Moraxella catarrhalis induces CEACAM3-Syk-CARD9-dependent activation of human granulocytes.

The human restricted pathogen Moraxella catarrhalis is an important causal agent for exacerbations in chronic obstructive lung disease in adults. In such patients, increased numbers of granulocytes are present in the airways, which correlate with bacteria-induced exacerbations and severity of the disease. Our study investigated whether the interaction of M. catarrhalis with the human granulocyte-specific carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-3 is linked to NF-κB activation, resulting in chemokine production. Granulocytes from healthy donors and NB4 cells were infected with M. catarrhalis in the presence of different inhibitors, blocking antibodies and siRNA. The supernatants were analysed by enzyme-linked immunosorbent assay for chemokines. NF-κB activation was determined using a luciferase reporter gene assay and chromatin-immunoprecipitation. We found evidence that the specific engagement of CEACAM3 by M. catarrhalis ubiquitous surface protein A1 (UspA1) results in the activation of pro-inflammatory events, such as degranulation of neutrophils, ROS production and chemokine secretion. The interaction of UspA1 with CEACAM3 induced the activation of the NF-κB pathway via Syk and the CARD9 pathway and was dependent on the phosphorylation of the CEACAM3 ITAM-like motif. These findings suggest that the CEACAM3 signalling in neutrophils is able to specifically modulate airway inflammation caused by infection with M. catarrhalis.

A micro RNA-146a polymorphism is associated with coronary restenosis.

The association of the miRNA-146a polymorphism rs2910164 with atherosclerosis and restenosis was investigated. We found no association with atherosclerosis; however, we found a negative association for the G/C (P = 0.007) and a positive association for the C/C genotype with the risk of restenosis, which is the main drawback for cardiac surgery.

Association of vitamin D receptor gene polymorphisms with severe atopic dermatitis in adults.

BACKGROUND: Vitamin D mediates immunomodulatory functions, and beneficial functions in allergic diseases have been suggested. Vitamin D receptor gene (VDR) polymorphisms are known but have not been studied in patients with atopic dermatitis (AD). OBJECTIVES: To investigate the frequency of four common VDR gene polymorphisms in patients with AD, and their potential functional relevance. METHODS: In this case-control study, 265 patients with AD [n=142 severe AD, Scoring AD index (SCORAD) > 40; n=123 moderate AD, SCORAD 15-40] and 265 healthy controls were genotyped for four common VDR gene polymorphisms by restriction fragment length polymorphism analysis. The VDR haplotype sequences were analysed in silico. Baseline and activation-induced gene expression of VDR and the vitamin D metabolizing enzyme CYP24A1 were analysed in monocytes of homozygous VDR haplotype carriers by quantitative reverse transcription-polymerase chain reaction. RESULTS: In patients with severe AD, the VDR BsmI (rs1544410) G allele, ApaI (rs7975232) C allele and TaqI (rs731236) T alleles were over-represented compared with healthy controls. These single nucleotide polymorphisms (SNP) were tightly linked, and the VDR haplotype GCT was correlated with severe AD and complementary AAC with protection from AD. The VDR haplotype GCT region is evolutionarily conserved. The VDR FokI (rs2228570) SNP was not associated with AD. Baseline VDR expression in monocytes and short-term activation were haplotype independent. CONCLUSION: A specific VDR haplotype is more frequent in patients with severe AD. These data indicate that VDR contributes to the control of AD, e.g. by regulation of the epidermal barrier function and/or local immune response.

Targeted deletion of the lipopolysaccharide (LPS)-binding protein gene leads to profound suppression of LPS responses ex vivo, whereas in vivo responses remain intact.

Gram-negative bacterial lipopolysaccharide (LPS) stimulates phagocytic leukocytes by interacting with the cell surface protein CD14. Cellular responses to LPS are markedly potentiated by the LPS-binding protein (LBP), a lipid-transfer protein that binds LPS aggregates and transfers LPS monomers to CD14. LBP also transfers LPS to lipoproteins, thereby promoting the neutralization of LPS. LBP present in normal plasma has been shown to enhance the LPS responsiveness of cells in vitro. The role of LBP in promoting LPS responsiveness in vivo was tested in LBP-deficient mice produced by gene targeting in embryonic stem cells. Whole blood from LBP-deficient animals was 1,000-fold less responsive to LPS as assessed by the release of tumor necrosis factor (TNF)-alpha. Blood from gene-targeted mice was devoid of immunoreactive LBP, essentially incapable of transferring LPS to CD14 in vitro, and failed to support cellular responses to LPS. These activities were restored by the addition of exogenous recombinant murine LBP to the plasma. Despite these striking in vitro findings, no significant differences in TNF-alpha levels were observed in plasma from wild-type and LBP-deficient mice injected with LPS. These data suggest the presence of an LBP-independent mechanism for responding to LPS. These LBP knockout mice may provide a tool for discovering the nature of the presumed second mechanism for transferring LPS to responsive cells.

