Genes other than TLR4 are involved in the response to inhaled LPS

Loss of Nucleobindin-2/Nesfatin-1 increases lipopolysaccharide-induced murine acute lung inflammation

NUCB2/nesfatin-1 is expressed in variety of tissues. Treatment with nesfatin-1 reduces inflammation in rat models of subarachnoid hemorrhage-induced oxidative brain damage and traumatic brain injury as well as myocardial injury. There is only one study showing anti-inflammatory actions of nesfatin-1 on acute lung inflammation. To more precisely determine the role of NUCB2/nesfatin-1 in acute lung inflammation, we conducted a study using NUCB2/nesfatin-1 knockout (NKO) mice as well as neutrophils isolated from the bone marrows of WT and NKO mice. Our findings suggest that the absence of NUCB2/nesfatin-1 significantly increases the accumulation of adherent neutrophils by approximately 3 times compared with WT within LPS-treated lungs. Integrating this with observations from both BALF and neutrophil cytokine expression, we propose that although neutrophils lacking NUCB2/nesfatin-1 individually secrete less pro-inflammatory cytokines compared with stimulated WT cells, the result of knocking out NUCB2/nesfatin-1 is net pro-inflammatory. No change was found in NUCB2/nesfatin-1 mRNA or protein expression comparing WT LPS and PBS-treated samples. Taken together, our results show that NUCB2/nesfatin-1 is constitutively expressed in mouse lungs and neutrophils and demonstrates anti-inflammatory properties in mouse lungs during acute lung injury, by inhibiting adherent neutrophil accumulation and inflammatory cytokine expression.

Comparison of response to LPS-induced sepsis in three DBA/2 stocks derived from different sources

Sepsis, one of the most fatal diseases in the world, is known to culminate in multiple organ failure due to an uncontrolled inflammatory response. Hence, the use of animal models in sepsis research is very important to study complex immune responses. The current study was undertaken to compare commercial stocks with KFDA stocks of DBA/2 mice as an animal model for sepsis study. To compare responses of DBA/2 mice to lipopolysaccharides (LPS)-induced sepsis, we measured altered characteristics of various factors associated with sepsis, including survival curves, organ failure and inflammatory response, in DBA/2Korl stock and two commercial stocks (DBA/2A and DBA/2B). Survival rates after LPS exposure were similar for DBA/2Korl and DBA/2B; however, for times over 20 h, survival rates were reduced and concentration dependent in DBA/2A. In order to evaluate multiple organ failure caused by sepsis, H&E stains were evaluated for liver and spleen tissues obtained in the early (2 h) and later (20 h) stages after exposure to LPS; no significant differences were observed between the three stocks. mRNA and protein levels of proinflammatory cytokines were assessed for evaluating inflammatory reactions, and were found to increase in a dose-dependent manner in most DBA/2 mice after LPS treatment. However, no changes were observed in the mRNA levels of proinflammatory cytokines at 20 h after LPS exposure in the DBA/2A stock. The induction of inflammation-mediated factors by LPS exposure did not induce alterations in the mRNA levels of COX-2 and iNOS in all three DBA/2 stocks. Our results indicate that response of DBA/2Korl to LPS-induced sepsis is similar to the two commercial DBA/2 stocks, thus representing its potential as a useful biological resource established in Korea.

TRPV4 activation triggers protective responses to bacterial lipopolysaccharides in airway epithelial cells

Lipopolysaccharides (LPS), the major components of the wall of gram-negative bacteria, trigger powerful defensive responses in the airways via mechanisms thought to rely solely on the Toll-like receptor 4 (TLR4) immune pathway. Here we show that airway epithelial cells display an increase in intracellular Ca²⁺ concentration within seconds of LPS application. This response occurs in a TLR4-independent manner, via activation of the transient receptor potential vanilloid 4 cation channel (TRPV4). We found that TRPV4 mediates immediate LPS-induced increases in ciliary beat frequency and the production of bactericidal nitric oxide. Upon LPS challenge TRPV4-deficient mice display exacerbated ventilatory changes and recruitment of polymorphonuclear leukocytes into the airways. We conclude that LPS-induced activation of TRPV4 triggers signaling mechanisms that operate faster and independently from the canonical TLR4 immune pathway, leading to immediate protective responses such as direct antimicrobial action, increase in airway clearance, and the regulation of the inflammatory innate immune reaction.

LPS is a major component of gram-negative bacterial cell walls, and triggers immune responses in airway epithelium by activating TLR4. Here the authors show that LPS also activates TRPV4, thereby inducing fast defense responses such as nitric oxide production and increased ciliary beating in mice.

Association between Toll-Like Receptor 4 and Occurrence of Type 2 Diabetes Mellitus Susceptible to Pulmonary Tuberculosis in Northeast China

The purpose of this study is to explore why type 2 diabetes mellitus (T2DM) patients are susceptible to pulmonary tuberculosis through detection of serum Toll-like receptor 4 (TLR₄), an important immune-related receptor, especially in terms of content and TLR₄ gene polymorphism. Patients with T2DM complicated by pulmonary tuberculosis (T2DMTB) were selected as the case group and T2DM patients without tuberculosis were selected as the control group. Forty patients in each group were randomly selected and their serum TLR₄ levels were detected and compared. Determination of six sites of TLR₄ gene polymorphism was carried out in 238 T2DMTB patients and 310 patients with T2DM, and results showed that the serum TLR₄ content of the T2DMTB group was significantly lower than that of the T2DM group (p < 0.05). The six sites of TLR₄ gene polymorphism did not show significant associations with T2DMTB risk. No statistically significant differences in genotype distributions were observed between T2DMTB patients and patients with T2DM when studied using the recessive and dominant genetic models. How two diseases with contradictory nutritional statuses can occur in the same person is difficult to explain from environmental factors perspective alone. Future research should study the causes of T2DMTB from the perspective of genetics.

How the Intricate Interaction among Toll-Like Receptors, Microbiota, and Intestinal Immunity Can Influence Gastrointestinal Pathology

The gut is able to maintain tolerance to microbial and food antigens. The intestine minimizes the number of harmful bacteria by shaping the microbiota through a symbiotic relationship. In healthy human intestine, a constant homeostasis is maintained by the perfect regulation of microbial load and the immune response generated against it. Failure of this balance may result in various pathological conditions. Innate immune sensors, such as Toll-like receptors (TLRs), may be considered an interface among intestinal epithelial barrier, microbiota, and immune system. TLRs pathway, activated by pathogens, is involved in the pathogenesis of several infectious and inflammatory diseases. The alteration of the homeostasis between physiologic and pathogenic bacteria of intestinal flora causes a condition called dysbiosis. The breakdown of homeostasis by dysbiosis may increase susceptibility to inflammatory bowel diseases. It is evident that environment, genetics, and host immunity form a highly interactive regulatory triad that controls TLR function. Imbalanced relationships within this triad may promote aberrant TLR signaling, critically contributing to acute and chronic intestinal inflammatory processes, such as in IBD, colitis, and colorectal cancer. The study of interactions between different components of the immune systems and intestinal microbiota will open new horizons in the knowledge of gut inflammation.

Cathelicidin related antimicrobial peptide, laminin, Toll-like receptors and chemokines levels in experimental hypersensitivity pneumonitis in mice

INTRODUCTION

Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by unresolved inflammation and tissue repair pathologies triggered by repeated organic dust exposure. The aim of the study was to investigate changes in levels of the cathelicidin related antimicrobial peptide (CRAMP), laminin (LAM-A1), selected Toll-like receptors (TLR) and chemokines in experimental HP in mice.

MATERIALS AND METHODS

Three and 18-month-old female C57BL/6J mice underwent inhalations of the saline extract of Pantoea agglomerans cells, Gram-negative bacterium common in organic dust and known for its pathogenic impact. The inhalations were repeated daily (28 days). ELISA was used for measuring in lung tissue homogenates concentration of CRAMP, LAM-A1, TLR2, TLR4, TLR8, CXCL9 (chemokine [C-X-C motif] ligand) and CXCL10.

