TY - JOUR
T1 - Mechanisms of Cross Hyporesponsiveness to Toll-Like Receptor Bacterial Ligands in Intestinal Epithelial Cells
AU - Otte, Jan Michel
AU - Cario, Elke
AU - Podolsky, Daniel K.
N1 - Funding Information:
Supported by grants from the Deutsche Forschungsgemeinschaft (to J.-M.O.; Ot 186/4-1) and the National Institutes of Health (to D.K.P.; DK60049 and DK43351).
PY - 2004/4
Y1 - 2004/4
N2 - Background & Aims: Despite the ability to participate in immune responses and the continuous presence of bacteria and bacterial products, functional responses of intestinal epithelial cells (IEC) seem to be muted. Previously, tolerance to Toll-like receptors (TLRs) ligands has been described in monocytic cells. However, mechanisms in the intestine are unknown. Methods: The effect of purified lipopolysaccharide (LPS) and lipoteichoicacid (LTA) on expression and function of TLRs in intestinal epithelial cells (Colo205, SW480, T84) was assessed by Northern and Western blot and FACS analysis, kinase activity assays, immunohistochemistry, and ELISA. Results: Expression of TLRs except 10 was detected in primary IEC and TLR1-10 in the cultured cells. Short-term stimulation with LPS or LTA activated proinflammatory signaling cascades in IEC, including phosphorylation of IRAK and MAP kinases and increased IL-8 secretion, whereas prolonged incubation resulted in a state of hyporesponsiveness with no reactivation of the cells by a second challenge with either substance detected. The cells remained responsive to tumor necrosis factor (TNF). Hyporesponsive cells showed no alteration in expression of TLR or signaling molecules but revealed a decrease in TLR surface expression and IRAK activity. Toll-interacting protein (Tollip) mRNA and protein expression were increased in hyporesponsive cells, and overexpression of Tollip in IEC resulted in a significantly decreased proinflammatory response. Conclusions: Continuous presence of specific bacterial components results in a status of hyporesponsiveness in otherwise reactive IEC. Down-regulation of TLR surface expression and up-regulation of inhibitory Tollip with decreased phosphorylation of IRAK might all contribute to this hyporesponsiveness.
AB - Background & Aims: Despite the ability to participate in immune responses and the continuous presence of bacteria and bacterial products, functional responses of intestinal epithelial cells (IEC) seem to be muted. Previously, tolerance to Toll-like receptors (TLRs) ligands has been described in monocytic cells. However, mechanisms in the intestine are unknown. Methods: The effect of purified lipopolysaccharide (LPS) and lipoteichoicacid (LTA) on expression and function of TLRs in intestinal epithelial cells (Colo205, SW480, T84) was assessed by Northern and Western blot and FACS analysis, kinase activity assays, immunohistochemistry, and ELISA. Results: Expression of TLRs except 10 was detected in primary IEC and TLR1-10 in the cultured cells. Short-term stimulation with LPS or LTA activated proinflammatory signaling cascades in IEC, including phosphorylation of IRAK and MAP kinases and increased IL-8 secretion, whereas prolonged incubation resulted in a state of hyporesponsiveness with no reactivation of the cells by a second challenge with either substance detected. The cells remained responsive to tumor necrosis factor (TNF). Hyporesponsive cells showed no alteration in expression of TLR or signaling molecules but revealed a decrease in TLR surface expression and IRAK activity. Toll-interacting protein (Tollip) mRNA and protein expression were increased in hyporesponsive cells, and overexpression of Tollip in IEC resulted in a significantly decreased proinflammatory response. Conclusions: Continuous presence of specific bacterial components results in a status of hyporesponsiveness in otherwise reactive IEC. Down-regulation of TLR surface expression and up-regulation of inhibitory Tollip with decreased phosphorylation of IRAK might all contribute to this hyporesponsiveness.
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U2 - 10.1053/j.gastro.2004.01.007
DO - 10.1053/j.gastro.2004.01.007
M3 - Article
C2 - 15057745
AN - SCOPUS:1842583729
SN - 0016-5085
VL - 126
SP - 1054
EP - 1070
JO - Gastroenterology
JF - Gastroenterology
IS - 4
ER -