Immunoradiometric assay of a recombinant human alpha-2 interferon (SCH 30500)

A sensitive immunoradiometric assay for recombinant alpha-2 interferon (IFN-alpha 2; SCH 30500) was developed by using the monoclonal antibody NK2. A polystyrene bead with polyclonal sheep anti-human IFN-alpha (Hu IFN-alpha) antibody adsorbed to it formed the solid phase of the assay. The monoclonal antibody, labeled with 125I, reacted with the IFN-alpha 2 which bound to the polyclonal antibody on the bead. The assay was sensitive, capable of measuring less than 5 IU/ml, and it was precise. Coefficients of variation were less than 10%, often less than 5%. Interassay coefficients of variation for the same sample were also less than 10%. Specificity of the monoclonal antibody for IFN-alpha 2 was greater than for Hu IFN-alpha produced by leukocytes. In specificity studies it was necessary to add at least 200 IU of Hu IFN-alpha per ml to 25 IU of IFN-alpha 2 per ml before the Hu IFN-alpha affected the accuracy of the assay of IFN-alpha 2. Accuracy as determined by correlation studies with the antiviral cytopathic effect assay was very high. Results of the two assays usually agreed within 15%. This correlation was maintained in studies of IFN-alpha 2 after storage under accelerated degradation conditions, when the IFN was cleaved into smaller sequences of amino acids by cyanogen bromide and when the IFN was carboxymethylated.