Isolation, structure elucidation, and synthesis of a macrophage stimulatory lipopeptide from Mycoplasma fermentans acting at picomolar concentration

Comparison of lipopeptide-based immunocontraceptive vaccines containing different lipid groups

We have previously shown that incorporating the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys) into peptide structures effectively adjuvants otherwise weak immunogens. In this study lipopeptides based on luteinising hormone releasing hormone (LHRH) as a B cell epitope, [B], were synthesised in tandem with a 17-residue T-helper epitope, [T], derived from the fusion protein of the morbillivirus canine distemper virus. In this way vaccine candidates with the structure [T]-[B] were produced. These peptides were then lipidated with different diacylated moieties. The acyl moieties used were: palmitic acid (C16) to give Pam2Cys, stearic acid (C18) to give Ste2Cys, lauric acid (C12) to give Lau2Cys and octanoic acid (C8) to give Oct2Cys. We compared the immunogenicities of these simple lipopeptides in BALB/c mice by measuring their ability to induce anti-LHRH antibodies and found that immunogenicity was dependent on the length of the alkane chains of the incorporated lipid moieties with the hierarchy C16=C18>C12>C8. The antibody levels elicited by the lipopeptides also correlated with their ability to inhibit the reproductive capability of female mice in fertility trials. Furthermore, the C16 lipopeptide was the most effective in activating dendritic cells, measured by up regulation of surface MHC Class II molecules, and also in activating NF-kappaB in a Toll-like receptor-2 (TLR2)-dependent manner.

CD14 directly binds to triacylated lipopeptides and facilitates recognition of the lipopeptides by the receptor complex of Toll-like receptors 2 and 1 without binding to the complex

It has demonstrated that the recognition of triacylated lipopeptides by Toll-like receptor (TLR) 2 requires TLR1 as a coreceptor. In the NF-kappaB reporter assay system in which human embryonic kidney 293 cells were transfected with TLR2 and TLR1 together with an NF-kappaB luciferase reporter gene, S-(2,3-bispalmitoyloxypropyl)-N-palmitoyl-Cys-Lys-Lys-Lys-Lys (Pam(3)CSK(4)) and Pam(3)CSSNA were recognized by TLR2/TLR1, but the recognition level was unexpectedly very low. However, cotransfection of CD14 drastically enhanced the recognition of triacylated lipopeptides by TLR2/TLR1. The CD14-induced enhancement did not occur without cotransfection of TLR1. Both CD14(dS39-A48), a mutant with deletion of the part of possible N-terminal ligand-binding pocket, and anti-CD14 monoclonal antibody reduced the CD14-induced enhancement. Transfection of a TIR domain-deficient mutant of TLR2 (TLR2(dE772-S784)) or TLR1 (TLR1(dQ636-K779)) completely abrogated the CD14-induced enhancement. Soluble recombinant CD14 added extracellularly enhanced the recognition of Pam(3)CSSNA by TLR2/TLR1. Immunoprecipitation analysis demonstrated that CD14 was not associated with TLR2 but that TLR1 was associated with TLR2. In addition, surface plasmon resonance-based assay demonstrated that CD14 binds to Pam(3)CSK(4) at a dissociation constant of 5.7 microM. This study suggests that CD14 directly binds to triacylated lipopeptides and facilitates recognition of the lipopeptides by the TLR2/TLR1 complex without binding to the receptor complex.

Toll-like receptor-2 is essential for the development of palmitate-induced insulin resistance in myotubes

Fatty acids can activate proinflammatory pathways leading to the development of insulin resistance, but the mechanism is undiscovered. Toll like receptor 2 (TLR2) recognizes lipids, activates proinflammatory pathways, and is genetically associated with inflammatory diseases. This study aimed to examine the role of TLR2 in palmitate-induced insulin resistance in C2C12 myotubes. Treatment with palmitate rapidly induced the association of myeloid differentiation factor 88 (MyD88) with the TLR2 receptor, activated the stress-linked kinases p38, JNK, and protein kinase C, induced degradation of IkappaBalpha, and increased NF-kappaB DNA binding. The activation of these pathways by palmitate was sensitive and temporally regulated and occurred within the upper physiologic range of saturated fatty acid concentrations in vivo, suggesting a receptor-mediated event and not simple lipotoxicity. When compared with an equimolar concentration of palmitate, fibroblast-stimulating lipopeptide-1, a known TLR2 ligand, was a slightly more potent activator of signal transduction and interleukin (IL)-6 production. Palmitate inhibited insulin signal transduction in C2C12 cells beginning 1-2 h after exposure and reached a maximum at 12-16 h. An antagonist TLR2 antibody, mAb 2.5, led to a 50-60% decrease in palmitate-induced IL-6 production and partially restored insulin signal transduction, whereas an isotype-matched control antibody had no effect. RNA interference-mediated inhibition of TLR2 and MyD88 expression in C2C12 muscle cells resulted in a near complete inhibition of palmitate-induced insulin resistance and IL-6 production. This study provides strong evidence that TLR2 mediates the initial events of fatty acid-induced insulin resistance in muscle.

Mycoplasma fermentans and TNF-beta interact to amplify immune-modulating cytokines in human lung fibroblasts

Mycoplasma can establish latent infections and are associated with arthritis, leukemia, and chronic lung disease. We developed an experimental model in which lung cells are deliberately infected with Mycoplasma fermentans. Human lung fibroblasts (HLF) were exposed to live M. fermentans and immune-modulating cytokine release was assessed with and without known inducers of cytokine production. M. fermentans increased IL-6, IL-8/CXCL8, MCP-1/CCL2, and Gro-alpha/CXCL1 production. M. fermentans interacted with TNF-beta to release more IL-6, CXCL8, and CXCL1 than predicted by the responses to either stimulus alone. The effects of live infection were recapitulated by exposure to M. fermentans-derived macrophage-activating lipopeptide-2 (MALP-2), a Toll-like receptor-2- and receptor-6-specific ligand. The synergistic effect of combined stimuli was more pronounced with prolonged incubations. Preexposure to TNF-beta sensitized the cells to subsequent MALP-2 challenge, but preexposure to MALP-2 did not alter the IL-6 response to TNF-beta. Exposure to M. fermentans or MALP-2 did not enhance nuclear localization, DNA binding, or transcriptional activity of NF-kappaB and did not modulate early NF-kappaB activation in response to TNF-beta. Application of specific inhibitors of various MAPKs suggested that p38 and JNK/stress-activated protein kinase were involved in early IL-6 release after exposure to TNF-beta and M. fermentans, respectively. The combined response to M. fermentans and TNF-beta, however, was uniquely sensitive to delayed application of SP-600125, suggesting that JNK/stress-activated protein kinase contributes to the amplification of IL-6 release. Thus M. fermentans interacts with stimuli such as TNF-beta to amplify lung cell production of immune-modulating cytokines. The mechanisms accounting for this interaction can now be dissected with the use of this in vitro model.

Antimicrobial activity of inducible human beta defensin-2 against Mycoplasma pneumoniae

Defensins in innate immunity are known to play critical roles to protect the host from infection by invasive microbes, including Gram-positive and -negative bacteria. However, little is known about the interactions between defensins and mycoplasmas. Human beta defensin (hBD)-2 and hBD-3, but not hBD-1, were found to exert strikingly antimicrobial activity against Mycoplasma pneumoniae. To elucidate the role of defensins in M. pneumoniae infection, a human pulmonary squamous cell line EBC-1 was stimulated with M. pneumoniae and interleukin (IL)-1beta. hBD-2 was markedly upregulated by IL-1beta as well as M. pneumoniae, but neither hBD-1 nor hBD-3 was apparently upregulated. Thus, the results suggest that inducible hBD-2 would play a critical role in the protection of M. pneumoniae infection.

