Distinct Dendritic Cells Research Articles

Nuclear receptor signalling in dendritic cells connects lipids, the genome and immune function

Dendritic cells (DCs) are sentinels of the immune system and represent a heterogeneous cell population. The existence of distinct DC subsets is due to their inherent plasticity and to the changing microenvironment modulating their immunological properties. Numerous signalling pathways have impacts on DCs. It appears that besides cytokines/chemokines, lipid mediators also have profound effects on the immunogenicity of DCs. Some of these lipid mediators exert an effect through nuclear hormone receptors. Interestingly, more recent findings suggest that DCs are able to convert precursors to active hormones, ligands for nuclear receptors. Some of these DC-derived lipids, in particular retinoic acid (RA), have a central function in shaping T-cell development and effector functions. In this review, we summarize and highlight the function of a set of nuclear receptors (PPARγ, RA receptor, vitamin D receptor and glucocorticoid receptor) in DC biology. Defining the contribution of nuclear hormone receptor signalling in DCs can help one to understand the regulatory logic of lipid signalling and allow the exploitation of their potential for therapeutic intervention in various immunological diseases.

The Induction of Inflammation by Dectin-1 In Vivo Is Dependent on Myeloid Cell Programming and the Progression of Phagocytosis

Dectin-1 is the archetypal signaling, non-Toll-like pattern recognition receptor that plays a protective role in immune defense to Candida albicans as the major leukocyte receptor for beta-glucans. Dectin-1-deficiency is associated with impaired recruitment of inflammatory leukocytes and inflammatory mediator production at the site of infection. In this study, we have used mice to define the mechanisms that regulate the dectin-1-mediated inflammatory responses. Myeloid cell activation by dectin-1 is controlled by inherent cellular programming, with distinct macrophage and dendritic cell populations responding differentially to the engagement of this receptor. The inflammatory response is further modulated by the progression of the phagocytosis, with "frustrated phagocytosis" resulting in dramatically augmented inflammatory responses. These studies demonstrate that dectin-1 in isolation is sufficient to drive a potent inflammatory response in a context-dependent manner. This has implications for the mechanism by which myeloid cells are activated during fungal infections and the processes involved in the therapeutic manipulation of the immune system via exogenous dectin-1 stimulation or blockade.

Identification of ITGA4/ITGB7 and ITGAE/ITGB7 Expressing Subsets of Decidual Dendritic-Like Cells Within Distinct Microdomains of the Pregnant Mouse Uterus1

Several leukocyte populations have been described within the pregnant mouse uterus, some of which express the integrin beta 7 (ITGB7). Here we demonstrate that the majority of the ITGB7(+) decidual leukocytes belong to the dendritic cell (DC) lineage. By multiparameter flow cytometric analysis we demonstrated the existence of three distinct DC subsets, characterized by differential expression of ITGA4/ITGB7 (formerly alpha4beta7-integrin) and ITGAE/ITGB7 (formerly alphaEbeta7-integrin). Importantly, the predominant DC subsets reside in distinct microdomains of the Day 9 pregnant mouse uterus. ITGAX(+) ITGAM(med) ITGA4/ITGB7(+) ITGAE(-) (formerly CD11c(+) CD11b(med) alpha4beta7(+) alphaE(-)) cells represent the majority of DCs in the vascular zone (VZ), whereas ITGAX(+) ITGAM(-) ITGAE/ITGB7(+) (formerly CD11c(+) CD11b(-) alphaEbeta7(+)) DCs are mainly located in the lower central decidua basalis (cDB) and the underlying myometrium. A population of ITGAX(+) ITGAM(low) DCs lacking ITGB7 are restricted to the cDB. Confocal microscopy studies show direct contact of VZ DCs with uterine natural killer (uNK) cells, suggesting a functional relationship between both cell populations. Collectively, our data identify three phenotypically distinct DC subsets residing in distinct microdomains of the uterus. The differential expression of ITGA4/ITGB7 and ITGAE/ITGB7 suggests distinct functional roles of the different DC subsets during early pregnancy.

