Two major surface glycoproteins are displayed by IAV, the haemagglutinin (HA) and neuraminidase (NA) proteins. HA is the more abundant glycoprotein; current influenza vaccines are designed to elicit antibody responses towards HA epitopes from strains of concern. HA binds to terminal sialic acid residues on the cell surface for attachment and has a further role in membrane fusion. Expression of HA in HEK293T cells is sufficient to induce the IRE1 signalling cascade . Although HA is the principal factor inducing the UPR in IAV infection , NA is also associated with induction of all three sensors in human A549 cells . The variable affinity of NA variants for BiP is a strong determinant of UPR activation in different IAV strains .