In vitro characterization of influenza a virus attachment in the upper and lower respiratory tracts of pigs

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The binding of influenzaAviruses to epithelial cells in the respiratory tract of mammals is a key step in the infection process. Therefore, direct assessment of virus-host cell interaction using virus histochemistry (VH) will enhance our understanding of the pathogenesis of these new viruses. For this study, the authors selected viruses that represented the 4 main genetic clusters of North American swine H1(SwH1) viruses, along withA/California/04/2009H1N1 and a vaccine strain for the positive controls, and the virus label, fluorescein isothiocyanate (FITC), for the negative control. A group of 5 viruses containing a 2-amino acid insertion adjacent to the binding site of the hemagglutinin protein and their presumed ancestral viruses were also examined for changes in binding patterns. Viruses were bound to formalin-fixed paraffin-embedded, 6-week-old (6w) and adult pig tissues. Qualitative VHscores per respiratory zone ranged from + to +++, with bronchioles having the highest and most consistent scores, regardless of animal age. For the 6w bronchioles, a quantitative VH score was calculated using digital images of 5 bronchioles per tissue section using image analysis software. Significant differences in attachment were found among the SwH1 viruses (P <.0001) and among the ancestral and insertion viruses (P <.0001). These results provide new insights on virus binding to porcine respiratory epithelial cells and the usefulness of morphometric scores. The results also highlight limitations of in vitro techniques, including VH for predicting virulence and host range.

Original languageEnglish (US)
Pages (from-to)648-658
Number of pages11
JournalVeterinary pathology
Issue number4
StatePublished - Aug 2013

Bibliographical note

Funding Information:
The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was funded by USDA Discretionary GAR Funds AES0060014 as part of the Signature Program Funding at the College of Veterinary Medicine, University of Minnesota. SD and MG were funded in part by federal funds from the NIAID, NIH, HHS, under Contract No. HHSN266200700007C.


  • H1N1
  • Histochemistry
  • Influenza a virus
  • Swine influenza


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