title: A beneficiary role for neuraminidase in influenza virus penetration through the respiratory mucus.
abstract: Swine influenza virus (SIV) has a strong tropism for pig respiratory mucosa, which consists of a mucus layer, epithelium, basement membrane and lamina propria. Sialic acids present on the epithelial surface have long been considered to be determinants of influenza virus tropism. However, mucus which is also rich in sialic acids may serve as the first barrier of selection. It was investigated how influenza virus interacts with the mucus to infect epithelial cells. Two techniques were applied to track SIV H1N1 in porcine mucus. The microscopic diffusion of SIV particles in the mucus was analyzed by single particle tracking (SPT), and the macroscopic penetration of SIV through mucus was studied by a virus in-capsule-mucus penetration system, followed by visualizing the translocation of the virions with time by immunofluorescence staining. Furthermore, the effects of neuraminidase on SIV getting through or binding to the mucus were studied by using zanamivir, a neuraminidase inhibitor (NAI), and Arthrobacter ureafaciens neuraminidase. The distribution of the diffusion coefficient shows that 70% of SIV particles were entrapped, while the rest diffused freely in the mucus. Additionally, SIV penetrated the porcine mucus with time, reaching a depth of 65 µm at 30 min post virus addition, 2 fold of that at 2 min. Both the microscopic diffusion and macroscopic penetration were largely diminished by NAI, while were clearly increased by the effect of exogenous neuraminidase. Moreover, the exogenous neuraminidase sufficiently prevented the binding of SIV to mucus which was reversely enhanced by effect of NAI. These findings clearly show that the neuraminidase helps SIV move through the mucus, which is important for the virus to reach and infect epithelial cells and eventually become shed into the lumen of the respiratory tract.
authors.affiliation: Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Yang
authors.affiliation: Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Lennert
authors.initials: L
authors.lastname: Steukers
authors.affiliation: Laboratory of General Biochemistry and Physical Pharmacy, Ghent University, Ghent, Belgium; Center for Nano- and Biophotonics, Ghent University, Ghent, Belgium.
authors.forename: Katrien
authors.initials: K
authors.lastname: Forier
authors.affiliation: Laboratory of General Biochemistry and Physical Pharmacy, Ghent University, Ghent, Belgium; Center for Nano- and Biophotonics, Ghent University, Ghent, Belgium.
authors.forename: Ranhua
authors.initials: R
authors.lastname: Xiong
authors.affiliation: Laboratory of General Biochemistry and Physical Pharmacy, Ghent University, Ghent, Belgium; Center for Nano- and Biophotonics, Ghent University, Ghent, Belgium.
authors.forename: Kevin
authors.initials: K
authors.lastname: Braeckmans
authors.affiliation: Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Kristien
authors.initials: K
authors.lastname: Van Reeth
authors.affiliation: Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Nauwynck
mesh_terms: D000818:Animals; D002460:Cell Line; D004058:Diffusion; D009980:Influenza A virus / Q000201:enzymology*; D009093:Mucus / Q000378:metabolism* / Q000821:virology*; D009439:Neuraminidase / Q000378:metabolism*; D009976:Orthomyxoviridae Infections / Q000821:virology*; D012794:Sialic Acids / Q000378:metabolism; D013552:Swine
chemical_list: D012794:Sialic Acids; D009439:Neuraminidase