Bruton's tyrosine kinase regulates TLR9 but not TLR7 signaling in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDCs) represent a key cell type for both innate and adaptive immunity. PDCs express both TLR7 and TLR9 and the recognition of nucleic acids by these two receptors triggers the production of a large amount of type‐I IFN and the induction of PDC maturation into APCs. This unique feature of PDCs is at the basis of clinical development of both TLR7 and TLR9 agonists for infectious diseases, allergy, cancer, and asthma. However, TLR7 and TLR9 recognition of self‐nucleic acids is linked to many autoimmune diseases including lupus, and a better understanding of the signaling pathways of these two receptors in PDCs is thus important. We have identified Bruton's tyrosine kinase (Btk) as an important player for TLR9 but not TLR7 signaling in human PDCs. Blocking Btk using a specific inhibitor leads to the reduction of all TLR9‐induced responses in PDCs, including cytokine production and expression of costimulatory molecules, while this has no impact on the TLR7 response. This identifies Btk as a key molecule in TLR9 signaling in PDCs and is the first demonstration that the TLR7 and TLR9 pathways can be dissociated in human PDCs.     

PACSIN1 regulates the TLR7/9-mediated type I interferon response in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are the professional interferon (IFN)-producing cells of the immune system. pDCs specifically express Toll-like receptor (TLR)7 and TLR9 molecules and produce massive amounts of type I IFN by sensing microbial nucleic acids via TLR7 and TLR9. Here we report that protein kinase C and casein kinase substrate in neurons (PACSIN) 1, is specifically expressed in human and mouse pDCs. Knockdown of PACSIN1 by short hairpin RNA (shRNA) in a human pDC cell line significantly inhibited the type I IFN response of the pDCs to TLR9 ligand. PACSIN1-deficient mice exhibited normal levels of conventional DCs and pDCs, demonstrating that development of pDCs was intact although PACSIN1-deficient pDCs showed reduced levels of IFN-α production in response to both cytosine guanine dinucleotide (CpG)-oligonucleotide (ODN) and virus. In contrast, the production of proinflammatory cytokines in response to those ligands was not affected in PACSIN1-deficient pDCs, suggesting that PACSIN1 represents a pDC-specific adaptor molecule that plays a specific role in the type I IFN signaling cascade.     

Replication-independent activation of human plasmacytoid dendritic cells by the paramyxovirus SV5 Requires TLR7 and autophagy pathways

The paramyxovirus Simian Virus 5 (SV5) is a poor inducer of interferon (IFN) secretion in all cell types tested so far, including primary epithelial cells and primary human myeloid dendritic cells. SV5 is hypothesized to limit induction of antiviral responses through control of viral gene expression and production of the V protein antagonist. Plasmacytoid dendritic cells (pDCs) are known to uniquely express toll-like receptor (TLR)-7 and are a main producer of IFN-alpha among peripheral blood mononuclear cells in response to many viruses. Here, we tested whether SV5 would remain a poor inducer of IFN in primary human pDCs. The efficiency of SV5 infection of pDCs could be increased by an increasing multiplicity of infection. pDCs infected by both live and UV-inactivated SV5 induced large amounts of IFN-alpha secretion and resulted in upregulation of maturation markers CD80 and CD86. However, IL-6 secretion was not induced by SV5 infection. When TLR7 signaling was inhibited, SV5 induced less IFN secretion and CD80 expression, and there was a corresponding increase in number of infected cells. Similar effects were seen with inhibitors of cellular autophagy pathways, suggesting that the SV5 activation of pDC requires access to the cytoplasm and autophagic sampling of cytoplasmic contents. These results have implications for control of SV5 infections in vivo and for development of SV5 as a vaccine vector.     

Analysis of HLDA9 mAbs on plasmacytoid dendritic cells

Dendritic cells are a heterogeneous population of bone marrow derived leucocytes that play a crucial role in both pathogen recognition and the initiation of primary T cell immune responses. Plasmacytoid dendritic cells (pDCs), also known as natural interferon-producing cells, comprise one of two major human dendritic cell subsets that strongly influences immune balance. pDCs remain a poorly characterized subset. Several studies have suggested the existence of a close phenotypic and functional relationship between B-cells and pDCs. The surface reactivity of a panel of 96 monoclonal antibodies submitted to the ninth Human Leukocyte Differentiation Antigens workshop (HLDA9) B cell section was analyzed using pDCs as target cells. The results showed that eight of the mAbs reacted positively on pDCs: CD86, CD229, CD319, CD305, CD184, CD84, CD85g and Fc?RIa, confirming previously published reports. Interestingly, this study also revealed the expression of eight surface molecules not previously described on pDCs, including CD352(NTBA), CD272(BTLA), CD357(GITR), CD48, CD270(HVEM), Galectin-3, CD148, and CD361. The present report summarizes the expression of these molecules on freshly isolated pDCs. Significantly, we have identified several new molecules expressed by these intriguing cells, ones we believe will open new avenues for the study of pDC functionality and their role in human health and diseases.     