Transcriptional profiling of human skin-resident Langerhans cells and CD1a+ dermal dendritic cells: differential activation states suggest distinct functions

In human skin, two main populations of dendritic cells (DC) can be discriminated: dermal DC (DDC) and epidermal Langerhans cells (LC). Although extensively studied, most of the knowledge about DDC and LC phenotype and function is obtained from studying DDC and LC cultured in vitro or DDC and LC migrated from skin explants. These studies have left the exact relationship between steady-state human LC and DDC unclear: in particular, whether CD1a+ DDC represent migrated LC or whether they constitute a separate subset. To gain further insight in the kinship between skin-resident CD1a+ DDC and LC, we analyzed CD1a+ DDC and LC, isolated from steady-state skin samples, by high-density microarray analysis. Results show that the CD1a+ DDC specifically express markers associated with DDC phenotype, such as the macrophage mannose receptor, DC-specific ICAM-grabbing nonintegrin, the scavenger receptor CD36, coagulation factor XIIIa, and chemokine receptor CCR5, whereas LC specifically express Langerin, membrane ATPase (CD39), and CCR6, all hallmarks of the LC lineage. In addition, under steady-state conditions, both DC subsets display a strikingly different activation status, indicative of distinct functional properties. CD1a+ DDC exhibit a more activated, proinflammatory, migratory, and T cell-stimulatory profile, as compared with LC, whereas LC mainly express molecules involved in cell adhesion and DC retention in the epidermis. In conclusion, transcriptional profiling is consistent with the notion that CD1a+ DDC and LC represent two distinct DC subsets but also that under steady-state conditions, CD1a+ DDC and epidermal LC represent opposites of the DC activation spectrum.

Nanoparticles target distinct dendritic cell populations according to their size

The efficiency of a vaccine largely depends on the appropriate targeting of the innate immune system, mainly through prolonged delivery of antigens and immunomodulatory substances to professional antigen-presenting cells in the lymphoid environment. Particulate antigens, such as virus-like particles (VLP) induce potent immune responses. However, little is known about the relative importance of direct drainage of free antigen to lymph nodes (LN) versus cellular transport and the impact of particle size on the process. Here, we show that nanoparticles traffic to the draining LN in a size-dependent manner. Whereas large particles (500-2000 nm) were mostly associated with dendritic cells (DC) from the injection site, small (20-200 nm) nanoparticles and VLP (30 nm) were also found in LN-resident DC and macrophages, suggesting free drainage of these particles to the LN. In vivo imaging studies in mice conditionally depleted of DC confirmed the capacity of small but not large particles to drain freely to the LN and demonstrated that DC are strictly required for transport of large particles from the injection site to the LN. These data provide evidence that particle size determines the mechanism of trafficking to the LN and show that only small nanoparticles can specifically target LN-resident cells.

Cover Picture: Nanoparticles target distinct dendritic cell populations according to their size – Eur. J. Immunol. 5/2008

AbstractThe cover shows a colour series of mouse footpads injected with small fluorescent nanoparticles. The image depicts the afferent lymphatic vessels connecting the injection site with the draining popliteal lymph node and the more distal sciatic lymph node. Lymphatic vessels (in green in the left row) run together with the veins (darker curves) and carry free draining antigen to the lymph nodes. This image was provided by the authors of Manolova (pp. 1404–1413), in which it is demonstrated that particle size critically influences the mode of antigen transport to the draining lymph nodes; DC are strictly required for transport of large (500–2000 nm) particles, whereas smaller particles (20–200 nm), such as virus‐like particles (30 nm), drain freely.

Human invariant Vα24+ natural killer T cells acquire regulatory functions by interacting with IL-10–treated dendritic cells

AbstractGlycolipid-reactive Vα24+ invariant natural killer T (iNKT) cells have been implicated in regulating a variety of immune responses and in the induction of immunologic tolerance. Activation of iNKT cells requires interaction with professional antigen-presenting cells, such as dendritic cells (DCs). We have investigated the capacity of distinct DC subsets to modulate iNKT cell functions. We demonstrate that tolerogenic DCs (tolDCs), generated by treatment of monocyte-derived DC with interleukin (IL)-10, induced regulatory functions in human iNKT cells. tolDCs, compared with immunogenic DCs, had reduced capacity to induce iNKT-cell proliferation, but these cells produced large amounts of IL-10 and acquired an anergic phenotype. These anergic Vα24+ iNKT cells were able to potently inhibit allogeneic CD4+ T-cell proliferation in vitro. Furthermore, the anergic Vα24+ iNKT cells could suppress DC maturation in vitro. We conclude that the interaction of iNKT cells with tolDCs plays an important role in the immune regulatory network, which might be exploited for therapeutic purposes.

