MD‐2 is involved in the stimulation of matrix metalloproteinase‐1 expression by interferon‐γ and high glucose in mononuclear cells – a potential role of MD‐2 in Toll‐like receptor 4‐independent signalling

We reported recently that treatment of diabetic apolipoprotein E‐deficient mice with the Toll‐like receptor 4 (TLR4) antagonist Rs‐LPS, a lipopolysaccharide isolated from Rhodobacter sphaeroides, inhibited atherosclerosis. Since it is known that Rs‐LPS antagonizes TLR4 by targeting TLR4 co‐receptor MD‐2, this finding indicates that MD‐2 is a potential target for the treatment of atherosclerosis. In this study, we determined if MD‐2 is involved in the gene expression regulated by signalling pathways independent of TLR4. Given that interferon‐γ (IFNγ) and hyperglycaemia play key roles in atherosclerosis, we determined if MD‐2 is involved in IFN‐γ and high‐glucose‐regulated gene expression in mononuclear cells. Results showed that IFN‐γ and high glucose synergistically stimulated matrix metalloproteinase 1 (MMP‐1), a proteinase essential for vascular tissue remodelling and atherosclerosis, in U937 mononuclear cells, but Rs‐LPS inhibited the MMP‐1 stimulation. To provide more evidence for a role of MD‐2 in IFN‐γ‐stimulated MMP‐1, studies using antibodies and small interfering RNA demonstrated that MD‐2 blockade or knockdown attenuated the effect of IFN‐γ on MMP‐1. Furthermore, studies using PCR arrays showed that MD‐2 blockade had a similar effect as IFN‐γ receptor blockade on the inhibition of IFN‐γ‐stimulated pro‐inflammatory molecules. Although these findings indicate the involvement of MD‐2 in IFN‐γ signalling, we also observed that MD‐2 was up‐regulated by IFN‐γ and high glucose. We found that MD‐2 up‐regulation by IFN‐γ played an essential role in the synergistic effect of IFN‐γ and LPS on MMP‐1 expression. Taken together, these findings indicate that MD‐2 is involved in IFN‐γ signalling and IFN‐γ‐augmented MMP‐1 up‐regulation by LPS.     

CD14‐independent responses induced by a synthetic lipid A mimetic

CRX‐527 belongs to a new family of synthetic lipid A mimetics, the aminoalkyl glucosaminide 4‐phosphates, which are considered as potential vaccine adjuvants or stand‐alone immunotherapeutics to harness innate immune defenses. Since natural lipid A from bacterial LPS depends on membrane‐bound (mCD14) or soluble CD14 for its TLR4 ligand activity, we investigated the involvement of both forms of CD14 in the responses elicited by CRX‐527. First, we found that CRX‐527 induces NF‐κB and interferon regulatory factor‐3 (IRF‐3) activation in human embryonic kidney cells transfected with TLR4 and MD‐2 genes alone, whereas the responses to LPS require either co‐transfection of the gene encoding mCD14 or addition of soluble CD14. We then observed that monocyte‐derived DC, which are devoid of mCD14 respond to CRX‐527 but not to LPS in serum‐free medium. Furthermore, we found that, in contrast to LPS, CRX‐527 induces the production of cytokines in whole blood of a patient with paroxysmal nocturnal hemoglobinuria, a disease in which mCD14‐dependent responses are defective. Finally, we demonstrated that splenocytes from CD14‐deficient mice produce cytokines in response to CRX‐527 but not to LPS. We conclude that the lipid A mimetic CRX‐527 does not require the CD14 co‐receptor to elicit TLR4‐mediated responses.     

