What Is Immunohistochemistry?

Individual cells are too small to be visible to the naked eye, so scientists have designed different tools for visualizing cells. Modern techniques include very powerful microscopes. Using immunohistochemistry techniques, scientists can identify individual types of cells under the microscope. These techniques are valuable in fields such as hematology, oncology and histology.

Cells

• Cells are the basic units that make up tissues and organs in plants and animals. Cell membranes in animals are made up of proteins and lipids. Some of those proteins, called antigens, work as markers, identifying specific cell types. Antigens are different from one cell type to another, and cells change their antigens when they undergo changes, as is the case with cancer cells. Antibodies are used to identify these particular antigens.

Antibodies

• Antibodies are proteins produced by certain types of white blood cells in response to foreign cells and their foreign antigens. For example, when bacteria invade the body, it is the antibodies that coat the bacteria, inactivating them and tagging them for destruction. Antibodies are very specific. An antibody will attach only to its specific antigen. Immunohistochemistry is the use of these antibodies to visualize the antigens on cells through the use of chemical "tags" on the antibodies.

Antibodies as Tags

• The "immune" in immunohistochemistry comes from the use of antibodies in the process of identifying cells of a specific kind, such as cancer cells. The process begins by introducing specific types of cells into a lab animal. The animal's antibodies against those cells are then collected and purified. When a sample of tissue from a suspected tumor is sent to the lab, the antibodies specific for known cancers are added to the tissue sample. If the cancer cells that are suspected are in the tissue sample, the antibodies will attach. Chemicals are used in order to see these antibody-antigen complexes.

Chemicals Used

• The "chemistry" in immunohistochemistry relates to when chemicals--which are luminescent under certain lights or are detectable in other ways--are used as tags. Because antibody-antigen complexes are also very small, the antibodies are labeled with a special chemical compound. Other non-luminescent chemicals for labeling the antibodies may be used, such as those that are seen with plain light or labeled with radioactive isotopes for detection with instruments other than microscopes.

Careers in Histology and Cytology

• In the pathology laboratory, pathologists are medical doctors who diagnose conditions such as cancer based on the tissue samples delivered to the lab. To assist them in making the diagnoses, histologists prepare and stain tissue slices (with immunohistochemical stains), putting them onto glass slides. Cytologists look at some of the slides to screen for abnormal cells before the slides are passed on to the pathologist for final diagnosis. Both careers are in demand and require associate degrees in histology and cytology, respectively.