Association of the toll-like receptor 2 A-16934T promoter polymorphism with severe atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease with a multifactorial pathogenesis and increasing incidence in the Western world. A genetically determined defective function of pattern recognition receptors such as toll-like receptors (TLRs) has been proposed as a candidate mechanism in the pathogenesis of AD. AIM: To study the impact of genetic predisposition of five genes encoding for pattern recognition-related molecules for the phenotype of AD. METHODS: We examined nine different single-nucleotide polymorphism (SNP) frequencies in the genes encoding TLR1, -2, -4, -9 and the adapter molecule TIRAP by PCR with subsequent melting curve analysis in a case/control cohort of 136 adult AD patients and 129 age and gender matched non-atopic, healthy individuals. TLR2-expression and -function in cells from genotyped individuals were analysed. RESULTS: For the SNPs examined, similar genotype frequencies were found in both groups. In a subgroup of patients suffering from severe AD (SCORAD >50), a significantly increased representation of the A-allele in position -16934 of the tlr2 gene was present (P = 0.004). Constitutive tlr2 mRNA expression in peripheral monocytes was independent of this tlr2 promoter SNP. Stimulation assays indicated that IL-6, but not TNF-alpha secretion following TLR2 stimulation is reduced in homozygous tlr2-16934-A allele carriers. CONCLUSION: These data indicate that TLR2 is relevant for the phenotype of severe AD in adults.

Structure and function of lipopolysaccharide binding protein.

The primary structure of lipopolysaccharide binding protein (LBP), a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides (LPSs), was deduced by sequencing cloned complementary DNA. LBP shares sequence identity with another LPS binding protein found in granulocytes, bactericidal/permeability-increasing protein, and with cholesterol ester transport protein of the plasma. LBP may control the response to LPS under physiologic conditions by forming high-affinity complexes with LPS that bind to monocytes and macrophages, which then secrete tumor necrosis factor. The identification of this pathway for LPS-induced monocyte stimulation may aid in the development of treatments for diseases in which Gram-negative sepsis or endotoxemia are involved.

LPS-binding protein protects mice from septic shock caused by LPS or gram-negative bacteria.

LPS-binding protein (LBP) recognizes bacterial LPS and transfers it to CD14, thereby enhancing host cell stimulation, eventually resulting in pathogenic states such as septic shock. Recently, LBP also was shown to detoxify LPS by transferring LPS into HDL particles in vitro. Thus, the predominant in vivo function of LBP has remained unclear. To investigate the biological activity of acute phase concentrations of recombinant murine LBP, high concentrations of LBP were investigated in vitro and in vivo. Although addition of low concentrations of LBP to a murine macrophage cell line enhanced LPS-induced TNF-alpha synthesis, acute phase concentrations of LBP blocked this effect in comparison to low-dose LBP. When injected into mice intraperitoneally, LBP inhibited LPS-mediated cytokine release and prevented hepatic failure resulting in a significantly decreased mortality rate in LPS-challenged and D-galactosamine-sensitized mice, as well as in a murine model of bacteremia. These results complement a recent study revealing LBP-deficient mice to be dramatically more susceptible to an intraperitoneal Salmonella infection as compared with normal mice. We conclude that acute phase LBP has a protective effect against LPS and bacterial infection and may represent a physiologic defense mechanism against infection. Despite the limitations of any murine sepsis model, the results shown may imply that LBP could have beneficial effects during gram-negative peritonitis in humans.

The lipopolysaccharide-binding protein is a secretory class 1 acute-phase protein whose gene is transcriptionally activated by APRF/STAT/3 and other cytokine-inducible nuclear proteins.

