DC Populations Research Articles

Anti-melanoma vaccinal capacity of CD11c-positive and -negative cell populations present in GM-CSF cultures derived from murine bone marrow precursors

We have initially shown that DC/ApoNec vaccine can induce protection against the poorly immunogenic B16F1 melanoma in mice. The population of DC obtained for vaccination after 7days culture with murine GM-CSF is heterogeneous and presents about 60% of CD11c+ DC. Therefore, our purpose was to identify the phenotype of the cells obtained after differentiation and its immunogenicity once injected. DC were separated with anti-CD11c microbeads and the two populations identified in terms of CD11c positivity (DC+ and DC−) were also studied. Approximately 26.6% of the cells in DC+ fraction co-expressed CD11c+ and F4/80 markers and 75.4% were double positive for CD11c and CD11b markers. DC+ fraction also expressed Ly6G. DC− fraction was richer in CD11c-/F4/80+ macrophages (44.7%), some of which co-expressed Ly6G (41.8%), and F4/80-/Ly6-G+ neutrophils (34.6%). Both DC+ and DC− fractions displayed similar capacity to phagocyte and endocyte antigens and even expressed levels of MHC Class II and CD80, CD83 and CD86 costimulatory molecules similar to those in the DC fraction. However, only DC/ApoNec vaccine was capable to induce protection in mice (p<0.01). After 24h co-culture, no detectable level of IL-12 was recorded in DC/ApoNec vaccine, either in supernatant or intracellularly. Therefore, the protection obtained with DC/ApoNec vaccine seemed to be independent of the vaccine's ability to secrete this inflammatory cytokine at the time of injection. In conclusion, we demonstrated that all cell types derived from the culture of mouse bone marrow with GM-CSF are necessary to induce antitumor protection in vivo.

INHIBITION OF MICRORNA LET-7I DEPRESSES MATURATION AND FUNCTIONAL STATE OF DENDRITIC CELLS IN RESPONSE TO LPS STIMULATION VIA TARGETING SOCS1

ObjectivesDendritic cells (DCs) can initiate immune responses or confer immune tolerance depending on functional status. MicroRNAs (miRNAs) are critical for the regulation of DC function and immunity. Therefore, we try...

Alveolar epithelial cells orchestrate DC function in murine viral pneumonia

Influenza viruses (IVs) cause pneumonia in humans with progression to lung failure. Pulmonary DCs are key players in the antiviral immune response, which is crucial to restore alveolar barrier function. The mechanisms of expansion and activation of pulmonary DC populations in lung infection remain widely elusive. Using mouse BM chimeric and cell-specific depletion approaches, we demonstrated that alveolar epithelial cell (AEC) GM-CSF mediates recovery from IV-induced injury by affecting lung DC function. Epithelial GM-CSF induced the recruitment of CD11b+ and monocyte-derived DCs. GM-CSF was also required for the presence of CD103+ DCs in the lung parenchyma at baseline and for their sufficient activation and migration to the draining mediastinal lymph nodes (MLNs) during IV infection. These activated CD103+ DCs were indispensable for sufficient clearance of IVs by CD8+ T cells and for recovery from IV-induced lung injury. Moreover, GM-CSF applied intratracheally activated CD103+ DCs, inducing increased migration to MLNs, enhanced viral clearance, and attenuated lung injury. Together, our data reveal that GM-CSF-dependent cross-talk between IV-infected AECs and CD103+ DCs is crucial for effective viral clearance and recovery from injury, which has potential implications for GM-CSF treatment in severe IV pneumonia.

Induction of T cell responses and recruitment of an inflammatory dendritic cell subset following tumor immunotherapy with Mycobacterium smegmatis.

Mycobacteria and their cell wall components have been used with varying degrees of success to treat tumors, and Mycobacterium bovis BCG remains in use as a standard treatment for superficial bladder cancer. Mycobacterial immunotherapy is very effective in eliciting local immune responses against solid tumors when administered topically; however, its effectiveness in eliciting adaptive immune responses has been variable. Using a subcutaneous mouse thymoma model, we investigated whether immunotherapy with Mycobacterium smegmatis, a fast-growing mycobacterium of low pathogenicity, induces a systemic adaptive immune response. We found that M. smegmatis delivered adjacent to the tumor site elicited a systemic anti-tumor immune response that was primarily mediated by CD8(+) T cells. Of note, we identified a CD11c(+)CD40(int)CD11b(hi)Gr-1(+) inflammatory DC population in the tumor-draining lymph nodes that was found only in mice treated with M. smegmatis. Our data suggest that, rather than rescuing the function of the DC already present in the tumor and/or tumor-draining lymph node, M. smegmatis treatment may promote anti-tumor immune responses by inducing the involvement of a new population of inflammatory cells with intact function.

