PREPARATION AND CHARACTERIZATION OF LABELED INTERFERON-GAMMA AND THE DEVELOPMENT OF RADIORECEPTOR ASSAY FOR INTERFERON-GAMMA

A I-125-labelled recombinant interferon-gamma (IFN-gamma) was prepared by the lactoperoxidase-glucose oxidase method. The specific activity of the labelled IFN-gamma was 31 Bq U-1 and its molecular weight, immunoreactivity and receptor binding ability remained the same after the labelling. Using the labelled IFN-gamma and FL5-1 cells from human amniotic membrane, a radioreceptor assay was developed. Natural IFN-gamma, recombinant IFN-gamma and the labelled IFN-gamma were observed to bind to the same binding sites on the cells with similar affinity (K(d) = 1.3-2.2 x 10(-10) M). The radioreceptor assay was more specific than a bioassay because the labelled IFN-gamma did not compete with IFN-alpha or IFN-beta. It was much more sensitive (90 pM) than conventional competitive radioimmunoassay (300 pM) using the same labelled IFN-gamma, and as sensitive as immunoenzymometric assay (60 pM). The radioreceptor assay should be useful not only for research on IFN-gamma but also for the determination of biological activity in process control and/or quality control of IFN-gamma manufacturing.