CD45 negatively regulates tumour necrosis factor and interleukin-6 production in dendritic cells

CD45 is known to regulate signalling through many different surface receptors in diverse haemopoietic cell types. Here we report for the first time that CD45-/- bone marrow dendritic cells (BMDC) are more activated than CD45+/+ cells and that tumour necrosis factor (TNF) and interleukin-6 (IL-6) production by BMDC and splenic dendritic cells (sDC), is increased following stimulation via Toll-like receptor (TLR)3 and TLR9. Nuclear factor-kappaB activation, an important downstream consequence of TLR3 and TLR9 signalling, is also increased in CD45-/- BMDC. BMDC of CD45-/- mice also produce more TNF and IL-6 following stimulation with the cytokines TNF and interferon-alpha. These results show that TLR signalling is increased in CD45-/- dendritic cells and imply that CD45 is a negative regulator of TLR and cytokine receptor signalling in dendritic cells.     

Autophagy is involved in regulating the immune response of dendritic cells to influenza A (H1N1) pdm09 infection

Autophagy can mediate antiviral immunity. However, it remains unknown whether autophagy regulates the immune response of dendritic cells (DCs) to influenza A (H1N1) pdm09 infection. In this study, we found that infection with the H1N1 virus induced DC autophagy in an endocytosis‐dependent manner. Compared with autophagy‐deficient Beclin‐1^+/? mice, we found that bone‐marrow‐derived DCs from wild‐type mice (WT BMDCs) presented a more mature phenotype on H1N1 infection. Wild‐type BMDCs secreted higher levels of interleukin‐6 (IL‐6), tumour necrosis factor‐ α (TNF‐α), interferon‐β (IFN‐β), IL‐12p70 and IFN‐γ than did Beclin‐1^+/? BMDCs. In contrast to Beclin‐1^+/? BMDCs, H1N1‐infected WT BMDCs exhibited increased activation of extracellular signal‐regulated kinase, Jun N‐terminal kinase, p38, and nuclear factor‐κB as well as IFN regulatory factor 7 nuclear translocation. Blockade of autophagosomal and lysosomal fusion by bafilomycin A1 decreased the co‐localization of H1N1 viruses, autophagosomes and lysosomes as well as the secretion of IL‐6, TNF‐α and IFN‐β in H1N1‐infected BMDCs. In contrast to Beclin‐1^+/? BMDCs, H1N1‐infected WT BMDCs were more efficient in inducing allogeneic CD4⁺ T‐cell proliferation and driving T helper type 1, 2 and 17 cell differentiation while inhibiting CD4⁺ Foxp3⁺ regulatory T‐cell differentiation. Moreover, WT BMDCs were more efficient at cross‐presenting the ovalbumin antigen to CD8⁺ T cells. We consistently found that Beclin‐1^+/? BMDCs were inferior in their inhibition of H1N1 virus replication and their induction of H1N1‐specific CD4⁺ and CD8⁺ T‐cell responses, which produced lower levels of IL‐6, TNF‐α and IFN‐β in vivo. Our data indicate that autophagy is important in the regulation of the DC immune response to H1N1 infection, thereby extending our understanding of host immune responses to the virus.     

UC‐1V150, a potent TLR7 agonist capable of activating macrophages and potentiating mAb‐mediated target cell deletion

Toll‐like receptors (TLR ) are critical mediators of the immune system with their activation linked to infection, inflammation and the pathogenesis of immune diseases including autoimmunity and cancer. For this reason, over the last 2 decades, TLR and their associated signalling pathways have been targeted therapeutically to enhance innate and adaptive immunity. Several TLR ligands, both endogenous and synthetic are at various phases of clinical testing, and new ligands are continually emerging. Agonists of TLR 7 are known immune response modifiers, simultaneously stimulating several cell types, resulting in immune cell activation and cytokine and chemokine release. The immune stimulating properties of the TLR 7 agonist Imiquimod has also been exploited for use in the treatment of malignant superficial tumours of the skin. Here, we investigated a novel TLR 7 agonist UC ‐1V150 and demonstrate it activates both human and mouse myeloid cells in vitro and in vivo, to deliver potent FcγR‐mediated engulfment of opsonized target cells.     

