Impact of Mutations in the Hemagglutinin of H10N7 Viruses Isolated from Seals on Virus Replication in Avian and Human Cells

Abstract

Wild birds are the reservoir for low-pathogenic avian influenza viruses, which are frequently transmitted to domestic birds and occasionally to mammals. In 2014, an H10N7 virus caused severe mortality in harbor seals in northeastern Europe. Although the hemagglutinin (HA) of this virus was closely related to H10 of avian H10N4 virus, it possessed unique nonsynonymous mutations, particularly in the HA1 subunit in or adjacent to the receptor binding domain and proteolytic cleavage site. Here, the impact of these mutations on virus replication was studied in vitro. Using reverse genetics, an avian H10N4 virus was cloned, and nine recombinant viruses carrying one of eight unique mutations or the complete HA from the seal virus were rescued. Receptor binding affinity, replication in avian and mammalian cell cultures, cell-to-cell spread, and HA cleavability of these recombinant viruses were studied. Results show that wild-type recombinant H10N4 virus has high affinity to avian-type sialic acid receptors and no affinity to mammalian-type receptors. The H10N7 virus exhibits dual receptor binding affinity. Interestingly, Q220L (H10 numbering) in the rim of the receptor binding pocket increased the affinity of the H10N4 virus to mammal-type receptors and completely abolished the affinity to avian-type receptors. No remarkable differences in cell-to-cell spread or HA cleavability were observed. All viruses, including the wild-type H10N7 virus, replicated at higher levels in chicken cells than in human cells. These results indicate that H10N7 acquired adaptive mutations (e.g., Q220L) to enhance replication in mammals and retained replication efficiency in the original avian host.

Aerosol Transmission of Gull-Origin Iceland Subtype H10N7 Influenza A Virus in Ferrets

“…S2). These results are consistent with other studies that also used biolayer interferometry analyses to determine binding affinity for avian-origin H10 viruses (27), and they are consistent with results for a study, using turkey erythrocytes expressing both SA␣2,3GA and SA␣2,6GA or only SA␣2,6GA receptors, of seal-origin H10 IAVs that showed significant binding ability to SA␣2,3GA and SA␣2,6GA (19). However, our results showed that the binding affinities to SA␣2,6GA could vary to some extent, depending on the virus strain, but sequence analyses for the reported HA receptor binding sites were mostly conserved among the isolates (Table S1).…”

“…However, our results showed that the binding affinities to SA␣2,6GA could vary to some extent, depending on the virus strain, but sequence analyses for the reported HA receptor binding sites were mostly conserved among the isolates (Table S1). Of note, a mutation, Q220L (corresponding to 226 in H3 numbering), which was reported to have been acquired in the 220 loop of the HA receptor binding site during the subtype H10N7 IAV outbreaks among European seals, increased replication ability in mammalian cells (A549 cells) and retained replication efficiency in the avian cells (chicken embryo kidney primary cells) (19). This mutation seems to increase the binding affinity of avian-origin H10N7 IAV to SA␣2,6GA (19).…”

“…Of note, a mutation, Q220L (corresponding to 226 in H3 numbering), which was reported to have been acquired in the 220 loop of the HA receptor binding site during the subtype H10N7 IAV outbreaks among European seals, increased replication ability in mammalian cells (A549 cells) and retained replication efficiency in the avian cells (chicken embryo kidney primary cells) (19). This mutation seems to increase the binding affinity of avian-origin H10N7 IAV to SA␣2,6GA (19). Mutations Q226L and G228S (in position H3) can increase the ability of avian IAV to infect humans (24,(28)(29)(30)(31)(32)(33).…”

“…The Iceland gull-origin H10N7 isolates and other wild bird-origin H10 isolates had amino acid 222Q (corresponding to 226 at H3), which is identical to those at the HA sequences of two H10 isolates from the 2014 outbreak among European seals (Table S1). However, the other four seal isolates from the 2014 outbreak among European seals have amino acid 222L instead (19) (Table S1). All H10 isolates had amino acid 224G (corresponding to 228 at H3) (Table S1).…”

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

“…Human infections with H10N7 were occasionally reported from Egypt (2004) and Australia (2010) [ 143 ]. Recent H10N7 AIV-associated natural outbreaks in harbor seals and experimental infection of ferrets emphasize that H10N7 may possess a zoonotic potential [ 144 , 145 , 146 ].…”