Wild-type Dendritic Cells Research Articles

Fcγ Receptor IIb Strongly Regulates Fcγ Receptor-Facilitated T Cell Activation by Dendritic Cells

FcγR ligation by Ag-Ab immune complexes (IC) not only mediates effective Ag uptake, but also strongly initiates dendritic cell (DC) maturation, a requirement for effective T cell activation. Besides the activating FcγRI, FcγRIII, and FcγRIV, the inhibitory FcγRIIb is expressed on DCs. It is unclear how the ratio between signals from the activating FcγR and the inhibitory FcγRIIb determines the outcome of FcγR ligation on DCs. By microarray analysis, we compared the transcriptomes of steady state and IC-activated bone marrow-derived wild-type (WT) DCs expressing all FcγR or DCs expressing only activating FcγR (FcγRIIb knockout [KO]) or only the inhibitory FcγRIIb (FcR γ-chain KO). In WT DCs, we observed a gene expression profile associated with effective T cell activation, which was absent in FcR γ-chain KO, but strikingly more pronounced in FcγRIIb KO bone marrow-derived DCs. These microarray results, confirmed at the protein level for many cytokines and other immunological relevant genes, demonstrate that the transcriptome of IC-activated DCs is dependent on the presence of the activating FcγR and that the modulation of the expression of the majority of the genes was strongly regulated by FcγRIIb. Our data suggest that FcγRIIb-deficient DCs have an improved capacity to activate naive T lymphocytes. This was confirmed by their enhanced FcγR-dependent Ag presentation and in vivo induction of CD8(+) T cell expansion compared with WT DCs. Our findings underscore the potency of FcγR ligation on DCs for the effective induction of T cell immunity by ICs and the strong regulatory role of FcγRIIb.

IL‐10 deficiency blocks the ability of LPS to regulate expression of tolerance‐related molecules on dendritic cells

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that plays an important role in regulating the local inflammatory immune response, but regulatory mechanisms of this cytokine have not been fully elucidated. Here, we demonstrate that IL-10 deficiency renders LPS treatment ineffective in regulating the expression of CD40, CD80, CD86, B7-H2, and B7-DC on dendritic cells (DCs) and blocks upregulation of IL-27. This inability to respond to LPS was found in both IL-10(-/-) bone marrow derived and splenic DCs. Compared with wild-type DCs, IL-10(-/-) DCs expressed similar levels of TLR4 and CD14, but produced less LPS-binding protein. The deficiency in LPS-binding protein production may explain the failure of IL-10(-/-) DCs to respond normally to LPS. Moreover, lack of IL-10 modulated the proportions of CD11c(+) CD8(+) and CD11c(+) B220(+) DCs, which play an important role in local inflammatory responses and tolerance. IL-10 deficiency also blocked expression of galectin-1, CD205, and CD103, which are necessary for central and peripheral tolerance. While they did not respond to LPS, IL-10(-/-) DCs produced increased levels of IL-6 and CCL4 after TNF-α treatment. Together, our results demonstrate that IL-10 deficiency affects the immune functions of DCs, which may contribute to the increased severity of autoimmune diseases seen in IL-10(-/-) mice.

Distinct functions of CXCL9/Mig and CXCL10/IP-10 in the priming of tumor-specific IFN-g producing effector T cells (46.2)

Abstract Major factors limiting immune-mediated elimination of tumors are poor activation and/or insufficient effector functions of tumor-reactive T cells. Chemokines CXCL9/Mig and CXCL10/IP-10 share many anti-tumor functions as potent T cell chemoattractants and angiostatics. However, the individual contribution of each chemokine to the activation of anti-tumor T cell responses remains unclear. Here we tested the role of Mig and IP-10 in the activation of tumor-reactive T cells to the immunogenic murine fibrosarcoma MCA205. Tumor antigen-presenting dendritic cells (DC) deficient in Mig were less potent in activating IFN-g producing MCA205-reactive T cells than were Mig-sufficient DC. In contrast, IP-10-deficient DC were significantly more stimulatory for IFN-g producing tumor-specific T cells than were wild type DC. Activation of tumor-reactive IFN-g producing T cells in tumor hosts was markedly increased in IP-10-/- mice and was decreased in Mig-/- mice when compared to wild type mice. These differences in T cell activation correlated with either accelerated or decreased tumor growth in Mig-/- or in IP-10-/- mice, respectively. In contrast, host DC deficiency either in Mig or in IP-10 did not affect IL-17 producing tumor-specific T cells. These results demonstrate antagonistic functions of Mig and IP-10 during priming of tumor-reactive T cells producing IFN-g and suggest that manipulating the expression of these chemokines by DC can generate more potent anti-tumor immune responses.

