A Single Amino Acid in the HA of pH1N1 2009 Influenza Virus Affects Cell Tropism in Human Airway Epithelium, but Not Transmission in Ferrets

Abstract

The first pandemic of the 21st century, pandemic H1N1 2009 (pH1N1 2009), emerged from a swine-origin source. Although human infections with swine-origin influenza have been reported previously, none went on to cause a pandemic or indeed any sustained human transmission. In previous pandemics, specific residues in the receptor binding site of the haemagglutinin (HA) protein of influenza have been associated with the ability of the virus to transmit between humans. In the present study we investigated the effect of residue 227 in HA on cell tropism and transmission of pH1N1 2009. In pH1N1 2009 and recent seasonal H1N1 viruses this residue is glutamic acid, whereas in swine influenza it is alanine. Using human airway epithelium, we show a differential cell tropism of pH1N1 2009 compared to pH1N1 2009 E227A and swine influenza suggesting this residue may alter the sialic acid conformer binding preference of the HA. Furthermore, both pH1N1 2009 E227A and swine influenza multi-cycle viral growth was found to be attenuated in comparison to pH1N1 2009 in human airway epithelium. However this altered tropism and viral growth in human airway epithelium did not abrogate respiratory droplet transmission of pH1N1 2009 E227A in ferrets. Thus, acquisition of E at residue 227 was not solely responsible for the ability of pH1N1 2009 to transmit between humans.

The Short Stalk Length of Highly Pathogenic Avian Influenza H5N1 Virus Neuraminidase Limits Transmission of Pandemic H1N1 Virus in Ferrets

“…Previously, we showed that recombinant E195 virus generated by reverse genetics transmitted to 3/3 ferrets via respiratory droplets (63). Others have reported a rate of 66% to 100% for respiratory droplet transmission using similar prototypic pandemic viruses in ferrets (47,(67)(68)(69)(70).…”

“…Indeed, initial reports showed that the 2009 pandemic H1 HA bound ␣2,6 SA strongly while retaining some residual binding to ␣2, . The six internal genes from the pandemic virus were also well suited for transmission studies, as they had been proven to support RD transmission in the ferret model (63,(68)(69)(70).…”

“…Animal studies were performed as described previously (48,63). Female ferrets (20 to 24 weeks old) weighing 650 to 1,100 g were obtained from a designated supplier.…”

Investigation of Influenza Virus Polymerase Activity in Pig Cells

“…Digested PCR products were introduced into pHPMO1-Firefly between XhoI and HindIII sites, replacing the human RNA polymerase I promoter sequence and generating pSPOM1-Firefly, pSPOM2-Firefly, and pSPOM3-Firefly, respectively. The human polymerase I promoter sequence present in pHPOM1-Firefly was also replaced by the avian polymerase I promoter (87) (92). Mutagenesis of PB2 genes in pCAGGS was performed by overlapping PCR.…”

Substitutions T200A and E227A in the Hemagglutinin of Pandemic 2009 Influenza A Virus Increase Lethality but Decrease Transmission

“…Residues 200 and 227 were recently reported to be responsible for the difference in the binding affinity for the sialic acid receptors between the HAs of swine and A(H1N1)pdm09 influenza virus isolates (6). Furthermore, recent publications have shed light on the role of HA residue 227 in cell tropism and transmission, confirming its role in sialic acid recognition (7). In swine influenza virus isolates, amino acids 200 and 227 of the HA are alanines (A), while in some A(H1N1)pdm09 viruses, residue 200 is a threonine (T) and 227 is invariably a glutamic acid (E).…”