RADIOIMMUNOASSAY

The technique of radioimmunoassay has revolutionized research and clinical practice in many areas, e.g.,
• blood banking
• diagnosis of allergies
• endocrinology
The technique was introduced in 1960 by Berson and Yalow as an assay for the concentration of insulin in plasma. It represented the first time that hormone levels in the blood could be detected by an in vitro assay.
The Technique

•  A mixture is prepared
•  radioactive antigen

                Because of the ease with which iodine atoms can be introduced into tyrosine residues in a protein, the radioactive isotopes 125I or 131I are often used.

    o antibodies against that antigen.

• Known amounts of unlabeled ("cold") antigen are added to samples of the mixture. These compete for the binding sites of the antibodies.
• At increasing concentrations of unlabeled antigen, an increasing amount of radioactive antigen is displaced from the antibody molecules.
• The antibody-bound antigen is separated from the free antigen in the supernatant fluid, and
• the radioactivity of each is measured.
• From these data, a standard binding curve, like this one shown in red, can be drawn.