CD14 is a cell-activating receptor for bacterial peptidoglycan

The influence of the long chain fatty acid on the antagonistic activities of Rhizobium sin-1 lipid A

The lipid A from nitrogen-fixing bacterial species Rhizobium sin-1 is structurally unusual due to lack of phosphates and the presence of a 2-aminogluconolactone and a very long chain fatty acid, 27-hydroxyoctacosanoic acid (27OHC28:0), moiety. This structurally unusual lipid A can antagonize TNF-alpha production by human monocytes induced by Escherichia coli LPS. To establish the relevance of the unusual long chain 27-hydroxyoctacosanoic acid for antagonistic properties, a highly convergent strategy for the synthesis of several derivatives of the lipid A of R. sin-1 has been developed. Compound 1 is a natural R. sin-1 lipid A having a 27-hydroxyoctacosanoic acid at C-2', compound 2 contains an octacosanoic acid moiety at this position, and compound 3 is modified by a short chain tetradecanoic acid. Cellular activation studies with a human monocytic cell line have shown that the octacosanoic acid is important for optimal antagonistic properties. The hydroxyl of the natural 27-hydroxyoctacosanoic moiety does, however, not account for inhibitory activity. The resulting structure-activity relationships are important for the design of compounds for the treatment of septic shock.

Peptidoglycan recognition proteins: pleiotropic sensors and effectors of antimicrobial defences

Peptidoglycan recognition proteins (PGRPs) are innate immunity molecules that are present in most invertebrate and vertebrate animals. All PGRPs function in antimicrobial defence and are homologous to the prokaryotic peptidoglycan-lytic type 2 amidases. However, only some PGRPs have the catalytic activity that protects the host from excessive inflammation, and most PGRPs have diversified to carry out other host-defence functions. Insect and mammalian PGRPs defend host cells against infection through very different mechanisms. Insect PGRPs activate signal transduction pathways in host cells or trigger proteolytic cascades in the haemolymph, both of which generate antimicrobial effectors. By contrast, mammalian PGRPs are directly bactericidal. Here, we review these contrasting modes of action.

Exertional heat illness and human gene expression

Microarray analysis of gene expression at the level of RNA has generated new insights into the relationship between cellular responses to acute heat shock in vitro, exercise, and exertional heat illness. Here we discuss the systemic physiology of exertional hyperthermia and exertional heat illness, and compare the results of several recent microarray studies performed in vitro on human cells subjected to heat shock and in vivo on samples obtained from subjects performing exercise or suffering from exertional heat injury. From these comparisons, a concept of overlapping component responses emerges. Namely, some of the gene expression changes observed in peripheral blood mononuclear cells during exertional heat injury can be accounted for by normal cellular responses to heat, exercise, or both; others appear to be specific to the disease state itself. If confirmed in future studies, these component responses might provide a better understanding of adaptive and pathological responses to exercise and exercise-induced hyperthermia, help find new ways of identifying individuals at risk for exertional heat illness, and perhaps even help find rational molecular targets for therapeutic intervention.

Association of CD14 promoter polymorphism with otitis media and pneumococcal vaccine responses

Innate immunity is of particular importance for protection against infection during early life, when adaptive immune responses are immature. CD14 plays key roles in innate immunity, including in defense against pathogens associated with otitis media, a major pediatric health care issue. The T allele of the CD14 C-159T polymorphism has been associated with increased serum CD14 levels. Our objective was to investigate the hypothesis that the CD14 C-159T allele is protective against recurrent acute otitis media in children. The association between the CD14 promoter genotype and the number of acute otitis media episodes was evaluated both retrospectively and prospectively in a cohort of 300 children. Serotype-specific immunoglobulin G (IgG) antibody responses after pneumococcal vaccinations were examined according to CD14 genotype to compare immune responsiveness across genotypes. An age-dependent association was found: compared with that for CC homozygotes aged between 12 to 24 months, TT homozygotes had fewer episodes of acute otitis media (79 versus 41%, respectively; P = 0.004); this relationship was absent in older children. Additionally, TT homozygotes showed higher serotype-specific anti-pneumococcal IgG antibody levels. Our data suggest that genetic variation in CD14, a molecule at the interface of innate and adaptive immune responses, plays a key role in the defense against middle ear disease in childhood and in pneumococcal vaccine responsiveness. These findings are likely to be important to these and other immune-mediated outcomes in early life.

The role of Toll-like receptors in CNS response to microbial challenge

The recent discovery of the family of Toll-like receptors has vastly expanded our understanding of the mechanisms by which the innate immune system recognizes and responds to a wide variety of microbial and endogenous pathogens. Toll-like receptors are transmembrane proteins that upon ligation with their cognate ligands trigger the production of cytokines, enzymes and other inflammatory agents. In the CNS Toll-like receptors are expressed predominantly by glial cells. In particular, the vastly abundant astrocytes are likely to be the major contributors to inflammatory responses within the CNS. Studies of the murine brain abscess model revealed that Toll-like receptor 2 plays a pivotal role in the generation of immune responses to Staphylococcus aureus. Although Toll-like receptor signaling is essential in antimicrobial defense, it may also lead to bystander injury of CNS tissue.

Innate recognition of bacteria: potential therapeutic targets for bacterial sepsis

Sepsis is a paradoxical and complex disorder that results from an over-reaction of our innate immune system to bacterial infections. Although this disorder has been known since ancient times, the history of clinical research into novel therapies for sepsis has been disappointing. The inability to translate our findings to the clinic could be attributed to our lack of knowledge of the molecular mechanisms involved in sensing microbial pathogens. However, in the last decade, the innate immune sensors responsible for triggering this disease have been discovered. This review will examine mediators that have been targeted in the past, as well as in the present, and propose novel therapeutic interventions for the future.

Cell activation of human macrophages by lipoteichoic acid is strongly attenuated by lipopolysaccharide-binding protein

Lipoteichoic acid (LTA) represents immunostimulatory molecules expressed by Gram-positive bacteria. They activate the innate immune system via Toll-like receptors. We have investigated the role of serum proteins in activation of human macrophages by LTA from Staphylococcus aureus and found it to be strongly attenuated by serum. In contrast, the same cells showed a sensitive response to LTA and a significantly enhanced production of tumor necrosis factor alpha under serum-free conditions. We show that LTA interacts with the serum protein lipopolysaccharide-binding protein (LBP) and inhibits the integration of LBP into phospholipid membranes, indicating the formation of complexes of LTA and soluble LBP. The addition of recombinant human LBP to serum-free medium inhibited the production of tumor necrosis factor alpha and interleukins 6 and 8 after stimulation of human macrophages with LTA in a dose-dependent manner. Using anti-LBP antibodies, this inhibitory effect could be attributed to soluble LBP, whereas LBP in its recently described transmembrane configuration did not modulate cell activation. Also, using primary alveolar macrophages from rats, we show a sensitive cytokine response to LTA under serum-free culture conditions that was strongly attenuated in the presence of serum. In summary, our data suggest that innate immune recognition of LTA is organ-specific with negative regulation by LBP in serum-containing compartments and sensitive recognition in serum-free compartments like the lung.

