Lipopolysaccharide and peptidoglycan: CD14-dependent bacterial inducers of inflammation

Brain Perivascular Macrophages Do Not Mediate Interleukin-1-Induced Sickness Behavior in Rats

Sickness behavior, characterized by on overall reduction in behavioral activity, is commonly observed after bacterial infection. Sickness behavior can also be induced by the peripheral administration of Gram-negative bacterial lipopolysaccharide (LPS) or interleukin-1beta (IL-1β), a pro-inflammatory cytokine released by LPS-activated macrophages. In addition to the microglia, the brain contains perivascular macrophages, which express the IL-1 type 1 receptor (IL-1R1). In the present study, we assessed the role of brain perivascular macrophages in mediating IL-1β-induced sickness behavior in rats. To do so, we used intracerebroventricular (icv) administration of an IL-1β-saporin conjugate, known to eliminate IL-R1-expressing brain cells, prior to systemic or central IL-1β injection. Icv IL-1β-saporin administration resulted in a reduction in brain perivascular macrophages, without altering subsequent icv or ip IL-1β-induced reductions in food intake, locomotor activity, and social interactions. In conclusion, the present work shows that icv IL-1β-saporin administration is an efficient way to target brain perivascular macrophages, and to determine whether these cells are involved in IL-1β-induced sickness behavior.

Effect of human breast milk on innate immune response: Up-regulation of bacterial pattern recognition receptors and innate cytokines in THP-1 monocytic cells

Human breast milk (HBM) contains many bioactive components that protect infants from various microorganisms. Pattern recognition receptors on phagocytic cells recognize microbial pathogens and promote the innate immune system. This study aimed to evaluate the effect of HBM on the expression of pattern recognition receptors and innate cytokines in the monocytic cell line THP-1 and the phagocytic activity of RAW264.7 macrophages. Expression levels of specific mRNAs in THP-1 cells were quantitated using reverse transcription-polymerase chain reaction. Phagocytic activity was measured by fluorescence microscopy to detect the uptake of fluorescent dye-labeled carboxylate-modified polystyrene latex beads in RAW264.7 macrophages. HBM stimulated the phagocytic activity of RAW264.7 macrophages. HBM increased mRNA expression of pattern recognition receptors, including the cluster of differentiation 14 and toll-like receptor 2 and 4, and various innate cytokines, including tumor necrosis factor α, interleukin-1β, C-X-C motif chemokine 8, and C-C motif chemokine ligand 2, in THP-1 monocytic cells. Furthermore, milk oligosaccharides in HBM, such as lacto- N-fucopentaose I, enhanced the expression of pattern recognition receptors and various innate cytokines. HBM is able to modulate the innate immune response by upregulating the expression of pattern recognition receptors and various innate cytokines in monocytes/macrophages.

Protective effect of puerarin against burn-induced heart injury in rats

The present study evaluated the potential protective effects of puerarin and its associated mechanism on burn-induced myocardial damage. A total of 40 healthy adult Wistar rats were randomly divided into four groups: i) Sham; ii) burn; iii) burn + puerarin; and iv) puerarin. Serum levels of interleukin (IL)-1β, tumor necrosis factor-α (TNF-α) and IL-6 were measured using ELISA. Myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels were determined in myocardial homogenates using a commercial assay kit. TUNEL staining and western blot analysis of cleaved and pro-caspase-3 were also performed to assess apoptosis. Activation of p38-MAPK, ERK, JNK and AKT were measured using western blot analysis. Left ventricular systolic pressure, maximum rates of increase/decrease in left ventricular pressure, creatine kinase MB activity and cardiac troponin T levels were found to be altered in the burn group 12 h after burn, which were reversed by puerarin treatment. Injection of puerarin following burn injury also reduced heart water content. Serum levels of IL-1β, TNF-α and IL-6 were significantly higher in the burn group compared with those in the sham group. Puerarin treatment reduced serum levels of IL-1β, TNF-α and IL-6, in addition to reducing MPO activity and MDA levels in myocardial tissues. Puerarin inhibited the activation of caspase-3, p38, ERK and JNK following severe burn, but elevated Akt activation following severe burn. In conclusion, puerarin improved cardiac function in rats following severe burn injury, which may be due to reduced myocardial injury, inhibition of cardiomyocyte apoptosis and reduced oxidative inflammatory stress; the MAPK and AKT signaling pathways are proposed to the underlying mechanism of these findings.

Effects of chronic cadmium exposure at food limitation-relevant levels on energy metabolism in mice

Cadmium (Cd) exposure has been implicated in the perturbation of energy metabolism and the development of cardiometabolic disease, but disease predisposition from chronic low-dose Cd exposure remains unclear. This study employed a mouse model to investigate the toxic effects of chronic Cd exposure at food limitation-relevant levels on energy metabolism and the associated liver and gut microbiome functions. Results showed that the Cd exposure induced the perturbation of energy metabolism in mice, evidenced by the alteration of various metabolites associated with the phosphorogen (adenosine triphosphate-creatine phosphate) system, tricarboxylic acid cycle, and lipid metabolism, as well as the increase of the cardiometabolic risk factor, triglyceride. Moreover, both liver and gut microbiome underwent marked structural/histological and functional alterations, prone to the onset of cardiometabolic disease following the Cd exposure. Certain hepatic transcription factors and gut microbes, specifically PPARα, SREBP1c, HNF4A and the Clostridiales_vadinBB60_group, were identified to be highly correlated with altered urinary metabolites, revealing potential toxicological interactions between the liver and gut microbiome, and energy metabolism. Our findings provide new insights into the progression of metabolic diseases induced by Cd exposure. We also propose a stricter Cd limitation in future food safety standards.

