Electron microscopy of mitotic cells in a measles-carrier human cell line

The occurrence and localization of measles virus nucleocapsids during mitosis of a measles-carrier human cell line (Lu106) were studied in the transmission electron microscope. During interphase, the virus nucleocapsids were present mainly in the cytoplasm and less frequently in the nucleus. Nucleocapsids were also observed at the different stages of mitosis, always in the cytoplasm outside prophase and telophase nuclei and outside the mitotic apparatus at metaphase and anaphase. The presence of viral materials during mitosis and at the two daughter cell stage indicates a vertical transmission of infection through cell division. The frequency of infected cells in the cell population was generally high and sometimes relatively low inferring a fluctuation state in the virus/cell equilibrium.