XBP1 and infection: Despite the evident activation of IRE1 during the lytic cycle of KSHV, we observed a minimal XBP1 mRNA splicing (XBP1s) and XBP1s protein, a direct product of IRE1 activity, indicating disruption of canonical IRE1 signaling during lytic infection in iSLK.219 cells (Fig 2A–2C).