NOD2 Agonist Muramyl Dipeptide Research Articles

NOD2-mediated HDAC6/NF-κb signalling pathway regulates ferroptosis induced by extracellular histone H3 in acute liver failure.

Acute liver failure (ALF) is life-threatening and often associated with high mortality rates. The aim of the present study was to investigate whether extracellular histone H3 could induce ferroptosis in hepatic macrophages in ALF and explore its potential mechanism. RAW264.7 macrophages and C57BL/6 mice were used in this study. LPS, D-galactosamine (D-Gal), histone H3, histone H3 antibody, NOD2 agonist Muramyl Dipeptide (MDP) and HDAC6-siRNA were administered in this study. The key molecules of ferroptosis, NOD2, HDAC6 and the NF-κb pathway, were detected. In vitro, histone H3 was released into the extracellular environment from cell nucleus after LPS exposure. In addition, histone H3 could induce ferroptosis in RAW264.7 macrophages with increased level of Fe2+ and ROS and decreased levels of GPX4 and GSH. MDP further aggravated ferroptosis in RAW264.7 macrophages stimulated by histone H3, which was accompanied by elevated NOD2, HDAC6, p-P65 and IκBα. HDAC6-siRNA ameliorated ferroptosis in RAW264.7 macrophages induced by histone H3, which was accompanied by decreased levels of HDAC6, p-P65 and IκBα. However, HDAC6-siRNA did not alter NOD2 levels in RAW264.7 macrophages administered histone H3. In vivo, the levels of NOD2, HDAC6 the NF-κb pathway and ferroptosis were increased in ALF mice, which were downregulated by histone H3 antibody and upregulated by histone H3. Extracellular histone H3 could induce ferroptosis in hepatic macrophages in ALF by regulating theNOD2-mediated HDAC6/NF-κb signalling pathway.

The Nod2 Agonist Muramyl Dipeptide Cooperates with the TLR4 Agonist Lipopolysaccharide to Enhance IgG2b Production in Mouse B Cells

Many studies have shown that Toll-like receptors (TLRs) and Nod-like receptors (NLRs) were expressed in B cells and their signaling affects B cell functions. Nonetheless, the roles played by these receptors in B cell antibody (Ab) production have not been completely elucidated. In the present study, we examined the effect of the Nod2 agonist muramyl dipeptide (MDP) in combination with the TLR4 agonist lipopolysaccharide (LPS), a well-known B cell mitogen, on B cell viability, proliferation, and activation, and Ab production by in vitro culture of purified mouse spleen resting B cells. MDP combined with LPS to reinforce B cell viability, proliferation, and activation. Moreover, MDP enhanced LPS-induced IgG2b production, germline γ2b transcript (GLTγ2b) expression, and surface IgG2b expression. In an experiment with Nod2- and TLR4-deficient mouse B cells, we observed that the combined effect of MDP and LPS is dependent on Nod2 and TLR4 receptors. Furthermore, the combined effect on B cell viability and IgG2b switching was not observed in Rip2-deficient mouse cells. Collectively, this study suggests that Nod2 signaling enhances TLR4-activated B cell proliferation, IgG2b switching, and IgG2b production.

74P - The bacterial receptor NOD2 mediates LGR5+ intestinal stem cells protection against irradiation via mitophagy activation

