Bacterial-modulated host immunity and stem cell activation for gut homeostasis.

Although it is widely accepted that dynamic cross-talk between gut epithelia and microorganisms must occur to achieve gut homeostasis, the critical mechanisms by which gut-microbe interactions are regulated remain uncertain. In this issue of Genes & Development, Buchon and colleagues (pp. 2333-2344) revealed that the reaction of the gut to microorganisms is not restricted to activating immune systems, but extends to integrated responses essential for gut tissue homeostasis, including self-renewal and the differentiation of stem cells. Further investigation of the connection between immune response and stem cell regulation at the molecular level in the microbe-laden mucosal epithelia will accelerate our understanding of the regulatory mechanisms of gut homeostasis and of the pathogenesis of diseases such as chronic inflammatory diseases and colorectal cancers.