TLR4 Blocking Research Articles

Toll-Like Receptor-2 Mediates Inflammation and Matrix Degradation in Human Atherosclerosis

Inflammation and matrix degradation are the hallmarks of high-risk atherosclerosis that leads to myocardial infarction and stroke. Toll-like receptors (TLRs), key players in innate immunity, are upregulated in atherosclerotic lesions, but their functional role in human atherosclerosis is unknown. We explored the effects of blocking TLR-2, TLR-4, and myeloid differentiation primary response gene 88 (MyD88), a signaling adaptor shared by most TLRs and interleukin-1 receptor (IL-1R), in an in vitro model of human atherosclerosis. Carotid endarterectomies were obtained from patients with symptomatic carotid disease. Cells were isolated via enzymatic tissue dissociation and cultured in the presence or absence of TLR signaling blockers. A dominant-negative form of MyD88 (MyD88(DN)) decreased the production of monocyte chemotactic protein-1/CCL2 (P=0.000), IL-8/CXCL8 (P=0.006), IL-6 (P=0.002), matrix metalloproteinase-1 (MMP-1; P=0.002), and MMP-3 (P=0.000), as well as nuclear factor-kappaB activation (P<0.05) in atheroma cell cultures. IL-1R antagonist, TLR-4 blocking antibodies, or overexpression of a dominant-negative form of the TLR-4 signaling adaptor TRIF-related adaptor molecule reduced nuclear factor-kappaB activity but did not have a broad impact on the production of the mediators studied. In contrast, TLR-2 neutralizing antibodies inhibited nuclear factor-kappaB activation (P<0.05) and significantly reduced monocyte chemotactic protein-1/CCL2 (P=0.000), IL-8/CXCL8 (P=0.009), IL-6 (P=0.000), and MMP-1 (P=0.000), MMP-2 (P=0.004), MMP-3 (P=0.000), and MMP-9 (P=0.006) production. Our data indicate that TLR-2 signaling through MyD88 plays a predominant role in inflammation and matrix degradation in human atherosclerosis. TLR-2 blockade may represent a therapeutic strategy for atherosclerosis and its complications.

Release of heat shock protein 70 and the effects of extracellular heat shock protein 70 on the production of IL-10 in fibroblast-like synoviocytes

It has recently been suggested that heat shock protein (Hsp) 70, an intracellular protein, can be released into the extracellular compartment and exert important immunomodulatory functions. Although elevated Hsp70 has been found in synovial fluid from patients with rheumatoid arthritis (RA), its sources and extracellular functions remain unclear. In this study, we explored whether stress response such as heat stress or exposure to tumor necrosis factor-alpha (TNF-alpha) could induce Hsp70 release from RA fibroblast-like synoviocytes (FLSs) and whether extracellular Hsp70 would stimulate cytokine production in RA FLSs. Cultured FLSs were obtained from patients with RA. The expression of intracellular Hsp70 was studied by Western blot. Hsp70 release and the production of interleukin (IL)-6, IL-8, and IL-10 by RA FLSs were studied by specific enzyme-linked immunosorbent assays. The levels of Toll-like receptor (TLR) 2 and 4 mRNA and protein in FLSs were analyzed using reverse transcription-polymerase chain reaction and Western blotting. Treatment with sublethal heat shock or TNF-alpha results in the up-regulation of intracellular Hsp70 in FLSs and Hsp70 release from RA FLSs. In vitro studies show that extracellular Hsp70 can induce anti-inflammatory cytokine IL-10 production in FLSs. The mRNA and protein expression of TLR2 and TLR4 was demonstrated in FLSs, and TLR4 blocking abrogated the up-regulatory effects of Hsp70 on IL-10 production. Thus, these results lend support to the hypothesis that Hsp70 is actively released from FLSs in response to heat shock or TNF-alpha and Hsp70 may be a major paracrine/autocrine inducer of IL-10 production in FLSs via TLR4.