Intranasal lipopeptide primes lung-resident memory CD8+ T cells for long-term pulmonary protection against influenza

The longevity of the influenza virus-specific CD8+ T cell response following intranasal delivery of a synthetic lipopeptide was investigated and the characteristics and location of the cells associated with viral clearance examined. The lipopeptide, incorporating an epitope for CD8+ T cells and another for CD4+ T cells with the lipid moiety S-[2,3-bis(palmitoyloxy)propyl]cysteine (Pam2Cys) attached, induced potent and long-lived pulmonary protection. Both the lipopeptide and its largely unprotective non-lipidated counterpart elicited comparable numbers of CD8+ T cells in the spleen, which was the main location of the memory pool. However, the lipopeptide, unlike the non-lipidated peptide, also induced a substantial memory population that remained in the lungs and was rapidly activated upon viral challenge months later. These lipopeptide-induced lung-resident CD8+ T cells were also very similar in number and IFN-gamma-secreting potential to those induced by prior exposure to the virus itself and are likely mediators of initial viral clearance prior to recruitment from the expanding lymph node T cell pool. Significant clearing responses were demonstrated as late as 9 months post-lipopeptide vaccination. This study shows that CD8+ T cells primed by the lipopeptide are not only long-lived but can take up residence in the lung where they are important early mediators of pulmonary protection.

Macrophage-activating lipopeptide-2 induces cyclooxygenase-2 and prostaglandin E(2) via toll-like receptor 2 in human placental trophoblast cells

We have examined whether toll-like receptor (TLR)2-mediated stimulation by macrophage-activating lipopeptide-2 (MALP-2), originally purified from Mycoplasma fermentans, induces cyclooxygenase (COX)-2 and prostaglandin (PG)E(2) in human placental trophoblast cells. The signaling mechanism by which MALP-2 exerts its effect has also been examined. Human placental trophoblast cells isolated from term placenta were used. TLR expression in trophoblast cells was confirmed by multiplex PCR and immunocytochemistry, and examined whether MALP-2 induces COX-2 and PGE(2) by Northern blotting, RT-PCR, Western blotting and ELISA, respectively. The activation of NF-kappaB and MAP kinases (ERK1/2 and p38) was examined by Western blotting. The effects of inhibitors of NF-kappaB, MEK1/2 and p38 on MALP-2-induced PGE(2) production were also evaluated. TLR2, TLR6 and TLR4 were expressed in human placental trophoblast cells. MALP-2 significantly induced COX-2 expression and enhanced PGE(2) production in a dose-dependent manner. MALP-2 induced the activation of NF-kappaB, ERK1/2 and p38 MAPK. Inhibitors of NF-kappaB, MEK1/2 and p38 blocked MALP-2-inducible PGE(2) production. TLR2-mediated stimulation by MALP-2 induces COX-2 and PGE(2) in human placental trophoblast cells via NF-kappaB and MAP kinases pathways.

Efficient systemic and mucosal responses against the HIV-1 Tat protein by prime/boost vaccination using the lipopeptide MALP-2 as adjuvant

A major goal of HIV-1 vaccine development is the induction of mucosal immune responses able to stop or reduce viral infection directly at the portal of entry. We established a heterologous prime/boost vaccination protocol based on intradermal priming with the HIV-1 Tat protein and intranasal boosting with the Tat protein co-administered with the mucosal adjuvant MALP-2. Strong Tat-specific humoral responses were elicited in vaccinated mice at both systemic and mucosal levels. The cellular responses were characterized by a Th1 dominant helper pattern. The heterologous prime/boost regimen was also able to induce Tat-specific CTL, which were absent in animals receiving the homologous prime boost scheme. Thus, the heterologous prime/boost protocol was the only regimen able to evoke both CTL and sIgA responses. This suggests that a similar approach can be exploited to develop multi-component vaccines against HIV-1 infections able to induce both systemic and mucosal immune responses.

Lipolanthionine Peptides Act as Inhibitors of TLR2-Mediated IL-8 Secretion. Synthesis and Structure−Activity Relationships

Lipoproteins from gram-positive and -negative bacteria, mycoplasma, and shorter synthetic lipopeptide analogues activate cells of the innate immune system via the Toll-like receptor TLR2/TLR1 or TLR2/TLR6 heterodimers. For this reason, these compounds constitute highly active adjuvants for vaccines either admixed or covalently linked. The lanthionine scaffold has structural similarity with the S-(2,3-dihydroxypropyl)cysteine core structure of the lipopeptides. Therefore, lanthionine-based lipopeptide amides were synthesized and probed for activity as potential TLR2 agonists or antagonists. A collection of analytically defined lipolanthionine peptide amides exhibited an inhibitory effect of the TLR2-mediated IL-8 secretion when applied in high molar excess to the agonistic synthetic lipopeptide Pam3Cys-Ser-(Lys)4-OH. Structure-activity relationships revealed the influence of the chirality of the two alpha-carbon atoms, the chain lengths of the attached fatty acids and fatty amines, and the oxidation level of the sulfur atom on the inhibitory activity of the lipolanthionine peptide amides.

TLR1- and TLR6-independent recognition of bacterial lipopeptides

Bacterial cell walls contain lipoproteins/peptides, which are strong modulators of the innate immune system. Triacylated lipopeptides are assumed to be recognized by TLR2/TLR1-, whereas diacylated lipopeptides use TLR2/TLR6 heteromers for signaling. Following our initial discovery of TLR6-independent diacylated lipopeptides, we could now characterize di- and triacylated lipopeptides (e.g. Pam(2)C-SK(4), Pam(3)C-GNNDESNISFKEK), which have stimulatory activity in TLR1- and in TLR6-deficient mice. Furthermore, for the first time, we present triacylated lipopeptides with short length ester-bound fatty acids (like PamOct(2)C-SSNASK(4)), which induce no response in TLR1-deficient cells. No differences in the phosphorylation of MAP kinases by lipopeptide analogs having different TLR2-coreceptor usage were observed. Blocking experiments indicated that different TLR2 heteromers recognize their specific lipopeptide ligands independently from each other. In summary, a triacylation pattern is necessary but not sufficient to render a lipopeptide TLR1-dependent, and a diacylation pattern is necessary but not sufficient to render a lipopeptide TLR6-dependent. Contrary to the current model, distinct lipopeptides are recognized by TLR2 in a TLR1- and TLR6-independent manner.

Lipopeptide structure determines TLR2 dependent cell activation level

Bacterial lipoproteins/peptides are composed of di-O-acylated-S-(2,3-dihydroxypropyl)-cysteinyl residues N-terminally coupled to distinct polypeptides, which can be N-acylated with a third fatty acid. Using a synthetic lipopeptide library we characterized the contribution of the lipid portion to the TLR2 dependent pattern recognition. We found that the two ester bound fatty acid length threshold is beyond eight C atoms because almost no response was elicited by cellular challenge with analogues carrying shorter acyl chains in HEK293 cells expressing recombinant human TLR2. In contrast, the amide bound fatty acid is of lesser importance. While two ester-bound palmitic acids mediate a high stimulatory activity of the respective analogue, a lipopeptide carrying one amide-bound and another ester-bound palmitic acid molecule was inactive. In addition, species specific LP recognition through murine and human TLR2 depended on the length of the two ester bound fatty acid chains. In conclusion, our results indicate the responsibility of both ester bound acyl chains but not of the amide bound fatty acid molecule for the TLR dependent cellular recognition of canonical triacylated LP, as well as a requirement for a minimal acyl chain length. Thus they might support the explanation of specific immuno-stimulatory potentials of different microorganisms and provide a basis for rational design of TLR2 specific adjuvants mediating immune activation to distinct levels.

The HIV-1 matrix protein p17 can be efficiently delivered by intranasal route in mice using the TLR 2/6 agonist MALP-2 as mucosal adjuvant

The HIV-1 matrix protein p17 is a structural protein essential in the life cycle of HIV, by acting as a virokine/immunomodulator that supports viral replication and spreading. The presence of p17-specific antibodies and CTL responses correlates with slower progression to AIDS. Intranasal vaccination with p17 and the TLR2/6 agonist MALP-2 stimulates strong humoral and cellular immune responses at systemic and mucosal levels. The antibodies blocked p17 binding to its receptor, which is a critical step for the exertion of its virokine activity. Our results suggest that p17 and MALP-2 are attractive candidates for incorporation in mucosal vaccines against HIV/AIDS.

Characterization and Partial Purification of a Macrophage-Stimulating Factor from Mycoplasma hominis

PROBLEM

Mycoplasma hominis is one of the most common pathogens of the genital tract and is associated with increased production of proinflammatory cytokines in reproductive tissues during preterm labor. The mechanism by which M. hominis, an organism lacking cell walls, increases the production of proinflammatory cytokines is unknown.

