Elemental Diet‐Induced Immune Suppression Is Caused by Both Bacterial and Dietary Factors

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Abstract
Because it is unclear whether elemental diet‐induced immune suppression is an indirect effect caused by the translocating bacteria or is directly caused by the elemental diet, we tested whether prevention of diet‐induced bacterial translocation or disruption of the gut microflora ecology would prevent diet‐induced impaired lymphocyte function in a rat elemental diet model. Prevention of diet‐induced bacterial translocation was accomplished by the addition of cellulose fiber or oral antibiotics (penicillin and streptomycin) to the elemental diet feeding regimen. Control groups consisted of rat food‐fed and elemental diet‐fed (4.25% amino acids; 28% glucose) rats. Immune function was quantitated by measuring the mitogen‐induced blastogenic response of peripheral blood or splenic mononuclear cells to the mitogens concanavalin A and phytohemagglutinin. Bacterial translocation from the gut to the mesenteric lymph node and cecal bacterial population levels were measured in all groups. Although the incidence of elemental diet‐induced bacterial translocation was reduced from 100% to 25% (p <.01) by the addition of dietary fiber, fiber did not prevent diet‐induced impaired lymphocyte function. Because fiber supplementation of the elemental diet did not completely prevent diet‐induced intestinal bacterial overgrowth or bacterial translocation, the experiment was repeated in antibiotic‐decontaminated rats. Antibiotic decontamination completely prevented diet‐induced intestinal bacterial overgrowth and bacterial translocation. Although antibiotic decontamination reduced the magnitude of lymphocyte mitogen suppression (p <.05), it was not fully effective in reversing the diet‐induced lymphocyte suppression. These results indicate that elemental diet‐induced lymphocyte blastogenic suppression is related to both bacterial and dietary factors. (Journal of Parenteral and Enteral Nutrition 17:332–336, 1993)