Intestinal Epithelial Barrier Dysfunction in Food Hypersensitivity
Figure 1
Intestinal barrier functions. (a) Differentiated intestinal villous epithelial cells and the covering mucus layer form a physical barrier to separate luminal contents from the lamina propria. The epithelial barrier prevents the entry of noxious substances, such as undigested food proteins and commensal bacteria, into the body proper. (b) Tight junctional complexes located at the most apical portion of the lateral plasma membrane between two cells excludes the influx of antigenic proteins and bacteria through paracellular routes. The transmembraneous junctional proteins, for example, claudins, occludin, or junction-associated molecule (JAM), are linked to intracellular zonula occludens (ZO) which are bridges to perijunctional actinomyosin rings. Most dietary proteins are digested to small peptides and amino acids before being absorbed into enterocytes via specific transporters. A very small percentage of intact proteins may be endocytosed into epithelial cells but are degraded by lysozymes and lose their antigenic properties. The lysosomal degradation pathway thus prevents the entry of intact proteins through transcellular routes.