Isolation and Characterization of Dendritic Cells and Macrophages from the Mouse Intestine

Within the intestine reside unique populations of innate and adaptive immune cells that are involved in promoting tolerance towards commensal flora and food antigens while concomitantly remaining poised to mount inflammatory responses toward invasive pathogens. Antigen presenting cells, particularly DCs and macrophages, play critical roles in maintaining intestinal immune homeostasis via their ability to sense and appropriately respond to the microbiota. Efficient isolation of intestinal DCs and macrophages is a critical step in characterizing the phenotype and function of these cells. While many effective methods of isolating intestinal immune cells, including DCs and macrophages, have been described, many rely upon long digestions times that may negatively influence cell surface antigen expression, cell viability, and/or cell yield. Here, we detail a methodology for the rapid isolation of large numbers of viable, intestinal DCs and macrophages. Phenotypic characterization of intestinal DCs and macrophages is carried out by directly staining isolated intestinal cells with specific fluorescence-labeled monoclonal antibodies for multi-color flow cytometric analysis. Furthermore, highly pure DC and macrophage populations are isolated for functional studies utilizing CD11c and CD11b magnetic-activated cell sorting beads followed by cell sorting.

Usp18 Promotes Conventional CD11b+ Dendritic Cell Development

Dendritic cells (DCs) represent the key cells linking innate and adaptive immune responses. It is critical to understand the molecular factors regulating DC differentiation. Usp18 is an IFN-inducible member of the ubiquitin-specific protease family, which deconjugates ubiquitin-like modifier ISG15 from target proteins and competitively inhibits IFN-α/β-induced JAK/STAT activation. This study demonstrates that the frequency of conventional CD11b(+) DCs in the spleen of Usp18(-/-) mice was significantly reduced, whereas the frequencies of conventional CD8(+) DCs and plasmacytoid DCs remained normal. In addition, Usp18(-/-) bone marrow (BM) cells generate DCs less efficiently in GM-CSF-supplemented culture, demonstrating a fundamental defect throughout the DC differentiation pathway. Usp18(-/-) BM cells were rescued by exogenous expression of either wild-type or deconjugation-inactive Usp18, and superimposition of an IFN-α/β receptor knockout returned in vivo DC populations to normal, clearly showing that the defect seen is due solely to Usp18's effect on IFN signaling. Finally, Usp18(-/-) BM-derived DCs expressed high levels of SOCS1/SOCS3, known inhibitors of GM-CSF signaling, providing a mechanistic explanation for the phenotype. In conclusion, we have identified a novel role of Usp18 in modulating conventional CD11b(+) DC development via its inhibitory effect on type I IFN signaling.

The Prolyl Isomerase Pin1 Modulates Development of CD8+ cDC in Mice

BackgroundPin1 has previously been described to regulate cells that participate in both innate and adaptive immunity. Thus far, however, no role for Pin1 has been described in modulating conventional dendritic cells, innate antigen presenting cells that potently activate naïve T cells, thereby bridging innate and adaptive immune responses.Methodology/Principal FindingsWhen challenged with LPS, Pin1-null mice failed to accumulate spleen conventional dendritic cells (cDC). Analysis of steady-state spleen DC populations revealed that Pin1-null mice had fewer CD8+ cDC. This defect was recapitulated by culturing Pin1-null bone marrow with the DC-instructive cytokine Flt3 Ligand. Additionally, injection of Flt3 Ligand for 9 days failed to induce robust expansion of CD8+ cDC in Pin1-null mice. Upon infection with Listeria monocytogenes, Pin1-null mice were defective in stimulating proliferation of adoptively transferred WT CD8+ T cells, suggesting that decreases in Pin1 null CD8+ cDC may affect T cell responses to infection in vivo. Finally, upon analyzing expression of proteins involved in DC development, elevated expression of PU.1 was detected in Pin1-null cells, which resulted from an increase in PU.1 protein half-life.Conclusions/SignificanceWe have identified a novel role for Pin1 as a modulator of CD8+ cDC development. Consistent with reduced numbers of CD8+ cDC in Pin1-null mice, we find that the absence of Pin1 impairs CD8+ T cell proliferation in response to infection with Listeria monocytogenes. These data suggest that, via regulation of CD8+ cDC production, Pin1 may serve as an important modulator of adaptive immunity.

