Improving tumor diagnostics by means of immunohistology
| Introduction |
Immunohistology (= immunohistochemistry, IHC) is used in paraffin embedded, formalin fixated tissues to search for certain epitopes (antigens). A histologic examination of the tissue is always the first step. Immunohistology is then used as second diagnostic step to help differentiating further (e.g. antigens specific for binding of drugs) or to identify certain antigens. It is essential, that the antigen to be diagnosed is not destroyed during fixation (formalin), that is why several antigens can not be detected by IHC.
In immunohistology an antigen is made visible by a reaction (staining) with an antibody after binding with the antigen. Specificity is usually improved by using a secondary antibody which is directed against the first one. The secondary antibody is conjugated with an enzyme which in a third step can be made visible by a dye. Often the primary antibody is obtained from mice or rabbits, that is why the secondary antibody has to be directed against immunoglobulins of those species. This secondary antibody is therefore obtained from another species (e.g. goat). The positive reaction in certain locations is considered as confirmation of presence of the antigen, whereas no reaction proofs the absence. Below an overview of the antibodies used at LABOKLIN together with an explanation of their meaning is given. In contrast to a popular opinion, IHC is not relevant for diagnosing autoimmune diseases.
By far the most common application is tumor diagnostics in those cases where histology is not distinct or the immunohistology is able to contribute to more specific details (e.g. degree of malignancy). Apart from diagnosing the origin of the tumor, the immunohistology will gain more influence in the future in evaluating the prognosis with consequences for the therapy, as it is practiced in human medicine for years already.
In some cases immunohistology is performed in order to detect infectious agents, but in many cases the direct histologic confirmation of the agent or typical inclusion bodies are already pathognomonic. Furthermore other techniques, especially molecular biology, gain more importance due to their higher sensitivity and specificity.
| CD3 |
An epitope expressed on T-lymphocytes, helpful to find out the percentage of
T-lymphocytes in a round cell population and also to differentiate between B- and T-cell-lymphoma. A differentiation is of prognostic importance, as T-cell-lymphomas are considered as highly malignant, independent of the histologic stage. Furthermore by this means T-cell-origin can be detected in poorly differentiated round cell tumors.
CD 3-positive T-lymphocytes in the epidermis in an epithe-liotropic lymphoma
| CD79a |
Is used for detecting B-lymphocytes. Usually both, anti-CD79a and anti-CD3 antibody are used at the same time, both serving as countercheck for the other, too. All statements for CD3 are true for CD79a related to B-lymphocytes.
If the results for both markers do not match, like for example a positive reaction for both in the same cell population, a differentiation between B- and T-lymphocytes is not possible.
A marker indicating epithelial origin of a tissue, especially to differentiate between carcinomas, sarcomas and malignant round cell tumors.
Detects smooth- and sceletal muscle cells and helps to differentiate between rhabdomyosarcoma and leiomyosarcoma and other spindle cell tumors.
Detects mesenchymal cells and is therefore an important diagnostic aid in diagnosing sarcomas.
Cyclooxygenase(Cox)-enzymes participate in the biosyntheses of prostaglandines. Non steroidal antiinflammatory drugs (NSAIDs) are blokking these enzymes. In some tumors positive for COX-2 NSAIDs seem to have an antitumoral effect. In human medicine this was proven especially in colorectal carcinomas. In veterinary medicine there exist reports about an improvement in transitional cell carcinomas of the urinary bladder by use of NSAIDs. Other tumors are likely to be influenced by these drugs as well.
Is expressed intracellulary in the active phase of the cell cycle in some cells. In those cells it may be used as marker for the active growing fraction within a tumor cell population.
A high percentage of positive cells in a mast cell tumor for instance is correlated with a decreased survival time.
|CD -117, c-kit protoonkogen|
Encodes for the transmembranous tyrosinkinase receptor KIT. To some extent this receptor is responsible for growth and differentiation of mast cells. The reaction pattern illustrating the distribution of c-kit receptors in a mast cell, is supposed to be of prognostic relevance.
With the help of this antibody a more accurate prediction on the biologic behaviour will be possible, hopefully. By use of both antibodies, Ki-67 and CD-117, it is planned to improve the prognostic prediction, which up to now is not satisfying on the basis of the histologic differentiation alone (according to Patnaik, grade I-III).
It is still true that a grade III tumor is expected to be highly malignant, but the histologic grading of grade I and II tumors has proven to be not reliable as far as prognosis is concerned in the past.
Detects histiocytes (not Langerhans-cells) and macrophages and is used to differentiate between those cells and other round cells.
Is used to identify Langerhans-histiocytes and therefore for differentiating between histiocytic and other round cell infiltrates/tumors.
S-100 positive tumor cells are often found in sarcomas, for example in chondroid tumors,
gliomas, nerve sheath tumors and melanomas.
Detects melanocytes and is helpful to exclude melanomas or to diagnose amelanotic melano-mas.
All in all, in special cases immunohistology can already serve
1. as diagnostic aid (differentiation of tumors consisting of undifferentiated cells)
2. as prognostic aid (especially in mast cell tumors and lymphomas)
3. as aid in designing appropriate therapy (e.g. COX2-positive tumors)
All these markers are already routinely available and can be used when asked for.