Use of competitive PCR to estimate the level of NS gene persisting in MDCK cells which survived productive replication of a mutant of influenza virus A/WSN.

Madin-Darby canine kidney (MDCK) cells, which received high multiplicity superinfections with a weakly cytolytic mutant of influenza A virus, could survive and be passaged stably, carrying the genes of the infected virus. The quantitation of the viral NS gene persisting in these cultured cells using competitive polymerase chain reaction revealed that the gene existed at a relatively constant level (approximately 10(5) to 10(6) copies per 8 x 10(6) cells) over a long range of cell generations without producing any detectable progeny virus, suggesting that the persisting NS gene was not silent, but was amplified and inherited to the daughter cells.