The gastrointestinal ecosystem: a precarious alliance among epithelium, immunity and microbiota

The gastrointestinal (GI) tract is a complex ecosystem generated by the all iance of GI epithelium, immune cells and resident microbiota. The three com ponents of the GI ecosystem have co-evolved such that each relies on the pr esence of the other two components to achieve its normal function and activ ity. Experimental systems such as cell culture, germ-free animal models and intestinal isografts have demonstrated that each member of the GI ecosyste m can follow a predetermined developmental pathway, even if isolated from t he other components of the ecosystem. However, the presence of all three co mponents is required for full physiological function. Genetic or functional alterations of any one component of this ecosystem can result in a broken alliance and subsequent GI pathology. A more detailed understanding of the interactions among microbiota, GI epithelium and the immune system should p rovide insight into multiple human disease states.