Molecular genetic analysis of an endotoxin nonresponder mutant cell line: a point mutation in a conserved region of MD-2 abolishes endotoxin-induced signaling

Exploration of gut microbiome and inflammation: A review on key signalling pathways

The gut microbiome, a crucial component of the human system, is a diverse collection of microbes that belong to the gut of human beings as well as other animals. These microbial communities continue to coexist harmoniously with their host organisms and perform various functions that affect the host's general health. Each person's gut microbiota has a unique makeup. The gut microbiota is well acknowledged to have a part in the local as well as systemic inflammation that underlies a number of inflammatory disorders (e.g., atherosclerosis, diabetes mellitus, obesity, and inflammatory bowel disease).The gut microbiota's metabolic products, such as short-chain fatty acids (butyrate, propionate, and acetate) inhibit inflammation by preventing immune system cells like macrophages and neutrophils from producing pro-inflammatory factors, which are triggered by the structural elements of bacteria (like lipopolysaccharide). The review's primary goal is to provide comprehensive and compiled data regarding the contribution of gut microbiota to inflammation and the associated signalling pathways.

Supramolecular assembly of micellar aggregates is the basis of low endotoxin recovery (LER) in a drug formulation that can be resolved by a whole blood assay

Lipopolysaccharide (LPS, endotoxin) is ubiquitous and represents a harmful contaminant of pharmaceutical compounds, recombinant biologicals and drug products. The pyrogen can induce severe immune responses and pathology in vitro and in vivo. Health authorities require strict control of endotoxin in parenteral drugs. However, for research and pre-clinical compound analysis, endotoxin testing is not a required quality control, which may cause potential drawbacks in the translational pipeline. Endotoxin testing is usually performed by the Limulus amebocyte lysate (LAL) assay, which is hampered by the so-called low endotoxin recovery (LER) effect when certain drug formulations are tested. A comprehensive study including structural, biophysical, and biological analyses was conducted to identify LER root cause for phosphate- and polysorbate-containing parenteral drug products. LPS in water showed extended ribbon-like aggregate structures. In placebo (formulation buffer without drug) and in drug product (drug in formulation buffer), a reaggregation of LPS into a network of interlinked micelles with hidden head group charges, and a strong reduction of the negative surface potential was observed. The non-accessibility of the LPS backbone has a direct impact leading (i) to a loss of activation of the LAL-cascade, (ii) reduced activation of the TLR4/MD-2 receptor system, and (iii) increased survival in a mouse model of endotoxemia. These data provide a structure-based explanation of the LER-underlying mechanisms. A human whole blood assay is shown to resolve LER and detect the pyrogenic activity of endotoxin with high sensitivity. This may open new test options to improve quality control in drug development and drug safety.

A comprehensive review on the dynamic role of toll-like receptors (TLRs) in frontier aquaculture research and as a promising avenue for fish disease management

Toll-like receptors (TLRs) represent a conserved group of germline-encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and play a crucial role in inducing the broadly acting innate immune response against pathogens. In recent years, the detection of 21 different TLR types in various fish species has sparked interest in exploring the potential of TLRs as targets for boosting immunity and disease resistance in fish. This comprehensive review offers the latest insights into the diverse facets of fish TLRs, highlighting their history, classification, architectural insights through 3D modelling, ligands recognition, signalling pathways, crosstalk, and expression patterns at various developmental stages. It provides an exhaustive account of the distinct TLRs induced during the invasion of specific pathogens in various fish species and delves into the disparities between fish TLRs and their mammalian counterparts, highlighting the specific contribution of TLRs to the immune response in fish. Although various facets of TLRs in some fish, shellfish, and molluscs have been described, the role of TLRs in several other aquatic organisms still remained as potential gaps. Overall, this article outlines frontier aquaculture research in advancing the knowledge of fish immune systems for the proper management of piscine maladies.

Small molecule modulators of immune pattern recognition receptors

Pattern recognition receptors (PRRs) represent a re-emerging class of therapeutic targets for vaccine adjuvants, inflammatory diseases and cancer. In this review article, we summarize exciting developments in discovery and characterization of small molecule PRR modulators, focusing on Toll-like receptors (TLRs), NOD-like receptors (NLRs) and the cGAS-STING pathway. We also highlight PRRs that are currently lacking small molecule modulators and opportunities for chemical biology and therapeutic discovery.

PCT, IL-6, and IL-10 facilitate early diagnosis and pathogen classifications in bloodstream infection

BACKGROUND

In the diagnosis of bloodstream infection (BSI), various inflammatory markers such as C-reactive protein (CRP), procalcitonin (PCT), interleukins (IL), white blood cell count (WBC), neutrophil percentage (NE%), platelet count (PLT), and erythrocyte sedimentation rate (ESR) have been extensively utilized. However, their specific roles in distinguishing BSI from local bacterial infection (LBI) and in classifying BSI pathogens remain uncertain.

METHODS

A historical cohort study was conducted, involving the enrollment of 505 patients with BSI and 102 patients with LBI. To validate the reliability of the clinical data obtained from this cohort, mouse models of BSI were utilized.

RESULTS

Our findings revealed that patients with BSI had significantly higher levels of inflammatory markers, including CRP, PCT, IL-6, IL-10, WBC, NE%, and ESR, compared to those with LBI (p < 0.05). The receiver operating characteristic (ROC) curve analysis demonstrated that CRP, PCT, IL-6, IL-10, ESR and NE% exhibited excellent diagnostic efficacy for BSI. Additionally, we observed significant differences in CRP, PCT, IL-6, and IL-10 levels between patients with BSI caused by Gram-positive bacteria (GP-BSI) and Gram-negative bacteria (GN-BSI), but no significant variations were found among specific bacterial species. Furthermore, our study also found that CRP, PCT, and IL-10 have good discriminatory ability for vancomycin-resistant Enterococcus (VRE), but they show no significant diagnostic efficacy for other multidrug-resistant organisms (MDROs) such as carbapenem-resistant Enterobacteriaceae (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA), and methicillin-resistant Staphylococcus aureus (MRSA). In our mouse model experiments, we observed a remarkable increase in PCT, IL-6, and IL-10 levels in mice with GN-BSI compared to those with GP-BSI.

CONCLUSION

Our study has confirmed that PCT, IL-6, and IL-10 are efficient biomarkers for distinguishing between BSI and LBI. Furthermore, they can be utilized to classify BSI pathogens and differentiate between VRE and vancomycin-susceptible Enterococcus. These findings are extremely valuable for clinicians as they enable timely initiation of empiric antibiotic therapies and ultimately lead to improved clinical outcomes for patients with BSI.

The Role of TLR4 in the Immunotherapy of Hepatocellular Carcinoma: Can We Teach an Old Dog New Tricks?

