Immune regulation via the epithelial barrier
The gut epithelial layer is a mechanical and immune barrier in the gut
that plays an essential role in immune regulation. It contains goblet
cells (produce mucus), M cells (present in Peyer’s patches and lymphoid
cells, sensing and transporting microbes), enterocytes (absorption),
stromal cells (tissue regeneration and wound repair of epithelium), and
Paneth cells (produce zinc, anti-microbial molecules like lysozyme, and
sense microbial products via Myd88-dependent
pathways)81-84. Commensal bacteria cause an
auto-activation of Myd88, an adaptor protein that plays a central role
in TLR activation, which limits bacterial access to the mucosal layer
(Fig. 1D)82,85. TLRs have a distinct placement in the
epithelial layer as they are located on both apical and basolateral
surfaces, and this placement prevents the immune response to the
commensal gut bacteria that crosses the mucus layer86.
The integrity of the epithelial cells is a structural feature of how
immune regulation takes place in the gut as the alteration of the tight
junctions between the epithelial cells is how pathogens like
Rotaviruses, C. difficile , Shigella flexneri , andSalmonella typhimurium cause diseases (Fig
2A)87-90.