Cells Persistently Infected with Newcastle Disease Virus

Abstract

The strain of Newcastle disease virus (NDV pi ) present in persistently infected L cells differed markedly from the Herts strain (NDV 0 ) used to initiate the infection. NDV pi produced small plaques (less than 1 mm) in chick embryo cell cultures, whereas the wild type (NDV 0 ) produced large plaques (2 to 3 mm). The two viruses differed in a number of additional properties. Whereas 80% of adsorbed NDV 0 eluted from chicken red blood cells at 37 C, only about 20% of NDV pi was recovered under similar conditions. There was no significant difference in the neuraminidase content of the two viruses. The infectivity of NDV 0 was stable for 1 hr at 48 C, whereas 99.9% of the infectivity of NDV pi was destroyed. The two viruses also differed in lethality for chick embryos; NDV pi had significantly reduced lethality for 9-day-old chick embryos when compared to NDV 0 . In contrast to NDV 0 , which produced an abortive infection in L cells, NDV pi not only replicated effectively and destroyed these cells, but also induced significantly higher quantities of interferon than did NDV 0 . These data furnished additional evidence for the lack of relationship of interferon production to abortive infection of L cells with NDV 0 . In contrast, interferon was found to play a significant role in the maintenance of persistent infection.