Ability of LPS to regulate expression of tolerance-related molecules on dendritic cells is blocked by IL-10 deficiency (48.18)

Abstract Interleukin-10 (IL-10) is an anti-inflammatory cytokine that plays an important role in regulating the local inflammatory immune response, but regulatory mechanisms of this cytokine have not been fully elucidated. Here we demonstrate that IL-10 deficiency renders LPS treatment ineffective in regulating expression of CD40, CD80, CD86, B7-H2 and B7-DC on dendritic cells (DCs) and blocks up-regulation of IL-27. This inability to respond to LPS was found in both IL-10-/- bone marrow-derived and splenic DCs. Compared to wild type DCs, IL-10-/- DCs expressed similar levels of TLR4 and CD14, but produced less LPS binding protein (LBP). The deficiency in LBP production may explain the failure of IL-10-/- DCs to respond normally to LPS. Moreover, lack of IL-10 modulated the proportions of CD11c+CD8+ and CD11c+B220+ DCs, which play an important role in local inflammatory responses and tolerance. IL-10 deficiency also blocked expression of galectin-1, CD205 and CD103, which are necessary for central and peripheral tolerance. While they did not respond to LPS, IL-10-/- DCs produced increased levels of IL-6 and CCL4 after TNF-α treatment. Together, our results demonstrate that IL-10 deficiency affects the immune functions of DCs, which may contribute to the increased severity of autoimmune diseases seen in IL-10-/- mice.

Influence of hypoxia‐inducible factor 1α on dendritic cell differentiation and migration

Dendritic cells(DCs) are important sentinels of the immune system and frequently reside in areas of low oxygen availability, in particular in the course of inflammatory processes. Hypoxia-inducible transcription factor (HIF)1α is responsible for major alterations in gene expression as part of the cellular adaptation to low oxygen concentration. In this study, we generated mice with a conditional deletion of HIF1α in DCs. Bone marrow-derived DCs from WT and conditional mutant mice expressed elevated levels of major histocompatibility complex class II and CD86 when grown in a hypoxic environment, whereas production of the cytokines interleukin (IL)-12p70, IL-10, IL-6, TNF-α, IL-1β, and IL-23 was reduced, both independent of HIF1α expression. In contrast, secretion of IL-22 was strongly enhanced under hypoxic conditions in an HIF1α-dependent manner. The chemokine receptor CCR7 was expressed at higher levels in wild-type DCs compared with HIF1α-deficient DCs, whereas the production of CCL17 and CCL22 was increased in conditions of low oxygen. Using in vitro as well as in vivo migration assays, we observed an enhanced migratory capability of DCs generated under hypoxia, which was HIF1α-dependent. Taken together, our data indicate that HIF1α plays an important role for DC differentiation and migration in a low oxygen environment.

Lpa2 Is a Negative Regulator of Both Dendritic Cell Activation and Murine Models of Allergic Lung Inflammation