Systematic analysis highlights the key role of TLR2/NF-κB/MAP kinase signaling for IL-8 induction by macrophage-like THP-1 cells under influence of Borrelia burgdorferi lysates

Lyme borreliosis is a spirochetal infection caused by the Borrelia burgdorferi sensu lato complex that can proceed towards an inflammatory joint manifestation known as Lyme arthritis. Production of chemokines orchestrating neutrophil infiltration is supposed to be key to early arthritic pathogenesis. Using PMA-differentiated macrophage-like THP-1 (mTHP-1) cells we identified by antibody array methodology or mRNA analysis IL-8, GRO-α, NAP-2, and SDF-1α as being among those chemokines that are upregulated by bacterial lysates obtained from B. burgdorferi. Based on these observations, we set out to characterize in detail mechanisms mediating IL-8 release in this cellular model. TLR2 blocking antibodies, analysis of p65 translocation, and electromobility-shift analysis revealed activation of the TLR2/NF-κB axis by B. burgdorferi. The functional importance of this pathway was substantiated by suppression of IL-8 after inhibition of IκB kinase. Notably, MAP kinases, specifically the MEK1/2–ERK1/2 pathway, were essential for IL-8 secretion. Those data were confirmed by using freshly isolated adherent peripheral blood mononuclear cells. On the contrary, B. burgdorferi-induced IL-8 in mTHP-1 was unlikely related to flagellin, α3β1-integrin signaling, lipopolysaccharide, bacterial DNA, NOD1/NOD2 agonists, or to intermediate production of IL-1β and TNF-α. Induction of IL-8 by B. burgdorferi was not due to amplification of constitutive AP-1 DNA-binding activity detectable in mTHP-1 cells. Data presented herein validate that TLR2, particularly on mTHP-1 cells, holds a central position in mediating IL-8 secretion associated with extracellular B. burgdorferi and beyond that suggest inhibition of IκB kinase and MEK1/2 kinases as promising pharmacological strategies aiming at IL-8 in early Lyme arthritis.

Amplifying elements of arthritis and joint destruction

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterised by chronic joint inflammation and variable degrees of bone and cartilage erosion. Studies in animal models of arthritis provide insight into...

Mycobacterium bovis BCG Toll-Like Receptors 2 and 4 Cooperation Increases the Innate Epithelial Immune Response

Although CXCL8 is known to be important both in enhancing local antimycobacterial activity and in driving recruitment of leukocyte subsets during inflammatory processes, little information is known about the relationship between transcriptional upregulation of the Mycobacterium bovis BCG-induced CXCL8 secretion and TLR signaling. Phosphorylation of ERK1/2 was analyzed by immunoblot analysis. The levels of immunoreactive CXCL8 were measured with cytokine-specific commercial ELISA kits. By using antibodies against both TLR2 and TLR4, the levels of CXCL8 mRNA were determined by RT-PCR. In this study, we found that the inhibition of TLR2 significantly, and that of TLR4 partially, decreased the ERK1/2 activation and the subsequent CXCL8 secretion induced by the M. bovis BCG when neutralizing antibodies to TLR2 or TLR4 were applied to human epithelial cells. Moreover, it is important to note that the levels of CXCL8 secretion and mRNA were markedly (94%) reduced by functional blocking of both TLR2 and TLR4. Under the same conditions, control stimulation with TLR4 (LPS) was markedly blocked with an anti-TLR4 antibody. Finally, when ERK1/2 activity was inhibited in TLR2- or TLR4-expressing cells, M. bovis BCG-dependent CXCL8 production resulted in a significant inhibition. Together these results suggest that the M. bovis BCG, acting through both TLR2 and TLR4, induces the activation of the ERK1/2 MAPK pathway, which in turn plays a major role in CXCL8 secretion.

Bcl10 mediates LPS-induced activation of NF-κB and IL-8 in human intestinal epithelial cells

