Surface features of vaccinia virus-infected human embryonic cells as studied by scanning electron microscopy

Human embryonic cells were studied sequentially following infection with vaccinia virus by scanning electron microscopy (SEM). Normal human embryonic cells have a flattened polygonal and elongated shape and relatively smooth surfaces with few microvilli and flipodia. Vaccinia virus induced surface changes 0.5 hr after infection, which included the appearance of aggregates of microvilli and blebs. These changes were more striking after 2 hr, and the number of filipodia increased. Four hours after infection, most of the cells rounded up and polymorphic ruffles covered the entire surface of the cells. Cytosine arabinoside did not prevent the early surface alterations induced by the virus while addition of cycloheximide did. These results indicate that de novo protein synthesis but not DNA synthesis is required for the early morphologic changes induced by vaccinia virus. Further studies are required to understand the nature and underlying mechanisms of these surface alterations.