Mouse Toll-like Receptor Research Articles

The Development of a Highly Potent and Selective Human Toll-like Receptor 2 Agonist: Synthesis and Biological Evaluation of CaLGL-1 and Its Derivatives.

Toll-like receptor 2 (TLR2) plays a crucial role in detecting microbial pathogen-associated molecular patterns, offering potential applications as an adjuvant for vaccines and antitumor therapies. Here, we present the gram-scale synthesis of CaLGL-1 and its derivatives, natural products known for activating mouse TLR2 (EC50 = 3.2 μM). This synthesis involves a streamlined six-step reaction sequence utilizing oxidant-promoted acetalization, effectively preserving the acid-sensitive glycosidic bond for maintaining the compounds' functional integrity. Our structure-activity relationship studies identified R-7d as a potent human TLR2 activator. It demonstrated subnanomolar activity (EC50 = 116 pM) in human THP-1 cells, comparable to that of diprovocim (EC50 = 110 pM). Experiments revealed that R-7d enhances NF-kB promoter activation through TLR2/TLR1 heterodimers rather than TLR2/TLR6. The discovery of R-7d as a robust human TLR2 agonist opens up new possibilities for combination therapies.

Homology Modeling, Molecular Dynamics Simulation, and Prediction of Bovine TLR2 Heterodimerization.

Toll-like receptor 2 (TLR2) is a major membrane-bound receptor with ligand and species specificity that activates the host immune response. Heterodimerization of TLR2 with TLR1 (TLR2/1) or TLR6 (TLR2/6), triggered by ligand binding, is essential to initiating the signaling pathway. Bovine TLR2 (bTLR2) heterodimerization has not been defined yet compared with human and mouse TLR2s (hTLR2 and mTLR2). The aim of the present study was to model bovine TLRs (TLRs 1, 2 and 6) and create the heterodimeric forms of the bovine TLR2 using molecular dynamics (MD) simulations. We compared the intermolecular interactions in bTLR2/1-PAM3 and bTLR2/6-PAM2 with the hTLR2 and mTLR2 complexes through docking simulations and subsequent MD analyses. The present computational findings showed that bTLR2 dimerization could have a biological function and activate the immune response, similar to hTLR2 and mTLR2. Agonists and antagonists that are designed for hTLR2 and mTLR2 can target bTLR2. However, the experimental approaches to comparing the functional immune response of TLR2 across species were missing in the present study. This computational study provides a structural analysis of the bTLR2 interaction with bTLR1 and bTLR6 in the presence of an agonist/antagonist and reveals the three-dimensional structure of bTLR2 dimerization. The present findings could guide future experimental studies targeting bTLR2 with different ligands and lipopeptides.

The anti-TLR4 monoclonal antibody Sa15-21 enhances inflammatory cytokine production in LPS-stimulated macrophages.

Sa15-21, a monoclonal antibody against mouse Toll-like receptor (TLR) 4, can protect mice from lipopolysaccharide (LPS)/D-galactosamine-induced acute lethal hepatitis. Herein, we investigated the molecular mechanisms underlying Sa15-21-mediated regulation of TLR4 signaling in macrophages. Results showed that Sa15-21 enhanced the production of proinflammatory cytokines and attenuated the production of anti-inflammatory cytokines in LPS-stimulated macrophages. Western botting analysis revealed that Sa15-21 pretreatment had no effect on NF-κB and MAPK signaling in LPS-stimulated macrophages; however, Sa15-21 treatment alone led to a weak and delayed activation of NF-κB and MAPK signaling without any effect on proinflammatory cytokine production. In contrast, Sa15-21 failed to induce the activation of interferon regulatory factor 3. Taken together, our results indicate that Sa15-21 sensitizes macrophages to facilitate the inflammatory response via TLR signaling.