Lipopolysaccharide (LPS) is recognized as an inducer of the inflammatory response associated with gram-negative sepsis and systemic inflammatory response syndrome. LPS induction proceeds through Toll-like receptor (TLR) in immune cells and intestinal epithelial cells (IEC). This report presents the first identification of Bcl10 (B-cell CLL/lymphoma 10) as a mediator of the LPS-induced activation of IL-8 in human IEC. Bcl10 is a caspase-recruitment domain-containing protein, associated with constitutive activation of NF-kappaB in MALT (mucosa-associated lymphoid tissue) lymphomas. The normal human IEC line NCM460, normal primary human colonocytes, and ex vivo human colonic tissue were exposed to 10 ng/ml of LPS for 2-6 h. Effects on Bcl10, phospho-IkappaBalpha, NF-kappaB, and IL-8 were determined by Western blot, ELISA, immunohistochemistry, and confocal microscopy. Effects of Bcl10 silencing by small-interfering RNA (siRNA), TLR4 blocking antibody, TLR4 silencing by siRNA, and an IL-1 receptor-associated kinase (IRAK)-1/4 inhibitor on LPS-induced activation were examined. Following Bcl10 silencing, LPS-induced increases in NF-kappaB, IkappaBalpha, and IL-8 were significantly reduced (P < 0.001). Increasing concentrations of LPS were associated with higher concentrations of Bcl10 protein when quantified by ELISA, and the association between LPS exposure and increased Bcl10 was also demonstrated by Western blot, immunohistochemistry, and confocal microscopy. Exposure to TLR4 antibody, TLR4 siRNA, or an IRAK-1/4 inhibitor eliminated the LPS-induced increases in Bcl10, NF-kappaB, and IL-8. Identification of Bcl10 as a mediator of LPS-induced activation of NF-kappaB and IL-8 in normal human IEC provides new insight into mechanisms of epithelial inflammation and new opportunities for therapeutic intervention.

Endogenous signals released from necrotic cells augment inflammatory responses to bacterial endotoxin

Stressed cells undergoing necrosis release molecules that acts as endogenous danger signals to alert and activate innate immune cells. Both HMGB1 and HSP70 are induced in activated monocytes/macrophages and also are released from stressed or injured cells. We investigated whether HMGB1 and HSP70 released from necrotic monocytes/macrophages, can act as danger signals to mediate proinflammatory cytokine responses to bacterial endotoxin or lipopolysaccharide (LPS). We show that cell lysate, obtained from necrotic cells directly stimulates the proinflammatory cytokine and chemokine responses in human monocyte/macrophage cell line, THP-1, as revealed by the induction of TNF-α, IL-6 and IL-8 mRNA expression and protein production. In the presence of LPS, necrotic cell lysate induced a more robust increase in all three proteins. We found that HMGB1 and HSP70 were indeed present in the necrotic cell lysate and were responsible for the significant induction of the proinflammatory cytokine expression, as neutralization with antibodies against both proteins blocked the increase in the cytokine production seen after incubating LPS-stimulated cells with the necrotic cell lysate. We also found that the newly identified triggering receptor expressed on myeloid cells-1 (TREM-1) was involved in mediating the HMGB1- and HSP70-induced cytokine production. Blocking TREM-1 on THP-1 cells with a recombinant chimera prevented the increase in cytokine production, while simultaneous blocking of TLR4 and TREM-1 completely abolished the proinflammatory response, suggesting that TREM-1 synergizes with TLR4 to mediate the effects of such signals from necrotic cells. In addition, blocking HMGB1 or HSP70 simultaneously with TREM-1 did not decrease the cytokine level further, confirming the involvement of TREM-1 in mediating the effect of HMGB1 and HSP70. Although the interaction of HMGB1 and HSP70 with TREM-1 induced IκBα and p38 expression, both of which are required for the inflammatory cytokine expression, blockade of TREM-1 did not affect IκBα expression but markedly reduced p38 activation, as revealed by Western blot analysis. Together, these results demonstrate that HMGB1 and HSP70 released from necrotic cells function as endogenous danger signals to augment the proinflammatory responses in monocytes/macrophage and that TREM-1 relays such signals to the cytokine expression cascade. This mechanism may contribute to the amplification and persistence of the inflammatory response to bacterial infection.

TLR2-dependent recognition of Streptococcus suis is modulated by the presence of capsular polysaccharide which modifies macrophage responsiveness

