For virus spread experiments, CHO cell lines were seeded into 96-well plates in the presence or absence of doxycycline. 24 h after induction, cells were infected with VSVDG/LASVGP or FPV and were grown without solid overlay. Cells were fixed at different time points post-infection and immunostaining was performed as described above using rabbit sera against VSV (kindly provided by Dr. G. Herrler, Institut für Virologie, Zentrum für Infektionsmedizin, Stiftung Tierä rztliche Hochschule Hannover, Germany), for the detection of VSVDG/LASVGP infected cells, and against FPV, for cells infected with FPV, respectively.