Resistance to endotoxin shock and reduced dissemination of gram-negative bacteria in CD14-deficient mice

Effect of Qinggan Huoxue recipe and its separated recipes on the expression of CD14 and TLR4 in rats with alcoholic liver disease

AIM: To study the effect of Qingganhuoxue Recipe (QGHXR) (liver-clearing blood-activating) and its separated recipes on the expression of CD14 and TLR₄ in rats with ALD.

METHODS: One hundred male Wistar rats were randomly divided into three groups, that is, experimental group (n = 80) which were established with compound factors, the control group (n = 10) treated with normal saline, and CCl₄ group (n= 10) which were intraperitoneally and continuously injected with CCl₄ twice a week. Four weeks later, the experimental group was randomly divided into 4 groups: QGHXR group (n = 15), Qinggan (liver-clearing) recipe group (QGR, n = 15), Huoxue (blood -activating) recipe group (HXR, n = 15) and model group (n = 50). All rats were given suitable drugs for two weeks. The serum levels of ALT and AST were detected. Pathological changes in liver tissues were observed using HE staining. The gene expression of CD14 and TLR4 in the liver were measured using RT-PCR, the protein expression of CD14 using immunohistochemical staining, and the expression of TLR₄ using Western blot.

RESULTS: Compared with the model group, QGHXR and its separated recipes improved the degree of liver steatosis and inflammation significantly (0.67 ± 0.50, 2.15 ± 1.28, 1.38 ± 1.06 vs 4.56 ± 0.73, all P < 0.01). QGHXR degraded blood level of ALT markedly (725.65 ± 111.02 vs 884.68 ± 177.54 P < 0.05), but QGR and HXR showed no remarkable effect. QGR, HXR and QGHXR reduced the serum level of AST significantly (2383.81 ± 888.18, 2158.93 ± 922.85, 2001.90 ± 519.27 vs 3210.98 ± 640.63, P < 0.01 or 0.05), and there was not significant difference among these groups. QGR and QGHXR down-regulated the expression of CD14 mRNA significantly (1.46 ± 0.52, 1.10 ± 0.40 vs 2.67 ± 0.66, both P < 0.01), but HXR showed no obvious effect. QGR, HXR and QGHXR decreased the expression of TLR₄ mRNA significantly (1.91 ± 0.03, 2.11 ± 0.03, 1.53 ± 0.01 vs 2.37 ± 0.03, all P < 0.01), and no significant difference was observed among groups. QGHXR decreased the expression of CD14 in the liver in model group rats (13 392.28 ± 9287.54 vs 32 288.89 ± 15 631.03, P<0.01), but QGR and HXR showed no obvious effect. QGR, HXR and QGHXR decreased the expression of TLR₄ significantly (1.06 ± 0.10, 1.19 ± 0.05, 0.98 ± 0.12 vs 1.40 ± 0.11, all P < 0.01).

CONCLUSION: QGHXR and its separated recipes may provide protection against ALD in rats through down-regulating the expression of CD14 and TLR₄.

The contributing role of CD14 in toll-like receptor 4 dependent neuropathic pain

We have previously demonstrated that CNS toll-like receptor 4 (TLR4) plays a key role in the development of behavioral hypersensitivity in a rodent model of neuropathic pain, spinal nerve L5 transection (L5Tx). TLR4 is a well-known receptor for lipopolysaccharide (LPS) in innate immune responses. In the current study, we further investigated the role of CD14, an accessory molecule in the LPS-TLR4 signaling pathway, in the development of L5Tx-induced neuropathic pain. CD14 knockout (KO) mice displayed significantly decreased behavioral sensitivity (mechanical allodynia and thermal hyperalgesia) as early as day 1 post-L5Tx, indicating a nociceptive role of CD14. By flow cytometric analyses, we observed significantly elevated microglial surface CD14 expression in the ipsilateral lumbar spinal cord 3 days post-L5Tx, as well as remarkable increases in microglial size (via forward scatter (FSC)) and granularity (via side scatter (SSC)). Further, intrathecal injection of soluble CD14 induced significantly greater mechanical hypersensitivity in wild type (C3H/HeN) mice compared with TLR4-deficient (C3H/HeJ) mice. Together, these data demonstrate that CD14 plays a contributing role in TLR4-dependent nerve injury-induced neuropathic pain.

Frequencies of genetic polymorphisms of TLR4 and CD14 and of HLA-DQ genotypes in children with celiac disease, type 1 diabetes mellitus, or both

OBJECTIVES

Besides the central role of the adaptive immune system, a disturbance of innate immunity is also involved in the pathogenesis of celiac disease (CD). Inasmuch as CD and type 1 diabetes mellitus (T1DM) frequently coexist because of a common genetic predisposition, our aim was to study the frequency of CD14 C-260T and TLR4 A+896G single nucleotide polymorphisms (SNPs) and the distribution of HLA-DQ genotypes in children affected by CD, T1DM, or both.

PATIENTS AND METHODS

TLR4 and CD14 SNPs were tested by polymerase chain reaction, followed by restriction fragment length polymorphism analysis in 80 children with T1DM, 100 children with CD, and 47 children with both CD and T1DM. Determination of HLA-DQ alleles was done by sequence-specific polymerase chain reaction. Frequencies were compared with those of healthy control children.

RESULTS

The prevalence of the homozygous CD14 C-260TT genotype was significantly (P = 0.0081) lower in children with T1DM but not in those with CD and T1DM, compared with control children. No difference was found in the genotype and allele frequencies of TLR4 between the studied groups. In patients with T1DM, the frequency of the homozygous HLA-DQ8 genotype was significantly higher than in CD, whereas the frequency of homozygous or heterozygous HLA-DQ2 genotypes did not differ from that in control children. In patients with CD, both homozygous and heterozygous HLA-DQ2 genotypes were significantly more frequent than in the control and T1DM groups, and no elevation in the frequency of the HLA-DQ8 genotypes was observed. In patients with T1DM and those with CD and T1DM, the occurrence of HLA-DQ2/8 heterozygosity was significantly higher than in children with CD only and in control children.

CONCLUSIONS

Our results suggest that in patients with T1DM, the CD14 C-260TT homozygous genotype increases the risk for the development of CD. The distribution of HLA-DQ genotype is different in children with CD and T1DM than in children with CD or T1DM only. Determination of the HLA-DQ genotype in children with T1DM may help in estimating the risk for the development of CD.

Varying importance of soluble and membrane CD14 in endothelial detection of lipopolysaccharide

The endothelial response to LPS is critical in the recruitment of leukocytes, thereby allowing the host to survive Gram-negative infection. Herein, we investigated the roles of soluble CD14 (sCD14) and membrane CD14 (mCD14) in the endothelial response to low level LPS (0.1 ng/ml), intermediate level LPS (10 ng/ml), and high level LPS (1000 ng/ml). Removal of sCD14 from serum and sCD14-negative serum prevented low level LPS detection and subsequent response. Addition of recombinant sCD14 back into the endothelial system rescued the endothelial response. GPI-linked mCD14 removal from endothelium or endothelial treatment with a CD14 mAb prevented responses to low-level LPS even in the presence of sCD14. This demonstrates essential nonoverlapping roles for both mCD14 and sCD14 in the detection of low-level LPS. At intermediate levels of LPS, sCD14 was not required, but blocking mCD14 still prevented endothelial LPS detection and E-selectin expression, even in the presence of sCD14, suggesting that sCD14 cannot substitute for mCD14. At very high levels of LPS, the absence of mCD14 and sCD14 did not abrogate TLR4-dependent, E-selectin synthesis in response to LPS. The MyD88 independent pathway was detected in endothelium (presence of TRIF-related adaptor molecule TRAM). The MyD88-independent response (IFN-beta) in endothelium required mCD14 even at the highest LPS dose tested. Our results demonstrate an essential role for endothelial mCD14 that cannot be replaced by sCD14. Furthermore, we have provided evidence for a TRAM pathway in endothelium that is dependent on mCD14 even when other responses are no longer mCD14 dependent.

