ABSTRACT
The main function of the immune system is to protect the body against harmful agents or pathogens, therefore, the immune cells are distributed throughout the body mainly at the mucosal sites, places that are continuously exposed to antigens from the external environment. However, one of the unresolved mysteries is how immune cells can distinguish between self and non-self antigens, especially between pathogenic and non-pathogenic microorganisms. Achieving this objective in the complex ecosystem
made up of three main components that are permanently in contact and interact with one another in a perfect balance: host cells, nutrients and the commensal microbiota.