METHOD OF STUDY

We characterized and purified a macrophage-activating factor from this organism.

RESULTS

Extraction of whole organisms with Triton-X-114 demonstrated that the activity was primarily associated with the detergent phase. Macrophage-stimulating activity (MSA) of detergent extracts of M. hominis was not inhibited by polymyxin B or heating but was completely abrogated by alkaline hydrolysis and partially reduced by proteinase K digestion. Further experiments that utilized Toll-like receptor (TLR)-2- and TLR-4-transfected cells, revealed that the detergent extracts activate TLR-2 but not TLR-4 signal transduction. Purification of the activity using preparative SDS-PAGE and reverse phase chromatography experiments led to the isolation of a 29-kDa protein.

CONCLUSIONS

These experiments suggest that the MSA of M. hominis is due to a lipophillic factor that interacts with TLR-2 rather than TLR-4 (as does lipopolysaccharide), to increase tumor necrosis factor (TNF)-alpha by macrophages. It is known that TNF-alpha can cause preterm labor and intrauterine fetal death and that it is upregulated in amniotic fluid samples infected with M. hominis.

Non-LPS targets and actions of LPS binding protein (LBP)

LPS binding protein (LBP) was discovered about 20 years ago because of its ability to bind to bacterial lipopolysaccharide (LPS). We have shown that in addition to its complex function of transferring LPS to its cellular receptor into the cell or into lipoproteins, LBP also binds to other bacterial compounds and can modulate their ability to stimulate the host's innate immune system. The majority of compounds found to also interact with LBP are amphiphilic molecules such as glycolipids or lipoproteins. Lipoteichoic acid (LTA) of different Gram-positive bacteria is recognized by LBP and both its complexation with CD14 and biological activity towards immune cells is modulated by LBP. LTA-like glycolipids isolated from spirochetes are recognized by LBP and initiate signaling in the presence of LBP. Lipopeptides corresponding to lipoproteins present in spirochetes, Mycobacterium spp. and Gram-negative bacteria as well as Mycoplasma spp. are also recognized by LBP. Together with the growing number of related proteins of the BPI-PLUNC family, LBP apparently as soluble mediator has the important ability to recognize a variety of bacterial pathogens before cellular contact has been established. The different sources of LBP in tissues such as lung and intestine further support its role as an important defense molecule.

Isolation and partial purification of macrophage- and dendritic cell-activating components from Mycoplasma arthritidis: association with organism virulence and involvement with Toll-like receptor 2

Mycoplasma arthritidis induces toxicity, arthritis, and dermal necrosis in mice. Virulence factors include a superantigen and membrane adhesins and possibly also a bacteriophage component. Here we compare the biological properties of Triton X-114 extracts derived from avirulent and virulent M. arthritidis strains. Macrophage cell lines and resident peritoneal macrophages were used to assess inflammatory potential as indicated by production of tumor necrosis factor alpha, interleukin-6, and/or nitric oxide. The activity resided exclusively within the hydrophobic detergent phase, was unaffected by heat treatment at 100 degrees C for 30 min, and was resistant to proteinase K digestion, suggesting involvement of a lipopeptide. Contamination of extracts with endotoxin or superantigen was excluded. Extracts of the more virulent strain had higher activity than did those of the avirulent strain. Using CHO cells expressing Toll-like receptor 2 (TLR2) or TLR4, both with transfected CD14, we showed that extracts activated these cells via TLR2 but not by TLR4. Also, macrophages from C57BL/6 TLR2(-/-) mice failed to respond to the extracts, whereas those from TLR2(+/+) cells did respond. The preparations from the virulent strain of M. arthritidis were also more potent in activating dendritic cells, as evidenced by up-regulation of major histocompatibility complex class II, CD40, B7-1, and B7-2. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent elution of gel slices revealed the presence of three active moieties which corresponded to molecular masses of approximately 24, 28, and 40 kDa. Three active components were also found by reverse-phase chromatography. We suggest that macrophage activation by M. arthritidis could play a significant role in the inflammatory response induced in the host by this organism.

A Dipalmitoylated Lipoprotein fromMycoplasma pneumoniaeActivates NF-κB through TLR1, TLR2, and TLR6

The pathogenesis of Mycoplasma pneumoniae infection is considered to be in part attributed to excessive immune responses. Recently, lipoproteins from mycoplasmas have been reported to induce NF-kappaB activation. In this study, we examined the ability of lipoproteins from M. pneumoniae to activate NF-kappaB, and the active component responsible for the NF-kappaB activation was identified. Lipid-associated membrane proteins from M. pneumoniae were found to induce NF-kappaB through TLR 2 in a human monocytic cell line, THP-1. The active component of the Lipid-associated membrane proteins was a subunit b of F0F1-type ATPase (F0F1-ATPase). The F0F1-ATPase is assumed to contain two palmitic acids. The activation of NF-kappaB by the F0F1-ATPase was inhibited by a dominant negative construct of TLR1 and TLR6. These results indicate that the activation of NF-kappaB by F0F1-ATPase is dependent on TLR1, TLR2, and TLR6. The activity of the F0F1-ATPase was decreased with pretreatment of lipoprotein lipase but not protease, indicating that the lipid moiety of the F0F1-ATPase was important for the NF-kappaB activation. Thus, a dipalmitoylated lipoprotein from M. pneumoniae was found to activate NF-kappaB through TLR1, TLR2, and TLR6.

Pyrexia, anorexia, adipsia, and depressed motor activity in rats during systemic inflammation induced by the Toll-like receptors-2 and -6 agonists MALP-2 and FSL-1

Macrophage-activating lipopeptide-2 (MALP-2) from Mycoplasma fermentans has been identified as a pathogen-associated molecular pattern of Mycoplasmas that causes activation of the innate immune system through the activation of the heterodimeric Toll-like receptors (TLRs)-2 and -6. The aim of this study was to characterize the ability of MALP-2 and a synthetic analog fibroblast-stimulating lipopeptide-1 (FSL-1; represents the NH2-terminal sequence of a lipoprotein from M. salivarium) to act as exogenous pyrogens, to induce formation of cytokines (endogenous pyrogens), and to cause sickness behavior, such as depressed motor activity, anorexia, and adipsia. For this purpose, body temperature, activity, food intake, and water intake were recorded for 3 days by use of telemetry devices in several groups of rats treated with MALP-2/FSL-1 or the respective control solutions. Intraperitoneal injections of FSL-1 caused fever at doses of 10 or 100 microg/kg, which was preceded by a pronounced phase of hypothermia in response to a dose of 1,000 microg/kg. The maximal fever (a peak of 1.5 degrees C above baseline) was caused by the 100 microg/kg dose with almost identical responses to both MALP-2 and FSL-1. Fever was accompanied by pronounced rises of the proinflammatory cytokines TNF and IL-6 in plasma. Treatment with the TLR-2 and -6 agonists further induced a dose-dependent manifestation of anorexia and adipsia, as well as a reduction of motor activity. We could thus demonstrate that activation of TLR-2 and -6 can induce systemic inflammation in rats accompanied by the classical signs of brain-controlled illness responses.

Improved intranasal immunization with live-attenuated measles virus after co-inoculation of the lipopeptide MALP-2

The macrophage-activating lipopeptide with a molecular weight of 2kDa (MALP-2) activates antigen presenting cells of human, mouse and rat origin in vitro and in vivo. Here, we demonstrate that MALP-2 induces MIP1alpha and beta, MIP-2, Gro, TNFalpha, IL1alpha and IL6 in cells of cotton rats (Sigmodon hispidus) in vitro. Intranasal inoculation into cotton rats leads to migration of neutrophils and other leucocytes into the lung lumen and lung tissue. After intranasal co-inoculation of MALP-2 with live-attenuated measles vaccine virus, higher titers of neutralizing antibodies are induced but the proliferative T cell response did not increase. Immunization leads to protective immunity in the absence, but not in the presence of passively transferred measles virus (MV) specific antibodies.