IFN‐γ stimulates CpG‐induced IL‐10 production in B cells via p38 and JNK signalling pathways

The production of IL‐10, a potent immunosuppressive cytokine, must be strictly regulated to ensure a balanced immune response. IFN‐γ, a key cytokine in multiple immune processes and pathologies, is known as an inhibitor of IL‐10 production by monocytes and macrophages, but also has some regulatory functions. In the present study, we explored the role of IFN‐γ on Toll‐like receptor (TLR)‐induced IL‐10 production in murine peritoneal and spleen cells and in human peripheral blood mononuclear cells. IFN‐γ inhibited IL‐10 production induced by TLR2, TLR3, TLR4 and TLR7/8 agonists, but stimulated IL‐10 production when cells were triggered with CpG oligodeoxynucleotides, a specific TLR9 agonist. The stimulatory effect of IFN‐γ on TLR9‐induced IL‐10 was restricted to B cells. In line with the increased IL‐10, B cells stimulated with CpG and IFN‐γ profoundly inhibited CD4 T cell proliferation. Further research into the mechanisms involved, revealed that the mitogen‐activated protein kinases p38 and JNK are essential players in this stimulatory effect, and that the phosphatase MKP1 – an inhibitor of p38 and JNK activity – is downregulated after combined stimulation with IFN‐γ and CpG. Our data may represent a novel immunoregulatory role of IFN‐γ in B cells after triggering of TLR9, by stimulating IL‐10 production.     

HMGB1 Promotes the Differentiation of Th17 via Up‐Regulating TLR2 and IL‐23 of CD14+ Monocytes from Patients with Rheumatoid Arthritis

High‐mobility group box 1 (HMGB1) is a non‐histone nuclear protein that is released extracellulary and has been implicated in autoimmune disease. Toll‐like receptor 2 (TLR2) signalling is thought to be essential for the inflammatory response and for immune disorders. In recent studies, enhanced HMGB1 and TLR2 expressions have been found in rheumatoid arthritis (RA), respectively. The aim of this study is to explore whether HMGB1 stimulation can up‐regulate the expression of TLR2 on CD14⁺ monocytes from patients with RA and to clarify the subsequent events involving Th17 cells and Th17 cell‐associated cytokine changes. Our results showed that the frequency of CD14⁺ cells in peripheral blood mononuclear cell (PBMC) was obviously increased, and enhanced expression of TLR2 on CD14⁺ monocytes was also found in patients with RA, compared with healthy controls with statistical significance (P < 0.001). In addition, the levels of IL‐17, IL‐23 and IL‐6 in supernatants from cultured monocytes from patients and in patient’s plasma were increased, and NF‐κB, the downstream target of TLR2, also showed a marked elevation after monocytes were stimulated by HMGB1. This implies that the enhanced TLR2 pathway and Th17 cell polarization may be due to HMGB1 stimulation in rheumatoid arthritis.     

Impaired NLRP3 inflammasome activity during fetal development regulates IL‐1β production in human monocytes

Interleukin‐1β (IL‐1β) production is impaired in cord blood monocytes. However, the mechanism underlying this developmental attenuation remains unclear. Here, we analyzed the extent of variability within the Toll‐like receptor (TLR)/NLRP3 inflammasome pathways in human neonates. We show that immature low CD14 expressing/CD16^pos monocytes predominate before 33 weeks of gestation, and that these cells lack production of the pro‐IL‐1β precursor protein upon LPS stimulation. In contrast, high levels of pro‐IL‐1β are produced within high CD14 expressing monocytes, although these cells are unable to secrete mature IL‐1β. The lack of secreted IL‐1β in these monocytes parallels a reduction of NLRP3 induction following TLR stimulation resulting in a lack of caspase‐1 activity before 29 weeks of gestation, whereas expression of the apoptosis‐associated speck‐like protein containing a CARD and function of the P2×7 receptor are preserved. Our analyses also reveal a strong inhibitory effect of placental infection on LPS/ATP‐induced caspase‐1 activity in cord blood monocytes. Lastly, secretion of IL‐1β in preterm neonates is restored to adult levels during the neonatal period, indicating rapid maturation of these responses after birth. Collectively, our data highlight important developmental mechanisms regulating IL‐1β responses early in gestation, in part due to a downregulation of TLR‐mediated NLRP3 expression. Such mechanisms may serve to limit potentially damaging inflammatory responses in a developing fetus.     

