Early responses of natural killer cells in pigs experimentally infected with 2009 pandemic H1N1 influenza A virus.

Hilde Forberg,Simon P Graham,Wilhelm Gerner,Mette Valheim,Kerstin H Mair,Sharon M Brookes,Alejandro Nunez,Anna G Hauge,Anne K Storset,Fanny Garcon,R Keith Reeves

doi:10.1371/journal.pone.0100619

Abstract

Natural killer (NK) cells are important players in the innate immune response against influenza A virus and the activating receptor NKp46, which binds hemagglutinin on the surface of infected cells, has been assigned a role in this context. As pigs are natural hosts for influenza A viruses and pigs possess both NKp46− and NKp46+ NK cells, they represent a good animal model for studying the role of the NKp46 receptor during influenza. We explored the role of NK cells in piglets experimentally infected with 2009 pandemic H1N1 influenza virus by flow cytometric analyses of cells isolated from blood and lung tissue and by immunostaining of lung tissue sections. The number of NKp46+ NK cells was reduced while NKp46− NK cells remained unaltered in the blood 1–3 days after infection. In the lungs, the intensity of NKp46 expression on NK cells was increased during the first 3 days, and areas where influenza virus nucleoprotein was detected were associated with increased numbers of NKp46+ NK cells when compared to uninfected areas. NKp46+ NK cells in the lung were neither found to be infected with influenza virus nor to be undergoing apoptosis. The binding of porcine NKp46 to influenza virus infected cells was verified in an in vitro assay. These data support the involvement of porcine NKp46+ NK cells in the local immune response against influenza virus.

Highlights

Natural killer (NK) cells are innate lymphocytes that provide early protection against a number of viral infections and are thought to participate in the early defence against influenza virus [1,2]
NK cells kill influenza virus infected cells from mice and humans in vitro [3,4,13,14,15]. They are important early producers of antiviral cytokines such as interferon gamma (IFN-c) and tumour necrosis factor (TNF), which have been associated with the acute stages of influenza virus infection in both humans and swine. [16,17,18,19,20]
To identify the most relevant time period to study NK cells, pigs were experimentally infected with influenza A(H1N1)pdm09 and pairs of infected and control animals were euthanized and sampled 128 days pi

Summary

Introduction

Natural killer (NK) cells are innate lymphocytes that provide early protection against a number of viral infections and are thought to participate in the early defence against influenza virus [1,2]. It has been proposed that NK cells migrate from the blood into the lungs [5,6,7] where they may become infected and killed by the influenza virus [8,9]. Supporting this theory are findings of increased numbers of NK cells in the lungs of influenza infected mice [10,11,12]. NK cells kill influenza virus infected cells from mice and humans in vitro [3,4,13,14,15]. They are important early producers of antiviral cytokines such as interferon gamma (IFN-c) and tumour necrosis factor (TNF), which have been associated with the acute stages of influenza virus infection in both humans and swine. [16,17,18,19,20]

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Conclusion