MDCK cells were mock-infected or infected (MOI 1.0) with WT or fluorescent-expressing IBVs. At 18 hpi, cells were fixed with 4% PFA and permeabilized with 0.5% Triton X-l 00 in PBS for 15 min at room temperature. The staining was performed as described pre¬viously (Nogales et al„ 2014a), using primary IBV NP (MAb B017; Abeam) or NS1 (PAb) (Dauber et al„ 2006) antibodies, and FITC- conjugated anti-mouse (NP) or anti-rabbit (NS1) antibodies (Dako). The cell nucleus were stained with 4',6'-diamidino-2-phenylindole (DAPI, Research Organics). Images were captured using a fluores¬cence microscope (Nikon Eclipse TE2000) at X20 magnification, and pictures were processed using Adobe Photoshop CS4 (vll.0) software.