Interleukin-1 reduces food intake and body weight in rat by acting in the arcuate hypothalamus

A reduction in food intake is commonly observed after bacterial infection, a phenomenon that can be reproduced by peripheral administration of Gram-negative bacterial lipopolysaccharide (LPS) or interleukin-1beta (IL-1β), a pro-inflammatory cytokine released by LPS-activated macrophages. The arcuate nucleus of the hypothalamus (ARH) plays a major role in food intake regulation and expresses IL-1 type 1 receptor (IL-1R1) mRNA. In the present work, we tested the hypothesis that IL-1R1 expressing cells in the ARH mediate IL-1β and/or LPS-induced hypophagia in the rat. To do so, we developed an IL-1β-saporin conjugate, which eliminated IL-R1-expressing neurons in the hippocampus, and micro-injected it into the ARH prior to systemic IL-1β and LPS administration. ARH IL-1β-saporin injection resulted in loss of neuropeptide Y-containing cells and attenuated hypophagia and weight loss after intraperitoneal IL-1β, but not LPS, administration. In conclusion, the present study shows that ARH NPY-containing neurons express functional IL-1R1s that mediate peripheral IL-1β-, but not LPS-, induced hypophagia. Our present and previous findings indicate that the reduction of food intake after IL-1β and LPS are mediated by different neural pathways.

Spirochetal Lipoproteins and Immune Evasion

Spirochetes are a major threat to public health. However, the exact pathogenesis of spirochetal diseases remains unclear. Spirochetes express lipoproteins that often determine the cross talk between the host and spirochetes. Lipoproteins are pro-inflammatory, modulatory of immune responses, and enable the spirochetes to evade the immune system. In this article, we review the modulatory effects of spirochetal lipoproteins related to immune evasion. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate pathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and treatment.

Increased Serum CD14 Level Is Associated with Depletion of TNF-α in Monocytes in Migraine Patients during Interictal Period

The aim of the present study was to investigate the levels of circulating CD14 in relation to the expression of tumor necrosis factor alpha (TNF-α) in monocytes, and serum levels of TNF-α and macrophage inflammatory protein-1 (MIP-1) in migraine patients. Numerous studies revealed controversial changes in the components of the immune system during attacks and the interictal period in migraine patients. Our study included 40 migraineurs and 39 controls. The levels of TNF-α, MIP-1 and CD14 were measured in peripheral monocytes and in sera with the Enzyme-Linked Immunosorbent Assay (ELISA) method, and the monocyte expression of TNF-α was also analysed by immunostaining. Serum CD14 concentrations were higher and the expression of TNF-α in monocytes was decreased in migraineurs. The serum MIP-1 level correlated with Verbal Rating Scale (VRS); the MIP-1:CD14 ratio in monocytes correlated with Visual Analogue Scale (VAS); the MIP-1:CD14 ratio correlated with Migraine Severity (MIGSEV)-Pain scores; and serum CD14 concentration correlated with migraine duration in years. Increased serum CD14 and depletion of TNF-α in monocytes can orchestrate other components of the immune system during the interictal period.

IEIIS Meeting minireview: Chemical synthesis of peptidoglycan fragments for elucidation of the immunostimulating mechanism

Partial structures of peptidoglycan were chemically synthesized for elucidation of their precise biological activities. By using an efficient synthetic strategy, mono-, di-, tetra- and octasaccharide fragments of peptidoglycan were synthesized in good yields. The biological activity of synthetic fragments of peptidoglycan was evaluated by induction of TNF-α from human monocytes, and TLR2 and NOD2 dependencies by using transfected HEK293 cells, respectively. We revealed that TLR2 was not stimulated by the series of synthetic peptidoglycan partial structures, whereas NOD2 recognizes the partial structures containing the MDP moiety. We also synthesized potent NOD1 agonists, which showed several hundred-fold stronger activity than γ-D-glutamyl- meso-diaminopimelic acid (iE-DAP). Interaction of PGRPs with synthetic peptidoglycan fragments is also described.

Cellular activating properties and morphology of membrane-bound and purified meningococcal lipopolysaccharide

Neisseria meningitidis, the cause of epidemic meningitis and acute lethal sepsis, synthesizes surplus lipopolysaccharides (LPSs) during growth, which are released as outer membrane vesicles (OMV) or `blebs'. Meningococcal disease severity is related to plasma LPS levels. We have compared the biological activities of native outer membrane vesicles (nOMV) to those of purified Nm-LPS (Nm-LPS) and LPS-depleted OMV (dOMV) prepared from N. meningitidis. The LPS content of nOMV was determined spectrophotometrically by quantifying KDO and by silver-stained SDS-PAGE gels. The morphology of the preparations was studied by transmission electron microscopy. The Limulus amoebocyte lysate (LAL) assay was used to quantify LPS in the plasma solutions. The preparations were diluted in endotoxin-free heparin plasma to equal amounts of LPS (w/w) in the range 50—5000 pg/ml. The biological reactivity was tested by: (i) a monocyte target-assay (monocyte purity ≥ 96%); and (ii) a whole blood model, measuring the secretion of TNF-α and IL-6 induction of procoagulant activity in monocytes (PCA). In both models, nOMV induced dose-dependent cell responses (TNF-α, IL-6, PCA) similar to purified Nm-LPS, whereas dOMV induced minimal responses. However, LAL activity was significantly higher for nOMV than for purified Nm-LPS and dOMV. The cellular responses of purified Nm-LPS and nOMV were reduced (>95%) by a specific anti-CD 14-antibody.

Antagonistic effect of peptidoglycan of Streptococcus sanguinis on lipopolysaccharide of major periodontal pathogens

Streptococcus sanguinis is often found in subgingival biofilm including periodontopathogens, and is correlated with a delay in colonization by periodontopathogens. However, the effect of S. sanguinis on inflammation induced by periodontopathogens is poorly understood. Thus, this study investigated the effect of S. sanguinis peptidoglycan (PGN) on induction of TNF-α, IL-6, and IL-8 expression by lipopolysaccharide (LPS) of periodontal pathogens. LPS was extracted from Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Tannerella forsythia, and PGN was isolated from S. sanguinis. THP-1 cells, a monocytic cell-line, were cotreated with LPS of the periodontal pathogens and S. sanguinis PGN, and then the expression of inflammatory cytokines was analyzed by real-time RT-PCR. To analyze the underlying mechanism, the binding assay of the LPS to CD14 or LPS-binding protein (LBP) was performed in the presence or absence of the PGN after coating recombinant human CD14 and LBP on EIA plate. The PGN inhibited the binding of LPS to CD14 and LBP in a dose-dependent manner. Also, THP-1 cells were co-treated with the LPS in the presence of N-acetylmuramic acid and N-acetylglucosamine, as components of PGN, and the competition binding assay to CD14 and LBP was performed. N-acetylmuramic acid inhibited the induction of inflammatory cytokine expression by LPS and the binding of LPS to CD14 or LBP whereas N-acetylglucosamine did not show such effect. Collectively, the results suggest that S. sanguinis PGN inhibited the cytokine expression induced by the LPS of periodontopathogens due to the inhibition of LPS binding to LBP and CD14. N-acetylmuramic acid of PGN may play a role in inhibition of the LPS binding of periodontopathogens to CD14 and LBP.