Hepatic stellate cells primed with cytokines upregulate inflammation in response to peptidoglycan or lipoteichoic acid

Gram-positive bacterial products such as peptidoglycan (PGN) and lipoteichoic acid (LTA) are potent stimulators of innate inflammatory responses. We previously reported that lipopolysaccharide (LPS), a major biologically active agent of gram-negative bacteria, induces a proinflammatory response via the Toll-like receptor (TLR) 4 in hepatic stellate cells (HSCs). Here we investigated the mechanism of proinflammatory action by PGN and LTA in activated human HSCs. Following treatment with either TNF-alpha or IL-1beta, expression of TLR2 and CD14 was determined by real-time PCR and Western blotting. NF-kappaB activation was assessed by NF-kappaB-driven luciferase assay and electrophoretic mobility shift assay. Interleukin-8 (IL-8) from culture supernatant was measured by ELISA. Activated human HSCs express TLR2 and CD14, which are receptors for PGN and LTA signaling. TNF-alpha and IL-1beta significantly upregulated the expression of TLR2 mRNA and protein in HSCs. PGN and LTA induced NF-kappaB activation and stimulated production of IL-8 in HSCs. Pretreatment with TNF-alpha or IL-1beta augmented NF-kappaB activation and IL-8 production in response to PGN or LTA. Both PGN- and LTA-induced NF-kappaB activation and IL-8 secretion were completely inhibited by anti-TLR2 blocking antibody (T2.5). These findings suggest that TNF-alpha or IL-1beta primed HSCs enhance the production of IL-8 in response to PGN and LTA through augmentation of the TLR2 system.

Toll-like receptors in central nervous system glial inflammation and homeostasis

Toll-like receptors (TLRs) are a family of pattern-recognition receptors expressed on cells of the innate immune system that allow for the recognition of conserved structural motifs on a wide array of pathogens, referred to as pathogen-associated molecular patterns, as well as some endogenous molecules. The recent emergence of studies examining TLRs in the central nervous system (CNS) indicates that these receptors not only play a role in innate immunity in response to infectious diseases but may also participate in CNS autoimmunity, neurodegeneration, and tissue injury. This review summarizes the experimental evidence demonstrating a role for TLRs in the context of CNS inflammation in both infectious and noninfectious conditions.

Differential expression of peptidoglycan recognition protein 2 in the skin and liver requires different transcription factors

Human peptidoglycan recognition protein 2 (PGLYRP2) is an N-acetylmuramoyl-L-alanine amidase that hydrolyzes bacterial peptidoglycan and is differentially expressed in the two major organs in the human body, liver and skin. PGLYRP2 has a high constitutive expression in the liver but is not expressed in healthy human skin. PGLYRP2 mRNA is also not expressed in cultured human keratinocytes but is highly induced upon exposure to bacteria. In this study we identified the transcription start site for pglyrp2 and demonstrated that the differential expression of PGLYRP2 in hepatocytes and keratinocytes is regulated by different transcription factors whose binding sequences are located in different regions of the pglyrp2 promoter. Induction of pglyrp2 in keratinocytes is regulated by sequences in the distal region of the promoter and requires transcription factors NF-kappaB and Sp1, whereas constitutive expression of pglyrp2 in a hepatocyte cell line is regulated by sequences in the proximal region of the promoter and requires transcription factors c-Jun and ATF2. Regulation of constitutive and inducible expression of pglyrp2 is important for systemic and local innate immune responses to bacterial infections.

Peptidoglycan--an endotoxin in its own right?

Studies aimed at dissecting the complex pathophysiology of sepsis with multiple organ failure have traditionally focused on lipopolysaccharide of gram-negative bacteria, which is widely regarded as the classical endotoxin. However, gram-positive sepsis now accounts for up to 50% of all cases, calling for a shift of focus. Peptidoglycan (PepG) is the major cell wall component of gram-positive bacteria and has been increasingly recognized as an important proinflammatory molecule. During gram-positive infections, PepG reaches the circulation by bacterial breakdown or translocation from the intestine. Administration of PepG induces all the classical features of infectious illness and endotoxemia and may cause systemic inflammation with organ failure in animal models. Its potency, however, is crucially dependent on various features of its complex structure. PepG interacts with the innate immune system through receptors mainly expressed on monocytes/macrophages but may induce inflammatory changes in other cell types as well. Among the most extensively studied receptor systems are the nucleotide-binding oligomerization domains, the toll-like receptors, and the PepG recognition proteins. Based on the current available literature, we would like to propose that PepG must be regarded as an endotoxin in its own right and to encourage further work in the field of PepG signaling.

The 2-aminogluconate isomer of rhizobium sin-1 lipid A can antagonize TNF-alpha production induced by enteric LPS

The naturally occurring lipopolysaccharide (LPS) from Rhizobium sin-1, a nitrogen-fixing bacterial species, can prevent the induction of the tumor necrosis factor TNF-alpha induced by enteric LPS. The proximal saccharide moiety of R. sin-1 lipid A can exist in two forms, namely as a 2-aminogluconolactone or 2-aminogluconate. As it is unknown which of these forms is responsible for the antagonistic properties of R. sin-1 lipid A, compound 4 was prepared, and its inflammatory properties were studied. This compound contains a methyl ether at the C-5 hydroxyl, which prevents lactonization and therefore is ideally suited to determine whether the 2-aminogluconate possesses antagonistic properties. Compound 4 was synthesized by a highly convergent approach with a key disaccharide building block functionalized with a set of orthogonal protecting groups. The novel synthetic compound lacks proinflammatory properties, as indicated by an absence of TNF-alpha protein production. This compound was, however, able to antagonize the production of TNF-alpha induced by enteric LPS; this indicates that the 2-aminogluconate form of R. sin-1 lipid A is responsible for its biological properties.

The role of the MHC on resistance to group a streptococci in mice

The severity of infection with Streptococcus pyogenes is strongly influenced by the host's genetics. This observation extends to the murine model of streptococcal infection, where the background of the mouse strain determines the infection outcome (BALB/c are resistant, whereas C3H/HeN are susceptible). To determine the extent to which the MHC complex (H2) contributed to diseases susceptibility, the response to S. pyogenes of congenic BALB mice from a resistant background (BALB/c), but carrying the H2(k) region of susceptible C3H/HeN mice (BALB/k), was examined. BALB/k were as susceptible as the H2 donor strain (C3H/HeN). Linkage analysis performed in F(2) backcross ([BALB/c x C3H/HeN] x BALB/c) mice confirmed the presence of a susceptibility locus within the H2 region on proximal chromosome 17. The possibility that modulation of T cell responses to streptococcal superantigens (GAS-SAgs) by different H2 haplotypes may influence disease severity was examined. BALB/k exhibited a significantly stronger response at the level of cell proliferation and cytokine production to GAS-SAgs than did BALB/c mice. However, the fact that T cell-deficient SCID-C3H/HeN mice also exhibited a susceptible phenotype suggests a more important contribution of innate effector cells to disease susceptibility. Lower transcriptional levels of certain inflammation-related regulatory genes located on chromosome 17 were detected in macrophages from susceptible than in those from resistant mice in response to infection. These results suggest that susceptibility to S. pyogenes may be associated with an altered transcription of specific genes that may compromise the endogenous regulatory processes controlling the inflammatory cascade and favor the progression to sepsis.