Dendritic cell-associated lectin 2 (DCAL2) defines a distinct CD8α− dendritic cell subset

CLRs on DCs play important roles in immunity and are expressed selectively on certain DC subsets. Murine DCAL2 (myeloid inhibitory C-type lectin/Clec12a) is a type-II CLR with an ITIM. Using a mouse DCAL2-specific mAb, we found that DCAL2 is expressed at relatively high levels on APCs and that DCAL2 expression can be used to divide CD8α- DCs into DCAL2+DCIR2- and DCAL2-DCIR2+ subpopulations. CD8α-DCAL2+ DC, CD8α-DCIR2+ DC, and CD8α+DCAL2+ DC subsets each express different levels of TLRs and respond to unique classes of TLR ligands by producing distinct sets of cytokines. Whereas CD8α-DCAL2+ DCs robustly produce cytokines, including IL-12, in response to CpG, CD8α-DCIR2+ DCs produce only TNF-α and IL-10 in modest amounts when stimulated with zymosan. However, CD8α-DCIR2+DCs, unlike the other DC subsets, strongly up-regulate OX40L when stimulated with bacterial flagellin. As predicted from their cytokine expression, CD8α-DCAL2+ DCs efficiently induced Th1 responses in the presence of CpG in vitro and in vivo, whereas CD8α-DCIR2+ DCs induced Th2 cells in response to flagellin. Thus, CD8α-DCAL2+ DCs comprise a distinct CD8α- DC subset capable of supporting Th1 responses. DCAL2 is a useful marker to identify a Th1-inducing CD8α- DC population.

Innate and Adaptive Interferons Suppress IL-1α and IL-1β Production by Distinct Pulmonary Myeloid Subsets during Mycobacterium tuberculosis Infection

Interleukin-1 (IL-1) receptor signaling is necessary for control of Mycobacterium tuberculosis (Mtb) infection, yet the role of its two ligands, IL-1α and IL-1β, and their regulation in vivo are poorly understood. Here, we showed that both IL-1α and IL-1β are critically required for host resistance and identified two multifunctional inflammatory monocyte-macrophage and DC populations that coexpressed both IL-1 species at the single-cell level in lungs of Mtb-infected mice. Moreover, we demonstrated that interferons (IFNs) played important roles in regulating IL-1 production by these cells in vivo. Type I interferons inhibited IL-1 production by both subsets whereas CD4(+) T cell-derived IFN-γ selectively suppressed monocyte-macrophages. These data provide a cellular basis for both the anti-inflammatory effects of IFNs and probacterial functions of type I IFNs during Mtb infection and reveal differential regulation of IL-1 production by distinct cell populations as an additional layer of complexity in the activity of IL-1 in vivo.

Early Events of Innate Immune Response to Influenza Virus in a Complex Cellular Environment Revisited with Multi-Parametric Flow Cytometry

Abstract 4931The development of an innate immune response against viruses involves multiple cellular interactions implying infected cells and the cells endowed with innate immune functions. These cells have to act in unison to develop a potent response. Although multiple interactions sustained the development of the innate response, much of the knowledge on the function of human innate immunity comes from investigations of isolated cells or dual partner coculture. Our aim was to investigate the early interactions of influenza virus with innate immune cells in a complex cellular environment in order to deepen our knowledge on the dynamics of the innate immune response. Polychromatic flow cytometry has been the appropriate method of exploration. We designed panels of 12 markers to explore PBMC stimulated with live-influenza virus or a mix of TLR agonists mimicking the interactions of influenza virus with TLR7/8 and TLR4. The DC populations were identified as lineage−HLA-DR+ cells and we took advantage of the polychromatic cytometry to split the lineage markers into separate channels to analyze NK, T cells and monocytes simultaneously to DC. Intra-cellular expression of IFN-a, TNF-a, IL-12, IL-6, IFN-g, and CD107 were analyzed in a time-dependent fashion. Our results demonstrate the benefits of using complex cell culture for the understanding of innate immune response to virus. We show a new field of application for multi-parametric flow cytometry as a powerful tool of investigation of innate immune responses in complex cell systems, with a sensibility to detect subtle modifications comparable to isolated cell systems. The multiple time-dependent results allowed to approach innate immune activation as correlated dynamic events. Dynamic studies lead to re-visit the relative roles of infection and TLR induced-DC response in the early specific features of Flu induced innate activation. Disclosures:No relevant conflicts of interest to declare.

