Immunological functions of the gut in relation to nutritional state and mode of delivery of nutrients.

Gut immunology encompasses the need for local cellular immunity and prevention of systemic immune reactions to dietary antigens. The relation between these factors and nutritional state or the presence of luminal nutrients in the enterally fed and parenterally fed is poorly defined. Most studies suggest that acquisition of lymphoid characteristics is independent of luminal nutrition and its responsiveness is related more to bacterial challenge. Protein malnutrition may impair immune responsiveness by moderating the generalised inflammatory response, rather than through reduced T cell function and IgA synthesis. Predisposition to the development of gut hypersensitivity can be induced in animals by longterm feeding with elemental diets. The efficient absorption of these diets reduces the caecal microflora burden and together with changed gastric acid secretion and small bowel motility, may affect the composition of the gut flora. Changed luminal nutrition, enhanced tissue damage and inappropriately increased mucosal T cell function may thus be related. The clinical effectiveness, however, of elemental diets in treatment of unresponsive coeliac disease is reassuring. To investigate intestinal immunity in humans, an approach based on whole gut lavage has been developed. Data from this non-invasive human technique will prove to be a useful means of assessing the effects of nutritional rehabilitation on mucosal immunity.