Association of Increased Receptor-Binding Avidity of Influenza A(H9N2) Viruses with Escape from Antibody-Based Immunity and Enhanced Zoonotic Potential

Abstract

We characterized 55 influenza A(H9N2) viruses isolated in Pakistan during 2014–2016 and found that the hemagglutinin gene is of the G1 lineage and that internal genes have differentiated into a variety of novel genotypes. Some isolates had up to 4-fold reduction in hemagglutination inhibition titers compared with older viruses. Viruses with hemagglutinin A180T/V substitutions conveyed this antigenic diversity and also caused up to 3,500-fold greater binding to avian-like and >20-fold greater binding to human-like sialic acid receptor analogs. This enhanced binding avidity led to reduced virus replication in primary and continuous cell culture. We confirmed that altered receptor-binding avidity of H9N2 viruses, including enhanced binding to human-like receptors, results in antigenic variation in avian influenza viruses. Consequently, current vaccine formulations might not induce adequate protective immunity in poultry, and emergence of isolates with marked avidity for human-like receptors increases the zoonotic risk.

Genetic determinants of receptor-binding preference and zoonotic potential of H9N2 avian influenza viruses

“…Each of these positions are in the 190-helix, proximal to the RBS. Position 190 has already been shown to play a role in receptor-binding in this and other studies [18, 20], and we see the effect of 196 and 198 on receptor-binding preference in this study (Figure 4E,F), further validating this modelling approach (Table 3).…”

“…Both 3SLN(6su) and 3SLN are analogues for avian-like receptors while 6SLN is an analogue for human-like receptors. The virus A/chicken/Pakistan/UDL-01/2008 (UDL1/08) displays high binding avidity to 3SLN(6su), but not 3SLN (avian-like), with residual binding to the human-like receptor 6SLN (Figure 1A), similar to the majority of contemporary H9N2 viruses [20–22]. The virus A/chicken/Emirates/R66/2002 (Em/R66) binds to both 3SLN(6su) and 3SLN but has no detectable binding to 6SLN (Figure 1B), similar to conventional avian-adapted H5N1 and H7 viruses [21, 23].…”

“…In addition to showing preference for different receptors, influenza viruses vary in receptor-binding avidity. In several previous studies we have inferred that escape mutants with the largest impact of polyclonal antisera binding may be driven by avidity effects [20, 25, 28]. To further investigate the genetic basis of variation in receptor-binding avidity we constructed a library of mutants in the UDL1/08 background and assessed their receptor-binding phenotypes.…”

“…Several molecular determinants have been shown to influence the receptor-binding profile of H9N2 viruses, including position 226 (H3 HA numbering used throughout; position 216 in mature polypeptide H9 numbering) – in one strain, Q226L alone could facilitate greater replication of an H9N2 isolate in human epithelial airway cells [17]. Furthermore, substitutions at positions 155, 190 and 227 (145, 180 and 217 in H9 numbering) have also been shown to play a role in receptor-binding preference in some H9N2 viruses [13, 18–20]. However, understanding of H9N2 receptor-binding preference remains piecemeal, with no studies having systematically looked at the roles of multiple residues, or residue combinations, in the variation in H9N2 receptor preference.…”

Poultry trading behaviours in Vietnamese live bird markets as risk factors for avian influenza infection in chickens

“…However, amino acid diversity at residue 180 of the HA protein could play an important role in zoonotic potential. Previously, we and others have shown that H9N2 viruses carrying the A180T/V substitution gain the ability to bind to human‐like receptor analogues (Sealy et al, ; Teng et al, ; Yang et al, ). The A180T/V substitution also enhances binding avidity towards avian‐like receptor analogues, which can attenuate virus replication in vitro ; however, the impact of this mutation in conjunction with a NA stalk deletion is currently unknown.…”