Loss of a single N-linked glycan from the hemagglutinin of influenza virus is associated with resistance to collectins and increased virulence in mice

Patrick C Reading,Paul G Whitney,Michelle D Tate,Danielle L Pickett,Emma R Job,Andrew G Brooks

doi:10.1186/1465-9921-10-117

Patrick C Reading, Paul G Whitney + Show 4 more

Open Access

https://doi.org/10.1186/1465-9921-10-117

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Abstract

BackgroundGlycosylation on the globular head of the hemagglutinin (HA) protein of influenza virus acts as an important target for recognition and destruction of virus by innate immune proteins of the collectin family. This, in turn, modulates the virulence of different viruses for mice. The role of particular oligosaccharide attachments on the HA in determining sensitivity to collectins has yet to be fully elucidated.MethodsWhen comparing the virulence of H3N2 subtype viruses for mice we found that viruses isolated after 1980 were highly glycosylated and induced mild disease in mice. During these studies, we were surprised to find a small plaque variant of strain A/Beijing/353/89 (Beij/89) emerged following infection of mice and grew to high titres in mouse lung. In the current study we have characterized the properties of this small plaque mutant both in vitro and in vivo.ResultsSmall plaque mutants were recovered following plaquing of lung homogenates from mice infected with influenza virus seed Beij/89. Compared to wild-type virus, small plaque mutants showed increased virulence in mice yet did not differ in their ability to infect or replicate in airway epithelial cells in vitro. Instead, small plaque variants were markedly resistant to neutralization by murine collectins, a property that correlated with the acquisition of an amino acid substitution at residue 246 on the viral HA. We present evidence that this substitution was associated with the loss of an oligosaccharide glycan from the globular head of HA.ConclusionA point mutation in the gene encoding the HA of Beij/89 was shown to ablate a glycan attachment site. This was associated with resistance to collectins and increased virulence in mice.

Highlights

Glycosylation on the globular head of the hemagglutinin (HA) protein of influenza virus acts as an important target for recognition and destruction of virus by innate immune proteins of the collectin family
Small plaque mutants of Beij/89 emerge following intranasal infection of mice In previous studies, we have used viruses of the H3 subtype (1968-1992) to examine the relationship between the degree of glycosylation of the HA glycoprotein, the sensitivity to the antiviral activities of collectins and the ability of a particular virus strain to grow in mouse lung [8]
Clearance of L virus, but not S or Mo viruses, from mice by the innate immune system C-type lectins, including mannose-binding lectin (MBL) and SP-D, play an important role in innate host defence and we have shown that S and Mo viruses are markedly more resistant to neutralization by rat SP-D and murine MBL (Fig. 3)

Summary

Introduction

Glycosylation on the globular head of the hemagglutinin (HA) protein of influenza virus acts as an important target for recognition and destruction of virus by innate immune proteins of the collectin family. Mammalian serum and respiratory fluids contain a complex mixture of proteins, some of which can inhibit hemagglutination activity or neutralize the infectivity of influenza viruses. Three classes of such inhibitors have been reported. For influenza viruses of the H3 subtype, the oligosaccharide side-chain at the tip of the HA spike was shown to be critical in determining the sensitivity of the virus to the antiviral activities of collectins in mouse and bovine serum [1]. Mutant viruses selected in the presence of bovine serum (a rich source of conglutinin) were shown to have lost this glycosylation site and were resistant to hemagglutination inhibition by β inhibitors [1]

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