M2000 (β‐D‐Mannuronic Acid) as a Novel Antagonist for Blocking the TLR2 and TLR4 Downstream Signalling Pathway

To date, selective blockade of Toll‐like receptor (TLR) signalling has been developed as a new approach for treatment for many inflammatory diseases. As β‐D‐mannuronic acid (M2000) has been known as an anti‐inflammatory molecule in several experimental models, we investigated the antagonistic effects of M2000 on TLR2 and TLR4 downstream signalling transduction pathway in human embryonic kidney (HEK) 293 cell lines overexpressing TLR2/CD14 and the TLR4/MD2/CD14 complex, respectively. M2000 effectively inhibited mRNA expression of MyD88 and p65, major subunit of nuclear factor‐κB, in HEK293 cells stimulated by lipoteichoic acid (LTA, a TLR2 agonist) and lipopolysaccharide (LPS, a TLR4 agonist) with no evidence of cytotoxicity. In addition, M2000 also suppressed LTA and LPS‐induced production of TNF‐α and IL‐6 inflammatory cytokines in these cells. Furthermore, the results revealed that M2000 had no significant effect on Tollip mRNA expression as a negative regulator of TLR signalling in aforesaid cells. Overall, these data point to M2000 inhibitory effect on Toll‐like receptor (TLR) 2, 4 signalling in HEK293 cells. This information might provide new insights into the possible roles of this small drug in order to introduce it as a TLR signalling pathway inhibitor. However, more studies are needed to confirm β‐D‐mannuronic acid antagonistic effects including the effects of M2000 on peritoneal isolated macrophages and also on blood cells in patients with inflammatory diseases such as ankylosing spondylitis.     

The DC‐HIL/syndecan‐4 pathway inhibits human allogeneic T‐cell responses

T‐cell activation is regulated by binding of ligands on APC to corresponding receptors on T cells. In mice, we discovered that binding of DC‐HIL on APC to syndecan‐4 (SD‐4) on activated T cells potently inhibits T‐cell activation. In humans, we now show that DC‐HIL also binds to SD‐4 on activated T cells through recognition of its heparinase‐sensitive saccharide moiety. DC‐HIL blocks anti‐CD3‐induced T‐cell responses, reducing secretion of pro‐inflammatory cytokines and blocking entry into the S phase of the cell cycle. Binding of DC‐HIL phosphorylates SD‐4's intracellular tyrosine and serine residues. Anti‐SD‐4 Ab mimics the ability of DC‐HIL to attenuate anti‐CD3 response more potently than Ab directed against other inhibitory receptors (CTLA‐4 or programmed cell death‐1). Among leukocytes, DC‐HIL is expressed highest by CD14⁺ monocytes and this expression can be upregulated markedly by TGF‐β. Among APC, DC‐HIL is expressed highest by epidermal Langerhans cells, an immature type of dendritic cells. Finally, the level of DC‐HIL expression on CD14⁺ monocytes correlates inversely with allostimulatory capacity, such that treatment with TGF‐β reduced this capacity, whereas knocking down the DC‐HIL gene augmented it. Our findings indicate that the DC‐HIL/SD‐4 pathway can be manipulated to treat T‐cell‐driven disorders in humans.     

DC‐SIGN reacts with TLR‐4 and regulates inflammatory cytokine expression via NF‐κB activation in renal tubular epithelial cells during acute renal injury

In the pathological process of acute kidney injury (AKI), innate immune receptors are essential in inflammatory response modulation; however, the precise molecular mechanisms are still unclear. Our study sought to demonstrate the inflammatory response mechanisms in renal tubular epithelial cells via Toll‐like receptor‐4 (TLR‐4) and dendritic cell‐specific intercellular adhesion molecule 3‐grabbing non‐integrin 1 (DC‐SIGN) signalling. We found that DC‐SIGN exhibited strong expression in renal tubular epithelial cells of human acute renal injury tissues. DC‐SIGN protein expression was increased significantly when renal tubular epithelial cells were exposed to lipopolysaccharide (LPS) for a short period. Furthermore, DC‐SIGN was involved in the activation of p65 by TLR‐4, which excluded p38 and c‐Jun N‐terminal kinases (JNK). Interleukin (IL)‐6 and tumour necrosis factor (TNF)‐α expression was decreased after DC‐SIGN knock‐down, and LPS induced endogenous interactions and plasma membrane co‐expression between TLR‐4 and DC‐SIGN. These results show that DC‐SIGN and TLR‐4 interactions regulate inflammatory responses in renal tubular epithelial cells and participate in AKI pathogenesis.     

