The relation of interferon and nonspecific inhibitors to virus levels in nasal washes of ferrets infected with influenza viruses of differing virulence.

Two clones (7a, virulent; 64d, attenuated) of a recombinant influenza virus (A/PR/8/34-A/ENGLAND/939/69 (H3N2)) were inactivated at the same rate by viral inhibitors present in nasal washes taken from both Clone 7a- and Clone 64d-infected ferrets. Both clones induced similar levels of interferon in the nasal washes of infected animals. The onset and rise of interferon production occurred at the same time for both clones, and was associated with a decline in virus titres. In addition, both clones showed a similar sensitivity to interferon. Thus, although nonspecific inhibitors and interferon may play a role in reducing nasal tract infection caused by both clones, the differences in virulence of the 2 clones do not appear to be determined by differential induction of, or resistance to, these host defence mechanisms.