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1.  The DEAH box RNA helicase DHX33 senses cytosolic RNA and activates the NLRP3 inflammasome 
Immunity  2013;39(1):123-135.
Summary
The NLRP3 inflammasome plays a major role in innate immune responses by activating caspase-1, resulting in secretion of interleukin (IL)-18 and IL-1β. Although cytosolic double-stranded RNA (dsRNA) and bacterial RNA are known to activate the NLRP3 inflammasome, the upstream sensor is unknown. We investigated the potential function of DExD/H-box RNA helicase family members (previously shown to sense cytosolic DNA and RNA to induce type 1 interferon responses) in RNA-induced NLRP3 inflammasome activation. Among the helicase family members tested, we found that targeting of DHX33 expression by short hairpin RNA efficiently blocked the activation of caspase-1 and secretion of IL-18/IL-1β in human macrophages that were activated by cytosolic poly I:C, reoviral RNA or bacterial RNA. DHX33 bound dsRNA via the helicase C domain. DHX33 interacted with NLRP3 and formed the inflammasome complex following stimulation with RNA. We, therefore, identified DHX33 as a cytosolic RNA sensor that activates the NLRP3 inflammasome.
doi:10.1016/j.immuni.2013.07.001
PMCID: PMC3756931  PMID: 23871209
2.  The interaction between the helicase DHX33 and IPS-1 as a novel pathway to sense double-stranded RNA and RNA viruses in myeloid dendritic cells 
In eukaryotes, there are at least 60 members of the DExD/H helicase family, many of which are able to sense viral nucleic acids. By screening all known family members, we identified the helicase DHX33 as a novel double-stranded RNA (dsRNA) sensor in myeloid dendritic cells (mDCs). The knockdown of DHX33 using small heteroduplex RNA (shRNA) blocked the ability of mDCs to produce type I interferon (IFN) in response to poly I:C and reovirus. The HELICc domain of DHX33 was shown to bind poly I:C. The interaction between DHX33 and IPS-1 is mediated by the HELICc region of DHX33 and the C-terminal domain of IPS-1 (also referred to MAVS and VISA). The inhibition of DHX33 expression by RNA interference blocked the poly I:C-induced activation of MAP kinases, NF-κB and IRF3. The interaction between the helicase DHX33 and IPS-1 was independent of RIG-I/MDA5 and may be a novel pathway for sensing poly I:C and RNA viruses in mDCs.
doi:10.1038/cmi.2013.40
PMCID: PMC4002151  PMID: 24037184
DHX33; helicase; innate immunity; IPS-1; myeloid dendritic cell; viral nucleic acid
3.  Evaluation of Compressive Strength Index of the Femoral Neck in Caucasians and Chinese 
Calcified tissue international  2010;87(4):324-332.
Compressive strength index (CSI) of the femoral neck is a parameter that integrates the information of bone mineral density (BMD), femoral neck width (FNW), and body weight. CSI is considered to have the potential to improve the performance of assessment for hip fracture risk. However, studies on CSI have been rare. In particular, few studies have evaluated the performance of CSI, in comparison with BMD, FNW, and bending geometry, for assessment of hip fracture risk. We studied two large populations, including 1683 unrelated U.S. Caucasians and 2758 unrelated Chinese adults. For all the study subjects, CSI, femoral neck BMD (FN_BMD), FNW, and bending geometry (section modulus [Z]) of the samples were obtained from dual-energy X-ray absorptiometry scans. We investigated the age-related trends of these bone phenotypes and potential sex and ethnic differences. We further evaluated the performance of these four phenotypes for assessment of hip fracture risk by logistic regression models. Chinese had significantly lower FN_BMD, FNW, and Z, but higher CSI than sex-matched Caucasians. Logistic regression analysis showed that higher CSI was significantly associated with lower risk of hip fracture, and the significance remained after adjusting for covariates of age, sex, and height. Each standard deviation (SD) increment in CSI was associated with odds ratios of 0.765 (95% confidence interval, 0.634, 0.992) and 0.724 (95% confidence interval, 0.569, 0.921) for hip fracture risk in Caucasians and Chinese, respectively. The higher CSI in Chinese may partially help explain the lower incidence of hip fractures in this population compared to Caucasians. Further studies in larger cohorts and/or longitudinal observations are necessary to confirm our findings.
doi:10.1007/s00223-010-9406-8
PMCID: PMC4176885  PMID: 20814670
Osteoporosis; Bone mineral density; Compressive strength index; Femoral neck width; Section modulus; Hip fracture
4.  Long-term outcome of ketoconazole and tacrolimus co-administration in kidney transplant patients 
World Journal of Nephrology  2014;3(3):107-113.
