Effect of an interferon inducer, 9-methylstreptimidone, on influenza virus infection in mice.

The antiviral effect of 9-MS was examined in mice infected with mouse-adapted influenza A2 (H2N2) virus. Either a single or a continuous prophylactic administration of 9-MS protected mice from virus infection, and comparison of the minimal effective dose with the lethal dose gave a therapeutic index of approximately 60. When the treatment was started after infection, however, no antiviral effect was demonstrated. A potent virus-inhibitory factor was detected in the lung and serum after a single intraperitoneal administration of 9-MS in uninfected mice, and on the basis of chemical characteristics of this inhibitory factor, it was assumed to be an interferon. These results suggest that the protective activity of the antibiotic in mice is due to interferon induction.