Intestinal epithelial cells and their role in innate mucosal immunity

Abstract

The mucosal surfaces of the respiratory, gastrointestinal and urogenital tracts are covered by a layer of epithelial cells that are responsible for sensing and promoting a host immune response in order to establish the limits not only for commensal microorganisms but also for foreign organisms or particles. This is a remarkable task as the human body represents a composite of about 10 trillion human-self cells plus non-self cells from autochthonous or indigenous microbes that outnumber human cells 10:1. Hence, the homeostasis of epithelial cells that line mucosal surfaces relies on a fine-tuned immune system that patrols the boundaries between human and microbial cells. In the case of the intestine, the epithelial layer is composed of at least six epithelial cell lineages that act as a physiological barrier in addition to aiding digestion and the absorption of nutrients, water and electrolytes. In this review, we highlight the immense role of the intestinal epithelium in coordinating the mucosal innate immune response.

Fig. 1

Representation of intestinal epithelial cell activities that regulate innate mucosal immunity (AMPs antimicrobial peptides, IILs interleukins, IgA immunoglobulin A, pIgAR polimeric immunoglobulin A receptor, LL-37 human cathelicidin, LPS lipopolysaccharide, M cells microfold cells, Mϕ macrophage, MAPK mitogen-activated protein kinases, MYD88, TRIF, TIRAP, TRAM, Rip2 adaptor proteins, NF-κB nuclear factor kappa-B, NOD Nucleotide-binding oligomerization domain, PAMP’s pathogen-associated molecular patterns, TLR Toll-like receptors)