307 Distinct Regulatory Dendritic Cell Subsets in Control of Treg Function in Acute Inflammation and Recovery from Colitis

307 Distinct Regulatory Dendritic Cell Subsets in Control of Treg Function in Acute Inflammation and Recovery from Colitis

M1972 Distinct Dendritic Cell Populations in Reflux Disease and Barrett's Esophagus; Implications for Understanding the Immune Response

M1972 Distinct Dendritic Cell Populations in Reflux Disease and Barrett's Esophagus; Implications for Understanding the Immune Response

Migration of Dendritic Cell Subsets and their Precursors

The ability of dendritic cells (DCs) to initiate and orchestrate immune responses is a consequence of their localization within tissues and their specialized capacity for mobilization. The migration of a given DC subset is typified by a restricted capacity for recirculation, contrasting markedly with T cells. Routes of DC migration into lymph nodes differ notably for distinct DC subsets. Here, we compare the distinct migratory patterns of plasmacytoid DCs (pDCs), CD8alpha(+) DCs, Langerhans cells, and conventional myeloid DCs and discuss how the highly regulated patterns of DC migration in vivo may affect their roles in immunity. Finally, to gain a more molecular appreciation of the specialized migratory properties of DCs, we review the signaling cascades that govern the process of DC migration.

The Signal Transducer STAT5 Inhibits Plasmacytoid Dendritic Cell Development by Suppressing Transcription Factor IRF8

The development of distinct dendritic cell (DC) subsets is regulated by cytokines. The ligand for the FMS-like tyrosine kinase 3 receptor (Flt3L) is necessary for plasmacytoid DC (pDC) and conventional DC (cDC) maturation. The cytokine GM-CSF inhibits Flt3L-driven pDC production while promoting cDC growth. We show that GM-CSF selectively utilized its signal transducer STAT5 to block Flt3L-dependent pDC development from the lineage-negative, Flt3+ (lin- Flt3+) bone-marrow subset. The signaling molecule STAT3, by contrast, was necessary for expansion of DC progenitors but not pDC maturation. In vivo, STAT5 suppressed pDC formation during repopulation of the DC compartment after bone-marrow ablation. GM-CSF-dependent STAT5 signaling rapidly extinguished pDC-related gene expression in lin- Flt3+ progenitors. Inspection of the Irf8 promoter revealed that STAT5 was recruited during GM-CSF-mediated suppression, indicating that STAT5 directly inhibited 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.

Significant Virus Replication in Langerhans Cells following Application of HIV to Abraded Skin: Relevance to Occupational Transmission of HIV

The cellular events that occur following occupational percutaneous exposure to HIV have not been defined. In this study, we studied relevant host cellular and molecular targets used for acquisition of HIV infection using split-thickness human skin explants. Blockade of CD4 or CCR5 before R5 HIV application to the epithelial surface of skin explants completely blocked subsequent HIV transmission from skin emigrants to allogeneic T cells, whereas preincubation with C-type lectin receptor inhibitors did not. Immunomagnetic bead depletion studies demonstrated that epithelial Langerhans cells (LC) accounted for >95% of HIV dissemination. When skin explants were exposed to HIV variants engineered to express GFP during productive infection, GFP+ T cells were found adjacent to GFP+ LC. In three distinct dendritic cell (DC) subsets identified among skin emigrants (CD1a+langerin+DC-specific intercellular adhesion molecule grabbing non-integrin (SIGN)- LC, CD1a+langerin-DC-SIGN- dermal DC, and CD1a-langerin-DC-SIGN+ dermal macrophages), HIV infection was detected only in LC. These results suggest that productive HIV infection of LC plays a critical role in virus dissemination from epithelium to cells located within subepithelial tissue. Thus, initiation of antiretroviral drugs soon after percutaneous HIV exposure may not prevent infection of LC, which is likely to occur rapidly, but may prevent or limit subsequent LC-mediated infection of T cells.