Streptococcus suis capsular type 2 is an important swine pathogen and an agent of zoonosis. Although meningitis is the most common form of disease, septicemia and septic shock are also frequently reported. Despite reports that CD14 is involved in the recognition of encapsulated S. suis by host cells, the mechanisms underlying exacerbated release of pro-inflammatory cytokines, which may have a negative impact on disease outcome, are unclear. Here, we demonstrated that stimulation of human monocytes by whole encapsulated S. suis or its purified cell wall components influences the relative expression of Toll-like receptor (TLR)-2 and CD14 mRNA. Moreover, this stimulation triggered the release of cytokines (tumor necrosis factor-alpha, IL-1beta and IL-6) and chemokines (IL-8 and monocyte chemoattractant protein-1), which was significantly reduced by antibody-mediated blocking of TLR2 but not TLR4. Mouse macrophages deficient in TLR2 also showed impaired cytokine responses to encapsulated bacteria. Given that this response was completely abrogated in myeloid differentiation factor 88 (MyD88)-deficient macrophages, other TLRs might also be involved. Furthermore, we demonstrated that the presence of capsular polysaccharide (CPS)-modulated S. suis interactions with TLRs. In the absence of CPS, uncovered cell wall components induced cytokine and chemokine production via TLR2-dependent as well as -independent pathways, whereas CPS contributes to MCP-1 production in a MyD88-independent manner. Overall, this study contributes to a better understanding of the inflammatory processes induced by an encapsulated pathogen and suggests that the relative expression of CPS, known to be modulated during bacterial invasion and dissemination in the host, might alter interactions with host cells and, consequently, the outcome of the inflammatory response.

HtpG, the Porphyromonas gingivalis HSP-90 homologue, induces the chemokine CXCL8 in human monocytic and microvascular vein endothelial cells

CXCL8 (interlukin 8, IL-8) has a diverse spectrum of biological activities including T cell, neutrophil and basophil chemotactic properties. It is produced by a wide variety of cell types and plays a significant role in the initiation of the acute inflammatory response. During inflammation, CXCL8 attracts and activates leukocytes at the site of infection leading to leukocyte infiltration, which can lead to tissue damage. Porphyromonas gingivalis, an aetiological agent of periodontitis, induces production of CXCL8 from several types of cells via its LPS and outer membrane proteins. Bacterial chaperones elicit a strong pro-inflammatory response in cells of the innate immune system. In P. gingivalis the htpG gene codes for the homologue of human Hsp90, a chaperone that associates with transcription factors, hormone receptors and protein kinases, affecting signal transduction pathways. CXCL8 mRNA and CXCL8 protein production was induced in monocytic/human microvascular vein endothelial cells treated with P. gingivalis cells or rHtpG protein. Blocking of receptors CD91 and TLR4 reduced the production of CXCL8 by rHtpG either using receptor-specific antibody or by siRNA silencing. Pre-incubation of P. gingivalis rHtpG preparations with human anti-HtpG significantly inhibited CXCL8 production. A P. gingivalis HtpG disruption mutant also induced less CXCL8 mRNA and protein. These results suggest that P. gingivalis HtpG might be involved in CXCL8-mediated immunopathogenesis.

Pneumocystis-mediated IL-8 release by macrophages requires coexpression of mannose receptors and TLR2

Interaction with the unique fungus Pneumocystis (Pc) promotes IL-8 release by human alveolar macrophages (AM), although the receptor(s) mediating IL-8 release have not been identified. TLR2 recognizes fungal components and mediates release of host defense cytokines and chemokines, although whether TLR2 mediates signaling in response to Pc is not known. In the current study, Pc induced IL-8 release by human AM, and AM pretreatment with anti-TLR2 neutralizing antibody reduced IL-8 release. However, in nonphagocytic human embryonic kidney (HEK)293 cells transfected with human TLR2 cDNA, incubation with Pc did not induce IL-8 release, whereas these same cells released IL-8 in response to the TLR2 agonist lipoteichoic acid. Targeted gene silencing of AM mannose receptors (MR; phagocytic receptors for Pc) using small interfering RNA also reduced Pc-mediated IL-8 release in human AM. However, HEK293 cells transfected with human MR cDNA alone did not release IL-8 in response to Pc. In contrast, HEK293 cells cotransfected with human TLR2 and human MR cDNA released IL-8 in response to Pc. In human AM, Pc promoted direct interaction of MR and TLR2, IL-8 release was reduced markedly upon simultaneous blocking of TLR2 and gene silencing of MR, and IL-8 release was dependent in part on transcription factor NF-kappaB and ERK1/2 and JNK MAPKs. These studies demonstrate that Pc-mediated IL-8 release by human AM requires the coexpression of MR and TLR2 and further supports the concept that combinatorial interactions of macrophage innate receptors provide specificity of host defense cell responses to infectious challenge.

