One neutralization unit is the amount of antiserum required to neutralize one unit of
human interferon alpha (Hu-IFN-
alpha) to a 50% endpoint. Interferon was titrated with the use of the cytopathic effect
inhibition assay as described [Rubinstein, S., Familletti, P.C., and Pestka, S. (1981) "Convenient Assay for Interferons,"
. 37, 755-758; Familletti, P.C., Rubinstein, S., and Pestka, S. (1981) "A Convenient and Rapid Cytopathic Effect
Inhibition Assay for Interferon," in
Methods in Enzymology, Vol. 78 (S. Pestka, ed.), Academic Press, New York, 387-394].
In this antiviral assay for interferon, about 1 unit/ml of interferon is the quantity necessary to produce a cytopathic effect of
50%. The units are determined with respect to the international reference standard for Hu-IFN-
alpha provided by the National
Institutes of Health [see Pestka, S. (1986) "Interferon Standards and General Abbreviations," in
Methods in Enzymology
(S. Pestka, ed.), Academic Press, New York 119, 14-23].