Lipopolysaccharide challenge significantly influences lipid metabolism and proteome of white adipose tissue in growing pigs

Background

White adipose tissue is recognized as a highly active organ, which is closely related to a large number of physiological and metabolic processes besides storing triglycerides. However, little is known regarding the response of adipose tissue to acute inflammation. Therefore, in this study we employed growing pigs to investigate the changes of lipid metabolism and proteome in white adipose tissue after lipopolysaccharide (LPS) stimulation as a model for bacterial infection.

Methods

The expression of lipid metabolism and inflammation related genes was determined by quantitative real-time polymerase chain reaction. Label-free proteomics analysis was used to investigate changes of the protein profile in white adipose tissue and western blot was used to verify changes of selected adipokines.

Results

The results indicated that LPS significantly increased the expression of toll-like receptor (TLR) 2/4 pathway-related genes and pro-inflammatory factors. Lipid metabolism related genes, including acetyl-CoA carboxylase 1 (ACACA), fatty acid synthase (FASN), stearoyl-CoA desaturase (SCD), uncoupling protein 2 (UCP2), and 11 β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), were down-regulated and the lipolytic enzyme activity was decreased after LPS injection. Proteome analysis revealed 47 distinct proteins with > 2-fold changes. The down-regulation of two proteins (cAMP-dependent protein kinase type II-alpha regulatory subunit and β-tubulin) has been verified by western blot analysis. In addition, the abundance of two adipokines (adiponectin and zinc-α2-glycoprotein) was significantly increased after LPS injection.

Conclusion

In conclusion, LPS challenge can cause acute inflammation in white adipose tissue. Concurrently, lipid metabolism was significantly suppressed and the abundance of several proteins changed in white adipose tissue. The results provide new clues to understand the adipose dysfunction during inflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-015-0067-5) contains supplementary material, which is available to authorized users.

Carbonic anhydrase 2 deficiency leads to increased pyelonephritis susceptibility

Carbonic anhydrase 2 regulates acid-base homeostasis, and recent findings have indicated a correlation between cellular control of acid-base status and the innate defense of the kidney. Mice deficient in carbonic anhydrase 2 (Car2(-/-) mice) have metabolic acidosis, impaired urine acidification, and are deficient in normal intercalated cells. The objective of the present study was to evaluate the biological consequences of carbonic anhydrase 2 deficiency in a murine model of pyelonephritis. Infection susceptibility and transcription of bacterial response components in Car2(-/-) mice were compared with wild-type littermate controls. Car2(-/-) mice had increased kidney bacterial burdens along with decreased renal bacterial clearance after inoculation compared with wild-type mice. Standardization of the urine pH and serum HCO(3)(-) levels did not substantially alter kidney infection susceptibility between wild-type and Car2(-/-) mice; thus, factors other than acid-base status are responsible. Car2(-/-) mice had significantly increased neutrophil-gelatinase-associated lipocalin mRNA and protein and expression at baseline and a marked decreased ability to upregulate key bacterial response genes during pyelonephritis. Our findings provide in vivo evidence that supports a role for carbonic anhydrase 2 and intercalated cells in promoting renal bacterial clearance. Decreased carbonic anhydrase expression results in increased antimicrobial peptide production by cells other than renal intercalated cells, which is not sufficient to prevent infection after a bacterial challenge.

The Cross-Talk between Spirochetal Lipoproteins and Immunity

Spirochetal diseases such as syphilis, Lyme disease, and leptospirosis are major threats to public health. However, the immunopathogenesis of these diseases has not been fully elucidated. Spirochetes interact with the host through various structural components such as lipopolysaccharides (LPS), surface lipoproteins, and glycolipids. Although spirochetal antigens such as LPS and glycolipids may contribute to the inflammatory response during spirochetal infections, spirochetes such as Treponema pallidum and Borrelia burgdorferi lack LPS. Lipoproteins are most abundant proteins that are expressed in all spirochetes and often determine how spirochetes interact with their environment. Lipoproteins are pro-inflammatory, may regulate responses from both innate and adaptive immunity and enable the spirochetes to adhere to the host or the tick midgut or to evade the immune system. However, most of the spirochetal lipoproteins have unknown function. Herein, the immunomodulatory effects of spirochetal lipoproteins are reviewed and are grouped into two main categories: effects related to immune evasion and effects related to immune activation. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate immunopathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and to inflammatory events associated with spirochetal diseases.

Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Peptidoglycan (PGN), a component of bacterial cell wall and belonging to "Microbe-Associated Molecular Patterns" (MAMP) triggers host reactions contributing to the pathophysiology of infectious disease. Host cell responses to PGN exposure include apoptosis. Bacterial infections may result in activation of blood platelets and thrombocytopenia. The present study explored, whether HPLC-purified fractions of PGNs from Staphylococcus aureus 113 triggers apoptosis of platelets. To this end platelets were exposed to PGN fractions and annexin-V binding determined to depict cell membrane scrambling, DiOC6 fluorescence to estimate depolarization of mitochondrial potential, Fluo-3AM staining for intracellular Ca(2+) activity ([Ca(2+)](i)) and immunofluorescence to quantify protein abundance of active caspase-3. As a result, a 30 min exposure to monomeric fraction (mPGN) (≥50 ng/ml) was followed by annexin-V binding, paralleled by increase of [Ca(2+)](i), mitochondrial depolarization, caspase-3 activation and integrin α(IIb)β(3) upregulation. The annexin-V binding was significantly blunted by anti-TLR-2 antibodies, in absence of extracellular Ca(2+), and by pancaspase inhibitor zVAD-FMK (1 μM). In conclusion, PGN triggers apoptosis of platelets in activation-dependent manner, characterized by mitochondrial depolarization, caspase-3 activation and cell membrane scrambling.

