Fig. 1
From: M cell-dependent antigen uptake on follicle-associated epithelium for mucosal immune surveillance
M cells in the FAE specialize in antigen uptake on the mucosal surface. To protect against bacterial invasion, the villous epithelium is equipped with robust mucosal barriers composed of tight junctions, thick mucin layer, S-IgA, and AMPs. In contrast, the FAE is vulnerable because of a thin mucin layer and downregulation of the expression of polymeric immunoglobulin receptor (pIgR) and AMPs. Consequently, external antigens are able to easily gain access to M cells on the FAE. The expression of the Notch ligand and IL-22BP in the sub-epithelial region, at least partially, account for the attenuated barrier functions