Effects of the combination of a monoclonal agonistic mouse anti-OX40 antibody and toll-like receptor agonists: Unmethylated CpG and LPS on an MB49 bladder cancer cell line in a mouse model

PurposeThe basis of the antitumor immunotherapy, of which the purpose is the stimulation of the immune system. We have used two of the Pathogen Associated Molecular Patterns: unmethylated CpG oligonucleotide, a ligand of Toll-like receptor 9 (TLR9), and lipopolysaccharide (LPS) which is recognized by TLR4, combined with an agonistic OX40 receptor-specific monoclonal antibody (anti-OX40), which is expressed by activated regulatory T-cells (and by other activated T-cell populations as well). The objective of this study was to prove the effectiveness of the aforementioned compounds in an animal model, on a bladder cancer cell line.MethodsWe have instilled MB49 cells subcutaneously, to the left musculus biceps femoris. We have created three observation groups, each containing ten mice. After eleven days, all treated mice bearing the size of 5–8 mm (in diameter) tumor were administered CpG + anti-OX40 or LPS + anti-OX40 three times with a three-day lap between each treatment. Mice in the control group did not receive any treatment.ResultsAll the specimens from the control and LPS + anti-OX40 groups have died by the sixtieth day of the observation period, however, five mice from the CpG + anti-OX40 group were still alive. The experiment lasted until the last surviving mouse died, which occurred on the 357th day after tumor implantation.DiscussionThe treatment with LPS did not make anti-OX40 more potent and did not increase the survival times. However, CpG + anti-OX40 has shown increased antitumor activity compared to the other two groups.

Reduction of endotoxicity in Bordetella bronchiseptica by lipid A engineering: Characterization of lpxL1 and pagP mutants

ABSTRACT Whole-cell vaccines against Gram-negative bacteria commonly display high reactogenicity caused by the endotoxic activity of lipopolysaccharide (LPS), one of the major components of the bacterial outer membrane. Underacylation of the lipid A moiety of LPS has been related with reduced endotoxicity in several Gram-negative species. Here, we evaluated whether the inactivation of two genes encoding lipid A acylases of Bordetella bronchiseptica, i.e. pagP and lpxL1, could be used for the development of less reactogenic vaccines against this pathogen for livestock and companion animals. Inactivation of pagP resulted in the loss of the secondary palmitate chain at position 3' of lipid A, but hardly affected the potency of the LPS to activate the Toll-like receptor 4 (TLR4). Inactivation of lpxL1 resulted in the loss of the secondary 2-hydroxy laurate group present at position 2 of lipid A and, unexpectedly, in the additional loss of the glucosamines that decorate the phosphate groups at positions 1 and 4' and in an increase in LPS molecules carrying O-antigen. The resulting LPS showed greatly reduced potency to activate TLR4 in HEK-Blue reporter cells expressing human or mouse TLR4 as well as in porcine macrophages. Characterization of the lpxL1 mutant revealed many pleiotropic phenotypes, including increased resistance to SDS and rifampicin, increased susceptibility to cationic antimicrobial peptides, decreased auto-aggregation and biofilm formation, and a tendency to decreased infectivity of macrophages, which are all related to the altered LPS structure. We suggest that the lpxL1 mutant will be useful for the generation of safer vaccines.

Role of lipid metabolism and systemic inflammation in the development of atherosclerosis in animal models

Systemic inflammation makes a significant contribution to the pathogenesis of atherosclerosis and has been the subject of numerous studies. Works aiming to analyze the mechanisms of atherosclerosis development often include experiments on animals. A primary task of such research is the characterization, justification, and selection of an adequate model.
 Aim. To evaluate the peculiarities of lipid metabolism and systemic inflammation in chronic obstructive pulmonary disease (COPD) in the development of atherosclerosis in animal models.
 Materials and Methods. Analyses of cross-links between species-specific peculiarities of lipid metabolism and the immune response, as well as a bioinformatic analysis of differences in Toll-like receptor 4 (TLR4) in mice, rats, and rabbits in comparison with its human homolog, were carried out. A search for and analysis of the amino acid sequences of human, mouse, rat, and rabbit TLR4 was performed in the International database GenBank of National Center of Biotechnical Information and in The Universal Protein Resource (UniProt) database. Multiple alignments of the TLR4 amino acid sequences were implemented in the Clustal Omega program, version 1.2.4. Reconstruction and visualization of molecular phylogenetic trees were performed using the MEGA7 program according to the Neighbor-Joining and Maximum Parsimony methods.
 Results. Species-specific differences of the peculiarities of lipid metabolism and the innate immune response in humans, mice, and rabbits were shown that must be taken into account in analyses of study results.
 Conclusion.Disorders in lipid metabolism and systemic inflammation mediated by the innate immune system participating in the pathogenesis of atherosclerosis in COPD possess species-specific differences that should be taken into account in analyses of study results.

