Characterization of putative defective interfering (DI) A/WSN RNAs isolated from the lungs of mice protected from an otherwise lethal respiratory infection with influenza virus A/WSN (H1N1): a subset of the inoculum DI RNAs.

Defective interfering (DI) influenza virus A/WSN (H1N1) grown in embryonated eggs protected adult mice from a lethal respiratory infection with A/WSN virus. Eighteen bands of putative DI RNA, ranging in size from about 230 to 1020 nt, were identified in this preparation by reverse transcription and polymerase chain reaction using a segment-specific 3' primer and a segment-universal 5' primer. Every virion RNA segment was represented by one to four bands of putative DI RNA. However, only five bands of putative DI RNA could be isolated, using the same conditions, from lungs of WSN-infected mice protected from death by co-inoculation with egg-grown DI WSN. These five bands originated from PB1, PB2, PA, and M virion RNAs and were all about 350-450 nt in length. Four putative DI RNAs originating from PB1, PB2, and PA virion RNAs were sequenced, and three were identical (including deletion junctions and base substitutions) to putative DI RNAs from the inoculum. These data suggest that the mouse lung was highly selective for a subset of inoculum DI RNAs and that one or more of these DI RNAs was responsible for protection in vivo. All putative DI RNAs had a single internal deletion.