Aspergillus fumigatus activate human corneal epithelial cells via Toll-like receptor 2 and 4

To determine Toll-like receptors (TLR) 2 and TLR4 expression in human corneal epithelial tissue and cell line (THCE), and its activation by aspergillus fumigatus (AF) in inflammatory response. The expression of TLR2 and TLR4 protein in human corneal epithelial tissue and THCE was detected by Western blot and immunocytochemistry. THCE was challenged with AF mycelium fragment (5 x 10(6)/ml) and supernatant extract agent (equivalent to bovine serum albumin 10 microg/ml). IL-8 and TNF-alpha in THCE supernatant were detected by ELISA at 1, 2, 4 and 8 h post stimulation. The protein of IkappaBalpha in THCE cells was assayed by Western blot at 30 min, 1 h and 2 h after treatment. Antibody blocking test was utilized to evaluate the effect on IL-8 and TNF-alpha expression of THCE by blocking TLR2 and (or) TLR4 before challenge with AF agent. TLR2 and TLR4 protein were expressed in human corneal epithelial tissue and THCE. The IL-8 and TNF-alpha level in THCE supernatant was elevated at 1 h, increased to (64.71 +/- 5.15) pg/ml and (32.46 +/- 3.28) pg/ml (AF mycelium challenge group), (94.94 +/- 11.92) pg/ml and (48.70 +/- 3.32) pg/ml (AF supernatant challenge group) 8 h post-challenged, which was 3.0 times and 2.5 times, 4.5 times and 3.5 times to that of control group respectively (P < 0.01). The activity of IkappaBalpha in THCE cells was decreased to 10.31 +/- 1.30 (gray scale value) and 8.15 +/- 2.37 at 30 min after challenged with AF mycelium or supernatant extract agent compared to 51.57 +/- 5.58 and 49.23 +/- 3.49 of control group (P < 0.01), and was reverted at 2 h. The secretion of IL-8 and TNF-alpha was partly inhibited by blocking TLR2 or TLR4 (P < 0.05), obviously inhibited by blocking TLR2 and TLR4 (50% and 40% compared to that of control group) (P < 0.01) when challenged with AF mycelium. And that was markedly inhibited by blocking TLR4 or blocking TLR2 and TLR4 when challenged with AF supernatant (P < 0.01). The secretion of IL-8 and TNF-alpha was not inhibited by blocking TLR2 when challenged with AF supernatant (P > 0.05). AF agent may induce human corneal epithelial cells express inflammatory cytokines via TLR-NF-kappaB pathway. TLR2 and TLR4 possibly mediate the recognition to AF mycelium, and TLR4 may dominate the recognition to AF supernatant agent.

Toll-Like Receptor 2 as a Functional Receptor to Respiratory Syncytial Virus

RATIONALE: Since respiratory syncytial virus (RSV) infection in infancy may well cause for bronchiolitis and development of asthma and innate immunity is suggested to be involved in the recognition of RSV, we investigated the role of TLRs in defense against RSV. METHODS: 1) Human monocytic cell line THP-1 was stimulated by heat-inactivated RSV, mock (Hep2 cell), ultra-purified LPS or synthetic mycoplasmal lipoprotein FSL-1. Blocking analysis was performed by adding TLR4 blocking antibody (HTA125) or TLR2 blocking antibody (TL2.1). The level of IL-12p40 in the culture supernatant was measured by ELISA. 2) Peritoneal macrophage from C57BL/6 or TLR2-KO on BL/6 background mice were stimulated by heat-inactivated RSV, mock, Ultra-purified LPS or FSL-1. The level of IL-6 in the culture supernatant was measured by ELISA. 3) Various amount of soluble CD14 (sCD14) preincubated with RSV, mock, ultra-purified LPS or FSL-1 were used to stimulate THP-1 cells and the level of IL-12p40 in the culture supernatant was measured by ELISA. RESULTS: 1) TLR2 blocking antibody suppressed heat-inactivated RSV induced IL-12p40 production more strongly than TLR4 blocking antibody did. 2) TLR2-KO macrophage was defective in IL-6 production in response to stimulation with heat-inactivated RSV as well as FSL-1. 3) sCD14 enhanced RSV-induced IL-12p40 production as well as LPS-induced IL-12p40 production. On the other hand sCD14 did not affect FSL-1-induced IL-12p40 production. CONCLUSIONS: Our data suggest that TLR2 is a functional receptor for RSV and sCD14 may work as a co-receptor for RSV like TLR4 recognition of LPS. In contrast, FSL-1 recognition by TLR2 does not need sCD14.