Toll‐like receptor 6 mediated inflammatory and functional responses of zinc oxide nanoparticles primed macrophages

Macrophages are among the most sensitive immune cells because of their phagocytic activity and are prone to become dysfunctional or not able to perform properly if nanoparticle load increases. We have previously reported that zinc oxide nanoparticles (ZNPs) induce inflammatory responses in macrophages that contribute to their death. Recognition of ZNPs by pattern recognition receptors such as toll‐like receptors (TLRs) might be a factor in the initiation of these responses in macrophages. Therefore, in this study we explored the role played by TLR6 and mitogen‐activated protein kinase (MAPKs) pathways in the inflammatory responses of macrophages during ZNPs exposure. ZNPs‐activated macrophages showed enhanced expression of activation and maturation markers (CD1d, MHC‐II, CD86 and CD71). Among various TLRs screened, TLR6 emerged as the most potent activator for ZNPs‐induced inflammatory responses. Downstream signalling proteins myeloid differentiation 88, interleukin‐1 receptor associated kinase and tumour necrosis factor receptor‐associated factor were also enhanced. On inhibiting MAPKs pathways individually, the inflammatory responses such as interleukin‐1β, interleukin‐6, tumour necrosis factor‐α, cyclooxygenase‐2 and inducible nitric oxide synthase were suppressed. TLR6 silencing significantly inhibited the pro‐inflammatory cytokine levels, reactive nitrogen species generation and inducible nitric oxide synthase expression. Also, inhibition of MAPKs in the absence of TLR6 signalling validated the link between TLR6 and MAPKs in ZNPs‐induced inflammatory responses. TLR6 was found to be co‐localized with autophagosomes. Macrophages lacking TLR6 inhibited the autophagosome marker protein‐microtubule‐associated protein1 light chain 3‐isoform II formation and phagocytosis. These results demonstrate that inflammatory responses caused by ZNPs‐activated macrophages strongly depend on TLR6‐mediated MAPK signalling.     

Insights into the toll‐like receptors in sexually transmitted infections

Toll‐like receptors (TLRs) are like soldiers of an innate immune system, which protects vital biological processes against invading pathogens. TLR signalling pathways help in the removal of pathogens and mediate well‐established inflammatory processes. However, these processes may also aid in the development or augmentation of an infection or an autoimmune disease. Recent studies have delineated TLR polymorphism's role in the loss of function, making hosts more resistant or vulnerable to the development of an infection. In this review, we have discussed the association of TLRs with sexually transmitted infections (STIs), especially to the pathogen‐specific ligands. We have also assessed the impact on TLR downstream signalling and the maintenance of cellular homeostasis during immune responses. Besides, we have discussed the role of TLRs single nucleotide polymorphisms in various STIs. Since TLRs are known to play a part in defence mechanisms and in aiding infections therefore, a thorough understanding of TLRs structure and molecular mechanisms is required to explain how they can influence the outcome of an STI. Such a strategy may lead to the development of novel and useful immunotherapeutic approaches to control pathogen progression and prevent transmission.     

ATP conditions intestinal epithelial cells to an inflammatory state that promotes components of DC maturation

Intestinal epithelial cells (IECs) normally promote the development of gut resident tolerogenic dendritic cells (DCs) and regulatory T cells, but how this process is altered in inflammatory bowel disease is not well characterized. Recently, we published that the cell injury signal ATP modulates IEC chemokine responses to the TLR5 ligand flagellin and exacerbates colitis in the presence of flagellin. We hypothesized that ATP switches these IECs from tolerogenic to proinflammatory, enhancing DC activation and immune responses to commensal antigens. Here, we report that ATP enhanced murine IEC production of KC, IL‐6, TGF‐β, and thymic stromal lymphopoietin in response to TLR1/2 stimulation by Pam₃CSK₄ (PAM). Moreover, supernatants from IECs stimulated with ATP+PAM enhanced expression of CD80 on bone marrow derived dendritic cells, and increased their production of IL‐12, IL‐6, IL‐23, TGF‐β, and aldh1a2, suggesting a Th1/Th17 polarizing environment. DCs conditioned by stressed IECs stimulated an enhanced recall response to flagellin and supported the expansion of IFN‐γ⁺ and IL‐17⁺ memory T cells. Lastly, colonic administration of nonhydrolysable ATP increased production of IL‐6 and Cxcl1 (KC) by IECs. These findings indicate that ATP influences the response of IECs to TLR ligands and biases the maturation of DCs to become inflammatory.     