Molecular events in the cardiomyopathy of sepsis

Septic cardiomyopathy is a well-described complication of severe sepsis and septic shock. However, the interplay of its underlying mechanisms remains enigmatic. Consequently, we constantly add to our pathophysiological understanding of septic cardiomyopathy. Various cardiosuppressive mediators have been discovered, as have multiple molecular mechanisms (alterations of myocardial calcium homeostasis, mitochondrial dysfunction, and myocardial apoptosis) that may be involved in myocardial dysfunction during sepsis. Finally, the detrimental roles of nitric oxide and peroxynitrite have been unraveled. Here, we describe our present understanding of systemic, supracellular, and cellular molecular mechanisms involved in sepsis-induced myocardial suppression.

Bovine CD14 gene characterization and relationship between polymorphisms and surface expression on monocytes and polymorphonuclear neutrophils

Background

CD14 is an important player in host innate immunity in that it confers lipopolysaccharide sensitivity to cell types like neutrophils, monocytes and macrophages. The study was aimed at characterizing the CD14 gene of cattle for sequence variations and to determine the effect of variations on the expression of the protein on the surfaces of monocytes and neutrophils in healthy dairy cows.

Results

Five SNPs were identified: two within the coding regions (g.A1908G and g.A2318G, numbering is according to GenBank No. EU148609), one in the 5' (g.C1291T) and two in the 3' (g.A2601G and g.G2621T) untranslated regions. SNP 1908 changes amino acid 175 of the protein (p.Asn175Asp, numbering is according to GenBank No. ABV68569), while SNP 2318 involves a synonymous codon change. Coding region SNPs characterized three gene alleles A (GenBank No. EU148609), A₁ (GenBank No. EU148610) and B (GenBank No. EU148611) and two deduced protein variants A (ABV68569 and ABV68570) and B (ABV68571). Protein variant A is more common in the breeds analyzed. All SNPs gave rise to 3 haplotypes for the breeds. SNP genotype 1908AG was significantly (P < 0.01) associated with a higher percentage of neutrophils expressing more CD14 molecules on their surfaces. The promoter region contains several transcription factor binding sites, including multiple AP-1 and SP1 sites and there is a high conservation of amino acid residues between the proteins of closely related species.

Conclusion

The study has provided information on sequence variations within the CD14 gene and proteins of cattle. The SNP responsible for an amino acid exchange may play an important role in the expression of CD14 on the surfaces of neutrophils. Further observations involving a larger sample size are required to validate our findings. Our SNP and association analyses have provided baseline information that may be used at defining the role of CD14 in mediating bacterial infections. The computational analysis on the promoter and comparative analysis with other species has revealed regions of regulatory element motifs that may indicate important regulatory effects on the gene.

High mobility group box 1 protein binding to lipopolysaccharide facilitates transfer of lipopolysaccharide to CD14 and enhances lipopolysaccharide-mediated TNF-alpha production in human monocytes

LPS-binding protein (LBP) is a central mediator that transfers LPS to CD14 to initiate TLR4-mediated proinflammatory response. However, a possibility of another LPS transfer molecule has been suggested because LBP-deficient mice showed almost normal inflammatory response after LPS injection. In this study, we describe the novel finding that high mobility group box 1 protein (HMGB1) recently identified as a mediator of sepsis has a function of LPS transfer for a proinflammatory response. We used ELISA and surface plasmon resonance to show that HMGB1 binds LPS in a concentration-dependent manner and that the binding is stronger to lipid A moiety than to the polysaccharide moiety of LPS. This binding was inhibited by LBP and polymyxin B. Using native PAGE and fluorescence-based LPS transfer analyses, we show that HMGB1 can catalytically disaggregate and transfer LPS to both soluble CD14 protein and to human PBMCs in a dose-dependent manner. However, this effect was dramatically reduced to the baseline level when HMGB1 was heat inactivated. Furthermore, a mixture of HMGB1 and LPS treatment results in a higher increase in TNF-alpha production in human PBMCs and peripheral blood monocytes than LPS or HMGB1 treatment alone or their summation. Thus, we propose that HMGB1 plays an important role in Gram-negative sepsis by catalyzing movement of LPS monomers from LPS aggregates to CD14 to initiate a TLR4-mediated proinflammatory response.

Polymorphisms in the tumor necrosis factor/lipopolysaccharides pathway in Crohn disease in the Jewish Ashkenazi population

OBJECTIVE

Tumor necrosis factor (TNF)-alpha plays a role in the inflammatory process in Crohn disease, a disease with an apparent polygenic basis. We investigated whether polymorphisms in multiple genes involved in the lipopolysaccharide-TNF inflammatory pathway are independently associated with Crohn disease in the Jewish Ashkenazi population. Polymorphisms in CD14, Toll-like receptor 4 (TLR4), and TNF-alpha were studied. In addition, we investigated polymorphisms in the TNF-alpha converting enzyme (TACE) gene, which to date has not been studied for an association with Crohn disease.

PATIENTS AND METHODS

To examine whether TLR4 Asp299Gly, CD14-260C/T, TNF-1031T/C, TNF-863C/A, TNF-857C/T, TACE-172C/T, and TACE-154C/A polymorphisms are associated with Crohn disease in the Ashkenazi Jewish population, we analyzed families with at least 1 child with Crohn disease for association with these mutations using a family-based association test (transmission disequilibrium test) for analysis.

RESULTS

The allelic frequency in the patient population of TLR4 G allele was 8.0%, CD14 T allele was 51.3%, TNF-1031C was 18.8%, TNF-863A was 14.2%, TNF-857T was 25.2%, TACE172T was 20.7%, and TACE154A was 24.5%. The transmission disequilibrium test transmitted:untransmitted (T:U) result for TLR4G was T:U = 32:20, for CD14T was T:U = 103:88, for TNF-1031C was T:U = 48:56, for TNF-863A was T:U = 39:42, for TNF-857T was T:U = 63:62, for TACE-172C/T was T:U = 48:59, and for TACE-154C/A was T:U = 52:55. No statistically significant associations were observed.

CONCLUSIONS

The transmission disequilibrium test did not demonstrate preferential transmission of these variants in Jewish Ashkenazi patients with Crohn disease. These results suggest that these polymorphisms in the TNF/lipopolysaccharide pathway play little or no role in susceptibility to Crohn disease in the Jewish Ashkenazi population.

