Assay of interferon activity.

At present there is a lack of standard criteria for the identification and evaluation of activity of antiviral compounds. Interferon was used to explore comparatively several laboratory methods. Interferon was produced in chick embryos and in chorioallantoic membranes suspended in vitro. Evaluation of interferon activity was performed by several methods: (i) percentage of inhibition of plaque-forming units; (ii) hemagglutinin reduction of challenge virus; (iii) titer of cytopathic effect of challenge virus; and (iv) plaque-inhibition test. The suggested methods for measurement are those which express the titer of challenge virus in plaque-forming units or in hemagglutinating units.