TLR2‐activated human langerhans cells promote Th17 polarization via IL‐1β, TGF‐β and IL‐23

The cytokines IL‐6, IL‐1β, TGF‐β, and IL‐23 are considered to promote Th17 commitment. Langerhans cells (LC) represent DC in the outer skin layers of the epidermis, an environment extensively exposed to pathogenic attack. The question whether organ‐resident DC like LC can evoke Th17 immune response is still open. Our results show that upon stimulation by bacterial agonists, epidermal LC and LC‐like cells TLR2‐dependently acquire the capacity to polarize Th17 cells. In Th17 cells, expression of retinoid orphan receptor γβ was detected. To clarify if IL‐17⁺cells could arise per se by stimulated LC we did not repress Th1/Th2 driving pathways by antibodies inhibiting differentiation. In CD1c⁺/langerin⁺ monocyte‐derived LC‐like cells (MoLC), macrophage‐activating lipopeptide 2, and peptidoglycan (PGN) induced the release of the cytokines IL‐6, IL‐1β, and IL‐23. TGF‐β, a cytokine required for LC differentiation and survival, was found to be secreted constitutively. Anti‐TLR2 inhibited secretion of IL‐6, IL‐1β, and IL‐23 by MoLC, while TGF‐β was unaffected. The amount of IL‐17 and the ratio of IL‐17 to IFN‐γ expression was higher in MoLC‐ than in monocyte‐derived DC‐cocultured Th cells. Anti‐IL‐1β, ‐TGF‐β and ‐IL‐23 decreased the induction of Th17 cells. Interestingly, blockage of TLR2 on PGN‐stimulated MoLC prevented polarization of Th cells into Th17 cells. Thus, our findings indicate a role of TLR2 in eliciting Th17 immune responses in inflamed skin.     

Children with atopic histories exhibit impaired lipopolysaccharide‐induced Toll‐like receptor‐4 signalling in peripheral monocytes

Background The hygiene hypothesis states that early exposure to bacterial products such as lipopolysaccharide (LPS) may be protective against the development of allergic diseases. Whether atopic disease affects the ability of immune cells to respond to LPS is unclear. Our laboratory has demonstrated previously that children express high levels of Toll‐like receptor (TLR)‐4 on CD4⁺ cells in nasal mucosa. Objective To determine if children with a history of allergic disease have impaired responses to LPS on circulating CD4⁺ leucocytes. Methods Peripheral blood mononuclear cells from children (aged 2–18) and adults with or without a history of atopic conditions were cultured with/without IL‐4 or LPS for up to 24 h. Expression of surface TLR‐4, CD14, CD4, CD3, as well as of intracellular phosphorylated ^p42/p44ERK and p38 mitogen‐activated protein kinase (MAPK) were assessed by flow cytometry. Results A history of atopy in children was associated with impaired LPS‐induced TLR‐4‐dependent phosphorylation of ^p42/44ERK and p38 MAPK by CD4⁺ monocytes. Decreased LPS signalling was reproduced by pre‐incubation of control cells with recombinant IL‐4. LPS stimulation also decreased TLR‐4 expression on monocytes from children without atopic histories but not from atopic subjects. CD4⁺ T lymphocytes showed limited LPS responsiveness, regardless of atopic status. In contrast with non‐atopic children, TLR‐4 expression on monocytes of children with atopic histories decreased as a function of age. Conclusions This study provides evidence for defective LPS recognition on circulating CD4⁺ leucocytes of subjects with atopic histories compared with those from non‐atopic children. CD4⁺TLR4⁺ monocytes from children with atopic histories failed to phosphorylate MAPKs. Our results suggest that a history of atopic disease is associated with impaired TLR‐4‐mediated innate immune function compared with non‐atopic children. Cite this as: D. Préfontaine, A.‐A. Banville‐Langelier, P.‐O. Fiset, J. Guay, J. An, M. Mazer, Q. Hamid and B. D. Mazer, Clinical & Experimental Allergy, 2010 (40) 1648–1657.     