CD14 contributes to pulmonary inflammation and mortality during murine tuberculosis

Toll-like receptors play an essential role in the innate recognition of micro-organisms by the host. CD14 is one of the extracellular adaptor proteins required for recognition of Gram-negative bacteria and possibly also Mycobacterium tuberculosis. Therefore, we intranasally infected wild-type (WT) and CD14 knock-out (KO) mice with virulent M. tuberculosis H37Rv. We found no differences in bacterial load in the main target organ lung up to 32 weeks after infection. From 20 weeks onward 57% of WT mice succumbed, whereas all CD14 KO mice survived. The improved outcome of CD14 KO mice was accompanied by reduced pulmonary inflammation; lung cell counts and percentage of inflamed lung tissue were reduced in CD14 WT mice. These data suggest that during chronic infection CD14 KO mice are protected from lethality caused by lung tuberculosis because of a reduction of the inflammatory response.

Host defense genes in asthma and sepsis and the role of the environment

PURPOSE OF REVIEW

There is growing evidence that innate immunity genes contribute to asthma pathogenesis. At the core of the innate immune response are ubiquitous, soluble fragments of bacterial lipopolysaccharide or endotoxin, and chronic exposure to domestic endotoxin has been shown to influence asthma severity. Asthmatic and atopic individuals are more sensitive to endotoxin than nonallergic individuals, suggesting a role for genetics in the innate immunity response, and the potential for gene-environment interactions. Variants in genes associated with classic innate immunity-related disorders, such as sepsis, may be unique candidates for asthma susceptibility.

RECENT FINDINGS

Candidate genes for asthma and allergic diseases co-associated with sepsis including innate immunity receptors and related molecules (CD14, TLR4 and AOAH) and novel genes such as MYLK provide good examples of pleitropic effects of innate immunity genes, where variants conferring risk to specific traits (i.e. sepsis) under one set of genetic and environmental circumstances confer a reduced risk in a different (but possibly related) clinical outcome (i.e. allergic asthma), and support the 'common variant/multiple disease' hypothesis.

SUMMARY

Collectively, these observations suggest a greater role for the innate immunity response in allergic asthma than previously assumed, and implicate host defense genes in disease pathology.

Taurocholate-induced pancreatitis: a model of severe necrotizing pancreatitis in mice

OBJECTIVES

The outcome from acute pancreatitis depends on the severity of systemic complications. To be able to investigate mechanisms underlying the development of these systemic complications in acute pancreatitis in both wild-type and genetically engineered animal models, a mouse model of severe necrotizing pancreatitis was developed and characterized.

METHODS

Pancreatitis was induced by retrograde infusion of sodium taurocholate into the common bile duct in mice. After determining the optimum volume and concentration of taurocholate, the pancreatic damage and systemic inflammatory response were compared with those in cerulein-induced pancreatitis.

RESULTS

Pancreatic damage was higher in taurocholate pancreatitis than hyperstimulation-induced pancreatitis (24 hours: cerulein, 5.8 +/- 0.2 points; taurocholate, 14.8 +/- 0.8 points; P < 0.001) and mortality reached up to 60% within the first 24 hours after taurocholate administration. Pulmonary damage was detected, as measured by an increase in albumin in bronchoalveolar lavage fluid only in taurocholate-induced pancreatitis (12 hours: cerulein, 97.1 +/- 22.83 mg/g of protein; taurocholate, 234.0 +/- 32.7 mg/g of protein; P < 0.001). Furthermore, plasma interleukin 6 concentration was significantly elevated in mice with taurocholate-induced pancreatitis (12 hours: cerulein, 2.6 +/- 6.1 pg/mL; taurocholate, 2168.8 +/- 941.7 microg/mL; P < 0.001) as compared with all other groups.

CONCLUSIONS

Taurocholate pancreatitis is a reliable model for severe necrotizing pancreatitis in mice with significantly greater pancreatic damage and systemic inflammatory response in comparison with cerulein-induced pancreatitis.

Protective effect of bicyclol on acute alcohol-induced liver injury in mice

Oxidative stress, cytokine over expression and Kupffer cell activation are well-documented pathological factors in the development of alcoholic liver disease. Bicyclol is a novel synthetic anti-hepatitis drug with anti-oxidative and anti-inflammatory property. The present study was to investigate the effect of bicyclol on acute alcohol-induced liver injury and related mechanisms in mice. Bicyclol (200, 300 mg/kg) was given to mice by gavage for three times. Alcohol (6 g/kg) was administered orally 1 h after the last dose of bicyclol. All animals were sacrificed at different time points after alcohol administration. Liver injury was evaluated by biochemical and histopathological examination. Lipid peroxidation and the activity of antioxidants were measured by spectrophotometric method. Expression of cytokines and CD14 were determined by enzyme-linked immunosorbent assay, reverse transcriptional-polymerase chain reaction and immunohistochemical staining. As a result, bicyclol pretreatment significantly protected against acute alcohol-induced liver injury as evidenced by the decrease of elevated serum alanine aminotransferase and hepatic triglyceride, and the attenuation of histopathological changes in mice. In addition, bicyclol remarkably alleviated the formation of thiobarbituric acid-reactive substance and restored impaired antioxidants, including glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Over-expression of cytokines, such as tumor necrosis factor alpha and interleukin 1beta, elevated plasma endotoxin level, and up-regulation of CD14 were also suppressed by bicyclol in alcohol-intoxicated mice. The protective effect of bicyclol on alcohol-induced hepatotoxicity was mainly due to its ability to attenuate oxidative stress, suppress the cytokine expression at both protein and gene level, and inhibit the activation of Kupffer cells by decreasing plasma endotoxin level and CD14 expression.

Soluble CD14 discriminates slight structural differences between lipid as that lead to distinct host cell activation

Soluble CD14 (sCD14) in serum is known to sensitize host cells to LPS. In the present study, the contributions of sCD14 and LPS-binding protein to a lipid A moiety from LPS preparations of periodontopathogenic Fusobacterium nucleatum sp. nucleatum were compared with that of Escherichia coli-type synthetic lipid A (compound 506). F. nucleatum lipid A was identified to be a hexa-acylated fatty acid composed of tetradecanoate (C(14)) and hexadecanoate (C(16)), similar to dodecanoate (C(12)) and C(14) in compound 506. The two lipid A specimens exhibited nearly the same reactivity in Limulus amoebocyte lysate assays, though F. nucleatum lipid A showed a weaker lethal toxicity. Both lipid A specimens showed nearly the same activities toward host cells in the absence of FBS, though compound 506 exhibited much stronger activity in the presence of FBS, sCD14, or sCD14 together with LPS-binding protein. Furthermore, native PAGE/Western immunoblot assays demonstrated that F. nucleatum lipid A had a weaker binding to sCD14 as compared with compound 506. These results suggest that sCD14 is able to discriminate the slight structural differences between these lipid As, which causes their distinct host cell activation activities.

Role of gut microflora in the development of obesity and insulin resistance following high-fat diet feeding

A recent growing number of evidences shows that the increased prevalence of obesity and type 2 diabetes cannot be solely attributed to changes in the human genome, nutritional habits, or reduction of physical activity in our daily lives. Gut microflora may play an even more important role in maintaining human health. Recent data suggests that gut microbiota affects host nutritional metabolism with consequences on energy storage. Several mechanisms are proposed, linking events occurring in the colon and the regulation of energy metabolism. The present review discusses new findings that may explain how gut microbiota can be involved in the development of obesity and insulin resistance. Recently, studies have highlighted some key aspects of the mammalian host-gut microbial relationship. Gut microbiota could now be considered as a "microbial organ" localized within the host. Therefore, specific strategies aiming to regulate gut microbiota could be useful means to reduce the impact of high-fat feeding on the occurrence of metabolic diseases.

