Human intestinal epithelial cells are broadly unresponsive to Toll-like receptor 2-dependent bacterial ligands: implications for host-microbial interactions in the gut.
Intestinal epithelial cells (IEC) interact with a high density of Gram-positive bacteria and are active participants in mucosal immune responses. Recognition of Gram-positive organisms by Toll-like receptor (TLR)2 induces proinflammatory gene expression by diverse cells. We hypothesized that IEC are unresponsive to Gram-positive pathogen-associated molecular patterns and sought to characterize the functional responses of IEC to TLR2-specific ligands. Human colonic epithelial cells isolated by laser capture microscopy and IEC lines (Caco-2, T84, HT-29) were analyzed for expression of TLR2, TLR6, TLR1, and Toll inhibitory protein (Tollip) mRNA by RT-PCR and quantitative real-time PCR. Response to Gram-positive bacterial ligands was measured by NF-kappa B reporter gene activation and IL-8 secretion. TLR2 protein expression was analyzed by immunofluorescence and flow cytometry. Colonic epithelial cells and lamina propria cells from both uninflamed and inflamed tissue demonstrate low expression of TLR2 mRNA compared with THP-1 monocytes. IECs were unresponsive to TLR2 ligands including the staphylococcal-derived Ags phenol soluble modulin, peptidoglycan, and lipotechoic acid and the mycobacterial-derived Ag soluble tuberculosis factor. Transgenic expression of TLR2 and TLR6 restored responsiveness to phenol soluble modulin and peptidoglycan in IEC. In addition to low levels of TLR2 protein expression, IEC also express high levels of the inhibitory molecule Tollip. We conclude that IEC are broadly unresponsive to TLR2 ligands secondary to deficient expression of TLR2 and TLR6. The relative absence of TLR2 protein expression by IEC and high level of Tollip expression may be important in preventing chronic proinflammatory cytokine secretion in response to commensal Gram-positive bacteria in the gut.
Melmed
Gil
G
Inflammatory Bowel Disease Center, Division of Gastroenterology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
Thomas
Lisa S
LS
Lee
Nahee
N
Tesfay
Samuel Y
SY
Lukasek
Katie
K
Michelsen
Kathrin S
KS
Zhou
Yuehua
Y
Hu
Bing
B
Arditi
Moshe
M
Abreu
Maria T
MT
D001427:Bacterial Toxins / Q000378:metabolism*; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics; D002460:Cell Line; D029721:Drosophila Proteins; D005786:Gene Expression Regulation / Q000276:immunology; D019073:HT29 Cells; D006801:Humans; D007108:Immune Tolerance / Q000235:genetics; D007413:Intestinal Mucosa / Q000166:cytology / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008070:Lipopolysaccharides / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D010457:Peptidoglycan / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013211:Staphylococcus aureus / Q000276:immunology; D013212:Staphylococcus epidermidis / Q000276:immunology; D013682:Teichoic Acids / Q000378:metabolism*; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6; D051193:Toll-Like Receptors; D015533:Transcriptional Activation; D014162:Transfection; D019076:Transgenes / Q000276:immunology; D014407:Tumor Cells, Cultured
D001427:Bacterial Toxins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D010457:Peptidoglycan; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495368:TLR6 protein, human; C410602:TOLLIP protein, human; D013682:Teichoic Acids; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6; D051193:Toll-Like Receptors; C025971:staphylococcal delta toxin; C009900:lipoteichoic acid