Characterization of measles virus recovered from persistently infected Vero cells.

Vero cells were persistently infected with measles virus in medium with antimeasles serum. When antiserum was not added to the medium, the persistently infected cells (VMAS cells) proliferated in a cyclical manner alternating between extensive cell destruction and renewed cell growth. When these cells were grown at 33 C and 40 C, they released temperature-sensitive and temperature-dependent viruses. However, these viruses, upon further propagation, reverted to the wild type suggesting that such temperature-related functions were phenotypically determined and regulated by host-cell factors. The spontaneous viral yield was dependent upon the active cell growth.