Acute-phase reactants (APRs) are proteins synthesized in the liver following induction by interleukin-1 (IL-1), IL-6, and glucocorticoids, involving transcriptional gene activation. Lipopolysaccharide-binding protein (LBP) is a recently identified hepatic secretory protein potentially involved in the pathogenesis of sepsis, capable of binding the bacterial cell wall product endotoxin and directing it to its cellular receptor, CD14. In order to examine the transcriptional induction mechanisms by which the LBP gene is activated, we have investigated the regulation of expression of its mRNA in vitro and in vivo as well as the organization of 5' upstream regulatory DNA sequences. We show that induction of LBP expression is transcriptionally regulated and is dependent on stimulation with IL-1beta, IL-6, and dexamethasone. By definition, LBP thus has to be viewed as a class 1 acute-phase protein and represents the first APR identified which is capable of detecting pathogenic bacteria. Furthermore, cloning of the LBP promoter revealed the presence of regulatory elements, including the common APR promoter motif APRE/STAT-3 (acute-phase response element/signal transducer and activator of transcription 3). Luciferase reporter gene assays utilizing LBP promoter truncation and point mutation variants indicated that transcriptional activation of the LBP gene required a functional APRE/STAT-3 binding site downstream of the transcription start site, as well as an AP-1 and a C/EBP (CCAAT enhancer-binding protein) binding site. Gel retardation and supershift assays confirmed that upon cytokine stimulation APRF/STAT-3 binds to its recognition site, leading to strong activation of the LBP gene. Unraveling of the mechanism of transcriptional activation of the LBP gene, involving three known transcription factors, may contribute to our understanding of the acute-phase response and the pathophysiology of sepsis and septic shock.

Toll-like receptor (TLR) polymorphisms in African children: common TLR-4 variants predispose to severe malaria.

Genetic host factors play a substantial role in susceptibility to and severity of malaria, which continues to cause at least one million deaths per year. Recently, members of the toll-like receptor (TLR) family have been shown to be involved in recognition of the etiologic organism Plasmodium falciparum: The glycosylphosphatidylinisitol anchor induces signaling in host cells via TLR-2 and -4, while hemozoin-induced immune activation involves TLR-9. Binding of microbial ligands to the respective TLRs triggers the release of pro-inflammatory cytokines via the TLR/IL-1 receptor (TIR) domain and may contribute to the host response, including pro-inflammatory cytokine induction and malarial fever. In a case-control study among 870 Ghanaian children, we examined the influence of TLR-2, -4, and -9 polymorphisms in susceptibility to severe malaria. TLR-2 variants common in Caucasians and Asians were completely absent. However, we found a new, rare mutation (Leu658Pro), which impairs signaling via TLR-2. We failed to detect any polymorphisms within the TLR-9/interleukin-1 receptor domain. Two frequent TLR-9 promoter polymorphisms did not show a clear association with malaria severity. In contrast, the TLR-4-Asp299Gly variant occurred at a high rate of 17.6% in healthy controls, and was even more frequent in severe malaria patients (24.1%, p<0.05). Likewise, TLR-4-Thr399Ile was seen in 2.4% of healthy children and in 6.2% of patients (p=0.02). TLR-4-Asp299Gly and TLR-4-Thr399Ile conferred an 1.5- and 2.6-fold increased risk of severe malaria, respectively. These findings suggest TLR4-mediated responses to malaria in vivo and TLR-4 polymorphisms to be associated with disease manifestation. However some gray areas also suggest the scope for further improvements.

TLR2: cellular sensor for microbial and endogenous molecular patterns.

Toll-like receptor (TLR) 2 is a member of the vertebrate protein family of TLRs that has been studied in substantial detail over the last years. The extracellular domain of the type I receptor molecule TLR2 contains 18 to 20 leucine rich repeat (LRR) and LRR like motives. The intracellular domain of TLR2 contains a Toll/IL-1 receptor/resistance protein typical TIR domain. After the first implication of TLR4 in immunity thereinafter followed by the discovery of the lipopolysaccharide signal transducer function of TLR4, TLR2 was the first of ten mammalian TLRs proven to be directly involved in recognition of pathogen associated molecular patterns (PAMPs). Among the TLR2 specific agonists are microbial products representing broad groups of species such as Gram-positive and Gram-negative bacteria, as well as mycobacteria, spirochetes, and mycoplasm. PAMP induced phagosomal localization of TLR2 and TLR2 dependent apoptosis have been shown. Complex formation with other molecules involved in pattern recognition such as CD14, MD2, TLR1, and TLR6 has been implicated for TLR2. Surprisingly even proteinaceous host material such as heat shock protein (HSP) 60 has been demonstrated to activate cells through TLR2. Thus, TLR2 may be a sensor and inductor of specific defense processes, including oxidative stress and cellular necrosis initially spurred by microbial compounds. Here we summarize the current knowledge on the structure and function of TLR2, which is far from being complete. Detailed understanding of the biology of TLR2 will probably contribute to the characterization of a number of infectious diseases and potentially help in the development of novel intervention strategies.

