The gut microbiota shapes intestinal immune responses during health and disease

Abstract: Immunological dysregulation is the cause of many non-infectious human diseases such as autoimmunity, allergy and cancer. The gastrointestinal tract is the primary site of interaction between the host immune system and microorganisms, both symbiotic and pathogenic. In this Review the authors discuss findings indicating that developmental aspects of the adaptive immune system are influenced by bacterial colonisation of the gut. They also highlight the molecular pathways that mediate host-symbiont interactions that regulate proper immune function. Finally, they present recent evidence to support that disturbances in the bacterial microbiota result in dysregulation of adaptive immune cells, and this may underlie disorders such as inflammatory bowel disease. This raises the possibility that the mammalian immune system, which seems to be designed to control microorganisms, is in fact controlled by microorganisms.

The authors conclude: On the basis of clinical, epidemiological and immunological evidence, it seems possible that changes in the intestinal microbiota may be an essential factor in the incidence of numerous inflammatory disorders. It is conceivable that the absence of beneficial microorganisms (owing to dysbiosis) that promote the appropriate development of the immune system leads to the induction of inflammatory responses and immune-mediated disease. The recent identification of symbiotic bacteria with potent anti-inflammatory properties, and their correlative absence during disease, suggests that certain aspects of human health may depend on the status of the microbiota. The medical and social reconsideration of the microbial world may have profound consequences for the health of our future generations.

Round JL, Mazmanian SK., The gut microbiota shapes intestinal immune responses during health and disease. Nat Rev Immunol. 2009 May;9(5):313-23. View Abstract