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and is a leading cause of cancer-related death worldwide. Immunotherapy has emerged as the mainstay treatment option for unresectable HCC. Toll-like receptor 4 (TLR4) plays a crucial role in the innate immune response by recognizing and responding primarily to bacterial lipopolysaccharides. In addition to its role in the innate immune system, TLR4 has also been implicated in adaptive immunity, including specific anti-tumor immune responses. In particular, the TLR4 signaling pathway seems to be involved in the regulation of several cancer hallmarks, such as the continuous activation of cellular pathways that promote cell division and growth, the inhibition of programmed cell death, the promotion of several invasion and metastatic mechanisms, epithelial-to-mesenchymal transition, angiogenesis, drug resistance, and epigenetic modifications. Emerging evidence further suggests that TLR4 signaling holds promise as a potential immunotherapeutic target in HCC. The aim of this review was to explore the multilayer aspects of the TLR4 signaling pathway, regarding its role in liver diseases and HCC, as well as its potential utilization as an immunotherapy target for HCC.

TLR4 is one of the receptors for Chikungunya virus envelope protein E2 and regulates virus induced pro-inflammatory responses in host macrophages

Toll like receptor 4 (TLR4), a pathogen-associated molecular pattern (PAMP) receptor, is known to exert inflammation in various cases of microbial infection, cancer and autoimmune disorders. However, any such involvement of TLR4 in Chikungunya virus (CHIKV) infection is yet to be explored. Accordingly, the role of TLR4 was investigated towards CHIKV infection and modulation of host immune responses in the current study using mice macrophage cell line RAW264.7, primary macrophage cells of different origins and in vivo mice model. The findings suggest that TLR4 inhibition using TAK-242 (a specific pharmacological inhibitor) reduces viral copy number as well as reduces the CHIKV-E2 protein level significantly using p38 and JNK-MAPK pathways. Moreover, this led to reduced expression of macrophage activation markers like CD14, CD86, MHC-II and pro-inflammatory cytokines (TNF, IL-6, MCP-1) significantly in both the mouse primary macrophages and RAW264.7 cell line, in vitro. Additionally, TAK-242-directed TLR4 inhibition demonstrated a significant reduction of percent E2-positive cells, viral titre and TNF expression in hPBMC-derived macrophages, in vitro. These observations were further validated in TLR4-knockout (KO) RAW cells. Furthermore, the interaction between CHIKV-E2 and TLR4 was demonstrated by immuno-precipitation studies, in vitro and supported by molecular docking analysis, in silico. TLR4-dependent viral entry was further validated by an anti-TLR4 antibody-mediated blocking experiment. It was noticed that TLR4 is necessary for the early events of viral infection, especially during the attachment and entry stages. Interestingly, it was also observed that TLR4 is not involved in the post-entry stages of CHIKV infection in host macrophages. The administration of TAK-242 decreased CHIKV infection significantly by reducing disease manifestations, improving survivability (around 75%) and reducing inflammation in mice model. Collectively, for the first time, this study reports TLR4 as one of the novel receptors to facilitate the attachment and entry of CHIKV in host macrophages, the TLR4-CHIKV-E2 interactions are essential for efficient viral entry and modulation of infection-induced pro-inflammatory responses in host macrophages, which might have translational implication for designing future therapeutics to regulate the CHIKV infection.

A short history of innate immunity

Innate immunity refers to the mechanisms responsible for the first line of defense against pathogens, cancer cells and toxins. The innate immune system is also responsible for the initial activation of the body's specific immune response (adaptive immunity). Innate immunity was studied and further developed in parallel with adaptive immunity beginning in the first half of the 19th century and has been gaining increasing importance to our understanding of health and disease. In the present overview, we describe the main findings and ideas that contributed to the development of innate immunity as a continually expanding branch of modern immunology. We start with the toxicological studies by Von Haller and Magendie, in the late 18th and early 19th centuries, and continue with the discoveries in invertebrate immunity that supported the discovery and characterization of lipopolysaccharide (LPS) and pattern recognition receptors that led to the development of the pattern recognition and danger theory.

Flow cytometric reporter assays provide robust functional analysis of signaling complexes

Conventional assays to probe signaling protein interactions and function involve measurement of luciferase reporter expression within the bulk cell population, with lack of control over target-protein expression level. To address this issue, we have developed a rapid and robust flow cytometric assay for analysis of signaling protein function. A fluorescent reporter and fluorescent tagging of the target protein enables simultaneous assessment of protein expression and signaling within individual cells. We have applied our technique to the analysis of variants of the lipopolysaccharide receptor Toll-like receptor 4 (TLR4) and its adapter protein MyD88, using a NF-кB-responsive promoter driving mScarlet-I expression. The assay enables exclusion of nontransfected cells and overexpressing cells that signal spontaneously. Additionally, our assay allows the identification of protein variants that fail to express. We found that the assays were highly sensitive, with cells expressing an appropriate level of GFP-MyD88 showing approximately 200-fold induction of mScarlet-I by lipopolysaccharide, and we can detect subtle protein concentration-dependent effects of mutations. Importantly, the assay is adaptable to various signaling pathways.

Selective targeting of MD2 attenuates intestinal inflammation and prevents neonatal necrotizing enterocolitis by suppressing TLR4 signaling

Neonatal necrotizing enterocolitis (NEC) is an inflammatory disease that occurs in premature infants and has a high mortality rate; however, the mechanisms behind this disease remain unclear. The TLR4 signaling pathway in intestinal epithelial cells, mediated by TLR4, is important for the activation of the inflammatory storm in NEC infants. Myeloid differentiation protein 2 (MD2) is a key auxiliary component of the TLR4 signaling pathway. In this study, MD2 was found to be significantly increased in intestinal tissues of NEC patients at the acute stage. We further confirmed that MD2 was upregulated in NEC rats. MD2 inhibitor (MI) pretreatment reduced the occurrence and severity of NEC in neonatal rats, inhibited the activation of NF-κB and the release of inflammatory molecules (TNF-α and IL-6), and reduced the severity of intestinal injury. MI pretreatment significantly reduced enterocyte apoptosis while also maintaining tight junction proteins, including occludin and claudin-1, and protecting intestinal mucosal permeability in NEC rats. In addition, an NEC in vitro model was established by stimulating IEC-6 enterocytes with LPS. MD2 overexpression in IEC-6 enterocytes significantly activated NF-κB. Further, both MD2 silencing and MI pretreatment inhibited the inflammatory response. Overexpression of MD2 increased damage to the IEC-6 monolayer cell barrier, while both MD2 silencing and MI pretreatment played a protective role. In conclusion, MD2 triggers an inflammatory response through the TLR4 signaling pathway, leading to intestinal mucosal injury in NEC. In addition, MI alleviates inflammation and reduces intestinal mucosal injury caused by the inflammatory response by blocking the TLR4-MD2/NF-κB signaling axis. These results suggest that inhibiting MD2 may be an important way to prevent NEC.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

Inflammation and Cell Death of the Innate and Adaptive Immune System during Sepsis

Sepsis is a life-threatening medical condition that occurs when the host has an uncontrolled or abnormal immune response to overwhelming infection. It is now widely accepted that sepsis occurs in two concurrent phases, which consist of an initial immune activation phase followed by a chronic immunosuppressive phase, leading to immune cell death. Depending on the severity of the disease and the pathogen involved, the hosts immune system may not fully recover, leading to ongoing complications proceeding the initial infection. As such, sepsis remains one of the leading causes of morbidity and mortality world-wide, with treatment options limited to general treatment in intensive care units (ICU). Lack of specific treatments available for sepsis is mostly due to our limited knowledge of the immuno-physiology associated with the disease. This review will provide a comprehensive overview of the mechanisms and cell types involved in eliciting infection-induced immune activation from both the innate and adaptive immune system during sepsis. In addition, the mechanisms leading to immune cell death following hyperactivation of immune cells will be explored. The evaluation and better understanding of the cellular and systemic responses leading to disease onset could eventuate into the development of much needed therapies to combat this unrelenting disease.