Recognition of Staphylococcus aureus-derived peptidoglycan (PGN) but not intact bacteria is mediated by CD14 in microglia

Recognition of Staphylococcus aureus and its cell-wall component peptidoglycan (PGN) by microglia is mediated, in part, by Toll-like receptor 2 (TLR2). However, the pattern recognition receptor (PRR) CD14 can also bind PGN and enhance TLR2-mediated signaling in macrophages, suggesting a similar phenomenon might occur in microglia. To assess the functional significance of CD14 on microglial activation, we evaluated the responses of primary microglia isolated from CD14 knockout (KO) and wild type (WT) mice. PGN-dependent microglial activation was partially CD14-dependent as demonstrated by the attenuated expression of TNF-alpha, macrophage inflammatory protein-2 (MIP-2/CXCL2), and the soluble PRR pentraxin-3 in CD14 KO microglia compared to WT cells. In contrast, microglial responses to intact S. aureus occurred primarily via a CD14-independent manner. Collectively, these findings reveal the complex nature of gram-positive bacterial recognition by microglia, which occurs, in part, via CD14.

GENETIC POLYMORPHISMS AND SEPSIS

Sepsis is a polygenic and complex syndrome that is initiated by infection and is characterized by a systemic inflammatory response. Genetic polymorphisms in the immune response to infection have been shown to be associated with clinical outcomes. Functional and association studies involving genetic polymorphisms in essential genes, including Toll-like receptors, cytokines, and coagulation factors, have provided important insights into the mechanisms involved in the pathogenesis of sepsis-induced organ dysfunction. The advancement of high-throughput single nucleotide polymorphism (SNP) genotyping will provide valuable information on the interaction of multiple allelic variants and clinical outcome. More precise categorization of patients based on genetic background is likely to lead to individualized targeted treatment. Future therapeutic trials as well as actual treatment regimens for patients with sepsis are likely to be designed to target specific genotypes and associated cellular responses, maximizing clinical response and patient safety.

Signal transduction pathways of nitric oxide release in primary microglial culture challenged with gram-positive bacterial constituent, lipoteichoic acid

Between one-third and one-half of all cases of sepsis are known to be caused by gram-positive microorganisms through the cell wall component, e.g. lipoteichoic acid (LTA). Gram-positive bacteria are also known to induce encephalomyelitis and meningeal inflammation, and enhance the production of nitric oxide (NO) via expression of inducible nitric oxide synthase (iNOS) in murine tissue macrophages. It remains to be explored if LTA could activate microglia considered to be resident brain macrophages. We report here that LTA derived from gram-positive bacteria (Staphylococcus aureus) significantly induces NO release and iNOS expression in primary microglia. LTA-induced NO accumulation was detected at 2 h in microglial culture and was significantly attenuated by pretreatment with anti-CD14, complement receptor type 3 (CR3) or scavenger receptor (SR) antibodies. LTA activated mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase, p38 MAPK or c-Jun N-terminal kinase in cultured microglia. LTA-elicited microglial NO production was also drastically suppressed by SB203580 (p38 MAPK inhibitor) or pyrrolidine dithiocarbamate (an inhibitor of nuclear factor kappaB), indicating that p38 MAPK and nuclear factor kappaB were involved in microglial NO release after LTA challenge. These results suggest that gram-positive bacterial product such as LTA can activate microglia to release NO via the signal transduction pathway involving multiple LTA receptors (e.g. CD14, CR3 or SR), p38 MAPK and nuclear factor kappaB. The in vivo study further confirmed that administered intracerebrally LTA induced considerable noticeable iNOS, phospho-IkappaB and phospho-p38 MAPK expression in microglia/macrophages.

Staphylococcus aureus peptidoglycan is a toll-like receptor 2 activator: a reevaluation

Since the ability of peptidoglycan (PGN) to activate Toll-like receptor 2 (TLR2) was recently questioned, we reevaluated activation of TLR2 by PGN. Polymeric soluble or insoluble Staphylococcus aureus PGN, repurified by sodium dodecyl sulfate or phenol extraction, activated TLR2 at 0.1 to 1 or 10 mug/ml, respectively, and induced tumor necrosis factor alpha production. The TLR2 activation by PGN, but not by lipoteichoic acid, was abolished by muramidase digestion. We conclude that polymeric S. aureus PGN is a TLR2 activator.

Recognition of Staphylococcus aureus by the innate immune system

The gram-positive bacterium Staphylococcus aureus is a major pathogen responsible for a variety of diseases ranging from minor skin infections to life-threatening conditions such as sepsis. Cell wall-associated and secreted proteins (e.g., protein A, hemolysins, and phenol-soluble modulin) and cell wall components (e.g., peptidoglycan and alanylated lipoteichoic acid) have been shown to be inflammatory, and these staphylococcal components may contribute to sepsis. On the host side, many host factors have been implicated in the innate detection of staphylococcal components. One class of pattern recognition molecules, Toll-like receptor 2, has been shown to function as the transmembrane component involved in the detection of staphylococcal lipoteichoic acid and phenol-soluble modulin and is involved in the synthesis of inflammatory cytokines by monocytes/macrophages in response to these components. Nod2 (nucleotide-binding oligomerization domain 2) is the intracellular sensor for muramyl dipeptide, the minimal bioactive structure of peptidoglycan, and it may contribute to the innate immune defense against S. aureus. The staphylococcal virulence factor protein A was recently shown to interact directly with tumor necrosis factor receptor 1 in airway epithelium and to reproduce the effects of tumor necrosis factor alpha. Finally, peptidoglycan recognition protein L is an amidase that inactivates the proinflammatory activities of peptidoglycan. However, peptidoglycan recognition protein L probably plays a minor role in the innate immune response to S. aureus. Thus, several innate immunity receptors may be implicated in host defense against S. aureus.

Human CD14 is an efficient target for recombinant immunoglobulin vaccine constructs that deliver T cell epitopes

It has been shown in the mouse that recombinant immunoglobulin (Ig) molecules with T cell epitopes inserted into the constant domain (Troybodies) can target antigen-presenting cells (APC) for efficient delivery of T cell epitopes. Here, we have extended the Troybody concept to human applications. Moreover, we show that a receptor of innate immunity, CD14, which is a part of the lipopolysaccharide receptor complex on monocyte APC, is an efficient target. For construction of CD14-specific Troybodies, we used rearranged variable(diversity)joining regions cloned from the 3C10 mouse B cell hybridoma. As a model T cell epitope, amino acids 40-48 of mouse Ckappa, presented on human leukocyte antigen-DR4, were inserted into a loop connecting beta-strands in C(H)1 of human gamma3. In the presence of monocytes, CD14-specific Troybodies were >100 times as efficient as a nontargeting control antibody (Ab) at stimulating Ckappa(40-48)-specific/DR4-restricted T cells. Presentation was dependent on the conventional processing pathway for presentation on major histocompatibility complex (MHC) class II molecules. Enhanced presentation of the Ckappa epitope was most likely a result of increased loading of MHC class II molecules, as the CD14-specific monoclonal Ab 3C10 did not induce maturation of the APC. The results show that CD14, a receptor of innate immunity, may be a promising target of recombinant Ig-based vaccines for elicitation of T cell responses in humans.

Structural basis for peptidoglycan binding by peptidoglycan recognition proteins

Peptidoglycan (PGN) recognition proteins (PGRPs) are pattern-recognition receptors of the innate immune system that bind and, in some cases, hydrolyze bacterial PGNs. We determined the crystal structure, at 2.30-A resolution, of the C-terminal PGN-binding domain of human PGRP-Ialpha in complex with a muramyl tripeptide representing the core of lysine-type PGNs from Gram-positive bacteria. The peptide stem of the ligand is buried at the deep end of a long binding groove, with N-acetylmuramic acid situated in the middle of the groove, whose shallow end can accommodate a linked N-acetylglucosamine. Although most interactions are with the peptide, the glycan moiety also seems to be essential for specific recognition by PGRPs. Conservation of key PGN-contacting residues shows that all PGRPs employ this basic PGN-binding mode. The structure pinpoints variable residues that likely mediate discrimination between lysine- and diaminopimelic acid-type PGNs. We also propose a mechanism for PGN hydrolysis by Zn(2+)-containing PGRPs.