Negative regulation of innate immune responses is essential to prevent excess inflammation and tissue injury and promote homeostasis. Lysophosphatidic acid (LPA) is a pleiotropic lipid that regulates cell growth, migration, and activation and is constitutively produced at low levels in tissues and in serum. Extracellular LPA binds to specific G protein-coupled receptors, whose function in regulating innate or adaptive immune responses remains poorly understood. Of the classical LPA receptors belonging to the Edg family, lpa2 (edg4) is expressed by dendritic cells (DC) and other innate immune cells. In this article, we show that DC from lpa2(-/-) mice are hyperactive compared with their wild-type counterparts and are less susceptible to inhibition by different LPA species. In transient-transfection assays, we found that lpa2 overexpression inhibits NF-κB-driven gene transcription. Using an adoptive-transfer approach, we found that allergen-pulsed lpa2(-/-) DC induced substantially more lung inflammation than did wild-type DC after inhaled allergen challenge. Finally, lpa2(-/-) mice develop greater allergen-driven lung inflammation than do their wild-type counterparts in models of allergic asthma involving both systemic and mucosal sensitization. Taken together, these findings identify LPA acting via lpa2 as a novel negative regulatory pathway that inhibits DC activation and allergic airway inflammation.

Blocking CCR7 at the Ocular Surface Impairs the Pathogenic Contribution of Dendritic Cells in Allergic Conjunctivitis

CCR7 plays a key role in mobilizing tissue dendritic cells (DCs) to the lymphoid compartment for consequent elicitation of adaptive immunity. Interfering with CCR7 function therapeutically would therefore be anticipated to inhibit the progression of atopic conditions, for example, allergic conjunctivitis (AC). However, the CCR7-CCL19/CCL21 system in the ocular surface is poorly understood as is the precise role of DCs in AC immunopathogenesis. T cells from ovalbumin (OVA)-primed mice were adoptively transferred into wild-type (WT) hosts. Exogenous WT (eGFP(+)) versus CCR7(-/-) DCs were engrafted subconjunctivally (SCJ), and hosts were challenged with OVA (Texas-Red+) eye drops. AC immunopathogenesis was evaluated via clinical examinations, infiltration of mast cells and eosinophils, Th2 reactivity, and serum IgE levels. AC was also assessed in actively immunized mice challenged with OVA eye drops containing 1% anti-CCR7 antibody or isotype control. In eye-draining lymph nodes (LNs), OVA(+) SCJ engrafted WT DCs conferred upregulated CCR7 and caused augmentation of clinical signs. This result was corroborated by increased conjunctival infiltration, Th2 cytokines in LNs, and serum OVA-specific IgE. Strikingly, this was completely reversed with SCJ engrafted CCR7(-/-) DCs in all parameters tested. Furthermore, topical antibody blockade of CCR7 in actively immunized mice significantly inhibited AC. Ocular surface DCs via CCR7 expression contribute to the immunopathogenesis of AC, thereby allowing significant inhibition of this experimental condition via topical CCR7 antibody blockade.

Innate and adaptive immune responses to dead and dying cells

Under steady state conditions, billions of dead and dying cells are removed by extrusion from epithelial surfaces as well as by phagocytosis. Cells such as macrophages and dendritic cells have specialized receptors that directly recognize altered protein or lipids on apoptotic cells or opsonins that bind to the dying cell. Once engulfed, phagosomes containing apoptotic cells are rapidly acidified and the contents degraded by proteases and nucleases in lysozymes. During necrosis, cellular material is released prior to engulfment and extracellular nucleases as well as intracellular sensors dictate the inflammatory potential of the cellular debris. The outcome may be release of TNF-a, IL-1-b or interferon (IFN)-a depending upon the type of phagocyte, molecular nature of the cellular particle and the intracellular sensor engaged. In addition to responses by cells of the innate immune system, we have recently defined a link between processing of apoptotic cells and their debris to T cell activation [1]. MFG-E8 is an opsonin (bridging protein) that binds to phosphatidylserine on apoptotic cells and facilitates their removal through interaction with integrins on phagocytes. Mice deficient in MFG-E8 develop lupus like autoimmunity associated with accumulation of apoptotic cells in vivo. We observed that older MFG-8-/- mice spontaneously developed a dermatitis associated with CD8 T cell infiltration and striking activation of effector memory CD8 T cells. T cell responses to both exogenous and endogenous apoptotic cell associated antigens were enhanced in MFG-E8 deficient mice and transfer of ovalbumin (OVA) reactive OT-I CD8 T cells caused accelerated diabetes in MFG-E8-/- RIP-mOVA mice and skin disease in kmOVA transgenic mice. The enhanced CD8 T cell response was attributed to increased cross-presentation by dendritic cells (DCs) associated with increased detection of antigen peptide MHCI complexes. Investigation of intracellular trafficking revealed that, whereas intact apoptotic cells ingested by wild type DC rapidly fused with lysosomes, in the absence of MFG-E8, smaller apoptotic cell fragments persisted in endosomal compartments and failed to fuse with lysosomes. These observations suggest that in addition to altering the rate of clearance of apoptotic cells, MFG-E8 deficiency promotes immune responses to self antigens by altered intracellular processing leading to enhanced antigen presentation. Thus, handling of dead and dying cells impacts both innate and adaptive immune responses to self antigens.

