Induction of long-term lipopolysaccharide tolerance by an agonistic monoclonal antibody to the toll-like receptor 4/MD-2 complex

CFTR-mediated monocyte/macrophage dysfunction revealed by cystic fibrosis proband-parent comparisons

Cystic fibrosis (CF) is an inherited disorder caused by biallelic mutations of the CF transmembrane conductance regulator (CFTR) gene. Converging evidence suggests that CF carriers with only 1 defective CFTR copy are at increased risk for CF-related conditions and pulmonary infections, but the molecular mechanisms underpinning this effect remain unknown. We performed transcriptomic profiling of peripheral blood mononuclear cells (PBMCs) of CF child-parent trios (proband, father, and mother) and healthy control (HC) PBMCs or THP-1 cells incubated with the plasma of these participants. Transcriptomic analyses revealed suppression of cytokine-enriched immune-related genes (IL-1β, CXCL8, CREM), implicating lipopolysaccharide tolerance in innate immune cells (monocytes) of CF probands and their parents. These data suggest that a homozygous as well as a heterozygous CFTR mutation can modulate the immune/inflammatory system. This conclusion is further supported by the finding of lower numbers of circulating monocytes in CF probands and their parents, compared with HCs, and the abundance of mononuclear phagocyte subsets, which correlated with Pseudomonas aeruginosa infection, lung disease severity, and CF progression in the probands. This study provides insight into demonstrated CFTR-related innate immune dysfunction in individuals with CF and carriers of a CFTR mutation that may serve as a target for personalized therapy.

A mouse model of human TLR4 D299G/T399I SNPs reveals mechanisms of altered LPS and pathogen responses

Two cosegregating single-nucleotide polymorphisms (SNPs) in human TLR4, an A896G transition at SNP rs4986790 (D299G) and a C1196T transition at SNP rs4986791 (T399I), have been associated with LPS hyporesponsiveness and differential susceptibility to many infectious or inflammatory diseases. However, many studies failed to confirm these associations, and transfection experiments resulted in conflicting conclusions about the impact of these SNPs on TLR4 signaling. Using advanced protein modeling from crystallographic data of human and murine TLR4, we identified homologous substitutions of these SNPs in murine Tlr4, engineered a knock-in strain expressing the D298G and N397I TLR4 SNPs homozygously, and characterized in vivo and in vitro responses to TLR4 ligands and infections in which TLR4 is implicated. Our data provide new insights into cellular and molecular mechanisms by which these SNPs decrease the TLR4 signaling efficiency and offer an experimental approach to confirm or refute human data possibly confounded by variables unrelated to the direct effects of the SNPs on TLR4 functionality.

Human monoclonal anti‑TLR4 antibody negatively regulates lipopolysaccharide‑induced inflammatory responses in mouse macrophages

Previous studies have revealed that activation of the Toll‑like receptor 4 (TLR4)‑mediated proinflammatory signaling pathway plays an important role in acute inflammation, sepsis and chronic inflammatory disorders. Moreover, TLR4 significantly contributes to lipopolysaccharide (LPS)‑induced immune response. Thus, modulation of the TLR4 pathway is an important strategy to specifically target these pathologies. The aim of the present study was to develop a complete human anti‑TLR4 IgG2 antibody by screening human TLR4 Fab from a phage‑display library and integrating it with constant regions of the heavy chain of human IgG2 via antibody engineering. ELISA, a BLItz system and fluorescence‑activated cell sorting were used to assess its affinity. Furthermore, mouse‑derived peritoneal macrophages were treated with human anti‑TLR4 IgG2 and induced with LPS in vitro. Reverse transcription‑quantitative PCR and western blotting were used to determine mRNA expression levels of cytokines and phosphorylation levels of signaling pathways, respectively. It was found that human anti‑TLR4 IgG2 bound to TLR4 with a high affinity of 8.713x10‑10 M, and that preincubation with anti‑TLR4 IgG2 inhibited the LPS‑induced production of tumor necrosis factor‑α, interferon‑β and interleukin‑6 mRNA expression levels in mouse peritoneal macrophages. It was also demonstrated that human anti‑TLR4 IgG2 inhibited LPS‑induced TLR4 signaling by reducing the phosphorylation of the NF‑κB, mitogen‑activated protein kinase and interferon regulatory factor 3 signaling pathways. In addition, human anti‑TLR4 IgG2 protected mice from LPS challenge with a survival rate of 40% and also significantly increased the survival time in the cecal ligation and puncture model. Therefore, it was speculated that human anti‑TLR4 IgG2 plays a protective role against sepsis‑associated injury and is potentially applicable for the treatment of infection‑associated immune dysfunction.

