Influenza viruses initiate
infection via specific interactions of
hemagglutinin (HA) with host cell surface
sialic acid-containing
glycans. Antigenic drift has resulted in HA amino acid sequence changes that affect binding properties for
sialic acids. Further, viral propagation in eggs and cell culture for
vaccine production can yield variants with mutations that affect the conformation and affinity of HA for
sialic acids. Therefore,
influenza vaccine researchers and manufacturers need robust analytical methods to assess directly the ability of
vaccine candidates to bind to their specific
sialic acid ligand. We developed a surface plasmon resonance method that uses an extended, biantennary
glycan terminating with α-2,6 linked
sialic acids to bind
influenza HA and assess this interaction. Recombinant HA (rHA) from both
influenza A and B viruses isolated from 1999 to 2017 strongly and specifically bind this
sialic acid ligand, suggesting the binding ability of divergent HA for this
ligand is resistant to antigenic drift. Importantly, the method can differentiate between wild type and mutant rHA for which binding to this sialylated
glycan and red blood cells in hemagglutination assays is compromised. We believe this method can be a powerful tool to screen
influenza A and B
vaccine candidates and final
vaccine preparations for their functional ability to bind
sialic acids, which allows manufacturers to identify preparations in which mutations that affect
sialic acid binding have arisen during propagation. Evaluation of
vaccine rHA
antigen integrity by confirmation of the receptor binding site functionality is a prudent cautionary step to assure the antigenic quality of seasonal
influenza vaccines.