RESULTS

Levels of TLR2, TLR4 and CXCL9 were significantly higher in both young and old mice lungs already after 7 days of inhalations, while significant increase of LAM-A1 and CXCL10 was noted after 28 days, compared to untreated samples. TLR8 level was significantly augmented only in young mice. Only CRAMP level significantly declined. Significantly higher TLR8 and CXCL9 concentration in untreated samples were noted in old animals compared to young ones.

CONCLUSION

Significant alterations of the examined factors levels indicate their role in HP pathogenesis.

Chronic low-grade systemic inflammation causes DNA damage in the lungs of mice

BACKGROUND

Whether systemic inflammation compromises the pulmonary system is largely unknown. We tested the hypothesis that chronic low-grade systemic inflammation damages alveolar wall cells.

METHODS

A chronic low-grade systemic inflammatory state was induced in 8-week-old male C57/BL6J mice by administration of lipopolysaccharide (LPS, 44.4 μg/day) for a 90-day period by subcutaneous implantation of a delayed-release pellet system. Acute systemic inflammation was induced in another group of mice by a single intraperitoneal injection of LPS (125 μg/body). The lungs of mice were examined for histologic changes and genetic damage to alveolar wall cells.

RESULTS

Chronic LPS exposure for a 30-day period or a 90-day period did not cause any obvious architectural changes in the lungs except for a mild level of alveolar macrophage infiltration. Despite the lack of architectural changes in the lung, immunofluorescence staining for γH2AX and phosphorylated 53BP1 showed that chronic LPS exposure resulted in an almost doubling of the number of DNA double-strand breaks (DSBs) in type 1 and type 2 alveolar epithelial cells and in alveolar endothelial cells. Acute LPS exposure also resulted in a doubling of the number of DSBs in type 1 and type 2 alveolar epithelial cells and in alveolar endothelial cells at 24 h, but the increased number of DSBs returned to the baseline level by 48 h.

CONCLUSIONS

These results suggest that chronic systemic low-grade inflammation induces persistent DNA damage in alveolar epithelial and endothelial cells before architectural changes in the lung become evident.

Enhancement of methacholine-evoked tracheal contraction induced by bacterial lipopolysaccharides depends on epithelium and tumor necrosis factor

Inhaled bacterial lipopolysaccharides (LPSs) induce an acute tumour necrosis factor-alpha (TNF-α-) dependent inflammatory response in the murine airways mediated by Toll-like receptor 4 (TLR4) via the myeloid differentiation MyD88 adaptor protein pathway. However, the contractile response of the bronchial smooth muscle and the role of endogenous TNFα in this process have been elusive. We determined the in vivo respiratory pattern of C57BL/6 mice after intranasal LPS administration with or without the presence of increasing doses of methacholine (MCh). We found that LPS administration altered the basal and MCh-evoked respiratory pattern that peaked at 90 min and decreased thereafter in the next 48 h, reaching basal levels 7 days later. We investigated in controlled ex vivo condition the isometric contraction of isolated tracheal rings in response to MCh cholinergic stimulation. We observed that preincubation of the tracheal rings with LPS for 90 min enhanced the subsequent MCh-induced contractile response (hyperreactivity), which was prevented by prior neutralization of TNFα with a specific antibody. Furthermore, hyperreactivity induced by LPS depended on an intact epithelium, whereas hyperreactivity induced by TNFα was well maintained in the absence of epithelium. Finally, the enhanced contractile response to MCh induced by LPS when compared with control mice was not observed in tracheal rings from TLR4- or TNF- or TNF-receptor-deficient mice. We conclude that bacterial endotoxin-mediated hyperreactivity of isolated tracheal rings to MCh depends upon TLR4 integrity that signals the activation of epithelium, which release endogenous TNFα.

Small interference RNA targeting TLR4 gene effectively attenuates pulmonary inflammation in a rat model

Objective. The present study was to investigate the feasibility of adenovirus-mediated small interference RNA (siRNA) targeting Toll-like receptor 4 (TLR4) gene in ameliorating lipopolysaccharide- (LPS-) induced acute lung injury (ALI). Methods. In vitro, alveolar macrophages (AMs) were treated with Ad-siTLR4 and Ad-EFGP, respectively, for 12 h, 24 h, and 48 h, and then with LPS (100 ng/mL) for 2 h, and the function and expression of TLR4 were evaluated. In vivo, rats received intratracheal injection of 300 μL of normal saline (control group), 300 μL of Ad-EGFP (Ad-EGFP group), or 300 μL of Ad-siTLR4 (Ad-siTLR4 group) and then were intravenously treated with LPS (50 mg/kg) to induce ALI. Results. Ad-siTLR4 treatment significantly reduced TLR4 expression and production of proinflammatory cytokines following LPS treatment both in vitro and in vivo. Significant alleviation of tissue edema, microvascular protein leakage, and neutrophil infiltration was observed in the AdsiTLR4-treated animals. Conclusion. TLR4 plays a critical role in LPS-induced ALI, and transfection of Ad-siTLR4 can effectively downregulate TLR4 expression in vitro and in vivo, accompanied by alleviation of LPS-induced lung injury. These findings suggest that TLR4 may serve as a potential target in the treatment of ALI and RNA interfering targeting TLR4 expression represents a therapeutic strategy.

Role of acute ethanol exposure and TLR4 in early events of sepsis in a mouse model

Sepsis is a major cause of death worldwide. The associated risks and mortality are known to significantly increase on exposure to alcohol (chronic or acute). The underlying mechanisms of the association of acute ethanol ingestion and poor prognosis of sepsis are largely unknown. The study described here was designed to determine in detail the role of ethanol and TLR4 in the pathogenesis of the sepsis syndrome. The effects of acute ethanol exposure and TLR4 on bacterial clearance, spleen cell numbers, peritoneal macrophage numbers, and cytokine production were evaluated using wild-type and TLR4 hyporesponsive mice treated with ethanol and then challenged with a nonpathogenic strain of Escherichia coli. Ethanol-treated mice exhibited a decreased clearance of bacteria and produced lesser amounts of most pro-inflammatory cytokines in both strains of mice at 2h after challenge. Neither ethanol treatment nor a hyporesponsive TLR4 had significant effects on the cell numbers in the peritoneal cavity and spleen 2h postinfection. The suppressive effect of acute ethanol exposure on cytokine and chemokine production was more pronounced in the wild-type mice, but the untreated hyporesponsive mice produced less of most cytokines than untreated wild-type mice. The major conclusion of this study is that acute ethanol exposure suppresses pro-inflammatory cytokine production and that a hyporesponsive TLR4 (in C3H/HeJ mice) decreases pro-inflammatory cytokine levels, but the cytokines and other mediators induced through other receptors are sufficient to ultimately clear the infection but not enough to induce lethal septic shock. In addition, results reported here demonstrate previously unknown effects of acute ethanol exposure on leukemia inhibitory factor and eotaxin, and provide the first evidence that interleukin (IL)-9 is induced through TLR4 in vivo.

A locus on chromosome 9 is associated with differential response of 129S1/SvImJ and FVB/NJ strains of mice to systemic LPS

Although polymorphisms in TLR receptors and downstream signaling molecules affect the innate immune response, these variants account for only a portion of the ability of the host to respond to microorganisms. To identify novel genes that regulate the host response to systemic lipopolysaccharide (LPS), we created an F2 intercross between susceptible (FVB/NJ) and resistant (129S1/SvImJ) strains, challenged F2 progeny with LPS via intraperitoneal injection, and phenotyped 605 animals for survival and another 500 mice for serum concentrations of IL-1β and IL-6. Genome-wide scans were performed on pools of susceptible and resistant mice for survival, IL-1β, and IL-6. This approach identified a locus on the telomeric end of the q arm of chromosome 9 (0-40 Mb) that was associated with the differences in morbidity and serum concentrations of IL-1β and IL-6 following systemic LPS in FVB/NJ and 129S1/SvImJ strains of mice. Fine mapping narrowed the locus to 3.7 Mb containing 11 known genes, among which are three inflammatory caspases. We studied expression of genes within the locus by quantitative RT-PCR and showed that Casp1 and Casp12 levels are unaffected by LPS in both strains, whereas Casp4 is highly induced by LPS in FVB/NJ but not in 129S1/SvImJ mice. In conclusion, our mapping results indicate that a 3.7-Mb region on chromosome 9 contains a gene that regulates differential response to LPS in 129S1/SvImJ and FVB/NJ strains of mice. Differences in the induction of Casp4 expression by LPS in the two strains suggest that Casp4 is the most likely candidate gene in this region.