Detection of two variants of complement component C3 in C3-deficient guinea pigs distinguished by the absence and presence of a thiolester.

The complement system is an essential part of the innate defense, and C3 is an integral part of this powerful system. In previously identified complement C3 deficient guinea pigs only approx. 5% of the normal serum C3 level is detectable. No differences were found between in vitro C3 protein synthesis and C3 mRNA levels of cells from C3-deficient and wild-type animals and the amino acid sequences of both C3 proteins are identical as deduced from cDNA sequencing. Previously, the principal inability to form a C3 thiolester was discussed as a possible reason for this C3-deficiency. Here we report the isolation of two functionally different C3 species from the C3-deficient animals. Only one of these C3 proteins exhibits normal hemolytic activity and contains a thiolester group. The second C3 species is exclusively present in C3-deficient animals and lacks a thiolester, explaining its failure to express hemolytic activity. The presence of a second C3 species lacking a thiolester structure only in C3-deficient animals indicates that the stability of the thiolester may play a role in C3 deficiency. However further analysis of the in vitro stability of the thiolesters of C3 from normal and C3-deficient guinea pigs revealed no differences. A decreased in vivo thiolester stability might lead to the presence of C3 with and without a thiolester or alternatively the expression of two isoforms of C3 in these animals. Considering the central role of C3 in host defense, the mechanisms of C3 thiolester formation require further analysis.

Microglial activation by components of gram-positive and -negative bacteria: distinct and common routes to the induction of ion channels and cytokines.

Gram-positive Streptococcus pneumoniae is the major pathogen causing lethal meningitis in adults. We used pneumococcal cell walls (PCW) to investigate microglial consequences of a bacterial challenge and to determine the role of serum in the activation process. PCW caused the characteristic induction of an outwardly rectifying K+ channel (IK+(OR)), together with a concomitant suppression of the constitutively expressed inward rectifier K+ current, and evoked the release of tumor necrosis factor-alpha (TNF alpha), interleukin-6 (IL-6), IL-12, KC, macrophage inflammatory protein (MIP) 1alpha and MIP-2. Serum presence strongly facilitated the PCW effects, similarly as observed for lipopolysaccharide (LPS) from gram-negative Escherichia coli. The inflammatory cytokine, interferon-gamma (IFNgamma) induced the same electrophysiological changes, but independent of serum. Recombinant LPS binding protein (LBP) could partially replace serum activity in LPS stimulations. In contrast, neither LBP nor an antibody-mediated blockade of the LPS receptor, CD14 had significant influences on PCW-inducible changes. Cell surface interactions and cofactor involvement in microglial activation by gram-positive bacteria are thus distinct from the mechanisms employed by LPS. Moreover, tyrphostin AG126, a protein kinase inhibitor that prevents activation of the mitogen-activated protein kinase, p42MAPK (ERK2), potently blocked the PCW-stimulated cytokine release while having only a limited effect on LPS-inducible cytokines. In contrast, AG126 did not influence IK+(OR) inductions. This indicates that PCW recruits more than 1 intracellular signaling pathway to trigger the various responses and that different bacterial agents signal through both common and individual routes during microglial activation.

Induced hypothermia in experimental pneumococcal meningitis.

Pneumococcal meningitis resulting from Streptococcus pneumoniae has a death rate of 28% in adults. In severe head injury and stroke, inflammatory changes and intracranial hypertension are improved by induced hypothermia, which also is neuroprotective. We hypothesized that moderate hypothermia ameliorates inflammatory changes in experimental pneumococcal meningitis. Wistar rats were cooled systemically, and meningitis was induced by pneumococcal cell wall components. The increase of regional cerebral blood flow in the meningitis animals was blocked by hypothermia at 6 hours. The reduction of intracranial pressure correlated with temperature. The influx of leukocytes into the cerebrospinal fluid and levels of tumor necrosis factor alpha in the cerebrospinal fluid were decreased. Cooling the animals 2 hours after meningitis induction to 30.5 degrees C was also protective. We conclude that hypothermia is a new adjuvant approach to reduce meningitis-induced changes, in particular intracranial pressure, in the early phase of the disease.