Innate immune response of corneal epithelial cells to Staphylococcus aureus infection: role of peptidoglycan in stimulating proinflammatory cytokine secretion

PURPOSE

This study sought to elucidate the innate immune responses of cultured human corneal epithelial cells (HCECs) to infection by the Gram-positive bacterium Staphylococcus aureus and to determine the underlying mechanisms.

METHODS

HUCL, a telomerase-immortalized HCEC line, and primary cultures of HCECs were challenged with live or heat-killed S. aureus, its exoproducts, or cell wall components lipoteichoic acid (LTA) and peptidoglycan (PGN). IkappaB-alpha phosphorylation and degradation as well as phosphorylation of MAPKs, p38, and JNK-1/2, were assessed by Western blot analysis. The expression of interleukin (IL)-6, IL-8, TNF-alpha, and beta-defensin-2 were determined using RT-PCR and secretion of IL-6, IL-8, TNF-alpha, and beta-defensin were measured using enzyme-linked immunosorbent assay and immunoblot analysis of culture medium.

RESULTS

Exposure of HUCL cells to live, but not heat-killed, S. aureus resulted in NF-kappaB activation in a time-dependent manner, as assessed by the increase in IkappaB-alpha phosphorylation and degradation. Live bacteria also activated the p38 and JNK pathways. The effects of live bacteria on HUCL cells may be attributable to bacterial exoproducts, since the conditioned medium of S. aureus also effectively stimulated these signaling pathways. PGN, but not LTA, activated the NF-kappaB and MAPK pathways in a dose- and time-dependent manner. Concomitant with activation of NF-kappaB and MAPKs, transcriptional expression of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were induced in cells challenged with bacterial exoproducts and PGN. Secretion of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were also significantly increased in HCECs in response to bacterial exoproducts and PGN challenge.

CONCLUSIONS

Corneal epithelial cells possess the ability to recognize the presence of Gram-positive bacteria and to initiate the innate immune responses by the expression and/or release of proinflammatory cytokines and beta-defensin-2 in the cornea.

Lipoteichoic Acid and Toll-like Receptor 2 Internalization and Targeting to the Golgi Are Lipid Raft-dependent

Lipoteichoic acid (LTA), a key cell wall component of Gram-positive bacteria, seems to function as an immune activator with characteristics very similar to lipopolysaccharide from Gram-negative bacteria. It has been shown that LTA binds CD14 and triggers activation via Toll-like receptor 2, but whether the activation occurs at the cell surface or internalization is required to trigger signaling has yet to be demonstrated. In this work we have investigated LTA binding and internalization and found that LTA and its receptor molecules accumulate in lipid rafts and are subsequently targeted rapidly to the Golgi apparatus. This internalization seems to be lipid raft-dependent because raft-disrupting drugs inhibited LTA/Toll-like receptor 2 colocalization in the Golgi. Similarly to lipopolysaccharide, LTA activation occurs at the cell surface, and the observed trafficking is independent of signaling.

Crystal structure of the Drosophila peptidoglycan recognition protein (PGRP)-SA at 1.56 A resolution

Peptidoglycan recognition proteins (PGRPs) form a recently discovered protein family, which is conserved from insect to mammals and is implicated in the innate immune system by interacting with/or degrading microbial peptidoglycans (PGNs). Drosophila PGRP-SA is a member of this family of pattern recognition receptors and is involved in insect Toll activation. We report here the crystal structure of PGRP-SA at 1.56 A resolution, which represents the first example of a "recognition" PGRP. Comparison with the catalytic Drosophila PGRP-LB reveals an overall structure conservation with an L-shaped hydrophilic groove that is likely the PGN carbohydrate core binding site, but further suggests some possible functional homology between recognition and catalytic PGRPs. Consistent with sequence analysis, PGRP-SA does not contain the canonical zinc-binding residues found in catalytic PGRPs. However, substitution of the zinc-binding cysteine residue by serine, along with an altered coordinating histidine residue, assembles a constellation of residues that resembles a modified catalytic triad. The serine/histidine juxtaposition to a threonine residue and a carbonyl oxygen atom, along with conservation of the catalytic water molecule found in PGRP-LB, tantalizingly suggests some hydrolytic function for this member of receptor PGRPs.

Peptidoglycan and lipoteichoic acid in gram-positive bacterial sepsis: receptors, signal transduction, biological effects, and synergism

In sepsis and multiple organ dysfunction syndrome (MODS) caused by gram-negative bacteria, lipopolysaccharide (LPS) initiates the early signaling events leading to the deleterious inflammatory response. However, it has become clear that LPS can not reproduce all of the clinical features of sepsis, which emphasize the roles of other contributing factors. Gram-positive bacteria, which lack LPS, are today responsible for a substantial part of the incidents of sepsis with MODS. The major wall components of gram-positive bacteria, peptidoglycan and lipoteichoic acid, are thought to contribute to the development of sepsis and MODS. In this review, the literature underlying our current understanding of how peptidoglycan and lipoteichoic acid activate inflammatory responses will be presented, with a focus on recent advances in this field.

A promoter polymorphism in the CD14 gene is associated with elevated levels of soluble CD14 but not with IgE or atopic diseases

BACKGROUND

A polymorphism in the promoter region of the CD14 gene, C-159T, has been shown to be associated with increased levels of soluble CD14 (sCD14) and decreased serum immunoglobulin E (IgE) and the expression of a more severe atopic phenotype in previous studies.

METHODS

To test if these associations are consistently found in different populations and different age groups, we genotyped 2048 children of different age groups as well as 888 adults from different regions of Germany for the CD14 C-159T polymorphism.

RESULTS

While an association between this promoter polymorphism and levels of sCD14 could be confirmed in our study population (CC: 1017 ng/ml vs TT: 1370 ng/ml, P = 0.03), no association between CD14 C-159T genotypes and IgE levels or the prevalence of atopic diseases was seen.

CONCLUSIONS

The lack of association between CD14 genotypes and IgE as well as atopic outcomes in this large German study population seems to indicate that CD14 genotypes may not directly be involved in the development of allergies during childhood.

CD14 mediates the innate immune responses to arthritopathogenic peptidoglycan-polysaccharide complexes of Gram-positive bacterial cell walls

Bacterial infections play an important role in the multifactorial etiology of rheumatoid arthritis. The arthropathic properties of Gram-positive bacteria have been associated with peptidoglycan-polysaccharide complexes (PG-PS), which are major structural components of bacterial cell walls. There is little agreement as to the identity of cellular receptors that mediate innate immune responses to PG-PS. A glycosylphosphatidylinositol-linked cell surface protein, CD14, the lipopolysaccharide receptor, has been proposed as a PG-PS receptor, but contradictory data have been reported. Here, we examined the inflammatory and pathogenic responses to PG-PS in CD14 knockout mice in order to examine the role for CD14 in PG-PS-induced signaling. We found that PG-PS-induced responses in vitro, including transient increase in intracellular calcium, activation of nuclear factor-kappaB, and secretion of the cytokines tumor necrosis factor-alpha and interleukin-6, were all strongly inhibited in CD14 knockout macrophages. In vivo, the incidence and severity of PG-PS induced acute polyarthritis were significantly reduced in CD14 knockout mice as compared with their wild-type counterparts. Consistent with these findings, CD14 knockout mice had significantly inhibited inflammatory cell infiltration and synovial hyperplasia, and reduced expression of inflammatory cytokines in PG-PS arthritic joints. These results support an essential role for CD14 in the innate immune responses to PG-PS and indicate an important role for CD14 in PG-PS induced arthropathy.