AIM: To study the long-term outcome of ketoconazole and tacrolimus combination in kidney transplant recipients.
METHODS: From 2006 to 2010, ketoconazole was given in 199 patients and was continued for at least 1 year or until graft failure (Group 1), while 149 patients did not receive any ketoconazole (Group 2). A combination of tacrolimus, mycophenolate and steroid was used as maintenance therapy. High risk patients received basiliximab induction.
RESULTS: Basic demographic data was similar between the 2 groups. The 5-year cumulative incidence of biopsy-confirmed and clinically-treated acute rejection was significantly higher in Group 1 than in Group 2 (34% vs 18%, P = 0.01). The 5-year Kaplan-Meier estimated graft survival (74.3% vs 76.4%, P = 0.58) and patient survival (87.8% vs 87.5%, P = 0.93) were not different between the 2 groups. Multivariable analyses identified ketoconazole usage as an independent risk of acute rejection (HR = 2.33, 95%CI: 1.33-4.07; P = 0.003) while tacrolimus dose in the 2nd month was protective (HR = 0.89, 95%CI: 0.75-0.96; P = 0.041).
CONCLUSION: Co-administration of ketoconazole and tacrolimus is associated with significantly higher incidence of acute rejection in kidney transplant recipients.
doi:10.5527/wjn.v3.i3.107
PMCID: PMC4202487  PMID: 25332902
Kidney transplant; Rejection; Survival; Tacrolimus Ketoconazole; Pharmacokinetics; Cytochrome P450
5.  The Development of Murine Plasmacytoid Dendritic Cell Precursors Is Differentially Regulated by FLT3-ligand and Granulocyte/Macrophage Colony-Stimulating Factor 
Plasmacytoid predendritic cells or type 1 interferon (IFN)-producing cells (IPCs) have recently been identified in mice. Although culture systems giving rise to different murine dendritic cell subsets have been established, the developmental regulation of murine plasmacytoid IPCs and the culture conditions leading to their generation remain unknown. Here we show that large numbers of over 40% pure CD11c+CD11b−B220+Gr-1+ IPCs can be generated from mouse bone marrow cultures with FLT3-ligand. By contrast GM-CSF or TNF-α, which promote the generation of CD11c+CD11b+B220− myeloid DCs, block completely the development of IPCs. IPCs generated display similar features to human IPCs, such as the plasmacytoid morphology, the ability to produce large amounts of IFN-α in responses to herpes simplex virus, and the capacity to respond to ligands for Toll-like receptor 9 (TLR-9; CpG ODN 1668), but not to ligands for TLR-4 (lipopolysaccharide [LPS]). Unlike human IPCs which produce little IL-12p70, mouse IPCs produce IL-12p70 in response to CpG ODN 1668 and herpes simplex virus. This study demonstrates that the development of murine CD11c+CD11b−B220+Gr-1+ IPCs and CD11c+CD11b+B220− myeloid DCs is differentially regulated by FLT3-ligand and granulocyte/macrophage colony-stimulating factor. Human IPCs and mouse IPCs display different ability to produce IL-12p70. Large numbers of mouse IPCs can now be obtained from total bone marrow culture.