Toll-like receptor ligand activation of murine bone marrow-derived dendritic cells

Dendritic cells (DCs) are required for the initiation of primary immune responses. The pattern of Toll-like receptor (TLR) expression on various subsets of these cells has been shown to differ, suggestive of distinct roles in influencing immune responses. We have examined here the responses of immature DCs derived from murine bone marrow (BMDCs) to a range of TLR ligands. BMDCs cultured for 6 days in the presence of granulocyte-macrophage colony-stimulating factor were stimulated for 24 hr with ligands to TLR1-2 [Pam(3)Cys-Ser-(Lys)(4) (PAM)], TLR2-6 (macrophage-activating lipopeptide-2 (MALP-2); zymosan or peptidoglycan (PG)], TLR3 (polyinosinic-polycytidylic acid), TLR4 [lipopolysaccharide R515 (LPS)], TLR5 (flagellin), TLR7 (polyuridylic acid) and TLR9 [CpG ODN2395 (CpG)]. DC activation was monitored using membrane marker expression and analysis of culture supernatants for cytokine/chemokine release. Ligands to TLR3 and TLR7 failed to activate BMDCs. All other TLR ligands caused elevated expression of membrane markers. PAM, MALP-2 and LPS induced high-level expression of proinflammatory cytokines and chemokines. Treatment with CpG was associated with a preferential type 1 cytokine and chemokine profile. Zymosan and PG were proinflammatory but also skewed towards a type 2 pattern of cytokines and chemokines. In contrast, flagellin did not cause marked secretion by BMDCs of cytokines or chemokines. These data for BMDCs are largely consistent with the reported TLR repertoire of freshly isolated murine Langerhans cells. In addition, murine BMDCs show selective responses to TLR ligands with respect to general activation, with differentiated cytokine patterns suggestive of potential priming for divergent immune responses.     

Common variable immunodeficiency revisited: normal generation of naturally occurring dendritic cells that respond to Toll‐like receptors 7 and 9

Patients with common variable immunodeficiency (CVID) have reduced numbers and frequencies of dendritic cells (DCs) in blood, and there is also evidence for defective activation through Toll‐like receptors (TLRs). Collectively, these observations may point to a primary defect in the generation of functional DCs. Here, we measured frequencies of plasmacytoid DCs (pDCs) and myeloid DCs (mDCs) in peripheral blood of 26 CVID patients and 16 healthy controls. The results show that the patients have reduced absolute counts of both subsets. However, the decreased numbers in peripheral blood were not reflected in reduced frequencies of CD34⁺ pDC progenitors in the bone marrow. Moreover, studies at the single cell level showed that DCs from CVID patients and healthy controls produced similar amounts of interferon‐α or interleukin‐12 and expressed similar levels of activation markers in response to human cytomegalovirus and ligands for TLR‐7 and TLR‐9. The study represents the most thorough functional characterization to date, and the first to assess bone marrow progenitor output, of naturally occurring DCs in CVID. In conclusion, it seems unlikely that CVID is secondary to insufficient production of naturally occurring DCs or a defect in their signalling through TLR‐7 or TLR‐9.     

