Effects of parenteral and enteral nutrition on gut-associated lymphoid tissue

Changes in mucosal defense have been implicated as important factors affecting infectious complications in critically ill patients. To study the effects of nutrient administration on gut-associated lymphatic tissue (GALT), ICR mice were randomized to receive chow plus intravenous saline, intravenous feeding of a total parenteral nutrition (TPN) solution, or enteral feeding of the same TPN solution. In a second series of experiments, a more complex enteral diet (Nutren) was compared with chow feeding and enteral TPN. After 5 days of feeding with experimental diets, lymphocytes were harvested from the mesenteric lymph nodes (MLNs), Peyer's patches (PPs), lamina propria (LP) cells, and intraepithelial (IE) spaces of the small intestine to determine cell yields and phenotypes. Small intestinal washings, gallbladder contents, and sera were collected and analyzed for immunoglobulin A (IgA) levels. In both series of experiments, there were no significant changes within the MLNs. There were significant decreases in total cell yields from the PPs, IE spaces, and LP in animals fed with TPN solution, either enterally or parenterally, as compared with chow-fed mice. Total T cells were decreased in both TPN-fed groups in the PPs and LP, whereas total B cells were decreased in the PP, IE, and LP populations. Total cell numbers remained normal in the Nutren-fed group, except for a decrease in LP T cells. CD4⁺ LP cells decreased significantly with a reduction in the CD4/CD8 ratio in mice fed TPN solution either intravenously or enterally, whereas IgA recovery from small intestinal washings was significantly decreased in the same groups. These data demonstrate that TPN solution feeding in mice, either intravenously or as an elemental enteral diet, alters GALT populations, resulting in atrophy in LP, IE, and PP T-cell and B-cell populations and decreased intestinal IgA levels. A more complex enteral diet is not associated with most of these significant changes.