Origin and filiation of human plasmacytoid dendritic cells

Human plasmacytoid dendritic cells represent a rare population of leukocytes which produce high amounts of type I interferon in response to certain viruses. Although those cells were first described in 1958, there are still unsolved issues related to their origin and function. Recently, a leukemic counterpart of plasmacytoid dendritic cells was identified. Molecular approaches using either normal or leukemic plasmacytoid dendritic cells provide some new insights into the controversial lymphoid origin of those cells. The need for specific markers is still a critical aspect for the identification of plasmacytoid dendritic cells, whatever stage of differentiation, in normal as well as in pathological conditions. Hopefully, novel markers will allow delineation of the relationships between dendritic cells at different stages of differentiation/maturation along the myeloid and lymphoid lineages.     

Immature myeloid and plasmacytoid dendritic cells infiltrate renal tubulointerstitium in patients with lupus nephritis

Systemic lupus erythematosus (SLE) is an autoimmune disease involving several organs. SLE patients developing lupus nephritis (LN) frequently have the worst outcome. Recent data have shown that dendritic cells (DCs) may have a central role in SLE pathogenesis directing the immune response against auto-antigens. In this study we describe a reduction in circulating BDCA1+ and BDCA3+ myeloid DCs, and BDCA2+ plasmacytoid DCs in patients with active LN compared to those in the remission state. Analysis of LN biopsies revealed a strong tubulo-interstitial infiltrate of BDCA1+, BDCA3+ and BDCA4+ DCs which were negative for DC-LAMP, a specific marker of mature DCs. The extent of the DCs infiltrate was higher in class III/IV LN than in normal kidney. These results show for the first time that three DCs subsets, decreased at circulating levels, are recruited within the kidney, indicating that DCs might play a pathogenic role in SLE patients with nephritis.     

Prostaglandin E2 is a negative regulator on human plasmacytoid dendritic cells

Prostaglandin E2 (PGE2), a major lipid derived from the metabolism of arachidonic acid, is an environmentally bioactive substance produced by inflammatory processes and acts as a cAMP up-regulator that plays an important role in immune responses. It has been reported that PGE2 has the ability to inhibit the production of interleukin-12 by myeloid dendritic cells (MDCs) and macrophages, and then induce preferential T helper type 2 (Th2) cell responses. However, little is known of the function of PGE2 for plasmacytoid dendritic cells (PDCs), which may contribute to the innate and adaptive immune response to viral infection, allergy and autoimmune diseases. In the present study, we compared the biological effect of PGE2 on human PDCs and MDCs. PGE2 caused the death of PDCs but MDCs survived. Furthermore, we found that, whereas PGE2 inhibited interferon-alpha production by PDCs in response to virus or cytosine-phosphate-guanosine, it inhibited interleukin-12 production by MDCs in response to lipopolysaccharide (LPS) or poly(I:C). Although both virus-stimulated PDCs and LPS-stimulated MDCs preferentially induced the development of interferon-gamma-producing Th1 cells, pretreatment with PGE2 led both DC subsets to attenuate their Th1-inducing capacity. These findings suggest that PGE2 represents a negative regulator on not only MDCs but also PDCs.     

Distinct roles of myeloid and plasmacytoid dendritic cells in systemic lupus erythematosus

Dendritic cells (DCs) constitute a heterogeneous population of professional antigen presenting cells which are the initiators and key regulators for both immunity and tolerance induction. The significance and impact of DC biology in contemporary immunology and medical research is heightened by the award of the 2011 Nobel Prize for Medicine and Physiology to Ralf Steinman for his discovery and subsequent work on the role of DC in adaptive immunity. As a central regulator of immune responses, DCs also play a pivotal role in the pathogenesis of chronic inflammatory autoimmune conditions such as systemic lupus erythematosus (SLE). In this review, we will focus on the respective role of the two major subsets of blood DC, namely myeloid (m)-DC and plasmacytoid (p)-DC, in SLE immunopathogenesis. Accumulating evidence has highlighted pDCs as the culprit for SLE pathogenesis, mainly through type-I interferon production. Latest findings in the field also decipher the mechanisms by which pDCs interact with neutrophils and platelets and contribute to SLE development. The recent surge of interest in studying microRNA regulation in SLE pathogenesis will also be discussed.     

