RADIOIMMUNOASSAY

Minute Measures

Critical to any scientific research is the ability to measure. Various measuring methods have been used in biochemistry over the years—some crude, some sophisticated. Most assay systems for materials in the body have limited use because they require a greater quantity of what is to be measured than is available. The body can spare only small amounts of hormones and other biological molecules for testing purposes.

The Researchers

Rosalind Yalow and Solomon Berson were well prepared as a research team to tackle the problem of measurement testing. Yalow had a Ph.D. in physics and expertise in radioactive materials. Berson was a physician and researcher. Together they developed the radioimmunoassay (RIA) technique, which has been applied not only in medical science but also in a wide range of fields.

The Procedure

The concept of RIA is simple, but it requires some background knowledge. Part of the immune system functions by producing antibodies to foreign substances. With various manipulations, the immune systems of mammals can be forced to make antibodies to almost anything. Antibodies are very specific. An antibody recognizes a chemical structure, and it will bind only to that one structure. Even similar structures will not be recognized by the antibody. But antibodies are also sensitive: they will find and bind to even tiny amounts of the substances they recognize. If a researcher wants an exact measure of hormone X, which is present in small amounts in the blood, RIA is the best method to use. First the researcher needs some pure hormone X that has a radioactive atom in its structure. This can often be produced by a chemical reaction of a small molecule with a radioactive atom and nonradioactive X. Then the researcher needs an antibody that recognizes X,

Measuring Leftovers

To perform the RIA, the researcher puts carefully measured amounts of radioactive X and its antibody into a test tube. Next, a carefully measured amount of blood is added. When hormone X in the blood goes into the test tube, it displaces some of the radioactive X from the antibody. The more X in the blood, the more radioactive X it displaces. Now everything except the antibody and the molecules to which it is bound is removed. The amount of radioactive X left in the tube indicates how much X was in the blood.

The Prize

Yalow and two other physicians, Roger C. L. Guillemin and Andrew V. Serially, received the Nobel Prize for physiology in 1977 for their research into the role of hormones in the chemistry of the body—work made possible by RIA.

Source:

Ira Flatow, They All Laughed-From Light Bulbs to Lasers, the Fascinating Stories Behind the Great Inventions That Have Changed Our Lives (New York: Harper Collins, 1992).

Radioimmunoassay (RIA)

Radioimmunoassay (RIA) is a sensitive method for measuring very small amounts of a substance in the blood. Radioactive versions of a substance, or isotopes of the substance, are mixed with antibodies and inserted in a sample of the patient's blood. The same non-radioactive substance in the blood takes the place of the isotope in the antibodies, thus leaving the radioactive substance free.

The amount of free isotope is then measured to see how much of the original substance was in the blood. This isotopic measuring method was developed in 1959 by two Americans, biophysicist Rosalyn Yalow (1921-) and physician Solomon A. Berson (1918-1972).

History

Yalow and Berson developed the first radioisotopic technique to study blood volume and iodine metabolism. They later adapted the method to study how the body uses hormones, particularly insulin, which regulates sugar levels in the blood. The researchers proved that Type II (adult onset) diabetes is caused by the inefficient use of insulin. Previously, it was thought that diabetes was caused only by a lack of insulin.

In 1959 Yalow and Berson perfected their measurement technique and named it radioimmunoassay (RIA). RIA is extremely sensitive. It can measure one trillionth of a gram of material per milliliter of blood. Because of the small sample required for measurement, RIA quickly became a standard laboratory tool.

How RIA Works

As an example of how this technique works, let's apply it to insulin. To measure insulin, the first step is to mix known amounts of radioisotope-tagged insulin and antibodies. These combine chemically. Next, a small amount of the patient's blood is added. The insulin contained in the blood displaces some of the tagged insulin. The free-tagged insulin is then measured with isotope detectors and the patient's insulin level is calculated.

Uses for RIA

RIA has many uses, including narcotics (drug) detection, blood bank screening for the hepatitis (a highly contagious condition) virus, early cancer detection, measurement of growth hormone levels, tracking of the leukemia virus, diagnosis and treatment of peptic ulcers, and research with brain chemicals called neurotransmitters.

radioimmunoassay A technique for the very precise analysis of proteins such as polypeptide hormones, antigens, antibodies, and enzymes. It is based on the ability of unlabelled proteins to inhibit competitively the binding of labelled protein by specific antibodies (i.e. an immunological reaction). A radioactive label (e.g. radioactive iodine) may be used to follow the interaction of an antibody with an antigen. The amount of radioactivity in the antibody–antigen precipitate is a measure of the degree of inhibition. The protein concentration of the unknown sample is determined by comparing the degree of inhibition with that produced by a series of standards containing known amounts of the protein. The technique has been adapted to assay nonproteins, such as steroids and nucleotides.

radioimmunoassay (RIA), highly sensitive laboratory technique used to measure minute amounts of substances including antigens, hormones, and drugs present in the body. The substance or antigen (a foreign substance in the body that causes antibody production) to be measured is injected into an animal, causing it to produce antibodies. Serum containing the antibodies is withdrawn and treated with a radioactive antigen and later with a nonradioactive antigen. Measurements of the amount of radioactivity are then used to determine the amount of antigen present. The technique was developed by Solomon Berson and Rosalyn Yalow . Yalow was awarded the 1977 Nobel Prize in Physiology or Medicine for her work.

radioimmunoassay A technique for the very precise analysis of proteins, based on the ability of unlabelled proteins to inhibit competitively the binding of labelled protein by specific antibodies (i.e. an immunological reaction). The protein concentration of the unknown sample is determined by comparing the degree of inhibition with that produced by a series of standards containing known amounts of the protein. The technique has been adapted to assay nonproteins.

radioimmunoassay (ray-di-oh-im-yoo-noh-ass-ay) n. the technique of using radioactive antibodies as tracers to estimate the levels of natural substances, especially hormones, in the blood, which act as antigens. The amount of radioactivity trapped is a measure of the amount of the antigen present.

radioimmunoassay (RIA) A sensitive quantitative method for detecting trace amounts of a biomolecule, based on its capacity to displace a radioactively labelled form of the molecule from combination with its antibody. See also immunoassay.