NOS2 and digestive system infectious disorder: While these findings suggest that IEC-intrinsic MyD88 activation is sufficient to trigger the expression of several important epithelium-derived factors, we found that the expression of other molecules implicated in epithelial defense upon intestinal infection with Citrobacter, such as inducible nitric oxide synthase 2 (Nos2), reactive oxygen species (ROS)-generating enzyme dual oxidase 2 (Duox2) and its maturation factor Duoxa2 [48], was independent of MyD88 signaling in IEC (Fig 6B).