Role of epithelium in mucosal immunity

The mucosal surfaces that serve as absorptive surfaces-such as the intestinal epithelium-can be quite vast and are in contact with vast quantities of a diverse population of microbes and their metabolites including immunostimulatory/ proinflammatory products. The vast majority of these microbes and their metabolites are excluded from the internal access to the host by the physical barrier formed by the single layer of epithelial cells that line the mucosal surfaces. This barrier includes the epithelial cells themselves, their intercellular tight junctions, and the mucus that covers the epithelial surface. Further, this barrier is bathed in a milieu of antibacterial proteins to keep the microbial population in check. The intestinal epithelium has various specialized cell types that make crucial contributions to the mucosal immunity. Goblet cells-one of the most numerous intestinal epithelial cell type-are interspersed throughout the gut epithelium and are characterized by their brandy goblet shape and pale-stained mucin-filled granules. These cells produce the mucus layer that coats the gastrointestinal (GI) tract.