doi:10.1084/jem.20020045
PMCID: PMC2193725  PMID: 11927638
pre-DC2; IPC; T lymphocyte; antiviral immune response; innate immunity
6.  Generation of Human CD8 T Regulatory Cells by CD40 Ligand–activated Plasmacytoid Dendritic Cells 
Although CD8 T cell–mediated immunosuppression has been a well-known phenomenon during the last three decades, the nature of primary CD8 T suppressor cells and the mechanism underlying their generation remain enigmatic. We demonstrated that naive CD8 T cells primed with allogeneic CD40 ligand–activated plasmacytoid dendritic cells (DC)2 differentiated into CD8 T cells that displayed poor secondary proliferative and cytolytic responses. By contrast, naive CD8 T cells primed with allogeneic CD40 ligand–activated monocyte-derived DCs (DC1) differentiated into CD8 T cells, which proliferated to secondary stimulation and killed allogeneic target cells. Unlike DC1-primed CD8 T cells that produced large amounts of interferon (IFN)-γ upon restimulation, DC2-primed CD8 T cells produced significant amounts of interleukin (IL)-10, low IFN-γ, and no IL-4, IL-5, nor transforming growth factor (TGF)-β. The addition of anti–IL-10–neutralizing monoclonal antibodies during DC2 and CD8 T cell coculture, completely blocked the generation of IL-10–producing anergic CD8 T cells. IL-10–producing CD8 T cells strongly inhibit the allospecific proliferation of naive CD8 T cells to monocytes, and mature and immature DCs. This inhibition was mediated by IL-10, but not by TGF-β. IL-10–producing CD8 T cells could inhibit the bystander proliferation of naive CD8 T cells, provided that they were restimulated nearby to produce IL-10. IL-10–producing CD8 T cells could not inhibit the proliferation of DC1-preactivated effector T cells. This study demonstrates that IL-10–producing CD8 T cells are regulatory T cells, which provides a cellular basis for the phenomenon of CD8 T cell–mediated immunosuppression and suggests a role for plasmacytoid DC2 in immunological tolerance.
doi:10.1084/jem.20011603
PMCID: PMC2193733  PMID: 11901196
dendritic cells; T regulatory cells; CD8 T cells; immunosuppression; IL-10
7.  The E3 ubiquitin ligase TRIM21 negatively regulates the innate immune response to intracellular double-stranded DNA 
Nature immunology  2012;14(2):172-178.
DDX41 is a sensor of intracellular double-stranded DNA (dsDNA) in myeloid dendritic cells (mDCs) that triggers a type I interferon response via the signaling adaptor STING. We identified the E3 ligase TRIM21 as a DDX41-interacting protein and found that knockdown of or deficiency in TRIM21 resulted in enhanced type I interferon responses to intracellular dsDNA and DNA viruses. Overexpression of TRIM21 resulted in more degradation of DDX41 and less production of interferon-β (IFN-β) in response to intracellular dsDNA. The SPRY-PRY domain of TRIM21 interacted with the DEADc domain of DDX41. Lys9 and Lys115 of DDX41 were the targets of TRIM21-mediated ubiquitination. TRIM21 is therefore an interferon-inducible E3 ligase that induces the Lys48 (K48)-linked ubiquitination and degradation of DDX41 and negatively regulates the innate immune response to intracellular dsDNA.
doi:10.1038/ni.2492
PMCID: PMC3645272  PMID: 23222971
8.  Regulation of TLR7/9 signaling in plasmacytoid dendritic cells 
Protein & cell  2012;4(1):40-52.
Plasmacytoid dendritic cells (pDCs), also known as type I interferon (IFN)-producing cells, are specialized immune cells characterized by their extraordinary capabilities of mounting rapid and massive type I IFN response to nucleic acids derived from virus, bacteria or dead cells. PDCs selectively express endosomal Toll-like receptor (TLR) 7 and TLR9, which sense viral RNA and DNA respectively. Following type I IFN and cytokine responses, pDCs differentiate into antigen presenting cells and acquire the ability to regulate T cell-mediated adaptive immunity. The functions of pDCs have been implicated not only in antiviral innate immunity but also in immune tolerance, inflammation and tumor microenvironments. In this review, we will focus on TLR7/9 signaling and their regulation by pDC-specific receptors.
doi:10.1007/s13238-012-2104-8
PMCID: PMC3667388  PMID: 23132256
plasmacytoid dendritic cells; Toll-like receptors; immunoreceptor tyrosine-based activation motif; immunoreceptor tyrosine-based inhibitory motif; immunoglobulin-like transcript; BDCA2; phospholipid scramblase 1; protein kinase C and casein kinase substrate in neurons 1
9.  The interaction between the helicase DHX33 and IPS-1 as a novel pathway to sense double-stranded RNA and RNA viruses in myeloid dendritic cells 
In eukaryotes, there are at least 60 members of the DExD/H helicase family, many of which are able to sense viral nucleic acids. By screening all known family members, we identified the helicase DHX33 as a novel double-stranded RNA (dsRNA) sensor in myeloid dendritic cells (mDCs). The knockdown of DHX33 using small heteroduplex RNA (shRNA) blocked the ability of mDCs to produce type I interferon (IFN) in response to poly I:C and reovirus. The HELICc domain of DHX33 was shown to bind poly I:C. The interaction between DHX33 and IPS-1 is mediated by the HELICc region of DHX33 and the C-terminal domain of IPS-1 (also referred to MAVS and VISA). The inhibition of DHX33 expression by RNA interference blocked the poly I:C-induced activation of MAP kinases, NF-κB and IRF3. The interaction between the helicase DHX33 and IPS-1 was independent of RIG-I/MDA5 and may be a novel pathway for sensing poly I:C and RNA viruses in mDCs.