Activation of invariant natural killer T cells in regional lymph nodes as new antigen‐specific immunotherapy via induction of interleukin‐21 and interferon‐γ

Invariant natural killer T (iNKT) cells play important immunoregulatory functions in allergen‐induced airway hyperresponsiveness and inflammation. To clarify the role of iNKT cells in allergic rhinitis (AR), we generated bone marrow‐derived dendritic cells (BMDCs), which were pulsed by ovalbumin (OVA) and α‐galactosylceramide (OVA/α‐GalCer‐BMDCs) and administered into the oral submucosa of OVA‐sensitized mice before nasal challenge. Nasal symptoms, level of OVA‐specific immunoglobulin (IgE), and T helper type 2 (Th2) cytokine production in cervical lymph nodes (CLNs) were significantly ameliorated in wild‐type (WT) mice treated with OVA/α‐GalCer‐BMDCs, but not in WT mice treated with OVA‐BMDCs. These anti‐allergic effects were not observed in Jα18^–/– recipients that lack iNKT cells, even after similar treatment with OVA/α‐GalCer‐BMDCs in an adoptive transfer study with CD4⁺ T cells and B cells from OVA‐sensitized WT mice. In WT recipients of OVA/α‐GalCer‐BMDCs, the number of interleukin (IL)‐21‐producing iNKT cells increased significantly and the Th1/Th2 balance shifted towards the Th1 dominant state. Treatment with anti‐IL‐21 and anti‐interferon (IFN)‐γ antibodies abrogated these anti‐allergic effects in mice treated with α‐GalCer/OVA‐BMDCs. These results suggest that activation of iNKT cells in regional lymph nodes induces anti‐allergic effects through production of IL‐21 or IFN‐γ, and that these effects are enhanced by simultaneous stimulation with antigen. Thus, iNKT cells might be a useful target in development of new treatment strategies for AR.     

Virus infection-associated bone marrow B cell depletion and impairment of humoral immunity to heterologous infection mediated by TNF-alpha/LTalpha

We previously showed that influenza virus infection of mice induces a depletion of bone marrow B lineage cells due to apoptosis of early B cells mediated by a mechanism involving TNF-alpha/LTalpha. Here we demonstrate that this effect is also observed with acute lymphocytic choriomeningitis virus (LCMV) infection and resulted in a deficiency of both splenic transitional B cells and mature follicular B cells. To determine whether there was an associated impairment of humoral immunity, we infected mice with LCMV and 10 days later at the peak of the B cell depletion, inoculated them with influenza virus. We found that influenza virus-specific antibody titers were dramatically reduced in mice recovering from LCMV infection compared to those in mice infected with influenza virus alone. Further, we showed that there was no reduction of the influenza virus-specific antibody response in LCMV-infected TNF-alpha/LTalpha-deficient mice, suggesting that TNF-alpha/LTalpha-mediated effects on bone marrow and/or peripheral lymphocytes were responsible for the observed impairment in humoral immunity. These results show that the TNF-alpha/LTalpha production induced following infection with diverse viruses has detrimental effects on early B cells in the bone marrow, and may be among the factors that lead to the severely compromised humoral immunity observed to subsequent heterologous infections.     

CD300a and CD300f differentially regulate the MyD88 and TRIF-mediated TLR signalling pathways through activation of SHP-1 and/or SHP-2 in human monocytic cell lines

CD300a, a membrane protein expressed on myeloid lineages and specific subsets of CD4(+) T cells, has been reported to have inhibitory activities in cellular activation. However, the role of CD300a in Toll-like receptor (TLR) -mediated macrophage activation has not been investigated. The human monocytic cell lines THP-1 and U937 were stimulated with various TLR ligands after triggering of CD300a with specific monoclonal antibody. Interestingly, CD300a blocked TLR4-mediated and TLR9-mediated expression of pro-inflammatory mediators without affecting TLR3-mediated events. In contrast, CD300f, another member of the CD300 family, blocked the activation of cells induced by all TLR ligands. A transient transfection assay using luciferase reporter gene under the regulation of nuclear factor-κB binding sites indicated that co-transfection of CD300f blocked reporter expression induced by over-expression of both myeloid differentiation factor 88 (MyD88) and toll-interleukin 1 receptor-domain-containing adapter-inducing interferon-β (TRIF), whereas CD300a blocked only MyD88-induced events. Synthetic peptides representing immunoreceptor tyrosine-based inhibitory motifs of CD300a or CD300f mimicked the differential inhibition patterns of their original molecules. The use of various signalling inhibitors and Western blotting analysis revealed that TLR9/MyD88-mediated signalling was regulated mainly by SH2-containing tyrosine phosphatase 1 (SHP-1), which could be activated by CD300a or CD300f. In contrast, regulation of the TLR3/TRIF-mediated pathway required the combined action of SHP-1 and SHP-2, which could be accomplished by CD300f but not CD300a. These data indicate that CD300a and CD300f regulate the MyD88 and TRIF-mediated TLR signalling pathways through differential activation of SHP-1 and SHP-2.     