An agonistic anti-Toll-like receptor 4 monoclonal antibody as an effective adjuvant for cancer immunotherapy

Immune-checkpoint blockade antibodies have been approved for the treatment of cancer. However, poorly immunogenic tumours are less responsive to such therapies. Agonistic anti-Toll-like receptor 4 (TLR4) monoclonal antibodies (mAbs) activate only cell-surface TLR4; in contrast, lipopolysaccharide (LPS) activates both TLR4 and intracellular inflammatory caspases. In this study, we investigated the adjuvant activity of an anti-TLR4 mAb in T-cell-mediated antitumour immunity. The anti-TLR4 mAb induced the activation of antigen-specific T-cells in adoptive transfer studies. The growth of ovalbumin (OVA)-expressing tumours was significantly suppressed by administration of OVA and the anti-TLR4 mAb in combination, but not individually. The antitumour effect of anti-PD-1 mAb was enhanced in mice administered with OVA plus the anti-TLR4 mAb. The OVA-specific IFN-γ-producing CD8 T-cells were induced by administration of OVA and the anti-TLR4 mAb. The suppression of tumour growth was diminished by depletion of CD8, but not CD4, T-cells. The inflammatory response to the anti-TLR4 mAb was of significantly lesser magnitude than that to LPS, as assessed by NF-κB activation and production of TNF-α, IL-6 and IL-1β. Administration of LPS (at a dose that elicited levels of proinflammatory cytokines comparable to those by the anti-TLR4 mAb) plus OVA induced no or less-marked activation of OVA-specific T-cells and failed to suppress tumour growth in mice. In conclusion, the agonistic anti-TLR4 mAb induces potent CD8 T-cell-dependent antitumour immunity and an inflammatory response of lesser magnitude than does LPS. The agonistic anti-TLR4 mAb has potential as an adjuvant for use in vaccines against cancer.

Targeting toll-like receptor 4 to modulate neuroinflammation in central nervous system disorders

Introduction: Adverse immune activation contributes to many central nervous system (CNS) disorders. All main CNS cell types express toll-like receptor 4 (TLR 4). This receptor is critical for a myriad of immune functions such as cytokine secretion and phagocytic activity of microglia; however, imbalances in TLR 4 activation can contribute to the progression of neurodegenerative diseases. Areas covered: We considered available evidence implicating TLR 4 activation in the following CNS pathologies: Alzheimer's disease, Parkinson's disease, ischemic stroke, traumatic brain injury, multiple sclerosis, multiple systems atrophy, and Huntington's disease. We reviewed studies reporting effects of TLR 4-specific antagonists and agonists in models of peripheral and CNS diseases from the perspective of possible future use of TLR 4 ligands in CNS disorders. Expert opinion: TLR 4-specific antagonists could suppress neuroinflammation by reducing overproduction of inflammatory mediators; however, they may interfere with protein clearance mechanisms and myelination. Agonists that specifically activate myeloid differentiation primary-response protein 88 (MyD88)-independent pathway of TLR 4 signaling could facilitate beneficial glial phagocytic activity with limited activity as inducers of proinflammatory mediators. Deciphering the disease stage-specific involvement of TLR 4 in CNS pathologies is crucial for the future clinical development of TLR 4 agonists and antagonists.

Impaired antigen-specific lymphocyte priming in mice after Toll-like receptor 4 activation via induction of monocytic myeloid-derived suppressor cells