BackgroundThe NOD2 agonist muramyl-dipeptide (MDP), a peptidoglycan motif common to all bacteria, supports LGR5+ intestinal stem cells (ISCs) survival through NOD2 activation upon an otherwise lethal oxidative-stress-mediated signal. Yet the underlying protective mechanisms remains unknown. MethodsIrradiation was used as stressor and primarily murine-derived intestinal organoids as a model system. ResultsMDP induced a strong reduction of total and mitochondrial reactive oxygen species (ROS) within ISCs, which was associated with mitophagy induction. ATG16L1 KO and NOD2 KO organoids did not benefit from the MDP-induced cytoprotection. We showed the MDP-dependent induction of ISC mitophagy upon stress in vivo. ConclusionsIn LGR5+ ISCs, NOD2 allows irradiation-generated ROS clearance through ATG16L1-activated mitophagy. Legal entity responsible for the studyThe authors. FundingThis work was supported by European Research Council (ERC) advanced grant 339579-DECRYPT to P.J.S and by French National Research Agency (ANR) grant 17-CE14-0022 (i-Stress) to P.S.. A.L. was personally funded by: i) Poste d’Accueil INSERM and ii) Soutien pour la formation à la recherche translationnelle en cancérologie (ITMO Cancer, INCa - Plan Cancer 2014-2019, allocation number: ASC17040JSA). DisclosureAll authors have declared no conflicts of interest.

Relation between NOD2 genotype and changes in innate signaling in Crohn\u2019s disease on mRNA and miRNA levels

Crohn’s disease is associated with an altered innate immune response of pathogenic importance. This altered response can be associated to loss-of-function polymorphisms in the NOD2 (nucleotide-binding oligomerization domain-containing protein 2) gene, but also changes in transcriptional and post-transcriptional regulatory layers, including microRNA activity. Here, we characterized the link between NOD2 genotype and inflammatory-mediated changes in innate signaling by studying transcriptional and post-transcriptional activity in response to NOD2-agonist muramyl dipeptide in monocytes from healthy controls, and Crohn’s disease patients with and without NOD2 loss-of-function polymorphisms. We measured the expression of genes and microRNAs in monocytes from these subjects after stimulation with muramyl dipeptide. Gene expression profiles mainly distinguished the actual muramyl dipeptide response, but not the genotype. A hyper-responsive phenotype was found in Crohn’s disease patients without NOD2 mutations, characterized by upregulated cytokine receptors and general downregulation of microRNA expression. Conversely, microRNA expression could identify genotype-specific differences between subject groups but exhibited little change upon muramyl dipeptide treatment. Only two microRNAs showed muramyl dipeptide-induced response, including miR-155, which was found to regulate multiple genes and whose host gene was one of the highest muramyl dipeptide responders. miR-155 was upregulated in Crohn’s disease patients with NOD2 mutations following lipopolysaccharide and Escherichia coli treatment, but the upregulation was substantially reduced upon muramyl dipeptide treatment. While Crohn’s disease patients with NOD2 mutations on average showed a reduced muramyl dipeptide response, the cohort exhibited large individual variance: a small subset had inflammatory responses almost comparable to wild-type patients on both gene and miR-155 regulatory levels.

Aberrant interleukin-1 signalling does not increase susceptibility of mice to NOD2-dependent uveitis.

NOD2 is the genetic cause of Blau syndrome, an autoinflammatory disease that manifests as coincident uveitis and arthritis. Since dysregulation of IL-1 signalling is considered a pathogenic mechanism in a number of related autoinflammatory conditions, we examined the extent to which unimpeded interleukin (IL)-1 signalling influences NOD2-dependent inflammation of the eye versus the joint. Mice deficient for IL-1R antagonist (IL-1Ra) were administered the NOD2 agonist muramyl dipeptide (MDP) by systemic (intraperitoneal) or local (intraocular and/or intra-articular) injections. NOD2-deficient mice received an intraocular injection of recombinant IL-1β. Uveitis was evaluated by intravital videomicroscopy and histopathology, and arthritis was assessed by near-infrared imaging and histopathology. Ocular levels of IL-1α, IL-1β and IL-1Ra were quantified by enzyme-linked immunosorbent assay. IL-1Ra deficiency did not render mice more responsive to systemic exposure of MDP. Despite the increased production of IL-1R agonists IL-1α and IL-1β in response to intraocular injection of MDP, deficiency in IL-1Ra did not predispose mice to MDP-triggered uveitis, albeit intravascular cell rolling and adherence were exacerbated. NOD2 expression was dispensable for the potential of IL-1 to elicit uveitis. However, we find that IL-1Ra does play an important protective role in arthritis induced locally by MDP injection in the joint. Our findings highlight the complexity of NOD2 activation and IL-1 signalling effects that can be compounded by local environmental factors of the target organ. These observations may impact how we understand the molecular mechanisms by which NOD2 influences inflammation of the eye versus joint, and consequently, treatment options for uveitis versus arthritis.

