Quantitative Assay of Interferon by the Immunofluorescent Cell-counting Technique

Although numerous methods have been devised for the assessment of interferon activity, the majority are adaptations of established virus assay techniques based on the reduction of cytopathic effects. The various interferon assay methods that are currently employed have been described by Finter (1966) along with comments on their advantages and limitations. Recently, immunofluorescent cell-counting assays have been developed for a number of viruses that are highly sensitive, precise, reproducible and rapid (cf. Hahon & Cooke, 1967). This report describes an extension of the technique for the quantitative assay of interferon within 24 hr after virus challenge of treated cell monolayers.

Virus strains employed in the study were vaccinia (ihd), yellow fever (asibi), psittacosis agent (borg) and Venezuelan equine encephalomyelitis (trinidad). The established McCoy cell line was used for the assay of virus infectivity.