Characterization of four cell lines persistently infected with measles virus.

Persistently infected cell lines were established by infecting Vero cells with four different strains of measles virus: Edmonston "wild type", Schwarz vaccine strain passaged at high multiplicity of infection, Hallé SSPE strain, and a temperature sensitive mutant of Edmonston strain, designated ts 841. The four cell lines have continued to produce virus at a constant low level over a period of more than two years, although cytopathology and hemagglutinating ability have varied with cell passage. Only virus from cells originally infected with ts 841 appears to be temperature sensitive. In each of the cell lines a sizable population of low density, interfering virus particles was generated, indicating that this is an important mechanism for these four cell lines in maintenance of the measles virus persistent infection.