Ken-ichiro Shibata

Synergistic Effect of Nod1 and Nod2 Agonists with Toll-Like Receptor Agonists on Human Dendritic Cells To Generate Interleukin-12 and T Helper Type 1 Cells

ABSTRACT A synthetic Nod2 agonist, muramyldipeptide (MDP), and two Nod1 agonists, FK565 and FK156, mimic the bacterial peptidoglycan moiety and are powerful adjuvants that induce cell-mediated immunity, especially delayed-type hypersensitivity. In this study, we used human dendritic cell (DC) cultures to examine possible T helper type 1 (Th1) responses induced by MDP and FK565/156 in combination with various synthetic Toll-like receptor (TLR) agonists, including synthetic lipid A (TLR4 agonist), the synthetic triacyl lipopeptide Pam3CSSNA (TLR2 agonist), poly(I:C) (TLR3 agonist), and CpG DNA (TLR9 agonist). Immature DCs derived from human monocytes expressed mRNAs for Nod1, Nod2, TLR2, TLR3, TLR4, and TLR9. The stimulation of DCs with MDP and FK565 in combination with lipid A, poly(I:C), and CpG DNA, but not with Pam3CSSNA, synergistically induced interleukin-12 (IL-12) p70 and gamma interferon (IFN-γ), but not IL-18, in culture supernatants and induced IL-15 on the cell surface. In correlation with the cytokine induction, an upregulation of the mRNA expression of these cytokine genes was observed. Notably, IL-12 p35 mRNA expression increased >1,000-fold upon stimulation with lipid A plus either MDP or FK565 compared with stimulation with each stimulant alone. In contrast, for the expression of CD83 and costimulatory molecules such as CD40, CD80, and CD86, no synergistic effects were observed upon stimulation with Nod plus TLR agonists. The culture supernatants of DCs stimulated with lipid A plus either MDP or FK565 activated human T cells to produce high levels of IFN-γ, and the activity was attributable to DC-derived IL-12. These findings suggest that Nod1 and Nod2 agonists in combination with TLR3, TLR4, and TLR9 agonists synergistically induce IL-12 and IFN-γ production in DCs to induce Th1-lineage immune responses.

Saccharomyces cerevisiae- and Candida albicans-derived mannan induced production of tumor necrosis factor alpha by human monocytes in a CD14- and Toll-like receptor 4-dependent manner.

The cytokine‐inducing activities of fungal polysaccharides were examined in human monocytes in culture, with special reference to CD14 and Toll‐like receptors (TLRs). Tumor necrosis factor alpha (TNF‐α) production by monocytes was markedly induced in a dose‐dependent manner upon stimulation with cell walls from Candida albicans and mannan from Saccharomyces cerevisiae and C. albicans, although relatively high concentrations (10 to 100 μg/ml) of stimulants were required for activation as compared with the reference lipopolysaccharide (LPS) (1 to 10 ng/ml). The yeast form C. albicans and its mannan and cell wall fractions exhibited higher TNF‐α production than respective preparations from the hyphal form. Only slight TNF‐α production was induced by the S. cerevisiae glucan. The TNF‐α production triggered by reference LPS and purified fungal mannans required the presence of LPS‐binding protein (LBP), and these responses were inhibited by anti‐CD14 and anti‐TLR4 antibodies, but not by anti‐TLR2 antibody. In contrast to the activity of LPS, the activity of purified S. cerevisiae mannan was not inhibited by polymyxin B. These findings suggested that the mannan‐LBP complex is recognized by CD14 on monocytes and that signaling through TLR4 leads to the production of proinflammatory cytokines in a manner similar to that induced by LPS.

Muramyldipeptide and diaminopimelic acid‐containing desmuramylpeptides in combination with chemically synthesized Toll‐like receptor agonists synergistically induced production of interleukin‐8 in a NOD2‐ and NOD1‐dependent manner, respectively, in human monocytic cells in culture

