Sialic acid dependent infection of oviduct explants with the QX strain. Explants were treated with neuraminidase to remove the sialic acids. After infection with the QX strain 12 hpi antigen could only be detected in mock treated explants. The nuclei were stained with DAPI (blue). T the infection was detected with a monoclonal antibody against the N-protein and a FITC-labeled secondary antibody (green).