Overview of antigen detection through enzymatic activity.

The identification of antigenic substances with antibodies can only occur through the use of a reporter molecule. One way of doing this is through the use of enzymes. Enzymes act upon a substrate and that substrate, or a molecule affected by that substrate, in turn becomes detectable by a variety of methods. There are many enzymes available for this purpose. The most common is peroxidase. Another widely used enzyme is alkaline phosphatase. Each enzyme has a few chromogenic substrate solutions with which it can react to change a color visualized through the use of selected instruments, including the microscope. Antibodies can be labeled with an enzyme directly, or secondary antibodies can be labeled with the enzyme and employed in an indirect technique. Also, immunoglobulin labeled polymers labeled with enzyme can be used and the enzymes themselves can serve as antigens in immunoenzyme complex procedures. Finally, avidin or biotin can be labeled with enzyme, and used either singly or in complexes, and peroxidase mediated biotin amplification can be used to increase the sensitivity in some procedures.