Effect of bacterial peptidoglycan on erythrocyte death and adhesion to endothelial cells

Peptidoglycans, bacterial wall components, have previously been shown to trigger eryptosis, the suicidal erythrocyte death, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Phosphatidylserine exposing erythrocytes adhere to the vascular wall at least partially by interaction of erythrocytic phosphatidylserine with endothelial CXC chemokine ligand 16 (CXCL16). The present study explored whether peptidoglycan exposure fosters the adhesion of erythrocytes to human umbilical vein endothelial cells (HUVEC). To this end, HUVEC were treated for 48 h with peptidoglycan (10 μg/ml) and CXCL16 abundance determined by confocal microscopy and FACS analysis. Moreover, human erythrocytes were exposed for 48 h to peptidoglycan (10 μg/ml) and phosphatidylserine exposure estimated from binding of fluorescent annexin-V, cell volume from forward scatter in FACS analysis and erythrocyte adhesion to human umbilical vein endothelial cells (HUVEC) from trapping of labeled erythrocytes in a flow chamber. As a result, bacterial peptidoglycan exposure was followed by increased CXCL16 expression in HUVEC as well as erythrocyte shrinkage, phosphatidylserine exposure and adhesion to HUVEC under flow conditions at arterial shear rates. The adhesion was significantly attenuated but not abrogated in the presence of either, erythrocyte phosphatidylserine-coating annexin-V (5 μl/ml) or CXCL16 neutralizing antibody directed against endothelial CXCL16 (4 μg/ml). In conclusion, exposure to peptidoglycan increases endothelial CXCL16 expression and leads to eryptosis followed by phosphatidylserine- and CXCL16-mediated adhesion of eryptotic erythrocytes to vascular endothelial cells.

A facile synthesis of fully protected meso-diaminopimelic acid (DAP) and its application to the preparation of lipophilic N-acyl iE-DAP

Synthesis of beneficial protected meso-DAP 9 by cross metathesis of the Garner aldehyde-derived vinyl glycine 1b with protected allyl glycine 2 in the presence of Grubbs second-generation catalyst was performed. Preparation of lipophilic N-acyl iE-DAP as potent agonists of NOD 1-mediated immune response from 9 is described.

Intracellular inflammatory sensors for foreign invaders and substances of self-origin

In order to survive, all organisms must recognize and eliminate foreign invaders such as infectious pathogens, chemicals, ultraviolet rays, metabolites and damaged or transformed self-tissues, as well as allogenic organs in cases of transplantation. Recent research in innate immunity has elucidated that there are versatile inflammatory sensors on spatiotemporal 'sentry duty' that recognize substances derived from both 'nonself' and 'self', e.g., Toll-like receptors, retinoic acid-inducible gene-I-like receptors, nucleotide oligomerization domain-like receptors and c-type lectin receptors. Having acquired high-level functions through the development of multiple molecules, higher organisms have established both extracellular and intracellular sensors that can discriminate danger-associated molecular patterns from promiscuous, but biologically similar, molecular patterns. In addition, 'loss-of-function' or 'gain-of-function' mutations in these inflammatory sensors have been linked (at least in part) with the etiology and severity of autoimmune diseases, autoinflammatory diseases and immunocompromised diseases in humans. Further studies focusing on the role of these inflammatory sensors in the development of immune disorders would highlight new avenues for the development of novel diagnostic and therapeutic applications with regard to these diseases.

DPP-4 (CD26) inhibitor alogliptin inhibits atherosclerosis in diabetic apolipoprotein E-deficient mice

Dipeptidyl peptidase-4 (DPP-4 or CD26) inhibitors, a new class of antidiabetic compounds, are effective in the treatment of hyperglycemia. Because atherosclerosis-related cardiovascular diseases are the major complications of diabetes, it is important to determine the effect of DPP-4 inhibitors on atherosclerosis. In this study, nondiabetic and diabetic apolipoprotein E-deficient mice were treated with DPP-4 inhibitor alogliptin for 24 weeks, and atherosclerotic lesions in aortic origins were examined. Results showed that diabetes significantly increased atherosclerotic lesions, but alogliptin treatment reduced atherosclerotic lesions in diabetic mice. Metabolic studies showed that diabetes increased plasma glucose and that alogliptin treatment reduced glucose. Furthermore, immunohistochemistry study showed that diabetes increased interleukin-6 (IL-6) and IL-1β protein expression in atherosclerotic plaques, but alogliptin treatment attenuated diabetes-augmented IL-6 and IL-1β expression. In consistence with the observations from the mouse models, our in vitro studies showed that alogliptin-inhibited toll-like receptor 4 (TLR-4)-mediated upregulation of IL-6, IL-1β, and other proinflammatory cytokines by mononuclear cells. Taken together, our findings showed that alogliptin-inhibited atherosclerosis in diabetic apolipoprotein E-deficient mice and that the actions of alogliptin on both glucose and inflammation may contribute to the inhibition.

PAMPs, PRRs and the genomics of gram negative bacterial recognition in fish

Understanding the mechanisms that underpin pathogen recognition and subsequent orchestration of the immune response in fish is an area of significant importance for both basic research and management of health in aquaculture. In recent years much attention has been given to the identification of pattern recognition receptors (PRRs) in fish, however, characterisation of interactions with specific pathogen-associated molecular patterns (PAMPs) is still incomplete. Microarray studies have significantly contributed to functional studies and early descriptions of PAMP-PRR driven activation of specific response cassettes in the genome have been obtained although much is left to be done. In this review we will address gram negative (G-negative) bacterial recognition in fish addressing contributing factors such as structure-function relationships between G-negative PAMPs, current knowledge of fish PRRs and the input achieved by microarray-based studies ranging from in vivo infection studies to directed in vitro PAMP-cell studies. Finally we revisit the endotoxic recognition paradigm in fish and suggest a series of future perspectives that could contribute toward the further elucidation of G-negative bacterial recognition across the highly diverse group of vertebrates that encompass the fishes.