Chlamydophila pneumoniae induces expression of Toll-like Receptor 4 and release of TNF-α and MIP-2 via an NF-κB pathway in rat type II pneumocytes

BackgroundThe role of alveolar type II cells in the regulation of innate and adaptive immunity is unclear. Toll-like receptors (TLRs) have been implicated in host defense. The purpose of the present study was to investigate whether Chlamydophila pneumoniae (I) alters the expression of TLR2 and/orTLR4 in type II cells in a (II) Rho-GTPase- and (III) NF-κB-dependent pathway, subsequently (IV) leading to the production of (IV) pro-inflammatory TNF-α and MIP-2.MethodsIsolated rat type II pneumocytes were incubated with C. pneumoniae after pre-treatment with calcium chelator BAPTA-AM, inhibitors of NF-κB (parthenolide, SN50) or with a specific inhibitor of the Rho-GTPase (mevastatin). TLR2 and TLR4 mRNA expressions were analyzed by PCR. Activation of TLR4, Rac1, RhoA protein and NF-κB was determined by Western blotting and confocal laser scan microscopy (CLSM) and TNF-α and MIP-2 release by ELISA.ResultsType II cells constitutively expressed TLR4 and TLR2 mRNA. A prominent induction of TLR4 but not TLR2 mRNA was detected after 2 hours of incubation with C. pneumoniae. The TLR4 protein expression reached a peak at 30 min, began to decrease within 1–2 hours and peaked again at 3 hours. Incubation of cells with heat-inactivated bacteria (56°C for 30 min) significantly reduced the TLR4 expression. Treated bacteria with polymyxin B (2 μg/ml) did not alter TLR4 expression. C. pneumoniae-induced NF-κB activity was blocked by TLR4 blocking antibodies. TLR4 mRNA and protein expression were inhibited in the presence of BAPTA-AM, SN50 or parthenolide. TNF-α and MIP-2 release was increased in type II cells in response to C. pneumoniae, whereas BAPTA-AM, SN50 or parthenolide decreased the C. pneumoniae-induced TNF-α and MIP-2 release. Mevastatin inhibited C. pneumoniae-mediated Rac1, RhoA and TLR4 expression.ConclusionThe TLR4 protein expression in rat type II cells is likely to be mediated by a heat-sensitive C. pneumoniae protein that induces a fast Ca2+-mediated NF-κB activity, necessary for maintenance of TLR4 expression and TNF-α and MIP-2 release through possibly Rac and Rho protein-dependent mechanism. These results indicate that type II pneumocytes play an important role in the innate pulmonary immune system and in inflammatory response mechanism of the alveolus.

Hyaluronan Fragments Stimulate Endothelial Recognition of Injury through TLR4

Tissues must quickly recognize injury to respond to the rapid pace of microbial growth. In skin, dermal microvascular endothelial cells must also react to danger signals from the surrounding tissue and immediately participate by initiating the wound repair process. Components of the extracellular matrix such as hyaluronan are rapidly broken down into smaller molecular weight oligosaccharides in a wound, and these can activate a variety of biological processes. This study set out to determine if hyaluronan fragments released following injury can stimulate endothelial cells and what mechanism is responsible for this response. Using genechip microarray analysis, a response to hyaluronan fragments was detected in endothelial cells with the most significant increase observed for the chemokine IL-8. This observation was verified with qualitative reverse transcriptase-PCR and ELISA in human endothelial cell culture, and in a mouse model by observing serum levels of MIP-2 and KC following hyaluronan fragment administration in vivo. Activation was TLR4-dependent, as shown by use of TLR4 blocking antibody and TLR4-deficient mice, but not due to the presence of undetected contaminants as shown by inactivation following digestion with the hyaluronan-degrading enzyme chondroitinase ABC or incubation with the hyaluronan-specific blocking peptide Pep-1. Inactivation of LPS activity failed to diminish the action of hyaluronan fragments. These observations suggest that endogenous components of the extracellular matrix can stimulate endothelia to trigger recognition of injury in the initial stages of the wound defense and repair response.