Cathelicidin and PMB neutralize endotoxins by multifactorial mechanisms including LPS interaction and targeting of host cell membranes

Antimicrobial peptides (AMPs) contribute to an effective protection against infections. The antibacterial function of AMPs depends on their interactions with microbial membranes and lipids, such as lipopolysaccharide (LPS; endotoxin). Hyperinflammation induced by endotoxin is a key factor in bacterial sepsis and many other human diseases. Here, we provide a comprehensive profile of peptide-mediated LPS neutralization by systematic analysis of the effects of a set of AMPs and the peptide antibiotic polymyxin B (PMB) on the physicochemistry of endotoxin, macrophage activation, and lethality in mice. Mechanistic studies revealed that the host defense peptide LL-32 and PMB each reduce LPS-mediated activation also via a direct interaction of the peptides with the host cell. As a biophysical basis, we demonstrate modifications of the structure of cholesterol-rich membrane domains and the association of glycosylphosphatidylinositol (GPI)-anchored proteins. Our discovery of a host cell-directed mechanism of immune control contributes an important aspect in the development and therapeutic use of AMPs.

Pathogenesis of Borrelia burgdorferi and Babesia microti in TLR4-Competent and TLR4-dysfunctional C3H mice

Toll‐like receptors (TLRs) are a class of membrane‐spanning proteins of host cells. TLR2 and TLR4 are displayed on the surface of macrophages, neutrophils and dendritic cells and recognise structurally conserved microbial signatures defined as Pathogen associated molecular patterns (PAMPs). C3H mice are susceptible to tick‐borne pathogens; Lyme disease causing Borrelia burgdorferi that manifests arthritis and carditis and Apicomplexan protozoan, Babesia microti (Bm) that causes significant parasitemia associated with erythrocytopenia and haemoglobinuria. B. burgdorferi lacks typical TLR4 ligand lipopolysaccharides (LPS) and Bm TLR ligand(s) remain unknown. Only Borrelia lipoproteins that signal through TLR2 are established as PAMPs of these pathogens for TLR2/TLR4. Infection of C3H mice with each pathogen individually resulted in increase in the percentage of splenic B, T and FcR+ cells while their co‐infection significantly diminished levels of these cells and caused increased B. burgdorferi burden in the specific organs. The most pronounced inflammatory arthritis was observed in co‐infected C3H/HeJ mice. Parasitemia levels and kinetics of resolution of Bm in both mice strains were not significantly different. Transfected HEK293 cells showed pronounced signalling by B. burgdorferi through TLR2 and to some extent by TLR4 while Bm and infected erythrocytes did not show any response confirming our results in mice.

An update on endotoxin neutralization strategies in Gram-negative bacterial infections

INTRODUCTION

Gram-negative bacterial infections represent still a severe problem of human health care, regarding the increase in multi-resistance against classical antibiotics and the lack of newly developed antimicrobials. For the fight against these germs, anti-infective agents must overcome and/or bind to the Gram-negative outer membrane consisting of a lipopolysaccharide (LPS, endotoxin) outer leaflet and an inner leaflet from phospholipids, with additional peripheral or integral membrane proteins (OMP's).

AREAS COVERED

The current article reviews data of existing therapeutic options and summarizes newer approaches for targeting and neutralizing endotoxins, ranging from in vitro over in vivo animal data to clinical applications by using databases such as Medline.

EXPERT OPINION

Conventional antibiotic treatment of the bacteria leads to their killing, but not necessary LPS neutralization, which may be a severe problem in particular for the systemic pathway. This is the reason why there is an increasing number of therapeutic approaches, which - besides combating whole bacteria - at the same time try to neutralize endotoxin within or outside the bacterial cells mainly responsible for the high inflammation induction in Gram-negative species.

Lipopolysaccharide Downregulates CD163 Expression to Inhibit PRRSV Infection via TLR4-NF-κB Pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) has been recognized to induce proinflammatory cytokine production and modulate the host interferon (IFN) system. Proinflammatory cytokines and type I IFNs contribute to the prevention of viral infection. Lipopolysaccharide (LPS), a specific agonist to Toll-like receptor 4 (TLR4), provokes signal transduction and activates immune response in vivo and in vitro. Here we identified LPS inhibited PRRSV infection in porcine alveolar macrophages (PAMs) and in Marc-145 cells. To investigate the possible mechanism, we found TLR4-NF-κB pathway was obviously activated in LPS-treated PAMs at the early stage of PRRSV infection. As a result, the expression of proinflammatory cytokines was strongly induced following LPS and PRRSV co-treatment. Due to the enhanced proinflammatory response, CD163 expression was significantly reduced and a disintegrin and metalloproteinase 17 was activated, which promotes the cleavage of membrane CD163. Ultimately, CD163 down-regulation led to the suppression of PRRSV replication. Our data demonstrate that LPS has an impact on PRRSV infection via inflammation response, which provides a new insight of inflammation-mediated antiviral immunity and a new strategy to control PRRSV infection.

The oxidation state of cysteine thiols on the ectodomain of TLR2 and TLR4 influences intracellular signaling

Signal transduction by the Toll-like receptors (TLRs) is a key component of innate immunity against many pathogens and also underlies a large burden of human diseases. Therefore, the mechanisms and regulation of signaling from the TLRs are of considerable interest. Here we seek to determine the molecular mechanism by which TLR2 and TLR4, members of the Toll-like receptor family, are activated by bacterial LPS, hyperoxia, and zymosan respectively. Our central hypothesis is that the oxidation state of cysteine thiols on the ectodomain of TLR2 and TLR4 are critical for pathogen-initiated intracellular signaling as well in hyperoxia. Cysteine thiols of TLR4 and its co-receptor MD2 have been shown to aid binding between the two molecules and also bacterial LPS binding to the receptor complex. We extend these findings by demonstrating the oxidation of free thiols on the ectodomain of hTLR4, after exposure to LPS or hyperoxia suggesting that the cysteines on the ectodomain of TLR4 could form intra- or intermolecular disulfide bonds. We also demonstrated blockade of intracellular signaling from TLR4 and TLR2 by thiol-modifying compounds which suggest a novel therapeutic intervention for sepsis, hyperoxia-induced cell injury and yeast infection. In these experiments CHO-3E10, HEK293 cells expressing hTLR2 or hTLR4 and mouse peritoneal macrophages cells were pretreated with cell impermeable maleimides to alkylate thiols on the extracellular domain of TLRs, cells were then exposed to LPS, hyperoxia or zymosan. In all of these models, we detected decreased intracellular signaling from TLR2 or TLR4. Furthermore, incubation with phenyl arsine oxide - which forms stable complexes with vicinal cysteine residues - prevented LPS induced HEK293/hTLR4 intracellular signaling which was reversed by DMPS. Sequence analysis of different TLRs revealed Leucine-Rich Repeat C-terminal (LRRCT) domain that contains 4 conserved cysteines. Further work is required to pinpoint the role of each cysteine in receptor dimerization, pathogen binding, hyperoxia modulation, and intracellular signaling.