Blood Monocyte Subsets Differentially Give Rise to CD103+ and CD103− Pulmonary Dendritic Cell Populations

There are two major myeloid pulmonary dendritic cell (DC) populations: CD103+ DCs and CD11bhigh DCs. In this study, we investigated in detail the origins of both myeloid DC pools using multiple experimental approaches. We show that, in resting lung, Ly-6ChighCCR2high monocytes repopulated CD103+ DCs using a CCR2-dependent mechanism, and these DCs preferentially retained residual CCR2 in the lung, whereas, conversely, Ly-6ClowCCR2low monocytes repopulated CD11bhigh DCs. CX3CR1 was required to generate normal numbers of pulmonary CD11bhigh DCs, possibly because Ly-6Clow monocytes in the circulation, which normally express high levels of CX3CR1, failed to express bcl-2 and may have diminished survival in the circulation in the absence of CX3CR1. Overall, these data demonstrate that the two circulating subsets of monocytes give rise to distinct tissue DC populations.

Role of the cytokine environment and cytokine receptor expression on the generation of functionally distinct dendritic cells from human monocytes

Myeloid dendritic cells (DC) and macrophages evolve from a common precursor. However, factors controlling monocyte differentiation toward DC or macrophages are poorly defined. We report that the surface density of the GM-CSF receptor (GM-CSFR) alpha subunit in human peripheral blood monocytes varies among donors. Although no correlation was found between the extent of GM-CSFR and monocyte differentiation into DC driven by GM-CSF and IL-4, GM-CSFR expression strongly influenced the generation of CD1a(+) dendritic-like cells in the absence of IL-4. CD1a(+) cells generated in the presence of GM-CSF express CD40, CD80, MHC class I and II, DC-SIGN, MR, CCR5, and partially retain CD14 expression. Interestingly, they spontaneously induce the expansion of CD4(+) and CD8(+) allogeneic T lymphocytes producing IFN-gamma, and migrate toward CCL4 and CCL19. Upon stimulation with TLR ligands, they acquire the phenotypic features of mature DC. In contrast, the allostimulatory capacity is not further increased upon LPS activation. However, by blocking LPS-induced IL-10, a higher T cell proliferative response and IL-12 production were observed. Interestingly, IL-23 secretion was not affected by endogenous IL-10. These results highlight the importance of GM-CSFR expression in monocytes for cytokine-induced DC generation and point to GM-CSF as a direct player in the generation of functionally distinct DC.

Flt-3 Ligand (FL) Treatment Upregulates PDL2 and Downregulates CCR7 in Distinct Myeloid Dendritic Cell (DC) Populations in the Lungs of Asthmatic Mice

