Abstract
A significant body of clinical literature demonstrates that enteral feeding significantly reduces the incidence of pneumonia compared with patients fed parenterally. An immunologic link between the gastrointestinal tract and respiratory tract is postulated through the common mucosal immune hypothesis. This hypothesis states that cells are sensitized within the Peyer's patches of the small intestine and are subsequently distributed to submucosal locations in both intestinal and extraintestinal sites. This system is exquisitely sensitive to route and type of nutrition. This review examines the laboratory data regarding cell numbers, cell phenotypes, cytokine profile, and immunologic function in both intestinal and extraintestinal sites in animals that have been administered either parenteral feeding or various types of enteral feeding. It also establishes links between a specific nutrient (glutamine), the enteric nervous system (by way of neuropeptides), and mucosal immunity. Progress in understanding relationships between nutrient availability, enteric nervous system stimulation, and nutrient delivery on mucosal immunity offers opportunities to explore immune systems previously not appreciated by clinicians and basic scientists. These opportunities offer new challenges to the physician scientist, basic scientist, and clinician to understand, manipulate, and apply these concepts to the critically ill patient population by favorably influencing immunologic barriers and the inflammatory response.
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