Alveolar-Capillary Membrane-Related Pulmonary Cells as a Target in Endotoxin-Induced Acute Lung Injury

The main function of the lungs is oxygen transport from the atmosphere into the blood circulation, while it is necessary to keep the pulmonary tissue relatively free of pathogens. This is a difficult task because the respiratory system is constantly exposed to harmful substances entering the lungs by inhalation or via the blood stream. Individual types of lung cells are equipped with the mechanisms that maintain pulmonary homeostasis. Because of the clinical significance of acute respiratory distress syndrome (ARDS) the article refers to the physiological role of alveolar epithelial cells type I and II, endothelial cells, alveolar macrophages, and fibroblasts. However, all these cells can be damaged by lipopolysaccharide (LPS) which can reach the airspaces as the major component of the outer membrane of Gram-negative bacteria, and lead to local and systemic inflammation and toxicity. We also highlight a negative effect of LPS on lung cells related to alveolar-capillary barrier and their response to LPS exposure. Additionally, we describe the molecular mechanism of LPS signal transduction pathway in lung cells.

Histamine causes influx via T-type voltage-gated calcium channels in an enterochromaffin tumor cell line: potential therapeutic target in adverse food reactions

The P-STS human ileal neuroendocrine tumor cells, as a model for gut enterochromaffin cells, are strongly and synergistically activated by histamine plus acetylcholine (ACh), presumably via histamine 4 receptors, and weakly activated by histamine alone. Sensing these signals, enterochromaffin cells could participate in intestinal intolerance or allergic reactions to food constituents associated with elevated histamine levels. In this study we aimed to analyze the underlying molecular mechanisms. Inhibition by mepyramine and mibefradil indicated that histamine alone caused a rise in intracellular calcium concentration ([Ca²⁺]_i) via histamine 1 receptors involving T-type voltage-gated calcium channels (VGCCs). Sensitivity to histamine was enhanced by pretreatment with the inflammatory cytokine tumor necrosis factor-α (TNF-α). In accordance with the relief it offers some inflammatory bowel disease patients, otilonium bromide, a gut-impermeable inhibitor of T-type (and L-type) VGCCs and muscarinic ACh receptors, efficiently inhibited the [Ca²⁺]_i responses induced by histamine plus ACh or by histamine alone in P-STS cells. It will take clinical studies to show whether otilonium bromide has promise for the treatment of adverse food reactions. The cells did not react to the nutrient constituents glutamate, capsaicin, cinnamaldehyde, or amylase-trypsin inhibitors and the transient receptor potential channel vanilloid 4 agonist GSK-1016790A. The bacterial product butyrate evoked a rise in [Ca²⁺]_i only when added together with ACh. Lipopolysaccharide had no effect on [Ca²⁺]_i despite the presence of Toll-like receptor 4 protein. Our results indicate that inflammatory conditions with elevated levels of TNF-α might enhance histamine-induced serotonin release from intestinal neuroendocrine cells. NEW & NOTEWORTHY We show that histamine synergistically enhances the intracellular calcium response to the physiological agonist acetylcholine in human ileal enterochromaffin tumor cells. This synergistic activation and cell activation by histamine alone largely depend on T-type voltage-gated calcium channels and are inhibited by the antispasmodic otilonium bromide. The cells showed no response to wheat amylase-trypsin inhibitors, suggesting that enterochromaffin cells are not directly involved in nongluten wheat sensitivity.

Mass Spectrometry-based Structural Analysis and Systems Immunoproteomics Strategies for Deciphering the Host Response to Endotoxin

One cause of sepsis is systemic maladaptive immune response of the host to bacteria and specifically, to Gram-negative bacterial outer-membrane glycolipid lipopolysaccharide (LPS). On the host myeloid cell surface, proinflammatory LPS activates the innate immune system via Toll-like receptor-4/myeloid differentiation factor-2 complex. Intracellularly, LPS is also sensed by the noncanonical inflammasome through caspase-11 in mice and 4/5 in humans. The minimal functional determinant for innate immune activation is the membrane anchor of LPS called lipid A. Even subtle modifications to the lipid A scaffold can enable, diminish, or abolish immune activation. Bacteria are known to modify their LPS structure during environmental stress and infection of hosts to alter cellular immune phenotypes. In this review, we describe how mass spectrometry-based structural analysis of endotoxin helped uncover major determinations of molecular pathogenesis. Through characterization of LPS modifications, we now better understand resistance to antibiotics and cationic antimicrobial peptides, as well as how the environment impacts overall endotoxin structure. In addition, mass spectrometry-based systems immunoproteomics approaches can assist in elucidating the immune response against LPS. Many regulatory proteins have been characterized through proteomics and global/targeted analysis of protein modifications, enabling the discovery and characterization of novel endotoxin-mediated protein translational modifications.

The Role of Endotoxin in the Setting of Cardiorenal Syndrome Type 5

Lipopolysaccharide or endotoxin, the major cell wall component of gram-negative bacteria, plays a pivotal role in the pathogenesis of sepsis. It is able to activate the host defense system through the interaction with Toll-like receptor 4, thus triggering pro-inflammatory mechanisms. When the production of inflammatory mediators becomes uncontrolled and excessive, septic shock develops with multiple organ dysfunction, such as myocardial and renal impairment, which are hallmarks of cardiorenal syndrome type 5. In this review, we will analyze the role of endotoxin in the pathogenesis of sepsis, its effects on cardiac and renal interactions in the setting of cardiorenal syndrome type 5 and the possible use of extracorporeal therapies in this clinical condition.

Comparative genomic analysis of innate immunity reveals novel and conserved components in crustacean food crop species

BACKGROUND

Growing global demands for crustacean food crop species have driven large investments in aquaculture research worldwide. However, large-scale production is susceptible to pathogen-mediated destruction particularly in developing economies. Thus, a thorough understanding of the immune system components of food crop species is imperative for research to combat pathogens.

RESULTS

Through a comparative genomics approach utilising extant data from 55 species, we describe the innate immune system of the class Malacostraca, which includes all food crop species. We identify 7407 malacostracan genes from 39 gene families implicated in different aspects of host defence and demonstrate dynamic evolution of innate immunity components within this group. Malacostracans have achieved flexibility in recognising infectious agents through divergent evolution and expansion of pathogen recognition receptors genes. Antiviral RNAi, Toll and JAK-STAT signal transduction pathways have remained conserved within Malacostraca, although the Imd pathway appears to lack several key components. Immune effectors such as the antimicrobial peptides (AMPs) have unique evolutionary profiles, with many malacostracan AMPs not found in other arthropods. Lastly, we describe four putative novel immune gene families, potentially representing important evolutionary novelties of the malacostracan immune system.

