Abstract
Susceptibility of eight strains of influenza A and B viruses to interferon and to poly (I) · poly (C) were determined by the plaque reduction method. All strains tested were slightly less susceptible than vesicular stomatitis virus (VSV) in an established line of canine kidney (MDCK) cells. The 50% plaque depression doses (PD50) of poly (I) · poly (C) for influenza A and B viruses were as high as 3.0-to 4.5-fold and 6-to 18-fold that for VSV, respectively. The amounts of interferon required to inhibit plaque formation of influenza A and B viruses by 50% were 3.0-6.2 and 7.3-15.2 units/ml, respectively. The ratio of PD50 of poly (I) · poly (C) for each strain of influenza viruses tested to that for VSV in chick embryo cells was almost the same as in MDCK cells. Furthermore, in chick embryo cells, the strains of influenza virus tested were demonstrated to be much more susceptible to poly (I) · poly (C) than both Newcastle disease virus and vaccinia virus. It is suggested that influenza viruses may be relatively susceptible to interferon and to poly (I) · poly (C).