Domain exchange between human toll-like receptors 1 and 6 reveals a region required for lipopeptide discrimination

Among the 10 human Toll-like receptors (TLRs), TLR2 appears to be unique in its requirement for cooperation with other TLRs, namely TLR1 and TLR6, to mediate cell signaling. Through reconstitution experiments, we have defined more precisely the function of these human TLRs. Human colonic epithelial cells cotransfected with TLR1 and -2 preferentially respond to a synthetic tripalmitoylated bacterial lipopeptide analogue (Pam(3)CSK(4)). However, examination of a wide variety of lipopeptide derivatives indicates that recognition by human TLR1 and -2 does not strictly correlate with the number or position of the acyl chains on the modified cysteine residue. Conversely, human TLR2 and -6 exclusively respond to lipopeptides possessing a diacylglycerol group. Most surprisingly, we have found that an R stereoisomer of diacylated macrophage-activating lipopeptide 2 (MALP-2) exclusively activates epithelial cells through TLR6 and -2 but not through TLR1 and -2. These results suggest that the chirality of the central carbon of the diacylglycerol group of these agonists is a structural determinant for human TLR recognition. Examination of chimeric receptors, generated by domain exchange between TLR1 and -6, has revealed that leucine-rich repeats 9-12 of the extracellular domain enable these receptors to discriminate between structurally similar lipopeptides. However, additional chimeric constructs reveal that this region alone is not sufficient to generate receptors that can functionally cooperate with TLR2. Our results support the idea that TLR1 and TLR6 diverged during evolution to differentially recognize natural lipoprotein structures and that this function has been conserved with respect to the human receptors.

Binding of mycoplasmas to solid phase adsorbents

The capture of mycoplasmas (M. hominis, M. buccale, M. fermentans, M. bovis, M. synoviae, M. gallisepticum and M. arthritidis) based on lipid structures and adhesion molecules present in the mycoplasmal membrane was tested using different chromatographic resins (ActiClean Etox, ClarEtox, Heparin-Actigel, Sulfated Hiflow and SulfEtox). All of the resins efficiently reduced mycoplasma concentrations in Phosphate Buffered Saline (PBS) and in Fetal Bovine Serum (FBS) by 3-8 logs in a few minutes. This technology could be used for removing mycoplasmas from tissue culture components such as serum, and for concentrating mycoplasmas in vaccine production.

Synthesis and conformational properties of phosphopeptides related to the human tau protein

In the brains of Alzheimer's disease patients, the tau protein dissociates from the axonal microtubule and abnormally aggregates to form a paired helical filament (PHF). One of the priorities in Alzheimer research is to determine the effects of abnormal phosphorylation on the local structure. A series of peptides corresponding to isolated regions of tau protein have been successfully synthesized using Fmoc-based chemistry and their conformations were determined by 1H NMR spectroscopy and circular dichroism (CD) spectroscopy. Immunodominant peptides corresponding to tau-(256-273), tau-(350-367) and two phosphorylated derivatives in which a single Ser was phosphorylated at positions 262 and 356, respectively, were the main focus of the study. A direct alteration of the local structure after phosphorylation constitutes a new strategy through which control of biological activity can be enforced. In our study on Ser262 in R1 peptide and Ser356 in R4 peptide, phosphorylation modifies both the negative charge and the local conformation nearby the phosphorylation sites. Together, these structural changes indicate that phosphorylation may act as a conformational switch in the binding domain of tau protein to alter specificity and affinity of binding to microtubule, particularly in response to the abnormal phosphorylation events associated with Alzheimer's disease.

Experimental genital mycoplasmosis causes increased levels of mRNA for IL-6 and TNF-alpha in the placenta

PROBLEM

Previous studies with animal models have shown that injection of lipopolysaccharide (LPS) results in fetal loss and increases production of proinflammatory cytokines at the maternal-fetal interface. Most intrauterine infections, however, are associated with Ureaplasma urealyticum, a microorganism that lacks a cell wall and therefore does not contain LPS. Previous work in our laboratory with an animal model for genital infection with a similar organism, Mycoplasma pulmonis, revealed that widespread infection in maternal and fetal tissues can be experimentally induced with minimal manipulation of the animal. For this project, we tested the hypothesis that administration of the organism by a hematogenous route at gestational day (gd) 14 would result in increased tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 production by the placenta.

STUDY DESIGN

Timed-pregnant, Sprague-Dawley rats were anesthetized on gd 14 and 10(7) CFU of M. pulmonis strain X1048 or an equivalent volume of sterile medium was injected into the heart. Rats were necropsied on gd 18 or 21, and ex vivo production of TNF-alpha and IL-6 was evaluated from six randomly selected placentas from each litter. The remaining placentas were harvested and either snap-frozen or placed in formalin. Frozen placentas were processed for real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of TNF-alpha and IL-6 mRNA. Formalin-fixed placentas were sectioned and stained with hematoxylin and eosin for lesion analysis.

RESULTS

Concentrations of TNF-alpha but not IL-6 were significantly higher in conditioned medium from placentas harvested from infected dams at gd 21. Levels of mRNA for IL-6 and TNF-alpha, however, were increased by M. pulmonis at gd 18 and 21. Analysis of gd 21 placentas by light microscopy revealed that significant histological chorioamnionitis was present in infected animals with accumulations of neutrophils in the capsular decidua.

CONCLUSION

These data indicate that experimental infection with M. pulmonis causes histological chorioamnionitis, elevated mRNA levels of TNF-alpha and IL-6 in placental tissues, and the secretion of TNF-alpha by the placenta during late gestation.

Attenuated pathogenesis of polymicrobial peritonitis in mice after TLR2 agonist pre-treatment involves ST2 up-regulation

The innate immune system uses Toll-like receptors (TLRs) to activate and instruct immune responses against microbial pathogens. Administration of TLR agonists to mice induces a state of hyporesponsiveness, or tolerance, characterized by reduced cytokine production upon subsequent second challenge. The present study examined the effects of pre-treatment of mice with TLR2-dependent stimuli on the host defense against acute polymicrobial infection. Immune priming of mice with macrophage-activating lipopeptide-2 (MALP-2) 4 days prior to infection greatly improves survival and bacterial clearance in a model of polymicrobial septic peritonitis which is associated with enhanced accumulation of effector neutrophils in the peritoneal cavity. Further, the systemic and local production of both myeloid differentiation factor 88 (MyD88)-dependently and MyD88-independently produced cytokines was substantially diminished, but not completely absent, in TLR2-treated mice. While pre-treatment with MALP-2 does not involve differential expression of TLR and IL-1R-associated kinase proteins, ST2, a negative regulator of TLR signaling, was up-regulated after treatment of mice with either MALP-2 or N-alpha-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-L-cysteine. Therefore, ST2 may be a mechanism, among others, to attenuate the sepsis-induced cytokine burst. Thus, these results suggest that immune protection in mice after pre-treatment with TLR2-dependent stimuli involves the induction of enhanced pathogen defense by neutrophils. In addition, up-regulation of ST2 could contribute to the diminished cytokine production.

Efficacy of macrophage-activating lipopeptide-2 combined with interferon-gamma in a murine asthma model

RATIONALE

The incidence and prevalence of allergic asthma, caused by Th2-mediated inflammation in response to environmental antigens, is increasing. Epidemiologic data suggest that a lack of Th1-inducing factors may play a pivotal role in the development of this disease. We have previously shown that dendritic cells treated with macrophage-activating lipopeptide-2 (MALP-2) combined with IFN-gamma modulate the Th2 response toward Th1 in an in vitro allergy model.

OBJECTIVE

To test in vivo efficacy of this regime, the effects of the substances were evaluated in a mouse model of allergic airway inflammation.

METHODS

Female Balb/c mice were sensitized to ovalbumin, whereas control animals were sham-sensitized with adjuvant only. After 4 weeks, MALP-2 and IFN-gamma or NaCl, respectively, were intratracheally instillated. After inhalational ovalbumin challenge, airway hyperreactivity (AHR) to inhaled methacholine was measured by head-out body plethysmography. The animals were subsequently killed to sample bronchoalveolar lavage fluid and lungs.

RESULTS

Sensitized NaCl-treated mice developed marked AHR compared with sham-sensitized animals. This coincided with eosinophilia as well as the amplification of eotaxin and the Th2 cytokines interleukin (IL)-5 and IL-13 in the bronchoalveolar lavage fluid. Treatment of sensitized mice with MALP-2 and IFN-gamma significantly reduced AHR compared with the sensitized, NaCl-treated positive control. Eosinophilia as well as Th2 cytokines were reduced to the levels of unsensitized animals. In contrast, IL-12p70 and neutrophils were markedly increased by treatment with both substances.