CONCLUSION

Our analyses across the broader Malacostraca have allowed us to not only draw analogies with other arthropods but also to identify evolutionary novelties in immune modulation components and form strong hypotheses as to when key pathways have evolved or diverged. This will serve as a key resource for future immunology research in crustacean food crops.

Identification of a novel transcript of human MD2 gene

Myeloid differentiation protein 2 (MD2) regulates bacterial lipopolysaccharide (LPS) triggered anti-bacterial immune response as a broker between LPS and Toll-like receptor 4 (TLR4). In this study, we identified a novel naturally occurring spliceosome of human MD2, termed as MD2-T3. This transcript lacked two exons of MD2 gene. By protein structure analysis and literature review, we predicted that MD2-T3 isoform might execute regulatory biological effects such as limiting LPS-triggered TLR4 signaling.

Ligand-dependent Toll-like receptor 4 (TLR4)-oligomerization is directly linked with TLR4-signaling

Toll-like receptor 4 (TLR4) and MD-2 recognize lipid A, the active moiety of microbial lipopolysaccharide (LPS). Little is known about mechanisms for LPS recognition by TLR4/MD-2. We here showed, by using in vitro transfectants, ligand-induced TLR4-oligomerization, which required both membrane CD14 and MD-2. We previously reported that lipid IVa, a lipid A precursor, is agonistic on mouse TLR4/MD-2 but antagonistic on human TLR4/MD-2 and chimeric mouse TLR4/human MD-2. Lipid IVa triggered oligomerization of mouse TLR4/MD-2 but not human TLR4/MD-2 or chimeric mouse TLR4/human MD-2. Further, lipid IVa inhibited lipid A-dependent oligomerization of chimeric mouse TLR4/human MD-2. These results demonstrate that ligand-induced TLR4-oligomerization is directly linked with TLR4-signaling and suggest that MD-2 has an important role in regulating TLR4-oligomerization.

Invited review: Tolerance to microbial TLR ligands: molecular mechanisms and relevance to disease

Many host cell types, including endothelial and epithelial cells, neutrophils, monocytes, natural killer cells, dendritic cells and macrophages, initiate the first line of defense against infection by sensing conserved microbial structures through Toll-like receptors (TLRs). Recognition of microbial ligands by TLRs induces their oligomerization and triggers intracellular signaling pathways, leading to production of pro- and anti-inflammatory cytokines. Dysregulation of the fine molecular mechanisms that tightly control TLR signaling may lead to hyperactivation of host cells by microbial products and septic shock. A prior exposure to bacterial products such as lipopolysaccharide (LPS) may result in a transient state of refractoriness to subsequent challenge that has been referred to as `tolerance'. Tolerance has been postulated as a protective mechanism limiting excessive inflammation and preventing septic shock. However, tolerance may compromise the host's ability to counteract subsequent bacterial challenge since many septic patients exhibit an increased incidence of recurrent bacterial infection and suppressed monocyte responsiveness to LPS, closely resembling the tolerant phenotype. Thus, by studying mechanisms of microbial tolerance, we may gain insights into how normal regulatory mechanisms are dysregulated, leading ultimately to microbial hyporesponsivess and life-threatening disease. In this review, we present current theories of the molecular mechanisms that underlie induction and maintenance of `microbial tolerance', and discuss the possible relevance of tolerance to several infectious and non-infectious diseases.

Conserved mechanisms of signal transduction by Toll and Toll-like receptors

In recent years, considerable progress has been made towards understanding the mechanism by which endotoxin is detected by the cells of the immune system. Lipopolysaccharides are extracted in a soluble form by the serum LPS binding protein and then transferred sequentially to the extrinsic membrane protein CD14 and the co-receptor complex TLR4/MD-2. Our modelling studies suggest that acyl chains of lipid A are buried within the hydrophobic core of MD-2 and this induces crosslinking of the two TLR4/MD-2 complexes, an event that is required to trigger signal transduction. We also propose that, by analogy with the Drosophila Toll receptor, the mechanism of signal transduction is likely to be complex and to involve concerted protein conformational changes. In particular, we propose that receptor—receptor interactions mediated by juxtamembrane sequences play a critical role.

Essential role of MD-2 in B-cell responses to lipopolysaccharide and Toll-like receptor 4 distribution

Toll-like receptor 4 (TLR4) mediates lipopolysaccharide (LPS) signaling in a variety of cell types. MD-2 is associated with the extracellular domain of TLR4 and augments TLR4-dependent LPS responses in vitro. Moreover, mice lacking MD-2 (MD-2— /—) do not respond to LPS, survive endotoxin shock, and are susceptible to Salmonella typhimurium infection. Here, we further show that B cells lacking MD-2 do not up-regulate CD23 in response to LPS. TLR4 predominantly resides in the Golgi apparatus without MD-2. MD-2 is essential for LPS responses in vivo.

Endotoxin: physical requirements for cell activation

Lipopolysaccharide (LPS) is the eminent lipid component of the outer leaflet of the outer membrane of Gram-negative bacteria and the major initiator of innate immune response to bacterial infection. Below the critical micellar concentration (CMC), LPS is exclusively present as a monomer. Above this concentration, aggregates are formed. Increasing the concentration beyond the CMC leads to an increase in aggregate concentration, whereas the concentration of monomers remains constant or even decreases. The question how LPS activates immune cells and whether the aggregate or the monomer is the biologically active unit has been and still is controversial. To prepare clearly defined monomeric solutions, we utilized a dialysis set-up consisting of a donor and an acceptor chamber, separated by a dialysis diaphragm with a cut-off of 5 kDa, thus allowing only monomers to pass. Human mononuclear cells (MNCs) were then stimulated with equal concentrations of aggregates and monomers, respectively, of deep rough mutant LPS from Escherichia coli strain F515 (Re LPS) and TNF-α release was determined. In contrast to earlier and very recent work of others, we started with a preparation of aggregate-suspensions and pure monomer-solutions and show that monomers are significantly less active than aggregates in the absence and presence of serum proteins at identical concentrations. In our model, we propose that LPS aggregates are detected by membrane-associated LBP and intercalated into the cell membrane to bring LPS into close proximity to signaling proteins in the membrane, thus finally leading to cell activation. To support this model, we present data showing that LBP is indeed present in or at the cell membrane of human macrophages.

