Immunohistochemistry – Definition and Applications
Immunohistochemistry (IHC) is a diagnostic technique that uses antibodies to detect specific proteins in tissue samples. It is an essential tool in pathology and cancer diagnostics.
Things worth knowing about "Immunohistochemistry"
Immunohistochemistry (IHC) is a diagnostic technique that uses antibodies to detect specific proteins in tissue samples. It is an essential tool in pathology and cancer diagnostics.
What is Immunohistochemistry?
Immunohistochemistry (IHC) is a laboratory technique that uses specific antibodies to detect and visualize particular proteins or other molecules within tissue sections. The method combines principles of immunology with classical histology (the study of tissues) and is today one of the most important techniques in pathology and diagnostic medicine.
By labeling target proteins with color-producing substances, pathologists can identify under the microscope which proteins are present in which cells of a tissue. This provides critical information about the identity, origin, and behavior of cells – especially in the context of cancer and other diseases.
Principle of the Method
The fundamental principle of immunohistochemistry is based on the specific binding of antibodies to their corresponding antigen (target protein). The process typically involves the following steps:
- Tissue preparation: A tissue sample (biopsy or surgical specimen) is fixed – usually with formalin – and embedded in paraffin. Very thin sections are then cut from the block.
- Antigen retrieval: Fixation can mask antigens. Heat or enzymatic treatment is used to restore their accessibility.
- Incubation with primary antibody: A specific antibody is applied to the tissue section and binds selectively to the target protein.
- Detection: A secondary antibody, which binds to the primary antibody, is conjugated with an enzyme or fluorescent dye. In enzymatic methods, a chemical reaction produces a visible color (e.g., brown in DAB staining).
- Counterstaining and evaluation: The tissue section is counterstained with a nuclear dye and examined under a microscope.
Clinical Applications
Tumor Diagnostics
The most important application of immunohistochemistry is in cancer diagnosis. It helps classify tumor types, determine the origin of metastases, and evaluate prognostic and predictive markers. Well-known examples include:
- HER2 status in breast cancer – relevant for treatment decisions involving trastuzumab
- Ki-67 index – reflects the proliferation rate of a tumor
- Estrogen receptor (ER) and progesterone receptor (PR) – important for hormone therapy in breast cancer
- PD-L1 expression – relevant for immunotherapies using checkpoint inhibitors
Infectious Disease Diagnostics
Pathogens such as viruses or bacteria can be directly detected in tissue samples using immunohistochemical methods – for example, Helicobacter pylori in gastric tissue or certain viruses in inflamed tissue.
Inflammatory and Autoimmune Diseases
In neuropathology, dermatology, and rheumatology, immunohistochemistry helps identify characteristic deposits or cellular infiltrates that point to specific diseases.
Direct and Indirect Methods
There are two main variants of the immunohistochemical detection approach:
- Direct method: The primary antibody itself carries a label (enzyme or dye). This method is simpler but less sensitive.
- Indirect method: An unlabeled primary antibody binds to the antigen; a labeled secondary antibody then binds to the primary antibody. This method is significantly more sensitive and is more widely used.
Advantages and Limitations
Immunohistochemistry offers several key advantages:
- High specificity through antibody-mediated detection
- Preservation of tissue architecture – proteins can be assessed in their exact cellular location
- Simultaneous morphological evaluation of the tissue is possible
- Wide range of available antibodies targeting thousands of proteins
Limitations and potential sources of error include:
- Non-specific background staining (false positive results)
- Dependence on the quality of tissue fixation
- Need for standardized procedures and validated antibodies
- Interpretation requires experienced pathologists
References
- Taylor CR, Rudbeck L. Immunohistochemical Staining Methods, 6th edition. Dako/Agilent, 2013.
- Rammele A et al. The Human Protein Atlas as a proteomic resource for biomarker discovery. Nature Methods, 2023.
- World Health Organization (WHO). WHO Classification of Tumours, 5th edition. IARC Press, Lyon, 2021.
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