Interaction between the Intestinal Immune System and Commensal Bacteria and Its Effect on the Regulation of Allergic Reactions

The immune system and the commensal bacteria in the intestine, which together form the intestinal symbiotic system, greatly contribute to regulation of allergy. Of the various types of cells constituting the intestinal immune system, this review focuses on epithelial cells and mast cells and the interaction of these cells with commensals. Mast cells express the high affinity IgE receptor Fc epsilon RI which is essential to the induction of allergic inflammatory reactions. The molecular mechanisms of transcriptional regulation of genes encoding Fc epsilon RI have been clarified. On the other hand, the expression of the molecules involved in microbe recognition is regulated in a specific manner in intestinal epithelial cells, which are continuously exposed to the commensals inhabiting the intestinal lumen, to prevent excessive inflammatory reactions. Microbial components directly regulate the functions of mast cells through Toll-like receptors. These aspects provide targets for the regulation of allergy based on the maintenance of the intestinal symbiotic system.