A novel phosphoglycerol serine-glycine lipodipeptide of Porphyromonas gingivalis is a TLR2 ligand

Porphyromonas gingivalis is a Gram-negative anaerobic periodontal microorganism strongly associated with tissue-destructive processes in human periodontitis. Following oral infection with P. gingivalis, the periodontal bone loss in mice is reported to require the engagement of Toll-like receptor 2 (TLR2). Serine-glycine lipodipeptide or glycine aminolipid classes of P. gingivalis engage human and mouse TLR2, but a novel lipid class reported here is considerably more potent in engaging TLR2 and the heterodimer receptor TLR2/TLR6. The novel lipid class, termed Lipid 1256, consists of a diacylated phosphoglycerol moiety linked to a serine-glycine lipodipeptide previously termed Lipid 654. Lipid 1256 is approximately 50-fold more potent in engaging TLR2 than the previously reported serine-glycine lipid classes. Lipid 1256 also stimulates cytokine secretory responses from peripheral blood monocytes and is recovered in selected oral and intestinal Bacteroidetes organisms. Therefore, these findings suggest that Lipid 1256 may be a microbial TLR2 ligand relevant to chronic periodontitis in humans.

Mas-related G protein-coupled receptor D participates in inflammatory pain by promoting NF-κB activation through interaction with TAK1 and IKK complex

Mas-related G protein-coupled receptor D (MrgprD) is mainly expressed in small-diameter sensory neurons of the dorsal root ganglion (DRG). Results from previous studies suggest that MrgprD participates in mechanical hyperalgesia and nerve injury-induced neuropathic pain. However, it remains elusive whether and how MrgprD is involved in inflammatory pain. Here, we used a mouse model of chronic inflammatory pain established by intraperitoneal administration of lipopolysaccharide (LPS). The LPS injection induced an evident peripheral neuroinflammation and mechanical hyperalgesia in the mice and increased MrgprD expression in the DRG. The LPS administration also augmented the proportion of MrgprD-expressing neurons in the lumbar 4 DRG. Behaviorally, the LPS-induced hypersensitivities to mechanical and cold stimuli, but not to a heat stimulus, were substantially attenuated in Mrgprd-knockout mice compared with wildtype littermates. Mrgprd deletion in DRGs suppressed the LPS-triggered activation of the NF-κB signaling pathway and attenuated LPS-induced up-regulation of pro-inflammatory factors. Moreover, ectopic overexpression of MrgprD in HEK293 cells stably expressing mouse toll-like receptor 4 (TLR4) markedly promoted the LPS-induced NF-κB activation and enhanced NF-κB's DNA-binding activity. Furthermore, MrgprD physically interacted with TGF-β-activated kinase 1 (TAK1) and I-kappa-B-kinase (IKK) complexes, but not with mitogen-activated protein kinases (MAPKs) in mouse DRGs. In macrophage-like RAW 264.7 cells, MrgprD also interacted with TAK1 and IKK complex, and the treatment of MrgprD agonist elicited the activation of NF-κB signaling, but not of mitogen-activated protein kinases (MAPKs) signaling pathway. Our findings indicate that MrgprD facilitates the development of LPS-triggered persistent inflammatory hyperalgesia by promoting canonical NF-κB activation, highlighting the important roles of MrgprD in NF-κB-mediated inflammation and chronic pain.

Leptospiral LPS escapes mouse TLR4 internalization and TRIF‑associated antimicrobial responses through O antigen and associated lipoproteins.