RationaleWe observed that Flt-3 ligand reversed airway hyperresponsiveness (AHR) in a mouse model of asthma. FL preferentially affects the development and differentiation of myeloid DCs. In this study, we examined the phenotype of lung myeloid dendritic cells and their responses to ovalbumin (OVA) sensitization and FL treatment.MethodsA mouse model of asthma was established by administration of OVA and confirmed by AHR to methacholine. Sensitized and challenged mice were given either recombinant human FL or PBS. Non-sensitized mice received PBS as controls. CD11c+ lung DCs sorted by MACS were further labeled with CD11c, CD11b, CD8, PDL1, PDL2, and CCR7 antibodies conjugated with fluorochrome. FACS was used to identify phenotypic myeloid DC populations. The expression levels of cell surface markers were analyzed using flow cytometry.ResultsThree distinct lung myeloid DC populations, CD11c+CD11blow, CD11chiCD11bint, and CD11c+CD11bhi were identified. CD11chiCD11bint cells accounted for the majority of the lung myeloid DCs in non-sensitized condition. OVA sensitization significantly increased the proportion of CD11c+CD11bhi cells and decreased CD11chiCD11bint cells but FL treatment reversed the trend. CD11chiCD11bint cells had a higher expression of CD8, PDL1, and PDL2 as compared to CD11c+CD11bhi cells. CCR7 expression was higher in CD11c+CD11bhi cells. PDL2 was upregulated after sensitization and was further unregulated after FL treatment in CD11chiCD11bint cell population. CCR7 was upregulated after sensitization and downregulated after FL treatment in CD11c+CD11bhi cells.ConclusionsCD11chiCD11bint and CD11chiCD11bint DCs may be responsible for immune tolerance and immune response, respectively. FL reverses AHR in asthmatic mice possibly through upregulating PDL2 and downregulating CCR7 on DCs. RationaleWe observed that Flt-3 ligand reversed airway hyperresponsiveness (AHR) in a mouse model of asthma. FL preferentially affects the development and differentiation of myeloid DCs. In this study, we examined the phenotype of lung myeloid dendritic cells and their responses to ovalbumin (OVA) sensitization and FL treatment. We observed that Flt-3 ligand reversed airway hyperresponsiveness (AHR) in a mouse model of asthma. FL preferentially affects the development and differentiation of myeloid DCs. In this study, we examined the phenotype of lung myeloid dendritic cells and their responses to ovalbumin (OVA) sensitization and FL treatment. MethodsA mouse model of asthma was established by administration of OVA and confirmed by AHR to methacholine. Sensitized and challenged mice were given either recombinant human FL or PBS. Non-sensitized mice received PBS as controls. CD11c+ lung DCs sorted by MACS were further labeled with CD11c, CD11b, CD8, PDL1, PDL2, and CCR7 antibodies conjugated with fluorochrome. FACS was used to identify phenotypic myeloid DC populations. The expression levels of cell surface markers were analyzed using flow cytometry. A mouse model of asthma was established by administration of OVA and confirmed by AHR to methacholine. Sensitized and challenged mice were given either recombinant human FL or PBS. Non-sensitized mice received PBS as controls. CD11c+ lung DCs sorted by MACS were further labeled with CD11c, CD11b, CD8, PDL1, PDL2, and CCR7 antibodies conjugated with fluorochrome. FACS was used to identify phenotypic myeloid DC populations. The expression levels of cell surface markers were analyzed using flow cytometry. ResultsThree distinct lung myeloid DC populations, CD11c+CD11blow, CD11chiCD11bint, and CD11c+CD11bhi were identified. CD11chiCD11bint cells accounted for the majority of the lung myeloid DCs in non-sensitized condition. OVA sensitization significantly increased the proportion of CD11c+CD11bhi cells and decreased CD11chiCD11bint cells but FL treatment reversed the trend. CD11chiCD11bint cells had a higher expression of CD8, PDL1, and PDL2 as compared to CD11c+CD11bhi cells. CCR7 expression was higher in CD11c+CD11bhi cells. PDL2 was upregulated after sensitization and was further unregulated after FL treatment in CD11chiCD11bint cell population. CCR7 was upregulated after sensitization and downregulated after FL treatment in CD11c+CD11bhi cells. Three distinct lung myeloid DC populations, CD11c+CD11blow, CD11chiCD11bint, and CD11c+CD11bhi were identified. CD11chiCD11bint cells accounted for the majority of the lung myeloid DCs in non-sensitized condition. OVA sensitization significantly increased the proportion of CD11c+CD11bhi cells and decreased CD11chiCD11bint cells but FL treatment reversed the trend. CD11chiCD11bint cells had a higher expression of CD8, PDL1, and PDL2 as compared to CD11c+CD11bhi cells. CCR7 expression was higher in CD11c+CD11bhi cells. PDL2 was upregulated after sensitization and was further unregulated after FL treatment in CD11chiCD11bint cell population. CCR7 was upregulated after sensitization and downregulated after FL treatment in CD11c+CD11bhi cells. ConclusionsCD11chiCD11bint and CD11chiCD11bint DCs may be responsible for immune tolerance and immune response, respectively. FL reverses AHR in asthmatic mice possibly through upregulating PDL2 and downregulating CCR7 on DCs. CD11chiCD11bint and CD11chiCD11bint DCs may be responsible for immune tolerance and immune response, respectively. FL reverses AHR in asthmatic mice possibly through upregulating PDL2 and downregulating CCR7 on DCs.