Synergistic effects of NOD1 or NOD2 and TLR4 activation on mouse sickness behavior in relation to immune and brain activity markers.

Toll-like receptors (TLRs) and nuclear-binding domain (NOD)-like receptors (NLRs) are sensors of bacterial cell wall components to trigger an immune response. The TLR4 agonist lipopolysaccharide (LPS) is a strong immune activator leading to sickness and depressed mood. NOD agonists are less active but can prime immune cells to augment LPS-induced cytokine production. Since the impact of NOD and TLR co-activation in vivo has been little studied, the effects of the NOD1 agonist FK565 and the NOD2 agonist muramyl dipeptide (MDP), alone and in combination with LPS, on immune activation, brain function and sickness behavior were investigated in male C57BL/6N mice.Intraperitoneal injection of FK565 (0.001 or 0.003 mg/kg) or MDP (1 or 3 mg/kg) 4 h before LPS (0.1 or 0.83 mg/kg) significantly aggravated and prolonged the LPS-evoked sickness behavior as deduced from a decrease in locomotion, exploration, food intake and temperature. When given alone, FK565 and MDP had only minor effects. The exacerbation of sickness behavior induced by FK565 or MDP in combination with LPS was paralleled by enhanced plasma protein and cerebral mRNA levels of proinflammatory cytokines (IFN-γ, IL-1β, IL-6, TNF-α) as well as enhanced plasma levels of kynurenine. Immunohistochemical visualization of c-Fos in the brain revealed that NOD2 synergism with TLR4 resulted in increased activation of cerebral nuclei relevant to sickness.These data show that NOD1 or NOD2 synergizes with TLR4 in exacerbating the immune, sickness and brain responses to peripheral immune stimulation.Our findings demonstrate that the known interactions of NLRs and TLRs at the immune cell level extend to interactions affecting brain function and behavior.

Nucleotide Oligomerization Domain 1 Ligation Suppressed Murine Allergen–Specific T-Cell Proliferation and Airway Hyperresponsiveness

The cytosolic nucleotide oligomerization domain (NOD)-like receptors NOD1 and NOD2 are important contributors to the intracellular recognition of pathogens including Chlamydophila pneumoniae, but little is known about their influence on allergen-induced airway inflammation. In BALB/c mice, we observed that infection with C. pneumoniae before systemic sensitization with ovalbumin (OVA) and local OVA airway exposure diminished airway hyperresponsiveness (AHR). Thus, the impact of the NOD1 agonist FK156 and the NOD2 agonist muramyl dipeptide given 6 hours before each sensitization or airway challenge was evaluated regarding AHR, OVA-specific plasma immunoglobulins, bronchoalveolar lavage fluid differentials, and cytokines. Spleen dendritic cells of FK156-treated mice were isolated and cocultured with OVA-specific T cells isolated from DO11.10 mice, and T-cell proliferation was quantified after OVA restimulation. T-cell proliferation was investigated in vivo in lungs and lymph nodes of FK156-treated and OVA-exposed DO11.10 mice. FK156, but not muramyl dipeptide, reduced AHR and pulmonary eosinophilic infiltration if given before OVA sensitization or challenge, whereas T-helper (Th)2 cytokines were not diminished. Dendritic cells from FK156-treated mice evoked less OVA-specific T-cell proliferation as compared with solvent-treated controls. Similarly, antigen-specific T-cell activation in lung tissue was diminished after FK156 treatment. We conclude that NOD1 activation reduced AHR in allergen-induced lung inflammation, which was accompanied by a reduction of allergen-specific T-cell proliferation.