Molecular mechanisms of macrophage activation and deactivation by lipopolysaccharide: roles of the receptor complex

Bacterial lipopolysaccharide (LPS), the major structural component of the outer wall of Gram-negative bacteria, is a potent activator of macrophages. Activated macrophages produce a variety of inflammatory cytokines. Excessive production of cytokines in response to LPS is regarded as the cause of septic shock. On the other hand, macrophages exposed to suboptimal doses of LPS are rendered tolerant to subsequent exposure to LPS and manifest a profoundly altered response to LPS. Increasing evidence suggests that monocytic cells from patients with sepsis and septic shock survivors have characteristics of LPS tolerance. Thus, an understanding of the molecular mechanisms underlying activation and deactivation of macrophages in response to LPS is important for the development of therapeutics for septic shock and the treatment of septic shock survivors. Over the past several years, significant progress has been made in identifying and characterizing several key molecules and signal pathways involved in the regulation of macrophage functions by LPS. In this paper, we summarize the current findings of the functions of the LPS receptor complex, which is composed of CD14, Toll-like receptor 4 (TLR4), and myeloid differentiation protein-2 (MD-2), and the signal pathways of this LPS receptor complex with regard to both activation and deactivation of macrophages by LPS. In addition, recent therapeutic approaches for septic shock targeting the LPS receptor complex are described.

Childhood nephrotic syndrome in relapse is associated with down-regulation of monocyte CD14 expression and lipopolysaccharide-induced tumour necrosis factor-alpha production

Interleukin-13 (IL-13) is a known modulator of monocyte function, down-regulating monocyte surface markers such as CD14 and proinflammatory cytokines. We have shown previously that lymphocyte IL-13 gene expression was up-regulated during relapses in children with steroid-responsive nephrotic syndrome (SRNS). In this study, we examined the monocyte mRNA expression and lipopolysaccharide (LPS)-stimulated intracellular production of tumour necrosis factor-alpha (TNF-alpha) and IL-8 in children with SRNS during relapse and remission. Additionally, we investigated CD14 mRNA levels, CD14 surface expression and its soluble component (sCD14) in serum. Our results showed that the percentages of TNF-alpha positive monocytes following LPS stimulation were significantly lower in nephrotic children in relapse (64.4 +/- 13.7%) compared to remission (81.6 +/- 9.0%, P < 0.005). This was associated with down-regulation of CD14 mRNA, as well as both membrane and sCD14 in patients with nephrotic relapse (82.9 +/- 10.1% and 1.23 +/- 0.30 micro g/ml, respectively) compared to remission (93.9 +/- 3.2% and 1.77 +/- 0.82 micro g/ml, respectively) (P < 0.003). Although we demonstrated a decrease in LPS-stimulated intracellular production of TNF-alpha in monocytes from patients with nephrotic relapse, we were unable to show a concomitant decrease in mRNA expression during relapses. This could be explained by down-regulation of gene expression at the translational rather than transcriptional level. In conclusion, it is conceivable that up-regulation of T-cell IL-13 production in children with active nephrotic relapse was associated with suppression of monocyte CD14 expression, down-regulating pro-inflammatory cytokine production, and could account for the increased susceptibility to bacterial sepsis seen in nephrotic children in active relapse.

Role of immunoreactions and mast cells in pathogenesis of human endometriosis -morphologic study and gene expression analysis-

STUDY OBJECTIVES

To investigate the pathophysiology of human endometriosis, we examined by morphological and molecular biological methods.

METHODS

Samples of ovarian endometriosis and normal ovarian tissues were obtained laparoscopically after informed consent. A morphological study by toluidine blue staining, immunohistochemistry of c-kit and electron microscopy demonstrated the localization of mast cells in the stromal lesions of endometriosis. Oligonucleotide microarrays were used for gene expression analysis.

RESULTS

Infiltration of numerous mast cells and development of fibrosis was observed throughout the stromal lesions. Gene expression analysis by oligonucleotide microarrays indicated inflammatory immunoreactions in the lesions. Expressions of the FCER1G and PGDS, which are considered to be mast cell-specific genes, were upregulated in the ovarian endometriotic lesions as compared to the normal ovarian tissues. Furthermore, expressions of genes associated with immunological inflammation, such as IL-8, GRO1, GRO2, CXCR4, MCP1, and those related to tissue remodeling (MMP, COL4A2, and COL5A2) were also higher in endometriotic lesions than in the normal ovarian tissue.

CONCLUSIONS

Thus it is likely that mast cells and their related inflammatory immunoreactions via chemokines play important roles in producing fibrosis and adhesions in endometriotic lesions.

Innate sensors for Gram-positive bacteria

More than half of invasive bacterial infections are Gram-positive in origin. This class of bacteria has neither endotoxins nor an outer membrane, yet it generates some of the most powerful inflammatory responses known in medicine. Some recent seminal studies go a long way toward settling the controversies that surround the process by which Gram-positive bacterial surfaces trigger the human immune system. Although the components of the cell wall are now chemically defined in exquisite detail and the interaction with the toll-like receptor 2 pathway has been discovered, it is only very recently that definitive studies combining these advanced biochemical and cell biological tools have been carried out. It is these breakthrough studies that have finally confirmed the paradigm of innate sensors for Gram-positive bacteria.

Defect in neutrophil killing and increased susceptibility to infection with nonpathogenic gram-positive bacteria in peptidoglycan recognition protein-S (PGRP-S)-deficient mice

Insect peptidoglycan recognition protein-S (PGRP-S), a member of a family of innate immunity pattern recognition molecules conserved from insects to mammals, recognizes bacterial cell wall peptidoglycan and activates 2 antimicrobial defense systems, prophenoloxidase cascade and antimicrobial peptides through Toll receptor. We show that mouse PGRP-S is present in neutrophil tertiary granules and that PGRP-S-deficient (PGRP-S-/-) mice have increased susceptibility to intraperitoneal infection with gram-positive bacteria of low pathogenicity but not with more pathogenic gram-positive or gram-negative bacteria. PGRP-S-/- mice have normal inflammatory responses and production of tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6). Neutrophils from PGRP-S-/- mice have normal phagocytic uptake of bacteria but are defective in intracellular killing and digestion of relatively nonpathogenic gram-positive bacteria. Therefore, mammalian PGRP-S functions in intracellular killing of bacteria. Thus, only bacterial recognition by PGRP-S, but not its effector function, is conserved from insects to mammals.