Leptospirosis is a worldwide re-emerging zoonosis caused by pathogenic Leptospira spp. All vertebrate species can be infected; humans are sensitive hosts whereas other species, such as rodents, may become long-term renal carrier reservoirs. Upon infection, innate immune responses are initiated by recognition of Microbial Associated Molecular Patterns (MAMPs) by Pattern Recognition Receptors (PRRs). Among MAMPs, the lipopolysaccharide (LPS) is recognized by the Toll-Like-Receptor 4 (TLR4) and activates both the MyD88-dependent pathway at the plasma membrane and the TRIF-dependent pathway after TLR4 internalization. We previously showed that leptospiral LPS is not recognized by the human-TLR4, whereas it signals through mouse-TLR4 (mTLR4), which mediates mouse resistance to acute leptospirosis. However, although resistant, mice are known to be chronically infected by leptospires. Interestingly, the leptospiral LPS has low endotoxicity in mouse cells and is an agonist of TLR2, the sensor for bacterial lipoproteins. Here, we investigated the signaling properties of the leptospiral LPS in mouse macrophages. Using confocal microscopy and flow cytometry, we showed that the LPS of L. interrogans did not induce internalization of mTLR4, unlike the LPS of Escherichia coli. Consequently, the LPS failed to induce the production of the TRIF-dependent nitric oxide and RANTES, both important antimicrobial responses. Using shorter LPS and LPS devoid of TLR2 activity, we further found this mTLR4-TRIF escape to be dependent on both the co-purifying lipoproteins and the full-length O antigen. Furthermore, our data suggest that the O antigen could alter the binding of the leptospiral LPS to the co-receptor CD14 that is essential for TLR4-TRIF activation. Overall, we describe here a novel leptospiral immune escape mechanism from mouse macrophages and hypothesize that the LPS altered signaling could contribute to the stealthiness and chronicity of the leptospires in mice.

Insights into Sensing of Murine Retroviruses.

Retroviruses are major causes of disease in animals and human. Better understanding of the initial host immune response to these viruses could provide insight into how to limit infection. Mouse retroviruses that are endemic in their hosts provide an important genetic tool to dissect the different arms of the innate immune system that recognize retroviruses as foreign. Here, we review what is known about the major branches of the innate immune system that respond to mouse retrovirus infection, Toll-like receptors and nucleic acid sensors, and discuss the importance of these responses in activating adaptive immunity and controlling infection.

Glycine Lipids of Porphyromonas gingivalis Are Agonists for Toll-Like Receptor 2.

The serine-glycine dipeptide lipid classes, including lipid 430 and lipid 654, are produced by the periodontal pathogen Porphyromonas gingivalis and can be detected in lipid extracts of diseased periodontal tissues and teeth of humans. Both serine-glycine lipid classes were previously shown to engage human and mouse Toll-like receptor 2 (TLR2) and to inhibit mouse osteoblast differentiation and function through engagement of TLR2. It is not clear if other lipids related to serine-glycine lipids are also produced by P. gingivalis The goal of this investigation was to determine whether P. gingivalis produces additional lipid classes similar to the serine-glycine lipids that possess biological properties. P. gingivalis (ATCC 33277) was grown in broth culture, and lipids were extracted and fractionated by high-performance liquid chromatography (HPLC). Lipids were separated using semipreparative HPLC, and specific lipid classes were identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-multiple reaction monitoring (LC-MRM) mass spectrometric approaches. Two glycine lipid classes were identified, termed lipid 567 and lipid 342, and these lipid classes are structurally related to the serine-glycine dipeptide lipids. Both glycine lipid classes were shown to promote TLR2-dependent tumor necrosis factor alpha (TNF-α) release from bone marrow macrophages, and both were shown to activate human embryonic kidney (HEK) cells through TLR2 and TLR6 but not TLR1. These results demonstrate that P. gingivalis synthesizes glycine lipids and that these lipids engage TLR2 similarly to the previously reported serine-glycine dipeptide lipids.

Abstract B19: Cowpea mosaic virus stimulates antitumor immunity through recognition by MYD88-dependent signaling of multiple Toll-like receptors