A vitamin D3 analog augmented interleukin-8 production by human monocytic cells in response to various microbe-related synthetic ligands, especially NOD2 agonistic muramyldipeptide

Active metabolite vitamin D3, 1α,25-dihydroxyvitamin D3, is a pleiotropic factor and exhibits various physiological functions, including immunomodulating activities. In this study, the possible regulation of innate immune responses of human monocytic cells by a vitamin D3 analog was examined. Human monocytic THP-1 cells were pre-treated with OCT, vitamin D3 analog, 1α,25-dihydroxy-22-oxavitamin D3, followed by stimulation with various chemically synthesized Toll-like receptors (TLR) and NOD1 and NOD2 ligands. OCT-treated cells produced more IL-8 than non-treated cells upon stimulation with various chemically-synthesized ligands: TLR2-agonistic lipopeptide (FSL-1), TLR3-agonistic poly I:C, TLR4-agonistic lipid A (E. coli-type LA-15-PP), NOD1-agonistic FK565 and NOD2-agonistic muramyldipeptide (MDP). Among the ligands, MDP was the highest inducer of IL-8 production in OCT-treated THP-1 cells, and IL-8 production increased depending on the treatment time until 72h. OCT up-regulated the expression of NOD2 in THP-1 cells, and OCT-treated cells exhibited higher activation of p38, JNK and ERK in the MAPK pathway, IκBα in the NF-κB pathway, and TAK1 upstream in response to MDP than non-treated cells. Analysis using siRNA against NOD2 and inhibitors of specific signal molecules indicated that the existence of NOD2 and activation of the above signaling molecules are required for enhanced production of IL-8 in OCT-treated THP-1 cells. These findings suggested that NOD2, NF-κB and MAPK pathways are involved in the activity of OCT to augment the response of human monocytic cells to MDP.

Down-Regulated NOD2 by Immunosuppressants in Peripheral Blood Cells in Patients with SLE Reduces the Muramyl Dipeptide-Induced IL-10 Production

BackgroundPattern recognition receptors (PRRs) such as Toll-like receptors are aberrantly expressed of peripheral blood mononuclear cells (PBMCs) in systemic lupus erythematosus (SLE) patients, for playing immunopathological roles.Methodology/Principal FindingsWe investigated the expression and function of the PRR nucleotide-binding oligomerization domain (NOD2) in SLE. NOD2 expression in T, B lymphocytes, monocytes, myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) was assessed in SLE patients and healthy controls (HCs) using flow cytometric analysis. Ex vivo production of cytokines from PBMCs upon NOD2 agonist muramyl dipeptide (MDP) stimulation was assessed using Cytometric Bead Array. Over-expression of NOD2 in monocytes was observed in immunosuppressant naïve SLE patients, and was positively associated with longer disease duration. Immunosuppressive therapy was an independent explanatory variable for downregulating NOD2 expression in CD8+ T, monocytes, mDCs and pDCs. Ex vivo basal productions of cytokines (IL-6, IL-8 and IL-10) were significantly increased in immunosuppressant naïve patients and patients with active disease despite immunosuppressants compared with HCs. Upon MDP stimulaiton, relative induction (%) of cytokines (IL-1β) from PBMC was significantly increased in immunosuppressant naïve patients with inactive disease, and patients with active disease despite immunosuppressant treatment compared with HCs. Immunosuppressant usage was associated with a decreased basal production and MDP induced relative induction (%) of IL-10 in patients with inactive disease compared with immunosuppressant naïve patients and HCs.Conclusions/SignificanceBacterial exposure may increase the NOD2 expression in monocytes in immunosuppressant naïve SLE patients which can subsequently lead to aberrant activation of PBMCs to produce proinflammatory cytokines, implicating the innate immune response for extracellular pathogens in the immunopathological mechanisms in SLE. Immunosuppressant therapy may downregulate NOD2 expression in CD8+ T lymphocytes, monocytes, and DCs in SLE patients which subsequently IL-10 reduction, contributing towards the regulation of immunopathological mechanisms of SLE, at the expense of increasing risk of bacterial infection.