The forward genetic dissection of afferent innate immunity

Recognition of the microbial world is mediated chiefly by a small group of immune receptors that activate a characteristic host inflammatory response, the innate immune response. Known as the Toll-like receptors (TLRs), these molecules are represented among most metazoans. In mammals, forward genetic analysis of the lipopolysaccharide (LPS) response led to the identification of TLR4 as the LPS receptor. Through a combination of forward and reverse genetic studies, a relatively detailed understanding of the functions of mammalian TLRs has now been achieved. As discussed here, mutagenesis has revealed proteins that participate in TLR signaling pathways, and informed our understanding of the subtleties of these molecules' structure and function.

Injection of lipopolysaccharide induces the migration of splenic neutrophils to the T cell area of the white pulp: role of CD14 and CXC chemokines

There is increasing evidence that neutrophils are involved in the regulation of adaptive immunity. We therefore tested whether these cells may colocalize with T lymphocytes in lymphoid organs. Our results demonstrate that administration of the microbial product LPS induces the migration of neutrophils in the spleen from the red pulp and the marginal zone to the area of the white pulp where T cells reside. This movement is CD14-dependent, whereas the recruitment of neutrophils in the peritoneal cavity is increased in the absence of CD14. Our data further suggest the involvement of the chemokine MIP-2 and keratinocyte-derived chemokine and their receptor CXCR2. We conclude that neutrophils may interact with naïve T cells upon infection/inflammation and that the migration of neutrophils in the lymphoid organs and in the periphery is regulated differently by a signal transduced by CD14.

Soluble MD-2 is an acute-phase protein and an opsonin for Gram-negative bacteria

Myeloid differentiation factor-2 (MD-2) is a lipopolysaccharide (LPS)-binding protein usually coexpressed with and binding to Toll-like receptor 4 (TLR4), conferring LPS responsiveness of immune cells. MD-2 is also found as a soluble protein. Soluble MD-2 (sMD-2) levels are markedly elevated in plasma from patients with severe infections, and in other fluids from inflamed tissues. We show that sMD-2 is a type II acute-phase protein. Soluble MD-2 mRNA and protein levels are up-regulated in mouse liver after the induction of an acute-phase response. It is secreted by human hepatocytic cells and up-regulated by interleukin-6. Soluble MD-2 binds to Gram-negative but not Gram-positive bacteria, and sMD-2 secreted by hepatocytic cells is an essential cofactor for the activation of TLR4-expressing cells by Gram-negative bacteria. Soluble MD-2 opsonization of Gram-negative bacteria accelerates and enhances phagocytosis, principally by polymorphonuclear neutrophils. In summary, our results demonstrate that sMD-2 is a newly recognized type II acute-phase reactant, an opsonin for Gram-negative bacteria, and a cofactor essential for the activation of TLR4-expressing cells. This suggests that sMD-2 plays a key role in the host innate immune response to Gram-negative infections.

The toll-like receptor-4 (TLR-4) pathway and its possible role in the pathogenesis of Escherichia coli mastitis in dairy cattle

Mastitis is one of the most costly production diseases in the dairy industry that is caused by a wide array of microorganisms. In this review, we focus on the Gram-negative Escherichia coli infections that often occur at periods when the innate immune defence mechanisms are impaired (i.e., parturition through the first 60 days of lactation). There is substantial evidence demonstrating that at these periods, the expected influx of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland is delayed during inflammation after intramammary infection with E. coli. Here, we provide some hypotheses on the potential mechanisms of action on how the disease may develop under circumstances of immunosuppression, and describe the potential involvement of the toll-like receptor-4 signal transduction pathway in the pathogenesis of E. coli mastitis. In addition, some ideas are proposed to help prevent E. coli mastitis and potentially other diseases caused by Gram-negative infections in general.

Genetic analysis of host responses in sepsis

During much of the past century, the microbe itself stood at the heart of microbial pathogenesis. Little thought was devoted to the host per se, though it was granted that differences in susceptibility to certain infections did exist between individuals, and between different ethnic groups. During the past 20 years, extraordinary strides in our grasp of mammalian genetics have made the host side of the equation far more approachable. A restricted collection of genes now presents itself as the likely repository for genetic differences that foretell susceptibility to infectious disease. The Toll-like receptors, of which 10 are presently known to exist in humans, offer an excellent example of this genetic reductionism, in that they embody the afferent component of the innate immune system, and strongly influence the containment of an infection from its earliest stages. The Toll-like receptors were identified as the culmination of a long and relentless inquiry into the yet-unsolved clinical problem of sepsis.

Anti-beta2-glycoprotein I antibodies induce monocyte release of tumor necrosis factor alpha and tissue factor by signal transduction pathways involving lipid rafts

OBJECTIVE

To investigate the association of beta(2)-glycoprotein I (beta(2)GPI) with lipid rafts in monocytic cells and to evaluate the proinflammatory and procoagulant effects of anti-beta(2)GPI binding to its target antigen on the monocyte plasma membrane.

METHODS

Human monocytes were fractionated by sucrose density-gradient centrifugation and analyzed by Western blotting. Immunoprecipitation experiments were performed to analyze the association of beta(2)GPI with lipid rafts and the possible interaction of beta(2)GPI with annexin A2 and Toll-like receptor 4 (TLR-4). Monocytes were then stimulated with affinity-purified anti-beta(2)GPI antibodies from patients with the antiphospholipid syndrome (APS). Interleukin-1 receptor-associated kinase (IRAK) phosphorylation and NF-kappaB activation were evaluated by immunoprecipitation and transcription factor assay, respectively. Supernatants from monocytes were tested for tumor necrosis factor alpha (TNFalpha) and tissue factor (TF) levels by enzyme-linked immunosorbent assay.

RESULTS

We found beta(2)GPI and its putative receptor annexin A2 in lipid raft fractions of human monocytes. Moreover, there was an association between beta(2)GPI and TLR-4, suggesting that it was partially dependent on raft integrity. Triggering with anti-beta(2)GPI antibodies induced IRAK phosphorylation and consequent NF-kappaB activation, which led to the release of TNFalpha and TF.

CONCLUSION

Anti-beta(2)GPI antibodies react with their target antigen, likely in association with annexin A2 and TLR-4, in lipid rafts in the monocyte plasma membrane. Anti-beta(2)GPI binding triggers IRAK phosphorylation and NF-kappaB translocation, leading to a proinflammatory and procoagulant monocyte phenotype characterized by the release of TNFalpha and TF, respectively. These findings provide new insight into the pathogenesis of APS, improving our knowledge of valuable therapeutic targets.