CONCLUSION

These data demonstrate the in vivo efficacy of MALP-2 and IFN-gamma to reduce allergic inflammation and AHR in allergic asthma.

The Mucosal Adjuvant Macrophage-Activating Lipopeptide-2 Directly Stimulates B Lymphocytes via the TLR2 without the Need of Accessory Cells

The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.

Heat shock protein 60: specific binding of lipopolysaccharide

Human heat shock protein 60 (HSP60) has been shown to bind to the surface of innate immune cells and to elicit a proinflammatory response. In this study we demonstrate that the macrophage stimulatory property of recombinant human HSP60 is tightly linked to the HSP60 molecule and is lost after protease treatment. However, inhibition of macrophage stimulation was reached by the LPS-binding peptide magainin II amide. Indeed, HSP60 specifically bound [(3)H]LPS. [(3)H]LPS binding to HSP60 was saturable and competable by the unlabeled ligand. To identify the epitope region of the HSP60 molecule responsible for specific LPS binding, we analyzed the effect of several anti-HSP60 mAbs on HSP60-induced production of inflammatory mediators from macrophages. We identified only one mAb, clone 4B9/89, which blocked the macrophage stimulatory activity of the chaperone. The epitope specificity of this mAb points to the region aa 335-366 of HSP60. Clone 4B9/89 also strongly inhibited [(3)H]LPS binding to HSP60. A more detailed analysis was performed by screening with selected overlapping 20-mer peptides of the HSP60 sequence, covering the region aa 331-380. Only one peptide blocked LPS binding to HSP60, thereby restricting the potential LPS-binding region to aa 351-370 of HSP60. Finally, analysis of selected 15-mer peptides and a 13-mer peptide of the HSP60 sequence revealed that most of the LPS-binding region was accounted for by aa 354-365 of HSP60, with the motif LKGK being critical for binding. Our studies identified a defined region of HSP60 involved in LPS binding, thereby implicating a physiological role of human HSP60 as LPS-binding protein.

Immunostimulants and Toll-like receptor ligands obtained by screening combinatorial lipopeptide collections*

Synthetic lipopeptides carrying the head group of bacterial lipoproteins are specific ligands of Toll-like receptors (TLR). The three fatty acids containing lipopeptides with the tripalmitoyl-S-glyceryl-cysteinyl N-terminus (Pam(3)Cys) are agonists of TLR2. The structurally related lipopeptides with a head group lacking the fatty acyl residue at the amino-terminus (Pam(2)Cys) stimulate TLR2 and 6. To investigate the influence of the peptide chain of lipohexapeptides with a free N-terminus with regard to their ability to enhance B-cell proliferation, a randomized S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteinyl-pentapeptide amide collection Pam(2)CysXXXXX and 5 x 19 subcollections (Pam(2)CysOXXXX, Pam(2)CysXOXXX, Pam(2)CysXXOXX, Pam(2)CysXXXOX, Pam(2)CysXXXXO, O: all protein amino acids except Cys) were prepared by parallel solid-phase synthesis. The collection represents synthetic lipopeptide analogues of the numerous bacterial lipoproteins and of mycoplasma lipoprotein. Each of the 95 subcollections is characterized by one defined and four degenerated amino acid positions thus comprising 19(4) individual lipopeptides with free N-terminal amino groups. High-performance liquid chromatography electrospray mass spectrometry (HPLC-ESI-MS) was applied for the analytical characterization of the lipohexapeptide amide subcollections and for the individual lipohexapeptide amides. The subcollections were tested for polyclonal activation of murine spleen cells, deconvolution led to highly active single S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteinyl-pentapeptide amides.

Toll-like receptor 6-independent signaling by diacylated lipopeptides

Bacterial lipopeptides are strong immune modulators that activate early host responses after infection as well as initiating adjuvant effects on the adaptive immune system. These lipopeptides induce signaling in cells of the immune system through Toll-like receptor 2 (TLR2)-TLR1 or TLR2-TLR6 heteromers. So far it has been thought that triacylated lipopeptides, such as the synthetic N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteine (Pam3)-CSK4, signal through TLR2-TLR1 heteromers, whereas diacylated lipopeptides, like the macrophage-activating lipopeptide from Mycoplasma fermentans (MALP2) or S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteine (Pam2)-CGNNDESNISFKEK, induce signaling through TLR2-TLR6 heteromers. Using new synthetic lipopeptide derivatives we addressed the contribution of the lipid and, in particular, the peptide moieties with respect to TLR2 heteromer usage. In contrast to the current model of receptor usage, not only triacylated lipopeptides, but also diacylated lipopeptides like Pam2CSK4 and the elongated MALP2 analog Pam2CGNNDESNISFKEK-SK4 (MALP2-SK4) induced B lymphocyte proliferation and TNF-alpha secretion in macrophages in a TLR6-independent manner as determined with cells from TLR6-deficient mice. Our results indicate that both the lipid and the N-terminal peptides of lipoproteins contribute to the specificity of recognition by TLR2 heteromers and are responsible for the ligand-receptor interaction on host cells.

Characterization of a B220+Lymphoid Cell Subpopulation with Immune Modulatory Functions in Nasal-Associated Lymphoid Tissues

Complex mechanisms operate on mucosal tissues to regulate immune responsiveness and tolerance. When the lymphocyte subpopulations from murine nasal-associated lymphoid tissues (NALT) were characterized, we observed an accumulation of B220(low)CD3(low)CD4(-)CD8(-)CD19(-)c-Kit(+) cells. TCR transgenic mice and athymic mice were used for monitoring T cell lineage and the presence of extrathymic T cell precursors. The majority of cells from NALT exhibited a T cell precursor phenotype (CD4(-)CD8(-)CD19(-)c-Kit(+)). Fas-independent apoptosis was their main mechanism of cell death. We also demonstrated that B220(low)CD4(-)CD8(-)CD19(-) cells from NALT exhibited the potential to down-regulate the activation of mature T cells. However, the innate immunity receptor TLR2 was also highly expressed by this cell subpopulation. Moreover, nasal stimulation with a TLR2/6 agonist resulted in a partial activation of the double-negative cells. These results suggest that the immune responses in NALT may be in part modulated by a cell subpopulation that maintains a tolerogenic milieu by its proapoptotic status and suppressive activity, which can be reverted through stimulation of a TLR signaling cascade.

The Mycoplasma-derived macrophage-activating 2-kilodalton lipopeptide triggers global immune activation on nasal mucosa-associated lymphoid tissues

A better knowledge on how immune responses are initiated in mucosal tissues would facilitate the design of new mucosal vaccines, as well as improve our understanding on host defense against infection. We investigated the mechanisms of adjuvanticity of the Mycoplasma-derived macrophage-activating 2-kDa lipopeptide (MALP-2), which binds to the heterodimer formed by the Toll-like receptors 2 and 6 (TLR2 and -6), at the level of the murine nasal mucosa-associated lymphoid tissues (NALT). TLR2 expression analysis demonstrated that several cell types from the nasal cavity were able to overexpress this receptor, either constitutively (such as B cells) or after stimulation (i.e., T cells). MALP-2 stimulated a strong B-cell activation. In addition, the antigen presentation capacity of dendritic cells was improved after in vivo loading with antigen in the presence of MALP-2. We also observed an up-regulated expression of activation markers and adhesion molecules on T cells, suggesting that they have enhanced responsiveness and interaction potential. Quantitative reverse transcription-PCR analysis showed that MALP-2 administration resulted in the stimulation of a proinflammatory cascade. We observed an early up-regulated expression of IP-10, MCP-1, MCP-3, MIP-1alpha, MIP-2, and CCR-2 which was reversed within 36 h. The obtained results demonstrated that MALP-2 creates a reversible local microenvironment which promotes effective priming of T and B cells in the NALT.