CD14 is required for influenza A virus-induced cytokine and chemokine production

Infection of monocytes and macrophages by influenza A virus leads to proinflammatory and chemotactic cytokine production. The signalling pathways linking innate immune virus recognition to cytokine expression are little understood. Here, we report that blocking of CD14 on human monocytes by specific antibody or use of CD14-deficient murine macrophages abolished influenza A virus-induced cytokine production. Toll-like receptor (TLR) 2 and 4-deficient murine macrophages remained fully responsive. These results suggest that CD14, together with a TLR other than TLR2 or 4, is an essential coreceptor of the influenza A virus sensing recognition system.     

Modulation of IL‐33/ST2‐TIR and TLR Signalling Pathway by Fingolimod and Analogues in Immune Cells

For the immune modulatory drug fingolimod (FTY720), lymphocyte sequestration has been extensively studied and accepted as mode of action. Further, direct effects on immune cell signalling are incompletely understood. Herein, we used the parent drug and newly synthesized analogues to investigate their effects on dendritic cell (DC) calcium signalling and on Th1, Th2 and Th17 responses. DC calcium signalling was determined with a single cell‐based confocal assay and IL‐33/ST2‐TIR Th2‐like response with ST2‐transduced EL4‐6.1 thymoma cells. The Th1/Th17 responses were examined with a LPS/TLR‐enhanced antigen presentation assay with OVA‐TCRtg CD4 and CD8 spleen cells. Our results revealed a comparable influence of fingolimod and S1P on intracellular calcium level in DC, while an oxy‐derivative of fingolimod exhibited an EC₅₀ of 3.3 nm , being 14 times more potent than FTY720‐P. The IL‐33/ST2‐TIR Th2‐like response in ST2‐EL4 cells was inhibited by fingolimod and analogues at varying degrees. Using the OVA‐TCRtg LPS/TLR‐enhanced spleen cell assay, we found that fingolimod inhibited both IL‐17 and IFN‐γ production. In contrast, fingolimod phosphate failed to decrease Th1 cytokines. Interestingly, the effects of the parent compound fingolimod were modulated by the PP2A inhibitor okadaic acid, thus suggesting PP2A as relevant intracellular target. These studies describe detailed immune‐modulating properties of fingolimod, including interference with a prototypical Th2 response via IL‐33/ST2‐TIR. Moreover, differential effects of fingolimod versus its phosphorylated derivative on TLR‐activated and antigen‐dependent Th1 activation suggest PP2A as an additional target of fingolimod immune therapy. Together with the analogues tested, these data may guide the development of more specific fingolimod derivatives.     

Hematopoietic and nonhematopoietic cells promote Type I interferon‐ and TLR7‐dependent monocytosis during low‐dose LCMV infection

Release of inflammatory monocytes from the bone marrow (BM) into the blood is an important physiological response to infection, but the mechanisms regulating this phenomenon during viral infection are not completely defined. Here, we show that low‐dose infection with lymphocytic choriomeningitis virus (LCMV) caused rapid, transient inflammatory monocytosis that required type I interferon (IFN) and Toll‐like receptor (TLR) 7 signaling. Type I IFN and TLR7 signals were critical for induction of IFN‐stimulated gene expression and CCR2 ligand upregulation in the BM microenvironment in response to LCMV infection. Experiments utilizing BM chimeric mice demonstrated that type I IFN and TLR7 signaling on either hematopoietic or nonhematopoietic cells was sufficient to initiate monocytosis in response to LCMV infection. BM plasmacytoid dendritic cells (pDCs) generated type I IFN directly ex vivo, suggesting that pDCs are a hematopoietic contributor of type I IFN in the BM early during LCMV infection. Overall, we describe novel roles for type I IFN and TLR7 signaling in nonhematopoietic cells and BM pDCs in directing IFN‐stimulated gene and CCR2 ligand expression in the BM to initiate an increase in blood inflammatory monocytes during viral infection.     