The role of membrane-bound LBP, endotoxin aggregates, and the MaxiK channel in LPS-induced cell activation

We have previously shown in patch-clamp experiments on excised outside-out cytoplasmic membrane patches from human macrophages that the activation of a high-conductance Ca2+ - and voltage-dependent potassium channel, the MaxiK channel, is an early step in LPS-induced transmembrane signal transduction in macrophages. MaxiK can be activated by agonistically active LPS, and activation can be completely inhibited by LPS antagonists ( e.g. synthetic compound 406) and by anti-CD14 antibodies. Furthermore, by inhibiting MaxiK with the specific MaxiK blocker paxilline, we could show that activation of MaxiK is essential for LPS-induced cytokine production. As shown by RT-PCR, blockade of MaxiK by paxilline also inhibits induction of the mRNA of TNF-α and IL-6. This observation together with the fact that all patch-clamp experiments were done on excised outside-out patches reveal that MaxiK activation is an early step in cell activation by endotoxins. Thus, since cells lacking TLR4 on their surface can also not be activated to produce cytokines, these data allow the conclusion that TLR4 and MaxiK are both essential for activation by LPS and may form a co-operative signaling complex. We have also shown that LBP not only exists as a soluble acute-phase serum protein, but is also incorporated as a transmembrane protein (mLBP) in the cytoplasmic membrane of MNC; in this configuration, it is obviously involved in the binding of endotoxin and its transfer to the transmembrane signaling proteins finally triggering cell activation. Complexation of soluble LBP and LPS in the serum prior to binding of LPS to mLBP, in contrast, leads to neutralization of LPS. Here, we provide evidence from fluorescence resonance energy transfer spectroscopy that endotoxin aggregates are intercalated into reconstituted membranes by mLBP. In addition, cell culture assays and patch-clamp experiments demonstrate that endotoxin activates macrophages and the MaxiK channel in the aggregated, but not in the monomeric, state at similar concentrations.

A designed TLR4/MD-2 complex to capture LPS

The family of Toll-like receptors (TLRs) is involved in the defense of an organism to microbial attack. TLR4-induced signaling is involved in infectious diseases, chronic inflammatory diseases and sepsis; therefore, we aimed at modulating TLR4-signaling via ligand-binding soluble receptors. Because recognition of microbial structures shows some species-specific traits, we specifically selected the mouse model for later in vivo studies. We first prepared the N-terminally Flag-tagged mouse (m) recombinant (r) soluble (s) fusion proteins mrsTLR4-IgGFc (T4Fc) and mrsMD-2 in Drosophila melanogaster Schneider 2 (S2) cells. The function of these molecules was tested by inhibition of synthesis of pro-inflammatory cytokines after stimulation of mouse macrophage RAW 264.7 cells with purified lipopolysaccharide (LPS). T4Fc alone had no inhibitory activity; however, a T4Fc/MD-2 complex blocked LPS activity. By analogy with `cytokine traps', we then prepared a designer molecule (LPS-Trap) by fusing MD-2 to the C-terminus of soluble TLR4 via a flexible linker. LPS-Trap significantly inhibited TNF production by LPS-stimulated RAW 264.7 cells. Thus, the T4Fc/MD-2 complex as well as the LPS-Trap blocked LPS activity in vitro and might thus represent a new therapeutic option in sepsis by neutralization of TLR4-activating ligands.

The Role of Toll-Like Receptor 4 in Infectious and Noninfectious Inflammation

Toll-like receptor 4 (TLR4) belongs to the family of pattern recognition receptors (PRRs). They are highly conserved receptors that recognize conserved pathogen-associated molecular patterns (PAMPs), thus representing the first line of defense against infections. TLR4 has been long recognized as the sensing receptor for gram-negative lipopolysaccharide (LPS). In addition, it also binds endogenous molecules produced as a result of tissue injury. Hence, TLR4 represents a key receptor on which both infectious and noninfectious stimuli converge to induce a proinflammatory response. TLR4-mediated inflammation, triggered by exogenous or endogenous ligands, is also involved in several acute and chronic diseases, having a pivotal role as amplifier of the inflammatory response. This review focuses on the research progress about the role of TLR4 activation in infectious and noninfectious (e.g., sterile) inflammation and the effects of TLR4 signaling in some pathological conditions.

Molecular Basis of the Functional Differences between Soluble Human Versus Murine MD-2: Role of Val135 in Transfer of Lipopolysaccharide from CD14 to MD-2

Myeloid differentiation factor 2 (MD-2) is an extracellular protein, associated with the ectodomain of TLR4, that plays a critical role in the recognition of bacterial LPS. Despite high overall structural and functional similarity, human (h) and murine (m) MD-2 exhibit several species-related differences. hMD-2 is capable of binding LPS in the absence of TLR4, whereas mMD-2 supports LPS responsiveness only when mMD-2 and mTLR4 are coexpressed in the same cell. Previously, charged residues at the edge of the LPS binding pocket have been attributed to this difference. In this study, site-directed mutagenesis was used to explore the hydrophobic residues within the MD-2 binding pocket as the source of functional differences between hMD-2 and mMD-2. Whereas decreased hydrophobicity of residues 61 and 63 in the hMD-2 binding pocket retained the characteristics of wild-type hMD-2, a relatively minor change of valine to alanine at position 135 completely abolished the binding of LPS to the hMD-2 mutant. The mutant, however, retained the LPS binding in complex with TLR4 and also cell activation, resulting in a murine-like phenotype. These results were supported by the molecular dynamics simulation. We propose that the residue at position 135 of MD-2 governs the dynamics of the binding pocket and its ability to accommodate lipid A, which is allosterically affected by bound TLR4.

Lipopolysaccharide-binding protein is bound and internalized by host cells and colocalizes with LPS in the cytoplasm: Implications for a role of LBP in intracellular LPS-signaling

The lipopolysaccharide-binding protein (LBP) is critically involved in innate immune responses to Gram-negative infections. We show here that human peripheral blood-derived monocytes, but not lymphocytes, stain positive for endogenous LBP on the cell surface. Studies on human macrophages demonstrate LBP binding at normal serum concentrations of 1-10 μg/ml. Binding was increased in a concentration-dependent manner by lipopolysaccharide (LPS). Fluorescence quenching experiments and confocal microscopy revealed constitutive and LPS-induced internalization of LBP by macrophages. Experiments with macrophages and HEK293 cell lines showed that binding and uptake of LBP do not depend on the LPS receptors CD14 and TLR4/MD-2. Fractionation of Triton X-100 solubilized cytoplasmic membranes revealed that LBP was primarily localized in non-raft domains under resting conditions. Cellular LPS stimulation elevated LBP levels and induced enrichment in fractions marking the transition between non-raft and raft domains. LBP was found to colocalize with LPS at the cytoplasmic membrane and in intracellular compartments of macrophages. In macrophages stimulated with LPS and ATP for inflammasome activation, LBP was observed in close vicinity to activated caspases. Furthermore, LBP conferred IL-1β production by LPS in the absence of ATP. These data establish that LBP serves not only as an extracellular LPS shuttle but in addition facilitates intracellular transport of LPS. This observation adds a new function to this central immune regulator of LPS biology and raises the possibility for a role of LBP in the delivery of LPS to TLR4-independent intracellular receptors.

