Radioimmunoassay for human beta interferon.

Pure human beta interferon (Hu IFN-beta) (formerly human fibroblast interferon) was used to raise antibodies in rabbits. Anti-IFN-beta immunoglobulins from rabbit serum were purified by IFN-beta affinity chromatography and were used in the development of a sandwich-type radioimmunoassay for Hu IFN-beta. This radioimmunoassay consisted of (i) incubating Hu IFN-beta with anti-IFN-beta immunoglobulins immobilized on Sepharose 4B beads and (ii) incubating the resulting solid-phase IFN antibody complex with 125I-labeled anti-Hu IFN-beta immunoglobulins. The amount of 125I-labeled anti-Hu IFN-beta bound to the complex was linearly proportional to the amount of antiviral activity present in the complex from 0 to 500 U of standard IFN-beta per ml; 1 U of antiviral activity was equivalent to about 40 cpm of 125I-labeled anti-IFN immunoglobulins in the radioimmunoassay. The results of the radioimmunoassay were not influenced by the protein content of the IFN sample assayed, and the degree of intraassay variability was low; coefficients of variability were 9.4% at 5 U/ml and 1.1% at 500 U/ml. Thus, compared with the traditional antiviral assay for IFN, this radioimmunoassay was equally sensitive and more precise. In addition, it was highly specific for Hu IFN-beta and took only 5 h to complete.