doi:10.1038/cmi.2013.40
PMCID: PMC4002151  PMID: 24037184
DHX33; helicase; innate immunity; IPS-1; myeloid dendritic cell; viral nucleic acid
10.  CD2AP/SHIP1 Complex Positively Regulates Plasmacytoid Dendritic Cell Receptor Signaling by Inhibiting the E3 Ubiquitin Ligase Cbl 
The human plasmacytoid dendritic cell (pDC) receptor BDCA2 forms a complex with the adaptor FcεR1γ to activate an ITAM-signaling cascade. BDCA2 receptor signaling negatively regulates the TLR7/9-mediated type 1 IFN responses in pDCs, which may play a key role in controlling self-DNA/RNA–induced autoimmunity. We report in this article that CD2-associated adaptor protein (CD2AP), which is highly expressed in human pDCs, positively regulates BDCA2/FcεR1γ receptor signaling. By immunoprecipitation and mass spectrometry analyses, we found that CD2AP bound to SHIP1. Knockdown of CD2AP or SHIP1 reduced the BDCA2/FcεR1γ-mediated ITAM signaling and blocked its inhibition of TLR9-mediated type 1 IFN production. Knockdown of CD2AP or SHIP1 also enhanced the ubiquitination and degradation of Syk and FcεR1γ that was mediated by the E3 ubiquitin ligase Cbl. This led us to discover that, upon BDCA2 cross-linking, the CD2AP/SHIP1 complex associated with Cbl and inhibited its E3 ubiquitin ligase activity. In human primary pDCs, cross-linking of the BDCA2/FcεR1γ complex induced the recruitment of the CD2AP/SHIP1/Cbl complex to the plasma membrane of pDCs, where it colocalized with the BDCA2/FcεR1γ complex. Therefore, CD2AP positively regulates BDCA2/FcεR1γ signaling by forming a complex with SHIP1 to inhibit the E3 ubiquitin ligase Cbl.
doi:10.4049/jimmunol.1200887
PMCID: PMC3665352  PMID: 22706086
11.  DHX9 Pairs with IPS-1 To Sense Double-Stranded RNA in Myeloid Dendritic Cells 
The innate immune system is equipped with many molecular sensors for microbial DNA/RNA to quickly mount antimicrobial host immune responses. In this paper, we identified DHX9, a DExDc helicase family member, as an important viral dsRNA sensor in myeloid dendritic cells (mDCs). Knockdown of DHX9 expression by small heteroduplex RNA dramatically blocked the ability of mDCs to produce IFN-α/β and proinflammatory cytokines in response to polyinosine-polycytidylic acid, influenza A, and reovirus. DHX9 could specifically bind polyinosine-polycytidylic acid via its double-strand RNA binding motifs. DHX9 interacted with IPS-1 via the HelicC-HA2-DUF and CARD domains of DHX9 and IPS-1, respectively. Knockdown of DHX9 expression in mDCs blocked the activation of NF-κB and IFN regulatory factor 3 by dsRNA. Collectively, these results suggest that DHX9 is an important RNA sensor that is dependent on IPS-1 to sense pathogenic RNA.
doi:10.4049/jimmunol.1101307
PMCID: PMC3656476  PMID: 21957149
12.  PACSIN1 regulates the TLR7/9-mediated type I interferon response in plasmacytoid dendritic cells 
European journal of immunology  2012;42(3):573-579.