Mechanisms of Toll-like Receptor 4 Endocytosis Reveal a Common Immune-Evasion Strategy Used by Pathogenic and Commensal Bacteria

Microbe-induced receptor trafficking has emerged as an essential means to promote innate immune signal transduction. Upon detection of bacterial lipopolysaccharides (LPS), CD14 induces an inflammatory endocytosis pathway that delivers Toll-like receptor 4 (TLR4) to endosomes. Although several regulators of CD14-dependent TLR4 endocytosis have been identified, the cargo-selection mechanism during this process remains unknown. We reveal that, in contrast to classic cytosolic interactions that promoted the endocytosis of transmembrane receptors, TLR4 was selected as cargo for inflammatory endocytosis entirely through extracellular interactions. Mechanistically, the extracellular protein MD-2 bound to and dimerized TLR4 in order to promote this endocytic event. Our analysis of LPS variants from human pathogens and gut commensals revealed a common mechanism by which bacteria prevent inflammatory endocytosis. We suggest that evasion of CD14-dependent endocytosis is an attribute that transcends the concept of pathogenesis and might be a fundamental feature of bacteria that inhabit eukaryotic hosts.

PPARγ ameliorated LPS induced inflammation of HEK cell line expressing both human Toll-like receptor 4 (TLR4) and MD2

TLR4 is transmembrane pattern-recognition receptor that initiates signals in response to diverse pathogen-associated molecular patterns especially LPS. Recently, there have been an increasing number of studies about the role of TLRs in the pathogenesis of several disorders as well as the therapeutic potential of TLR intervention in such diseases. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a ligand-activated transcription factor with numerous biological effects. PPARγ has been shown to exert a potential anti-inflammatory effect through suppression of TLR4-mediated inflammation. Therefore, PPARγ agonists may have a potential to combat inflammatory conditions in pathologic states. The current study aims to show the decrease of inflammation by overexpression of PPARγ in a cell reporter model. To reach this goal, recombinant pBudCE4.1 (+) containing encoding sequences of human TLR4 and MD2 was constructed and used to transfect HEK cells. Subsequently, inflammation was induced by LPS treatment as control group. In the treatment group, overexpression of PPARγ prior to inflammation was performed and the expression of inflammatory markers was assessed in this condition. The expression of inflammatory markers (TNFα and iNOS) was defined by quantitative real time PCR and the amount of phosphorylated NF-κB was measured by western blot. Data indicated expression of TNFα and iNOS increased in LPS induced inflammation of stably transformed HEK cells with MD2 and TLR4. In this cell reporter model overexpression of PPARγ dramatically prevented LPS-induced inflammation through the blocking of TLR4/NF-κB signaling. PPARγ was shown to negatively regulate TLR4 activity and therefore exerts its anti-inflammatory action against LPS induced inflammation.

Modulating LPS signal transduction at the LPS receptor complex with synthetic Lipid A analogues

Sepsis, defined as a clinical syndrome brought about by an amplified and dysregulated inflammatory response to infections, is one of the leading causes of death worldwide. Despite persistent attempts to develop treatment strategies to manage sepsis in the clinical setting, the basic elements of treatment have not changed since the 1960s. As such, the development of effective therapies for reducing inflammatory reactions and end-organ dysfunction in critically ill patients with sepsis remains a global priority. Advances in understanding of the immune response to sepsis provide the opportunity to develop more effective pharmaceuticals. This article details current information on the modulation of the lipopolysaccharide (LPS) receptor complex with synthetic Lipid A mimetics. As the initial and most critical event in sepsis pathophysiology, the LPS receptor provides an attractive target for antisepsis agents. One of the well-studied approaches to sepsis therapy involves the use of derivatives of Lipid A, the membrane-anchor portion of an LPS, which is largely responsible for its endotoxic activity. This article describes the structural and conformational requirements influencing the ability of Lipid A analogues to compete with LPS for binding to the LPS receptor complex and to inhibit the induction of the signal transduction pathway by impairing LPS-initiated receptor dimerization.

Alternatively spliced myeloid differentiation protein-2 inhibits TLR4-mediated lung inflammation

We previously identified a novel alternatively spliced isoform of human myeloid differentiation protein-2 (MD-2s) that competitively inhibits binding of MD-2 to TLR4 in vitro. In this study, we investigated the protective role of MD-2s in LPS-induced acute lung injury by delivering intratracheally an adenovirus construct that expressed MD-2s (Ad-MD-2s). After adenovirus-mediated gene transfer, MD-2s was strongly expressed in lung epithelial cells and readily detected in bronchoalveolar lavage fluid. Compared to adenovirus serotype 5 containing an empty vector lacking a transgene control mice, Ad-MD-2s delivery resulted in significantly less LPS-induced inflammation in the lungs, including less protein leakage, cell recruitment, and expression of proinflammatory cytokines and chemokines, such as IL-6, keratinocyte chemoattractant, and MIP-2. Bronchoalveolar lavage fluid from Ad-MD-2s mice transferred into lungs of naive mice before intratracheal LPS challenge diminished proinflammatory cytokine levels. As house dust mite (HDM) sensitization is dependent on TLR4 and HDM Der p 2, a structural homolog of MD-2, we also investigated the effect of MD-2s on HDM-induced allergic airway inflammation. Ad-MD-2s given before HDM sensitization significantly inhibited subsequent allergic airway inflammation after HDM challenge, including reductions in eosinophils, goblet cell hyperplasia, and IL-5 levels. Our study indicates that the alternatively spliced short isoform of human MD-2 could be a potential therapeutic candidate to treat human diseases induced or exacerbated by TLR4 signaling, such as Gram-negative bacterial endotoxin-induced lung injury and HDM-triggered allergic lung inflammation.

Intestinal ischemia-reperfusion of macaques triggers a strong innate immune response

AIM: To investigate inflammatory injury in the intestinal mucosa after intestinal ischemia-reperfusion (IIR) with Toll-like receptor (TLR)-mediated innate immunity.

METHODS: Ten macaques were randomized into control and IIR groups. The distribution and expression level of TLR2, TLR4, MD2, nuclear factor (NF)-κB p65 and interferon (IFN)-γ were measured by immunohistochemical stain and western blotting. The mRNA expression of TLR4, TLR2, MD2, interleukin (IL)-1β and tumor necrosis factor (TNF)-α were measured by reverse transcriptase-polymerase chain reaction. The cytokine levels in blood and intestinal tissues were measured by ELISA.

RESULTS: Obvious hemorrhage and erosion of mucosae were seen in the IIR group. Expression of TLR2, TLR4, MD2, NF-κB p65 and IFN-γ was significantly higher in the IIR group than in the control group (0.13 ± 0.04, 0.22 ± 0.04, 0.16 ± 0.06, 0.65 ± 0.12, 0.38 ± 0.10 vs 0.07 ± 0.04, 0.08 ± 0.03, 0.04 ± 0.02, 0.19 ± 0.06, 0.14 ± 0.05, P < 0.05). In addition, the expression of TLR2, TLR4, MD2, IL-1β and TNF-α mRNA in the IIR group were significantly higher than those of control group(1.52 ± 0.15, 1.39 ± 0.06, 1.94 ± 0.12, 1.48 ± 0.15, 0.66 ± 0.08 vs 0.31 ± 0.05, 0.5 ± 0.04, 0.77 ± 0.05, 0.35 ± 0.08, 0.18 ± 0.04, P < 0.05). Furthermore, IL-1β, IL-6 and TNF-α levels in the macaques ileum and plasma were significantly higher than in the control group (plasma: 86.3 ± 15.2, 1129 ± 248.3, 77.8 ± 16.2 vs 29.5 ± 7.3, 19.8 ± 8.2, 5.6 ± 1.7; ileum: 273.4. ± 44.7, 1636 ± 168.0, 205.5 ± 30.7 vs 76.8 ± 20.5, 663.4 ± 186.9, 49.0 ± 9.4; P < 0.05).