Novel regulators of the systemic response to lipopolysaccharide

Our understanding of the role that host genetic factors play in the initiation and severity of infections caused by gram-negative bacteria is incomplete. To identify novel regulators of the host response to lipopolysaccharide (LPS), 11 inbred murine strains were challenged with LPS systemically. In addition to two strains lacking functional TLR4 (C3H/HeJ and C57BL/6J(TLR4-/-)), three murine strains with functional TLR4 (C57BL/6J, 129/SvImJ, and NZW/LacJ) were found to be relatively resistant to systemic LPS challenge; the other six strains were classified as sensitive. RNA from lung, liver, and spleen tissue was profiled on oligonucleotide microarrays to determine if unique transcripts differentiate susceptible and resistant strains. Gene expression analysis identified the Hedgehog signaling pathway and a number of transcription factors (TFs) involved in the response to LPS. RNA interference-mediated inhibition of six TFs (C/EBP, Cdx-2, E2F1, Hoxa4, Nhlh1, and Tead2) was found to diminish IL-6 and TNF-α production by murine macrophages. Mouse lines with targeted mutations were used to verify the involvement of two novel genes in innate immunity. Compared with wild-type control mice, mice deficient in the E2F1 transcription factor were found to have a reduced inflammatory response to systemic LPS, and mice heterozygote for Ptch, a gene involved in Hedgehog signaling, were found to be more responsive to systemic LPS. Our analysis of gene expression data identified novel pathways and transcription factors that regulate the host response to systemic LPS. Our results provide potential sepsis biomarkers and therapeutic targets that should be further investigated in human populations.

Toll-like receptors in inflammatory bowel diseases: a decade later

Differential alteration of Toll-like receptor (TLR) expression in inflammatory bowel disease (IBD) was first described 10 years ago. Since then, studies from many groups have led to the current concept that TLRs represent key mediators of innate host defense in the intestine, involved in maintaining mucosal as well as commensal homeostasis. Recent findings in diverse murine models of colitis have helped to reveal the mechanistic importance of TLR dysfunction in IBD pathogenesis. It has become evident that environment, genetics, and host immunity form a multidimensional and highly interactive regulatory triad that controls TLR function in the intestinal mucosa. Imbalanced relationships within this triad may promote aberrant TLR signaling, critically contributing to acute and chronic intestinal inflammatory processes in IBD colitis and associated cancer.

Susceptibility of TLR4-defective C3H/HeJ mice to Coccidioides posadasii infection

Coccidioides posadasii is one of the two fungal pathogens that cause coccidioidomycosis. The inhalation of air-borne arthroconidia leads to the formation of endospore-forming spherules in the lungs and pulmonary infection. In severe condition, the endospores are disseminated to other non-pulmonary organs in the body. The Toll-like receptors (TLR) expressed by a number of immune and non-immune cells can significantly impact the host defense and susceptibility to C. posadasii infection. In this study, we infected TLR4-defective C3H/HeJ mice with a sublethal dose of C. posadasii and studied fungal dissemination, mortality and humoral response. We also measured IL-12 cytokine secreted by C. posadasii-infected dendritic cells. We found that the C3H/HeJ mice were equally susceptible to C. posadasii as compared to C3H/OuJ mice which have intact TLR4. No significant changes were observed in pulmonary fungal load, survival and humoral response. The blockade of TLR4 did not affect C. posadasii-induced IL-12 secretion. However, the fungal counts were 10 times less in spleens of C3H/HeJ mice as compared to C3H/OuJ mice (P<0.05). Our results suggest that the TLR4 may not be involved in inducing protective host defense against C. posadasii, but it appears to be critical for fungal dissemination.

Identification of novel genes that mediate innate immunity using inbred mice

Innate immunity is the first line of defense against microbial infections. Although polymorphisms in toll-like receptors (TLRs) and downstream signaling molecules (CD14, TLR2, TLR4, TLR5, and IRAK4) affect the innate immune response, these variants account for only a portion of the ability of the host to respond to bacteria, fungi, and viruses. To identify other genes involved in the innate immune response, we challenged 16 inbred murine strains with lipopolysaccharide (LPS) systemically and measured serum concentrations of pro-inflammatory cytokines IL-1beta, IL-6, and TNFalpha, and the chemokine KC 6 hr post-treatment. Loci that segregate with strain phenotypes were identified by whole genome association (WGA) mapping of cytokine concentrations. Published gene expression profiles and quantitative trait loci (QTL) were then utilized to prioritize loci and genes that potentially regulate the host response to LPS. Sixteen loci were selected for further investigation by combining WGA analysis with previously published QTL for murine response to LPS or gram negative bacteria. Thirty-eight genes within these loci were then selected for further investigation on the basis of the significance of the identified locus, transcriptional response to LPS, and biological plausibility. RNA interference-mediated inhibition of 4 of 38 candidate genes was shown to block the production of IL-6 in J774A.1 macrophages. In summary, our analysis identified 4 genes that have not previously been implicated in innate immunity, namely, 1110058L19Rik, 4933415F23Rik, Fbxo9, and Ipo7. These genes could represent potential sepsis biomarkers or therapeutic targets that should be further investigated in human populations.

Gene by environment interaction in asthma

Marked international differences in rates of asthma and allergies and the importance of family history highlight the primacy of interactions between genetic variation and the environment in asthma etiology. Environmental tobacco smoke (or secondhand smoke), ambient air pollutants, and endotoxin and/or other pathogen-associated molecular patterns are the ambient exposures studied most frequently for interactions with genetic polymorphisms in asthma. To date, results from the literature remain inconclusive. Most published studies are underpowered to study interactions between genetic polymorphisms and ambient exposures, each with weak effects. Strategies to increase power include cooperation across studies to increase sample sizes and improve measures of both exposure and asthma phenotypes. Genome-wide association studies hold promise for identifying unexpected gene environment interactions, but given the statistical power issues, candidate gene association studies will remain important. New tools are enabling the study of epigenetic mechanisms for environmental interactions.

House dust mite allergen induces asthma via Toll-like receptor 4 triggering of airway structural cells

Barrier epithelial cells and airway dendritic cells (DCs) make up the first line of defense against inhaled substances such as house dust mite (HDM) allergen and endotoxin (lipopolysaccharide, LPS). We hypothesized that these cells need to communicate with each other to cause allergic disease. We show in irradiated chimeric mice that Toll-like receptor 4 (TLR4) expression on radioresistant lung structural cells, but not on DCs, is necessary and sufficient for DC activation in the lung and for priming of effector T helper responses to HDM. TLR4 triggering on structural cells caused production of the innate proallergic cytokines thymic stromal lymphopoietin, granulocyte-macrophage colony-stimulating factor, interleukin-25 and interleukin-33. The absence of TLR4 on structural cells, but not on hematopoietic cells, abolished HDM-driven allergic airway inflammation. Finally, inhalation of a TLR4 antagonist to target exposed epithelial cells suppressed the salient features of asthma, including bronchial hyperreactivity. Our data identify an innate immune function of airway epithelial cells that drives allergic inflammation via activation of mucosal DCs.

