Epithelial barrier function and innate immunity are fundamental to the pathogenesis of inflammatory and infectious disease. Along with plasma membranes, epithelial cells are the primary cellular determinant of epithelial barrier function. The mechanism by which polarized epithelia form a permeability barrier is of fundamental importance to the prevention of many infectious and inflammatory diseases. Moreover, epithelial cells express Toll-like receptors (TLRs) which upon recognition of conserved microbial factors such as lipopolysaccharide (LPS) induce epithelial responses including epithelial cell proliferation, secretion of secretory IgA into the lumen and production mucins and antimicrobial peptides, thereby promoting intestinal barrier function. Understanding gut barrier integrity and regulation of permeability is crucial to increase our understanding of the pathogenesis of intestinal disease. A variety of tests have been developed to assess this barrier, including assessing intestinal epithelial cell proliferation or death, intestinal tight junction status and the consequence of intestinal barrier integrity loss such as increased intestinal permeability and susceptibility to bacterial infection. Using a mouse model, this chapter describes some of the methods to assess the functional integrity of this epithelial barrier and the part played by a TLR signalling pathway.