In sepsis, the pathology involves a shift from a proinflammatory state toward an immunosuppressive phase. We previously showed that an agonistic anti-TLR4 antibody induced long-term endotoxin tolerance and suppressed antigen-specific secondary IgG production when primed prior to immunization with antigen. These findings led us to speculate that TLR4-induced innate tolerance due to primary infection causes an immunosuppressive pathology in sepsis. Therefore, the mechanism underlying impaired antigen-specific humoral immunity by the TLR4 antibody was investigated. We showed, in a mouse model, that primary antigen-specific IgG responses were impaired in TLR4 antibody-induced tolerized mice, which was the result of reduced numbers of antigen-specific GC B cells and plasma cells. Ovalbumin-specific CD4 and CD8 T-cell responses were impaired in TLR4 antibody-injected OT-I and -II transgenic mice ex vivo. Adoptive transfer studies demonstrated suppression of OVA-specific CD4 and CD8 T-cell responses by the TLR4 antibody in vivo. The TLR4 antibody induced Gr1⁺ CD11b⁺ myeloid-derived suppressor cell (MDSC) expansion with suppression of T-cell activation. Monocytic MDSCs were more suppressive and exhibited higher expression of PD-L1 and inducible nitric oxidase compared with granulocytic MDSCs. In conclusion, immune tolerance conferred by TLR4 activation induces the expansion of monocytic MDSCs, which impairs antigen-specific T-cell priming and IgG production.

Toll-Like Receptor 4 Agonistic Antibody Promotes Host Defense against Chronic Pseudomonas aeruginosa Lung Infection in Mice

Chronic lower respiratory tract infection with Pseudomonas aeruginosa is difficult to treat due to enhanced antibiotic resistance and decreased efficacy of drug delivery to destroyed lung tissue. To determine the potential for restorative immunomodulation therapies, we evaluated the effect of Toll-like receptor 4 (TLR4) stimulation on the host immune response to Pseudomonas infection in mice. We implanted sterile plastic tubes precoated with P. aeruginosa in the bronchi of mice, administered the TLR4/MD2 agonistic monoclonal antibody UT12 intraperitoneally every week, and subsequently analyzed the numbers of viable bacteria and inflammatory cells and the levels of cytokines. We also performed flow cytometry-based phagocytosis and opsonophagocytic killing assays in vitro using UT12-treated murine peritoneal neutrophils. UT12-treated mice showed significantly enhanced bacterial clearance, increased numbers of Ly6G(+) neutrophils, and increased concentrations of macrophage inflammatory protein 2 (MIP-2) in the lungs (P < 0.05). Depletion of CD4(+) T cells eliminated the ability of the UT12 treatment to improve bacterial clearance and promote neutrophil recruitment and MIP-2 production. Additionally, UT12-pretreated peritoneal neutrophils exhibited increased opsonophagocytic killing activity via activation of the serine protease pathway, specifically neutrophil elastase activity, in a TLR4-dependent manner. These data indicated that UT12 administration significantly augmented the innate immune response against chronic bacterial infection, in part by promoting neutrophil recruitment and bactericidal function.

Reversal of New-Onset Type 1 Diabetes With an Agonistic TLR4/MD-2 Monoclonal Antibody

Type 1 diabetes (T1D) is currently an incurable disease, characterized by a silent prodromal phase followed by an acute clinical phase, reflecting progressive autoimmune destruction of insulin-producing pancreatic β-cells. Autoreactive T cells play a major role in β-cell destruction, but innate immune cell cytokines and costimulatory molecules critically affect T-cell functional status. We show that an agonistic monoclonal antibody to TLR4/MD-2 (TLR4-Ab) reverses new-onset diabetes in a high percentage of NOD mice. TLR4-Ab induces antigen-presenting cell (APC) tolerance in vitro and in vivo, resulting in an altered cytokine profile, decreased costimulatory molecule expression, and decreased T-cell proliferation in APC:T-cell assays. TLR4-Ab treatment increases T-regulatory cell (Treg) numbers in both the periphery and the pancreatic islet, predominantly expanding the Helios(+)Nrp-1(+)Foxp3(+) Treg subset. TLR4-Ab treatment in the absence of B cells in NOD.scid mice prevents subsequent T cell-mediated disease, further suggesting a major role for APC tolerization in disease protection. Specific stimulation of the innate immune system through TLR4/MD-2, therefore, can restore tolerance in the aberrant adaptive immune system and reverse new-onset T1D, suggesting a novel immunological approach to treatment of T1D in humans.