Mrp8 and Mrp14 are endogenous activators of Toll-like receptor 4, promoting lethal, endotoxin-induced shock

To identify new components that regulate the inflammatory cascade during sepsis, we characterized the functions of myeloid-related protein-8 (Mrp8, S100A8) and myeloid-related protein-14 (Mrp14, S100A9), two abundant cytoplasmic proteins of phagocytes. We now demonstrate that mice lacking Mrp8-Mrp14 complexes are protected from endotoxin-induced lethal shock and Escherichia coli-induced abdominal sepsis. Both proteins are released during activation of phagocytes, and Mrp8-Mrp14 complexes amplify the endotoxin-triggered inflammatory responses of phagocytes. Mrp8 is the active component that induces intracellular translocation of myeloid differentiation primary response protein 88 and activation of interleukin-1 receptor-associated kinase-1 and nuclear factor-kappaB, resulting in elevated expression of tumor necrosis factor-alpha (TNF-alpha). Using phagocytes expressing a nonfunctional Toll-like receptor 4 (TLR4), HEK293 cells transfected with TLR4, CD14 and MD2, and by surface plasmon resonance studies in vitro, we demonstrate that Mrp8 specifically interacts with the TLR4-MD2 complex, thus representing an endogenous ligand of TLR4. Therefore Mrp8-Mrp14 complexes are new inflammatory components that amplify phagocyte activation during sepsis upstream of TNFalpha-dependent effects.

Oxidative stress, lipid rafts, and macrophage reprogramming

Oxidant stress, induced under a variety of conditions, is known to lead to the molecular reprogramming of the tissue-fixed macrophage. This reprogramming is associated with an altered response to subsequent inflammatory stimuli, such as lipopolysaccharide (LPS), leading to enhanced liberation of proinflammatory chemokines and cytokines. Due to this altered response, dysregulated immunity ensues, leading to the development of clinical syndromes such as multiple organ dysfunction syndrome (MODS). Although the mechanisms responsible for this altered macrophage activity by oxidant stress remains complex and poorly elucidated, it appears, based on recent research, that early and direct alterations within lipid rafts are responsible. This early and direct interaction with lipid rafts by oxidants leads to the mobilization of annexin VI from lipid raft constructs, leading to the release of calcium. This increased cytosolic concentration of this secondary messenger, in turn, results in the activation of calcium-dependent kinases, leading to further alterations in lipid raft lipids and eventually lipid raft proteins. Due to these lipid raft compositional changes, preassembly of receptor complexes occur, leading to enhanced proinflammatory activation. Within this review, the complexity of oxidant-induced reprogramming within the tissue fixed macrophage as currently understood is explained.

Role of CD14 in responses to clinical isolates of Escherichia coli: effects of K1 capsule expression

Severe bacterial infections leading to sepsis or septic shock can be induced by bacteria that utilize different factors to drive pathogenicity and/or virulence, leading to disease in the host. One major factor expressed by all clinical isolates of gram-negative bacteria is lipopolysaccharide (LPS); a second factor expressed by some Escherichia coli strains is a K1 polysaccharide capsule. To determine the role of the CD14 LPS receptor in the pathogenic effects of naturally occurring E. coli, the responses of CD14-/- and CD14+/+ mice to three different isolates of E. coli obtained from sepsis patients were compared; two isolates express both smooth LPS and the K1 antigen, while the third isolate expresses only LPS and is negative for K1. An additional K1-positive isolate obtained from a newborn with meningitis and a K1-negative isogenic mutant of this strain were also used for these studies. CD14-/- mice were resistant to the lethal effects of the K1-negative isolates. This resistance was accompanied by significantly lower levels of systemic tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) in these mice than in CD14+/+ mice, enhanced clearance of the bacteria, and significantly fewer additional gross symptoms. In contrast, CD14-/- mice were as sensitive as CD14+/+ mice to the lethal effects of the K1-positive isolates, even though they had significantly lower levels of TNF-alpha and IL-6 than CD14+/+ mice. These studies show that different bacterial isolates can use distinctly different mechanisms to cause disease and suggest that new, nonantibiotic therapeutics need to be directed against multiple targets.

EFFECTS OF CD14-159 C/T POLYMORPHISM ON CD14 EXPRESSION AND THE BALANCE BETWEEN PROINFLAMMATORY AND ANTI-INFLAMMATORY CYTOKINES IN WHOLE BLOOD CULTURE

CD14 is an important receptor of innate immunity. When CD14 is anchored by ligands to LPS, peptidoglycans, or lipoteichoic acid, it can result in either proinflammatory or anti-inflammatory responses. To determine whether CD14-159 C/T polymorphism is associated with CD14 expression and the balance of proinflammatory and anti-inflammatory responses, we studied 118 healthy ethnic Han Chinese using a whole blood culture model. The CD14-159 C/T polymorphism was determined by polymerase chain reaction and subsequent HaeIII restriction enzyme digestion of the polymerase chain reaction products. Meanwhile, CD14 mRNA expression in leukocytes and the levels of soluble CD14, TNF-alpha, IL-6, and IL-10 were also determined in the supernatants. Among the 118 individuals, there were 40 TT homozygotes, 62 heterozygotes, and 16 subjects homozygous for C allele. After LPS stimulation, the levels of CD14 mRNA expression in TT and TC genotypes were significantly higher than in CC homozygotes (P = 0.017), and soluble CD14 levels were also higher than in CC genotypes (P = 0.008). In addition, TT homozygotes had the highest LPS-stimulated TNF-alpha, IL-6 production (P = 0.044, P = 0.004), and the lowest IL-10 release (P = 0.003). In conclusion, CD14-159 C/T polymorphism is correlated with CD14 expression and may thus influence the balance of proinflammatory and anti-inflammatory responses in ethnic Han Chinese. These results suggest that CD14-159 C/T polymorphism might partly explain the difference in predisposition to develop complications of infectious diseases in different patients and may provide a therapeutic target for sepsis intervention strategies.

Toll‐like receptors: structural pieces of a curve‐shaped puzzle

The toll-like receptors are responsible for recognizing invading pathogens and triggering a primary innate immune response by initiating a signalling pathway that ultimately leads to the activation of nuclear factor-kappaB (NF-kappaB). NF-kappaB induces the transcription of many genes that regulate both the inflammatory response and interferons that help control the development of adaptive immunity. In this review, we concentrate on the structure and function of toll-like receptors and our current understanding of the complexities of ligand binding, receptor dimerization and signal transduction.

Metabolic endotoxemia initiates obesity and insulin resistance

Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPS-containing microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in high-fat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not whole-body, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases.

Characterization of heme as activator of Toll-like receptor 4

Heme is an ancient and ubiquitous molecule present in organisms of all kingdoms, composed of an atom of iron linked to four ligand groups of porphyrin. A high amount of free heme, a potential amplifier of the inflammatory response, is a characteristic feature of diseases with increased hemolysis or extensive cell damage. Here we demonstrate that heme, but not its analogs/precursors, induced tumor necrosis factor-alpha (TNF-alpha) secretion by macrophages dependently on MyD88, TLR4, and CD14. The activation of TLR4 by heme is exquisitely strict, requiring its coordinated iron and the vinyl groups of the porphyrin ring. Signaling of heme through TLR4 depended on an interaction distinct from the one established between TLR4 and lipopolysaccharide (LPS) since anti-TLR4/MD2 antibody or a lipid A antagonist inhibited LPS-induced TNF-alpha secretion but not heme activity. Conversely, protoporphyrin IX antagonized heme without affecting LPS-induced activation. Moreover, heme induced TNF-alpha and keratinocyte chemokine but was ineffective to induce interleukin-6, interleukin-12, and interferon-inducible protein-10 secretion or co-stimulatory molecule expression. These findings support the concept that the broad ligand specificity of TLR4 and the different activation profiles might in part reside in its ability to recognize different ligands in different binding sites. Finally, heme induced oxidative burst, neutrophil recruitment, and heme oxygenase-1 expression independently of TLR4. Thus, our results presented here reveal a previous unrecognized role of heme as an extracellular signaling molecule that affects the innate immune response through a receptor-mediated mechanism.

