Rapid bioassay of human interferon by direct enzyme immunoassay of encephalomyocarditis virus in HEp-2 cell monolayers after a single cycle of infection.

Multiplication of encephalomyocarditis virus (EMCV) in human HEp-2 cells, and its suppression by interferon (IFN), was demonstrated by direct enzyme immunoassay (EIA) in cell culture. EMCV was detected in glutaraldehyde fixed HEp-2 cell monolayers, in wells of 96-well plates, with a horse radish peroxidase (HRPO) labelled EMCV specific monoclonal antibody. Multiplication of EMCV (multiplicity of infection: 50) was indicated by a steep rise of absorbance values measured against infected monolayers starting as early as 5 h after infection and reaching relatively high values at 6 and 7 h. The rise in absorbance values did not occur after preincubation of the HEp-2 cells with either Newcastle disease virus-induced IFN, recombinant gamma IFN or recombinant alfa-2a IFN. Absorbance values were inversely dependent on the amount of IFN used. Therefore the EIA was suitable for rapid titration of IFN. The titres of recombinant gamma and alfa-2a IFN determined with EIA proved to be similar to those given by the manufacturers. The described bioassay of human IFN is objective, rapid and easy to perform and suitable for large scale experiments.