CD14 dependence of TLR4 endocytosis and TRIF signaling displays ligand specificity and is dissociable in endotoxin tolerance

Dimerization of Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD2) heterodimers is critical for both MyD88- and TIR-domain-containing adapter-inducing IFN-β (TRIF)-mediated signaling pathways. Recently, Zanoni et al. [(2011) Cell 147(4):868-880] reported that cluster of differentiation 14 (CD14) is required for LPS-/Escherichia coli- induced TLR4 internalization into endosomes and activation of TRIF-mediated signaling in macrophages. We confirmed their findings with LPS but report here that CD14 is not required for receptor endocytosis and downstream signaling mediated by TLR4/MD2 agonistic antibody (UT12) and synthetic small-molecule TLR4 ligands (1Z105) in murine macrophages. CD14 deficiency completely ablated the LPS-induced TBK1/IRF3 signaling axis that mediates production of IFN-β in murine macrophages without affecting MyD88-mediated signaling, including NF-κB, MAPK activation, and TNF-α and IL-6 production. However, neither the MyD88- nor TRIF-signaling pathways and their associated cytokine profiles were altered in the absence of CD14 in UT12- or 1Z105-treated murine macrophages. Eritoran (E5564), a lipid A antagonist that binds the MD2 "pocket," completely blocked LPS- and 1Z105-driven, but not UT12-induced, TLR4 dimerization and endocytosis. Furthermore, TLR4 endocytosis is induced in macrophages tolerized by exposure to either LPS or UT12 and is independent of CD14. These data indicate that TLR4 receptor endocytosis and the TRIF-signaling pathway are dissociable and that TLR4 internalization in macrophages can be induced by UT12, 1Z105, and during endotoxin tolerance in the absence of CD14.

Differential requirements of MyD88 and TRIF pathways in TLR4-mediated immune responses in murine B cells

LPS stimulates the TLR4/Myeloid differentiation protein-2 (MD-2) complex and promotes a variety of immune responses in B cells. TLR4 has two main signaling pathways, MyD88 and Toll/IL-1R (TIR)-domain-containing adaptor-inducing interferon-β (TRIF) pathways, but relatively few studies have examined these pathways in B cells. In this study, we investigated MyD88- or TRIF-dependent LPS responses in B cells by utilizing their knockout mice. Compared with wild-type (WT) B cells, MyD88(-/-) B cells were markedly impaired in up-regulation of CD86 and proliferation induced by lipid A moiety of LPS. TRIF(-/-) B cells were also impaired in these responses compared with WT B cells, but showed better responses than MyD88(-/-) B cells. Regarding class switch recombination (CSR) elicited by lipid A plus IL-4, MyD88(-/-) B cells showed similar patterns of CSR to WT B cells. However, TRIF(-/-) B cells showed the impaired in the CSR. Compared with WT and MyD88(-/-) B cells, TRIF(-/-) B cells exhibited reduced cell division, fewer IgG1(+) cells per division, and decreased activation-induced cytidine deaminase (Aicda) mRNA expression in response to lipid A plus IL-4. Finally, IgG1 production to trinitrophenyl (TNP)-LPS immunization was impaired in TRIF(-/-) mice, while MyD88(-/-) mice exhibited increased IgG1 production. Thus, MyD88 and TRIF pathways differently regulate TLR4-induced immune responses in B cells.

Toll-like receptor 4 agonistic antibody promotes innate immunity against severe pneumonia induced by coinfection with influenza virus and Streptococcus pneumoniae

Coinfection with bacteria is a major cause of mortality during influenza epidemics. Recently, Toll-like receptor (TLR) agonists were shown to have immunomodulatory functions. In the present study, we investigated the effectiveness and mechanisms of the new TLR4 agonistic monoclonal antibody UT12 against secondary pneumococcal pneumonia induced by coinfection with influenza virus in a mouse model. Mice were intranasally inoculated with Streptococcus pneumoniae 2 days after influenza virus inoculation. UT12 was intraperitoneally administered 2 h before each inoculation. Survival rates were significantly increased and body weight loss was significantly decreased by UT12 administration. Additionally, the production of inflammatory mediators was significantly suppressed by the administration of UT12. In a histopathological study, pneumonia in UT12-treated mice was very mild compared to that in control mice. UT12 increased antimicrobial defense through the acceleration of macrophage recruitment into the lower respiratory tract induced by c-Jun N-terminal kinase (JNK) and nuclear factor kappaB (NF-κB) pathway-dependent monocyte chemoattractant protein 1 (MCP-1) production. Collectively, these findings indicate that UT12 promoted pulmonary innate immunity and may reduce the severity of severe pneumonia induced by coinfection with influenza virus and S. pneumoniae. This immunomodulatory effect of UT12 improves the prognosis of secondary pneumococcal pneumonia and makes UT12 an attractive candidate for treating severe infectious diseases.

