NUTRITION AND THE IMMUNE-SYSTEM OF THE GUT

Studies suggest that the development and expression of the regional im mune system in the gastrointestinal (GT) tract is relatively independe nt of systemic immunity. This is reflected in significant differences in functional response of T cells and B cells and affects cytokine pat terns and activation pathways when regional immunity is compared to sy stemic immunity. Nutrients have fundamental and regulatory influences on the immune response of the GI tract and, therefore, on host defense . In addition to the effect of nutrition during development,the local impact of different dietary and antigenic elements on the regional imm une system contributes to potential diversion of the two systems throu ghout Life. The route of exposure during antigenic contact is known to affect host immune response, whether it be a normal process, happenin g in the context of normal environmental encounter with nonpathogenic microbes or planned immunization, or occurring as a result of resoluti on of a potentially pathologic process i.e., an infectious encounter. Interactions at the local level profoundly influence systemic immune r esponse, in part because of intrinsic differences in these systems, an d also because of different requirements for optimal function. Althoug h inflammatory processes are central to host defense in the periphery, the protective blocking action of the secretory immunoglobulin A immu ne response is crucial to local host defense, and, therefore, to the i ntegrity of GI tract immune function. For these reasons, interaction w ith normal bacteria of the GI tract may be seen as the model of how th e system has evolved and provide clues to the restoration of balance i n the immunocompromised host. Reduction of normal commensal bacteria i n the context of infection or after antibiotic treatment may interfere with nutrient availability and impair beneficial stimulation of GI im mune response. This impairment may be associated with continued coloni zation with opportunistic microbes and inflammatory immune response th at could lead.to malabsorption and malnutrition. Study of the impact o f nutrient imbalance on the function of the GI tract has profound impl ications for clinical medicine and may in the future lead to the ratio nal design of preventive approaches to support immune response and hos t defense. Nutrition 1998;14:573-579. (C) Elsevier Science Inc. 1998.