Receptor binding specificity of recent human H3N2 influenza viruses

Kshama Kumari,Upma Gulati,Richard D Cummings,Shelly Gulati,Gillian M Air,David F Smith

doi:10.1186/1743-422x-4-42

Kshama Kumari, Upma Gulati + Show 4 more

Open Access

https://doi.org/10.1186/1743-422x-4-42

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Abstract

BackgroundHuman influenza viruses are known to bind to sialic acid linked α2-6 to galactose, but the binding specificity beyond that linkage has not been systematically examined. H3N2 human influenza isolates lost binding to chicken red cells in the 1990s but viruses isolated since 2003 have re-acquired the ability to agglutinate chicken erythrocytes. We have investigated specificity of binding, changes in hemagglutinin sequence of the recent viruses and the role of sialic acid in productive infection.ResultsViruses that agglutinate, or do not agglutinate, chicken red cells show identical binding to a Glycan Array of 264 oligosaccharides, binding exclusively to a subset of α2-6-sialylsaccharides. We identified an amino acid change in hemagglutinin that seemed to correlate with chicken red cell binding but when tested by mutagenesis there was no effect. Recombinant hemagglutinins expressed on Sf-9 cells bound chicken red cells but the released recombinant baculoviruses agglutinated only human red cells. Similarly, an isolate that does not agglutinate chicken red cells show hemadsorption of chicken red cells to infected MDCK cells. We suggest that binding of chicken red cells to cell surface hemagglutinin but not to virions is due to a more favorable hemagglutinin density on the cell surface. We investigated whether a virus specific for α2-6 sialyloligosaccharides shows differential entry into cells that have varying proportions of α2-6 and α2-3 sialic acids, including human A549 and HeLa cells with high levels of α2-6 sialic acid, and CHO cells that have only α2-3 sialic acid. We found that the virus enters all cell types tested and synthesizes viral nucleoprotein, localized in the nucleus, and hemagglutinin, transported to the cell surface, but infectious progeny viruses were released only from MDCK cells.ConclusionAgglutination of chicken red cells does not correlate with altered binding to any oligosaccharide on the Glycan Array, and may result from increased avidity due to density of hemagglutinin and not increased affinity. Absence of α2-6 sialic acid does not protect a cell from influenza infection and the presence of high levels of α2-6-sialic acids on a cell surface does not guarantee productive replication of a virus with α2-6 receptor specificity.

Highlights

Human influenza viruses are known to bind to sialic acid linked α2-6 to galactose, but the binding specificity beyond that linkage has not been systematically examined
We previously found that influenza viruses with HA from A/NWS/33 can bind to α2-8 linked sialic acids [11], raising the possibility of other forms of sialic acid receptor in human influenza infection
We demonstrate that the presence of α2-6 sialic acid on a cell surface has little to do with its ability to be productively infected by human influenza viruses

Summary

Introduction

Human influenza viruses are known to bind to sialic acid linked α2-6 to galactose, but the binding specificity beyond that linkage has not been systematically examined. We have investigated specificity of binding, changes in hemagglutinin sequence of the recent viruses and the role of sialic acid in productive infection. We previously found that influenza viruses with HA from A/NWS/33 can bind to α2-8 linked sialic acids [11], raising the possibility of other forms of sialic acid receptor in human influenza infection. A solid phase assay with multivalent sialylsaccharides attached to a polyacrylamide backbone showed that human isolates from the beginning of the H2N2 pandemic in 1957 and the 1968 H3N2 pandemic had fourfold higher binding affinity to 6'sialyllactosamine than avian viruses [12]. It was suggested that a change in receptor binding specificity is a prerequisite for effective transmission and replication to cause a new human pandemic

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