Intestinal Macrophages Lack CD14 and CD89 and Consequently Are Down-Regulated for LPS- and IgA-Mediated Activities

Smith, Phillip D.; Smythies, Lesley E.; Mosteller-Barnum, Meg; Sibley, David; Russell, Michael W.; Merger, Michael; Sellers, Marty T.; Orenstein, Jan M.; Shimada, Toshihide; Graham, Martin F.; Kubagawa, Hiromi

doi:10.4049/jimmunol.167.5.2651

Cited by 294 publications

(262 citation statements)

References 34 publications

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“…Recent studies demonstrate that intestinal macrophages are also poorly LPS responsive and lack CD14 (90). In this study, we have addressed the regulation of TLR2 signaling by IEC.…”

Section: Discussionmentioning

confidence: 99%

Human Intestinal Epithelial Cells Are Broadly Unresponsive to Toll-Like Receptor 2-Dependent Bacterial Ligands: Implications for Host-Microbial Interactions in the Gut

Melmed¹,

Thomas²,

Lee³

et al. 2003

The Journal of Immunology

396

281

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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-κB 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.

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“…Recent studies demonstrate that intestinal macrophages are also poorly LPS responsive and lack CD14 (90). In this study, we have addressed the regulation of TLR2 signaling by IEC.…”

Section: Discussionmentioning

confidence: 99%

Human Intestinal Epithelial Cells Are Broadly Unresponsive to Toll-Like Receptor 2-Dependent Bacterial Ligands: Implications for Host-Microbial Interactions in the Gut

Melmed¹,

Thomas²,

Lee³

et al. 2003

The Journal of Immunology

396

281

View full text Add to dashboard Cite

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“…Staining of lamina propria macrophages has shown that expression of TLR2 and TLR4 is low in uninflamed intestine (18). In addition, isolated lamina propria macrophages do not express CD14 and are LPS unresponsive (19). Human lamina propria dendritic cells in the intestine are difficult to isolate and characterize but functional studies suggest that intestinal dendritic cells respond to TLR3 and TLR4 ligands (Table III) (20).…”

Section: Location Location Locationmentioning

confidence: 99%

TLR Signaling in the Gut in Health and Disease

Abreu

Fukata

Arditi

2005

The Journal of Immunology

536

382

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The human intestine has evolved in the presence of diverse enteric microflora. TLRs convert the recognition of pathogen-associated molecules in the gut into signals for anti-microbial peptide expression, barrier fortification, and proliferation of epithelial cells. Healing of injured intestinal epithelium and clearance of intramucosal bacteria require the presence of intact TLR signaling. Nucleotide oligomerization domain (Nod)1 and Nod2 are additional pattern recognition receptors that are required for defense against invasive enteric pathogens. Through spatial and functional localization of TLR and Nod molecules, the normal gut maintains a state of controlled inflammation. By contrast, patients with inflammatory bowel disease demonstrate inflammation in response to the normal flora. A subset of these patients carry polymorphisms in TLR and CARD15/NOD2 genes. A better understanding of the delicate regulation of TLR and Nod molecules in the gut may lead to improved treatment for enteric infections and idiopathic inflammatory bowel diseases.

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“…23,24 We therefore treated KG-1 cells with 100 nM PMA for 4 days. 25,26 where small bacterial peptide products are present. Interestingly, it has been shown that macrophages expressing triggering receptor expressed on myeloid cells-1 (TREM-1), which is a receptor on neutrophils and monocytes/macrophages involved in inflammatory responses, are under-represented in the human intestine.…”

Section: The Monocytic Kg-1 Cell Line Expresses a Functional Hpept1 Tmentioning

confidence: 99%

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes

Charrier

Driss

Yan

et al. 2006

Laboratory Investigation

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Here, we examined hPepT1 expression in the monocytic cell line, KG-1. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that hPepT1 is expressed in KG-1 cells, while cDNA cloning and direct sequencing confirmed the sequence of KG-1 hPepT1 (accession number, AY634368). Immunoblotting of cell lysates from KG-1 cells or macrophages isolated from human peripheral blood revealed a B100 kDa immunoreactive band mainly present in the membrane fraction. Uptake experiments showed that the transport of 20 lM radiolabeled Gly-Sarcosine ([ 14 C]Gly-Sar) in KG-1 cells was Na þ , Cl À dependent and disodium 4,4 0 -diisothiocyanatostilbene-2,2 0 -disulfonate (DIDS)-sensitive. In addition, hPepT1 activity was likely to be coupled to a Na þ /H þ exchanger, as evidenced by the fact that [ 14 C]Gly-Sar uptake was not affected by the absence of Na þ when cells were incubated at low pH (5.2). Interestingly, hPepT1-mediated transport was reduced in KG-1 cells incubated at low pH as it was also observed in nonpolarized Caco2-BBE cells. This pattern of pH-dependence is due to a disruption of the driving force of hPepT1-mediated transport events. This was supported by our finding that nonpolarized cells, Caco2-BBE cells and KG-1 cells, have an increased permeability to H þ when compared to polarized Caco2-BBE cells. Finally, we showed that hPepT1 is responsible for transporting fMLP into undifferentiated and differentiated (macrophage-like) KG-1 cells. Together, these results show that hPepT1 is expressed in nonpolarized immune cells, such as macrophages, where the transporter functions best at the physiological pH 7.2. Furthermore, we provide evidence for hPepT1-mediated fMLP transport, which might constitute a novel immune cell activation pathway during intestinal inflammation.

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Intestinal Macrophages Lack CD14 and CD89 and Consequently Are Down-Regulated for LPS- and IgA-Mediated Activities

Cited by 294 publications

References 34 publications

Human Intestinal Epithelial Cells Are Broadly Unresponsive to Toll-Like Receptor 2-Dependent Bacterial Ligands: Implications for Host-Microbial Interactions in the Gut

Human Intestinal Epithelial Cells Are Broadly Unresponsive to Toll-Like Receptor 2-Dependent Bacterial Ligands: Implications for Host-Microbial Interactions in the Gut

TLR Signaling in the Gut in Health and Disease

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes

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