The gut microbiota has an essential role in stimulating the development and maintenance of the intestinal immune system – in fact, without the gut microbiome the human body would be unable to protect its health from being affected by all environmental pathogens that enter the body, e.g. through our daily food. The cellular and molecular mechanisms by which this is achieved are nicely illustrated in a video animation that Nature Immunology has released with the expertise of world-renown immunologist Tom MacDonald from London: