Final maturation of dendritic cells is associated with impaired responsiveness to IFN-gamma and to bacterial IL-12 inducers: decreased ability of mature dendritic cells to produce IL-12 during the interaction with Th cells.
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Activation of immature CD83- dendritic cells (DC) in peripheral tissues induces their maturation and migration to lymph nodes. Activated DC become potent stimulators of Th cells and efficient inducers of Th1- and Th2-type cytokine production. This study analyzes the ability of human monocyte-derived CD1a+ DC at different stages of IL-1 beta and TNF-alpha-induced maturation to produce the major Th1-driving factor IL-12. DC at the early stages of maturation (2 and 4 h) produced elevated amounts of IL-12 p70 during interaction with CD40 ligand-bearing Th cells or, after stimulation with the T cell-replacing factors, soluble CD40 ligand and IFN-gamma. The ability to produce IL-12 was strongly down-regulated at later time points, 12 h after the induction of DC maturation, and in fully mature CD83+ cells, at 48 h. In contrast, the ability of mature DC to produce IL-6 was preserved or even enhanced, indicating their intact responsiveness to CD40 triggering. A reduced IL-12-producing capacity of mature DC resulted mainly from their impaired responsiveness to IFN-gamma, a cofactor in CD40-induced IL-12 p70 production. This correlated with reduced expression of IFN-gamma R (CD119) by mature DC. In addition, while immature DC produced IL-12 and IL-6 after stimulation with LPS or Staphylococcus aureus Cowan I strain, mature DC became unresponsive to these bacterial stimuli. Together with the previously described ability of IL-10 and PGE2 to stably down-regulate the ability to produce IL-12 in maturing, but not in fully mature, DC, the current data indicate a general resistance of mature DC to IL-12-modulating factors. (+info)
Evidence for distinct intracellular signaling pathways in CD34+ progenitor to dendritic cell differentiation from a human cell line model.
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Intracellular signals that mediate differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have previously shown that protein kinase C (PKC) activation (with phorbol ester (PMA) alone) specifically induces differentiation of primary human CD34+ hemopoietic progenitor cells (HPC) to mature DC. We now find that cytokine-driven (granulocyte-macrophage CSF and TNF-alpha) CD34+ HPC-->DC differentiation is preferentially blocked by inhibitors of PKC activation. To further identify intracellular signals and downstream events important in CD34+ HPC-->DC differentiation we have characterized a human leukemic cell line model of this process. The CD34+ myelomonocytic cell line KG1 differentiates into dendritic-like cells in response to granulocyte-macrophage CSF plus TNF-alpha, or PMA (with or without the calcium ionophore ionomycin, or TNF-alpha), with different stimuli mediating different aspects of the process. Phenotypic DC characteristics of KG1 dendritic-like cells include morphology (loosely adherent cells with long neurite processes), MHC I+/MHC IIbright/CD83+/CD86+/CD14- surface Ag expression, and RelB and DC-CK1 gene expression. Functional DC characteristics include fluid phase macromolecule uptake (FITC-dextran) and activation of resting T cells. Comparison of KG1 to the PMA-unresponsive subline KG1a reveals differences in expression of TNF receptors 1 and 2; PKC isoforms alpha, beta I, beta II, and mu; and RelB, suggesting that these components/pathways are important for DC differentiation. Together, these findings demonstrate that cytokine or phorbol ester stimulation of KG1 is a model of human CD34+ HPC to DC differentiation and suggest that specific intracellular signaling pathways mediate specific events in DC lineage commitment. (+info)
Toward a role of dendritic cells in the germinal center reaction: triggering of B cell proliferation and isotype switching.
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We have reported previously that in vitro generated dendritic cells (DC) can directly regulate B cell responses. Recently, germinal center DC (GCDC) were identified within B cell follicles. Due to their particular localization, we have tested in the present study whether GCDC could contribute to key events characteristic of the GC reaction. Our present results demonstrate that 1) ex vivo GCDC induce a dramatic GC B cell expansion upon CD40 and IL-2 activation and drive plasma cell differentiation, 2) this property is shared by GCDC and blood DC, but not by Langerhans cells, 3) IL-12 production by GCDC is critical in GC B cell expansion and differentiation, and 4) importantly, GCDC also induce IL-10-independent isotype switching toward IgG1. These observations support the novel concept that GCDC directly contribute to the germinal center reaction. (+info)
Differential effects of CD40 ligand/trimer stimulation on the ability of dendritic cells to replicate and transmit HIV infection: evidence for CC-chemokine-dependent and -independent mechanisms.
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The role of exogenous stimulation of CD40 by CD40 ligand (CD40L) in dendritic cell (DC) maturation, CC-chemokine production, and CCR5 receptor expression was examined using a soluble trimeric CD40L agonist protein (CD40LT). Stimulation of monocyte-derived DCs with CD40LT enhanced the production of the CC-chemokines macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, and RANTES and diminished surface expression of CCR5. Based on these findings, the functional role of CD40LT stimulation on the ability of DCs to replicate and transmit HIV viral infection was studied. The addition of CD40LT to cocultures of naive CD4+ T cells and autologous DCs (T/DC) infected with the macrophage-tropic isolate, HIVBaL, caused a striking reduction in reverse transcriptase (RT) activity after 10 and 14 days of culture. The addition of a mixture of Abs against CC-chemokines abrogated the decrease in RT activity, demonstrating that the inhibitory effect mediated by CD40LT was CC-chemokine-dependent. In contrast, the presence of CD40LT in T/DC cocultures infected with the T cell-tropic isolate, HIV IIIB, caused an increase in RT activity that was CC-chemokine-independent. Of note, CD40LT stimulation also inhibited RT activity in cultures containing macrophage-tropic virus (HIVBaL)-infected DC only. However, in contrast to the results seen in the T/DC cocultures, CD40LT stimulation inhibited RT activity in cultures of DCs alone in a CC-chemokine-independent manner. Together, these results show that CD40LT stimulation of DCs suppresses HIV replication and transmission to CD4+ T cells by two potentially different mechanisms. (+info)
Expression and a role of functionally coupled P2Y receptors in human dendritic cells.