低氧对人成熟树突状细胞MMP9/TIMP1及CCR7 表达的影响

目的： 观察低氧对人单核细胞来源成熟树突状细胞（mDCs）趋化因子受体（CCR7）,基质金属蛋白酶-9（MMP-9）及其组织抑制剂（TIMP-1）表达的影响,以期为改进DCs疫苗体内迁移能力低下提供新策略。方法： 分离制备人外周血单核细胞（PBMCs）,采用体外常规培养体系 ［粒-巨噬细胞集落刺激因子（GM-CSF）与白细胞介素-4（IL-4）共同刺激］ 诱导DCs,于诱导后第5 d加入TNF-α促成熟,48 h后将mDCs置低氧环境下（1％ O2、5％ CO2、94％ N2）分别继续培养6 h、12 h,设常氧对照组（21% O2、5% CO2）,收获细胞及培养上清;采用RT-PCR技术检测MMP-9、TIMP-1及CCR7的表达;明胶酶谱法检测培养上清中MMP-9的水平与活性,流式细胞术检测mDCs表面CCR7的表达。结果： RT-PCR及酶谱实验结果显示,低氧6 h、12 h处理组mDCs MMP-9水平显著下降;与对照组比较,各低氧处理组mDCs均未检测到TIMP-1 mRNA表达的变化;转录及细胞表面表达分析结果显示,与常氧对照组比较,低氧6 h处理组趋化因子受体CCR7表达显著降低,而12 h处理组其表达显著回升至近常氧组水平。结论： 低氧下调mDCs MMP-9表达,破坏MMP-9/TIMP-1平衡,可能是DCs疫苗体内迁移能力低下的主要因素之一。趋化因子受体CCR7在mDCs对低氧应答中可能起重要作用。     

Plasmacytoid dendritic cell precursors/type I interferon-producing cells sense viral infection by Toll-like receptor (TLR) 7 and TLR9

Plasmacytoid dendritic cell (pDC) precursors, also called type I IFN (//)-producing cells (IPCs), are the key effectors in the innate immune system because of their extraordinary capacity to produce type I IFNs against microbial infection, particularly viral infection. In contrast to myeloid DCs, human pDC/IPCs selectively express Toll-like receptor (TLR) 7 and TLR9 within the endosomal compartment. These receptors are specifically designed to recognize the nucleoside-based products derived from RNA viruses and DNA viruses. Therefore, this expression profile potentially enables pDC/IPCs to sense a variety of viruses. Stimulation of TLR7 or TLR9 leads to type I IFN responses through the MyD88 pathway. Thus, pDC/IPCs may play a central role in host defense against viral infection through the TLR7 and TLR9 system.     

Impaired CCR7 expression on plasmacytoid dendritic cells of HIV-infected children and adolescents with immunologic and virologic failure

BACKGROUND: Defects of plasmacytoid (p) and myeloid (m) dendritic cells (DCs) occur in HIV infection. The aim of this study was to evaluate the maturation and function of DCs in children with perinatal HIV infection who were on antiretroviral therapy. MATERIALS AND METHODS: Twenty HIV-infected children (median age = 12.9 years) classified as immunologic/virologic responders and failures were evaluated in a whole-blood assay with resiquimod (RSQ), a potent agonist to Toll-like receptors 7 and 8, as the DC stimulant. RESULTS: In comparison to controls, pDC and mDC numbers were decreased in patients, but RSQ stimulation resulted in upregulation of CD83, CD80, and tumor necrosis factor-alpha in both DC subsets and upregulation of interferon (IFN)-alpha in pDCs. Patients with immunologic and virologic failure demonstrated a selective impairment in upregulation of lymph node homing marker CCR7 in pDCs. Plasma virus load was negatively correlated with IFNalpha and CCR7 expression, whereas CD4 percentage correlated only with CCR7 expression in pDCs. CONCLUSIONS: A novel defect of pDCs, impaired CCR7 upregulation, is described in association with immunologic or virologic failure. This deficiency could impair homing of pDCs to lymph nodes, leading to secondary defects of mDC maturation and poor T-cell activation.     

