HA stabilization promotes replication and transmission of swine H1N1 gamma influenza viruses in ferrets

Abstract

Pandemic influenza A viruses can emerge from swine, an intermediate host that supports adaptation of human-preferred receptor-binding specificity by the hemagglutinin (HA) surface antigen. Other HA traits necessary for pandemic potential are poorly understood. For swine influenza viruses isolated in 2009–2016, gamma-clade viruses had less stable HA proteins (activation pH 5.5–5.9) than pandemic clade (pH 5.0–5.5). Gamma-clade viruses replicated to higher levels in mammalian cells than pandemic clade. In ferrets, a model for human adaptation, a relatively stable HA protein (pH 5.5–5.6) was necessary for efficient replication and airborne transmission. The overall airborne transmission frequency in ferrets for four isolates tested was 42%, and isolate G15 airborne transmitted 100% after selection of a variant with a stabilized HA. The results suggest swine influenza viruses containing both a stabilized HA and alpha-2,6 receptor binding in tandem pose greater pandemic risk. Increasing evidence supports adding HA stability to pre-pandemic risk assessment algorithms.

Cell Culture Adaptation of H3N2 Influenza Virus Impacts Acid Stability and Reduces Ferret Airborne Transmission

“…Consistent with this, we found that human seasonal viruses have an HA pH of fusion of 4.9-5.5 while swine H3N2 viruses have a pH of fusion >5.5. Previous work has shown a similar phenotype with human and gamma clade swine H1N1 viruses [34]. Additionally, gamma clade swine H1 viruses replicate to higher titers in MDCK cells [34], which is consistent with our observations of rPerth mutant.…”

“…As expected, the biological A/Perth/16/2009 had the same pH of inactivation (EC50 = 5.57) as the rPerth WT while the seasonal human viruses tested range in pH from 5.5 to 4.9 (Figure 3B). These data are consistent with human seasonal H1N1 viruses, which have been shown to have a pH of inactivation <5.5 [34]. The two H3N2 swine viruses tested had EC50 values that were higher (EC50 = 5.88 and 5.68) and more similar to rPerth mutant (Figure 3B).…”

Human Interferon Inducible Transmembrane Protein 3 (IFITM3) Inhibits Influenza Virus A Replication and Inflammation by Interacting with ABHD16A

“…Everitt et al found that the single nucleotide polymorphism in the IFITM3 allele is related to the susceptibility to IAV [12,13]. In addition, Gerlach et al reported that the toxicity and spread of IAV are also related to the pH of the cell membrane and that the stable expression of IFITM2 and IFITM3 proteins can effectively reduce virus replication [14,15]. In this study, influenza virus replication was inhibited from HEK293 cells overexpressing hlFITM3 protein.…”

Human Interferon Inducible Transmembrane Protein 3 (IFITM3) Inhibits Influenza Virus A Replication and Inflammation by Interacting with ABHD16A

“…Everitt et al found that the single nucleotide polymorphism in the IFITM3 allele is related to the susceptibility of IAV [12,13]. In addition, Gerlach et al reported that the toxicity and spread of IAV are also related to the pH of the cell membrane, and that the stable expression of IFITM2 and IFITM3 proteins can effectively reduce virus replication [14,15]. In this study, in uenza virus replication was inhibited in HEK293 cells overexpressing hlFITM3 protein.…”