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.
doi:10.1002/eji.201142045
PMCID: PMC3656478  PMID: 22488361
Interferon; Plasmacytoid dendritic cells (pDCs); TLR9
13.  Cutting Edge: Hematopoietic-Derived APCs Select Regulatory T Cells in Thymus 
Recognition of self-peptide–MHC complexes by high-affinity TCRs and CD28 signaling are critical for the development of forkhead-winged helix box transcription factor 3+ regulatory T cells (Tregs) in thymus. However, the type of APCs that are responsible for selecting Tregs has remained unclear. To dissect the role of hematopoietic-derived APCs (HCs) and thymic epithelial cells (TECs) in Treg selection, we constructed bone marrow chimeras with disrupted CD28/B7 signaling in the HC or TEC compartment and analyzed the generation of Tregs in the thymus. We found that both HCs and TECs were independently able to fully reconstitute the Treg population in the thymus of bone marrow chimeras. In addition, Treg selection requires the TCR signal and CD28 costimulation presented in cis on the same APC type in vivo. This study demonstrates a new role, to our knowledge, for HCs in the development of Tregs in thymus.
doi:10.4049/jimmunol.0900665
PMCID: PMC3325783  PMID: 20802149
14.  Thymic Stromal Lymphopoietin-Activated Plasmacytoid Dendritic Cells Induce the Generation of FOXP3+ Regulatory T Cells in Human Thymus 
Human thymus contains major dendritic cell (DC) subsets, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs). We previously showed that mDCs, educated by thymic stromal lymphopoietin (TSLP) produced by the epithelial cells of the Hassall’s corpuscles, induced differentiation of CD4+CD25− thymocytes into Forkhead Box P3+ (FOXP3+) regulatory T cells (TR) within the medulla of human thymus. In this study, we show that pDCs expressed the TSLP receptor and IL-7 receptor a complexes upon activation and became responsive to TSLP. TSLP-activated human pDCs secrete macrophage-derived chemokine CCL-22 and thymus- and activation-regulated chemokine CCL-17 but not Th1- or Th2-polarizing cytokines. TSLP-activated pDCs induced the generation of FOXP3+ TR from CD4+CD8−CD25− thymocytes, which could be strongly inhibited by Th1-polarizing cytokine IL-12 or Th2-polarizing cytokine IL-4. Interestingly, the FOXP3+ TR induced by the TSLP-pDCs expressed more IL-10 but less TGF-b than that induced by the TSLP-mDCs. These data suggest that TSLP expressed by thymic epithelial cells can activate mDCs and pDCs to positively select the FOXP3+ TR with different cytokine production potential in human thymus. The inability of TSLP to induce DC maturation without producing Th1- or Th2-polarizing cytokines may provide a thymic niche for TR development.
doi:10.4049/jimmunol.0804106
PMCID: PMC3325785  PMID: 20173030
15.  Melanoma cells express ICOS ligand to promote the activation and expansion of T-regulatory cells 
Cancer research  2010;70(23):9581-9590.
CD4+CD25+Foxp3+ T-regulatory cells (Tregs) accumulate in tumors, however little is known about how the tumor environment influences this process. Here we show that human melanomas express ICOS-ligand (ICOS-L/B7H) that can provide costimulation through ICOS for the expansion of activated Tregs maintaining high Foxp3 and CD25 expression as well as suppressive function. Thus, ICOS-L expression by melanoma tumor cells may directly drive Treg activation and expansion in the tumor microenvironment as another mechanism of immune evasion.
doi:10.1158/0008-5472.CAN-10-1379
PMCID: PMC3058814  PMID: 21098714
Melanoma; ICOSL; Treg; Foxp3; ICOS
16.  Copy Number Variation in CNP267 Region May Be Associated with Hip Bone Size 
PLoS ONE  2011;6(7):e22035.
Osteoporotic hip fracture (HF) is a serious global public health problem associated with high morbidity and mortality. Hip bone size (BS) has been identified as one of key measurable risk factors for HF, independent of bone mineral density (BMD). Hip BS is highly genetically determined, but genetic factors underlying BS variation are still poorly defined. Here, we performed an initial genome-wide copy number variation (CNV) association analysis for hip BS in 1,627 Chinese Han subjects using Affymetrix GeneChip Human Mapping SNP 6.0 Array and a follow-up replicate study in 2,286 unrelated US Caucasians sample. We found that a copy number polymorphism (CNP267) located at chromosome 2q12.2 was significantly associated with hip BS in both initial Chinese and replicate Caucasian samples with p values of 4.73E-03 and 5.66E-03, respectively. An important candidate gene, four and a half LIM domains 2 (FHL2), was detected at the downstream of CNP267, which plays important roles in bone metabolism by binding to several bone formation regulator, such as insulin-like growth factor-binding protein 5 (IGFBP-5) and androgen receptor (AR). Our findings suggest that CNP267 region may be associated with hip BS which might influence the FHL2 gene downstream.
doi:10.1371/journal.pone.0022035
PMCID: PMC3137628  PMID: 21789208
17.  A novel subset of CD4+ TH2 memory/effector cells that produce inflammatory IL-17 cytokine and promote the exacerbation of chronic allergic asthma 
The Journal of Experimental Medicine  2010;207(11):2479-2491.
