Effect of human alpha A interferon on influenza virus replication in MDBK cells.

To determine the molecular mechanism whereby interferon induces resistance to influenza virus, we began an investigation of influenza virus replication in MDBK cells treated with recombinant human alpha A interferon. Negative- and positive-strand virus-specific RNA accumulation was monitored by blot hybridization with cloned probes. Primary transcription (transcription of infecting viral negative strands by the virion-associated polymerase) was inhibited by interferon treatment of MDBK cells. At moderate levels of interferon treatment (10 U/ml), this inhibition was restricted to transcripts of polymerase genes, whereas at higher levels of interferon treatment (50 U/ml), accumulation of all primary transcripts was markedly inhibited. Secondary transcripts and viral negative strands did not accumulate to any significant extent in interferon-treated MDBK cells. These results suggest that interferon-induced mechanisms which inhibit influenza virus replication in MDBK cells act at the level of primary transcription.