ABSTRACT

The follicle-associated epithelium (FAE) overlying organized mucosal lymphoid tissues play a major role in mucosal immunity. Representing a very small fraction of the total mucosal surface area of the gastrointestinal tract mucosa, the FAE contains a unique epithelial cell type, the microfold (M) cell, whose primary function is to translocate luminal material across the epithelial barrier to dendritic cells and lymphocytes within and below the epithelium. In contrast to the well-defended villus and surface epithelium of the intestine, the FAE lacks many defensive features and appears designed to allow macromolecules, particles, and microorganisms access to the apical surface. FAE cells differ from villus cells in their ability to release certain chemokines that attract immune cells toward the FAE and thus to sites of organized lymphoid tissue. Gene expression in the FAE may be modulated by microorganisms that contact the FAE or are transported by M cells into the mucosa.