Th17 Cell Induction by Adhesion of Microbes to Intestinal Epithelial Cells.

Intestinal Th17 cells are induced and accumulate in response to colonization with a subgroup of intestinal microbes such as segmented filamentous bacteria (SFB) and certain extracellular pathogens. Here, we show that adhesion of microbes to intestinal epithelial cells (ECs) is a critical cue for Th17 induction. Upon monocolonization of germ-free mice or rats with SFB indigenous to mice (M-SFB) or rats (R-SFB), M-SFB and R-SFB showed host-specific adhesion to small intestinal ECs, accompanied by host-specific induction of Th17 cells. Citrobacter rodentium and Escherichia coli O157 triggered similar Th17 responses, whereas adhesion-defective mutants of these microbes failed to do so. Moreover, a mixture of 20 bacterial strains, which were selected and isolated from fecal samples of a patient with ulcerative colitis on the basis of their ability to cause a robust induction of Th17 cells in the mouse colon, also exhibited EC-adhesive characteristics.

Adhesion of enterohemorrhagic Escherichia coli O157:H7 to the intestinal epithelia is essential for inducing secretory IgA antibody production in the intestine of mice.

We examined whether adherence of enterohemorrhagic Escherichia coli (EHEC) O157:H7 to intestinal epithelial cells contributed to the induction of secretory immunoglobulin A (IgA) antibody production in mice. Wild-type EHEC O157:H7 and its mutants deficient in the espA, sepL, tir and eae genes, encoding adherent factors on the locus of enterocyte effacement (LEE), were inoculated intragastrically into mice. Inoculation of wild-type EHEC induced fecal IgA antibodies specific to EHEC at 4 weeks after the inoculation, but that of espA- and sepL-deletion mutants did not. Furthermore, even 4 inoculations at weekly intervals with espA-deletion mutant, heat-killed wild-type EHEC and nonpathogenic E. coli did not induce fecal IgA antibodies, although these bacterial inoculations induced serum antibodies. Kanamycin (Km)-treated mice showed prolonged and similar fecal shedding of Km-resistant mutants of EHEC O157:H7 including A2-F6 having intact LEE, A6-E7 (sepL-insertion mutant), G1-E11 (tir-insertion mutant) and Δeae (eae-deletion mutant). In this case, A2-F6 induced fecal IgA antibodies, but the other mutants with defective LEE did not. In contrast to the fecal IgA antibodies, serum IgM and IgG antibodies were induced in mice inoculated with any of the LEE defective mutants as well as A2-F6. Thus, adhesion of EHEC to epithelial cells is essential for inducing the mucosal immune response in the intestine but not for inducing the systemic immune response.

Inhibition of interferon-γ-induced nitric oxide production by 10-hydroxy-trans-2-decenoic acid through inhibition of interferon regulatory factor-8 induction.

10-Hydroxy-trans-2-decenoic acid (10H2DA) is a major lipid component of royal jelly, a honey bee secretion used to nourish the queen bee and young larvae. In this study, we examined the effect of 10H2DA on interferon (IFN)-γ-induced nitric oxide (NO) production. IFN-γ-induced NO production and activation of the inducible NO synthase promoter were significantly inhibited by 10H2DA. IFN-γ-induced phosphorylation of signal transducer and activator of transcription-1 was not affected by 10H2DA. In contrast, IFN-γ-induced tumor necrosis factor (TNF)-α production and nuclear factor (NF)-κB activation were inhibited by 10H2DA. IFN-γ-mediated induction of interferon regulatory factor (IRF)-8, but not IRF-1, was also inhibited by 10H2DA. IFN-γ-induced TNF-α production followed by activation of NF-κB is known to be essential for NO production. Together, 10H2DA inhibited IFN-γ-induced NO production by inhibiting IRF-8 induction and TNF-α production. 10H2DA might modulate IFN-γ-mediated cellular responses by inhibiting the induction of IRF-8 and IRF-8-dependent genes.

Recombinant Shiga toxin B subunit can induce neutralizing immunoglobulin Y antibody.

Previously, we have shown that chickens immunized with Shiga toxin (Stx) produce Stx-neutralizing egg yolk immunoglobulin Y (IgY) antibody. The anti-Stx-1 IgY and anti-Stx-2 IgY exert their neutralizing activity through their antibody activity against the B subunit of the toxin but not the A subunit. In the present study, chickens were immunized with recombinant Stx-1 B subunit (rStx-1B) and recombinant Stx-2 B subunit (rStx-2B). Induced anti-rStx-1B and anti-rStx-2B IgY neutralized the toxicity of Stx-1 and Stx-2 against HeLa 229 cells. The neutralizing activity of anti-rStx-1B IgY on Stx-1 was almost 10 times stronger than that of anti-Stx-1 IgY, and that of anti-rStx-2B IgY was 2.6 times stronger than that of anti-Stx-2 IgY. Anti-rStx-1B and anti-rStx-2B IgY reacted with multimeric and monomeric forms of the B subunits in contrast to anti-Stx-1 and anti-Stx-2 IgY that reacted with only the multimeric form. These results indicated that recombinant B subunits were promising antigens for induction of neutralizing antibodies in chickens.

