Determinants of measles virus (hamster neurotropic strain) replication in mouse brain

In newborn mice the hamster neurotropic strain of measles virus produces a severe meningoencephalitis with readily recoverable virus, while in weanling mice a fatal encephalopathy is produced with scant histopathology and no viral infectivity in brain homogenates. In this study various host factors that may change with maturation and determine the restriction of viral expression were investigated, including immune response, interferon production, host temperature, and the possible role of proteases. None of these factors appeared to be responsible for host restriction of viral expression. Recovery of virus from brains of weanling mice was not significantly enhanced by cocultivation with Vero cells, complementation with temperature-sensitive mutants, or phenotypic mixing with the Edmonston strain of measles virus. These data, combined with our previous observations of production of viral proteins including nucleocapsid proteins without development of recognizable nucleocapsids in neurons of weanling mice, suggest that with maturation the neural cells fail to replicate sufficient amounts of encapsidated viral ribonucleic acid.