Confluent monolayers of MDCK cells (6-well plate format, 106 cells/well) were infected with WT or fluorescent-expressing IBVs for 1 h at room temperature, overlaid with agar and incubated at 33 : c. Three days post-infection, cells were fixed overnight with 4% paraformaldehyde (PFA), and the overlays were removed. For visualization of mCherry, PBS was added and plates were imaged with a Kodak image station (4000MM Pro molecular imaging system; Carestream Health, Inc., NY) (Nogales et al„ 2014a) and Kodak molecular imaging software (v5.0.1.30). Plates were then perme- abilized (0.5% Triton X-l 00 in PBS for 15 min at room temperature) and prepared for immunostaining as previously described (Nogales et al„ 2014a) using the anti IBVNP MAb B017 and vector kits according to manufacturer’s specifications.