Measles virus: evolution of a persistent infection in BGM cells

An African green monkey kidney cell line (BGM) persistently infected with measles virus (BGM/Hallé cells) has been studied during 3 years in culture. The early cell passages were characterized by slow growing cultures producing high yields of infections virus (10(6)--10(7) PFU/ml). These cells were gradually replaced by a population of cells multiplying at a similar rate as non-infected cells. During this evolution, the virus released from the cells changed from a large plaque variant, to a small plaque and eventually unlysed foci. Despite greater than or equal to 95 per cent of the cells being infected, the virus yield fell to the limits of detection. [35S]-methionine labelling of BGM/Hallé cultures at the 20th and 140th passage showed that in both cases all the measles virus structural proteins were synthesized. There were no changes in the apparent molecular sizes of the viral proteins during passage. Cell surface [125I]-labelling of BGM/Hallé cells indicates that viral envelope antigens are inserted into the membrane despite the diminution in virus yield. Several cell proteins not labelled in non-infected BGM cells are also labelled. These proteins could also be [125I]-labelled in clones of BGM/Hallé cells with had been "cured" of virus. Chase experiments of [125I]-pre-labelled BGM/Hallé cultures showed the radiolabelled antigen to be incorporated into virus particles. Non-infections virus particles released from the cells contained the same polypeptides as those released from a lytic infection.