Biological characteristics of avian H1N1 and swine H3N2 influenza A viruses (IAVs).

(A) Receptor binding properties of avian H1N1 (left panel) and swine H3N2 (right panel) IAVs. Biolayer interferometry data for the binding of avian H1N1 and swine H3N2 IAVs to avian (3ʹSLN) and human (6ʹSLN) receptor analogues. Streptavidin-coated biosensors were immobilized with biotinylated glycans at different levels. Sugar loading–dependent binding signals were captured in the association step and normalized to the same background. Binding curves were fitted by using the binding-saturation method in GraphPad Prism version 7 (https://www.graphpad.com/scientific-software/prism/). Horizontal dashed line indicates half of the fractional saturation (f = 0.5), and vertical dashed line indicates relative sugar loading (RSL0.5) at f = 0.5; the higher the RSL0.5, the smaller the binding affinity. (B) Infectivity of avian H1N1 IAV in feral swine. The animals in treatment group were intranasally inoculated with 106 EID50 of avian H1N1 IAV, and animals in the control group were intranasally inoculated with 1 mL of PBS. On indicated days, nasal wash fluids and respiratory tract tissues were collected from each animal for viral titration in 10-day-old specific pathogen–free eggs. Cumulative infectivity calculations were based on titration results.