Teichoic acids are not required for Streptococcus pneumoniae and Staphylococcus aureus cell walls to trigger the release of tumor necrosis factor by peripheral blood monocytes

In gram-negative bacteria, the outer membrane lipopolysaccharide is the main component triggering cytokine release from peripheral blood mononuclear cells (PBMCs). In gram-positive bacteria, purified walls also induce cytokine release, but stimulation requires 100 times more material. Gram-positive walls are complex megamolecules reassembling distinct structures. Only some of them might be inflammatory, whereas others are not. Teichoic acids (TA) are an important portion (> or =50%) of gram-positive walls. TA directly interact with C3b of complement and the cellular receptor for platelet-activating factor. However, their contribution to wall-induced cytokine-release by PBMCs has not been studied in much detail. In contrast, their membrane-bound lipoteichoic acids (LTA) counterparts were shown to trigger inflammation and synergize with peptidoglycan (PGN) for releasing nitric oxide (NO). This raised the question as to whether TA are also inflammatory. We determined the release of tumor necrosis factor (TNF) by PBMCs exposed to a variety of TA-rich and TA-free wall fragments from Streptococcus pneumoniae and Staphylococcus aureus. TA-rich walls from both organisms induced measurable TNF release at concentrations of 1 microg/ml. Removal of wall-attached TA did not alter this activity. Moreover, purified pneumococcal and staphylococcal TA did not trigger TNF release at concentrations as high as > or =100 microg/ml. In contrast, purified LTA triggered TNF release at 1 microg/ml. PGN-stem peptide oligomers lacking TA or amino-sugars were highly active and triggered TNF release at concentrations as low as 0.01 microg/ml (P. A. Majcherczyk, H. Langen, et al., J. Biol. Chem. 274:12537-12543,1999). Thus, although TA is an important part of gram-positive walls, it did not participate to the TNF-releasing activity of PGN.

Purification and characterization of human soluble CD14 expressed in Pichia pastoris

CD14 is a protein that mediates lipopolysaccharide (LPS)-induced biological responses such as activation of a transcriptional factor, nuclear factor (NF)-kappaB. It exists as a soluble form (sCD14) in serum and mediates LPS responses of epithelial and endothelial cells as well as a membrane-bound form (mCD14) on monocytes and macrophages. To obtain sCD14 in large quantity for its structural and functional characterization, we expressed the full-length form of human recombinant sCD14 (rsCD14) in a methylotrophic yeast, Pichia pastoris. The recombinant protein was expressed as a major protein in the culture supernatant and purified by ammonium sulfate precipitation, followed by three steps of ion exchange chromatographies. Finally, 1.6 mg of the protein was obtained in high purity from 2L of the supernatant and its identity to sCD14 was confirmed by NH(2)-terminal amino acid sequence analysis. The purified protein was found to have N-linked sugars by an analysis of enzymatic deglycosylation. A native PAGE analysis revealed that the protein was able to form complexes with LPS. In addition, the rsCD14 protein could mediate the LPS-mediated activation of NF-kappaB in human embryonic kidney 293 cells transfected with Toll-like receptor 4 and MD-2, indicating that the purified protein is biologically active. Thus, the rsCD14 protein expressed in P. pastoris and highly purified in a large amount is useful for its structural and functional studies.

Saccharomyces cerevisiae- and Candida albicans-derived mannan induced production of tumor necrosis factor alpha by human monocytes in a CD14- and Toll-like receptor 4-dependent manner

The cytokine-inducing activities of fungal polysaccharides were examined in human monocytes in culture, with special reference to CD14 and Toll-like receptors (TLRs). Tumor necrosis factor alpha (TNF-alpha) production by monocytes was markedly induced in a dose-dependent manner upon stimulation with cell walls from Candida albicans and mannan from Saccharomyces cerevisiae and C. albicans, although relatively high concentrations (10 to 100 microg/ml) of stimulants were required for activation as compared with the reference lipopolysaccharide (LPS) (1 to 10 ng/ml). The yeast form C. albicans and its mannan and cell wall fractions exhibited higher TNF-alpha production than respective preparations from the hyphal form. Only slight TNF-alpha production was induced by the S. cerevisiae glucan. The TNF-alpha production triggered by reference LPS and purified fungal mannans required the presence of LPS-binding protein (LBP), and these responses were inhibited by anti-CD14 and anti-TLR4 antibodies, but not by anti-TLR2 antibody. In contrast to the activity of LPS, the activity of purified S. cerevisiae mannan was not inhibited by polymyxin B. These findings suggested that the mannan-LBP complex is recognized by CD14 on monocytes and that signaling through TLR4 leads to the production of proinflammatory cytokines in a manner similar to that induced by LPS.

Lipopolysaccharide down-regulates the leukotriene C4 synthase gene in the monocyte-like cell line, THP-1

We studied the effects of LPS on cysteinyl leukotriene (LT) synthesis and LTC(4) synthase expression in mononuclear phagocytes. Conditioning of the monocyte-like cell line, THP-1, with LPS for 7 days resulted in significantly decreased ionophore-stimulated LTC(4) release. The putative LPS receptor, Toll-like receptor 4, was expressed in THP-1 cells. LPS down-regulated LTC(4) synthase mRNA in THP-1 cells in a dose- and time-dependent manner, with down-regulation observed as early as 4 h. Conditioning of actinomycin D-treated cells with LPS resulted in no change in the rate of LTC(4) synthase mRNA decay. LPS treatment of THP-1 cells, transiently transfected with a LTC(4) synthase promoter (1.35 kb)-reporter construct, decreased promoter activity. Neutralization of TNF-alpha and inhibition of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase did not inhibit the effect of LPS. Treatment of cells with a Toll-like receptor 4-blocking Ab and an inhibitor of NF-kappaB activation resulted in inhibition of the LPS effect, while activation of NF-kappaB and p50/p65 overexpression down-regulated the LTC(4) synthase gene. LPS down-regulates cysteinyl LT release and LTC(4) synthase gene expression in mononuclear phagocytes by an NF-kappaB-mediated mechanism.

The differentially spliced mouse tagL gene, homolog of tag7/PGRP gene family in mammals and Drosophila, can recognize Gram-positive and Gram-negative bacterial cell wall independently of T phage lysozyme homology domain

Tag7/PGRP, a recently characterized antimicrobial protein, is conserved from insects to mammals. Recently its involvement in Toll signalling in Drosophila was demonstrated. A number of genes representing a new family homologous to PGRP were identified in Drosophila and human. Here we describe a splicing pattern of the tagL gene, mouse member of tag7/PGRP family. Some of the identified splice variants lacked characteristics for the family T phage lysozyme homology domain (also known as PGRP domain). Accordingly to the predicted transmembrane domains, mouse TagL may be secreted as inducible proteins or retained on intracellular membranes. All detected splice variant isoforms of TagL bound Gram-positive, Gram-negative bacteria and peptidoglycan. This binding did not depend on the presence of T phage lysozyme homology domain but was associated with the C-terminal portion of the polypeptides. Thus, this variety of isoforms of a single gene may play a role in circulating bacteria recognition in mammals.

Contrasting responses of human gingival and periodontal ligament fibroblasts to bacterial cell-surface components through the CD14/Toll-like receptor system

We compared human periodontal ligament fibroblasts with human gingival fibroblasts isolated from the same donor to examine interleukin-8 (IL-8) responses of the cells to Salmonella lipopolysaccharide, a water-soluble peptidoglycan from Staphylococcus epidermidis and the synthetic muramyldipeptide, with special reference to the possible involvement of the CD14/Toll-like receptor (TLR) system of the cells in the responses. Human gingival fibroblasts expressed CD14 on their surfaces and strongly expressed CD14 mRNA, while human periodontal ligament fibroblasts showed considerably lower levels of expression in both respects. Both cells expressed mRNA of TLR-related molecules, i.e. TLR2, TLR4, MD-2 and MyD88, although human periodontal ligament fibroblasts expressed TLR2 more strongly than human gingival fibroblasts. Human gingival fibroblasts exhibited a stronger IL-8 response than human periodontal ligament fibroblasts to lipopolysaccharide, while human periodontal ligament fibroblasts exhibited a response comparable to, or slightly stronger than, that of human gingival fibroblasts to S. epidermidis peptidoglycan and muramyldipeptide. The IL-8 responses of both cells to lipopolysaccharide and S. epidermidis peptidoglycan were completely inhibited by antihuman CD14 monoclonal antibody (MAb). The responses of both cells to lipopolysaccaride were significantly inhibited by antihuman TLR4 MAb, while those to S. epidermidis peptidoglycan were inhibited by antihuman TLR2 MAb. In contrast, muramyldipeptide activated both types of cells in a TLR2- and TLR4-independent manner, although the activities of muramyldipeptide on human gingival fibroblasts, but not human periodontal ligament fibroblasts, were significantly inhibited by anti-CD14 MAb.