The macrophage-activating lipopeptide-2 accelerates wound healing in diabetic mice

Wound healing in healthy individuals proceeds at an optimal rate. However, in patients, with -- e.g.-- locally impaired blood flow or diabetes, chronic wounds develop and often become infected. Chronic wounds mean a low quality of life for the afflicted patients, not to mention enormous costs. Rather than using recombinant growth factors to accelerate wound healing, we employed the toll-like receptor agonist macrophage-activating lipopeptide-2 (MALP-2) to improve the healing of full-thickness excision skin wounds in an animal model with obese, diabetic mice. A gene array experiment suggested that MALP-2 stimulates the release of various mediators involved in wound healing. Further data to be presented in this study will show (i) that MALP-2 is capable of stimulating the appearance of the monocyte chemoattractant protein-1 at the wound site, (ii) that this leads to increased leucocyte and, in particular, macrophage infiltration and (iii) that MALP-2-treated wounds closed 2 weeks earlier than vehicle-treated controls. MALP-2, thus, appears to stimulate the early inflammatory process needed to set in motion the ensuing consecutive natural steps of wound healing resulting in wound closure.

Selective impairment of TLR-mediated innate immunity in human newborns: neonatal blood plasma reduces monocyte TNF-alpha induction by bacterial lipopeptides, lipopolysaccharide, and imiquimod, but preserves the response to R-848

Newborns are at increased risk of overwhelming infection, yet the mechanisms underlying this susceptibility are incompletely defined. In this study we report a striking 1- to 3-log decrease in sensitivity of monocytes in human neonatal cord blood, compared with monocytes in adult peripheral blood, to the TNF-alpha-inducing effect of multiple TLR ligands, including bacterial lipopeptides (BLPs), LPS, and the imidazoquinoline compound, imiquimod. In marked contrast, TNF-alpha release in response to R-848, a TLR ligand that is a congener of imiquimod, was equivalent in newborn and adult blood. Differences in ligand-induced TNF-alpha release correlated with divergent ligand-induced changes in monocyte TNF-alpha mRNA levels. Newborn and adult monocytes did not differ in basal mRNA or protein expression of TLRs or mRNA expression of functionally related molecules. Newborn monocytes demonstrated diminished LPS-induced, but equivalent R-848-induced, phosphorylation of p38 mitogen-activated protein kinase and altered BLP- and LPS-induced acute modulation of cognate receptors, suggesting that the mechanism accounting for the observed differences may be localized proximal to ligand recognition by surface TLRs. Remarkably, newborn plasma conferred substantially reduced BLP-, LPS-, and imiquimod-induced TNF-alpha release on adult monocytes without any effect on R-848-induced TNF-alpha release, reflecting differences in a plasma factor(s) distinct from soluble CD14. Impaired response to multiple TLR ligands may significantly contribute to immature neonatal immunity. Conversely, relative preservation of responses to R-848 may present unique opportunities for augmenting innate and acquired immunity in the human newborn.

Purification and characterization of a lipopeptide produced by Bacillus thuringiensis CMB26

AIMS

To isolate an antagonist for use in the biological control of phytopathogenic fungi including Colletotrichum gloeosporioides, then to purify and characterize the biocontrol agent produced by the antagonist.

METHODS AND RESULTS

Bacteria that exhibited antifungal activity against the causative agent pepper anthracnose were isolated from soil, with Bacillus thuringiensis CMB26 showing the strongest activity. A lipopeptide produced by B. thuringiensis CMB26 was precipitated by adjusting the pH 2 with 3 n HCl and extracted using chloroform/methanol (2:1, v/v) and reversed-phase HPLC. The molecular weight was estimated as 1447 Da by MALDI-TOF mass spectrometry. Scanning electron and optical microscopies showed that the lipopeptide has activity against Escherichia coli O157:ac88, larvae of the cabbage white butterfly (Pieris rapae crucivora) and phytopathogenic fungi. The lipopeptide had cyclic structure and the amino acid composition was L-Glu, D-Orn, L-Tyr, D-allo-Thr, D-Ala, D-Val, L-Pro, and L-Ile in a molar ratio of 3:1:2:1:1:2:1:1. The purified lipopeptide showed the same amino acid composition as fengycin, but differed slightly in fatty acid composition, in which the double bond was at carbons 13-14 (m/z 303, 316) and there was no methyl group.

CONCLUSION

A lipopeptide was purified and characterized from B. thuringiensis CMB26 and found to be similar to the lipopeptide fengycin. This lipopeptide can function as a biocontrol agent, and exhibits fungicidal, bactericidal, and insecticidal activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Compared with surfactin and iturin, the lipopeptide from B. thuringiensis CMB26 showed stronger antifungal activity against phytopathogenic fungi. This lipopeptide is a candidate for the biocontrol of pathogens in agriculture.

A totally synthetic vaccine of generic structure that targets Toll-like receptor 2 on dendritic cells and promotes antibody or cytotoxic T cell responses

A simple generic peptide-based vaccine structure that targets Toll-like receptor 2-expressing dendritic cells and causes their activation is described. The vaccines are totally synthetic, serve as their own adjuvant, and are composed of (i) a single helper T cell epitope, (ii) a target epitope that is either recognized by CD8+ T cells or B cells, and (iii) a Toll-like receptor 2-targeting lipid moiety, S-[2,3-bis(palmitoyloxy)propyl]cysteine, that is situated between the peptide epitopes to form a branched configuration. The different CD8+ T cell epitopes examined were from (i) influenza virus, (ii) the intracellular bacterium Listeria monocytogenes, and (iii) ovalbumin as a model tumor antigen. Vaccines containing a B cell epitope from gastrin or luteinizing hormone-releasing hormone as a B cell epitope were also examined for their ability to elicit antibody against the parent hormones. Each of the vaccines was capable of inducing either CD8+ T cell or antibody-mediated immune responses. The lipidated vaccines, but not the nonlipidated vaccines, were able to mediate protection against viral or bacterial infection and mediate prophylactic and therapeutic anticancer activity. The two hormone-based vaccines induced high antibody titers, which in the case of luteinizing hormone-releasing hormone resulted in abrogation of reproductive function. These results highlight the utility of simple, totally synthetic, epitope-based vaccines.

Lipid-associated membrane proteins of Mycoplasma fermentans and M. penetrans activate human immunodeficiency virus long-terminal repeats through Toll-like receptors

Mycoplasmas are known to enhance human immunodeficiency virus (HIV) replication, and mycoplasma-derived lipid extracts have been reported to activate nuclear factor-kappaB (NF-kappaB) through Toll-like receptors (TLRs). In this study, we examined the involvement of TLRs in the activation of HIV long-terminal repeats (LTR) by mycoplasma and their active components responsible for the TLR activation. Lipid-associated membrane proteins (LAMPs) from two species of mycoplasma (Mycoplasma fermentans and M. penetrans) that are associated with acquired immune-deficiency syndrome (AIDS), were found to activate HIV LTRs in a human monocytic cell line, THP-1. NF-kappaB deletion from the LTR resulted in inhibition of the activation. The LTR activation by M. fermentans LAMPs was inhibited by a dominant negative (DN) construct of TLR1 and TLR6, whereas HIV LTR activation by M. penetrans LAMPs was inhibited by DN TLR1, but not by DN TLR6. These results indicate that the activation of HIV LTRs by M. fermentans and M. penetrans LAMPs is dependent on NF-kappaB, and that the activation of HIV LTR by M. fermentans LAMPs is mediated through TLR1, TLR2 and TLR6. In contrast, the LTR activation by M. penetrans LAMPs is carried out through TLR1 and TLR2, but not TLR6. Subsequently, the active component of M. penetrans and M. fermentans LAMPs was purified by reverse-phase high-performance liquid chromatography (HPLC). Interestingly, the purified lipoprotein of M. penetrans LAMPs (LPMp) was able to activate NF-kappaB through TLR1 and TLR2. On the other hand, the activation of NF-kappaB by purified lipoprotein of M. fermentans LAMPs (LPMf) was mediated through TLR2 and TLR6, but not TLR1.

