Fig. 1

Mucosal barriers in the gut. Chemical barriers including AMPs and Reg3γ secreted by Paneth cells mainly contribute to the separation between intestinal bacteria and IECs in the small intestine. By contrast, in the large intestine where a tremendous number of bacteria exist, intestinal bacteria and IECs are largely segregated by physical barriers such as the inner mucus layer composed of polymerized MUC2 mucin. Lypd8, a highly glycosylated GPI-anchored protein expressed on IECs, inhibits the bacterial invasion of the inner mucus layer by binding to intestinal bacteria, especially flagellated bacteria. AMP: antimicrobial peptide