Role of the gut microbiota in immunity and inflammatory disease

Key Points The gut microbiota is important for the development and functional maturation of the gut immune system, including gut-associated lymphoid tissue, T helper 17 cells, inducible regulatory T cells, IgA-producing B cells and innate lymphoid cells. The gut microbiota prevents exogenous pathogen infection through direct (for example, competition for common nutrients and niches) and indirect (for example, enhancement of host defence) mechanisms. Pathogens have evolved strategies to evade direct competition with the resident microbiota by eradicating bacterial competitors, localizing to niches that are distinct from those occupied by commensal bacteria and by using alternative resources. Potential pathobionts can accumulate in a host with inherent genetic susceptibility or environmental factors that lead to the development of inflammatory bowel disease. The gut microbiota regulates susceptibility to extra-intestinal autoimmune diseases, such as multiple sclerosis, type 1 diabetes, arthritis and allergy.