Crosstalk between Intestinal Epithelial Cells and Commensal Bacteria

Abstract

A huge number of commensal bacteria inhabit the intestinal tract. Although these bacteria are not immunological “self” to the host, the intestinal immune system, the largest immune system in the body, does not exclude them completely, resulting in a symbiotic relationship. Since the vast area of intestinal mucosa is covered by a single layer of intestinal epithelial cells (IECs), IECs are continually exposed to the luminal bacteria. IECs not only physically separate the luminal contents from the internal milieu but also actively participate in induction or conditioning of intestinal immune reactions. In this review, the regulation of the epithelial barrier and immune reactions by the crosstalk between IECs and commensal bacteria as well as the expression and function of microbe recognition molecules in IECs as a basis of the crosstalk are discussed.