Enhanced induction of a histamine-forming enzyme, histidine decarboxylase, in mice primed with NOD1 or NOD2 ligand in response to various Toll-like receptor agonists

We investigated the immunopharmacological aspects of innate immune responses via Toll-like receptors (TLRs), NOD1 and NOD2, in terms of induction of the histamine-forming enzyme, histidine decarboxylase (HDC), activity in mice. Intravenous injection of TLR4-agonistic synthetic lipid A definitely induced HDC activity in the liver, spleen, and lungs, especially the lungs, in mice, where maximum activity was induced about 3 h after the injection of lipid A. The TLR2/6 agonistic synthetic diacyl-type lipopeptide FSL-1 and TLR3-agonistic poly I:C were also effective in inducing HDC, while the NOD2-agonistic synthetic muramyldipeptide (MDP) and NOD1-agonistic synthetic FK156 and FK565 exhibited only weak activities in this respect. Mice primed with intravenous injection of NOD1 or NOD2 agonists produced higher HDC activity following the 4-6 h later intravenous challenge with the above TLR agonists. Among the priming agents, FK565 exhibited the strongest activity, and it was effective via various administration routes - intraperitoneal, subcutaneous, intramuscular, as well as intravenous injection; furthermore, oral (gastric) administration was effective, although it needed a dose 10 times higher than that required for other administration routes. These findings suggest that HDC is induced in association with TLRs and NOD1/2, and that the newly formed histamine by the induced HDC might play important roles in the regulation of inflammatory and immune responses in various organs.

NOD2 receptors in adenopituitary folliculostellate cells: expression and function

Folliculostellate cells (FS cells) are non-endocrine cells from the pituitary gland that respond to bacterial endotoxins by producing cytokines. In immune cells, an important component of bacterial recognition are the toll-like receptors (TLRs). Previously, we showed that FS cells express TLR4. The TLR4 ligand lipopolysaccharide (LPS) stimulates interleukin-6 (IL6) production through nuclear factor kappaB (NFKB) induction. Binding of IL6 to gp130 receptor activates signal transducer and activator of transcription 3 (STAT3), an important mediator of inflammatory response. Another family involved in innate immune response following bacterial infection is the nucleotide-binding oligomerisation domain (NOD) intracellular receptor family. Herein, we describe for the first time the expression and function of NOD receptors in human pituitary and FS TtT/GF cell line. The NOD2 agonist muramyl dipeptide (MDP) increased Nf kappa b1-transcriptional activity, -protein expression and IL6 secretion in TtT/GF cells. Furthermore, these effects were potentiated by the combination of MDP and LPS. Silencing NOD2 abolished the action of LPS on NFKB transcriptional activity and IL6 production, indicating that, in TtT/GF cells, TLR4 transduces its signal through NOD2 receptor. We show here that in TtT/GF cells, Nod2 overexpression or stimulation by MDP increased STAT3 transcriptional activity. Furthermore, silencing STAT3 inhibited basal, LPS and MDP stimulated NFKB protein expression and overexpression of protein inhibitor of activated STAT3 (Pias3) markedly decreased basal NFKB activity. These data suggest that in TtT/GF cells, STAT3 acting upstream to NFKB mediates NOD2 receptor signalling pathway. In conclusion, the present study demonstrates that NOD molecules play a modulatory role in the pituitary by regulating the function and activation of FS cells in response to bacterial components.

