Abstract
The 448-PI-Vero, African green monkey kidney cell line (Vero) persistently infected (PI) with a temperature sensitive (ts) mutant, P-448 of measles virus has been studied in culture for 6 years.
The Edmonstone strain of measles virus induced interferon (IFN) in BSC-1 cells derived from African green monkey kedney, but the P-448 virus with which the persistent infection was established, did not produce IFN in BSC-1 cells. Both of the Edmonstone and P-448 viruses did not induce IFN in Vero cell culture.
Vero cell culture which was maintained during the 6 years, but not infected with measles virus, produced IFN by the infection of Newcastle disease virus, but another Vero cell line(Vero-F) obtained commercially did not.
The virus derived from the persistently infected 448-PI-Vero at 500 days (19 passages) after the initial infection showed decreased temperature sensitivity but did not produce IFN.
The virus derived at 558 days (20 passages) showed reversion to ts' phenotype and produced IFN.
Viruses from 448-PI-Vero maintained longer than 715 days (29 passages) steadily had the IFN-inducing capacity and showed unstable temperature sensivity. The culture showed definitely decreased cytopathic change, when excreted the is virus.
In Veto-F cells, persistent infection was easily established with viruses from 448-PI-Vero which had been maintained for 558 to 1, 500 days, only when the virus was inoculated at multiplicity of infection (MOI) of 0.08 or more.
From the results described above, it is concluded that firstly IFN-production is not necessary to establish the PI culture, and secondly the maintenance of the PI culture could be related to the IFN-production in cells and a selection of mutants with decreasing cytopathogenicity as well as presumably a development of defective interfering particles. 448-PI-Vero produced highly heterogeneous mutant viruses after a long incubation periods.