Dendritic Cells Matured with a TLR7/8 Agonist Induce T Helper 1 Cell Polarization, Activate NK Cells and Are Thus Highly Suitable for Application in Cancer Immunotherapy

Abstract 358▪FN2▪This icon denotes a clinically relevant abstractDendritic cells (DCs) are important regulators of the human immune response. By means of direct intercellular interactions and secretion of cytokines, they can induce a stimulatory or a regulatory response, depending on the environment in which they developed. In vitro, it is possible to imitate this process by addition of various cytokines. The aim of this study was to evaluate DCs matured by different cytokine cocktails for expression of immunostimulatory and -inhibitory molecules and correspondent activation of T helper 1 (Th1) and natural killer (NK) cells. The selection of these cocktails was guided by potential clinical application and usage in a GMP setting.We compared three different ways of DC generation from peripheral blood monocytes of healthy donors: 1) maturation by a cocktail including the TLR7/8 agonist R848 (TLR-mDCs), 2) DC generation by the standard combination of proinflammatory cytokines (IL-4, GM-CSF, IL-1β, PGE2, TNF-α, and IL-6) applied in many clinical studies so far (cc-mDCs), and 3) addition of IL-10 in order to induce a more regulatory phenotype (IL10-mDCs). The expression of a broad range of costimulatory and coinhibitory molecules (CD80, CD86, CD273, CD274, CD275, CD276, B7-H4, HVEM, CD30L, CD70, CD134L = OX40L, CD137L = 4-1BBL) on the surface of these DC populations was analyzed by FACS. Secretion of various cytokines crucial for interaction with other immune cells (IL-12p70, IL-10, TNF-α, IFN-γ, IL-2, and TGF-β) was measured by cytometric bead array after stimulation with CD40 ligand. In order to assess the functional importance of these signals, we performed in vitro polarization assays for T helper cells after co-culture with DCs and measured the in vitro stimulatory potential of the DCs for natural killer (NK) cells by CD69 upregulation and intracellular IFN-γ staining.We could show that TLR-mDCs were characterized by a predominance of costimulatory (e.g. CD80, CD86) relative to coinhibitory molecules (e.g. CD273, CD274, HVEM). When stimulated by CD40L, they displayed a cytokine profile with very high IL-12p70 and TNF-α, but little if any IL-10 production. In a co-culture with autologous T cells, the combination of these signals resulted in a strong polarization toward IFN-γ secreting Th1 cells, with little or no stimulation of Th2 and Th17 cells. The costimulatory profile of cc-mDCs, in comparison, was shifted toward a lower expression of costimulatory molecules and similar or higher expression of coinhibitory molecules (ratio of CD86 to CD273 expression around 40 compared to > 60 for TLR-mDCs, p < 0.005). No IL-12p70 and low levels of IL-10 were secreted. These signals were reflected in a less pronounced type 1 polarization of T helper cells. IL10-mDCs expressed very low levels of CD80 and CD86 and displayed a coinhibitory molecule pattern similar to cc-mDCs. Additionally, they secreted the immunoregulatory molecule IL-10 in higher amounts and did not activate T helper cells at all. As IL-12p70 is an important factor for NK cell activation, only TLR-mDCs were capable of upregulating the activation marker CD69 on NK cells and inducing significant secretion of IFN-γ.Both Th1 and NK cells play an important role in tumor defense. With this set of data, we clearly showed that TLR-mDCs, in consequence of their positive costimulatory profile and their high IL-12p70 secretion, are superior with respect to type 1 polarization of T cells and activation of NK cells. They are therefore highly suitable for application in cancer immunotherapy. This DC type will be used in a phase I/II trial for postremission therapy in patients with non-favorable AML, which will start in our clinic in 2012. Disclosures:No relevant conflicts of interest to declare.