Two types of synthetic peptidoglycan fragments, diaminopimelic acid (DAP)‐containing desmuramylpeptides (DMP) and muramyldipeptide (MDP), induced secretion of interleukin (IL)‐8 in a dose‐dependent manner in human monocytic THP‐1 cells, although high concentrations of compounds are required as compared with chemically synthesized Toll‐like receptor (TLR) agonists mimicking bacterial components: TLR2 agonistic lipopeptide (Pam3CSSNA), TLR4 agonistic lipid A (LA‐15‐PP) and TLR9 agonistic bacterial CpG DNA. We found marked synergistic IL‐8 secretion induced by MDP or DAP‐containing DMP in combination with synthetic TLR agonists in THP‐1 cells. Suppression of the mRNA expression of nucleotide‐binding oligomerization domain (NOD)1 and NOD2 by RNA interference specifically inhibited the synergistic IL‐8 secretion induced by DMP and MDP with these TLR agonists respectively. In accordance with the above results, enhanced IL‐8 mRNA expression and the activation of nuclear factor (NF)‐κB induced by MDP or DMP in combination with synthetic TLR agonists were markedly suppressed in NOD2‐ and NOD1‐silenced cells respectively. These findings indicated that NOD2 and NOD1 are specifically responsible for the synergistic effects of MDP and DMP with TLR agonists, and suggested that in host innate immune responses to invading bacteria, combinatory dual signalling through extracellular TLRs and intracellular NODs might lead to the synergistic activation of host cells.

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

ABSTRACT The lipopeptide FSL-1 [S-(2,3-bispalmitoyloxypropyl)-Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe, Pam2CGDPKHPKSF] 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 (Pam2CGNNDESNISFKEK), 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-κB reporter activity of FSL-1 to human embryonic kidney 293 cells transfected with Toll-like receptor 2 and 6, together with a NF-κB-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.

Stimulation of human Toll-like receptor (TLR) 2 and TLR6 with membrane lipoproteins of Mycoplasma fermentans induces apoptotic cell death after NF-κB 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‐κB, 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‐κB 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‐κB 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‐κB 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.

Toll-like Receptors, NOD1, and NOD2 in Oral Epithelial Cells

Oral epithelium might be the first barrier against oral bacteria in periodontal tissue. We hypothesized that oral epithelium is endowed with innate immune receptors for bacterial components, which play roles in host defense against bacterial infection without being accompanied by excessive inflammatory responses. We found clear expression of Toll-like receptor (TLR)4 as well as TLR2, and strong expression of NOD1 and NOD2 in normal oral epithelial tissues by immunohistochemical analysis. We also showed that primary oral epithelial cells in culture expressed these molecules using PCR, flow cytometry, and immunostaining. In inflamed oral epithelium, cell-surface localizations of TLR2 and TLR4 were more clearly observed than in healthy tissue. Upon stimulation with synthetic ligands for these receptors, the expression of β-defensin 2 was markedly up-regulated. These findings indicate that these molecules in oral epithelial cells are functional receptors that induce antibacterial responses.

The N-terminal lipopeptide of a 44-kDa membrane-bound lipoprotein of Mycoplasma salivarium is responsible for the expression of intercellular adhesion molecule-1 on the cell surface of normal human gingival fibroblasts.

The activities to induce TNF-α production by a monocytic cell line, THP-1, and ICAM-1 expression and IL-6 production by human gingival fibroblasts were detected in plural membrane lipoproteins of Mycoplasma salivarium. Although SDS-PAGE of the lipoproteins digested by proteinase K did not reveal any protein bands with molecular masses higher than approximately10 kDa, these activities were detected in the front of the gel. A lipoprotein with a molecular mass of 44 kDa (Lp44) was purified. Proteinase K did not affect the ICAM-1 expression-inducing activity of Lp44, but lipoprotein lipase abrogated the activity. These results suggested that the proteinase K-resistant and low molecular mass entity, possibly the N-terminal lipid moiety, played a key role in the expression of the activity. The N-terminal lipid moiety of Lp44 was purified from Lp44 digested with proteinase K by HPLC. Judging from the structure of microbial lipopeptides as well as the amino acid sequence and infrared spectrum of Lp44, the structure of the N-terminal lipid moiety of Lp44 was speculated to be S-(2, 3-bisacyloxypropyl)-cysteine-GDPKHPKSFTEWV-. Its analogue, S-(2, 3-bispalmitoyloxypropyl)-cysteine-GDPKHPKSF, was synthesized. The lipopeptide was similar to the N-terminal lipid moiety of Lp44 in the infrared spectrum and the ICAM-1 expression-inducing activity. Thus, this study suggested that the active entity of Lp44 was its N-terminal lipopeptide moiety, the structure of which was very similar to S-(2, 3-bispalmitoyloxypropyl)-cysteine-GDPKHPKSF.