Inhibition of antibody production in vivo by pre-stimulation of Toll-like receptor 4 before antigen priming is caused by defective B-cell priming and not impairment in antigen presentation

Stimulation of Toll-like receptor 4 (TLR4) induces not only innate but also adaptive immune responses, and has been suggested to exert adjuvant effects. Additional to such positive effects, pre-stimulation of TLR4 induces endotoxin tolerance where animals are unresponsive to subsequent lethal challenges with lipopolysaccharide (LPS). We examined the effects of pre-stimulation of TLR4 using an agonistic anti-TLR4 mAb (UT12) on antibody production in vivo. Pre-injection of UT12 prior to both primary and secondary immunization completely inhibited antigen-specific antibody responses. Cellular analysis revealed that the inhibition was not due to impairment of T-cell activation. Accordingly, T-helper activities in UT12 pre-injected mice were not impaired. In contrast, B-cell priming was defective in UT12 pre-injected mice. The observation that the expression of activation markers such as CD69 and CD86 on B cells was blocked by UT12 pre-injection supports this. Interestingly, UT12 pre-injection only showed inhibitory effects at the primary and not the secondary immunization. These results provide important information concerning the regulatory mechanisms of antibody production, especially in endotoxin-tolerant states.

The RP105/MD-1 complex is indispensable for TLR4/MD-2-dependent proliferation and IgM-secreting plasma cell differentiation of marginal zone B cells

Marginal zone (MZ) B cells mount rapid T-cell-independent (T-I) immune responses against microbial components such as LPS. While Toll-like receptor 4 (TLR4) is essential for LPS responses, MZ B cells uniquely express high levels of another LPS sensor Radioprotective 105 (RP105). However, little is known about how RP105 is used by MZ B cells. In this study, we investigated TLR4- or RP105-dependent MZ B cell responses by utilizing agonistic monoclonal antibodies (mAbs) to each receptor. Cross-linking TLR4 and RP105 at the same time with the mAbs induced robust IgM-secreting plasma cell generation as lipid A moiety of LPS. In contrast, stimulation with either mAb alone did not elicit such responses. RP105-deficient MZ B cells failed to produce IgM-secreting plasma cells in response to lipid A. TLR4 or lipid A stimulation of MZ B cells up-regulated their B lymphocyte-induced maturation protein 1 (Blimp-1) and X-box-binding protein 1 (Xbp-1) mRNA expression. RP105 stimulation alone did not give these responses and in fact decreased TLR4-mediated their expression. Compared with wild-type (WT) MZ B cells, RP105-deficient MZ B cells exhibited increased levels of Blimp-1 and Xbp-1 mRNA expression in response to lipid A. Lipid A or TLR4 plus RP105 stimulation induced massive proliferation and expression of Bcl-xL and c-Myc in WT but not RP105-deficient MZ B cells. These responses contributed to TLR4-mediated anti-apoptotic responses in MZ B cells. Thus, RP105 contributes in a unique way to the TLR4-dependent survival, proliferation and plasma cell generation of MZ B cells.

Prolonged hepatomegaly in mice that cannot inactivate bacterial endotoxin

Transient hepatomegaly often accompanies acute bacterial infections. Reversible, dose-dependent hepatomegaly also occurs when animals are given intravenous infusions of bacterial lipopolysaccharide (LPS). We found that recovery from LPS-induced hepatomegaly requires a host enzyme, acyloxyacyl hydrolase (AOAH), that inactivates LPS. When we challenged Aoah(-/-) mice with low doses of LPS or gram-negative bacteria, their livers remained enlarged (as much as 80% above normal) many weeks longer than did the livers of Aoah(+/+) animals. When compared with livers from LPS-primed Aoah(+/+) mice, LPS-primed Aoah(-/-) livers had (1) more numerous and larger Kupffer cells, (2) intrasinusoidal leukocyte aggregates and activated sinusoidal endothelial cells, and (3) sustained production of interleukin (IL)-10 and messenger RNAs (mRNAs) for tumor necrosis factor (TNF), IL-10, and IRAK-M. Depleting Kupffer cells decreased the liver enlargement by ≈40%, whereas depletion of neutrophils, dendritic cells, natural killer (NK) cells, NK-T cells, or B cells had no effect. Pretreatment with dexamethasone almost completely prevented prolonged hepatomegaly in Aoah(-/-) mice, whereas neutralizing TNF or interleukin-1β was only partially effective. In contrast, an antagonistic antibody to the IL-10 receptor increased LPS-induced hepatomegaly by as much as 50%.

