Immunohistokemia

Immunohistokemia, commonly known as immunohistochemistry (IHC), is a laboratory technique used to detect specific antigens in fixed tissue sections by exploiting the binding of antibodies to their target proteins. In IHC, primary antibodies bind to the antigen of interest, and a labeled secondary antibody enables visualization either through an enzyme-catalyzed color reaction or by fluorescent labeling, allowing localization of the antigen within cells and tissues.

The typical workflow involves tissue fixation and embedding, sectioning, and antigen retrieval to unmask epitopes altered by fixation. After blocking non-specific binding, a primary antibody is applied, followed by a labeled secondary antibody. Visualization is achieved with chromogenic substrates (e.g., DAB) that yield a brown color, or with fluorescence for multiplex staining. Controls, including known positive and negative tissues, are essential to assess assay performance. Automated platforms and standardized protocols are commonly used in diagnostic settings.

IHC is widely employed in diagnostic pathology to classify tumors, determine lineage, and assess predictive or prognostic markers. Commoner examples include cytokeratins for epithelial origin, CD markers for lymphoid lineage, and specific markers such as HER2, estrogen receptor, and progesterone receptor in breast cancer, or Ki-67 for proliferation. IHC also aids in detecting infectious agents and in research to study protein distribution and function.

Interpretation relies on staining pattern (cellular localization: nuclear, cytoplasmic, membranous), intensity, and percentage of positive cells. Limitations include fixation-related variability, non-specific staining, background signal, and subjective interpretation. Rigorous controls and adherence to standardized guidelines help ensure reliability.