Mucosal Immunobiology Section, Laboratory of Molecular Immunology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-1886, USA. kelsall@nih.gov
The intestine is the home of a tremendous number of commensal organisms that have a primary role in host metabolism. As a consequence, the gut mucosa has evolved multiple layers of protection. This review highlights both innate and adaptive mechanisms that prevent bacterial invasion and abnormal intestinal inflamamation, how a failure of these mechanisms may be involved in the pathogenesis of inflammatory bowel diseases, and discusses new findings implicating dendritic cells as central to the induction of active mucosal tolerance to commensal bacteria. 2007 Pathological Society of Great Britain and Ireland