Intrinsic interference between influenza A and B viruses.

Reproduction and synthesis of virus-specific macromolecules were studied in chick embryo fibroblast cultures co-infected with influenza viruses type A (FPV) and B (B/Japan/73). When a multiplicity of infection (MOI) of B/Japan/73 virus (10 EID50/cell and higher) was equal to, or exceeded that of FPV, formation of infectious FPV virions in coinfected cells was suppressed significantly. At equal MOI of FPV and B/Japan/73 synthesis of all proteins of one partner and some proteins of the other was observed. However, when a MOI of one virus was 10 times higher than that of the other, proteins of the virus used at a higher MOI were formed. Studies of the synthesis of virus-specific cRNAs formed in the presence of cycloheximide have shown that at equal MOI. cRNAs were detected that corresponded only to one of the partners involved in the reproduction. The data obtained suggest that intrinsic interference between A and B viruses occurs at a stage of primary transcription.