A very powerful and specialised immune system exists in the gut. It is thought that around 80% of our body's immune cells reside here. This may seem exaggerated, but we need to understand why. The digestive tract is one of the barriers that separate our body from the outside world, along with the lungs, skin and other mucous membranes such as the oral and vaginal mucosa. Of all these barriers, it is the one with the largest surface area. Classically, it has been said to be about 250 to 300 metres in length.2 exchange surface, i.e. the size of a tennis court. However, recent publications speak of a smaller, but still very important, surface area of about 32 m2The equivalent of half a badminton court. We can therefore consider it to be the main "customs house" of our body. Every day, millions of substances (food molecules, micro-organisms, toxins, etc.) reach the intestine, and this organ has to decide for each of them whether to let them pass into the body or not. To do this, in addition to the function of the enterocytes (the cells that line the intestinal wall), it is assisted by the immune system, which acts as a customs police officer and asks for a "passport" for each of these substances.
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