CONCLUSION

our findings suggest that persistently active LPS induces Kupffer cells to elaborate mediators that promote the accumulation of leukocytes within enlarged sinusoids. Large increases in IL-10 and several other modulatory molecules are unable to prevent prolonged hepatomegaly in mice that cannot inactivate LPS. The striking findings in this mouse model should encourage studies to find out how AOAH contributes to human liver physiology and disease.

The transport and inactivation kinetics of bacterial lipopolysaccharide influence its immunological potency in vivo

The extraordinary potency and pathological relevance of gram-negative bacterial LPSs have made them very popular experimental agonists, yet little is known about what happens to these stimulatory molecules within animal tissues. We tracked fluorescent and radiolabeled LPS from a s.c. inoculation site to its draining lymph nodes (DLN), blood, and liver. Although we found FITC-labeled LPS in DLN within minutes of injection, drainage of radiolabeled LPS continued for >6 wk. Within the DLN, most of the LPS was found in the subcapsular sinus or medulla, near or within lymphatic endothelial cells and CD169(+) macrophages. Whereas most of the LPS seemed to pass through the DLN without entering B cell follicles, by 24 h after injection a small amount of LPS was found in the paracortex. In wild-type mice, ≥70% of the injected radiolabeled LPS underwent inactivation by deacylation before it left the footpad; in animals that lacked acyloxyacyl hydrolase, the LPS-deacylating enzyme, prolonged drainage of fully acylated (active) LPS boosted polyclonal IgM and IgG3 Ab titers. LPS egress from a s.c. injection site thus occurred during many weeks and was mainly via lymphatic channels. Its immunological potency, as measured by its ability to stimulate polyclonal Ab production, was greatly influenced by the kinetics of both lymphatic drainage and enzymatic inactivation.

Toll-like receptor 4 promotes α-synuclein clearance and survival of nigral dopaminergic neurons

Toll-like receptors (TLRs) mediate innate immunity, and their dysregulation may play a role in α-synucleinopathies, such as Parkinson's disease or multiple system atrophy (MSA). The aim of this study was to define the role of TLR4 in α-synuclein-linked neurodegeneration. Ablation of TLR4 in a transgenic mouse model of MSA with oligodendroglial α-synuclein overexpression augmented motor disability and enhanced loss of nigrostriatal dopaminergic neurons. These changes were associated with increased brain levels of α-synuclein linked to disturbed TLR4-mediated microglial phagocytosis of α-synuclein. Furthermore, tumor necrosis factor-α levels were increased in the midbrain and associated with a proinflammatory astroglial response. Our data suggest that TLR4 ablation impairs the phagocytic response of microglia to α-synuclein and enhances neurodegeneration in a transgenic MSA mouse model. The study supports TLR4 signaling as innate neuroprotective mechanism acting through clearance of α-synuclein.

Endotoxin removing method based on lipopolysaccharide binding protein and polyhydroxyalkanoate binding protein PhaP

Polyhydroxyalkanoates (PHAs) granule associated protein PhaP has a strong affinity to PHA and other hydrophobic polymers. Human lipopolysaccharide binding protein (hLBP) is a natural endotoxin receptor in plasma. In this study, genes encoding hLBP fused with PhaP were expressed in Pichia pastoris GS115 for production of the fusion protein. The purified rhLBP-PhaP fusion protein was immobilized on particles of polyhydroxybutyrate (PHB), which is a member of microbial polyhydroxyalkanoates (PHA). The rhLBP-PhaP-coated PHB particles were added to endotoxin containing water and protein solutions to study their endotoxin removal and protein recovery efficiencies. The influences of ionic strengths and pH on endotoxin removal and protein recovery in different protein solutions were also studied using acidic proteins including bovine serum albumin (BSA), ovalbumin, and basic protein α-chymotrypsinogen as model proteins. The results showed that rhLBP-PhaP particles could remove endotoxin with an efficiency of over 90%. All endotoxin removal and protein recovery efficiencies were only slightly affected by ionic strengths but were drastically affected by pH changes. Our results demonstrated that rhLBP-PhaP particles with their high efficiency, ease of preparation, and nontoxicity will be a suitable system for endotoxin removal in the protein purification industry.

