Measurement of interferon from in vitro stimulated lymphocytes by bioassay and monoclonal antibody-based immunoassay

Peripheral blood mononuclear cells (PBMC) derived from healthy individuals were stimulated with u.v.-inactivated Newcastle disease virus and the cell supernatants were assayed for both antiviral activity and alpha interferon (IFN-alpha) immunoreactivity. IFN-alpha concentrations determined by two immunoradiometric assays (IRMAs) based on monoclonal antibodies that recognize different IFN-alpha subtypes correlated well together (r = 0.96) and with interferon concentrations determined by the two bioassays (r = 0.82 to 0.89), but the agreement between the results of the two bioassays was not as close (r = 0.79). As judged by the agreement between determinations on duplicate inductions of the same PBMC, the IRMAs were considerably more precise than the bioassays. Despite the use of a common IFN standard there were marked differences in the absolute titres of IFN determined by the IRMAs and bioassays, highlighting the difficulties in standardizing assays for IFN-alpha. The IRMA results suggest that there are no major differences in the spectrum of IFN-alpha subtypes produced by healthy individuals under conditions of viral stimulation.