Mouse models for human otitis media

Otitis media (OM) remains the most common childhood disease and its annual costs exceed $5 billion. Its potential for permanent hearing impairment also emphasizes the need to better understand and manage this disease. The pathogenesis of OM is multifactorial and includes infectious pathogens, anatomy, immunologic status, genetic predisposition, and environment. Recent progress in mouse model development is helping to elucidate the respective roles of these factors and to significantly contribute toward efforts of OM prevention and control. Genetic predisposition is recognized as an important factor in OM and increasing numbers of mouse models are helping to uncover the potential genetic bases for human OM. Furthermore, the completion of the mouse genome sequence has offered a powerful set of tools for investigating gene function and is generating a rich resource of mouse mutants for studying the genetic factors underlying OM.

MD-2-dependent pulmonary immune responses to inhaled lipooligosaccharides: effect of acylation state

Endotoxins represent one of the most potent classes of microbial immunoactive components that can cause pulmonary inflammation. The aim of this study was to compare the inflammatory potency of two types of Neisseria meningitidis endotoxins (lipooligosaccharides) in lungs: wild type (hexaacylated, LOS(wt)) and mutant type (pentaacylated, LOS(msbB)), and to determine the importance of MD-2 in endotoxin responses in lungs in vivo. Endotoxin-normoresponsive mice (BALB/c) were exposed to selected doses of penta- and hexaacylated lipooligosaccharides (LOS) by nasal aspiration. Cellular and cytokine/chemokine inflammatory responses in bronchoalveolar lavage were measured at 1-, 4-, 8-, 16-, 24-, and 48-hour time points. MD-2-null mice were exposed to one dose of hexaacylated LOS and inflammatory responses were measured after 4 and 24 hours. Inhalation of hexaacylated LOS resulted in strong inflammatory responses, while pentaacylated LOS was much less potent in inducing increases of neutrophils, TNF-alpha, macrophage inflammatory protein-1 alpha, IL-6, granulocyte colony-stimulating factor, and IL-1 beta concentration in bronchoalveolar lavage. Similar kinetics of inflammatory responses in lungs were found in both types of endotoxin exposures. Inhalation of hexaacylated LOS in MD-2-null mice resulted in significantly lower numbers of neutrophils in bronchoalveolar lavage than in normoresponsive mice. Markedly lower inflammatory potency of pentaacylated LOS was observed compared with hexaacylated LOS. Hyporesponsiveness in MD-2-null mice after nasal aspiration of wild-type LOS indicate its essential role in airway responsiveness to endotoxin.

Toll-like receptor 2 participates in the response to lung injury in a murine model of pulmonary contusion

Blunt chest trauma resulting in pulmonary contusion with an accompanying acute inflammatory response is a common but poorly understood injury. We report that Toll-like receptor (TLR) 2 participates in the inflammatory response to lung injury. To show this, we use a model of pulmonary contusion in the mouse that is similar to that observed clinically in humans based on histologic, morphologic, and biochemical criteria of acute lung injury. The inflammatory response to pulmonary contusion in our mouse model is characterized by pulmonary edema, neutrophil transepithelial migration, and increased expression of the innate immunity proinflammatory cytokines IL 1beta and IL 6, the adhesion intracellular adhesion molecule 1, and chemokine (CXC motif) ligand 1. Compared with wild-type animals, contused Tlr2(-/-) mice have significantly reduced pulmonary edema and neutrophilia. These findings are associated with decreased levels of circulating chemokine (CXC motif) ligand 1. In contrast, systemic IL 6 levels remain elevated in the TLR2-deficient phenotype. These results show that TLR2 has a primary role in the neutrophil response to acute lung injury. We suggest that an unidentified noninfectious ligand generated by pulmonary contusion acts via TLR2 to generate inflammatory responses.

In vitro production of tumor necrosis factor-alpha by human monocytes stimulated with lipopolysaccharide is positively correlated with increased blood monocytes after exposure to a swine barn

Recently there has been interest in the air quality in and around intensive livestock production facilities, such as modern swine production barns, where agricultural workers and surrounding residents may be exposed to elevated levels of organic dusts. The health effects of these exposures are not completely understood. The study that is reported here is a component of a larger investigation of the relationships among the acute effects of high-concentration endotoxin exposure (swine barn dust), polymorphisms in the TLR4 gene, and respiratory outcomes following exposure to swine confinement buildings. The relationships among a mediator of acute lung inflammation, tumor necrosis factor alpha (TNF-alpha), and clinical responses to acute swine barn exposure were characterized. Analysis of the results showed that in vitro stimulation of human monocytes with as little as 1 ng/ml of lipopolysaccharide (LPS) produced a significant increase in the monocytes that produced TNF-alpha. Although the proportion of TNF-alpha-positive monocytes after in vitro stimulation with 1 ng/ml of LPS was not associated with gender or TLR4 genotype, it was positively associated with the concentration of monocytes in blood after barn exposure. Thus, these two responses to different forms of LPS exposure are significantly correlated, and more responsive monocytes in vitro indicate a forthcoming relative monocytosis, post barn exposure, which may initiate a cascade of chronic inflammation.

Toll-like receptors in inflammation, infection and cancer

Members of the Toll-like receptor (TLR) family play key roles in both innate and adaptive immune responses. TLR proteins enable host to recognize a large number of pathogen-associated molecular patterns such as bacterial lipopolysaccharides, viral RNA, CPG-containing DNA, and flagellin, among others. TLRs are also apparently able to mediate responses to host molecules, including one defensin, ROS, HMGB1 (high-mobility group box protein 1), surfactant protein A, fibrinogen, breakdown products of tissue matrix, heat shock proteins (hsp) and eosinophil-derived neurotoxin (EDN). Thus, TLR are involved in the development of many pathological conditions including infectious diseases, tissue damage, autoimmune and neurodegenerative diseases and cancer. In this review, the contribution of TLRs to diseases of the central nervous system (CNS), lung, gastrointestinal tract, kidney and skin as well as cancer is evaluated. We hope to provide new insight into the pathogenesis and progression of diseases and more importantly, into the potential for TLRs as targets of therapeutics.

Functional significance of the TLR4/11367 polymorphism identified in Chinese Han population

Toll-like receptor 4 (TLR4) is the central signaling receptor for lipopolysaccharide (LPS) in mammals. This study was designed to investigate the functional significance of the G11367C polymorphism, which is a novel variant we identified in the 3' untranslated region of TLR4 gene in Chinese Han population. Three hundred seventy healthy volunteers were selected. The TLR4/11367 polymorphism was genotyped using single-tube bidirectional allele-specific amplification method. The TLR4 protein expression on peripheral leukocytes and plasma tumor necrosis factor alpha levels were determined by means of flow cytometry and enzyme-linked immunosorbent assay. The post-transcriptional effect of the 11367 polymorphism was evaluated by means of reporter gene assay and real-time quantitative polymerase chain reaction. The G11367C polymorphism is a common allele in Chinese Han population, with minor allele frequency of 14.7%. In response to ex vivo LPS stimulation, the TLR4 expression on the surface of peripheral leukocytes and the plasma tumor necrosis factor alpha levels were significantly lower in carriers of 11367C variant allele than in carriers of 11367G allele. This association was allele dose dependent. We also found that the activity and the mRNA expression of luciferase was significantly smaller in human embryonic kidney 293 cells transfected with construct containing 11367C allele than in those transfected with construct containing 11367G allele. Together, these results suggest that the TLR4/11367 polymorphism may be a functional single nucleotide polymorphism, which could attenuate the LPS-induced transmembrane signaling through the alteration of post-transcriptional regulation of 3' untranslated region and target gene expression.

The IL-1 type 1 receptor is required for the development of LPS-induced airways disease

BACKGROUND

The contribution of IL-1beta signaling through the IL-1 type 1 receptor (IL-1R1) to the development of persistent LPS-induced airway disease has not been investigated.

OBJECTIVE

To determine the importance of signaling through the IL-1 type 1 receptor in the development of LPS-induced airway disease.

METHODS

We exposed IL-1R1-deficient (C57BL/6(IL-1RI-/-)) mice to an aerosol of LPS or filtered air for 1 day, 1 week, or 4 weeks.

