Fecal Stream Diversion Changes Intestinal Environment, Modulates Mucosal Barrier, and Attenuates Inflammatory Cells in Crohn's Disease

The intestinal environment plays important roles in mucosal barrier homeostasis and intestinal inflammation, as clarified in studies using experimental animals but not in humans. We investigated whether environmental changes in the fecal stream cause phenotypic changes in the human mucosal barrier. We obtained human ileal samples after fecal stream diversions in patients with rectal cancer or Crohn’s disease. We investigated the bacterial load and diversity in the human defunctioned ileum, defined as the anal side of the ileum relative to the ileostomy. We also examined the epithelium and lamina propria cell phenotypes in the defunctioned ileum. After fecal stream diversion, bacterial loads decreased significantly in the defunctioned ileum. Based on the Chao1, Shannon, and observed species indices, the diversity of mucosa-associated microbiota was lower in the defunctioned ileum than in the functional ileum. Moreover, the healthy defunctioned ileum showed reductions in villous height, goblet cell numbers, and Ki-67+ cell numbers. Additionally, interferon-γ+, interleukin-17+, and immunoglobulin A+ cell abundance in the lamina propria decreased. After the intestinal environment was restored with an ileostomy closure, the impaired ileal homeostasis recovered. The defunctioned ileum samples from patients with Crohn’s disease also showed reductions in interferon-γ+ and interleukin-17+ cell numbers. Fecal stream diversion reduced the abundance and diversity of intestinal bacteria. It also altered the intestinal mucosal barrier, similar to the alterations observed in germ-free animals. In patients with Crohn’s disease, Th1 and Th17 cell numbers were attenuated, which suggests that the host–microbiome interaction is important in disease pathogenesis.