Epitope mapping of human recombinant interferon alpha molecules by monoclonal antibodies

The epitopes of six recombinant human interferon alpha (IFN alpha) subtypes have been analysed using 22 monoclonal antibodies (MAbs) obtained from different sources. The IFN alpha subtype specificity of each MAb was determined by a combined immunoprecipitation-bioassay. Eight different epitopes were identified; the number of epitopes on a given IFN alpha subtype varied between four and eight. Each subtype possessed a unique combination of epitopes. Using the best pair of monoclonal antibodies, predicted from epitope mapping studies, subtype-specific two-site (tandem) assays were developed. It was observed that some non-cross-reactive MAbs influenced each other's binding, indicating the flexible nature of IFN molecules. Competitive radioimmunoassay and the combined immunoprecipitation-bioassay were used to identify a common epitope, present on IFN alpha-A, B, C, F and J but not on IFN alpha-D. In neutralization studies, all MAbs that identified this common epitope inhibited the antiviral activity of all IFN alpha molecules tested. It was concluded that the epitope is located within the receptor-binding region of IFN molecules and is important for biological activity. A tentative localization of the common epitope and the other identified epitopes is proposed.