Enhancement of effector CD8+ T-cell function by tumour-associated B7-H3 and modulation of its counter-receptor triggering receptor expressed on myeloid cell-like transcript 2 at tumour sites

Little is known of how the Toll‐like receptor (TLR) system can modulate the function of non‐parenchymal liver cells (NPC) as a major component of the innate and adaptive immune system of the liver. To investigate the diversification of TLR signalling pathways in NPC, we isolated Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild‐type C57BL/6 mice and examined their responses to TLR1 to TLR9 agonists. The data show that KC respond to all TLR ligands by producing tumour necrosis factor‐α (TNF‐α) or interleukin‐6 (IL‐6), to TLR3 and TLR4 ligands only by producing interferon‐β (IFN‐β), to TLR1 and TLR8 ligands by significantly up‐regulating major histocompatibility complex (MHC) class II and costimulatory molecules, and to TLR1, ‐2, ‐4 and ‐6 ligands by inducing high levels of T‐cell proliferation and IFN‐γ production in the mixed lymphocyte reaction (MLR). Similarly, LSEC respond to TLR1 to ‐4, ‐6, ‐8 and ‐9 ligands by producing TNF‐α, to TLR3 and ‐4 ligands by producing IL‐6, and to TLR3 ligands by producing IFN‐β. Interestingly, despite significant up‐regulation of MHC class II and co‐stimulatory molecules in response to TLR8 ligands, LSEC stimulated by TLR1, ‐2 or ‐6 could stimulate allogeneic T cells as assessed by MLR. By contrast, myeloid dendritic cells, used as positive control for classical antigen‐presenting cells, respond to TLR1, ‐2, ‐4 and ‐9 ligands by both up‐regulation of CD40 and activation of allogeneic T cells. In conclusion, NPC display a restricted TLR‐mediated activation profile when compared with ‘classical’ antigen‐presenting cells which may, at least in part, explain their tolerogenic function in the liver.     

Impact of culture medium on maturation of bone marrow-derived murine dendritic cells via the aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AhR) plays a role in modulating dendritic cell (DC) immunity. Iscove's modified Dulbecco's medium (IMDM) contains higher amounts of AhR ligands than RPMI1640 medium. Here, we examined the influence of AhR ligand-containing medium on the maturation and T-cell stimulatory capacity of bone marrow-derived murine dendritic cells (BMDCs). BMDCs generated in IMDM (BMDCs/IMDM) expressed higher levels of co-stimulatory and MHC class II molecules, and lower levels of pattern-recognition receptors, especially toll-like receptor (TLR) 2, TLR4, and scavenger receptor class A (SR-A), compared to BMDCs generated in RPMI1640 medium (BMDCs/RPMI). Cytokine responses against ligands of TLRs and antigen uptake mediated by SR-A were remarkably reduced in BMDCs/IMDM, whereas the T-cell stimulatory capacity of the cells was enhanced, compared to BMDCs/RPMI. The enhanced maturation of BMDCs/IMDM was attenuated in the presence of an AhR antagonist, indicating involvement of AhR in the maturation. Interestingly, BMDCs/IMDM induced Th2 and Th17 differentiation at low and high concentrations of antigen respectively, when co-cultured with CD4(+) T-cells from antigen-specific T-cell receptor transgenic mice. In contrast, BMDCs/RPMI induced Th1 differentiation predominantly in the co-culture. Taken together, optimal selection of medium seems necessary when studying BMDCs, depending on the target receptors on the cell surface of DCs and type of helper T-cells for the co-culture.     