Interaction of pulmonary surfactant protein C with CD14 and lipopolysaccharide

In addition to their effects on alveolar surface tension, some components of lung surfactant also have immunological functions. We found recently that the hydrophobic lung surfactant protein SP-C specifically binds to the lipid A region of lipopolysaccharide (LPS). In this study, we show that SP-C also interacts with CD14. Four observations showed cross talk between the three molecules SP-C, LPS, and CD14. (i) Like LBP, SP-C allows the binding of a fluorescent LPS to cells expressing CD14 (the other surfactant components were ineffective). (ii) Recombinant radiolabeled CD14 and SP-C (or a synthetic analog of SP-C) interact in a dose-dependent manner. (iii) LPS blocks the binding of radiolabeled CD14 to SP-C-coated wells. (iv) SP-C enhances the binding of radiolabeled CD14 to LPS-coated wells. These results, obtained with native murine SP-C and with three synthetic analogs, suggest that LPS and CD14 interact with the same region of SP-C and that binding of SP-C modifies the conformation of CD14 or the accessibility of its LPS-binding site, allowing it to bind LPS. This ability of SP-C to interact with the pattern recognition molecule CD14 extends the possible immunological targets of SP-C to a large panel of microorganisms that can enter the airways.

Regions of the mouse CD14 molecule required for toll-like receptor 2- and 4-mediated activation of NF-kappa B

Regions of mouse CD14 required for Toll-like receptor 2 (TLR2)- and TLR4-mediated activation of NF-kappaB were studied in transiently transfected 293 cells. Wild-type CD14 enhanced lipopolysaccharide (LPS)-induced NF-kappaB-dependent reporter activity in cells expressing TLR4/MD-2, and deletion of amino acid regions 35-44, 144-153, 235-243, and 270-275 impaired the TLR4-mediated activation. Unlike human CD14, mouse CD14 truncated at amino acid 151 lost the activity. Deletion of amino acids 35-44 or 235-243 also abrogated TLR2-mediated activation of NF-kappaB, whereas mutants lacking 144-153 and 270-275 retained the activity. Deletion and alanine substitution experiments revealed that amino acids 151-153 and 273-275 were required for the TLR4-mediated activation. Both deletion mutants lacking amino acids 35-44 and 235-243 and alanine substitution mutants in regions 151-153 and 273-275 were expressed on the cell surface and retained the ability to associate with TLR4. A cross-linking study with photoreactive LPS showed that the labeling intensities to CD14 mutants/TLR4/MD-2 were paralleled by the ability of CD14 mutants to increase TLR4-mediated activation. These results indicate that different regions of mouse CD14 are required for TLR4- and TLR2-mediated activation of NF-kappaB and suggest that amino acids 35-44, 151-153, 235-243, and 273-275 of mouse CD14 play an important role in LPS binding and its transfer to TLR4/MD-2.

The origin of the synergistic effect of muramyl dipeptide with endotoxin and peptidoglycan

Although the basis for the high mortality rate for patients with mixed bacterial infections is likely to be multifactorial, there is evidence for a synergistic effect of muramyldipeptide (MDP) with lipopolysaccharide (LPS) on the synthesis of proinflammatory cytokines by mononuclear phagocytes. In this study, co-incubation of human Mono Mac 6 cells with MDP and either LPS or peptidoglycan (PGN) resulted in an apparent synergistic effect on tumor necrosis factor-alpha (TNF-alpha) secretion. Although incubation of cells with MDP alone produced minimal TNF-alpha, it caused significant expression of TNF-alpha mRNA. These findings suggest that the majority of TNF-alpha mRNA induced by MDP alone is not translated into protein. Furthermore, simultaneous incubation of cells with MDP and either LPS or PGN resulted in TNF-alpha mRNA expression that approximated the sum of the amounts expressed in response to MDP, LPS, and PGN individually. These findings indicate that the apparent synergistic effect of MDP on TNF-alpha production induced by either LPS or PGN is due to removal of a block in translation of the mRNA expressed in response to MDP. In subsequent studies, the effects of MDP alone and its effect on the production of TNF-alpha by LPS and PGN were determined to be independent of CD14, Toll-like receptor 2, and Toll-like receptor 4. These findings indicate that MDP acts through receptor(s) other than those primarily responsible for transducing the effects of LPS and PGN. Successful treatment of patients having mixed bacterial infections is likely to require interventions that address the mechanisms involved in responses induced by a variety of bacterial cell wall components.

Candidate genes for atopic asthma: current results from genome screens

Atopic asthma is one of the most common childhood diseases in developed countries. Asthma is characterized by reversible airway obstruction, bronchial hyper-responsiveness, and airway inflammation. Atopy in childhood is considered the strongest predisposing factor for asthma. The etiology of asthma is complex and is thought to involve the interaction of multiple genes and a variety of environmental factors such as allergens and viral and bacterial infections. To identify genes conferring susceptibility for asthma and atopy, many genome-wide screens for asthma and its associated traits have now been carried out, and genetic linkage has been consistently identified in several regions. Several independent genome-wide screens found regions of linkage with asthma on chromosomes 5, 6, 11, 12, 13, 16 and 19, identifying candidate susceptibility genes including FCER1B, the IL-4 gene cluster, TNFalpha, HLA loci and others. However, the evidence for linkage is still only suggestive for most regions. In an effort to clarify the mechanism underlying the development of asthma, further studies utilizing new technologies and data from the Human Genome Project are ongoing. It is hoped that this accumulation of data will lead to improved genetic testing and assist in the development of new drugs.

CD14 gene -159C/T polymorphism is not associated with coronary artery disease and myocardial infarction

BACKGROUND

Monocyte differentiation antigen CD14 is considered an important cell-activating mediator of inflammatory responses that may result in atherosclerosis, coronary artery disease (CAD), thrombus formation, and myocardial infarction (MI). We assessed the possibility that a C --> T nucleotide substitution polymorphism in the promoter (position -159) of the gene encoding CD14 constitutes a risk factor for CAD and MI.

METHODS

Consecutive patients with significant, angiographically documented coronary stenoses but without symptoms or signs of old or acute MI constituted the group with CAD (n = 998). Consecutive patients with angiographic examination with old or acute MI constituted the group with MI (n = 793). Subjects matched with patients for age and gender but without angiographic evidence of CAD and without symptoms or signs of MI (n = 340) and a group of healthy blood donors (n = 104) served as controls.

RESULTS

Genotype distributions of the -159C/T polymorphism were similar across the groups; CC:CT:TT was 26.9%:51.0%:22.1% in blood donors, 25.9%:52.0%:22.1% in matched control subjects, 27.4%:49.9%:22.7% in patients with CAD, and 29.2%:49.2%:21.6% in patients with MI. The lack of association persisted also after adjustment for the presence of conventional cardiovascular risk factors. In addition, no significant differences were found between genotype distributions of control subjects and selected subgroups of patients with CAD or MI.

