Practice question

Radioimmunoassay utilizes gamma-emitting isotopes to label antigens or antibodies for competition and quantification. Iodine-125 is preferred because its high specific activity, half-life near 60 days and gamma photons are efficiently counted in solid scintillation counters without liquid scintillant. Proteins can be radioiodinated on tyrosine residues via chloramine-T method with minimal loss of immunoreactivity. ELISA, Western blot and flow cytometry typically employ enzymatic or fluorescent labels, not radioisotopes, due to safety and disposal issues. Therefore presence of 125I in protocol strongly points toward classical radioimmunological technique developed by Berson and Yalow.