Memory CD4+ T cells that produce both Th2 and Th17 cytokines are increased in the blood of patients with atopic asthma and in the lungs of asthmatic mice, where they contribute to inflammation.
The inflammatory cytokine interleukin (IL)-17 is involved in the pathogenesis of allergic diseases. However, the identity and functions of IL-17–producing T cells during the pathogenesis of allergic diseases remain unclear. Here, we report a novel subset of TH2 memory/effector cells that coexpress the transcription factors GATA3 and RORγt and coproduce TH17 and TH2 cytokines. Classical TH2 memory/effector cells had the potential to produce IL-17 after stimulation with proinflammatory cytokines IL-1β, IL-6, and IL-21. The number of IL-17-TH2 cells was significantly increased in blood of patients with atopic asthma. In a mouse model of allergic lung diseases, IL-17–producing CD4+ TH2 cells were induced in the inflamed lung and persisted as the dominant IL-17–producing T cell population during the chronic stage of asthma. Treating cultured bronchial epithelial cells with IL-17 plus TH2 cytokines induced strong up-regulation of chemokine eotaxin-3, Il8, Mip1b, and Groa gene expression. Compared with classical TH17 and TH2 cells, antigen-specific IL-17–producing TH2 cells induced a profound influx of heterogeneous inflammatory leukocytes and exacerbated asthma. Our findings highlight the plasticity of TH2 memory cells and suggest that IL-17–producing TH2 cells may represent the key pathogenic TH2 cells promoting the exacerbation of allergic asthma.
doi:10.1084/jem.20101376
PMCID: PMC2964570  PMID: 20921287
18.  The Signal Transducer STAT5 Inhibits Plasmacytoid Dendritic Cell Development by Suppressing Transcription Factor IRF8 
Immunity  2008;28(4):509-520.
SUMMARY
The development of distinct dendritic cell (DC) subsets is regulated by cytokines. Flt3-ligand- (Flt3L) is necessary for plasmacytoid (pDC) and conventional DC (cDC) maturation. GM-CSF inhibits Flt3L-driven pDC production while promoting cDC growth. We show that GM-CSF selectively utilizes STAT5 to block Flt3L-dependent pDC development from the lineage-negative, Flt3+ (lin−/Flt3+) bone marrow subset. STAT3, by contrast, is necessary for expansion of DC progenitors but not pDC maturation. In vivo, STAT5 suppresses pDC formation during repopulation of the DC compartment following bone marrow ablation. GM-CSF/STAT5 signaling rapidly extinguishes pDC-related gene expression in lin−/Flt3+ progenitors. Inspection of the Irf8 promoter revealed that STAT5 is recruited during GM-CSF-mediated suppression, indicating STAT5 directly inhibits transcription of this critical pDC gene. Our results therefore show that GM-CSF controls the production of pDCs by employing STAT5 to suppress IRF8 and the pDC transcriptional network in lin−/Flt3+ progenitors.
doi:10.1016/j.immuni.2008.02.013
PMCID: PMC2864148  PMID: 18342552
plasmacytoid dendritic cells; GM-CSF; STAT5; development; FLT3
19.  TSLP and IL-7 use two different mechanisms to regulate human CD4+ T cell homeostasis 
The Journal of Experimental Medicine  2009;206(10):2111-2119.