CONCLUSION: After IIR, general inflammatory injury in the intestinal mucosa is correlated with a strong innate immune response, mediated by activation of the TLR-NF-κB-cytokine pathway.

Fungal glycans and the innate immune recognition

Polysaccharides such as α- and β-glucans, chitin, and glycoproteins extensively modified with both N- and O-linked carbohydrates are the major components of fungal surfaces. The fungal cell wall is an excellent target for the action of antifungal agents, since most of its components are absent from mammalian cells. Recognition of these carbohydrate-containing molecules by the innate immune system triggers inflammatory responses and activation of microbicidal mechanisms by leukocytes. This review will discuss the structure of surface fungal glycoconjugates and polysaccharides and their recognition by innate immune receptors.

Vizantin inhibits endotoxin-mediated immune responses via the TLR 4/MD-2 complex

Vizantin has immunostimulating properties and anticancer activity. In this study, we investigated the molecular mechanism of immune activation by vizantin. THP-1 cells treated with small interfering RNA for TLR-4 abolished vizantin-induced macrophage activation processes such as chemokine release. In addition, compared with wild-type mice, the release of MIP-1β induced by vizantin in vivo was significantly decreased in TLR-4 knockout mice, but not in TLR-2 knockout mice. Vizantin induced the release of IL-8 when HEK293T cells were transiently cotransfected with TLR-4 and MD-2, but not when they were transfected with TLR-4 or MD-2 alone or with TLR-2 or TLR-2/MD-2. A dipyrromethene boron difluoride-conjugated vizantin colocalized with TLR-4/MD-2, but not with TLR-4 or MD-2 alone. A pull-down assay with vizantin-coated magnetic beads showed that vizantin bound to TLR-4/MD-2 in extracts from HEK293T cells expressing both TLR-4 and MD-2. Furthermore, vizantin blocked the LPS-induced release of TNF-α and IL-1β and inhibited death in mice. We also performed in silico docking simulation analysis of vizantin and MD-2 based on the structure of MD-2 complexed with the LPS antagonist E5564; the results suggested that vizantin could bind to the active pocket of MD-2. Our observations show that vizantin specifically binds to the TLR-4/MD-2 complex and that the vizantin receptor is identical to the LPS receptor. We conclude that vizantin could be an effective adjuvant and a therapeutic agent in the treatment of infectious diseases and the endotoxin shock caused by LPS.

BK channels regulate myometrial contraction by modulating nuclear translocation of NF-κB

The large-conductance Ca(2+)-activated K(+) (BK) channel plays an essential role in maintaining uterine quiescence during pregnancy. Growing evidence has shown a link between the BK channel and bacterial lipopolysaccharide (LPS)-induced nuclear factor-κB (NF-κB) activation in macrophages. In the uterus, NF-κB activation plays an important role in inflammatory processes that lead to parturition. Our objective was to determine whether the BK channel regulates uterine contraction, in part, by modulating NF-κB translocation into the nucleus. We compared the effects of BK channel modulation to those of LPS on NF-κB nuclear translocation and contraction in an immortalized human myometrial cell line (human telomerase reverse transcriptase [hTERT]) and uterine myocytes. Our results showed that BK channel inhibitors paxilline and penitrem A induced translocation of NF-κB into the nucleus in both hTERT cells and uterine myocytes to a similar extent as LPS treatment, and LPS and paxilline similarly reduced BK channel currents. Conversely, neither BK channel openers nor blockade of the small conductance Ca(2+)-activated K(+) channel protein 3 had an effect on NF-κB translocation. Additionally, collagen-based assays showed that paxilline induced contraction of hTERT cells and uterine myocytes. This was dependent upon cyclooxygenase-2 activity. Moreover, paxilline-induced contractility and increased cyclooxygenase-2 expression both depended on availability of free NF-κB. This study suggests that BK channels regulate myometrial contraction, in part, by modulating nuclear translocation of NF-κB.

Activation of c-Src: a hub for exogenous pro-oxidant-mediated activation of Toll-like receptor 4 signaling

To study the role of c-Src kinase in pro-oxidant-induced stimulation of Toll-like receptor 4 (TLR4), we used lipopolysaccharide from Escherichia coli K12 (LPS-EK) and monophosphoryl lipid A, as TLR4-specific agonists and positive controls, and SIN-1 and potassium peroxychromate as pro-oxidant sources. We used the HEK-Blue mTLR4 cell line, which is stably transfected with mouse TLR4 and expresses optimized SEAP reporter under the control of a promoter inducible by NF-κB transcription factor. The level of SEAP released due to TLR4 stimulation was a measure of NF-κB activation. Treatment with either the pro-oxidants or LPS-EK increased SEAP release and TNF-α production in these cells. These treatments also increased intracellular reactive oxygen species accumulation, with an enhanced production of nitric oxide and TBARS to confirm oxidant stress in these cells. Pretreatment with c-Src kinase inhibitors, PP2 and Ca-pY, which act by different mechanisms, decreased these parameters. Pretreatment with SSG, a c-Src activator, enhanced the effects promoted by LPS-EK and pro-oxidants and rescued cells from the PP2- and Ca-pY-induced effects. Curiously, pro-oxidants, but not TLR4 agonist, increased the ratio of TNF-α to IL-10 released, suggesting that pro-oxidants can initiate and maintain an imbalance of TNF-α production over IL-10. To different degrees, both pro-oxidants and TLR4 agonist increased formation of c-Src complexes with TLR4 and IκB-α as coimmunoprecipitates. Both pro-oxidants and TLR4 agonist increased c-Src phosphorylation of the Tyr42 residue in IκB-α, but the pro-oxidant-induced effect was more robust and much longer lasting. Taken together, these studies provide a mechanism whereby c-Src assumes a central role in pro-oxidant-induced NF-κB activation in TLR4 signaling. Pro-oxidant-induced activation of TLR4 through c-Src/NF-κB/IκB-α coupling provides a basis for a molecular dissection of the initiation and maintenance of sterile inflammation that may serve as a "pathophysiologic primer" for many diseases.

New and emerging vaccination strategies for prevention and treatment of dermatological diseases

Accelerated by the rapid advancements of our understanding of the molecular and cellular pathology of diseases and of the components and mechanisms of cellular and humoral immune responses, new vaccination strategies are being developed and explored for treatment and prevention of infectious diseases, cancer, autoimmune disorders and allergies. Many newly developed vaccination strategies are already in clinical trials, some with very promising results. Although most of these strategies are still at very early stages of their development, it is foreseeable that vaccination will evolve to play an important role in prevention, treatment and management of all the above classes of diseases.