer more precise and personalized treatments.

The fundamental principle of immunohistochemistry involves the use of antibodies that recognize and bind to unique target molecules within the tissue. These antibodies are linked to detectable labels, such as enzymes or fluorescent dyes that produce a visible signal under a microscope when the antigen-antibody reaction occurs. The tissue samples are typically fixed and embedded in paraffin to preserve structure, then thinly sectioned and mounted on glass slides. The process includes steps to expose the target antigens, block non-specific binding and apply the primary and secondary antibodies that generate the final visual signal. The result is a clear and specific staining pattern that reveals the location and abundance of the target molecule.

IHC has become indispensable in cancer diagnosis and classification. Many tumors are morphologically similar under conventional histology, but they differ significantly in their protein expression profiles. By detecting tumor-specific markers, IHC helps differentiate between cancer types, determine the tissue of origin in metastatic cases and assess the tumor’s aggressiveness. For example, the detection of estrogen and progesterone receptors in breast cancer tissue guides decisions about hormone therapy, while Human Epidermal Growth Factor Receptor 2 (HER2) testing identifies patients who may benefit from targeted drugs like trastuzumab.

Similarly, in lymphomas, IHC markers such as CD20 or CD3 distinguish between B-cell and T-cell origin, shaping treatment strategies.

Beyond oncology, immunohistochemistry is valuable in diagnosing infectious diseases, neurodegenerative disorders and autoimmune conditions. In infections, IHC can detect specific microbial antigens directly within tissues, confirming the presence of pathogens such as viruses, bacteria, or fungi. In neurodegenerative diseases like Alzheimer’s, it helps identify abnormal protein accumulations, such as beta-amyloid plaques or tau tangles, providing both diagnostic and research value. In autoimmune conditions, IHC can reveal the distribution of immune system components within affected tissues, offering insights into disease mechanisms and guiding targeted therapies.

The technique is also widely used in research to study normal and abnormal tissue biology. By visualizing the expression of proteins involved in cell signalling, growth, or apoptosis, researchers can better understand the molecular pathways driving disease. This knowledge is essential for developing new therapeutic approaches and identifying biomarkers for early detection. In developmental biology, IHC provides a way to track the expression of key proteins during embryonic growth and organ formation, offering a deeper understanding of genetic regulation and cellular differentiation.

Advances in immunohistochemistry have expanded its capabilities and improved its accuracy. Automated staining systems standardize the process, reducing variability and improving reproducibility between laboratories. Multiplex IHC techniques allow the simultaneous detection of multiple antigens in the same tissue section, revealing complex interactions between different cell types and molecular pathways. High-sensitivity detection systems have improved the ability to identify low-abundance proteins, making the method more powerful in early disease detection. Digital pathology and image analysis software now complement IHC, enabling quantitative measurement of staining intensity and distribution, which adds objectivity to the interpretation.

In personalized medicine, IHC is a critical tool for matching patients with the most effective treatments. The expression patterns of certain proteins can predict how a patient will respond to specific drugs, helping to avoid ineffective therapies and unnecessary side effects. For example, Programmed Death-Ligand 1 (PD-L1) testing in tumors informs the use of immune checkpoint inhibitors in cancer immunotherapy. Such applications highlight the direct clinical impact of IHC on patient outcomes and healthcare efficiency.

The accuracy of immunohistochemistry depends on multiple factors, including the quality of antibodies, the condition of the tissue and the experience of the pathologist interpreting the results. False positives or negatives can occur if antibodies are not sufficiently specific or if antigen retrieval steps are inadequate. Therefore, rigorous quality control measures, including validation of antibodies and standardization of protocols, are essential. In many cases, IHC findings are interpreted alongside other diagnostic information, such as molecular tests or imaging studies, to provide a comprehensive clinical picture.

In public health, immunohistochemistry contributes to disease surveillance and outbreak investigation. It can be used to confirm the presence of infectious agents in tissue samples collected during epidemiological studies or post-mortem examinations. This capacity to link molecular information to tissue structure enhances our understanding of disease transmission and pathology, supporting better prevention and control measures.

In conclusion, immunohistochemistry is a vital diagnostic and research technique that bridges the gap between molecular biology and histopathology. Its ability to precisely localize specific proteins within tissue structures makes it invaluable for disease diagnosis, classification and the development of targeted therapies. As technology advances, IHC is becoming more sensitive, versatile and integrated with digital and molecular tools, further expanding its role in precision medicine. Whether guiding cancer treatment, revealing infectious agents, or uncovering the molecular mechanisms of disease, immunohistochemistry remains an indispensable component of modern healthcare and biomedical science.