title: Claudin expression in follicle-associated epithelium of rat Peyer's patches defines a major restriction of the paracellular pathway.
abstract: OBJECTIVE
  Members of the tight junction protein family of claudins have been demonstrated to specifically determine paracellular permeability of the intestinal epithelium. In small intestinal mucosa, which is generally considered to be a leaky epithelium, Peyer's patches are a primary part of the immune system. The aim of this study was to analyse the tight junctional barrier of follicle-associated epithelium covering Peyer's patches (lymphoid follicles).
  
  
  METHODS
  Employing small intestinal tissue specimens of male Wistar rats, electrophysiological analyses including the Ussing chamber technique, marker flux measurements and one-path impedance spectroscopy were performed. Morphometry of HE-stained tissue sections was taken into account. Claudin expression and localization was analysed by immunoblotting and confocal laser scanning immunofluorescence microscopy.
  
  
  RESULTS
  Almost twofold higher parameters of epithelial and transepithelial tissue resistance and a markedly lower permeability for the paracellular permeability markers 4 and 20 kDa FITC-dextran were detected in follicle-associated epithelium compared to neighbouring villous epithelium. Analysis of claudin expression and localization revealed a stronger expression of major sealing proteins in follicle-associated epithelium, including claudin-1, claudin-4, claudin-5 and claudin-8. Therefore, the specific expression and localization of claudins is in accordance with barrier properties of follicle-associated epithelium vs. neighbouring villous epithelium.
  
  
  CONCLUSIONS
  We demonstrate that follicle-associated epithelium is specialized to ensure maximum restriction of the epithelial paracellular pathway in Peyer's patches by selective sealing of tight junctions. This results in an exclusive transcellular pathway of epithelial cells as the limiting and mandatory route for a controlled presentation of antigens to the underlying lymphocytes under physiological conditions.
authors.affiliation: Institute of General Physiology, Biological Faculty, St. Petersburg State University, St. Petersburg, Russia.
authors.forename: A G
authors.initials: AG
authors.lastname: Markov
authors.affiliation: Institute of General Physiology, Biological Faculty, St. Petersburg State University, St. Petersburg, Russia.
authors.forename: E L
authors.initials: EL
authors.lastname: Falchuk
authors.affiliation: Institute of General Physiology, Biological Faculty, St. Petersburg State University, St. Petersburg, Russia.
authors.forename: N M
authors.initials: NM
authors.lastname: Kruglova
authors.affiliation: Institute of Veterinary Physiology, Freie Universität Berlin, Berlin, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Radloff
authors.affiliation: Institute of Veterinary Physiology, Freie Universität Berlin, Berlin, Germany.|Institute of Clinical Physiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Amasheh
mesh_terms: D000818:Animals; D057167:Claudins / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology; D004848:Epithelium / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D008297:Male; D010581:Peyer's Patches / Q000378:metabolism*; D017208:Rats, Wistar; D019108:Tight Junctions / Q000502:physiology*
chemical_list: D057167:Claudins
keywords: impedance spectroscopy; tight junctions; tissue barrier; villous epithelium