Tumour necrosis factor alpha induces only minor inflammatory changes in the central nervous system, but augments experimental meningitis.

Although tumour necrosis factor alpha is said to play a key role in bacterial meningitis and other CNS diseases, the effects of this pro-inflammatory cytokine have only been studied in part and are incompletely understood. In a rat model, we investigated the effect of intracisternal injection of recombinant rat-specific tumour necrosis factor alpha (5, 35, 70 and 280 microg tumour necrosis factor alpha) (i) alone, (ii) combined with pneumococcal cell wall components, on regional cerebral blood flow, intracranial pressure, white blood cell count in the cerebrospinal fluid, and brain water content. Tumour necrosis factor a dose-dependently caused an increase in regional cerebral blood flow (up to 221 +/- 43% of baseline values) over the six hour observation period and mild cerebrospinal fluid leukocytosis; intracranial pressure and brain water content were unchanged. Hypothesizing that regional cerebral blood flow changes are dependent on nitric oxide, tumour necrosis factor alpha-induced regional cerebral blood flow increase was abolished by Aminoguanidine, a selective inhibitor of inducible nitric oxide synthase. Combination of the lowest tumour necrosis factor alpha dose and a low dose pneumococcal cell wall preparation magnified the inflammatory effect of both. We conclude that intrathecally injected tumour necrosis factor alpha alone results in only minor inflammatory changes, whereas it dramatically augments experimental meningitis.

The transcriptional activation pattern of lipopolysaccharide binding protein (LBP) involving transcription factors AP-1 and C/EBP beta.

Lipopolysaccharide (LPS) Binding Protein (LBP) is an acute phase protein with the ability to recognize bacterial LPS and transport it to the CD14 molecule or into HDL particles. It is synthesized in hepatocytes and secreted into the blood stream. LBP levels significantly rise during the acute phase response and levels of LBP may be important for an appropriate host reaction to bacterial challenge and for developing the sepsis syndrome. In order to elucidate the mechanisms of LBP regulation we investigated its transcription pattern and performed promoter studies under experimental conditions mimicking an acute phase scenario. In human hepatoma cell lines stimulation with IL-1 beta, IL-6, TNF-alpha and dexamethasone leads to strong transcriptional activation of the LBP gene in a dose- and time-dependent manner. IL-6 alone induces LBP significantly, whereas IL-1 beta mainly increases the IL-6 effect when applied in combination. Our results furthermore show that AP-1 and C/EBP beta are transcription factors involved in the activation of the LBP gene, as revealed by Luciferase reporter gene analysis and electromobility shift assays. Elucidating the mechanism of transcriptional activation of LBP potentially may help in understanding host-pathogen response patterns and mechanisms involved in the acute phase reaction and in the pathophysiology of sepsis.

Lipopolysaccharide binding protein: a marker for intraperitoneal bacterial infection in patients with CAPD peritonitis.

During systemic infection, the serum lipopolysaccharide binding protein (LBP) binds to the lipid A component of bacterial endotoxins and facilitates its delivery to the CD 14 receptor on the cell surface of macrophages, where proinflammatory cytokines are released. There is no knowledge to date whether LBP is also present in the effluent of patients with continuous ambulatory peritoneal dialysis (CAPD)-associated peritonitis. We investigated the dialysis effluent of 37 patients with CAPD peritonitis for immunoreactive LBP, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1 beta and compared the findings with the cytokine levels in 20 noninfected CAPD patients. The mean +/- SEM concentrations of LBP, TNF-alpha, and IL-1 beta were significantly higher in the effluent of patients with peritonitis than in noninfected CAPD effluent. In comparison to controls (0.23 +/- 0.05 microgram/mL), LBP was 0.68 +/- 0.13 microgram/mL in the effluent of patients with CAPD-associated infectious peritonitis. For TNF-alpha, levels were 0.50 +/- 0.25 pg/mL in the control effluent versus 124.7 +/- 46.6 pg/mL in the effluent of peritonitis patients. For IL-1 beta the levels were 0.24 +/- 0.14 pg/mL in the control effluent and 71.23 +/- 17.53 pg/mL in the peritonitis patients. Our findings demonstrate that LBP is significantly elevated in the effluent of CAPD patients during an episode of CAPD-associated peritonitis and might be used as a marker of intraperitoneal bacterial infection.

