Temperature-Sensitive Mutants of Influenza Virus. IV. Induction of Interferon in the Nasopharynx by Wild-Type and a Temperature-Sensitive Recombinant Virus

The temperature-sensitive (ts) live influenza A virus vaccine (ts-1[E]), administered intranasally, induced interferon in the nasopharyngeal (NP) washes of volunteers. The amount of interferon in the NP washes of these volunteers was 15-fold less than that induced by wild-type virus. In addition, interferon was detected for a shorter period in men infected with the ts-1[E] virus. There was a strong correlation between the level of virus multiplication and the amount of interferon induced in the NP washes by either the ts or wild-type virus. In vitro, the ts and wild-type viruses had similar sensitivities to interferon; in addition, under conditions that were permissive for the ts virus (34 C), it stimulated as much interferon and interference in tissue culture as wild-type virus. It appeared that the low levels of interferon induced in the nasopharynx by the ts virus in vivo were a consequence of the low level of virus multiplication at that site. Furthermore, the mechanism(s) responsible for the attenuation of this ts virus does not seem to be related to an increased production of interferon in the nasopharynx or to an enhanced sensitivity of this virus to interferon.