Expression of langerin/CD207 reveals dendritic cell heterogeneity between inbred mouse strains.

Langerin/CD207 is expressed by a subset of dendritic cells (DC), the epithelial Langerhans cells. However, langerin is also detected among lymphoid tissue DC. Here, we describe striking differences in langerin-expressing cells between inbred mouse strains. While langerin+ cells are observed in comparable numbers and with comparable phenotypes in the epidermis, two distinct DC subsets bear langerin in peripheral, skin-draining lymph nodes of BALB/c mice (CD11c(high) CD8alpha(high) and CD11c(low) CD8alpha(low)), whereas only the latter subset is present in C57BL/6 mice. The CD11c(high) subset is detected in mesenteric lymph nodes and spleen of BALB/c mice, but is virtually absent from C57BL/6 mice. Similar differences are observed in other mouse strains. CD11c(low) langerin+ cells represent skin-derived Langerhans cells, as demonstrated by their high expression of DEC-205/CD205, maturation markers, and recruitment to skin-draining lymph nodes upon imiquimod-induced inflammation. It will be of interest to determine the role of lymphoid tissue-resident compared to skin-derived langerin+ DC.

The developmental program of human dendritic cells is operated independently of conventional myeloid and lymphoid pathways

AbstractTwo distinct dendritic cell (DC) subsets, conventional DCs (cDCs) and plasmacytoid DCs (pDCs), have been shown to develop via either the myeloid or the lymphoid pathway in murine hematopoiesis. Lineage-specific phenotypes or functions of “myeloid” and “lymphoid” DCs, however, still remain elusive. Furthermore, such analysis has been particularly difficult in humans, due to lack of an assay system appropriate for the analysis of human stem and progenitor cell differentiation. Here, using a highly efficient xenotransplantation model, we extensively analyze the origin and the molecular signature of human DCs. Purified human common myeloid progenitors (CMPs) and common lymphoid progenitors (CLPs) were intravenously transplanted into nonobese diabetic–severe combined immunodeficiency (NOD-scid)/IL2rγnull newborn mice. CMPs and CLPs displayed significant expansion in the xenogeneic host, and human cDC and pDC progeny were isolatable. Strikingly, each human DC subset possessed indistinguishable expression patterns of surface phenotype and gene transcripts regardless of their CMP or CLP origin, even at the genome-wide level. Thus, cDC and pDC normally develop after cells have committed to the myeloid or the lymphoid lineage in human hematopoiesis, while their transcriptional signatures are well preserved irrespective of their lineage origin. We propose that human DCs use unique and flexible developmental programs that cannot be categorized into the conventional myeloid or lymphoid pathway.

Synergistic Proinflammatory Effects of the Antiviral Cytokine Interferon-α and Toll-Like Receptor 4 Ligands in the Atherosclerotic Plaque

Interferon (IFN)-alpha is a pluripotent inflammatory cytokine typically induced by viral infections. In rupture-prone atherosclerotic plaques, plasmacytoid dendritic cells produce IFN-alpha. In the present study we explored the contribution of IFN-alpha to inflammation and tissue injury in the plaque microenvironment. In 53% of carotid plaques (n=30), CD123+ plasmacytoid dendritic cells clustered together with CD11c+ myeloid dendritic cells, a distinct dendritic cell subset specialized in sensing danger signals from bacteria and tissue breakdown. Tissue concentrations of IFN-alpha and tumor necrosis factor (TNF)-alpha transcripts were tightly correlated (r=0.76, P<0.001), suggesting a regulatory role of IFN-alpha in TNF-alpha production. Plaque tissue stimulation with CpG ODN, a Toll-like receptor (TLR) 9 ligand, increased IFN-alpha production (57.8+/-23.7 versus 25.9+/-8.6 pg/mL; P<0.001), whereas the TLR4 ligand lipopolysaccharide induced TNF-alpha secretion (225.1+/-3.0 versus 0.7+/-0.2 pg/mL; P<0.001). Treating plaque tissue with IFN-alpha markedly enhanced lipopolysaccharide-triggered TNF-alpha secretion (559.0+/-25.9 versus 225.1+/-3.0 pg/mL; P<0.001). IFN-alpha pretreatment also amplified the effects of lipopolysaccharide on interleukin-12, interleukin-23, and matrix metalloproteinase-9, suggesting that the antiviral cytokine sensitized myeloid dendritic cells and macrophages toward TLR4 ligands. Mechanistic studies demonstrated that IFN-alpha modulated the myeloid dendritic cell response pattern by upregulating TLR4 expression (P<0.001) involving both the STAT (signal transducer and activator of transcription) and the PI(3)K pathway. In the atherosclerotic plaque, IFN-alpha functions as an inflammatory amplifier. It sensitizes antigen-presenting cells toward pathogen-derived TLR4 ligands by upregulating TLR4 expression and intensifies TNF-alpha, interleukin-12, and matrix metalloproteinase-9 production, all implicated in plaque destabilization. Thus, IFN-alpha-inducing pathogens, even when colonizing distant tissue sites, threaten the stability of inflamed atherosclerotic plaque.

