What is "immunolabeling"

n. (context immunology English) A method of identifying antigens by using antibody containing a fluorescent tag vb. (present participle of immunolabel English)

Immunolabeling is a biochemical process that enables the detection and localization of an antigen to a particular site within a cell, tissue, or organ. Antigens are organic molecules, usually proteins, capable of binding to an antibody. These antigens can be visualized using a combination of antigen-specific antibody as well as a means of detection, called a tag, that is covalently linked to the antibody. If the immunolabeling process is meant to reveal information about a cell or its substructures, the process is called immunocytochemistry. Immunolabeling of larger structures is called immunohistochemistry.

There are two complex steps in the manufacture of antibody for immunolabeling. The first is producing the antibody that binds specifically to the antigen of interest and the second is fusing the tag to the antibody. Since it is impractical to fuse a tag to every conceivable antigen-specific antibody, most immunolabeling processes use an indirect method of detection. This indirect method employs a primary antibody that is antigen-specific and a secondary antibody fused to a tag that specifically binds the primary antibody. This indirect approach permits mass production of secondary antibody that can be bought off the shelf. Pursuant to this indirect method, the primary antibody is added to the test system. The primary antibody seeks out and binds to the target antigen. The tagged secondary antibody, designed to attach exclusively to the primary antibody, is subsequently added.

Typical tags include: a fluorescent compound, gold beads, a particular epitope tag, or an enzyme that produces a colored compound. The association of the tags to the target via the antibodies provides for the identification and visualization of the antigen of interest in its native location in the tissue, such as the cell membrane, cytoplasm, or nuclear membrane. Under certain conditions the method can be adapted to provide quantitative information.

Immunolabeling can be used in pharmacology, molecular biology, biochemistry and any other field where it is important to know of the precise location of an antibody-bindable molecule.