R-Ras is required for murine dendritic cell maturation and CD4+ T-cell priming

AbstractR-Ras is a member of the RAS superfamily of small GTP-binding proteins. The physiologic function of R-Ras has not been fully elucidated. We found that R-Ras is expressed by lymphoid and nonlymphoid tissues and drastically up-regulated when bone marrow progenitors are induced to differentiate into dendritic cells (DCs). To address the role of R-Ras in DC functions, we generated a R-Ras-deficient mouse strain. We found that tumors induced in Rras−/− mice formed with shorter latency and attained greater tumor volumes. This finding has prompted the investigation of a role for R-Ras in the immune system. Indeed, Rras−/− mice were impaired in their ability to prime allogeneic and antigen-specific T-cell responses. Rras−/− DCs expressed lower levels of surface MHC class II and CD86 in response to lipopolysaccharide compared with wild-type DCs. This was correlated with a reduced phosphorylation of p38 and Akt. Consistently, R-Ras–GTP level was increased within 10 minutes of lipopolysaccharide stimulation. Furthermore, Rras−/− DCs have attenuated capacity to spread on fibronectin and form stable immunologic synapses with T cells. Altogether, these findings provide the first demonstration of a role for R-Ras in cell-mediated immunity and further expand on the complexity of small G-protein signaling in DCs.

NADPH Oxidase-2 Derived ROS Dictates Murine DC Cytokine-Mediated Cell Fate Decisions during CD4 T Helper-Cell Commitment

NADPH oxidase-2 (Nox2)/gp91phox and p47phox deficient mice are prone to hyper-inflammatory responses suggesting a paradoxical role for Nox2-derived reactive oxygen species (ROS) as anti-inflammatory mediators. The molecular basis for this mode of control remains unclear. Here we demonstrate that IFNγ/LPS matured p47phox−/−-ROS deficient mouse dendritic cells (DC) secrete more IL-12p70 than similarly treated wild type DC, and in an in vitro co-culture model IFNγ/LPS matured p47phox−/− DC bias more ovalbumin-specific CD4+ T lymphocytes toward a Th1 phenotype than wild type (WT) DC through a ROS-dependent mechanism linking IL-12p70 expression to regulation of p38-MAPK activation. The Nox2-dependent ROS production in DC negatively regulates proinflammatory IL-12 expression in DC by constraining p38-MAPK activity. Increasing endogenous H2O2 attenuates p38-MAPK activity in IFNγ/LPS stimulated WT and p47phox−/− DC, which suggests that endogenous Nox 2-derived ROS functions as a secondary messenger in the activated p38-MAPK signaling pathway during IL-12 expression. These findings indicate that ROS, generated endogenously by innate and adaptive immune cells, can function as important secondary messengers that can regulate cytokine production and immune cell cross-talk to control during the inflammatory response.

