XBP1 and infection: Although we focused on the IRE1α–XBP1 branch of the unfolded protein response, Protein kinase RNA (PKR)-like ER kinase (PERK) and activating transcription factor-6 (ATF6) have also been found to be activated during infection with SARS-CoV-2, but interestingly not HCoV-OC43 (16, 19, 37, 38).