Differential effects of monophosphoryl lipid A and cytokine cocktail as maturation stimuli of immunogenic and tolerogenic dendritic cells for immunotherapy

Immunotherapy using monocyte-derived dendritic cells (MDDC) is increasingly being considered as alternative therapeutic approach in cancer, infectious diseases and also in autoimmunity when patients are not responsive to conventional treatments. In general, generation of MDDC from monocytes is induced in the presence of GM-CSF and IL-4, and a maturation stimulus is added to the culture to obtain mature DCs suitable for therapy. For DC maturation, different combinations of pro-inflammatory mediators and Toll-like receptor ligands have been tested, obtaining DCs that differ in their properties and the type of immune response they promote. Therefore, it is necessary to find an optimal cytokine environment for DC maturation to obtain a cellular product suitable for DC-based immunotherapeutic protocols. In this study, we have evaluated in vitro the effects of different maturation stimuli on the viability, phenotype, cytokine profile, stability and functionality of immunogenic and tolerogenic (1α,25-dihydroxyvitamin D(3)-treated) MDDC. Maturation was induced using the clinical grade TLR4-agonist: monophosphoryl lipid A (LA), compared to the traditional cytokine cocktail (CC; clinical grade TNF-α, IL-1β, PGE2) and a combination of both. Our results showed the combination of CC+LA rendered a potent immunogenic DC population that induced the production of IFN-γ and IL-17 in allogeneic co-cultures, suggesting a Th17 polarization. Moreover, these immunogenic DCs showed a high surface expression of CD83, CD86, HLA-DR and secretion of IL-12p70. When aiming to induce tolerance, using LA to generate mature TolDC did not represent a clear advantage, and the stability and the suppressive capability exhibited by CC-matured TolDC may represent the best option. Altogether, these findings demonstrate the relevance of an appropriate maturation stimulus to rationally modulate the therapeutic potential of DCs in immunotherapy.

Sun exposure rapidly reduces plasmacytoid dendritic cells and inflammatory dermal dendritic cells in psoriatic skin

Interferon (IFN)-α-producing plasmacytoid dendritic cells (pDCs), inflammatory CD11c+CD1c- myeloid dendritic cells (mDCs) and macrophages have been found to contribute to the pathogenesis of psoriasis. Heliotherapy is a well-established treatment modality of this disease, although the details of how the effects are mediated are unknown. To test the hypothesis that exposure to natural sun affects pathogenic DC subsets in lesional skin. Skin biopsies were obtained from lesional and nonlesional skin in 10 patients with moderate to severe psoriasis subjected to controlled sun exposure on Gran Canaria. Biopsies were obtained at baseline, day 2 and day 16 and examined by immunohistochemistry. Sixteen days of heliotherapy had excellent clinical effect on patients with psoriasis, with significant reductions in Psoriasis Area and Severity Index (PASI) scores. In lesional skin pDC numbers and expression of MxA, a surrogate marker for IFN-α, were rapidly reduced. Inflammatory CD11c+CD1c- mDCs were significantly reduced whereas resident dermal CD11c+CD1c+ mDCs were unaffected. Expression levels of the maturation marker DC-LAMP (CD208) on mDCs were significantly reduced after sun exposure, as were the numbers of lesional dermal macrophages. A decrease of dermal DC subsets and macrophages was already observed after 1 day of sun exposure. An additional finding was that DC-SIGN (CD209) is primarily expressed on CD163+ macrophages and not DCs. The clinical improvement in psoriasis following sun exposure is associated with rapid changes in dermal DC populations and macrophages in lesional skin, preceding the clinical effect. These findings support the concept that these DC subsets are involved in the pathogenesis of psoriasis and suggest that sun-induced clinical benefit may partly be explained by its effect on dermal DCs.

Inflammatory dendritic cells migrate in and out of transplanted chronic mycobacterial granulomas in mice

An estimated one-third of the world's population is infected with Mycobacterium tuberculosis, although most affected individuals maintain a latent infection. This control is attributed to the formation of granulomas, cell masses largely comprising infected macrophages with T cells aggregated around them. Inflammatory DCs, characterized as CD11c+CD11b+Ly6C+, are also found in granulomas and are an essential component of the acute immune response to mycobacteria. However, their function during chronic infection is less well understood. Here, we report that CD11c+ cells dynamically traffic in and out of both acute and chronic granulomas induced by Mycobacterium bovis strain bacillus Calmette-Guérin (BCG) in mice. By transplanting Mycobacterium-induced granulomas containing fluorescently labeled CD11c+ cells and bacteria into unlabeled mice, we were able to follow CD11c+ cell trafficking and T cell activation. We found that half of the CD11c+ cells in chronic granulomas were exchanged within 1 week. Compared with tissue-resident DC populations, CD11c+ cells migrating out of granuloma-containing tissue had an unexpected systemic dissemination pattern. Despite low antigen availability, systemic CD4+ T cell priming still occurred during chronic infection. These data demonstrate that surveillance of granulomatous tissue by CD11c+ cells is continuous and that these cells are distinct from tissue-resident DC populations and support T cell priming during both stages of Mycobacterium infection. This intense DC surveillance may also be a feature of Mycobacterium tuberculosis infection and other granuloma-associated diseases.