Inhibitory effect of 10-hydroxydecanoic acid on lipopolysaccharide-induced nitric oxide production via translational downregulation of interferon regulatory factor-1 in RAW264 murine macrophages.

Toll-like receptors (TLRs) play a critical role in innate immunity by recognizing pathogen-associated molecular patterns. Various environmental materials including lipids may affect TLR signaling and modulate innate immune responses. We previously reported that 10-hydroxy-trans-2-decenoic acid (10H2DA) inhibits lipopolysaccharide (LPS)-induced interleukin (IL)-6 and nitric oxide (NO) production via inhibiting NF-κB activation. In this study, we investigated the effect of 10-hydroxydecanoic acid (10HDA), a saturated fatty acid of 10H2DA, on LPS-induced cytokines/chemokines and NO production. 10HDA inhibited LPS-induced NO production, but not tumor necrosis factor-α or IL-6 production. LPS-induced activation of interferon (IFN)-stimulated response element, but not NF-κB, was inhibited by 10HDA. Phosphorylation of STAT1 and STAT2 was not affected, but IFN-regulatory factor (IRF)-1 production was significantly reduced by 10HDA. The LPS-induced increase of IRF-1 mRNA, however, was not affected by 10HDA. We found that IRF-1 mRNA level in the polysomal fraction was significantly decreased by 10HDA. Further, LPS-induced phosphorylation of Akt and 4E-BP1, which control mRNA translation, was markedly decreased. These results suggest that 10HDA inhibited LPS-induced NO production through inhibiting IRF-1 translation. These findings elucidate a novel mechanism for anti-inflammatory activity of medium-chain fatty acid 10HDA.

Inhibitory mechanism of 10-hydroxy-trans-2-decenoic acid (royal jelly acid) against lipopolysaccharide- and interferon-ß-induced nitric oxide production.

Royal jelly acid, 10-hydroxy-trans-2-decenoic acid (10H2DA), is a major lipid component of royal jelly, which is the exclusive diet of queen honeybees. Previously, we showed partial inhibition of lipopolysaccharide (LPS)-induced NF-κB activation by 10H2DA. In this study, the ability of 10H2DA to inhibit LPS-induced nitric oxide (NO) production was investigated. LPS-induced NO production and inducible NO synthase (iNOS) gene transcription were inhibited by 10H2DA. LPS-stimulated interferon (IFN)-ß production, IFN regulatory factor-1 induction and IFN-stimulated response element activation, which are required for iNOS induction, were unaffected by 10H2DA. IFN-ß-induced NO production, however, was significantly inhibited by 10H2DA. Furthermore, IFN-ß-induced nuclear factor (NF)-κB activation and tumour necrosis factor (TNF)-α production were significantly inhibited by 10H2DA, and TNF-α-induced NF-κB activation was also inhibited by 10H2DA. These results and our previous study suggest that 10H2DA inhibits LPS- and IFN-ß-induced NO production via inhibition of NF-κB activation induced by LPS or IFN-ß.

Inhibitory effect of 10-hydroxy-trans-2-decenoic acid on LPS-induced IL-6 production via reducing IκB-ζ expression.

The effect of 10-hydroxy-trans-2-decenoic acid (10H2DA), a major fatty acid component of royal jelly, was investigated on LPS-induced cytokine production in murine macrophage cell line, RAW264 cells. 10H2DA inhibited LPS-induced IL-6 production dose-dependently, but did not inhibit TNF-α production. 10H2DA inhibited LPS-induced NF-κB activation in a dose-dependent fashion. In addition, NF-κB activation induced by over-expression of either MyD88 or Toll/IL-1 receptor domain-containing adaptor inducing IFN-ß (TRIF) was also inhibited by 10H2DA. Degradation of IκB-α and phosphorylation of IκB kinase-α were not inhibited by 10H2DA. On the other hand, reduction of LPS-induced IκB-ζ expression was discovered. Production of lipocalin-2 and granulocyte colony-stimulating factor (G-CSF), which is dependent on IκB-ζ, was also inhibited by 10H2DA, whereas that of IκB-ζ-independent cytokines/chemokines, such as IFN-ß, murine monocyte chemotactic protein-1 (JE), macrophage inflammatory protein (MIP)-1α and MIP-2, was not. Together, 10H2DA specifically inhibited LPS-induced IκB-ζ expression, followed by inhibition of IκB-ζ-dependent gene production. These results suggest that 10H2DA is one of the components of royal jelly to show anti-inflammatory effects and could be a therapeutic drug candidate for inflammatory and autoimmune diseases associated with IκB-ζ and IL-6 production.