Recognition of hyaluronan released in sterile injury involves a unique receptor complex dependent on Toll-like receptor 4, CD44, and MD-2

Inflammation under sterile conditions is not well understood despite its importance in trauma and autoimmune disease. To investigate this process we established mouse models of sterile injury and explored the role of hyaluronan in mediating inflammation following injury. The response of cultured monocytes to hyaluronan was different than the response to lipopolysaccharide (LPS) despite both being dependent on Toll-like receptor 4 (TLR4). Cultured cells exposed to hyaluronan showed a pattern of gene induction that mimics the response seen in mouse skin after sterile injury with an increase in molecules such as transforming growth factor-beta2 and matrix metalloproteinase-13. These factors were not induced by LPS despite the mutual dependence of both hyaluronan and LPS on TLR4. Explanation for the unique response to hyaluronan was provided by observations that a lack of TLR4 or CD44 in mice diminished the response to sterile injury, and together with MD-2, was required for responsiveness to hyaluronan in vitro. Thus, a unique complex of TLR4, MD-2, and CD44 recognizes hyaluronan. Immunoprecipitation experiments confirmed the physical association of TLR4 and CD44. Taken together, our results define a previously unknown mechanism for initiation of sterile inflammation that involves recognition of released hyaluronan fragments as an endogenous signal of tissue injury.

CD14 is an essential mediator of LPS-induced airway disease

Chronic lipopolysaccharide (LPS) inhalation in rodents recapitulates many classic features of chronic obstructive pulmonary disease seen in humans, including airways hyperresponsiveness, neutrophilic inflammation, cytokine production in the lung, and small airways remodeling. CD14-deficient mice (C57BL/6(CD14-/-)) have an altered response to systemic LPS, and yet the role of CD14 in the response to inhaled LPS has not been defined. We observed that C57BL/6(CD14-/-) mice demonstrate no discernable physiological or inflammatory response to a single LPS inhalation challenge. However, the physiological (airways hyperresponsiveness) and inflammatory (presence of neutrophils and TNF-alpha in whole lung lavage fluid) responsiveness to inhaled LPS in C57BL/6(CD14-/-) mice was restored by instilling soluble CD14 intratracheally. Intratracheal instillation of wild-type macrophages into C57BL/6(CD14-/-) mice restored neutrophilic inflammation only and failed to restore airways hyperresponsiveness or TNF-alpha protein in whole lung lavage. These findings demonstrate that CD14 is critical to LPS-induced airway disease and that macrophage CD14 is sufficient to initiate neutrophil recruitment into the airways but that CD14 may need to interact with other cell types as well for the development of airways hyperresponsiveness and for cytokine production.

CD44 is a negative regulator of acute pulmonary inflammation and lipopolysaccharide-TLR signaling in mouse macrophages

CD44 is a transmembrane adhesion molecule and hemopoietic CD44 has an essential role in hyaluronan clearance and resolution of noninfectious lung injury. In this study, we examined the role of CD44 in acute pulmonary inflammation and in the regulation of LPS-TLR signaling. Following intratracheally LPS treatment, CD44(-/-) mice demonstrated an exaggerated inflammatory response characterized by increased inflammatory cell recruitment, elevated chemokine expression in bronchoalveolar lavage fluid, and a marked increase in NF-kappaB DNA-binding activity in lung tissue in vivo and in macrophages in vitro. Furthermore, CD44(-/-) mice were more susceptible to LPS-induced shock. Reconstitution of hemopoietic CD44 reversed the inflammatory phenotype. We further found that the induction of the negative regulators of TLR signaling IL-1R-associated kinase-M, Toll-interacting protein, and A20 by intratracheal LPS in vivo and in macrophages in vitro was significantly reduced in CD44(-/-) mice. Collectively, these data suggest CD44 plays a previously unrecognized role in preventing exaggerated inflammatory responses to LPS by promoting the expression of negative regulators of TLR-4 signaling.

Sp1 elements regulate transcriptional activity within the murine Toll-like receptor 4 promoter

BACKGROUND AND PURPOSE

Toll-like receptor 4 (TLR4) mediates the innate immune response to lipopolysaccharide (LPS) by a complex intracellular signaling pathway that activates the transcription factor nuclear factor (NF)-kappaB, with subsequent production of inflammatory cytokines. The precise mechanisms involved have not been delineated. We hypothesized that specific regulatory elements exist within the TLR4 promoter.

METHODS

We cloned regions of the murine TLR4 promoter (0.25 kb to 2 kb; -2000 bp to +244 bp) into the pGL3-Basic plasmid containing the firefly luciferase gene and used the resulting constructs to transfect HEK293 or RAW 264.7 cells. After 24 h, we used LPS to stimulate RAW 264.7 cells. We quantified relative light units (RLUs) of cell lysates and secreted tumor necrosis factor (TNF)-alpha. For pairwise comparison, we used Student's t-test. Sequence analysis of the promoter revealed several putative Sp1 sites. We used two constructs showing increased promoter activity, TLR4-750/-1 and TLR4-500/-1, to transfect cells in the presence of a specific Sp1 inhibitor, mithramycin A.

RESULTS

Of the six promoter constructs, four showed greater transcriptional activity (p < 0.05 vs. pGL3-Basic), as measured by luciferase activity. However, we did not observe differences in transcriptional activity of the promoter in five of those six constructs when we stimulated transfected RAW 264.7 cells with 10 ng of LPS. This finding suggests that transcriptional regulation of the promoter is unaffected by cellular changes caused by LPS. Both TLR4-750/-1 and TLR4-500/-1 showed dose-dependent reductions in transcriptional activity in the presence of increasing concentrations of the specific Sp1 inhibitor mithramycin A in both HEK293 and RAW 264.7 cells (p < 0.05 vs. no mithramycin A).

CONCLUSION

At least one Sp1 transcriptional regulatory element is present within the murine TLR4 promoter (range -750 bp to -250 bp). This finding holds promise for manipulating this fundamental inflammatory response.

Phosphatidyl inositol-3-phosphate kinase mediates CD14 dependent signaling

Lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria, is an important mediator of innate immunity and septic shock, but the exact mechanisms mediating cellular LPS recognition and the subsequent translation to inflammatory gene expression remain incompletely understood. CD14 has been established as a receptor that confers high sensitivity to LPS in cells of the myeloid lineage, probably by presenting LPS to Toll receptors. We use an anti CD14 blocking antibody to define a LPS stimulus that activates only this high affinity component of the LPS receptor and then examine CD14 dependent signaling events that are activated in response to LPS stimulation. We describe a novel LPS activated signaling pathway in human PBMC that leads to cytokine production and is mediated by PI3 kinase through Ras and the MEK/ERK cassette. Moreover, we show the PI3 kinase effectors PKB and PKC(zeta) are also activated by PI3 kinase in a CD14 dependent manner in LPS stimulated human PBMC. Thus, PI3 kinase appears to be an essential component in LPS signal transduction.