Lipopolysaccharide binding protein binds to triacylated and diacylated lipopeptides and mediates innate immune responses

LPS binding protein (LBP) is an acute-phase protein synthesized predominantly in the liver of the mammalian host. It was first described to bind LPS of Gram-negative bacteria and transfer it via a CD14-enhanced mechanism to a receptor complex including TLR-4 and MD-2, initiating a signal transduction cascade leading to the release of proinflammatory cytokines. In recent studies, we found that LBP also mediates cytokine induction caused by compounds derived from Gram-positive bacteria, including lipoteichoic acid and peptidoglycan fragments. Lipoproteins and lipopeptides have repeatedly been shown to act as potent cytokine inducers, interacting with TLR-2, in synergy with TLR-1 or -6. In this study, we show that these compounds also interact with LBP and CD14. We used triacylated lipopeptides, corresponding to lipoproteins of Borrelia burgdorferi, mycobacteria, and Escherichia coli, as well as diacylated lipopeptides, corresponding to, e.g., 2-kDa macrophage activating lipopeptide of Mycoplasma spp. Activation of Chinese hamster ovary cells transfected with TLR-2 by both lipopeptides was enhanced by cotransfection of CD14. Responsiveness of human mononuclear cells to these compounds was greatly enhanced in the presence of human LBP. Binding of lipopeptides to LBP as well as competitive inhibition of this interaction by LPS was demonstrated in a microplate assay. Furthermore, we were able to show that LBP transfers lipopeptides to CD14 on human monocytes using FACS analysis. These results support that LBP is a pattern recognition receptor transferring a variety of bacterial ligands including the two major types of lipopeptides to CD14 present in different receptor complexes.

TGF-beta receptor signaling is critical for mucosal IgA responses

TGF-beta receptor (TbetaR) signaling is important for systemic IgA production; however, its contribution to IgA secretion at mucosal sites remained uncertain. This important question was addressed using mice lacking the TbetaR in B cells (TbetaRII-B). Although reduced, IgA-secreting cells and IgA were still present in the systemic and mucosal compartments. The adaptive immune response was investigated after oral or nasal immunization using adjuvants acting on different molecular targets, namely, the cholera toxin B subunit and the macrophage-activating lipopeptide-2. Efficient Ag-specific cellular and humoral responses were triggered both in controls and TbetaRII-B mice. However, a significant reduction in Ag-specific IgG2b and increased levels of IgG3 were observed in sera from TbetaRII-B mice. Furthermore, Ag-specific IgA-secreting cells, serum IgA, and secretory IgA were undetectable in TbetaRII-B mice. These results demonstrate the critical role played by TbetaR in Ag-driven stimulation of secretory IgA responses in vivo.

Synthetic lipopeptide adjuvants and Toll-like receptor 2--structure-activity relationships

Bacterial lipoproteins and their synthetic analogues (sLP) are strong immune modulators of the early host responses after infection. Synthetic lipopeptides are strong adjuvants for the adaptive immune system. Lipoproteins and lipopeptides induce signalling in immune cells through Toll-like receptor-TLR2/TLR1 heterodimers. By screening a combinatorial lipohexapeptide amide collection in an in vitro IL-8 induction assay, we systematically evaluated the potential of 19 proteinogenic amino acids in the peptide moiety of Pam3Cys-lipopeptides to interact with TLR2. New Pam3Cys-lipopeptides with high activity were obtained. Different fatty acids were introduced to investigate the influence of the acyl moiety. Lipopeptides with modifications in the core structure of the unusual amino acid S-glycerylcysteine were synthesized and tested for IL-8 induction via TLR2.

The Toll-like receptor-2/6 agonist macrophage-activating lipopeptide-2 cooperates with IFN-gamma to reverse the Th2 skew in an in vitro allergy model

Dendritic cells (DC) are the most potent APCs with the capacity to induce, modulate, or shut down immune function. These features make them potentially useful for treating diseases associated with misled immunologic responses. Therefore, it was the aim of this study to reverse the allergen-dependent Th2 reaction responsible for allergic symptoms by modulating DC function. This issue was addressed in an in vitro test system consisting of human monocyte-derived allergen-pulsed DC from allergics cocultured with autologous lymphocytes. A Th2 reaction judged by the amplification of IL-4 and the down-regulation of IFN-gamma was induced by pulsing DC with the relevant allergen. To modulate this reaction, the Toll-like receptor 2/6 engaging mycoplasmal lipopetide macrophage-activating lipopeptide 2 kDa was combined with IFN-gamma to stimulate allergen-pulsed DC. Such treatment resulted in a 500-fold increase in IFN-gamma production in the supernatant of cocultured autologous lymphocytes, while the Th2 marker IL-4 was not affected. This phenomenon was associated with an increase in proliferation and the number of IFN-gamma-producing lymphocytes. Phenotype and function of thus treated DC remained stable. These data indicate that a former allergen-dependent Th2 reaction can be reversed toward a Th1-type response by an appropriate treatment of DC.

Microbial stimulation by Mycoplasma fermentans synergistically amplifies IL-6 release by human lung fibroblasts in response to residual oil fly ash (ROFA) and nickel

Mycoplasma (MP), such as the species M. fermentans, possess remarkable immunoregulatory properties and can potentially establish chronic latent infections with little signs of disease. Atmospheric particulate matter (PM) is a complex and diverse component of air pollution associated with adverse health effects. We hypothesized that MP modulate the cellular responses induced by chemical stresses such as residual oil fly ash (ROFA), a type of PM rich in transition metals. We assessed the release of interleukin-6 (IL-6), a prototypic immune-modulating cytokine, in response to PM from different sources in human lung fibroblasts (HLF) deliberately infected with M. fermentans. We found that M. fermentans and ROFA together synergistically stimulated production of IL-6 compared to either stimuli alone. Compared to several other PM, ROFA appeared most able to potentiate IL-6 release. The potentiating effect of live MP infection could be mimicked by M. fermentans-derived macrophage-activating lipopeptide-2 (MALP-2), a known Toll-like receptor-2 agonist. The aqueous fraction of ROFA also contained potent IL-6 inducing activity in concert with MALP-2, and exposure to several defined metal salts indicated that Ni and, to a lesser extent V, (but not Cu) could synergistically act with MALP-2 to induce IL-6. These data indicate that microorganisms like MP can interact with environmental stimuli such as PM-derived metals to synergistically activate signaling pathways that control lung cell cytokine production and, thus, can potentially modulate adverse health effects of PM exposure.

Synthesis of Thiol-Reactive Lipopeptide Adjuvants. Incorporation into Liposomes and Study of Their Mitogenic Effect on Mouse Splenocytes

Synthetic analogues of triacylated and diacylated lipopeptides derived from the N-terminal domain of respectively bacterial and mycoplasmal lipoproteins are highly potent immunoadjuvants when administered either in combination with protein antigens or covalently linked to small peptide epitopes. Because of their amphipathic properties, lipopeptides, such as S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-glycine (Pam(3)CAG), can be conveniently incorporated into liposomes and serve as anchors for antigens that are linked to them. To design vaccination constructs based on synthetic peptides and liposomes as vectors. we have accordingly synthesized a series of lipopeptides that differ by the number (Pam(3)C vs Pam(2)C) and nature of the acyl chains (palmitoyl vs oleoyl) and by the presence at their C-terminus of thiol-reactive functions, such as maleimide or bromoacetyl. When incorporated into liposomes, these latter functionalized lipopeptides allow, in aqueous media, a well controlled chemoselective conjugation of HS-peptides to the surface of the vesicles. Using a BALB/c mice splenocyte proliferation assay ([(3)H]thymidine incorporation), we have measured the lymphocyte activation potency of the different lipopeptides. We found that, compared to their free (emulsified) forms, the liposomal lipopeptides were endowed with enhanced mitogenic activities; i.e., up to 2 orders of magnitude for Pam(3)CAG which was more potent than Pam(2)CAG. The impact of functionalization on the cellular activity of Pam(3)CAG was dependent on the thiol-reactive group introduced: whereas the bromoacetyl derivative retained its full activity, the presence of a maleimide group virtually abolished the lymphocyte activation of the lipopeptide. Finally, the substitution of saturated palmitoyl chains by unsaturated oleoyl chains was inhibitory. Thus, thiol-reactive Ol(3)CAG derivatives were the least active mitogens in our assay. Taken together, our findings are of importance for the further optimization of antigen-specific liposomal-based synthetic vaccines; the bromoacetyl derivative of Pam(3)CAG should be a promising lipopeptide derivative serving as an anchor for peptide epitopes while retaining its lymphocyte activation activity.

