ABSTRACT
The mucosal surfaces, including the surface of the eye and the linings of the gastrointestinal, respiratory, reproductive, and urinary tracts, are the major interface between mammalian tissues and the potentially hostile external environment. This chapter describes the components of well-regulated barrier in mucosal surfaces and their regulation by innate and adaptive immunity, focusing mainly on the intestinal tract because it is the most thoroughly studied mucosal tissue and is continuously exposed to potential infection. Intestinal stem cells give rise to rapidly proliferating “transit amplifying” cells that generate progeny that then migrate up the crypt compartment, producing the terminally differentiated cells that constitute the villus epithelium. Fermentation by the gut microbiota leads to the production of short-chain fatty acids such as butyrate that can achieve millimolar concentrations in the colonic lumen, where it is the primary source of energy for the colonic epithelium.
