Professor of Medical Microbiology Graham Rook, from UCL (University College London), explains in this video the “surprisingly close” relationship between gut microbiota and the immune system. Prof. Rook, who was interviewed during the 2nd Gut Microbiota and Health Summit, compares the immune system to the brain, highlighting the need to educate it as it is “constantly learning”. At the same time, he suggests trying to imagine it as an army that must be properly controlled; in order not to have a deregulation of the immune system that could cause a reaction against natural and inoffensive environmental elements, leading to possible allergies or inflammatory diseases, among other conditions. Professor Rook also discusses the different elements that can affect or change gut microbiota, such as diet and environmental factors.