Interferon standardization and designations

A large number of different human and nonhuman interferon (IFN) preparations are now available for either research purposes or commercial use. Consistency of results can be achieved only through rigorous application of biologic standards and individual species designation. International standards for the potency determinations of these preparations have been produced in accordance with World Health Organization (WHO) guidelines and are available for calibrating assays. Until recently, potency has been assessed purely as a measure of antiviral activity expressed in international units. Other biologic properties are now also being considered, including antiproliferation and immunomodulation. Indirect methods of measuring IFN, such as radioimmunoassay or enzyme immunoassay, if fully validated, may also provide useful estimates of function. Reference antisera are useful for characterizing IFN preparations and for monitoring neutralization assays for detecting anti-IFN antibodies but should not have a function in assay calibration. Factors to be considered when referring to specific designations for pure IFN species include distinctions for the species of origin, any mutant or hybrid forms, the method of production, and the presence of additional glycosylation.