Abstract Cowpea mosaic virus (CPMV), a non-enveloped plant virus, and empty CPMV (eCPMV), a virus-like particle composed of CPMV capsid, have demonstrated strong activation of neutrophils, suppression of primary tumor growth, and durable systemic antitumor immunity in murine models with no side effects when administered intratumorally as an in situ vaccine. However, it is not known how immune cells recognize these nanoparticles. In this study, CPMV and eCPMV exhibited overlapping yet distinctive recognition patterns and immunostimulatory profiles. Specifically, CPMV generated stronger selective induction of cytokines and chemokines in naive splenocytes and exhibited more potent antitumor efficacy compared to eCPMV. We found that MyD88 is required for both CPMV- and eCPMV-elicited immune responses. Screening with HEK-BlueTM mouse and human Toll-like receptor (TLR) assays along with response and efficacy studies in corresponding TLR-/- mice indicated the recognition of both CPMV and eCPMV by MyD88-dependent TLR2 and TLR4 as well as recognition of CPMV by TLR7. Furthermore, the studies revealed that TLR2 and TLR4 are complementary to each other in recognizing the capsid of either particle in vivo and in vitro. We further confirmed that secretion of type I interferons (IFNs) by CPMV is critical to its stronger efficacy, which is dependent on the binding between TLR7 and the encapsulated single-stranded RNAs (ssRNAs) of CPMV. These findings link efficacy with molecular recognition and provide rationale for developing more potent viral particles as immunotherapeutic vaccines to cancer. Citation Format: Chenkai Mao, Veronique Beiss, Sourabh Shukla, Nicole Steinmetz, Steven Fiering. Cowpea mosaic virus stimulates antitumor immunity through recognition by MYD88-dependent signaling of multiple Toll-like receptors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B19.

Single Stranded DNA Immune Modulators with Unmethylated CpG Motifs: Structure and Molecular Recognition by Toll-Like Receptor 9.

Single stranded microbial DNA fragments with unmethylated deoxycytidylyldeoxyguanosine dinucleotide (CpG) motifs are interpreted as danger signals by the innate immune system via recognition by the Toll-like Receptor 9 (TLR9). Their synthetic analogues, Oligodeoxynucleotides (ODN) comprise a promising class of immune modulators with potential applications in the treatment of multiple diseases, such as cancer, autoimmune diseases or allergy. ODN molecules contain a core hexamer sequence, which is species specific consisting of GACGTT and AACGT for mouse and GTCGTT in humans. Assessment of structural features of different type of ODNs is highly challenging. NMR spectroscopic insights were gained for a short, single CpG motif containing ODN 1668. The structural basis of ODN recognition by TLR9 recently started to unravel as crystal structures of TLR9 orthologues in complex with ODN 1668 were solved. Systematic investigations of ODN sequences revealed that ODNs with a single CpG motif are capable of activating mouse TLR9, but two closely positioned CpG motifs are necessary for activation of human TLR9. Furthermore, longer ODNs with TCC and TCG sequences at the 5' end were shown to activate TLR9 with higher efficiency. It was revealed that 5'-xCx motif containing short ODNs (sODN) are able to augment the immune response of short, single CpG containing ODNs, which are incapable of activating of TLR9 alone. All these observations pointed to the existence of a second binding site on TLR9, which was characterized in crystal structures that delivered further insights of the nucleic acid recognition of the innate immune system by TLR9.

Tracing the evolution of novel features of human Toll-like receptor 4.

Toll-like receptor 4 (TLR4) is a critical innate immune protein that activates inflammation in response to extracellular cues. Much of the work to understand how the protein works in humans has been done using mouse models. Although human and mouse TLR4 have many shared features, they have also diverged significantly since their last common ancestor, acquiring 277 sequence differences. Functional differences include the extent of ligand-independent activation, whether lipid IVa acts as an antagonist or agonist, and the relative species cross-compatibility of their MD-2 cofactor. We set out to understand the evolutionary origins for these functional differences between human and mouse TLR4. Using a combination of phylogenetics, ancestral sequence reconstruction, and functional characterization, we found that evolutionary changes to the human TLR4, rather than changes to the mouse TLR4, were largely responsible for these functional changes. Human TLR4 repressed ancestral ligand-independent activity and gained antagonism to lipid IVa. Additionally, mutations to the human TLR4 cofactor MD-2 led to lineage-specific incompatibility between human and opossum TLR4 complex members. These results were surprising, as mouse TLR4 has acquired many more mutations than human TLR4 since their last common ancestor. Our work has polarized this set of transitions and sets up work to study the mechanistic underpinnings for the evolution of new functions in TLR4.

