Further Observations on Cell Cultures Infected Concurrently with Mumps and Sindbis Viruses

Summary The Sindbis virus plaque size enhancing property of mumps virus is shown to be closely associated with infectivity of mumps virus, and to be clearly different from mumps virus hemagglutinin and hemolysin. The enhancing property differs also from published descriptions of mumps virus cytolysin and mouse toxin. Sindbis virus was recovered in much higher titer from doubly infected cultures which exhibited enhancement than from cultures showing normal Sindbis virus plaques. However, in chick embryo or human amnion cell cultures with liquid medium, Sindbis virus multiplication was similar whether or not concurrent mumps virus infection was present. The development of hemagglutinin in the mumps infected system was not affected by concurrent Sindbis virus infection. Fluids harvested from doubly infected cultures interfered with vesicular stomatitis virus plaque development, while fluids from cultures infected solely with mumps or Sindbis virus failed to do so. Heated allantoic fluid from influenza virusinfected eggs or fluid from rubella virus-infected cultures interfered with Sindbis virus activity in chick embryo or human amnion cell cultures respectively. Mumps virus infection inhibited this interfering activity.