Although IRE1 and ATF6 activation are typical of RSV infection, in PERK-deficient mice RSV infection results in lower counts of myeloid and activated CD4 and CD8 T cells, mucous production, and cytokine responses . This suggests PERK activation is associated with increased immune recognition in RSV infection. In addition to the role of the UPR in RSV replication and immune replication, ER stress responses also induce mesenchymal transition in human small airway epithelial cells, a hallmark of pulmonary fibrosis, highlighting the importance of the UPR for disease pathogenesis in RSV infection .