Inhibition of MicroRNA let-7i Depresses Maturation and Functional State of Dendritic Cells in Response to Lipopolysaccharide Stimulation via Targeting Suppressor of Cytokine Signaling 1

Dendritic cells (DCs) can initiate immune responses or confer immune tolerance depending on functional status. LPS-induced DC maturation is defined by enhanced surface expression of CD80 and CD86. MicroRNAs are critical for the regulation of DC function and immunity, and the microRNA let-7i was upregulated during LPS-induced DC maturation. Downregulation of let-7i significantly impeded DC maturation as evidenced by reduced CD80 and CD86 expression. DCs stimulated by LPS promoted T cell proliferation in coculture, whereas LPS-stimulated DCs with downregulated let-7i were not effective at stimulating T cell proliferation but promoted expansion of the regulatory T cell (Treg) population. There were two subpopulations of LPS-stimulated DCs with downregulated let-7i, CD86(-) and CD86(+), and it was the CD86(-) DCs that were more effective in inducing T cell hyporesponsiveness and enhancing Treg numbers, indicating that this DC population had tolerogenic properties. Furthermore, Tregs with upregulated IL-10 underscored the tolerogenic effect of CD86(-) DCs. Suppressor of cytokine signaling 1 (SOCS1), a crucial mediator of DC maturation, was confirmed as a let-7i target gene by luciferase construct assay. Suppression or overexpression of let-7i caused reciprocal alterations in SOCS1 protein expression, but had no significant effects on SOCS1 mRNA levels, indicating that let-7i regulated SOCS1 expression by translational suppression. The modulation of SOCS1 protein by let-7i was mainly restricted to CD86(-) DCs. Our study demonstrates that let-7i regulation of SOCS1 is critical for LPS-induced DC maturation and immune function. Dynamic regulation of let-7i may fine-tune immune responses by inducing Ag-specific immune tolerance.

Identification of IDO-Positive and IDO-Negative Human Dendritic Cells after Activation by Various Proinflammatory Stimuli

Dendritic cells (DCs) can induce tolerance or immunity. We identified and characterized an IDO-expressing and an IDO-negative human DC population after stimulation by various proinflammatory stimuli. IDO expression was strongly dependent on the maturation status of the cells (CD83-positive cells only). The two DC subpopulations remained IDO positive and IDO negative, respectively, over a time period of at least 48 h. IDO enzyme activity of human DCs was highest during stimulation by strongly maturation-inducing TLR ligands such as highly purified LPS (TLR4 ligand) or polyriboinosinic-polyribocytidilic acid (TLR3 ligand); factors of the adaptive immune system such as IFN-γ, a mixture of cytokines, and IFN-α had lesser stimulatory capacity for IDO induction and activity. After stimulation with CD40L, IDO-positive DCs expressed significantly increased levels of B7 family molecules such as CD40, CD80, CD86, ICOS ligand, as well as PD-L1 (B7-H1) and PD-L2 (B7-DC) compared with the IDO-negative DC subset. At the same time, the inhibitory receptors Ig-like transcripts 3 and 4 were significantly downregulated on IDO-positive cells. Functionally, IDO-positive DCs produced significantly more IL-1β and IL-15 and less IL-10 and IL-6 than the IDO-negative subset after CD40L stimulation. These results show that IDO expression is associated with a distinctive phenotype and functional capacity in mature DCs. It seems likely that the IDO-positive DC subset possesses a regulatory function and might skew a T cell response toward tolerance.