The distinct response of γδ T cells to the Nod2 agonist muramyl dipeptide

Purified γδ T cells are primed directly in response to pathogen associated molecular patterns (PAMPs) to better respond to secondary signals and increase expression of chemokine and activation-related genes. Transcripts encoding the innate receptor Nod2 were detected in bovine and human γδ T cells. Nod2 is the intracellular receptor for muramyl dipeptide (MDP), functions in regulating innate activities, and was thought to be expressed primarily in APCs. The response of γδ T cells to MDP was analyzed by microarray, Q-PCR, proteome array and functional priming assays. MDP had a consistent priming effect on γδ T cells, characterized by changes in transcripts and enhanced proliferation response to secondary signaling. Knockdown experiments implicated Nod2 as the receptor for MDP in γδ T cell-enriched bovine PBLs. The results indicate priming of γδ T cells by MDP, and offer definitive evidence of the expression of functional Nod2 in γδ T cells.

NOD proteins expression and function in the pituitary folliculostellate cells

Folliculostellate (FS) cells were found to regulate hormonal secretion in pituitary endocrine cells. This cell type share properties with components of the innate immune response such as dendritic cells and macrophages, and it's suggested that they are able to initiate immune responses and act as part of an immunoendocrine regulation system. Members of toll-like receptor (TLR) family recognize bacterial cell wall components and initiate an immune response. Recently, we detected by RT-PCR the TLR4 mRNA expression in FS cell line, TtT/GF. In the present study, we detected the constitutive expression of two members of a novel nucleotide-binding oligomerization domain (NOD) family of proteins that act as cytosolic receptors. We show that NOD1 and NOD2 are expressed in the human and mouse pituitary glands, and in TtT/GF cells. Furthermore, NOD1-agonistic diaminopimelic acid (DAP) and NOD2-agonistic muramyl dipeptide (MDP) induced (NF)-κB activation in TtT/GF cell cultures. Both NOD agonists in combination with TLR4 agonistic, LPS enhanced NF-κB transcriptional activity, and interleukin-6 (IL-6) production in these cells. Knocking-down NOD1 and NOD2 markedly inhibited LPS induced IL-6 production in TtT/GF cells. RNA interference for NOD2, but not NOD1, downregulated NF-κB activity. LPS, MDP and LPS plus MDP increased NF-κB expression and transcriptional activity, in a mechanism involving STAT3, since knocking-down this protein abolished NF-κB activation. All together, we revealed that NOD1 and NOD2 are expressed in the pituitary gland and in TtT/GF cells. In addition our findings suggest that FS cells play a predominant role in the context of imune-endocrine interactions during bacterial infection and inflammation and NOD proteins have a central participation in these processes.

The phosphatidylinositol 3-kinase/Akt pathway negatively regulates Nod2-mediated NF-κB pathway

Nucleotide-binding oligomerization domain containing proteins (Nods) are intracellular pattern recognition receptors (PRRs) that recognize conserved moieties of bacterial peptidoglycan and activate downstream signaling pathways, including NF-κB pathway. Here, we show that Nod2 agonist muramyldipeptide (MDP) induces Akt phosphorylation in time and dose-dependent manner. The pharmacological inhibitor of phosphatidylinositol 3-kinase (PI3K) (wortmannin) and dominant-negative forms of p85 (the regulatory subunit of PI3K) or Akt enhance, while constitutive active forms of p110 (the catalytic subunit of PI3K) or Akt inhibit, NF-κB activation and the target gene interleukin (IL)-8 induced by MDP. In addition, the pharmacological inhibitors of PI3K (wortmannin and LY294002) enhance phosphorylation of NF-κB p65 on Ser529 and Ser536 residues, which result in enhanced p65 transactivation activity. Furthermore, we show that the inhibition of PI3K by the pharmacological inhibitors prevent the inactivation of glycogen synthase kinase (GSK)-3β, suggesting that the negative regulation of PI3K/Akt on MDP-induced NF-κB activation is at least in part mediated through inactivation of GSK-3β. Taken together, our results demonstrate that PI3K/Akt pathway is activated by Nod2 agonist MDP and negatively regulates NF-κB pathway downstream of Nod2 activation. Our results suggest that PI3K/Akt pathway may involve in the resolution of inflammatory responses induced by Nod2 activation.