Circulating Toll‐like receptor (TLR) 2, TLR4, and regulatory T cells in patients with chronic hepatitis C

Wang J‐P, Zhang Y, Wei X, Li J, Nan X‐P, Yu H‐T, Li Y, Wang P‐Z, Bai X‐F. Circulating Toll‐like receptor (TLR) 2, TLR4, and regulatory T cells in patients with chronic hepatitis C. APMIS 2010; 118: 261–70. The mechanism of hepatitis C virus (HCV) involvement in innate immune responses and immune modulation has not been well characterized. In the present work, we studied Toll‐like receptor (TLR) 2 and TLR4, which were recently recognized as the important components of innate immunity, as well as CD4⁺ CD25⁺ CD127^low/? regulatory T cells (Tregs), which actively suppress pathological and physiological immune response during HCV infection. The study involved 31 chronic hepatitis C patients and 20 healthy controls. TLR2 and TLR4 expression in peripheral blood monocytes and the number of Tregs were examined by flow cytometric analysis. Overexpression of TLR2 and TLR4 was found in chronic hepatitis C patients as compared with controls. Furthermore, increased cytokine production, including that of β‐interferon, tumor necrosis factor‐α, interleukin (IL)‐6, and IL‐8, was observed in peripheral blood mononuclear cells from chronic hepatitis C patients after challenge with TLR2 and TLR4 agonists. The number of Tregs was significantly higher in chronic hepatitis C patients and the increased Tregs were associated with HCV genotype 1b. In vitro studies demonstrated that circulating Tregs suppress T‐cell responses in chronic hepatitis C patients. Significant correlations were found between the viral load and Treg number and between TLR2 and TLR4 level in chronic hepatitis C patients. Taken together with other published data, these results suggest that TLR2, TLR4, and Tregs correlate closely with chronic HCV infection.     

Dysregulation of toll‐like receptor (TLR) 2 expression on monocytes and upregulation of the frequency of T cells expressing TLR2 in patients with chronic hepatitis C virus infection

Toll‐like receptors (TLRs) initiate inflammatory responses that may play a role in disease progression in patients infected with hepatitis C virus (HCV). TLR2 and TLR4 surface expression were assessed on CD14⁺ monocytes, CD4⁺ and CD8⁺ T cells in treatment naïve patients with chronic HCV infection with fibrosis, without fibrosis, co‐infected with human immunodeficiency virus (HIV), and in healthy controls. Increased expression of TLR2 was found on monocytes in HCV‐infected patients with fibrosis (p < 0.01), co‐infected with HIV (p = 0.03), and possibly in patients without fibrosis (p = 0.07) when compared to controls. TLR2 positive CD4⁺ and CD8⁺ T cells were upregulated in patients with fibrosis only (p < 0.01). However, expression of TLR2 was not associated with T cell activation. TLR4 expression was similar in patients and healthy controls. In conclusion, TLR2 expression on monocytes and the frequency of T cells expressing TLR2 may contribute to disease progression in chronic HCV infection.     

