Mucosal Immunology and Symbiotic Microbiota

Abstract

The host is continuously exposed to the external environment via a large surface area covered by mucosal epithelium. The surface area of human mucosa is as much as 400m², or nearly equivalent to the surface of 1.5 tennis courts including oral cavity, nasal passage, digestive tract, respiratory apparatus, urinary tissue and reproductive organ. Enormous numbers of commensal bacteria colonize symbiotically on the large mucosal surface by creating appropriate homeostatic conditions. The mucosal immune system may be exercising quiescent immunological conditions by identifying these symbiotic microbiota as pseudo-selves. In this review, we first provide an outline of the uniqueness of the mucosal immune system represented by secretory IgA (S-IgA), intraepithelial lymphocyte (IEL) and oral tolerance. Then we introduce the latest insights concerning the symbiotic interaction between the mucosal immune system and commensal bacteria. Currently, major scientific emphasis has been aiming at the boundary area between mucosal immunology and symbiotic microbiology for an understanding of molecular and cellular mechanisms of recognizing commensal microflora as the part of self (or pseudo-self) antigen.