Intestinal lymphoepithelial communication.

The close anatomic juxtaposition of epithelial cells with lymphocytes lining the intestinal tract facilitates communication between the two cell types. This intercellular dialogue is important for mucosal development and has a conditioning effect on mucosal structure, function, and response to tissue injury. Lymphoepithelial communication is bi-directional, and mediated in large part, by shared ligands and receptors. The chemical messengers involved include cytokines, growth factors, local hormones, and products of arachidonate metabolism. The interdependency between the epithelium and adjacent lymphoid cells is such that the epithelium is considered to have a central role in the mucosal immune system and is an active participant in both the afferent and efferent limbs of the mucosal immune response. The molecular crosstalk between the epithelium and adjacent lymphocytes is just one aspect of a more complex network of intercellular signalling within the intestinal mucosa and upon which the integrity of the mucosa is dependent. Thus, there are extensive interactions between nerve and immune cells and between the enteric flora and the epithelium and amongst intestinal mesenchymal cells including fibroblasts and vascular endothelial cells. Disruption of any aspect of the mucosal microenvironment, as has been achieved with selective genetically engineered murine models, is associated with impaired mucosal defence and inflammation.