Endotoxin tolerance attenuates airway allergic inflammation in model mice by suppression of the T-cell stimulatory effect of dendritic cells

Prior exposure of dendritic cells (DCs) and monocytes/macrophages to LPS causes unresponsiveness to subsequent LPS stimulation, a phenomenon called endotoxin tolerance (ET). ET impairs antigen presentation of these cells to T cells by down-regulating expression of MHC class II and co-stimulatory molecules such as CD86 and CD40. Some epidemiological studies have shown that endotoxin acts as a protective factor for allergic diseases. Accordingly, LPS has beneficial effects on the onset of airway allergic inflammation in model animals by T(h)1 skewing or induction of regulatory T cells. However, results derived from asthma model animals are controversial, probably due to the difficulty of handling LPS. We previously generated a monoclonal agonistic antibody against Toll-like receptor (TLR) 4, named UT12, which mimics the biological activities of LPS, exhibiting more potent and sustained ET than does LPS. In this study, we took advantage of UT12 to generate prolonged ET to explore the possibility that ET is involved in the inhibitory effects of the TLR4 signals on asthma model mice. Induction of ET by UT12 inhibited the capacity of DCs to expand ovalbumin (OVA)-specific T(h)2 and T(h)17 cells, without inducing T(h)1 cell or regulatory T-cell populations or producing inhibitory cytokines. Accordingly, administration of UT12 before the OVA sensitization significantly suppressed airway allergic inflammation by OVA inhalation. Taken together, these results demonstrate that ET induced by activating TLR4 signals attenuates airway allergic inflammation through direct suppression of the T-cell stimulatory effect of DCs in asthma model mice.

Overproduction of acyloxyacyl hydrolase by macrophages and dendritic cells prevents prolonged reactions to bacterial lipopolysaccharide in vivo

Although recognition of lipopolysaccharide (LPS) by the myeloid differentiation factor 2-Toll-like receptor 4 complex is important for triggering protective inflammatory responses in animals, terminating many of these responses requires LPS inactivation by a host lipase, acyloxyacyl hydrolase (AOAH). To test whether endogenously produced recombinant AOAH can modulate responses to LPS and gram-negative bacteria, we engineered transgenic mice that overexpress AOAH in dendritic cells and macrophages, cell types that normally produce it. Transgenic mice deacylated LPS more rapidly than did wild-type controls. They also were protected from LPS-induced hepatosplenomegaly, recovered more quickly from LPS-induced weight loss, and were more likely to survive when challenged with live Escherichia coli. Constitutive overexpression of AOAH in vivo hastened recovery from LPS exposure without interfering with the normal acute inflammatory response to this important microbial signal molecule. Our results suggest that the extent to which macrophages and dendritic cells produce AOAH may influence the outcome of many gram-negative bacterial diseases.

Cutting edge: NF-kappaB activating pattern recognition and cytokine receptors license NLRP3 inflammasome activation by regulating NLRP3 expression

The IL-1 family cytokines are regulated on transcriptional and posttranscriptional levels. Pattern recognition and cytokine receptors control pro-IL-1beta transcription whereas inflammasomes regulate the proteolytic processing of pro-IL-1beta. The NLRP3 inflammasome, however, assembles in response to extracellular ATP, pore-forming toxins, or crystals only in the presence of proinflammatory stimuli. How the activation of gene transcription by signaling receptors enables NLRP3 activation remains elusive and controversial. In this study, we show that cell priming through multiple signaling receptors induces NLRP3 expression, which we identified to be a critical checkpoint for NLRP3 activation. Signals provided by NF-kappaB activators are necessary but not sufficient for NLRP3 activation, and a second stimulus such as ATP or crystal-induced damage is required for NLRP3 activation.

Chapter 2: Kill the bacteria...and also their messengers?

We consider here a previously neglected aspect of recovery from infectious diseases: how animals dispose of the dead microbes in their tissues. For one of the most important disease-causing microorganisms, Gram-negative bacteria, there is now evidence that the host catabolism of a key microbial molecule is essential for full recovery. As might be expected, it is the same bacterial molecule that animals sense to detect the presence of Gram-negative bacteria in their tissues, the cell wall lipopolysaccharide (LPS). Here, we discuss current knowledge about LPS sensing with emphasis on the host enzyme that inactivates this microbial "messenger" molecule. We also consider the possibility that the rate at which stimulatory microbial molecules undergo inactivation may influence the duration and severity of diseases caused by other infectious agents.

