Journal of Endotoxin Research

 

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Journal of Endotoxin Research, Vol. 9, No. 5, 322-330 (2003)
DOI: 10.1177/09680519030090050901

TLR signaling at the intestinal epithelial interface

Maria T. Abreu

Inflammatory Bowel Disease Center, Division of Gastroenterology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA, maria.abreu{at}cshs.org

Lisa S. Thomas

Inflammatory Bowel Disease Center, Division of Gastroenterology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA

Elizabeth T. Arnold

Inflammatory Bowel Disease Center, Division of Gastroenterology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA

Katie Lukasek

Inflammatory Bowel Disease Center, Division of Gastroenterology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA

Kathrin S. Michelsen

Division of Pediatric Infectious Diseases, Department of Pediatrics, Steven Spielberg Pediatric Research Center, Burns and Allen Research Institute

Moshe Arditi

Division of Pediatric Infectious Diseases, Department of Pediatrics, Steven Spielberg Pediatric Research Center, Burns and Allen Research Institute

The intestinal epithelium provides a critical interface between lumenal bacteria and the mucosal immune system. Whereas normal commensal flora do not trigger acute inflammation, pathogenic bacteria trigger a potent inflammatory response. Our studies emanate from the hypothesis that the intestinal epithelium is normally hyporesponsive to commensal pathogen-associated molecular patterns (PAMPs) such as LPS. Our data demonstrate that normal human colonic epithelial cells and lamina propria cells express low levels of TLR4 and its co-receptor MD-2. This expression pattern is mirrored by intestinal epithelial cell (IEC) lines. Co-expression of TLR4 and MD-2 is necessary and sufficient for LPS responsiveness in IEC. Moreover, LPS sensing occurs along the basolateral membrane of polarized IEC in culture. Expression of MD-2 is regulated by IFN-{gamma}. Cloning of the MD-2 promoter demonstrates that promoter activity is increased by IFN-{gamma} and blocked by the STAT inhibitor SOCS3. We conclude from our studies that the intestinal epithelium down-regulates expression of TLR4 and MD-2 and is LPS unresponsive. The Th1 cytokine IFN-{gamma} up-regulates expression of MD-2 in a STAT-dependent fashion. The results of our studies have important implications for understanding human inflammatory bowel diseases.


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