Oxidized phospholipids inhibit phagocytosis and impair outcome in gram-negative sepsis in vivo

Oxidized phospholipids that are generated during inflammation exert anti-inflammatory properties and prevent death during murine endotoxemia. Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) inhibits the interaction of LPS with LPS-binding protein and CD14. In this study, we determined the functional properties of OxPAPC and potential interference with CD14 during abdominal sepsis caused by Escherichia coli. Administration of OxPAPC rendered mice highly susceptible to E. coli peritonitis, as indicated by an accelerated mortality and enhanced bacterial outgrowth and dissemination. CD14(-/-) mice also displayed increased mortality and bacterial outgrowth and OxPAPC did not further impair host defense in these animals. The mechanisms by which OxPAPC and CD14 deficiency impaired the immune response differed: whereas CD14(-/-) mice demonstrated a strongly reduced recruitment of phagocytes to the site of the infection, OxPAPC did not influence the influx of inflammatory cells but strongly diminished the phagocytosing capacity of neutrophils and macrophages by a CD14-independent mechanism. Furthermore, OxPAPC potently inhibited uptake of fluorospheres as well as receptor-mediated endocytosis and fluid-phase pinocytosis. These data suggest that oxidized phospholipids such as produced during inflammatory reactions may contribute to mortality during Gram-negative sepsis in vivo via impairment of the phagocytic properties of professional phagocytes.

Regulation of innate immunity by MAPK dual-specificity phosphatases: knockout models reveal new tricks of old genes

Throughout evolution, mammals have developed an elaborate network of positive and negative regulatory mechanisms, which provide balance between defensive measures against bacterial and viral pathogens and protective measures against unwarranted destruction of the host by the activated immune system. Kinases and phosphatases encompassing the MAPK pathway are key players in the orderly action of pro- and anti-inflammatory processes, forming numerous promiscuous interactions. Several lines of evidence demonstrate that the phosphorylation and activation status of kinases in the MAPK system has crucial impact on the outcome of downstream events that regulate cytokine production. At least 13 members of the family of dual-specificity phosphatases (DUSP) display unique substrate specificities for MAPKs. Despite the considerable amount of information obtained about the contribution of the different DUSP to MAPK-mediated signaling and innate immunity, the interpretation of available data remains problematic. The in vitro and ex vivo findings are often complicated by functional redundancy of signaling molecules and do not always accurately predict the situation in vivo. Until recently, DUSP research has been hampered by the lack of relevant mammalian knockout (KO) models, which is a powerful tool for delineating in vivo function and redundancy in gene families. This situation changed dramatically over the last year, and this review integrates recent insights into the precise biological role of the DUSP family in innate immunity gained from a comprehensive analysis of mammalian KO models.

Mice expressing high levels of soluble CD14 retain LPS in the circulation and are resistant to LPS-induced lethality

Despite significant progress in understanding the origin of soluble CD14 (sCD14), its physiological function remains largely unknown. Recent research has produced contradictory observations suggesting that sCD14 may have either beneficial or detrimental properties in protection against LPS-induced endotoxin shock. To resolve this controversy and to establish a mouse model suitable for elucidation of the functions of human CD14 (hCD14) in vivo, we generated several lines of transgenic mice bearing different copy numbers of the hCd14 transgene on a murine Cd14-/- background. The hCD14 was entirely capable of complementing loss of mouse CD14 to mediate cellular responses to LPS. Serum levels of sCD14 in a founder with multiple copies of the transgene were several times higher than in transgenic animals with a single copy of Cd14. Furthermore, mice with high levels of hCD14 were hypo-responsive to LPS and survived a lethal dose of LPS. Further inquiry into the mechanism of the hypo-response to LPS revealed that protection is associated with the higher amounts of circulating LPS. Most of this circulating LPS can be immunoprecipitated with anti-CD14 antibodies. These results suggest that sCD14 blocks circulating LPS by limiting the amount of monocyte-bound LPS and thus reduces inflammatory responses.

Cloning, characterization and mapping of porcine CD14 reveals a high conservation of mammalian CD14 structure, expression and locus organization

The cell surface protein CD14 plays a central role in innate immunity as a pattern recognition receptor. CD14 is part of a receptor complex also including toll-like receptor 4 and MD2 proteins. Binding of the ligand lipopolysaccharide to the complex on myeloid cells leads to release of pro-inflammatory cytokines and mediators from the cell. In this study, we present the cloning, characterization and tissue expression pattern of a porcine CD14 encoding cDNA, and the chromosomal localization of the porcine CD14 gene. The open reading frame is predicted to encode a protein of 373 amino acids, which shows conservation of structural as well as functional regions when compared to other mammalian species. The CD14 gene was localized to porcine chromosome 2 in a region syntenic to human chromosome 5q. Transcription analysis shows that CD14 is widely expressed in tissues examined in this study, which correlates well with expression primarily on myeloid cells.

CD14 facilitates invasive respiratory tract infection by Streptococcus pneumoniae

RATIONALE

CD14 is a pattern recognition receptor that can interact with a variety of bacterial ligands. During gram-negative infection, CD14 plays an important role in the induction of a protective immune response by virtue of its capacity to recognize lipopolysaccharide in the bacterial cell wall. Knowledge of the contribution of CD14 to host defense against gram-positive infections is limited.

OBJECTIVES

To study the role of CD14 in gram-positive bacterial pneumonia.

METHODS

CD14 knockout (KO) and normal wild-type (WT) mice were intranasally infected with Streptococcus pneumoniae.

MEASUREMENTS AND MAIN RESULTS

CD14 KO mice demonstrated a strongly reduced lethality, which was accompanied by a more than 10-fold lower bacterial load in lung homogenates but not in bronchoalveolar lavage fluid at 48 hours after infection. Strikingly, CD14 KO mice failed to develop positive blood cultures, whereas WT mice had positive blood cultures from 24 hours onward and eventually invariably had evidence of systemic infection. Lung inflammation was attenuated in CD14 KO mice at 48 hours after infection, as evaluated by histopathology and cytokine and chemokine levels. Intrapulmonary delivery of recombinant soluble CD14 to CD14 KO mice rendered them equally susceptible to S. pneumoniae as WT mice, resulting in enhanced bacterial growth in lung homogenates and bacteremia, indicating that the presence of soluble CD14 in the bronchoalveolar compartment is sufficient to cause invasive pneumococcal disease.

CONCLUSION

These data suggest that S. pneumoniae uses (soluble) CD14 present in the bronchoalveolar space to cause invasive respiratory tract infection.

Recognition and signaling by toll-like receptors

Toll-like receptors (TLRs) are transmembrane proteins that detect invading pathogens by binding conserved, microbially derived molecules and that induce signaling cascades for proinflammatory gene expression. A critical component of the innate immune system, TLRs utilize leucine-rich-repeat motifs for ligand binding and a shared cytoplasmic domain to recruit the adaptors MyD88, TRIF, TIRAP, and/or TRAM for downstream signaling. Despite significant domain conservation, TLRs induce gene programs that lead not only to the robust production of general proinflammatory mediators but also to the production of unique effectors, which provide pathogen-tailored immune responses. Here we review the mechanisms by which TLRs recognize pathogens and induce distinct signaling cascades.

The effect of CD14-c159T genotypes on the cytokine response to endotoxin by peripheral blood mononuclear cells from asthmatic children

BACKGROUND

A C-T polymorphism at position 159 in the promoter of CD14 (C-159T) modulates the cellular response to endotoxin and significantly influences total IgE levels. The effect of this genetic variant on the cytokine response of the inflammatory cells is incompletely understood.