RESULTS

After 4 weeks of LPS inhalation, C57BL/6(IL-1RI-/-) mice failed to develop significant submucosal thickening, whereas C57BL/6 mice had significantly thickened submucosa in small, medium, and large airways compared with those of unexposed control mice. Cell proliferation in the airways of both the 1-week and 4-week LPS-exposed C57BL/6(IL-1RI-/-) mice was significantly reduced compared with LPS-exposed C57BL/6 mice. mRNA for type III alpha-3 procollagen was significantly elevated over baseline in C57BL/6 yet remained unchanged compared with baseline in C57BL/6(IL-1RI-/-) mice after 1 week or 4 weeks of LPS inhalation. mRNA for tissue inhibitor of metalloprotease 1 in C57BL/6 mice in the 1-week and 4-week groups was significantly elevated over both control mice and C57BL/6(IL-1RI-/-) mice.

CONCLUSION

These data support the hypothesis that signaling through the IL-1 receptor modulates extracellular matrix homeostasis in response to inhaled LPS.

CLINICAL IMPLICATIONS

Attenuating IL-1R1-mediated signaling might be an effective therapy against the development of airway remodeling in chronic inflammatory diseases.

CD44 regulates macrophage recruitment to the lung in lipopolysaccharide-induced airway disease

LPS from bacteria is ubiquitous in the environment and can cause airway disease and modify allergic asthma. Identification of gene products that modulate the biologic response to inhaled LPS will improve our understanding of inflammatory airways disease. Previous work has identified quantitative trait loci for the response to inhaled LPS on chromosomes 2 and 11. In these regions, 28 genes had altered RNA expression after inhalation of LPS, including CD44, which was associated with differences in both TNF-alpha levels and neutrophil recruitment into the lung. It has previously been shown that CD44 can modulate macrophage recruitment in response to Mycobacterium tuberculosis, as well as clearance of neutrophils after lung injury with both bleomycin and live Escherichia coli bacteria. In this study, we demonstrate that the biologic response to inhaled LPS is modified by CD44. Macrophages failed to be recruited to the lungs of CD44-deficient animals at all time points after LPS exposure. CD44-deficient macrophages showed reduced motility in a Transwell migration assay, reduced ability to secrete the proinflammatory cytokine TNF-alpha, reduced in vivo migration in response to monocyte chemotactic protein-1, and diminished adhesion to vascular endothelia in the presence of TNF-alpha. In addition, CD44-deficient animals had 150% fewer neutrophils at 24 h and 50% greater neutrophils 48 h after LPS exposure. These results support the role of CD44 in modulating the biologic response to inhaled LPS.

Early exposure to a nonhygienic environment alters pulmonary immunity and allergic responses

The hygiene hypothesis suggests that early life exposure to a nonhygienic environment that contains endotoxin reduces the risk of developing allergic diseases. The mechanisms underlying the hygiene hypothesis are unclear and may involve subtle immune system interactions that occur during maturation. Experimental objectives of this study were to use a novel animal model to test the hygiene hypothesis and to characterize early life immune system responses to a nonhygienic environment. Mice were reared in corn dust, a grain-processing byproduct with a high-endotoxin content and microbial products or in a low-endotoxin environment. The influence of early or later life exposure to corn dust on a subsequent allergen stimulus (ovalbumin) was assessed by bronchoalveolar lavage (BAL) cell analysis, lung histology, serum IgE, and BAL cytokine measurements. The influence of the corn dust environment on the developing pulmonary immune system was assessed by BAL cell analysis and immunostaining of lung tissue. The corn dust environment contained significantly more endotoxin ( P < 0.001), and the dust exposures attenuated the cellular inflammatory response to ovalbumin in the adult mouse ( P < 0.01) but did not reduce serum IgE levels or alter baseline BAL fluid proinflammatory cytokine levels. The corn dust environment did not induce significant neutrophilia in lavage fluid but significantly increased the number of antigen-presenting cells in alveolar walls early in life by ∼37%. In conclusion, exposure to a nonhygienic environment did not induce significant airway neutrophilia, yet altered the population of immunologically active cells in the lung and reduced subsequent allergic inflammation.

The transcriptional response to lipopolysaccharide reveals a role for interferon-gamma in lung neutrophil recruitment

Neutrophil recruitment to the lung after lipopolysaccharide (LPS; endotoxin) inhalation is primarily dependent on Toll-like receptor 4 (Tlr4) signaling, because it is virtually absent in mice deficient in Tlr4. However, among strains wild type for Tlr4, the magnitude of neutrophil recruitment to the lung after LPS inhalation is variable, suggesting the involvement of genes other than Tlr4. To identify genes associated with the inflammatory response to inhaled LPS, we evaluated the transcriptional response in lungs of 12 inbred strains of mice, 8 which are wild type for Tlr4 and 4 of which lack functional Tlr4. Using the promoter integration in microarray analysis algorithm, we scanned our gene list for transcription factor-binding sites significantly overrepresented among Tlr4 wild-type strains with high neutrophil influx in the lung after LPS inhalation. This analysis identified the interferon (IFN)-stimulated response element (ISRE) as the most overrepresented transcription factor (present in 24% of the promoters) associated with the neutrophil influx to the lower respiratory tract. To test the validity of this observation, we evaluated IFN-gamma-deficient mice and found that the presence of IFN-gamma is essential for robust neutrophil recruitment to the lower respiratory tract and modulation of key regulatory cytokines and chemokines after LPS inhalation. In conclusion, using a genomic approach, we identified the ISRE as a transcriptional element associated with the neutrophil response to inhaled LPS and demonstrated for the first time that IFN-gamma plays a critical role in LPS-induced neutrophil recruitment to the lower airways.

Pulmonary effects of exposure to pig barn air

Swine production has undergone rapid transformation from family owned operation to a large scale industrial enterprise. Since increasing number of pigs are reared on a large scale in confined buildings, some of the swine barn workers may be employed to work eight hours per day. Swine barn workers suffer from higher incidences of impaired air flow and lung inflammation, which is attributed to high intensity and interrupted exposures to pig barn air. The air in these barns contains gases, dust, microbes and endotoxin with endotoxin being the major suspect as the cause of lung dysfunction. This review attempts to describe the current state of knowledge of incidences and mechanisms of pulmonary dysfunction following exposure to the barn air.

Genotyping of Toll-like receptor 4, myeloid differentiation factor 2 and CD-14 in the horse: An investigation into the influence of genetic polymorphisms on the LPS induced TNF-α response in equine whole blood

The inter- and intra-species differences in the response to lipopolysaccharides (LPS) are well recognised in mammalian species. It has been hypothesized that these differences can be attributed to genetic polymorphisms in the components involved in LPS signal transduction. These components include the cluster of differentiation factor 14 (CD-14), a membrane bound protein on the surface of mononuclear cells that recognises LPS and a receptor complex consisting of Toll-like receptor-4 (TLR-4) and myeloid differentiation factor-2 (MD-2). Sequencing of these three proteins in humans and mice revealed that all three are susceptible to polymorphic alterations, influencing the response to LPS. Previous experiments in the horse showed large inter-individual variations in the response to LPS. With the aim to assess this inter-individual variation, we performed a whole blood assay in 10 healthy horses as a functional assay to study the responsiveness to LPS. In 3 out of the 10 horses, LPS-induced TNF-alpha production was significantly lower compared to the overall mean. Subsequently the entire cDNA sequence encoding for the TLR-4, MD-2 and CD-14 protein was documented for each horse. Although mutations were observed in the sequence of TLR-4, these could not be related to an altered response to LPS in the concentration used in this study, as determined in the whole blood assay. Despite the various mutations found in the TLR-4 receptor protein, no alterations could be found in either the MD-2 or CD-14 gene, which are obviously more conserved structures.

