Microbiology. How to get along--friendly microbes in a hostile world.

Microbiologists have long been puzzled by the finding that the gut mucosa does not respond to the myriad varieties of bacteria that normally reside in the gut. As Xavier and Podolsky explain in their Perspective, this may be because bacteria that are indigenous to the gut have learned ways to switch off pathways in gut epithelial cells that lead to switching on of genes involved in inflammation (Neish et al.).