Propagation of vertically transmitted RSV.

<p>Extracts of whole fetuses delivered from dams inoculated with rrRSV or from pathogen-free controls and co-cultured with human airway epithelial cells. After 48 h of incubation, the cells were then stained with a polyclonal anti-NGF antibody. The micrographs show red fluorescence in the cytoplasm of cells exposed to fetal extracts from rrRSV-infected dams, confirming the presence of actively replicating infectious virus that is associated with markedly increased green NGF immunoreactivity. As RFP expression reflects virus infection and production of the transgene rather than virus spread and plaque formation, this methodology is more accurate than the standard plaque assay to assess RSV infectivity. <b><i>Magnification = 60X.</i></b>