Surface‐Mediated Priming During In Vitro Generation of Monocyte‐Derived Dendritic Cells

Ex vivo‐generated human dendritic cells (DC) are most commonly generated from monocytes using standard cell culture dishes. To elucidate the effect of the plastic surface during the differentiation process, we compared a standard adhesive plastic dish with four different mainly non‐adherent surfaces. Untouched monocytes were cultured for 3 days in the presence of IL‐4 and GM‐CSF. Time‐lapse videos were recorded, and the phenotype of the cells was analysed by flow cytometry. The cytokine profiles were analysed using a 25‐plex cytokine assay. The use of non‐adherent surfaces led to a significant reduction in expression of CD14 and CD38, and a significant increase in expression of CD86 compared to standard culture dishes. Expression levels of DC‐SIGN and PD‐L2 were reduced significantly on cells cultured on non‐adherent surfaces. The cytokine production was independent on the surface used. The surface‐mediated priming should therefore be considered when aiming to induce specific immune responses. This is especially important with regard to DC‐based immunotherapy, where an adjustment of the surface during the DC generation process might have highly beneficial effects.     

TLR8‐mediated activation of human monocytes inhibits TL1A expression

TLR play important roles in inflammation and innate immune response to pathogens. TLR8 recognizes ssRNA and induces NF‐κB via MyD88 signaling. TL1A is a member of the TNF superfamily that markedly enhances IFN‐γ production by IL‐12/IL‐18‐stimulated peripheral and mucosal CD4⁺ T cells. TL1A expression is increased in the mucosa of patients with inflammatory bowel disease and is considered a key mediator of Crohn's disease (CD). We have previously shown that TL1A is strongly induced by immune complexes (IC) but not TLR ligands in antigen‐presenting cells. However, a potential interaction between these pro‐inflammatory signaling pathways has not been investigated. IC‐induced TL1A expression of monocytes was potently inhibited by a TLR8 or TLR7/8 ligand (R848) in a dose‐dependent manner. Furthermore, when co‐cultured with CD4⁺ T cells, TLR8 ligands inhibited TL1A production, resulting in almost complete inhibition of IFN‐γ production by the CD4⁺ T cells. Furthermore, we demonstrate that IFN‐α is not required for this suppressive effect by TLR8 signaling. Our data demonstrate for the first time a direct interaction between TLR and TL1A signaling pathways. TLR8 activation may be an important, novel pathway for targeted treatment of Th1‐mediated diseases, such as CD.     

Mycobacterium tuberculosis RpfE promotes simultaneous Th1‐ and Th17‐type T‐cell immunity via TLR4‐dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation‐promoting factor (Rpf) E, a latency‐associated member of the Rpf family, in promoting naïve CD4⁺ T‐cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL‐6, IL‐1β, IL‐23p19, IL‐12p70, and TNF‐α but not IL‐10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF‐κB signaling. RpfE‐treated DCs effectively caused naïve CD4⁺ T cells to secrete IFN‐γ, IL‐2, and IL‐17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T‐bet and RORγt but not GATA‐3. Furthermore, lung and spleen cells from Mtb‐infected WT mice but not from TLR4^?/? mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1‐ and Th17‐polarized T‐cell expansion.     

Klebsiella pneumoniae‐triggered DC recruit human NK cells in a CCR5‐dependent manner leading to increased CCL19‐responsiveness and activation of NK cells

Besides their role in destruction of altered self‐cells, NK cells have been shown to potentiate T‐cell responses by interacting with DC. To take advantage of NK–DC crosstalk in therapeutic DC‐based vaccination for infectious diseases and cancer, it is essential to understand the biology of this crosstalk. We aimed to elucidate the in vitro mechanisms responsible for NK‐cell recruitment and activation by DC during infection. To mimic bacterial infection, DC were exposed to a membrane fraction of Klebsiella pneumoniae, which triggers TLR2/4. DC matured with these bacterial fragments can actively recruit NK cells in a CCR5‐dependent manner. An additional mechanism of DC‐induced NK‐cell recruitment is characterized by the induction of CCR7 expression on CD56^dimCD16⁺ NK cells after physical contact with membrane fraction of K. pneumoniae‐matured DC, resulting in an enhanced migratory responsiveness to the lymph node‐associated chemokine CCL19. Bacterial fragment‐matured DC do not only mediate NK‐cell migration but also meet the prerequisites needed for augmentation of NK‐cell cytotoxicity and IFN‐γ production, the latter of which contributes to Th1 polarization.