ISG15 and hepatitis A virus infection: As shown in S2B–S2D Fig, non-treated HBs-Tg mice showed higher baseline expression of XBP1s, phos-PERK, CHOP and ISGs (ISG15 and OAS2) in association with mild liver injury (sALT 100–300 U/L) than non-treated WT mice suggesting that HBsAg accumulation triggered UPR activation in association with mild spontaneous hepatitis.