Increased interferon alpha expression in circulating plasmacytoid dendritic cells of HIV-1-infected patients

BACKGROUND: The role of plasmacytoid dendritic cells (pDC) and interferon alpha (IFN alpha) in HIV-1 infection is still unclear. On one hand, HIV-1 disease is associated with a progressive decline of pDC, which displays reduced ability to produce IFN alpha after in vitro challenge. On the other hand, high IFN alpha serum levels in HIV-1-infected individuals have been proposed to promote immune hyper-activation and disease progression. METHODS: We sought to determine whether disappearance of pDC in HIV-1 disease is due to homing in lymphoid tissues. We also studied IFN alpha and myxovirus resistance protein A (MxA) expression in unstimulated pDC and correlated these results with selected clinical and laboratory parameters. RESULTS: We found that pDC decline markedly in peripheral blood of patients progressing to disease but at the same time express much higher levels of IFN alpha and MxA compared to control individuals. On the other hand, we observed steady pDC counts in lymph nodes of HIV-1 patients. The frequency of circulating pDC correlated directly with CD4 cell counts and inversely with viral load. However, we found no correlation between IFN alpha and MxA expression levels, CD4 counts, and viral load. CONCLUSIONS: Circulating pDC decline sharply in the course of HIV-1 disease, but express high levels of IFN alpha, which may represent a hallmark of systemic immune dysfunction.     

Adenovirus type 35, but not type 5, stimulates NK cell activation via plasmacytoid dendritic cells and TLR9 signaling

In hematopoietic stem cell transplant (HSCT) recipients, disseminated adenoviral infections during the first two months after HSCT can lead to severe complications and fatal outcome. Since NK cells are usually the first lymphocytes to reconstitute after HSCT and have been implicated in the clearance of adenovirus-infected cells, it was investigated whether NK cells are activated by adenovirus in vitro. Exposure of PBMC to human adenovirus type 5 (HAdV5) or HAdV35 resulted in the up-regulation of the activation marker CD69 on NK cells and enhanced the cytolytic activity of NK cells. HAdV5-induced NK cell activation relied on the contribution of T cells as the depletion of T cells from PBMC abolished NK cell activation. In contrast, NK cell activation in response to HAdV35 occurred in the absence of T cells. Plasmacytoid dendritic cells (pDC) were necessary and sufficient to mediate NK cell activation. HAdV35 induced significantly more interferon-α (IFN-α) production by pDC than HAdV5. The increased IFN-α production and NK cell activation correlated with a higher infection efficiency of viruses with the type 35 fiber. The IFN-α response of pDC was enhanced by the presence of NK cells, suggesting a reciprocal interaction between pDC and NK cells. Incubation with a TLR9 antagonist impaired the IFN-α production by pDC as well as NK cell activation, implying that TLR9 signaling is critically involved in the IFN-α response of pDC and NK cell activation after HAdV35 exposure. In conclusion, two human adenovirus serotypes from two different species differ considerably in their capacity to stimulate pDC and NK cells.     

Expression of CD33-related siglecs on human mononuclear phagocytes, monocyte-derived dendritic cells and plasmacytoid dendritic cells

Siglecs are sialic acid binding Ig-like lectins mostly expressed in the haemopoietic and immune systems. Amongst the 11 human siglecs, there are eight proteins highly related to CD33 which have biochemical features of inhibitory receptors, containing two conserved tyrosine-based inhibitory motifs. Five of these (CD33/siglec-3, -5, -7, -9 and -10) are expressed on circulating monocytes. Here we show that monocytes cultured to differentiate into macrophages using either GM-CSF or M-CSF retained expression of these siglecs and their levels were unaffected following stimulation with LPS. In comparison, monocyte-derived dendritic cells down-modulated siglec-7 and -9 following maturation with LPS. Plasmacytoid dendritic cells in human blood expressed siglec-5 only. On monocytes, siglec-5 was shown to mediate rapid uptake of anti-siglec-5 (Fab)2 fragments into early endosomes. This suggests, in addition to inhibitory signalling, a potential role in endocytosis for siglec-5 and the other CD33-related siglecs. Our results show that siglecs are differentially expressed on mononuclear phagocytes and dendritic cells and that some can be modulated by stimuli that promote maturation and differentiation.     

PGE_2促进人脐血CD34~+造血祖细胞向淋巴样树突状细胞分化

为了探讨前列腺素E2(protaglandin E2,PGE2)对人外周血CD14+单核细胞和脐血CD34+造血祖细胞(hematopoieticprogenitor cells,HPC)体外诱导pDC分化的影响。分别采用IL-4+GM-CSF+TNF-α和SCF+Flt-3L+GM-CSF+TNF-α诱导人外周血CD14+单核细胞和CD34+HPC向pDC分化,采用流式细胞仪分析细胞表型,并观察PGE2加入培养体系后对pDC分化的影响。结果:以CD34+HPC为来源,比CD14+单核细胞能诱导出更多数量且具有功能的pDC。培养体系中加入PGE2显著增强了CD34+HPC向pDC的分化,而对CD14+单核细胞的分化却无明显促进作用。PGE2可有效促进脐血CD34+HPC在多种细胞因子的作用下向pDC的成熟分化。