[Temperature-sensitive mutants of Japanese encephalitis virus, isolated from chronically infected cultures of suckling mouse brain cells].

Reproduction of Japanese encephalitis virus isolated at various passage levels from chronically infected GMS-1-K33 cell cultures was maximum in chick embryo fibroblast cultures at a temperature of 28 degrees C. A temperature of 42 degrees C was found to be nonpermissive for the majority of variants and restrictive for the 20th passage virus. Some decline in titers was also observed at 37 degrees C. The ts mutants derived from the population of the persisting virus had lower pathogenicity for laboratory animals, were sensitive to RNA-ase and resistant to 4 M urea. The data obtained by us and other authors suggest that appearance and selection of ts mutants in persistent infection in cell cultures in a regular phenomenon playing a significant role both in establishment and maintenance of persistently infected systems.