Mechanism of inhibition of lipopolysaccharide-induced interferon-ß production by 2-aminopurine.

2-Aminopurine (2-AP) is widely used as an inhibitor for double stranded RNA-dependent protein kinase (PKR). Previously, we reported that 2-AP inhibits Toll-like receptor (TLR) ligand-induced nitric oxide production through the prevention of interferon (IFN)-ß production. In this study, we investigated the mechanisms for 2-AP inhibition of lipopolysaccharide (LPS)-induced IFN-ß production. A reporter gene assay showed that LPS-induced IFN-ß promoter, but not nuclear factor (NF)-κB, activation was significantly inhibited by 2-AP. IFN-ß promoter activation induced by the overexpression of Toll/interleukin-1 receptor domain-containing adaptor inducing IFN-ß (TRIF) was significantly inhibited by 2-AP in a dose-dependent manner, while TRIF- or myeloid differentiation primary response gene 88-dependent NF-κB activation was not inhibited. IFN-ß promoter activation induced by expression of the downstream signaling molecules, tumor necrosis factor receptor-associated factor family member-associated NF-κB activator-binding kinase 1, inhibitor of NF-κB kinase i and a constitutively active mutant of interferon regulatory factor (IRF)-3, was also inhibited by 2-AP. Another PKR inhibitor harboring the imidazolo-oxindole structure, however, did not affect TRIF signaling molecules-induced IFN-ß promoter activation, suggesting that the inhibition of IFN-ß transcription by 2-AP is independent of PKR inhibition. Further, we examined the effect of 2-AP on LPS-induced IRF-3 activation by immunoblotting. While 2-AP did not affect LPS-induced phosphorylation of IRF-3, nuclear translocation of IRF-3 was inhibited. Moreover, we revealed that LPS-induced phosphorylation of Akt, another key molecule involved in IRF-3 activation, was inhibited by 2-AP. These results suggest that 2-AP inhibits nuclear translocation of phosphorylated-IRF-3 by inhibiting Akt activation.

Specific egg yolk immunoglobulin as a new preventive approach for Shiga-toxin-mediated diseases.

Shiga toxins (Stxs) are involved in the development of severe systemic complications associated with enterohemorrhagic Escherichia coli (EHEC) infection. Various neutralizing agents against Stxs are under investigation for management of EHEC infection. In this study, we immunized chickens with formalin-inactivated Stx-1 or Stx-2, and obtained immunoglobulin Y (IgY) from the egg yolk. Anti-Stx-1 IgY and anti-Stx-2 IgY recognized the corresponding Stx A subunit and polymeric but not monomeric B subunit. Anti-Stx-1 IgY and anti-Stx-2 IgY suppressed the cytotoxicity of Stx-1 and Stx-2 to HeLa 229 cells, without cross-suppressive activity. The suppressive activity of these IgY was abrogated by pre-incubation with the corresponding recombinant B subunit, which suggests that the antibodies directed to the polymeric B subunits were predominantly involved in the suppression. In vivo, the intraperitoneal or intravenous administration of these IgY rescued mice from death caused by intraperitoneal injection of the corresponding toxin at a lethal dose. Moreover, oral administration of anti-Stx-2 IgY reduced the mortality of mice infected intestinally with EHEC O157:H7. Our results therefore suggest that anti-Stx IgY antibodies may be considered as preventive agents for Stx-mediated diseases in EHEC infection.

Monovalent Gb3-/Gb2-derivatives conjugated with a phosphatidyl residue: a novel class of Shiga toxin-neutralizing agent.

Shiga toxin (Stx) exerts toxic activity by binding to glycosphingolipids, mainly globotriaosyl (Gb(3)) ceramide, on the surface of target cells. The inhibition of toxin-receptor binding is a promising therapeutic approach to prevent Stx-mediated diseases. In this study, we synthesized monovalent Stx-ligands of phosphatidylethanolamine dipalmitoyl-Gb(3) (Gb(3)-PEDP) and galabiosyl (Gb(2))-PEDP and we examined their neutralizing activity against Stx-1 and Stx-2 in vitro. Both Gb(3)-PEDP and Gb(2)-PEDP strongly neutralized the cytotoxicity of Stx-1 and Stx-2. It is likely that the mechanism of neutralization involved formation of liposomes and consequently clustering of sugar units. We propose monovalent Gb(3)-/Gb(2)-derivatives conjugated with phosphatidyl residue as a novel class of Stx-neutralizing agent.