Therapeutic targeting of innate immunity with Toll-like receptor 4 (TLR4) antagonists

Early recognition of invading bacteria by the innate immune system has a crucial function in antibacterial defense by triggering inflammatory responses that prevent the spread of infection and suppress bacterial growth. Toll-like receptor 4 (TLR4), the innate immunity receptor of bacterial endotoxins, plays a pivotal role in the induction of inflammatory responses. TLR4 activation by bacterial lipopolysaccharide (LPS) is achieved by the coordinate and sequential action of three other proteins, LBP, CD14 and MD-2 receptors, that bind lipopolysaccharide (LPS) and present it to TLR4 by forming the activated (TLR4-MD-2-LPS)(2) complex. Small molecules active in modulating the TLR4 activation process have great pharmacological interest as vaccine adjuvants, immunotherapeutics or antisepsis and anti-inflammatory agents. In this review we present natural and synthetic molecules active in inhibiting TLR4-mediated LPS signalling in humans and their therapeutic potential. New pharmacological applications of TLR4 antagonists will be also presented related to the recently discovered role of TLR4 in the insurgence and progression of neuropathic pain and sterile inflammations.

Preterm and term neonates transplacentally acquire IgG antibodies specific to LPS from Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa

High incidences of Gram-negative bacteria are found in neonatal nosocomial infections. Our aim was to investigate placental transmission of immunoglobulin G (IgG) reactive with lipopolysaccharide from Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli O111, O6 and O26. The total and lipopolysaccharide-specific IgM and IgG were determined in 11 maternal/umbilical-cord sera aged ≤33 weeks (GI); 21 aged >33 and <37 weeks (GII); and 32 term newborns (GIII). The total and lipopolysaccharide-specific IgM concentrations were equivalent in maternal sera. The total IgG concentrations were equivalent in maternal and newborn sera, with the exception of GIII newborns as compared with their mothers (P<0.0001) and with neonates from GI and GII (P<0.05). Lipopolysaccharide-specific IgG concentrations were lower in GI neonates than in their mothers (P<0.01) and lower in GII (P<0.05). Lower lipopolysaccharide-specific IgG levels were observed among neonates only for O111 in GI (P<0.05) and for O26 and Pseudomonas in GII, both as compared with GIII (P<0.05). The anti-lipopolysaccharide IgG transfer ratios were lower in GI (except for O26) and in GII (except for Klebsiella and O111) as compared with GIII (P<0.05). Our results suggest that the greater susceptibility to infections in preterm infants is influenced (besides the humoral response) by factors intrinsic and extrinsic to the condition of prematurity.

Involvement of nitric oxide in lipopolysaccharide induced anorexia

Treatment with the bacterial endotoxin lipopolysaccharide (LPS) is a commonly used model to induce disease-related anorexia. Following LPS treatment inducible nitric oxide synthase (iNOS) is expressed in the hypothalamic arcuate nucleus (ARC), where nitric oxide (NO) inhibits orexigenic neurons. Intracellular STAT signaling is triggered by inflammatory stimuli and has been linked to the transcriptional regulation of iNOS. We evaluated whether pharmacological blockade of iNOS by the specific inhibitor 1400W attenuates LPS-induced anorexia. Furthermore, we hypothesized that the tolerance to the anorectic effect occurring after repeated LPS treatment is paralleled by a blunted STAT3 phosphorylation in the ARC. Rats treated with a subcutaneous injection of 1400W (10 mg/kg) showed an attenuated anorectic LPS response relative to control rats receiving only LPS (100 µg/kg; i.p.). Similarly, iNOS blockade attenuated LPS-induced adipsia, hyperthermia, inactivity and the concomitant drop in energy expenditure. While single LPS treatment increased STAT3 phosphorylation in the ARC, rats treated repeatedly with LPS showed no anorectic response and also no STAT3 phosphorylation in the ARC after the second and third LPS injections, respectively. Hence, pSTAT3 signaling in the ARC might be part of the intracellular cascades translating pro-inflammatory stimuli into suppression of food intake. The current findings substantiate a role of iNOS dependent NO formation in disease-related anorexia.

TNF-alpha upregulates the A2B adenosine receptor gene: The role of NAD(P)H oxidase 4

Proliferation of vascular smooth muscle cells (VSMC), oxidative stress, and elevated inflammatory cytokines are some of the components that contribute to plaque formation in the vasculature. The cytokine tumor necrosis factor-alpha (TNF-alpha) is released during vascular injury, and contributes to lesion formation also by affecting VSMC proliferation. Recently, an A(2B) adenosine receptor (A(2B)AR) knockout mouse illustrated that this receptor is a tissue protector, in that it inhibits VSMC proliferation and attenuates the inflammatory response following injury, including the release of TNF-alpha. Here, we show a regulatory loop by which TNF-alpha upregulates the A(2B)AR in VSMC in vitro and in vivo. The effect of this cytokine is mimicked by its known downstream target, NAD(P)H oxidase 4 (Nox4). Nox4 upregulates the A(2B)AR, and Nox inhibitors dampen the effect of TNF-alpha. Hence, our study is the first to show that signaling associated with Nox4 is also able to upregulate the tissue protecting A(2B)AR.