Expression of nitric oxide synthase isoforms in the mouse kidney: cellular localization and influence by lipopolysaccharide and Toll-like receptor 4

We determined the cellular mRNA expression of all intrarenal nitric oxide (NO)-producing NO synthase (NOS) isoforms, endothelial NOS (eNOS) and neuronal NOS (nNOS) and inducible NOS (iNOS) in kidneys from wild-type mice (WT) and immune deficient Toll-like receptor 4 (TLR4) mutant mice, during normal physiological conditions and during a short-term (6-16 h) endotoxic condition caused by systemically administered lipopolysaccaride (LPS). Investigations were performed by means of in situ hybridization and polymerase chain reaction amplification techniques. In WT, LPS altered the expression rate of all intrarenal NOS isoforms in a differentiated but NOS-isoform coupled expression pattern, with iNOS induction, and up- and down-regulation of the otherwise constitutively expressed NOS isoforms, e.g. eNOS and nNOS and an iNOS isotype. In TLR4 mutants, LPS caused none or a lowered iNOS induction, but altered the expression rate of the constitutive NOS isoforms. It is concluded that the intrarenal spatial relation of individual NOS-isoforms and their alteration in expression provide the basis for versatile NO-mediated renal actions that may include local interactions between NOS isoforms and their individual NO-target sites, and that the NOS-isoform dependent events are regulated by TLR4 during endotoxic processes. These regulatory mechanisms are likely to participate in different pathophysiological conditions affecting NO-mediated renal functions.

Spontaneous mutations in recombinant inbred mice: mutant toll-like receptor 4 (Tlr4) in BXD29 mice

Recombinant inbred (RI) mice are frequently used to identify QTL that underlie differences in measurable phenotypes between two inbred strains of mice. Here we show that one RI strain, C57BL/6J x DBA/2J (BXD29), does not develop an inflammatory response following inhalation of LPS. Approximately 25% of F2 mice [F1(BXD29 x DBA/2J) x F1] are also unresponsive to inhaled LPS, suggesting the presence of a recessive mutation in the BXD29 strain. A genomic scan of these F2 mice revealed that unresponsive animals, but not responsive animals, are homozygous for C57BL/6J DNA at a single locus on chromosome 4 close to the genomic location of Tlr4. All progeny between BXD29 and gene-targeted Tlr4-deficient mice are unresponsive to inhaled LPS, suggesting that the mutation in the BXD29 strain is allelic with Tlr4. Moreover, the intact Tlr4 receptor is not displayed on the cell surface of BXD29 macrophages. Finally, a molecular analysis of the Tlr4 gene in BXD29 mice revealed that it is interrupted by a large insertion of repetitive DNA. These findings explain the unresponsiveness of BXD29 mice to LPS and suggest that data from BXD29 mice should not be included when using BXD mice to study phenotypes affected by Tlr4 function. Our results also suggest that the frequency of such unidentified, spontaneously occurring mutations is an issue that should be considered when RI strains are used to identify QTL.

TLR-4 pathway mediates the inflammatory response but not bacterial elimination in E. coli pneumonia

We examined the role of Toll-like receptor (TLR)-4 in modifying the lung inflammatory response and its effects on the bacterial recovery from the lungs following inhaled Escherichia coli in two different strains of TLR-4 mutant mice that are hyporesponsive to LPS. The C57BL/10ScN(tlr4(lps-del)) mice containing a deletion mutation in the TLR-4 gene showed lower proinflammatory cytokine levels, lower lung MPO activity, and less parenchymal and peribronchial inflammation compared with the C57BL/10ScSn mice, a related TLR-4 wild-type substrain. However, the C57BL/10ScN(tlr4(lps-del)) mutant showed lower bacterial recovery in the lungs following inhaled E. coli associated with a rapid but transient increase in air space neutrophil counts at 6 h. In comparison, the C3H/HeJ(tlr4(Lps-d)) mutant mice containing a Pro712His substitution in TLR-4 demonstrated lower proinflammatory cytokine levels, lower lung MPO activity, and lower neutrophil accumulation in the air spaces but showed no differences in the bacterial burden of inhaled E. coli at 6 h, when compared with the TLR-4 wild-type C3H/HeSnJ mice. Thus two different TLR-4 mutants showed attenuated inflammatory responses in the lungs, but the reduced inflammatory responses were not consistently associated with either improved or impaired bacterial elimination from the lungs. Our findings indicate that the inflammatory response to inhaled E. coli is TLR-4 dependent, but bacterial elimination depends on other factors in addition to TLR-4.

Sequential recruitment of neutrophils into lung and bronchoalveolar lavage fluid in LPS-induced acute lung injury

Infiltration of activated neutrophils [polymorphonuclear leukocytes (PMN)] into the lung is an important component of the inflammatory response in acute lung injury. The signals required to direct PMN into the different compartments of the lung have not been fully elucidated. In a murine model of LPS-induced lung injury, we investigated the sequential recruitment of PMN into the pulmonary vasculature, lung interstitium, and alveolar space. Mice were exposed to aerosolized LPS and bronchoalveolar lavage fluid (BAL), and lungs were harvested at different time points. We developed a flow cytometry-based technique to assess in vivo trafficking of PMN in the intravascular and extravascular lung compartments. Aerosolized LPS induced consistent PMN migration into all lung compartments. We found that sequestration in the pulmonary vasculature occurred within the first hour. Transendothelial migration into the interstitial space started 1 h after LPS exposure and increased continuously until a plateau was reached between 12 and 24 h. Transepithelial migration into the alveolar air space was delayed, as the first PMN did not appear until 2 h after LPS, reaching a peak at 24 h. Transendothelial migration and transepithelial migration were inhibited by pertussis toxin, indicating involvement of Galphai-coupled receptors. These findings confirm LPS-induced migration of PMN into the lung. For the first time, distinct transmigration steps into the different lung compartments are characterized in vivo.

Expression of toll-like receptor 2 and 4 in lipopolysaccharide-induced lung injury in mouse

Pattern recognition receptors, which include the toll-like receptors (TLRs), are considered to play an important role in the response against lipopolysaccharide (LPS). In this study, we performed a reverse transcriptase/polymerase chain reaction (RT-PCR) study, Western analysis, immunohistochemical staining, and RT-PCR-amplified in situ hybridization of TLR2 and TLR4 in the case of LPS-induced lung injury. The expression of TLR2 and TLR4 increased in the lung rapidly after LPS inhalation and peaked at 24 h, followed by a gradual decrease. TLR2 and TLR4 expression was observed on the bronchial epithelium and tissue macrophages. In the early hours after inhalation of fluorescein-isothiocyanate (FITC)-labeled LPS, LPS was detected mainly on the bronchial epithelium and on a few of tissue macrophages. One day after inhalation, the LPS signals disappeared in the lungs of the mice, except for a few alveolar macrophages. The expression of TLR2, TLR4, and CD14 was coincident with the signals of FITC-labeled LPS. Instillation of liposome-encapsulated dichloromethylene diphosphonate induced a significant decrease in alveolar macrophages. In the macrophage-depleted mice, however, expression of TLR2 and TLR4 mRNA or protein was slightly suppressed in the lung after LPS inhalation. These data suggest that the bronchial epithelium and macrophages play crucial roles in LPS-induced lung injury through TLR2 and TLR4.

Differential involvement of toll-like receptors 2 and 4 in the host response to acute respiratory infections with wild-type and mutant Haemophilus influenzae strains

We used a mouse model of acute respiratory infections to investigate the role of Toll-like receptor 2 (TLR2) and TLR4 in the host response to Haemophilus influenzae. Acute aerosol exposures to wild-type strains of H. influenzae showed that TLR4 function was essential for TNF-alpha induction, neutrophil influx, and bacterial clearance. To determine how lipooligosaccharide (LOS) modifications would affect the role of TLR4 in inducing the host response, we used acute infections with an H. influenzae strain expressing a mutation in the htrB gene. This mutant strain expresses an LOS subunit with decreased acylation. In response to H. influenzae htrB infection, tumor necrosis factor alpha (TNF-alpha) secretion remained TLR4 dependent. But the decrease in LOS acylation made the neutrophil influx and the bacterial clearance also dependent on TLR2, as shown by the decreased host response elicited in TLR2 knockout mice compared to C57BL/6 mice. A subsequent analysis of TLR2 and TLR4 gene expression by quantitative PCR indicated that TLR4 function induces TLR2 expression and vice versa. These results indicate that some changes in the LOS subunit of H. influenzae can favor signaling through non-TLR4 receptors, such as TLR2. The results also indicate a close interaction between TLR4 and TLR2 that tightly regulates the expression of both receptors.

