title: The gut as an organ of immunology.
abstract: BACKGROUND
  In normal conditions human gut mucosa is infiltrated with a large number of mononuclear cells due to continuous stimulation by luminal antigens. This state of "physiological" inflammation is tightly controlled, as several mucosal cells interact to maintain an appropriate local immune response. Moreover, gut-associated lymphoid tissue must constantly distinguish harmless antigens that are present in food and on commensal bacteria from pathogenic microbes.
  The oral administration of soluble protein antigens induces a state of systemic immunological unresponsiveness specific to the fed protein, termed oral tolerance. The two major mechanisms to explain oral tolerance are anergy/deletion of autoreactive lymphocytes and active suppression. Changes in the pathways of immune activation are detected in chronic intestinal inflammation, such as inflammatory bowel disease or celiac disease.
  
  
  CONCLUSIONS
  An appreciation of the current knowledge of the gut immune system is of importance for understanding and development of new treatment modalities in chronic intestinal inflammation.
authors.affiliation: First Department of Internal Medicine (Gastroenterology, Infectiology, Rheumatology), Universitätsklinik Benjamin Franklin, Freie Universität Berlin, Hindenburgdamm 30, 12200 Berlin, Germany. bianca.wittig@medizin.fu-berlin.de
authors.forename: B M
authors.initials: BM
authors.lastname: Wittig
authors.forename: M
authors.initials: M
authors.lastname: Zeitz
mesh_terms: D000276:Adjuvants, Immunologic / Q000627:therapeutic use; D000941:Antigens / Q000008:administration & dosage / Q000276:immunology; D002454:Cell Differentiation; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D003713:Dendritic Cells / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance; D007413:Intestinal Mucosa / Q000166:cytology / Q000276:immunology*; D010581:Peyer's Patches / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D000941:Antigens; D016207:Cytokines