TLR2 - promiscuous or specific? A critical re-evaluation of a receptor expressing apparent broad specificity

Of all pattern recognition receptors (PRR) in innate immunity, Toll-like receptor 2 (TLR2) recognizes the structurally broadest range of different bacterial compounds known as pathogen-associated molecular patterns (PAMPs). TLR2 agonists identified so far are lipopolysaccharides (LPSs) from different bacterial strains, lipoproteins, (synthetic) lipopeptides, lipoarabinomannans, lipomannans, glycosylphosphatidylinositol, lipoteichoic acids (LTA), various proteins including lipoproteins and glycoproteins, zymosan, and peptidoglycan (PG). Because these molecules are structurally diverse, it seems unlikely that TLR2 has the capability to react with all agonists to the same degree. The aim of this review is to identify and describe well-defined structure-function relationships for TLR2. Because of its biomedical importance and because its genetics and biochemistry are presently most completely known among all Gram-positive bacteria, we have chosen Staphylococcus aureus as a focus. Our data together with those reported by other groups reveal that only lipoproteins/lipopeptides are sensed at physiologically concentrations by TLR2 at picomolar levels. This finding implies that the activity of all other putative bacterial compounds so far reported as TLR2 agonists was most likely due to contaminating highly active natural lipoproteins and/or lipopeptides.

Peptidoglycan-mediated IL-8 expression in human alveolar type II epithelial cells requires lipid raft formation and MAPK activation

Staphylococcus aureus, a major sepsis-causing Gram-positive bacterium, invades pulmonary epithelial cells and causes lung diseases. In the lung, alveolar type II epithelial cells play an important role in innate immunity by secreting chemokines and antimicrobial peptides upon bacterial infection whereas type I cells mainly function in gas-exchange. In this study, we investigated the ability of S. aureus peptidoglycan (PGN) to induce expression of a chemokine, IL-8, in a human alveolar type II epithelial cell line, A549. PGN induces IL-8 mRNA and protein expression in a dose- and time-dependent manner. Supplementation of soluble CD14 further enhanced the PGN-induced IL-8 expression. Interestingly, PGN-induced IL-8 expression was inhibited by nystatin, a specific inhibitor for lipid rafts, but not by chlorpromazine, a specific inhibitor for clathrin-coated pits. Furthermore, PGN-induced IL-8 expression was attenuated by inhibitors for MAP kinases such as ERK, p38 kinase, and JNK/SAPK, whereas no inhibitory effect was observed by inhibitors for reactive oxygen species or protein kinase C. Electrophoretic mobility shift assay demonstrates that PGN increased the DNA binding of the transcription factors, AP-1 and NF-kappaB while minimally, NF-IL6, all of which are involved in the transcription of IL-8. Taken together, these results suggest that PGN induces IL-8 expression in a CD14-enhanced manner in human alveolar type II epithelial cells, through the formation of lipid rafts and the activation of MAP kinases, which ultimately leads to activation of AP-1, NF-kappaB, and NF-IL6.

Signals generating anorexia during acute illness

Anorexia is part of the body's acute-phase response to illness. Microbial products such as lipopolysaccharides (LPS), which are also commonly used to model acute illness, trigger the acute-phase response and cause anorexia mainly through pro-inflammatory cytokines. LPS stimulate cytokine production through the cell-surface structural molecule CD14 and toll-like receptor-4. Cytokines ultimately change neural activity in brain areas controlling food intake and energy balance. The blood-brain barrier endothelial cells (BBB EC) are an important site of cytokine action in this context. BBB EC and perivascular cells (microglia and macrophages) form a complex regulatory interface that modulates neuronal activity by the release of messengers (e.g. PG, NO) in response to peripheral challenges. Serotonergic neurons originating in the raphe nuclei and glucagon-like peptide-1-expressing neurons in the hindbrain may be among the targets of these messengers, because serotonin (5-HT), acting through the 5-HT2C receptor, and glucagon-like peptide-1 have recently emerged as neurochemical mediators of LPS anorexia. The central melanocortin system, which is a downstream target of serotonergic neurons, also appears to be involved in mediation of LPS anorexia. Interestingly, LPS also reduce orexin expression and the activity of orexin neurons in the lateral hypothalamic area of fasted mice. As the eating-stimulatory properties of orexin are apparently related to arousal, the inhibitory effect of LPS on orexin neurons might be involved in LPS-induced inactivity and anorexia. In summary, the immune signalling pathways of LPS-induced, and presumably acute illness-induced, anorexia converge on central neural signalling systems that control food intake and energy balance in healthy individuals.

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.

Thrombospondin-1 promotes cellular adherence of gram-positive pathogens via recognition of peptidoglycan

Thrombospondin-1 (TSP1) is a matricellular glycoprotein that has key roles in interactions between human cells and components of the extracellular matrix. Here we report a novel role for the lectin TSP1 in pathogen-host interactions. Binding assays and flow cytometric analysis demonstrate that Streptococcus pneumoniae and other gram-positive pathogens including S. pyogenes, Staphylococcus aureus, and Listeria monocytogenes interact specifically with human TSP1. We also show for the first time that host cell-bound TSP1 promotes adherence of gram-positive pathogens to human epithelial and endothelial cell lines. Pretreatment of bacteria with sodium periodate but not Pronase E substantially reduced TSP1-mediated bacterial adherence to host cells, suggesting that a glycoconjugate on the bacterial cell surface functions as the receptor for TSP1. Lipoteichoic acids did not affect TSP1-mediated adherence of S. pneumoniae to host cells. In contrast, attachment of S. pneumoniae and other gram-positive pathogens to host cells via TSP1 was blocked by soluble peptidoglycan, indicating recognition of bacterial peptidoglycan by TSP1. In conclusion, our results demonstrate that recognition of gram-positive pathogens by TSP1 promotes bacterial colonization of host tissue cells. In this scenario, peptidoglycan functions as adhesin and TSP1 acts as a molecular bridge linking gram-positive bacteria with receptors on the host cell.

