Recombinant HA proteins from human and avian influenza viruses bind <i>ex vivo</i> human tracheal epithelium in a sialic acid dependant manner.

<p>Histological sections of <i>ex vivo</i> human tracheal epithelium were probed with human H3 (A), avian H5 (B) or H5 mutants, (C) G228S, and (D) Q226L/G228S, with and without prior neuraminidase (NA) treatment. Slides were pre-incubated for 3 hours with 5 units of recombinant NA cloned from <i>Salmonella typhimurium</i> LT2 (NEBL) that shows a 260-fold preference for α2-3 over α2-6 linked SA or with 15 units of recombinant NA cloned from <i>Clostridium perfringens</i> (NEBL) that cleaves both α2-3 and α2-6 SA linkages. HA was detected as before using anti-human Fc (red) and anti-acetylated α-tubulin was used to indicate ciliated cells (green). White arrows indicate cells that exhibit HA binding. Open arrowheads indicate ciliated cells with HA binding; solid arrowheads indicate non-ciliated cells with HA binding.</p

Expression of recombinant HA-Fc proteins.

<p>(A) Recombinant baculoviruses encoding HA from a recent H3N2 human virus, (A/Panama/2007/99) or from a highly pathogenic H5N1 avian influenza virus (A/Vietnam/1194/04), were generated as previously described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007836#pone.0007836-Barclay1" target="_blank">[32]</a>. The HA proteins were expressed as soluble proteins secreted from infected <i>Sf9</i> cells by removing the HA transmembrane (TM) and cytoplasmic tail (CT) portions of the protein and replacing the HA signal peptide (SP) with the signal peptide of the baculovirus envelope protein gp64 (SP gp64). The HA proteins were tagged at the C-terminus by a human Fc (HuFc) and hexa-histidine (His6) tags. (B) All recombinant HA proteins were expressed at similar levels as determined by western blot analysis using an anti-human Fc antibody.</p

Recombinant HA proteins bind to human airway epithelial (HAE) cultures.

<p>(A) Morphological features of HAE cultures visualized by H&E counterstain. Cell types present include ciliated cells (C), mucin-secreting cells (MS) and non-ciliated cells (NC). HAE cultures were probed with recombinant HA proteins from human H3 (A/Panama/2007/99) (B,C) or avian H5 (A/Vietnam/1194/04) (D,E) viruses either directly to the apical surface of fixed cultures (B,D) or to histological sections (C,E). Receptor binding site mutants of H5 HA (F–J) were also analysed for binding to histological sections. Ciliated cells were identified using anti acetylated α-tubulin (green) and the HA-Fc proteins were visualized with anti human-Fc (red). Images are representative of cell-type binding seen in experiments. (K) Numbers and types of epithelial cells bound by HA proteins were quantified by counting 100–200 total cells from five different fields of view.</p

Nucleotide sequence changes required to switch H5 HA receptor binding preference.

<p>(A) Analysis of codon usage by 1374 H5 influenza viruses indicates that codon 228 is GGA in 93% strains and GGG in 7%. The table illustrates transversions and transitions by which coding capacity at this residue might change from glycine to serine. The ability of the two intermediate mutants 228R (B) and 228A (E) recombinant HA proteins to bind synthetic receptor ligands 3SLN (avian receptor) and 6SLN (human receptor) in a solid phase assay was assessed. The binding phenotype on HAE (C,F) or human tracheal epithelium (D,G) by recombinant proteins with each amino acid sequence changed at residue 228 are shown (C,D) G228R and (F,G) G228A.</p

Binding of recombinant HA proteins to synthetic receptor ligands 3SLN (avian receptor) and 6SLN (human receptor) in a solid phase assay.

<p>(A) Synthetic glycans on polyacrylamide linkers were immobilized on 96-well plates following UV treatment. Recombinant HA proteins were preformed into higher order complexes by incubation with anti-human Fc before incubation on the plate and detection with goat anti-human IgG conjugated to horse-radish peroxidise (HRP). (B) Recombinant HA-Fc proteins were adsorbed on 96 well plates coated with anti-human Fc antibody. Synthetic glycans on polyacrylamide linkers with biotin tags (6SLN and 3SL) were incubated on the plates and detected with Streptavidin – HRP conjugate.</p

Phylogenetic tree of NA sequences of the A(H1N1)pdm09 viruses for the period 2013.

<p>Sequences from Yucatan are indicated in blue, from other regions of Mexico in red and worldwide in black. Additional amino acid changes at the node are also indicated.</p

Amino acid changes and frequency of occurrence in the hemagglutinin (HA) protein of the influenza A(H1N1)pdm09 viruses isolated in Yucatan.

<p>Frequencies of detection for each mutation are also indicated for sequences from other regions of Mexico (non-Yucatan) and worldwide for the period 2012–2013. Percentages were calculated based on the total number of sequences analysed in this study (<i>n</i>). Empty cells indicate values = 0.</p

Temporal occurrence of genetic variants in Yucatan.

<p>Viruses from Yucatan with changes in HA and NA were distributed in time from epidemiological week 23 to 38. The bars represent the total number of influenza cases reported by the Regional Laboratory. The clear section indicates the number of confirmed cases of influenza A(H1N1)pdm09 and the grey section indicates the number of influenza A(H1N1)pdm09 viruses with genetic changes in HA and NA (HA–A141T / HA–S162I / NA–N341S / NA–L206S). The black section corresponds to the number of samples negative to influenza A(H1N1)pdm09 virus.</p

Schematic representation of the HA molecule of the A(H1N1)pdm09 virus.

<p>HA molecules were modelled using as template the crystal structure of A 2009 H1N1 virus hemagglutinin from A/California/04/2009 (PDB 3LZG). Molecules were generated under flusurver structural model database (<a href="http://flusurver.bii.a-star.edu.sg/" target="_blank">http://flusurver.bii.a-star.edu.sg</a>). Protein sequences were blast against A/California/07/2009 to identify differences on amino acid composition. Right side HA molecule was modelled based on the strain A/Yucatan/116/2013 to indicate localization of the amino acid change S162I (red oval). The HA molecule in the middle represents the amino acidic composition of the strain A/Yucatan/81/2013 indicating the position of the mutation A141T (blue oval). Mutations at residues V234I, K283E and E499K (HA2) placed these viruses in clade 6C. Left side molecule corresponds to the HA protein sequence of the strain A/Yucatan/18/2012.</p

Amino acid changes and frequency of detection in the Neuraminidase (NA) protein of the influenza A(H1N1)pdm09 virus isolated from Yucatan, Mexico (non-Yucatan) and other regions of the world for the period 2012–2013.

<p>Percentages were calculated based on the total number of sequences analysed in this study (<i>n</i>). Empty cells indicate values = 0.</p