CONCLUSION

These findings indicate that, in the sample of patients examined in this study, the -159C/T polymorphism of the CD14 gene is not related to CAD or MI.

Monocyte deactivation in severe human sepsis or following cardiopulmonary bypass

We investigated the specificity for gram-negative stimuli as well as the contribution of signal transduction pathways for leukocyte hyporesponsiveness in sepsis or following cardiopulmonary bypass (CPB). Whole blood of nine patients undergoing CPB and 25 patients with severe sepsis was stimulated ex vivo with LPS (E. coli O111:B4) or with Staphylococcus aureus Cowan strain I (SAC-I) lysate in the absence or presence of inhibitors of protein kinase C (PKC), protein-tyrosine kinase (PTK), or protein-tyrosine phosphatase (PTP). Both toxins stimulated a TNF-alpha response through PTK signaling. Although suppression of the cytokine response was similar for LPS and SAC-I after CPB, it was significantly more pronounced for SAC-I in sepsis. Inhibition of PTP failed to increase TNF-alpha upon LPS, whereas a moderate increase was observed with SAC-I. Impaired TNF-alpha responses occur in sepsis and after CPB. Although this has primarily been reported for gram-negative stimuli, our data suggest that this is even more pronounced for gram-positive stimuli in severe sepsis. Although PTK was the predominant signaling pathway, inhibition of PTP only partially restored the TNF-alpha response to SAC-I. Our results suggest that cellular mechanisms underlying monocyte deactivation are different in sepsis or following CPB and are discriminate for gram-positive and gram-negative toxins.

Augmentation of NKT and NK cell-mediated cytotoxicity by peptidoglycan monomer linked with zinc

BACKGROUND

Peptidoglycan monomer (PGM), which was originally prepared by biosynthesis from culture fluids of penicillin-treated Brevibacterium divaricatum, is an immunostimulator, the activities of which might be improved by addition of zinc (Zn) to the basic molecule.

METHODS

To test the possible cytotoxic effects of this new analogue, we analyzed the ability of PGM-Zn and PGM to change the phenotypic profile of hepatic and splenic mononuclear lymphatic cells and to affect the growth of malignant T-cell line YAC-1 and syngeneic thymocytes.

RESULTS

Pretreatment of C57BL/6 mice primarily with PGM-Zn over 6 days (10/mg/kg intraperitoneally) significantly enhanced the proportions of NK1.1high+, CD4-CD8-, CD69+, and CD3intermediate/NK1.1+/IL2R-beta+ (NKT) cells in the liver, and major histocompatibility complex class II+, CD69+, and CD8+ cells in the spleen. Both types of cells were highly cytotoxic against YAC-1 and syngeneic thymocytes, increasing the destruction of YAC-1 by 70% on addition of hepatic cells and by 30% on addition of splenic cells. Destruction of thymocytes increased by 10 and 50%, respectively.

CONCLUSION

The results point to PGM-Zn as a potent cytotoxicity-inducing agent, which also generates autoreactive NKT cells.

Bacterial peptidoglycan-induced tnf-alpha transcription is mediated through the transcription factors Egr-1, Elk-1, and NF-kappaB

Bacteria and their ubiquitous cell wall component peptidoglycan (PGN) activate the innate immune system of the host and induce the release of inflammatory molecules. TNF-alpha is one of the highest induced cytokines in macrophages stimulated with PGN; however, the regulation of tnf-alpha expression in PGN-activated cells is poorly understood. This study was done to identify some of the transcription factors that regulate the expression of the tnf-alpha gene in macrophages stimulated with PGN. Our results demonstrated that PGN-induced expression of human tnf-alpha gene is regulated by sequences proximal to -182 bp of the promoter. Mutations within the binding sites for cAMP response element, early growth response (Egr)-1, and kappaB3 significantly reduced this induction. The transcription factor c-Jun bound the cAMP response element site, Egr-1 bound the Egr-1 motif, and NF-kappaB p50 and p65 bound to the kappaB3 site on the tnf-alpha promoter. PGN rapidly induced transcription of egr-1 gene and this induction was significantly reduced by specific mutations within the serum response element-1 domain of the egr-1 promoter. PGN also induced phosphorylation and activation of Elk-1, a member of the Ets family of transcription factors. Elk-1 and serum response factor proteins bound the serum response element-1 domain on the egr-1 promoter, and PGN-induced expression of the egr-1 was inhibited by dominant-negative Elk-1. These results indicate that PGN induces activation of the transcription factors Egr-1 and Elk-1, and that PGN-induced expression of tnf-alpha is directly mediated through the transcription factors c-Jun, Egr-1, and NF-kappaB, and indirectly through the transcription factor Elk-1.

Distinct carbohydrate recognition domains of an invertebrate defense molecule recognize Gram-negative and Gram-positive bacteria

Coelomic fluid of Eisenia foetida earthworms (Oligochaeta, Annelida) contains a 42-kDa defense molecule named CCF for coelomic cytolytic factor. By binding microbial antigens, namely the O-antigen of lipopolysaccharide (LPS), beta-1,3-glucans, or N,N'-diacetylchitobiose present, respectively, on Gram-negative bacteria or yeast cell walls, CCF triggers the prophenoloxidase activating pathway. We report that CCF recognizes lysozyme-predigested Gram-positive bacteria or the peptidoglycan constituent muramyl dipeptide as well as muramic acid. To identify the pattern recognition domains of CCF, deletion mutants were tested for their ability to reconstitute the prophenoloxidase cascade in E. foetida coelomic fluid depleted of endogenous CCF in the presence of LPS, beta-1,3-glucans, N,N'-diacetylchitobiose, and muramic acid. In addition, affinity chromatography of CCF peptides was performed on immobilized beta-1,3-glucans or N,N'-diacetylchitobiose. We found that the broad specificity of CCF for pathogen-associated molecular patterns results from the presence of two distinct pattern recognition domains. One domain, which shows homology with the polysaccharide and glucanase motifs of beta-1,3-glucanases and invertebrate defense molecules located in the central part of the CCF polypeptide chain, interacts with LPS and beta-1,3-glucans. The C-terminal tryptophan-rich domain mediates interactions of CCF with N,N'-diacetylchitobiose and muramic acid. These data provide evidence for the presence of spatially distinct carbohydrate recognition domains within this invertebrate defense molecule.

Bacterial peptidoglycan binds to tubulin

A search for cellular binding proteins for peptidoglycan (PGN), a CD14- and TLR2-dependent macrophage activator from Gram-positive bacteria, using PGN-affinity chromatography and N-terminal micro-sequencing, revealed that tubulin was a major PGN-binding protein in mouse macrophages. Tubulin also co-eluted with PGN from anti-PGN vancomycin affinity column and bound to PGN coupled to agarose. Tubulin-PGN binding was preferential under the conditions that promote tubulin polymerization, required macromolecular PGN, was competitively inhibited by soluble PGN and tubulin, did not require microtubule-associated proteins, and had an affinity of 100-150 nM. By contrast, binding of tubulin to lipopolysaccharide (LPS) had 2-3 times lower affinity, faster kinetics of binding, and showed positive cooperativity. PGN enhanced tubulin polymerization in the presence of 4 M glycerol, but in the absence of glycerol, both PGN and LPS decreased microtubule polymerization. These results indicate that tubulin is a major PGN-binding protein and that PGN modulates tubulin polymerization.