Whether thymic stromal lymphopoietin (TSLP) directly induces potent human CD4+ T cell proliferation and Th2 differentiation is unknown. We report that resting and activated CD4+ T cells expressed high levels of IL-7 receptor a chain but very low levels of TSLP receptor (TSLPR) when compared with levels expressed in myeloid dendritic cells (mDCs). This was confirmed by immunohistology and flow cytometry analyses showing that only a subset of mDCs, with more activated phenotypes, expressed TSLPR in human tonsils in vivo. IL-7 induced strong STAT1, -3, and -5 activation and promoted the proliferation of naive CD4+ T cells in the presence of anti-CD3 and anti-CD28 monoclonal antibodies, whereas TSLP induced weak STAT5 activation, associated with marginally improved cell survival and proliferation, but failed to induce cell expansion and Th2 differentiation. The effect of TSLP on enhancing strong human T cell proliferation was observed only when sorted naive CD4+ T cells were cultured with mDCs at levels as low as 0.5%. TSLP could only induce naive CD4+ T cells to differentiate into Th2 cells in the presence of allogeneic mDCs. These results demonstrate that IL-7 and TSLP use different mechanisms to regulate human CD4+ T cell homeostasis.
doi:10.1084/jem.20090153
PMCID: PMC2757885  PMID: 19770269
20.  Regulation of TLR7/9 responses in plasmacytoid dendritic cells by BST2 and ILT7 receptor interaction 
The Journal of Experimental Medicine  2009;206(7):1603-1614.
Plasmacytoid dendritic cells (pDCs) produce copious type I interferon (IFN) upon sensing nucleic acids through Toll-like receptor (TLR) 7 and TLR9. Uncontrolled pDC activation and IFN production are implicated in lymphopenia and autoimmune diseases; therefore, a mechanism controlling pDC IFN production is essential. Human pDCs specifically express an orphan receptor, immunoglobulin-like transcript 7 (ILT7). Here, we discovered an ILT7 ligand expressed by human cell lines and identified it as bone marrow stromal cell antigen 2 (BST2; CD317). BST2 directly binds to purified ILT7 protein, initiates signaling via the ILT7–FcϵRIγ complex, and strongly inhibits production of IFN and proinflammatory cytokines by pDCs. Readily induced by IFN and other proinflammatory cytokines, BST2 may modulate the human pDC’s IFN responses through ILT7 in a negative feedback fashion.
doi:10.1084/jem.20090547
PMCID: PMC2715090  PMID: 19564354
21.  Two functional subsets of Foxp3+ regulatory T cells in human thymus and periphery 
Immunity  2008;28(6):870-880.
Summary
Previous studies suggest that thymus produces a homogenous population of natural regulatory T cells (TR) that express a transcriptional factor Foxp3 and control autoimmunity through a cell contact-dependent mechanism. We found two subsets of Foxp3+ natural TR defined by ICOS-expression in the human thymus and periphery. While the ICOS+Foxp3+ TR use IL-10 to suppress dendritic cell function and TGF-β to suppress T cell function, the ICOS−Foxp3+ TR use TGF-β only. The survival and proliferation of the two subsets of TR are differentially regulated by signaling through ICOS or CD28 respectively. We suggest that the selection of natural TR in thymus is coupled with TR differentiation into two subsets imprinted with different cytokine expression potentials and use both cell-contact-dependent and independent mechanisms for immunosuppression in periphery.
doi:10.1016/j.immuni.2008.03.018
PMCID: PMC2709453  PMID: 18513999
22.  IL-25 augments type 2 immune responses by enhancing the expansion and functions of TSLP-DC–activated Th2 memory cells 
The Journal of Experimental Medicine  2007;204(8):1837-1847.
Interleukin (IL) 25 (IL-17E), a distinct member of the IL-17 cytokine family, plays important roles in evoking T helper type 2 (Th2) cell–mediated inflammation that features the infiltrations of eosinophils and Th2 memory cells. However, the cellular sources, target cells, and underlying mechanisms remain elusive in humans. We demonstrate that human Th2 memory cells expressing distinctive levels of IL-25 receptor (R) are one of the responding cell types. IL-25 promotes cell expansion and Th2 cytokine production when Th2 central memory cells are stimulated with thymic stromal lymphopoietin (TSLP)–activated dendritic cells (DCs), homeostatic cytokines, or T cell receptor for antigen triggering. The enhanced functions of Th2 memory cells induced by IL-25 are associated with sustained expression of GATA-3, c-MAF, and JunB in an IL-4–independent manner. Although keratinocytes, mast cells, eosinophils, and basophils express IL-25 transcripts, activated eosinophils and basophils from normal and atopic subjects were found to secrete bioactive IL-25 protein, which augments the functions of Th2 memory cells. Elevated expression of IL-25 and IL-25R transcripts was observed in asthmatic lung tissues and atopic dermatitis skin lesions, linking their possible roles with exacerbated allergic disorders. Our results provide a plausible explanation that IL-25 produced by innate effector eosinophils and basophils may augment the allergic inflammation by enhancing the maintenance and functions of adaptive Th2 memory cells.
doi:10.1084/jem.20070406
PMCID: PMC2118667  PMID: 17635955
23.  OX40-OX40L interactions: a promising therapeutic target for allergic diseases? 
The Journal of Clinical Investigation  2007;117(12):3655-3657.