Secretory Nanoparticles of Neospora caninum Profilin-Fused with the Transmembrane Domain of GP64 from Silkworm Hemolymph.

Neosporosis, which is caused by Neospora caninum, is a well-known disease in the veterinary field. Infections in pregnant cattle lead to abortion via transplacental (congenitally from mother to fetus) transmission. In this study, a N. caninum profilin (NcPROF), was expressed in silkworm larvae by recombinant Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid and was purified from the hemolymph. Three NcPROF constructs were investigated, native NcPROF fused with an N-terminal PA tag (PA-NcPROF), PA-NcPROF fused with the signal sequence of bombyxin from B. mori (bx-PA-NcPROF), and bx-PA-NcPROF with additional C-terminal transmembrane and cytoplasmic domains of GP64 from BmNPV (bx-PA-NcPROF-GP64TM). All recombinant proteins were observed extra- and intracellularly in cultured Bm5 cells and silkworm larvae. The bx-PA-NcPROF-GP64TM was partly abnormally secreted, even though it has the transmembrane domain, and only it was pelleted by ultracentrifugation, but PA-NcPROF and bx-PA-NcPROF were not. Additionally, bx-PA-NcPROF-GP64TM was successfully purified from silkworm hemolymph by anti-PA agarose beads while PA-NcPROF and bx-PA-NcPROF were not. The purified bx-PA-NcPROF-GP64TM protein bound to its receptor, mouse Toll-like receptor 11 (TLR-11), and formed unique nanoparticles. These results suggest that profilin fused with GP64TM was secreted as a nanoparticle with binding affinity to its receptor and this nanoparticle formation is advantageous for the development of vaccines to N. caninum.

Adjuvant effect of the novel TLR1/TLR2 agonist Diprovocim synergizes with anti–PD-L1 to eliminate melanoma in mice

Successful cancer immunotherapy entails activation of innate immune receptors to promote dendritic cell (DC) maturation, antigen presentation, up-regulation of costimulatory molecules, and cytokine secretion, leading to activation of tumor antigen-specific cytotoxic T lymphocytes (CTLs). Here we screened a synthetic library of 100,000 compounds for innate immune activators using TNF production by THP-1 cells as a readout. We identified and optimized a potent human and mouse Toll-like receptor (TLR)1/TLR2 agonist, Diprovocim, which exhibited an EC50 of 110 pM in human THP-1 cells and 1.3 nM in primary mouse peritoneal macrophages. In mice, Diprovocim-adjuvanted ovalbumin immunization promoted antigen-specific humoral and CTL responses and synergized with anti-PD-L1 treatment to inhibit tumor growth, generating long-term antitumor memory, curing or prolonging survival of mice engrafted with the murine melanoma B16-OVA. Diprovocim induced greater frequencies of tumor-infiltrating leukocytes than alum, of which CD8 T cells were necessary for the antitumor effect of immunization plus anti-PD-L1 treatment.

Cleavage of Toll-Like Receptor 9 Ectodomain Is Required for In Vivo Responses to Single Strand DNA.

Mouse toll-like receptor 9 (TLR9) is an endosomal sensor for single-stranded DNA. TLR9 is transported from the endoplasmic reticulum to endolysosomes by a multiple transmembrane protein Unc93 homolog B1, and proteolytically cleaved at its ectodomain. The structure of TLR9 and its biochemical analyses have shown that the proteolytic cleavage of TLR9 ectodomain enables TLR9-dimerization and TLR9 activation. However, the requirement of TLR9 cleavage in vivo has not been studied. We here show that the 13 amino acids deletion at the cleavage site made TLR9 resistant to proteolytic cleavage. The deletion mutation in the Tlr9 gene impaired TLR9-dependent cytokine production in conventional dendritic cells from the mutant mice. Not only in vitro, in vivo production of inflammatory cytokines (TNF-α and IL-12p40), chemokine (CCR5/RANTES), and type I interferon (IFN-α) induced by administration of TLR9 ligand was also impaired. These results demonstrate that the TLR9 cleavage is required for TLR9 responses in vivo.