MyD88 But Not TRIF Is Essential for Osteoclastogenesis Induced by Lipopolysaccharide, Diacyl Lipopeptide, and IL-1α

Myeloid differentiation factor 88 (MyD88) plays essential roles in the signaling of the Toll/interleukin (IL)-1 receptor family. Toll–IL-1 receptor domain-containing adaptor inducing interferon-β (TRIF)-mediated signals are involved in lipopolysaccharide (LPS)-induced MyD88-independent pathways. Using MyD88-deficient (MyD88−/−) mice and TRIF-deficient (TRIF−/−) mice, we examined roles of MyD88 and TRIF in osteoclast differentiation and function. LPS, diacyl lipopeptide, and IL-1α stimulated osteoclastogenesis in cocultures of osteoblasts and hemopoietic cells obtained from TRIF−/− mice, but not MyD88−/− mice. These factors stimulated receptor activator of nuclear factor-κB ligand mRNA expression in TRIF−/− osteoblasts, but not MyD88−/− osteoblasts. LPS stimulated IL-6 production in TRIF−/− osteoblasts, but not TRIF−/− macrophages. LPS and IL-1α enhanced the survival of TRIF−/− osteoclasts, but not MyD88−/− osteoclasts. Diacyl lipopeptide did not support the survival of osteoclasts because of the lack of Toll-like receptor (TLR)6 in osteoclasts. Macrophages expressed both TRIF and TRIF-related adaptor molecule (TRAM) mRNA, whereas osteoblasts and osteoclasts expressed only TRIF mRNA. Bone histomorphometry showed that MyD88−/− mice exhibited osteopenia with reduced bone resorption and formation. These results suggest that the MyD88-mediated signal is essential for the osteoclastogenesis and function induced by IL-1 and TLR ligands, and that MyD88 is physiologically involved in bone turnover.

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‐κB reporter assay system in which human embryonic kidney 293 cells were transfected with TLR2 and TLR1 together with an NF‐κB luciferase reporter gene, S‐(2,3‐bispalmitoyloxypropyl)‐N‐palmitoyl‐Cys‐Lys‐Lys‐Lys‐Lys (Pam3CSK4) and Pam3CSSNA 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 CD14dS39‐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 (TLR2dE772‐S784) or TLR1 (TLR1dQ636‐K779) completely abrogated the CD14‐induced enhancement. Soluble recombinant CD14 added extracellularly enhanced the recognition of Pam3CSSNA 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 Pam3CSK4 at a dissociation constant of 5.7 µM. 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.

Involvement of Leucine Residues at Positions 107, 112, and 115 in a Leucine-Rich Repeat Motif of Human Toll-Like Receptor 2 in the Recognition of Diacylated Lipoproteins and Lipopeptides and Staphylococcus aureus Peptidoglycans

S-(2,3-bispalmitoyloxypropyl)Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe (FSL-1) derived from Mycoplasma salivarium stimulated NF-κB reporter activity in human embryonic kidney 293 (HEK293) cells transfected with Toll-like receptor 2 (TLR2) or cotransfected with TLR2 and TLR6, but not in HEK293 cells transfected with TLR6, in a dose-dependent manner. The activity was significantly higher in HEK293 cells transfected with both TLR2 and TLR6 than in HEK293 cells transfected with only TLR2. The deletion mutant TLR2ΔS40-I64 (a TLR2 mutant with a deletion of the region of Ser40 to Ile64) failed to activate NF-κB in response to FSL-1. The deletion mutant TLR2ΔC30-S39 induced NF-κB reporter activity, but the level of activity was significantly reduced compared with that induced by wild-type TLR2. A TLR2 point mutant with a substitution of Glu178 to Ala (TLR2E178A), TLR2E180A, TLR2E190A, and TLR2L132E induced NF-κB activation when stimulated with FSL-1, M. salivarium lipoproteins, and Staphylococcus aureus peptidoglycans, but TLR2L107E, TLR2L112E (a TLR2 point mutant with a substitution of Leu112 to Glu), and TLR2L115E failed to induce NF-κB activation, suggesting that these residues are essential for their signaling. Flow cytometric analysis demonstrated that TLR2L115E, TLR2L112E, and TLR2ΔS40-I64 were expressed on the cell surface of the transfectants as wild-type TLR2 and TLR2E190A were. In addition, these mutants, except for TLR2E180A, functioned as dominant negative form of TLR2. This study strongly suggested that the extracellular region of Ser40-Ile64 and leucine residues at positions 107, 112, and 115 in a leucine-rich repeat motif of TLR2 are involved in the recognition of mycoplasmal diacylated lipoproteins and lipopeptides and in the recognition of S. aureus peptidoglycans.