Recent advances in understanding the cellular and molecular mechanisms of atopy have shed light on potential targets for the development of new therapies for allergic diseases. In this issue of the JCI, Seshasayee et al. provide direct in vivo evidence that OX40 has critical roles in allergic inflammation mediated by thymic stromal lymphopoietin (TSLP) (see the related article beginning on page 3868). Blockade of interactions between OX40 on Th2 cells and OX40 ligand (OX40L) on TSLP-activated DCs using an OX40L-specific monoclonal antibody, inhibited Th2 cell–mediated immune responses in both mouse and nonhuman primate models of allergic inflammation. The results point to potential therapeutic approaches to targeting the cellular and molecular mechanism underlying TSLP-mediated allergic inflammation.
doi:10.1172/JCI34182
PMCID: PMC2121106  PMID: 18074001
24.  Plasmacytoid dendritic cell–specific receptor ILT7–FcɛRIγ inhibits Toll-like receptor–induced interferon production 
The Journal of Experimental Medicine  2006;203(6):1399-1405.
Immunoglobulin-like transcripts are a family of inhibitory and stimulatory cell surface immune receptors. Transcripts for one member of this family, ILT7, are selectively expressed in human plasmacytoid dendritic cells (pDCs). We demonstrate here that ILT7 protein associates with the signal adapter protein FcɛRIγ to form a receptor complex. Using an anti-ILT7 monoclonal antibody, we show that ILT7 is expressed specifically on human pDCs, but not on myeloid dendritic cells or other peripheral blood leukocytes. Cross-linking of ILT7 resulted in phosphorylation of Src family kinases and Syk kinase and induced a calcium influx in freshly isolated pDCs, which was blocked by Src family and Syk kinases inhibitors, thus indicating the activation of an immunoreceptor-based tyrosine activation motif–mediated signaling pathway. ILT7 cross-linking on CpG or influenza virus-stimulated primary pDCs inhibited the transcription and secretion of type I interferon and other cytokines. Therefore, the ILT7–FcɛRIγ receptor complex negatively regulates the innate immune functions of human pDCs.
doi:10.1084/jem.20052454
PMCID: PMC2118323  PMID: 16735691
25.  Thrombopoietin cooperates with FLT3-ligand in the generation of plasmacytoid dendritic cell precursors from human hematopoietic progenitors 
Blood  2003;103(7):2547-2553.
Type 1 interferon–producing cells (IPCs), also known as plasmacytoid dendritic cell (DC) precursors, represent the key effectors in antiviral innate immunity and triggers for adaptive immune responses. IPCs play important roles in the pathogenesis of systemic lupus erythematosus (SLE) and in modulating immune responses after hematopoietic stem cell transplantation. Understanding IPC development from hematopoietic progenitor cells (HPCs) may provide critical information in controlling viral infection, autoimmune SLE, and graft-versus-host disease. FLT3-ligand (FLT3-L) represents a key IPC differentiation factor from HPCs. Although hematopoietic cytokines such as interleukin-3 (IL-3), IL-7, stem cell factor (SCF), macrophage–colony-stimulating factor (M-CSF), and granulocyte M-CSF (GM-CSF) promote the expansion of CD34+ HPCs in FLT3-L culture, they strongly inhibit HPC differentiation into IPCs. Here we show that thrombopoietin (TPO) cooperates with FLT3-L, inducing CD34+HPCs to undergo a 400-fold expansion in cell numbers and to generate more than 6 × 106 IPCs per 106 CD34+ HPCs within 30 days in culture. IPCs derived from HPCs in FLT3-L/TPO cultures display blood IPC phenotype and have the capacity to produce large amounts of interferon-α (IFN-α) and to differentiate into mature DCs. This culture system, combined with the use of adult peripheral blood CD34+ HPCs purified from G-CSF–mobilized donors, permits the generation of more than 109 IPCs from a single blood donor.
doi:10.1182/blood-2003-09-3058
PMCID: PMC1510954  PMID: 14670916

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