Competitive radioimmunoassay (RIA) is a general method for the determination of the concentration of virtually any substance which is or can be rendered immunogenic. The principle is simple. The concentration of an unknown unlabeled antigen is obtained by comparing its inhibitory effect on the binding of radioactively-labeled antigen to specific antibody with the inhibitory effect of known standards. Although up to now, the principal impact of RIA has been in the field of endocrinology, recent developments have demonstrated its applicability to fields as diverse as toxicology, virology, and cancer detection.
Problems encountered in RIA relate to the presence of non-hormonal factors which interfere in a non-specific fashion with the reaction of antigen with antibody and to the presence of cross reacting prohormones, molecular fragments, and related hormonal antigens which may alter the specificity of the immune reaction. However, the latter problem has been turned to an advantage in that the method has been instrumental in broadening our understanding of the mechanisms involved in the synthesis and degradation of peptide hormones. It would appear that many, if not all, peptide hormones are synthesized in a "big" precursor form of low or no biological activity, followed by the enzymatic conversion to the smaller, better known biologically active form and then rapid degradation to peptide fragments or constituent amino acids or both. For none of these systems has there been developed a complete picture of the complex interrelationships among precursor, active form(s), and degradation products. Especially desirable is a model which correlates immunoreactivity and biological activity as measured in the intact animal and in receptor site assay. One can only be certain that radioimmunoassay will continue to be involved in both the questions and the answers which will be necessary for the solution of this problem, as it has been for so many others in medicine.
- 1971, by The Williams & Wilkins Co.