The Intestinal Immune System

The intestine contains the largest and busiest compartment of the immune system and employs a number of unique strategies to deal with constant challenge from pathogenic and harmless materials. As a result, the healthy intestinal mucosa contains vast numbers of effector lymphocytes and innate immune cells and it employs distinctive mechanisms for the uptake and presentation of antigens. These processes ensure that inflammatory reactions do not occur either in the intestine or in other parts of the body in response to antigens in food or the commensal microbiota. If these mechanisms break down, T cell–driven reactions against food protein or bacteria can lead to disorders like celiac disease and inflammatory bowel disease. The normal function of the intestinal immune system is dependent on the microbiota and influenced by the diet and a delicate balance between the host and its microbiota determines susceptibility to many other immunological and metabolic disorders.