Glycosylation of HA and NA plays a major modulatory role in UPR induction. A lack of glycosylation, specifically within the globular head domain of HA, is directly associated with an increased UPR response. Stepwise addition of glycosylation sites to the globular head of HA in A/X-31 (H3N2) reduces airway inflammation and pathology in infected mice, caused by reduced ER stress gene expression . Similar observations have also been made for avian H5N1 IAV infection, where removal of glycans from the HA globular head increases UPR activation .