OBJECTIVE

To investigate the effects of CD14-C159T genotypes on the response to endotoxin by peripheral blood mononuclear cells (PBMCs) in children with asthma.

METHODS

The PBMCs from asthmatic children with the TT (n = 11) and CC (n = 11) genotypes at the CD14 promoter were cultured in the presence of endotoxin, 100 ng/mL; concanavalin A, 10 microg/mL; or medium alone. Concentrations of soluble CD14 (sCD14), interleukin (IL) 1beta, IL-4, IL-10, IL-12, IL-13, interferon-gamma, and transforming growth factor beta were determined in culture supernatants by enzyme-linked immunosorbent assay, and the transcriptional differences were evaluated using reverse-transcriptase polymerase chain reaction.

RESULTS

Under unstimulated conditions, children with the TT genotype produced higher levels of sCD14 into the culture supernatant compared with children with the CC genotype (P = .03, Mann Whitney U test). Both IL-10 and IL-1beta concentrations were significantly higher in culture supernatants of children with the TT genotype after endotoxin stimulation (P = .02 and P = .009, respectively, by analysis of covariance [ANCOVA]). Messenger RNA expression was consistent with the results of protein concentration for IL-10 and sCD14. Concanavalin A stimulation resulted in lower levels of IL-4 in children with the TT genotype (P = .02, ANCOVA).

CONCLUSION

The genotype at the CD14 promoter C159T locus may significantly influence the cytokine response of PBMCs obtained from asthmatic children. Differences in IL-10 and IL-4 production by alternative genotypes may contribute to the observed genotype effect on total IgE.

Type I IFN Modulates Host Defense and Late Hyperinflammation in Septic Peritonitis

TLRs are considered important for the control of immune responses during endotoxic shock or polymicrobial sepsis. Signaling by TLRs may proceed through the adapter proteins MyD88 or TIR domain-containing adaptor inducinng IFN-beta. Both pathways can lead to the production of type I IFNs (IFN-alphabeta). In the present study, the role of the type I IFN pathway for host defense and immune pathology in sepsis was investigated using a model of mixed bacterial peritonitis. Systemic levels of IFN-alphabeta protein were markedly elevated during septic peritonitis. More detailed analyses revealed production of IFN-beta, but not IFN-alpha subtypes, and identified CD11b+ CD11c- macrophage-like cells as major producers of IFN-beta. The results further demonstrate that in IFN-alphabeta receptor I chain (IFNARI)-deficient mice, the early recruitment of neutrophils to the infected peritoneal cavity was augmented, most likely due to an increased local production of MCP-1 and leukotriene B4. In the absence of IFNARI, peritoneal neutrophils also exhibited enhanced production of reactive oxygen intermediates and elevated expression of Mac-1. Conversely, administration of recombinant IFN-beta resulted in reduced leukotriene B4 levels and decreased peritoneal neutrophil recruitment and activation. Analysis of the cytokine response to septic peritonitis revealed that IFNARI deficiency strongly attenuated late, but not early, hyperinflammation. In accordance with these findings, bacterial clearance and overall survival of IFNARI(-/-) mice were improved. Therefore, the present study reveals critical functions of the type I IFN pathway during severe mixed bacterial infections leading to sepsis. The results suggest that type I IFN exerts predominantly adverse effects under these conditions.

Systemic inflammation and remote organ damage following bilateral femur fracture requires Toll-like receptor 4

Extensive soft tissue injury and bone fracture are significant contributors to the initial systemic inflammatory response in multiply injured patients. Systemic inflammation can lead to organ dysfunction remote from the site of traumatic injury. The mechanisms underlying the recognition of peripheral injury and the subsequent activation of the immune response are unknown. Toll-like receptors (TLRs) recognize microbial products but also may recognize danger signals released from damaged tissues. Here we report that peripheral tissue trauma initiates systemic inflammation and remote organ dysfunction. Moreover, this systemic response to a sterile local injury requires toll-like receptor 4 (TLR4). Compared with wild-type (C3H/HeOuJ) mice, TLR4 mutant (C3H/HeJ) mice demonstrated reduced systemic and hepatic inflammatory responses to bilateral femur fracture. Trauma-induced nuclear factor (NF)-κB activation in the liver required functional TLR4 signaling. CD14−/− mice failed to demonstrate protection from fracture-induced systemic inflammation and hepatocellular injury. Therefore, our results also argue against a contribution of intestine-derived LPS to this process. These findings identify a critical role for TLR4 in the rapid recognition and response pathway to severe traumatic injury. Application of these findings in an evolutionary context suggests that multicellular organisms have evolved to use the same pattern recognition receptor for surviving traumatic and infectious challenges.

TLR4 Mediates LPS-Induced VEGF Expression in Odontoblasts

Lipopolysaccharide (LPS) from gram-negative bacteria cell walls such as Prevotella intermedia and Escherichia coli induce vascular endothelial growth factor (VEGF) expression in odontoblasts, but not in undifferentiated dental pulp cells. CD14 and TLR4 are responsible for LPS signaling in macrophages, but their expression levels and function in dental pulp cells are unknown. We showed here that murine odontoblast-like cells (MDPC-23) express CD14 and TLR4 by immunohistochemistry and flow cytometry. In contrast, undifferentiated dental pulp cells (OD-21) presented low or no expression of these two receptors. MDPC-23 cells showed CD14 and TLR4 up-regulation upon exposure to LPS, as determined by real time PCR. Dominant negative murine TLR4 (DN-mTLR4) transfected MDPC-23 cells did not show upregulated VEGF expression in response to LPS stimulation. These results demonstrate that odontoblast-like cells express CD14 and TLR4, and that LPS-induced VEGF expression is mediated, at least in part, by TLR4 signaling.

Ethanol suppresses LPS-induced Toll-like receptor 4 clustering, reorganization of the actin cytoskeleton, and associated TNF-alpha production

BACKGROUND

Ethanol (EtOH) suppresses cytokine responses induced through most Toll-like receptors (TLRs), but the mechanism of action is unclear. We recently found that acute EtOH alters lipopolysaccharide (LPS)-induced partitioning of CD14, a critical component of the LPS receptor complex, within lipid raft fractions in the macrophage-like cell line RAW264.7.

METHODS

Here we investigated the role of receptor clustering in alteration of the responses of cells to LPS caused by EtOH both in vitro and in vivo. The cellular distribution of CD14, TLR4, actin cytoskeleton, and tumor necrosis factor-alpha (TNF-alpha) were studied by confocal microscopy following exposure of cells to LPS with or without EtOH. TLR4 and CD14 were clustered into highly colocalized patches on the cell membrane accompanied by the reorganization of the actin cytoskeleton in some of the RAW264.7 cells as well as peritoneal cells following LPS treatment.

RESULTS

Addition of EtOH reduced the number of cells that had LPS-induced receptor patches and in which this reorganization occurred. Cells on which CD14 and TLR4 formed clusters or caps had substantially higher levels of membrane-bound TNF-alpha compared with cells without clustering or capping of these molecules. Interference with the actin cytoskeleton by cytochalasin D suppressed the production of TNF-alpha and receptor clustering, as EtOH did.

CONCLUSIONS

These data confirm our previous observations, suggest a novel mechanism of EtOH action that involves interference with receptor clustering, and indicate a potential role of actin filaments in the formation of receptor patches, subsequent activation of macrophages by LPS, and production of TNF-alpha.