Figure 1.

Mucosal barriers in the gut. In the small intestine, chemical barriers, including AMPs produced by Paneth cells, have major roles in the segregation of intestinal bacteria and intestinal epithelial cells. In contrast, in the large intestine, which is inhabited by a tremendous number of bacteria, intestinal bacteria and intestinal epithelial cells are separated by the inner mucus layer containing polymerized MUC2. Lypd8, a GPI-anchored protein expressed in the epithelial cells, promotes the segregation of the two by binding to intestinal bacteria, especially flagellated bacteria. AMP, antimicrobial peptides; LZ, lysozyme; TLR, toll-like receptor; ILC3, type 3 innate lymphoid cell.