Toll-like receptor 9-dependent immune activation by unmethylated CpG motifs in Aspergillus fumigatus DNA

Phagocytic defenses are critical for effective host defenses against the opportunistic fungal pathogen Aspergillus fumigatus. Previous studies found that following challenge with A. fumigatus, Toll-like receptor 9 (TLR9) knockout mice survived longer than wild-type mice. However, the mechanism responsible was not defined. Here we demonstrate that A. fumigatus contains unmethylated CpG sequences, the natural ligands for TLR9. A. fumigatus DNA and synthetic CpG-rich oligodeoxynucleotides (ODNs) containing sequences found in the A. fumigatus genome potently stimulated the production of proinflammatory cytokines in mouse bone marrow-derived dendritic cells (BMDCs) and human plasmacytoid dendritic cells. The response was decreased when the fungal DNA was treated with a CpG methylase or with CpG-specific endonucleases. A role for TLR9 was demonstrated as cytokine production was abolished in BMDCs from TLR9-deficient mice. Moreover, transfection of HEK293 cells with human TLR9 conferred responsiveness to synthetic CpG-rich ODNs containing sequences found in A. fumigatus DNA. Taken together, these data demonstrate that TLR9 detects A. fumigatus DNA, resulting in the secretion of proinflammatory cytokines, which may contribute to the immune response to the pathogen.     

Lack of SIGIRR/TIR8 aggravates hydrocarbon oil‐induced lupus nephritis

Multiple genetic factors contribute to the clinical variability of spontaneous systemic lupus erythematosus (SLE) but their role in drug‐induced SLE remain largely unknown. Hydrocarbon oil‐induced SLE depends on mesothelial cell apoptosis and Toll‐like receptor (TLR)‐7‐mediated induction of type I interferons. Hence, we hypothesized that TIR8/SIGIRR, an endogenous TLR inhibitor, prevents oil‐induced SLE. Sigirr‐deficient dendritic cells expressed higher TLR7 mRNA levels and TLR7 activation resulted in increased IL‐12 production in vitro. In vivo, lack of SIGIRR increased surface CD40 expression on spleen CD11c⁺ dendritic cells and MX‐1, TNF, IL‐12, BAFF and BCL‐2 mRNA expression 6 months after pristane injection. Spleen cell counts of CD4^?/CD8^? ‘autoreactive’ T cells and B220⁺ B cells were also increased in Sigirr^?/? mice. Serum autoantibody analysis revealed that Sigirr deficiency specifically enhanced the production of rheumatoid factor (from 4 months of age) and anti‐snRNP IgG (from 5 months of age), while anti‐Smith IgG or anti‐dsDNA IgG were independent of the Sigirr genotype. This effect was sufficient to significantly aggravate lupus nephritis in Sigirr‐deficient mice. Structure model prediction identified the BB loop of SIGIRR's intracellular TIR domain to interact with TLR7 and MyD88. BB loop deletion was sufficient to completely abrogate SIGIRR's inhibitory effect on TLR7 signalling. Thus, TIR8/SIGIRR protects from hydrocarbon oil‐induced lupus by suppressing the TLR7‐mediated activation of dendritic cells, via its intracellular BB loop. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Seoul virus suppresses NF-κB-mediated inflammatory responses of antigen presenting cells from Norway rats

Hantavirus infection reduces antiviral defenses, increases regulatory responses, and causes persistent infection in rodent hosts. To address whether hantaviruses alter the maturation and functional activity of antigen presenting cells (APCs), rat bone marrow-derived dendritic cells (BMDCs) and macrophages (BMDMs) were generated and infected with Seoul virus (SEOV) or stimulated with TLR ligands. SEOV infected both DCs and macrophages, but copies of viral RNA, viral antigen, and infectious virus titers were higher in macrophages. The expression of MHCII and CD80, production of IL-6, IL-10, and TNF-α, and expression of Ifnβ were attenuated in SEOV-infected APCs. Stimulation of APCs with poly I:C prior to SEOV infection increased the expression of activation markers and production of inflammatory cytokines and suppressed SEOV replication. Infection of APCs with SEOV suppressed LPS-induced activation and innate immune responses. Hantaviruses reduce the innate immune response potential of APCs derived from a natural host, which may influence persistence of these zoonotic viruses in the environment.     

