The gut: beyond immunology

The immune system is characterized by the ability to distinguish self from non-self. The intestinal immune system bears this latter property but, furthermore, it must discriminate among nutritious and beneficial substances from toxic or harmful ones. Considering that the gut has to be colonized by commensal bacteria participating in digestion as well as in the control of pathogen microorganisms, it is not surprising that mucosal surfaces are the largest and probably the most exquisitely specialized immune system's compartment. This means that not only innate and adaptive immunity are present, but further, particular structures, cells, and mechanisms such as physical barrriers, epithelia, Peyer's patches, M cells among others, which together are involved in the dynamic control of the homeostasis between gut and its flora. The present review deals with some popular conceptions about the digestive system with particular emphasis on the gut's immunology.