Immunohistochemistry (IHC) uses immunologic and histologic techniques to detect antigens in tissues. The antigen is recognized by a specific antibody that is added to the tissue section. The immunologic reaction is visualized under the microscope by adding an enzyme, a substrate to the enzyme, and a chromogen, producing a colored reaction. IHC is a very sensitive and specific technique. For diagnosticians, it is an important technique that allows us to colocalize antigens and lesions in the same tissue section.
Neoplastic and infectious diseases are the main focus of IHC in veterinary medicine. The ADDL IHC Service offers a variety of tests for both infectious and neoplastic diseases:
- Diagnosis of neoplasia: Often, the tissue of origin of a tumor cannot be determined with routine histology. Using specific antibodies for different tissues or cells (e.g. cytokeratin for epithelium, vimentin for mesenchymal cells, lymphoid markers, etc), the origin of many tumors can be determined with IHC.
- Diagnosis of micrometastases: Early metastasis can be difficult to detect using conventional histology. IHC highlights the presence of single or small groups of neoplastic cells in metastatic sites. Early detection of micrometastases increases the chances of survival with surgical removal of affected nodes or by modification of the treatment protocol.
- Prognostic markers: Some proteins are expressed in neoplastic, but not in normal, mature cells (e.g., embryonal proteins), expressed in neoplastic cells in larger amounts than in normal cells (e.g. cycle-related proteins), or structurally modified in neoplastic cells (mutant p53 protein). These changes may have prognostic significance in specific tumor types. For instance, it has been reported that the immunohistochemical detection of c-Kit protein in mast cell tumors of dogs has prognostic significance. Some of these markers are being tested to determine their significance in veterinary cancers.
- Diagnosis of infectious diseases: Detection of antigens of an infectious agent using IHC has etiologic significance. Antigen detection can be correlated with histopathologic changes and thus can confirm the significance of a particular microorganism detected by other methods.