A Rapid and Simple Method for Assaying Interferon1

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Abstract
A new procedure of assaying interferon (IF) has been developed. Cell suspension was dispensed into liquid scintillation counting vials together with IF sample. During an overnight incubation, the cells adhered sufficiently to the bottom of the vials and all the subsequent procedures were carried out without transfer of the cells from the vials. Vesicular stomatitis virus was inoculated and virus‐specific RNA was labeled by adding 3H‐uridine and actinomycin D to the medium. Incubation was terminated prior to completion of a single‐step growth of the virus and radioactivity of the labeled cells in each vial was determined. The reciprocal of the IF dilution which reduced the radioactivity in viral RNA by 50% was taken as the titer. The present procedure consists of simple manipulations and can be completed within 24 hr. Furthermore, it is quite reproducible and gives a titer almost identical to that obtained by the conventional plaque‐reduction dose method. The procedure can be applied to mouse L cells, rabbit RK‐13 cells and human FL cells, without modification.