Distinct roles of pattern recognition receptors CD14 and Toll-like receptor 4 in acute lung injury

Acute lung injury (ALI) induced by lipopolysaccharide (LPS) is a major cause of mortality among humans. ALI is characterized by microvascular protein leakage, neutrophil influx, and expression of proinflammatory mediators, followed by severe lung damage. LPS binding to its receptors is the crucial step in the causation of these multistep events. LPS binding and signaling involves CD14 and Toll-like receptor 4 (TLR4). However, the relative contributions of CD14 and TLR4 in the induction of ALI and their therapeutic potentials are not clear in vivo. Therefore, the aim of the present study was to compare the roles of CD14 and TLR4 in LPS-induced ALI to determine which of these molecules is the more critical target for attenuating ALI in a mouse model. Our results show that CD14 and TLR4 are necessary for low-dose (300-microg/ml) LPS-induced microvascular leakage, NF-kappaB activation, neutrophil influx, cytokine and chemokine (KC, macrophage inflammatory protein 2, tumor necrosis factor alpha, interleukin-6) expression, and subsequent lung damage. On the other hand, when a 10-fold-higher dose of LPS (3 mg/ml) was used, these responses were only partially dependent on CD14 and they were totally dependent on TLR4. The CD14-independent LPS response was dependent on CD11b. A TLR4 blocking antibody abolished microvascular leakage, neutrophil accumulation, cytokine responses, and lung pathology with a low dose of LPS but only attenuated the responses with a high dose of LPS. These data are the first to demonstrate that LPS-induced CD14-dependent and -independent (CD11b-dependent) signaling pathways in the lung are entirely dependent on TLR4 and that blocking TLR4 might be beneficial in lung diseases caused by LPS from gram-negative pathogens.

Genetic regulation of endotoxin-induced airway disease

To identify novel genes regulating the biologic response to lipopolysaccharide (LPS), we used a combination of quantitative trait locus (QTL) analysis and microarray-based gene expression studies of C57BL/6J x DBA/2J(BXD) F2 and recombinant inbred (RI) mice. A QTL affecting pulmonary TNF-alpha production was identified on chromosome 2, and a region affecting both polymorphonuclear leukocyte recruitment and TNF-alpha levels was identified on chromosome 11. Microarray analyses of unchallenged and LPS-challenged BXD RI strains identified approximately 500 genes whose expression was significantly changed by inhalation of LPS. Of these genes, 28 reside within the chromosomal regions identified by the QTL analyses, implicating these genes as high priority candidates for functional studies. Additional high priority candidate genes were identified based on their differential expression in mice having high and low responses to LPS. Functional studies of these genes are expected to reveal important molecular mechanisms regulating the magnitude of biologic responses to LPS.

Toll-like receptor 2 represses nonpilus adhesin-induced signaling in acute infections with the Pseudomonas aeruginosa pilA mutant

Expression of pili and associated proteins is an important means of host invasion by bacterial pathogens. Recent evidence has suggested that the binding of Pseudomonas aeruginosa through nonpilus adhesins may also be important in respiratory diseases, since adhesins bind mucins. Using wild-type C57BL/6 and TLR2KO mice, we compared the induction levels of the host response to P. aeruginosa that either expressed pili or lacked pilus expression due to a mutation in the structural gene pilA. In C57BL/6 mice, deletion of pili led to a decreased immune response, evidenced by a lower secretion of cytokines and a lack of neutrophil chemotaxis. By contrast, the P. aeruginosa pilA mutant induced a hyperresponsive phenotype in TLR2KO mice. TLR2KO mice showed an increased number of neutrophils in lavage fluid compared to the levels seen when either mouse strain was exposed to wild-type P. aeruginosa. Further analysis indicated that the increased neutrophil influx was associated with an increased expression of calgranulins, possibly through an induction of Toll-like receptor 4 (TLR4) expression. The hyperresponsive phenotype of TLR2KO mice exposed to the P. aeruginosa pilA mutant was associated with TLR4 induction and indicated that nonpilus adhesin-induced signaling was repressed by TLR2 function and, if not blocked by the host, could induce airway hyperresponsiveness.

Toll-like receptors and the genetics of innate immunity

PURPOSE OF REVIEW

The discovery that mammalian Toll-like receptors recognize microbial products and initiate innate immune responses to them has spawned a new field of biology, namely the study of molecular interactions linking microbial recognition to innate and adaptive immune responses. This field has grown very rapidly in recent years, due largely to recent advances in genetic technology. This review summarizes recent work in which genetic approaches have been used to identify novel and important facets of Toll-like receptor function.

RECENT FINDINGS

Recent genetic studies have uncovered a wealth of information relating to ligand-receptor interactions, Toll-like receptor gene regulation, signal transduction, dendritic cell activation and allele-phenotype associations.

SUMMARY

Information emerging from genetic studies of Toll-like receptors has improved our understanding of innate and acquired immunity. This improved understanding promises to facilitate the future development of novel therapies for many different inflammatory diseases including asthma, sepsis and atherosclerosis.

Toll-like receptors: function and roles in lung disease

Toll-like receptor (TLR) proteins have been shown to play a pivotal role in both innate and adaptive immune responses in higher vertebrates. TLR proteins enable the host to recognize a large number of pathogen-associated molecular patterns such as bacterial lipopolysaccharides, viral RNA, CpG-containing DNA, and flagellin, among others. Engagement of TLR proteins leads to the upregulation of costimulatory molecules and proinflammatory cytokines, as well as reactive nitrogen and oxygen products. The role of TLR proteins in lung-associated pathologies such as airway hyperreactivity, allergic asthma, and tuberculosis is being intensively studied. This review summarizes many of the findings made to date on the roles of TLR proteins in a variety of lung diseases. Generally, TLR proteins serve a protective role in infectious diseases, such as tuberculosis. The progression of chronic inflammatory lung diseases, such as allergic asthma, can also be influenced by TLR-dependent responses.

Respiratory epithelial cells regulate lung inflammation in response to inhaled endotoxin

To determine the role of respiratory epithelial cells in the inflammatory response to inhaled endotoxin, we selectively inhibited NF-kappa B activation in the respiratory epithelium using a mutant I kappa B-alpha construct that functioned as a dominant negative inhibitor of NF-kappa B translocation (dnI kappa B-alpha). We developed two lines of transgenic mice in which expression of dnI kappa B-alpha was targeted to the distal airway epithelium using the human surfactant apoprotein C promoter. Transgene expression was localized to the epithelium of the terminal bronchioles and alveoli. After inhalation of LPS, nuclear translocation of NF-kappa B was evident in bronchiolar epithelium of nontransgenic but not of transgenic mice. This defect was associated with impaired neutrophilic lung inflammation 4 h after LPS challenge and diminished levels of TNF-alpha, IL-1 beta, macrophage inflammatory protein-2, and KC in lung homogenates. Expression of TNF-alpha within bronchiolar epithelial cells and of VCAM-1 within peribronchiolar endothelial cells was reduced in transgenic animals. Thus targeted inhibition of NF-kappa B activation in distal airway epithelial cells impaired the inflammatory response to inhaled LPS. These data provide causal evidence that distal airway epithelial cells and the signals they transduce play a physiological role in lung inflammation in vivo.

