Enzyme immunoassay of interferon with peroxidase-labelled virus-specific monoclonal antibodies

To quantify the antiviral effect of interferon (IFN) we applied a mixture of two horseradish peroxidase-labelled monoclonal antibodies, specific for the E1 glycoprotein of Semliki Forest virus, in a direct enzyme immunoassay. This assay is suitable for detection of virus replication in L-cells, seeded as monolayers in 96-well plates. Inhibition of absorbance values caused by IFN was determined in a Flow Titertek Multiskan. Three IFN samples from different sources were titrated simultaneously in the enzyme immunoassay and in the vesicular stomatitis virus plaque reduction test in five consecutive experiments. Titres were calculated as the inverse value of the dilution of IFN causing 25% inhibition of absorbance values and 50% reduction of plaque counts respectively. The results show equality of precision and reproducibility between and within the two assays. However, the enzyme immunoassay is more convenient and objective than the plaque reduction assay.