α1-Antitrypsin regulates CD14 expression and soluble CD14 levels in human monocytes in vitro

The recognition of bacterial lipopolysaccharide (LPS) is principally mediated by either membrane-bound or soluble form of the glycoprotein CD14 and CD14-associated signal transducer, toll-like receptor 4 (TLR4). Recent findings indicate that the serine protease inhibitor, alpha1-antitrypsin (AAT), may not only afford protection against proteolytic injury, but may also neutralize microbial activities and affect regulation of innate immunity. We postulated that AAT affects monocyte responses to LPS by regulating CD14 expression and soluble CD14 release. Here we show that a short-term (up to 2h) monocyte exposure to AAT alone or in combination with LPS leads to a remarkable induction of CD14 levels. In parallel, a short-term (2h) cell exposure to AAT/LPS significantly enhances LPS-induced NF kappaB (p50 and p65) activation in conjunction with increased TNFalpha, IL-1 beta and IL-8 release. In contrast, longer term incubation (18 h) of monocytes with combined AAT/LPS results in a significant reduction in expression of both CD14 and TLR4, inhibition of LPS-induced TNFalpha, IL-1 beta and IL-8 mRNA and protein expression. These findings provide evidence that AAT is an important regulator of CD14 expression and release in monocytes and suggest that AAT may be involved in LPS neutralization and prevention of over-activation of monocytes in vivo.

Modification of the structure of peptidoglycan is a strategy to avoid detection by nucleotide-binding oligomerization domain protein 1

Nucleotide-binding oligomerization domain (NOD) protein 1 (NOD1) and NOD2 are pathogen recognition receptors that sense breakdown products of peptidoglycan (PGN) (muropeptides). It is shown that a number of these muropeptides can induce tumor necrosis factor alpha (TNF-alpha) gene expression without significant TNF-alpha translation. This translation block is lifted when the muropeptides are coincubated with lipopolysaccharide (LPS), thereby accounting for an apparently synergistic effect of the muropeptides with LPS on TNF-alpha protein production. The compounds that induced synergistic effects were also able to activate NF-kappaB in a NOD1- or NOD2-dependent manner, implicating these proteins in synergistic TNF-alpha secretion. It was found that a diaminopimelic acid (DAP)-containing muramyl tetrapeptide could activate NF-kappaB in a NOD1-dependent manner, demonstrating that an exposed DAP is not essential for NOD1 sensing. The activity was lost when the alpha-carboxylic acid of iso-glutamic acid was modified as an amide. However, agonists of NOD2, such as muramyl dipeptide and lysine-containing muramyl tripeptides, were not affected by amidation of the alpha-carboxylic acid of iso-glutamic acid. Many pathogens modify the alpha-carboxylic acid of iso-glutamic acid of PGN, and thus it appears this is a strategy to avoid recognition by the host innate immune system. This type of immune evasion is in particular relevant for NOD1.

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.

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.

Synthesis and proinflammatory properties of muramyl tripeptides containing lysine and diaminopimelic acid moieties

The unusual amino acid diaminopimelic acid (DAP) was prepared by cross metathesis of appropriately protected vinyl glycine and allyl glycine derivatives. Catalytic hydrogenation of the cross-coupling product resulted in reduction of the double bond and the removal of protecting groups. The resulting compounds were appropriately protected for the polymer-supported and solution-phase synthesis of muramyl tripeptides 2 and 3, which differ in the amidation of the alpha-carboxylic acids of the isoglutamine and DAP moieties. Muramyl dipeptide (1, MDP), the DAP-containing muramyl tripeptide 3, and the lysine-containing muramyl tripeptides 4 and 5 induced TNF-alpha gene expression without TNF-alpha protein production in a human monocytic cell line. The observed block in translation could be removed by co-incubation with LPS, resulting in an apparent synergistic effect. Compound 2 did not induce TNF-alpha gene expression, neither did it exhibit a synergistic effect with LPS; this indicates that amidation of the alpha-carboxylic acids of the isoglutamine and DAP moieties results in a loss of biological activity. It is proposed that amidation of alpha-carboxylic acids is a strategy that may be used by pathogens to avoid detection by the innate immune system. Furthermore, the pattern recognition receptors Nod1 and Nod2 have been implicated in the possible induction of a synergistic effect of muropeptides with LPS.

Synthesis of peptidoglycan fragments and evaluation of their biological activity

The peptidoglycan (PG) bacterial cell wall glycoconjugate has been well known as a strong immunopotentiator. Partial structures of PG were chemically synthesized for elucidation of precise biological activities. Effective construction of distinct repeating glycans of PG was accomplished by the coupling of a key disaccharide glucosaminyl-beta(1-4)-muramic acid unit. Stereoselective glycosylation of disaccharide units was achieved by neighboring group participation of the N-Troc (Troc = 2,2,2-trichloroethoxycarbonyl) group and appropriate reactivity of N-Troc-glucosaminyl trichloroacetimidate. By using an efficient synthetic strategy, mono-, di-, tetra- and octasaccharide fragments of PG were synthesized in high yields. The biological activity of synthetic fragments of PG was evaluated by induction of tumor necrosis factor-alpha (TNF-alpha) from human monocytes, and toll-like receptor 2 (TLR2) and Nod2 dependencies by using transfected HEK293 cells, respectively. Here we reveal that TLR2 was not stimulated by the series of synthetic PG partial structures, whereas Nod2 recognizes the partial structures containing the MDP moiety.

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.

The complete genome sequence of Chromobacterium violaceum reveals remarkable and exploitable bacterial adaptability

Chromobacterium violaceum is one of millions of species of free-living microorganisms that populate the soil and water in the extant areas of tropical biodiversity around the world. Its complete genome sequence reveals (i) extensive alternative pathways for energy generation, (ii) approximately 500 ORFs for transport-related proteins, (iii) complex and extensive systems for stress adaptation and motility, and (iv) widespread utilization of quorum sensing for control of inducible systems, all of which underpin the versatility and adaptability of the organism. The genome also contains extensive but incomplete arrays of ORFs coding for proteins associated with mammalian pathogenicity, possibly involved in the occasional but often fatal cases of human C. violaceum infection. There is, in addition, a series of previously unknown but important enzymes and secondary metabolites including paraquat-inducible proteins, drug and heavy-metal-resistance proteins, multiple chitinases, and proteins for the detoxification of xenobiotics that may have biotechnological applications.

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.

