Intestinal epithelial cells: regulators of barrier function and immune homeostasis

Key Points Intestinal epithelial cells (IECs) provide a physical and biochemical barrier that segregates host tissue and commensal bacteria to maintain intestinal homeostasis. Secretory IECs support this function through the secretion of mucins and antimicrobial peptides. IECs maintain specialized pathways for the delivery of luminal antigens and bacteria to lamina propria-resident antigen-presenting cells. Microbial signals are recognized by IECs to promote intestinal homeostasis. Host–commensal microorganism interactions not only support tissue repair in the setting of injury or acute inflammation but also promote the development of intestinal cancers during chronic inflammation. IECs possess mechanisms for maintaining altered responsiveness to microbial signals that allow for tolerance to continuous exposure to commensal bacteria. IECs convey microbial signals to mucosal immune cells and promote the coordination of appropriate immune responses against commensal bacteria and enteric pathogens. Interactions between antigen-presenting cells and IECs regulate B cell and T cell responses that act on the intestinal barrier. Both innate and adaptive effector cell function and homeostasis are influenced by IEC-derived signals. This allows IECs to locally regulate immune response at the intestinal barrier and promote the maintenance of intestinal homeostasis.