Gene expression analysis of dendritic cells that prevent diabetes in NOD mice: analysis of chemokines and costimulatory molecules

We have demonstrated previously that BM-derived DCs can prevent diabetes development and halt progression of insulitis in NOD mice, the mouse model of type 1 diabetes. The DC population that was most effective in this therapy had a mature phenotype, expressed high levels of costimulatory molecules, and secreted low levels of IL-12p70. The protective DC therapy induced Treg and Th2 cells in vitro and in vivo. Microarray analysis of therapeutic and nontherapeutic DC populations revealed differences in the expression of OX40L, CD200, Ym-1, CCL2, and CCL5, which could play important roles in the observed DC-mediated therapy. The unique pattern of costimulatory molecules and chemokines expressed by the therapeutic DCs was confirmed by flow cytometry and ELISA. Using a novel cell-labeling and (19)F NMR, we observed that the chemokines secreted by the therapeutic DCs altered the migration of diabetogenic Th1 cells in vivo and attracted Th2 cells. These results suggest that the therapeutic function of DCs is mediated by a combination of costimulatory and chemokine properties that results in the attraction of diabetogenic Th1 and the induction of Th2 and/or Treg differentiation.

Novel model of colitis induced by a non-inflammatory small bowel infection (166.10)

Abstract Introduction: Chronic colitis is sustained by aberrant T cells responding to normal microbiota, although how these cells develop is poorly understood. Our aim was to evaluate whether Giardia, a parasite that infects the small intestine but does not elicit inflammation, triggers colitis in a susceptible host and to elucidate mechanisms governing decisions leading to disease. Methods: IL-10-/- mice were infected with Giardia and evaluated up to 12 wks after infection. T cells and DC were isolated and characterized by FACS. Mechanistic studies were performed using neutralizing antibodies and double knockout mice. Results: Within 2 wks of Giardia infection, IL-10-/- mice developed colitis, which persisted after parasite eradication. Infection resulted in Th1 and Th17 expansion and increased expression of neutrophil-recruiting chemokines. Surprisingly, a similar response was measured in infected WT mice, which did not develop colitis. Mechanistic studies revealed that absence of T cells or Myd88 in IL-10-/- mice prevented Giardia-induced colitis. Giardia infection induced expansion of the colonic DC population and ablation of DC led to reduced severity of inflammation. Conclusions: These results suggest that Giardia functions as a microbial trigger of colitis in IL-10-/- mice. This is a powerful new model of chronic intestinal inflammation that can provide fresh insight into mechanisms controlling homeostasis and the development of colitogenic T cells.

Identification of a novel immunosuppressive dendritic cell population derived from conventional DC (113.5)

Abstract Dendritic cells (DC) play a central role in the initiation and regulation of immune responses. Conventional DC (cDC) arise from circulating immediate precursors (pre-cDC) and are currently thought to be terminally differentiated. Here we show, however, that cDC are capable of generating progeny that lost all characteristic features of cDC; and investigate the functional properties of this novel population. Sorted bone marrow pre-cDCs were cultured on a stromal monolayer in the presence/absence of granulocyte-macrophage colony stimulating factor (GM-CSF). On day three, proliferating CD11c+ MHCII+ cDC developed in both cultures. However, in the absence of GM-CSF, these cells gave rise to a homogeneous population of CD11clow MHClow cells (DC-regs) on day 8-10 of culture. In contrast to cDCs, DC-regs failed to up-regulate MHCII and co-stimulatory molecules in response to DC maturation stimuli. DC-regs displayed higher antigen capture capacity but were poor stimulators in T cell proliferation assays. Further, DC-regs not only induced T cell anergy, but also suppressed T cell proliferation in cultures containing immuno-stimulatory DC. Co-transfer of DC-regs with DCs in vivo inhibited T cell proliferation. DC-regs expressed know immunosuppressive molecules such as iNOS, arginase, ICOSL and PD-L1. Our findings challenge the prevalent view that cDC are terminally differentiated, and reveal their potential to generate a regulatory DC population with potent immunosuppressive properties.

Microscopic analysis of charge and spin photocurrents injected by circularly polarized one-color laser pulses in GaAs quantum wells

The dynamics of charge and spin injection currents excited by circularly polarized, one-color laser beams in semiconductor quantum wells is analyzed. Our microscopic approach is based on a $14\ifmmode\times\else\texttimes\fi{}14$ $k\ensuremath{\cdot}p$ band-structure theory in combination with multisubband semiconductor Bloch equations which allows a detailed analysis of the photogenerated carrier distributions and coherences in $k$ space. Charge and spin injection currents are numerically calculated for [110]- and [001]-grown GaAs quantum wells including dc population contributions and ac contributions that arise from intersubband coherences. The dependencies of the injection currents on the excitation conditions, in particular, the photon energy are computed and discussed.