Dynamic mechanical consequences of deep inflation in mice depend on type and degree of lung injury

In a previous study (Allen G, Lundblad LK, Parsons P, and Bates JH. J Appl Physiol 93: 1709-1715, 2002), our laboratory used deep inflations (DI) in mice to show that recruitment of closed lung units can be a very transient phenomenon in lung injury. The purpose of this study was to investigate how this transience of lung recruitment depends on the nature and degree of acute lung injury. Mice were administered 50 microl of either saline (n = 8), 0.01 M (n = 9) or 0.025 M (n = 8) hydrochloric acid, or 50 microg (n = 10) or 150 microg (n = 6) of LPS and were mechanically ventilated 24-48 h later. At various levels of positive end-expiratory pressure, two DIs were delivered, and forced oscillations were used to obtain a measure of lung stiffness (H) periodically over 7 min. After LPS exposure, pressure-volume curve hysteresis and recovery in H after DI were no different from saline-exposed controls despite 500 times more neutrophils in bronchoalveolar lavage fluid. Pressure-volume hysteresis and recovery in H were increased in acid-exposed mice (P < 0.001) and were correlated with bronchoalveolar lavage fluid protein content (R = 0.81). Positive end-expiratory pressure reduced recovery in H in all groups (P < 0.01) but reduced pressure-volume hysteresis in the acid-injured groups only (P < 0.001). We conclude that the effects of DIs in acute lung injury depend on the degree of lung injury but only to the extent that this injury reflects a disruption of the air-liquid interface.

Systemic responsiveness to lipopolysaccharide and polymorphisms in the toll-like receptor 4 gene in human beings

BACKGROUND

The response to lipopolysaccharide exposure is highly variable and might be a result of genetic diversity between individuals. The toll-like receptor 4 (TLR-4) is the principal receptor for lipopolysacharide.

OBJECTIVES

We investigated the association between single-nucleotide polymorphisms in the TLR4 locus and levels of systemic inflammatory markers in response to lipopolysaccharide.

METHODS

Healthy subjects (n = 116) were genotyped for the most frequent polymorphisms found in the promoter and coding region of the TLR4 gene (-2026A/T, -1607T/C, +896A/G, and +1196C/T relative to the translation start site). Subjects were challenged with 20 microg lipopolysaccharide by inhalation.

RESULTS

Polymorphisms at +896 and +1196 were in complete linkage disequilibrium, and no homozygotes for the less common allele, G and T respectively, were found. After lipopolysaccharide inhalation, subjects heterozygous for either TLR-4/+896 or TLR4/+1196 had significantly lower numbers of white blood cell counts and lower levels of C-reactive protein and lipopolysaccharide-binding protein compared with homozygotes with the common allele. None of the heterozygous subjects (n = 18) except 1 were high responders to lipopolysaccharide (defined as a rise in C-reactive protein > 10 mg/L), whereas 36 of 98 homozygous subjects were high responders (P <.02). No association was observed between the TLR-4/-2026 and TLR-4/-1607 polymorphisms and lipopolysaccharide responsiveness.

CONCLUSION

The single-nucleotide polymorphisms at position +896 or +1196 in the TLR-4 gene is associated with systemic inflammatory hyporesponsiveness to inhaled lipopolysaccharide.

Subchronic endotoxin inhalation causes persistent airway disease

The endotoxin component of organic dusts causes acute reversible airflow obstruction and airway inflammation. To test the hypothesis that endotoxin alone causes airway remodeling, we have compared the response of two inbred mouse strains to subchronic endotoxin exposure. Physiological and biological parameters were evaluated after 1 day, 5 days, or 8 wk of exposure to endotoxin [lipopolysaccharide (LPS)] in endotoxin-sensitive (C3HeB/FeJ) and endotoxin-resistant (C3H/HeJ) mice. After 5 days or 8 wk of LPS exposure, only C3HeB/FeJ had elevated airway hyperreactivity to inhaled methacholine. Only the C3HeB/FeJ mice had significant inflammation of the lower respiratory tract after 1 day, 5 days, or 8 wk of LPS exposure. Stereological measurements of small, medium, and large airways indicated that an 8-wk exposure to LPS resulted in expansion of the submucosal area only in the C3HeB/FeJ mice. Cell proliferation as measured by bromodeoxyuridine incorporation contributed to the expansion of the submucosa and was only significantly elevated in C3HeB/FeJ mice actively exposed to LPS. C3HeB/FeJ mice had significantly elevated levels of interleukin-1beta protein in whole lung lavage after 1 day and 5 days of LPS exposure and significantly elevated protein levels of total and active transforming growth factor-beta1 in whole lung lavage fluid after 5 days of LPS exposure. Our findings demonstrate that subchronic inhalation of LPS results in the development of persistent airway disease in endotoxin-responsive mice.

Beta-arrestin-2 regulates the development of allergic asthma

Asthma is a chronic inflammatory disorder of the airways that is coordinated by Th2 cells in both human asthmatics and animal models of allergic asthma. Migration of Th2 cells to the lung is key to their inflammatory function and is regulated in large part by chemokine receptors, members of the seven-membrane-spanning receptor family. It has been reported recently that T cells lacking beta-arrestin-2, a G protein-coupled receptor regulatory protein, demonstrate impaired migration in vitro. Here we show that allergen-sensitized mice having a targeted deletion of the beta-arrestin-2 gene do not accumulate T lymphocytes in their airways, nor do they demonstrate other physiological and inflammatory features characteristic of asthma. In contrast, the airway inflammatory response to LPS, an event not coordinated by Th2 cells, is fully functional in mice lacking beta-arrestin-2. beta-arrestin-2-deficient mice demonstrate OVA-specific IgE responses, but have defective macrophage-derived chemokine-mediated CD4+ T cell migration to the lung. This report provides the first evidence that beta-arrestin-2 is required for the manifestation of allergic asthma. Because beta-arrestin-2 regulates the development of allergic inflammation at a proximal step in the inflammatory cascade, novel therapies focused on this protein may prove useful in the treatment of asthma.

Allergen-induced airway disease is mouse strain dependent

We investigated the development of airway hyperreactivity (AHR) and inflammation in the lungs of nine genetically diverse inbred strains of mice [129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ] after sensitization and challenge with ovalbumin (OVA). At 24, 48, and 72 h post-OVA exposure, the severity of AHR and eosinophilic inflammation of the mouse strains ranged from relatively unresponsive to responsive. The severity of the airway eosinophilia of some strains did not clearly correlate with the development of AHR. The temporal presence of T helper type 2 cytokines in lung lavage fluid also varied markedly among the strains. The levels of IL-4 and IL-13 were generally increased in the strains with the highest airway eosinophilia at 24 and 72 h postexposure, respectively; the levels of IL-5 were significantly increased in most of the strains with airway inflammation over the 72-h time period. The differences of physiological and biological responses among the inbred mouse strains after OVA sensitization and challenge support the hypothesis that genetic factors contribute, in part, to the development of allergen-induced airway disease.

Polymorphisms in toll-like receptor 4 are not associated with asthma or atopy-related phenotypes

Toll-like receptor 4 (TLR4) is the principal receptor for bacterial endotoxin recognition, and functional variants in the gene confer endotoxin-hyporesponsiveness in humans. Furthermore, there is evidence that endotoxin exposure during early life is protective against the development of atopy and asthma, although this relationship remains poorly understood. It is therefore possible that genetic variation in the TLR4 locus contributes to asthma susceptibility. In this study we characterize the genetic diversity in the TLR4 locus and test for association between the common genetic variants and asthma-related phenotypes. In a cohort of 90 ethnically diverse subjects, we resequenced the TLR4 locus and identified a total of 29 single nucleotide polymorphisms. We assessed five common polymorphisms for evidence of association with asthma in two large family-based cohorts: a heterogeneous North American cohort (589 families), and a more homogenous population from northeastern Quebec, Canada (167 families). Using the transmission-disequilibrium test, we found no evidence of association for any of the polymorphisms tested, including two functional variants. Furthermore, we found no evidence for association between the TLR4 variants and four quantitative intermediate asthma- and atopy-related phenotypes. Based on these results, we found no evidence that genetic variation in TLR4 contributes to asthma susceptibility.