Host inactivation of bacterial lipopolysaccharide prevents prolonged tolerance following gram-negative bacterial infection

A transient state of tolerance to microbial molecules accompanies many infectious diseases. Such tolerance is thought to minimize inflammation-induced injury, but it may also alter host defenses. Here we report that recovery from the tolerant state induced by Gram-negative bacteria is greatly delayed in mice that lack acyloxyacyl hydrolase (AOAH), a lipase that partially deacylates the bacterial cell-wall lipopolysaccharide (LPS). Whereas wild-type mice regained normal responsiveness within 14 days after they received an intraperitoneal injection of LPS or Gram-negative bacteria, AOAH-deficient mice had greatly reduced proinflammatory responses to a second LPS injection for at least 3 weeks. In contrast, LPS-primed Aoah- knockout mice maintained an anti-inflammatory response, evident from their plasma levels of interleukin-10 (IL-10). LPS-primed Aoah-knockout mice experiencing prolonged tolerance were highly susceptible to virulent E. coli challenge. Inactivating LPS, an immunostimulatory microbial molecule, is thus important for restoring effective host defenses following Gram-negative bacterial infection in animals.

Accelerated prion disease pathogenesis in Toll-like receptor 4 signaling-mutant mice

Prion diseases such as scrapie involve the accumulation of disease-specific prion protein, PrP(Sc), in the brain. Toll-like receptors (TLRs) are a family of proteins that recognize microbial constituents and are central players in host innate immune responses. The TLR9 agonist unmethylated CpG DNA was shown to prolong the scrapie incubation period in mice, suggesting that innate immune activation interferes with prion disease progression. Thus, it was predicted that ablation of TLR signaling would result in accelerated pathogenesis. C3H/HeJ (Tlr4(Lps-d)) mice, which possess a mutation in the TLR4 intracellular domain preventing TLR4 signaling, and strain-matched wild-type control (C3H/HeOuJ) mice were infected intracerebrally or intraperitoneally with various doses of scrapie inoculum. Incubation periods were significantly shortened in C3H/HeJ compared with C3H/HeOuJ mice, regardless of the route of infection or dose administered. At the clinical phase of disease, brain PrP(Sc) levels in the two strains of mice showed no significant differences by Western blotting. In addition, compared with macrophages from C3H/HeOuJ mice, those from C3H/HeJ mice were unresponsive to fibrillogenic PrP peptides (PrP residues 106 to 126 [PrP(106-126)] and PrP(118-135)) and the TLR4 agonist lipopolysaccharide but not to the TLR2 agonist zymosan, as measured by cytokine production. These data confirm that innate immune activation via TLR signaling interferes with scrapie infection. Furthermore, the results also suggest that the scrapie pathogen, or a component(s) thereof, is capable of stimulating an innate immune response that is active in the central nervous system, since C3H/HeJ mice, which lack the response, exhibit shortened incubation periods following both intraperitoneal and intracerebral infections.

Pivotal involvement of Fcgamma receptor IIA in the neutralization of lipopolysaccharide signaling via a potent novel anti-TLR4 monoclonal antibody 15C1

The mammalian Toll-like receptor (TLR) family has evolved to sense pathogens in the environment and protect the host against infection. TLR4 recognizes lipopolysaccharide (LPS) from Gram-negative bacteria and induces a signaling cascade that, when exaggerated, has been associated with severe sepsis. We have generated a TLR4-specific monoclonal antibody, 15C1, which neutralizes LPS-induced TLR4 activation in a dose-dependent manner. 15C1 potently blocks the effects of LPS on a panel of primary cells and cell lines in vitro. The binding of 15C1 was mapped to an epitope in the second portion of the extracellular region of TLR4, which has been shown previously to be functionally important in the recognition of LPS. Furthermore, we demonstrate a novel mechanism of inhibition, as the effects of 15C1 are partially Fc-dependent, involving the regulatory Fcgamma receptor IIA (CD32A). In addition to introducing 15C1 as a potent clinical candidate for use in the treatment of LPS-mediated indications, our work demonstrates a newly discovered pathway whose manipulation is pivotal in achieving optimal neutralizing benefit.