KEY POINTS 
The human body is constantly being subjected to a barrage of chemical, physical, and biological insults from the gastrointestinal (GI) lumen. The body is protected by the so-called intestinal barrier.
1 The epithelial barrier is highly selective and semipermeable. It is a complex, dense mucous layer composed of IgA, antimicrobial peptides, and junctional complexes, including tight junctions (TJs).
Intestinal epithelium safeguards the mucosal barrier immunity.
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