Endospores of B subtilis are pyrogenic and activate Mono Mac 6 cells: importance of the CD14 receptor

The monocytic cell line Mono Mac 6 is sensitive to pyrogens and interleukin-6 secretion is induced after exposure to pyrogens. The aim of this study is to examine the pyrogenic activity and the interleukin-6-inducing capacity of the Gram-positive B. subtilis bacteria, endospores and isolated cell wall components. Furthermore the involvement of CD14 in activation of interleukin-6 release is investigated. All test substances are pyrogenic in the rabbit pyrogen test. The test substance is incubated with monocytic cells (Mono Mac 6) for 24 h and the secreted interleukin-6 is determined in a sandwich immunoassay. B. subtilis bacteria and endospores induce interleukin-6 in a dose-dependent manner. Endospores are less potent than bacteria. Lipoteichoic acid (LTA) isolated from B. subtilis induces interleukin-6 in a dose-dependent manner, whereas muramyl dipeptide (MDP) is unable to induce interleukin-6. Lipopolysaccharides (LPS) dose-dependently induce interleukin-6 release, but the curve differs from that of LTA both in shape and offset. The interleukin-6 secretion induced by LPS, LTA and B. subtilis bacteria can be blocked by 73-85% by an antibody directed against CD14, whereas the antibody only blocks 25% of B. subtilis endospores-induced interleukin-6 release. The results might indicate that B. subtilis endospores use an additional pathway to CD14 to activate mononuclear cells.

Initiation of humoral immunity. I. The role of cytokines and hormones in the initiation of humoral immunity using T-independent and T-dependent antigens

The early events during the initiation of immune responses following the injection of T-independent (lipopolysaccharide, LPS) and T-dependent (bovine serum albumin, BSA) antigens were studied in immature male chickens. Specifically, the role of cytokines and hormones in the initiation of humoral immunity against these antigens was investigated. Both interleukin-1 (IL-1) and tumor necrosis factor (TNF-alpha) increased significantly post-LPS but not post-BSA injection. While interleukin-2 (IL-2) significantly decreased post-LPS injection, IL-2 significantly increased post-BSA injection. Furthermore, corticosterone levels significantly increased and tri-iodothyronine (T(3)) levels significantly decreased post-LPS but not post-BSA injection. In this study, the results indicate that although LPS and BSA can induce a humoral antibody response in chickens, they activate different cytokines and neuroendocrine network systems.

'Ignorance' of antigen-specific murine CD4+ and CD8+ T cells is overruled by lipopolysaccharide and leads to specific induction of IFN-gamma

Lipopolysaccharide (LPS) can activate human and murine T cells in vivo and in vitro. Here we analysed the effects of LPS on T cells with defined specificities in T-cell receptor (TCR)-transgenic systems. LPS rapidly induced high amounts of interferon (IFN)-gamma in a subpopulation of purified T cells from DO11.10 (OVA323-339/H2-Ad) and OT-1 (OVA257-264/H2-Kb) mice when coincubated with antigen-pulsed peritoneal exudate cells (PECs). LPS induced IFN-gamma in T cell cultures even when the number of antigenic major histocompatibility complex (MHC) class-I complexes was too small to stimulate the T cells. LPS, thus, overruled the unresponsiveness of the otherwise 'antigen-ignorant' T cells. The release of IFN-gamma strictly correlates with the PECs' ability to produce interleukin (IL)-12. In contrast to the induction of IFN-gamma, antigen-specific IL-2 secretion and proliferation of T cells were rather decreased in the presence of LPS. Only very few IFN-gamma-secreting natural killer (NK) cells and natural killer T (NKT) cells in the given experimental system could be detected using intracellular fluorescence-activated cell sorter (FACS) staining. Taken together, our results indicate that LPS has the potential to activate quiescent T cells and to specifically induce IFN-gamma in CD4 and CD8 T cells. This may have direct consequences for the activation of autoreactive T cells following bacterial infections.

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.

Role of lipopolysaccharide susceptibility in the innate immune response to Salmonella typhimurium infection: LPS, a primary target for recognition of Gram-negative bacteria

Lipopolysaccharide is an important recognition marker by virtue of which the innate immune system senses and reacts against Gram-negative bacteria invading the LPS susceptible host. This review deals with the factors affecting LPS susceptibility and with the role of the latter in the course and outcome of Salmonella typhimurium infection.

Non-redundant roles for interleukin-1 alpha and interleukin-1 beta in regulating human IgG2

BACKGROUND

Serum concentrations of immunoglobulin G2 (IgG2) are elevated in localized aggressive periodontitis (LAgP) patients, and secretory products of monocytes from LAgP patients enhance IgG2 responses of lymphocytes from healthy subjects. Furthermore, genes regulating production of interleukin (IL)-1 influence the risk for both aggressive periodontitis (AgP) and chronic periodontitis. These observations, and the fact that IgG2 dominates responses to carbohydrates from Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis, prompted the hypothesis that IL-1 alpha, IL-1 beta, and IL-RA may help regulate human IgG2 responses.

METHODS

Human peripheral blood leukocytes (PBL) were stimulated in culture with pokeweed mitogen (PWM); the levels of available IL-1 gene products were manipulated; and the effect on IgG2 production was monitored. Manipulations of IL-1 were accomplished by adding specific neutralizing monoclonal antibodies or recombinant IL-1RA, IL-1 alpha, or IL-1 beta.

RESULTS

Blocking the IL-1 receptor with IL-1RA or neutralizing IL-1 alpha or IL-1 beta with specific antibody dramatically suppressed IgG2 production (50% to 70%). Additionally IL-1 alpha did not compensate for neutralized IL-1 beta, and additional IL-1 beta did not compensate for neutralized IL-1 alpha, suggesting the 2 monokines have separate roles in promoting IgG2. Furthermore, combinations of anti-IL-1 alpha and anti-IL-1 beta were more inhibitory than either antibody alone, and IL-1 alpha and IL-1 beta in combination appeared to work additively in promoting IgG2. Moreover, PBL cultures from a group of LAgP patients with high IgG2 levels had elevated levels of IL-1 beta.

CONCLUSION

IL-1 alpha and IL-1 beta appear to have critical and non-redundant roles in the generation and regulation of potent IgG2 responses, which appear to be important in human responses to carbohydrate-bearing bacteria.