For example, caspase 8 or Fadd deletion gradually induces ileitis in a non-inducible version of intestinal epithelium-specific gene deletion system,31, 32 whereas the same deletion system causes severe tissue damage and neonatal lethality when Tak1 is deleted.13 This suggests that additional mechanisms are involved in the ROS-induced tissue injury by Tak1 deletion. Here, CASP8 is linked to Crohn ileitis.