Computer-assisted learning in human and dental medicine.

This article describes the development and application of new didactic methods for use in computer-assisted teaching and learning systems for training doctors and dentists. Taking the Meducase project as an example, didactic models and their technological implementation are explained, together with the limitations of imparting knowledge with the "new media". In addition, legal concepts for a progressive, pragmatic, and innovative distribution of knowledge to undergraduate students are presented. In conclusion, potential and visions for the wide use of electronic learning in the German and European universities in the future are discussed. Self-directed learning (SDL) is a key component in both undergraduate education and lifelong learning for medical practitioners. E-learning can already be used to promote SDL at undergraduate level. The Meducase project uses self-directed, constructive, case- and problem-oriented learning within a learning platform for medical and dental students. In the long run, e-learning programs can only be successful in education if there is consistent analysis and implementation of value-added factors and the development and use of media-didactic concepts matched to electronic learning. The use of innovative forms of licensing - open source licenses for software and similar licenses for content - facilitates continuous, free access to these programs for all students and teachers. These legal concepts offer the possibility of innovative knowledge distribution, quality assurance and standardization across specializations, university departments, and possibly even national borders.

A functional toll-like receptor 8 variant is associated with HIV disease restriction.

BACKGROUND: Toll-like receptors (TLRs) play an important role in the innate immune response to pathogens. TLR8 has been found to recognize RNA derived from various viruses, including human immunodeficiency virus (HIV). Presently, very little is known about the influence of TLR8 genetic variation on susceptibility to and progression of HIV disease. METHODS AND RESULTS: We genotyped a population of 782 HIV-positive adults and 550 healthy control subjects for 3 nonsynonymous TLR8 single-nucleotide polymorphisms. We found that the presence of the most frequent TLR8 polymorphism, TLR8 A1G (rs3764880), confers a significantly protective effect regarding progression of the disease. In overexpression assays, we demonstrated that this receptor variant displays impaired NF-kappaB activation in vitro. Furthermore, we analyzed different cell types obtained from individuals differing in their TLR8 genotype and assessed their response to TLR8 ligands in vitro. The presence of the mutated receptor variant was associated with modulation of cytokine secretion profiles and lipid mediator synthesis patterns in monocytes and neutrophils. CONCLUSIONS: This first report of a functional TLR8 variant associated with a different clinical course of an RNA viral disease may have implications for the individual risk assessment of patients infected with HIV and other RNA viruses as well as for future HIV vaccine development.

Exacerbation of murine ileitis by Toll-like receptor 4 mediated sensing of lipopolysaccharide from commensal Escherichia coli.

BACKGROUND: In the course of inflammatory bowel diseases (IBD) and acute murine ileitis following peroral Toxoplasma gondii infection, commensal Escherichia coli accumulate at inflamed mucosal sites and aggravate small intestinal immunopathology. AIM: To unravel the molecular mechanisms by which commensal E coli exacerbate ileitis. METHODS: Ileitis was investigated in mice that lack Toll-like receptors (TLR) 2 or 4, specific for bacterial lipoproteins (LP) or lipopolysaccharide (LPS), respectively. Gnotobiotic mice, in which any cultivable gut bacteria were eradicated by antibiotic treatment, were used to study the role of LPS in ileitis. RESULTS: Microbiological analyses revealed that E coli increase in the inflamed ileum. TLR4(-/-), but not TLR2(-/-), mice displayed reduced mortality and small intestinal immunopathology. Decreased interferon (IFN)-gamma and nitric oxide (NO) levels in the inflamed terminal ileum of TLR4(-/-) mice indicated that TLR4 signalling aggravates ileitis via local mediator release from immune cells. E coli strains isolated from the inflamed ileum activated cultured mouse macrophages and induced TLR4-dependent nuclear factor kappaB activation and NO production in human embryonic kidney 293 cells and in peritoneal macrophages, respectively. Most strikingly, in contrast with wild-type mice, gnotobiotic TLR4(-/-) mice were protected from induction of ileitis by treatment with purified E coli lipid A or colonisation with live E coli. Finally, prophylactic treatment with the LPS scavenger polymyxin B ameliorated T gondii-induced ileitis. CONCLUSION: These findings highlight the innate immune system as a key player in T gondii-induced ileal immunopathology. Treatment with LPS or TLR4 antagonists may represent a novel strategy for prophylaxis and/or therapy of small intestinal inflammation in IBD.