Biological activities of Bacteroides forsythus lipoproteins and their possible pathological roles in periodontal disease

Bacteroides forsythus is a gram-negative, anaerobic, fusiform bacterium and is considered to be an etiological agent in periodontal disease. A lipoprotein fraction prepared from B. forsythus cells by Triton X-114 phase separation (BfLP) activated human gingival fibroblasts and a human monocytic cell line, THP-1, to induce interleukin-6 production and tumor necrosis factor alpha production. BfLP was found to be capable of inducing nuclear factor-kappaB translocation in human gingival fibroblasts and THP-1 cells. By using Chinese hamster ovary K1 cells transfected with Toll-like receptor genes together with a nuclear factor-kappaB-dependent CD25 reporter plasmid, it was found that signaling by BfLP was mediated by Toll-like receptor 2 but not by CD14 or Toll-like receptor 4. BfLP induced apoptotic cell death in human gingival fibroblasts, KB cells (an oral epithelial cell line), HL-60 cells (a human myeloid leukemia cell line), and THP-1 cells but not in MOLT4 cells (a T-cell leukemia cell line). Caspase-8, an initiator caspase in apoptosis, was found to be activated in these cells in response to BfLP stimulation. Thus, this study suggested that BfLP plays some etiological roles in oral infections, especially periodontal disease, by induction of cell activation or apoptosis.

Relationship between structures and biological activities of mycoplasmal diacylated lipopeptides and their recognition by toll-like receptors 2 and 6

The lipopeptide FSL-1 [S-(2,3-bispalmitoyloxypropyl)-Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe, Pam(2)CGDPKHPKSF] synthesized on the basis of the N-terminal structure of a Mycoplasma salivarium lipoprotein capable of activating normal human gingival fibroblasts to induce the cell surface expression of ICAM-1 revealed an activity to induce production of monocyte chemoattractant protein 1, interleukin-6 (IL-6), and IL-8. FSL-1 also activated macrophages to produce tumor necrosis factor alpha as the Mycoplasma fermentans-derived lipopeptide MALP-2 (Pam(2)CGNNDESNISFKEK), a potent macrophage-activating lipopeptide, did. The level of the activity of FSL-1 was higher than that of MALP-2. This result suggests that the difference in the amino acid sequence of the peptide portion affects the activity because the framework structure other than the amino acid sequence of the former is the same as that of the latter. To determine minimal structural requirements for the activity of FSL-1, the diacylglyceryl Cys and the peptide portions were examined for this activity. Both portions did not reveal the activity. A single amino acid substitution from Phe to Arg and a fatty acid substitution from palmitic acid to stearic acid drastically reduced the activity. Similar results were obtained in measuring the NF-kappaB reporter activity of FSL-1 to human embryonic kidney 293 cells transfected with Toll-like receptor 2 and 6, together with a NF-kappaB-dependent luciferase reporter plasmid. These results suggest that both the diacylglyceryl and the peptide portions of FSL-1 are indispensable for the expression of biological activities and for the recognition by Toll-like receptors 2 and 6 and that the recognition of FSL-1 by Toll-like receptors 2 and 6 appears to be hydrophobic.

The Toll-like receptor ligand MALP-2 stimulates dendritic cell maturation and modulates proteasome composition and activity

A 2-kDa synthetic derivative of the macrophage-activating lipopeptide (MALP-2) from Mycoplasma fermentans is a potent inducer of monocytes/macrophages and improves the immunogenicity of antigens co-administered by systemic and mucosal routes. Dendritic cells (DC) are the most potent antigen-presenting cells, which are able to prime naive T cells in vivo. To elucidate the underlying mechanisms of MALP-2 adjuvanticity, we analyzed its activity on bone marrow-derived murine DC. In vitro stimulation of immature murine DC with MALP-2 resulted in the induction of maturation with up-regulated expression of MHC class II, costimulatory (CD80, CD86) and adhesion (CD40, CD54) molecules. MALP-2 also enhances the secretion of cytokines (IL-1alpha, IL-6 and IL-12), and increases DC stimulatory activity on naive and antigen-specific T cells. Further studies demonstrated that MALP-2 treatment of DC results in a dose-dependent shift from the protein pattern of proteasomes to immunoproteasomes (up-regulation of LMP2, LMP7 and MECL1), which correlates with an increased proteolytic activity. Thus, the adjuvanticity of MALP-2 can be mediated, at least in part, by the stimulation of DC maturation, which in turn leads to an improved antigen presentation. Therefore, MALP-2 is a promising molecule for the development of immune therapeutic or prophylactic interventions.

Stimulation of human Toll-like receptor (TLR) 2 and TLR6 with membrane lipoproteins of Mycoplasma fermentans induces apoptotic cell death after NF-kappa B activation

Mycoplasmal membrane diacylated lipoproteins not only initiate proinflammatory responses through Toll-like receptor (TLR) 2 and TLR6 via the activation of the transcriptional factor NF-kappaB, but also initiate apoptotic responses. The aim of this study was to clarify the apoptotic machineries. Mycoplasma fermentans lipoproteins and a synthetic lipopeptide, MALP-2, showed cytocidal activity towards HEK293 cells transfected with a TLR2-encoding plasmid. The activity was synergically augmented by co-expression of TLR6, but not by co-expression of other TLRs. Under the condition of co-expression of TLR2 and TLR6, the lipoproteins could induce maximum NF-kappa B activation and apoptotic cell death in the cells 6 h and 24 h after stimulation respectively. Dominant-negative forms of MyD88 and FADD, but not IRAK-4, reduced the cytocidal activity of the lipoproteins. In addition, both dominant-negative forms also downregulated the activation of both NF-kappa B and caspase-8 in the cells. Additionally, the cytocidal activity was sufficiently attenuated by a selective inhibitor of p38 MAPK. These findings suggest that mycoplasmal lipoproteins can trigger TLR2- and TLR6-mediated sequential bifurcate responses: NF-kappa B activation as an early event, which is partially mediated by MyD88 and FADD; and apoptosis as a later event, which is regulated by p38 MAPK as well as by MyD88 and FADD.

Cytoplasmic Domain-mediated Dimerizations of Toll-like Receptor 4 Observed by β-Lactamase Enzyme Fragment Complementation

Toll-like receptors (TLRs) detect the presence of microbial challenge and initiate innate immune defensive responses. In this work we have explored the mechanism and role of TLR dimerization in signal transduction using the newly developed technique of beta-lactamase protein fragment complementation, among others. We observed that TLR4 interactions with itself, with MyD88, or with TLR2 were accurately reported by the enzyme complementation technique. That technique, as well as co-immunoprecipitation, transfection-initiated cell activation, and site-directed mutagenesis all suggest an important role for TLR intracellular domains in receptor dimerization. These findings broaden our understanding of TLR self-interactions as well as heterodimer formation.

Tumour suppression induced by the macrophage activating lipopeptide MALP-2 in an ultrasound guided pancreatic carcinoma mouse model

BACKGROUND AND AIM

Carcinoma of the exocrine pancreas has a particularly poor prognosis. Therefore, novel therapeutic strategies such as immunotherapy are required. Here we investigated the immunomodulatory capacity of macrophage activating lipopeptide 2 (MALP-2), which binds to toll-like receptors 2 and 6 and induces activation of nuclear factor kappaB in monocytes. This causes the release of early stage leucocyte attracting chemokines and proinflammatory cytokines.

METHODS

MALP-2 was tested in a new orthotopic ultrasound guided pancreatic cancer mouse model. This model is close to the biological situation and avoids the stress and immunostimulation caused by laparotomy. Cells from the syngeneic, highly aggressive, and metastatic cell line Panc 02 were administered orthotopically, by ultrasound guidance, to C57bl/6 mice. MALP-2 was administered intratumorally or intraperitoneally and tumour growth, immune status, and leucocyte infiltration at the tumour site were determined.

RESULTS

We showed a tumour suppressive effect induced by a single injection of MALP-2. Median survival increased from 21 to 30 days (p<0.002). Combining chemotherapy (gemcitabine) with MALP-2 treatment caused further prolonged survival (median survival 27 days with chemotherapy alone v 37 days for combined treatment; p<0.0002). The life prolonging effect was paralleled by a significant increase in cytotoxic T cells, restoration of beta2 integrin expression on lymphocytes, and high expression of CD45RB on T helper cells. Immunohistochemical stains showed strong cytotoxic T lymphocyte and natural killer cell infiltration.

CONCLUSIONS

In conclusion, in a model of orthotopic pancreatic cancer in mice, we induced a tumour suppressive effect by treatment with a synthetic lipopeptide. Treatment with MALP-2 could be an option for immunotherapy in pancreatic cancer.