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We investigated the physiology and function of P2Y receptors expressed in human dendritic cells (DCs) differentiated in vitro from CD14+ cells (DC-14). These were obtained after a 10 day stimulation period in GM-CSF, IL-4 and monocyte conditioned medium. DC-14 were found to express high amounts of MHC class II, B7, CD40 as well as CD83. The functional analysis, using single cell Ca2+ imaging, demonstrated the expression of at least three subtypes of P2Y receptors. We further found using patch-clamp measurements that ATP evoked a pertussis toxin insensitive non-selective cation current with a peak current amplitude of -276+/-43 pA (holding potential -80 mV, n = 23). This current was not Ca(2+)-activated, since it was still observed under conditions of high intracellular Ca2+ buffering and could be blocked by Gd3+ (0.5 mM). In addition, intracellular application of GTP-gamma-S (0.3 mM) also activated the current. Interestingly, DC-14 redirected the orientation of their dendrites as well as cell shape towards a pipette containing ATP as observed with time lapse microscopy. These data suggest that in human DCs, ATP acts via P2Y receptors and induces chemokine effects. (+info)
Induction of specific CD8+ T-lymphocyte responses using a human papillomavirus-16 E6/E7 fusion protein and autologous dendritic cells.
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When intracellular viral proteins are degraded, only a limited number of peptide epitopes are capable of eliciting specific CD8+ cellular immune responses for a given human leukocyte antigen (HLA) haplotype. We sought to induce CD8+ T-lymphocyte (CTL) responses to human papillomavirus-16 (HPV-16) E6 and E7 proteins using a recombinant E6/E7 fusion protein and autologous human dendritic cells (DCs). CTLs were generated by in vitro stimulation using a recombinant HPV-16 E6/E7 fusion protein and autologous DCs from a healthy HLA-A*0201 donor. CTL specificity was assessed by cytokine release assays when the cells were reacted with autologous DC targets coincubated with the E6/E7 fusion protein. These CTLs were also reacted with the immunodominant E7 peptides (E711-20 and E7(86-93)) and DCs as a target. As a negative control, DCs were incubated with or without an irrelevant control protein (Helicobacter pylori) as target for the E6/E7-induced CTLs. The E6/E7-induced CTLs were capable of specific recognition of target DCs coincubated with E6/E7 but not the control protein. When E6/E7-specific CTLs were reacted with DCs and either E7(11-20) or E7(86-93), specific peptide recognition was also detected. These data demonstrate that specific CTLs can be elicited using autologous human DCs and a HPV-16 E6/E7 fusion protein. Therefore, extracellular viral proteins seem to be engulfed and processed by DCs; then the immunodominant HLA-A2-restricted peptides become available for CD8+ T-lymphocyte recognition. These data suggest that vaccine strategies using recombinant viral proteins may overcome the limitation of peptide epitopes for specific HLA haplotypes and may, therefore, permit more generalized clinical application. (+info)
Mucosal dendritic cells and immunodeficiency viruses.
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Dendritic cells [DCs] have been implicated in the pathogenesis of human immunodeficiency virus type 1 (HIV-1). When skin was used as a model for mucosae, the cutaneous DC-T cell milieu allowed the growth of HIV-1 and much of the newly produced virus could be detected in multinucleated DC-T cell syncytia. Such virus replication occurs irrespective of the genetic subtype, the syncytium- and non-syncytium-inducing capacities of the viruses, and whether they are classified as T cell- or macrophage-tropic. Similar DC-syncytia have been identified within the mucosal surfaces of the tonsillar tissue of HIV-1-infected persons. More recently, it was demonstrated that DC-T cell mixtures from the skin, mucosae, and blood of healthy macaques similarly support the replication of simian immunodeficiency virus. In both the human and monkey systems, active virus replication requires the presence of both DCs and T cells. Further studies using the macaque model are underway to elucidate the role of DCs in the transmission and spread of HIV infection. (+info)
Expression of the nlsLacz gene in dendritic cells derived from retrovirally transduced peripheral blood CD34+ cells.
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BACKGROUND AND OBJECTIVE: Gene transfer and expression of exogenous genetic information coding for an immunogenic protein in antigen presenting cells (APCs) can promote an immune response. This was investigated by retroviral transfer of a marker gene into CD34+ derived APCs. DESIGN AND METHODS: To achieve long term expression of a specific transgene in APCs, G-CSF mobilized peripheral blood CD34+ cell populations were retrovirally transduced with the bacterial nlsLacZ, a marker gene used here as a model, in the presence of IL-3, IL-6, GM-CSF and SCF prior to being induced to differentiate into dendritic and macrophage cells by GM-CSF and TNF-a. RESULTS: Addition of IL-4 was found to induce dendritic differentiation preferentially by inhibiting proliferation and differentiation of the macrophage lineage. As assessed by X-Gal staining, LacZ gene expression was observed in cells from both the dendritic lineage (CD1a+/CD14-) which still exhibits the highest immunostimulatory activity in mixed lymphocyte reaction and from the macrophage lineage (CD1a-/ CD14+). INTERPRETATION AND CONCLUSIONS: This study sets out the possibility of transducing dendritic and macrophage progenitors present in the CD34+ cell population and in using a marker gene such as nlsLacZ to study gene expression in antigen presenting cell compartments. (+info)