Antibodies to proteinase 3 prime human monocytic cells via protease-activated receptor-2 and NF-κB for Toll-like receptor- and NOD-dependent activation

Anti-neutrophil cytoplasmic Abs against proteinase 3 (PR3) have been detected in relation to a wide range of inflammatory conditions, and the interaction of anti-PR3 Abs with leukocytes provokes cell activation, although how is not clear. Flow cytometric analysis revealed an increase in cell-surface CD14, Toll-like receptor (TLR)2, TLR4 and intracellular TLR3, TLR7, TLR8, TLR9, NOD1 and NOD2 expression during anti-PR3 priming in human monocytic THP-1 cells. Anti-RP3 Abs markedly promoted the release of IL-8 induced by chemically synthesized TLR and NOD ligands mimicking bacterial components: TLR2-agonistic lipopeptide (FSL-1), TLR3-agonistic poly I:C, TLR4-agonistic lipid A (LA-15-PP), TLR7/8-agonistic single stranded RNA (ssPolyU), TLR9-agonistic bacterial CpG DNA, NOD1-agonistic FK156/565 and NOD2-agonistic muramyldipeptide (MDP) in THP-1 cells and human peripheral blood mononuclear cells, although sole incubation with anti-PR3 Abs induced only a low level of IL-8. The priming response was evident after 2 h of preincubation with anti-PR3 Abs and peaked after 6 h. Priming was also observed for the production of TNF-α and monocyte chemoattractant protein-1. An RNA interference assay revealed that anti-PR3 Abs activated THP-1 cells in a PR3- and protease-activated receptor-2-dependent manner. Furthermore, the anti-PR3 Ab-mediated cell activation was significantly abolished by RNA interference targeted at PR3 mRNA and by inhibition of phospholipase C and NF-κB. These results suggest that anti-PR3 Abs prime human monocytic cells to produce cytokines upon stimulation with various bacterial components by up-regulating the TLR and NOD signaling pathway, and that these mechanisms may actively participate in the inflammatory process.

Various human epithelial cells express functional Toll-like receptors, NOD1 and NOD2 to produce anti-microbial peptides, but not proinflammatory cytokines

Epithelial cells may form the first barrier of defense against bacteria in human tissues. We recently revealed that oral epithelial cells generated anti-bacterial factors, such as peptidoglycan recognition proteins (PGRPs) and β-defensin 2, but not proinflammatory cytokines, such as interleukin-8 (IL-8), upon stimulation with bacterial cell-surface components. In this study, we found clear expressions of Toll-like receptor (TLR)2, TLR3, TLR4, TLR7, NOD1 and NOD2 in oral, tongue, salivary gland, pharyngeal, esophageal, intestinal, cervical, breast, lung, and kidney epithelial cells. However, tongue, salivary gland, pharyngeal, esophageal, intestinal, cervical, breast, lung, and kidney epithelial cells, as well as oral epithelial cells, did not secrete IL-6, IL-8 or monocyte chemoattractant protein-1 in response to chemically synthesized TLR and NOD agonists mimicking microbial components: TLR2 agonistic lipopeptide (Pam3CSSNA), TLR3 agonistic Poly I:C, TLR4 agonistic lipid A (LA-15-PP), TLR7 agonistic single stranded RNA (ssPoly U), NOD1 agonistic iE-DAP (γ- d-glumtamyl- meso-diaminopimelic acid), and NOD2 agonistic muramyldipeptide (MDP). Although PGRPs on oral epithelial cells were significantly up-regulated upon stimulation with these synthetic components, PGRPs on pharyngeal epithelial cells were only slightly up-regulated, and PGRPs on esophageal, intestinal and cervical epithelial cells were not up-regulated upon stimulation with the components. In contrast, stimulation with synthetic TLRs and NODs ligands induced β-defensin 2 generation in all epithelial cells examined. These findings indicate that TLR and NOD in various epithelial cells are functional receptors that induce anti-bacterial responses in general without being accompanied by inflammatory responses.