Commensal Bacteria of the GI Tract: Benefits of Probiotic Supplementation (post 4)

The mucosal barrier of the colon

The colon possesses a “mucosal barrier” which prevents most antigens from passing through its wall and interacting with immune cells. The mucosal barrier is a one-cell-thick layer of epithelium that lines the lumen of the colon. This epithelium is characterized by tight junctions between cells that open and close in response to messages within the cells, and orchestrate the entrance of microbes and other substances into the tissue. The gut must be able to distinguish between acceptable materials such as nutrients and normal microbes, and other matter such as pathogenic microbes or other antigens. The colonic microflora is an important part of the mucosal barrier. Gut epithelial cells possess receptors that recognize specific molecules on the cell walls of commensal flora and result in increasing mucosal barrier function. Normal flora also induces protective protein production by colonic epithelial cells; this protein serves as part of the mucosal barrier.³⁴

The importance of the microflora in infants is demonstrated by the fact that the barrier function is incompletely developed at birth and remains so through early infancy. Barrier function is even less developed in premature infants. In these children, increased binding of antigen to the immature gut tissues may lead to sensitization and allergy to various molecules such as foods. Breast feeding can provide a protective effect because antigens are less likely to be introduced than when animal byproducts or other molecules found in marketed formulas are ingested. In addition, many pharmaceutical drugs induce increased intestinal permeability and contribute to intestinal leakage.
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