Inhibition of a C-rich oligodeoxynucleotide on activation of immune cells in vitro and enhancement of antibody response in mice

To explore the possibility that human mitochondrial genomic DNA‐mimicking oligodeoxynucleotides could regulate the immune response, a series of mitochondrial DNA‐based oligodeoxynucleotides (MTODNs) were designed and studied to determine their immunoregulatory effects on immune cells activated by toll‐like receptor (TLR) stimulation. The results showed that a C‐rich MTODN, designated MT01, was able to inhibit the proliferation of human peripheral blood mononuclear cells (PBMCs) induced by cytosine–phosphate–guanosine (CpG) oligodeoxynucleotides (ODNs) and the production of type I interferon (IFN) from human PBMCs stimulated by TLR agonists, including inactivated influenza virus, imiquimod, inactivated herpes simplex virus‐1 (HSV‐1) and CpG ODNs. In addition, MT01 inhibited the CpG ODN‐enhanced antibody response and this inhibition could be related to the antagonism of TLR9‐activation pathways in B cells. Notably, unlike the G‐rich suppressive ODNs reported, MT01 is composed of ACCCCCTCT repeats. These data imply that MT01 represents a novel class of immunosuppressive ODNs that could be candidate biologicals with therapeutic use in TLR activation‐associated diseases.     

The dendritic cell mannose receptor mediates allergen internalization and maturation involving notch 1 signalling

Dendritic cells (DCs) have been shown recently to play a key role in inducing and mediating T helper type 2 (Th2) responses associated with atopic disease. These responses are mediated in part by ligation to different Toll‐like receptors (TLRs) and C‐type lectins, e.g. the mannose receptor (MR), depending upon the DC subset involved and the respective microenvironments. Because ovalbumin (OVA) (which is structurally related to various allergens) can engage the MR, we can use OVA stimulation as a model for understanding the roles of both TLRs and the MR in allergic inflammatory responses. We examined TLR‐ and MR‐mediated responses from mouse bone marrow‐derived DCs in the context of antigen recognition and presentation in addition to examining the relationship between notch 1, TLRs and MR signalling pathways. This work demonstrated that OVA‐mediated signalling up‐regulated both TLR‐2 and MR and that MR RNA interference (RNAi) but not TLR2 RNAi inhibited DC internalization of fluorescein isothiocyanate–OVA. Furthermore, MR RNAi inhibited OVA‐ and house dust mite allergen extract‐induced DC maturation and MR RNAi and TLR2 RNAi influenced DC interleukin‐12 production independently. Finally, we demonstrated that blocking notch 1 signalling inhibited both notch 1 and TLR‐2 expression but not MR expression levels. However, MR RNAi inhibited the expression of MR, TLR‐2 and notch 1. These results indicate that MR is the primary receptor mediating the internalization of environmental allergen glycoproteins. In addition, TLR‐2 and notch 1 play important roles in DC maturation and antigen presentation and signals originating from the MR and TLR‐2 receptors converge with the notch 1 signalling pathway.     

The pruritogenic mediator endothelin‐1 shifts the dendritic cell–T‐cell response toward Th17/Th1 polarization

Endothelin‐1 (ET‐1) is associated with skin diseases such as atopic dermatitis (AD) and psoriasis. ET‐1 is enhanced in the skin of patients AD and psoriasis. In addition, plasma levels of ET‐1 are elevated in AD and psoriasis. Although both AD and psoriasis are T‐cell–mediated skin diseases, the association between ET‐1 and the T‐cell immune response has not been clarified. To evaluate the role of ET‐1 in inflammatory skin disease, we sought to investigate the effects of ET‐1 on the functions of dendritic cells (DCs) and subsequent immune responses. For this purpose, we immunohistochemically confirmed the upregulation of ET‐1 in the epidermis of patients with AD or psoriasis. ET‐1 directly induced phenotypic maturation of bone marrow‐derived DCs (BMDCs). In addition, ET‐1 augmented the production of several cytokines and allogeneic stimulatory capacity of BMDCs. Interestingly, ET‐1–activated BMDCs primed T cells to produce Th1 and Th17 cytokines, but not Th2 cytokines. These findings indicate that ET‐1 polarizes the DC–T‐cell response toward Th17/1 differentiation and may augment the persistent course of inflammatory skin diseases.