Introduction

Abstract

The mucosal surface of the gastrointestinal tract is covered by a monolayer of columnar epithelial cells. This epithelium represents a vast surface area that is vulnerable to foreign antigens and microbial pathogens. By being in contact with a large number of potentially harmful substances and infectious organisms, the mucosal surface must provide mechanisms not only to regulate the entry of macromolecules but to serve as an exporter of secretory antibodies for mucosal defence. Consistent with these functions, the epithelial surface of the gastrointestinal tract is lubricated and protected by mucus secretion and by a highly specialised immune system underlying the epithelium which exports the appropriate immunoglobulins into the intestinal secretions.