ABSTRACT
The intestine is not only an important organ responsible for the digestion and absorption of foods but also a huge lymphatic tissue where more than half of the immune cells in our body are located and stand sentinel against a diverse set of harmful microorganisms and substances in the gut lumen. The mucosal immune system is totally different from the peripheral immune system, in that most intestinal lymphocytes are activated and can respond rapidly to the invasion of pathogenic microorganisms and at the same time their immune functions are controlled so as not to respond to non-harmful exogenous substances such as most food components and commensal bacteria. This dichotomy, the choice of either immune response or immunological tolerance, is the most peculiar property of the gut
immune system and it has been recently clarifi ed that a highly sophisticated regulatory system is established in the gut mucosa following the interaction with commensal gut microbiota.
