Quantitation of biologically active IL-1 by a sensitive assay based on immobilized human IL-1 receptor type II (IL-1RII)

Methodological aspects of quantitative receptor assays

Receptor assays occupy a particular position in the methods used in bioanalysis, as they do not exploit the physico-chemical properties of the analyte. These assays make use of the property of the analyte to bind to the specific binding site (receptor) and to competitively replace a labelled ligand from the same binding site. The amount of labelled ligand replaced is a measure of the amount as well as the affinity of the analyte. Thus, receptor assays offer additional information about the biological (pharmacological) activity of the analyte by distinguishing the compounds on the basis of their specific binding rather than specific molecular structure (chromatographic and non-chromatographic methods). This paper, starting with the general principles of receptor-ligand interaction, focuses on the application of ligand-binding techniques to the quantitative analysis. The factors which influence the sensitivity and the specificity of quantitative receptor assays, as well as the main directions in the improvement of the receptor preparation by using the solubilized and purified receptor are discussed. In order to enhance the use of these assays in routine practice, the development of solid-phase receptor assays is considered.