Development of plasmacytoid and conventional dendritic cell subtypes from single precursor cells derived in vitro and in vivo

The development of functionally specialized subtypes of dendritic cells (DCs) can be modeled through the culture of bone marrow with the ligand for the cytokine receptor Flt3. Such cultures produce DCs resembling spleen plasmacytoid DCs (pDCs), CD8(+) conventional DCs (cDCs) and CD8(-) cDCs. Here we isolated two sequential DC-committed precursor cells from such cultures: dividing 'pro-DCs', which gave rise to transitional 'pre-DCs' en route to differentiating into the three distinct DC subtypes (pDCs, CD8(+) cDCs and CD8(-) cDCs). We also isolated an in vivo equivalent of the DC-committed pro-DC precursor cell, which also gave rise to the three DC subtypes. Clonal analysis of the progeny of individual pro-DC precursors demonstrated that some pro-DC precursors gave rise to all three DC subtypes, some produced cDCs but not pDCs, and some were fully committed to a single DC subtype. Thus, commitment to particular DC subtypes begins mainly at this pro-DC stage.

Subpopulations of human dendritic cells display a distinct phenotype and bind differentially to proteins of the extracellular matrix

CD1a pos dendritic cells (DCs) and Langerhans cells (LCs) are highly specialized antigen-presenting cells mainly localized in the skin. Various cells have been identified as precursors of cutaneous DCs, but the definitive precursor subpopulations remain to be defined and characterized in detail. In this study, DCs were generated in vitro from monocytes (monocyte-derived DCs, MoDCs) and from CD34 pos stem cells (CD34 pos cell-derived DCs, CD34DCs). By virtue of their CD14 and CD1a expression, four CD34DC subpopulations were characterized while MoDCs contain three different subpopulations. Of these, CD14-expressing cells are considered to be precursors of fully differentiated DCs, which themselves are CD14 negCD1a pos. Both, MoDCs and CD34DCs expressed the α integrins LFA-1, Mac-1, CR4, VLA-4, VLA-5 and the β2 integrin CD18. CD34DCs and MoDCs were negative for VLA-3, whereas MoDCs, but not CD34DCs expressed VLA-6. Phenotypic and functional characterization of the cells generated herein at earlier time points revealed that DCs at day 3 of culture may reflect the in vivo situation more closely than at day 7. Adhesion of DC precursors to endothelial cells and to components of the extracellular matrix is a prerequisite for their migration towards the epidermis. To this end, we investigated adhesion of CD34DCs and MoDCs to components of the cutaneous extracellular matrix. Distinct DC subsets showed a differential binding pattern to proteins of the extracellular matrix. MoDCs and CD34DCs bound preferentially to laminin 332 via CD49f and to fibronectin via CD49e, but only weakly to laminin 111 or to collagens. While CD14 pos cells preferentially bound to laminin 332, CD1a pos cells adhered to fibronectin. In summary, subpopulations of CD34DCs and MoDCs are phenotypically related to each other, but not identical and display differential binding to components of the extracellular matrix.