Deposition and hydrolysis of serine dipeptide lipids of Bacteroidetes bacteria in human arteries: relationship to atherosclerosis

Multiple reaction monitoring-MS analysis of lipid extracts from human carotid endarterectomy and carotid artery samples from young individuals consistently demonstrated the presence of bacterial serine dipeptide lipid classes, including Lipid 654, an agonist for human and mouse Toll-like receptor (TLR)2, and Lipid 430, the deacylated product of Lipid 654. The relative levels of Lipid 654 and Lipid 430 were also determined in common oral and intestinal bacteria from the phylum Bacteroidetes and human serum and brain samples from healthy adults. The median Lipid 430/Lipid 654 ratio observed in carotid endarterectomy samples was significantly higher than the median ratio in lipid extracts of common oral and intestinal Bacteroidetes bacteria, and serum and brain samples from healthy subjects. More importantly, the median Lipid 430/Lipid 654 ratio was significantly elevated in carotid endarterectomies when compared with control artery samples. Our results indicate that deacylation of Lipid 654 to Lipid 430 likely occurs in diseased artery walls due to phospholipase A2 enzyme activity. These results suggest that commensal Bacteriodetes bacteria of the gut and the oral cavity may contribute to the pathogenesis of TLR2-dependent atherosclerosis through serine dipeptide lipid deposition and metabolism in artery walls.

Investigations on the molecular mode of action of the novel immunostimulator ZelNate: Activation of the cGAS-STING pathway in mammalian cells

Bovine respiratory disease (BRD) is usually prevented or treated with vaccines and/or antibiotics. The use of antibiotics is, however, of concern due to the potential promotion of microbial resistance and the occurrence of residues. Recently an alternative aid in the treatment of BRD, the cationic lipid/bacterial plasmid DNA liposome-based immunomodulator ZelNate, has entered the veterinary market. In the present study, we provide data on the molecular mode of action of ZelNate. Despite the presence of numerous non-methylated CpG motifs in its plasmid DNA, ZelNate proved to be inactive on human and mouse toll-like receptor 9 (TLR9) in cell culture, in both recombinant and natural cellular receptor settings. However, in the human monocyte cell line THP1 and in the mouse melanoma cell line B16, ZelNate activates strongly the stimulator of interferon genes (STING) pathway, which is known to lead predominantly to interferon response factor 3 (IRF3) activation. Further analysis in THP1 cells suggests that the ZelNate plasmid DNA activates STING via interaction with cyclic guanylate adenylate synthase (cGAS), but not via interferon induced gene 16 (IFI16). Our in vitro observations suggest that ZelNate may act predominantly via the cGAS/STING/IRF3 pathway.

Rationally Designed TLR4 Ligands for Vaccine Adjuvant Discovery.

ABSTRACTAdjuvant properties of bacterial cell wall components like MPLA (monophosphoryl lipid A) are well described and have gained FDA approval for use in vaccines such as Cervarix. MPLA is the product of chemically modified lipooligosaccharide (LOS), altered to diminish toxic proinflammatory effects while retaining adequate immunogenicity. Despite the virtually unlimited number of potential sources among bacterial strains, the number of useable compounds within this promising class of adjuvants are few. We have developed bacterial enzymatic combinatorial chemistry (BECC) as a method to generate rationally designed, functionally diverse lipid A. BECC removes endogenous or introduces exogenous lipid A-modifying enzymes to bacteria, effectively reprogramming the lipid A biosynthetic pathway. In this study, BECC is applied within an avirulent strain of Yersinia pestis to develop structurally distinct LOS molecules that elicit differential Toll-like receptor 4 (TLR4) activation. Using reporter cell lines that measure NF-κB activation, BECC-derived molecules were screened for the ability to induce a lower proinflammatory response than Escherichia coli LOS. Their structures exhibit varied, dose-dependent, TLR4-driven NF-κB activation with both human and mouse TLR4 complexes. Additional cytokine secretion screening identified molecules that induce levels of tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8) comparable to the levels induced by phosphorylated hexa-acyl disaccharide (PHAD). The lead candidates demonstrated potent immunostimulation in mouse splenocytes, human primary blood mononuclear cells (PBMCs), and human monocyte-derived dendritic cells (DCs). This newly described system allows directed programming of lipid A synthesis and has the potential to generate a diverse array of TLR4 agonist candidates.