Loss of Myeloid Related Protein-8/14 Exacerbates Cardiac Allograft Rejection

The calcium-binding proteins myeloid-related protein (MRP)-8 (S100A8) and MRP-14 (S100A9) form MRP-8/14 heterodimers (S100A8/A9, calprotectin) that regulate myeloid cell function and inflammatory responses and serve as early serum markers for monitoring acute allograft rejection. Despite functioning as a proinflammatory mediator, the pathophysiological role of MRP-8/14 complexes in cardiovascular disease is incompletely defined. This study investigated the role of MRP-8/14 in cardiac allograft rejection using MRP-14(-/-) mice that lack MRP-8/14 complexes. We examined parenchymal rejection after major histocompatibility complex class II allomismatched cardiac transplantation (bm12 donor heart and B6 recipients) in wild-type (WT) and MRP-14(-/-) recipients. Allograft survival averaged 5.9±2.9 weeks (n=10) in MRP-14(-/-) recipients compared with >12 weeks (n=15; P<0.0001) in WT recipients. Two weeks after transplantation, allografts in MRP-14(-/-) recipients had significantly higher parenchymal rejection scores (2.8±0.8; n=8) than did WT recipients (0.8±0.8; n=12; P<0.0001). Compared with WT recipients, allografts in MRP-14(-/-) recipients had significantly increased T-cell and macrophage infiltration and increased mRNA levels of interferon-γ and interferon-γ-associated chemokines (CXCL9, CXCL10, and CXCL11), interleukin-6, and interleukin-17 with significantly higher levels of Th17 cells. MRP-14(-/-) recipients also had significantly more lymphocytes in the adjacent para-aortic lymph nodes than did WT recipients (cells per lymph node: 23.7±0.7×10(5) for MRP-14(-/-) versus 6.0±0.2×10(5) for WT; P<0.0001). The dendritic cells (DCs) of the MRP-14(-/-) recipients of bm12 hearts expressed significantly higher levels of the costimulatory molecules CD80 and CD86 than did those of WT recipients 2 weeks after transplantation. Mixed leukocyte reactions with allo-endothelial cell-primed MRP-14(-/-) DCs resulted in significantly higher antigen-presenting function than reactions using WT DCs. Ovalbumin-primed MRP-14(-/-) DCs augmented proliferation of OT-II (ovalbumin-specific T cell receptor transgenic) CD4(+) T cells with increased interleukin-2 and interferon-γ production. Cardiac allografts of B6 major histocompatibility complex class II(-/-) hosts and of B6 WT hosts receiving MRP-14(-/-) DCs had significantly augmented inflammatory cell infiltration and accelerated allograft rejection compared with WT DCs from transferred recipient allografts. Bone marrow-derived MRP-14(-/-) DCs infected with MRP-8 and MRP-14 retroviral vectors showed significantly decreased CD80 and CD86 expression compared with controls, indicating that MRP-8/14 regulates B7-costimulatory molecule expression. Our results indicate that MRP-14 regulates B7 molecule expression and reduces antigen presentation by DCs and subsequent T-cell priming. The absence of MRP-14 markedly increased T-cell activation and exacerbated allograft rejection, indicating a previously unrecognized role for MRP-14 in immune cell biology.

Both Tissue-Derived and Bone Marrow-Derived Host IL-17 Producing Cells Are Required for Preventing Acute Graft-Versus-Host Disease

Abstract 2970Th17 is a newly identified T cell lineage, which secretes the proinflammatory cytokine IL-17. Th17 have been shown to play a crucial role in some immune-mediated diseases. We have reported that host-derived IL-17 has a protective effect against acute graft-versus-host disease (GVHD). In contrast, donor-derived IL-17 exacerbates chronic GVHD in rodent models. Briefly, in acute GVHD model, lethally irradiated IL-17 knockout (KO) recipient mice receiving allogeneic BM with low dose splenocytes developed more severe acute gut GVHD compared to wild type (WT) host mice and finally half of them died (p<0.05). To demonstrate the mechanisms of protective role of host derived IL-17 against acute GVHD in further detail, first we determined in vivo gut epithelial permeability by using FITC-dextran. No significant difference was observed between WT mice and IL-17KO mice, even in GVHD induced mice. Next, to exclude the possibility that alloreactivity of host IL-17KO derived mature dendritic cells (DCs) could be much more than that of WT DCs, mixed leukocyte reaction (MLR) was performed using stimulators from WT or IL-17KO mature DCs and responders from WT allogeneic splenocytes. There was no significant difference between WT mature DCs and IL-17KO mature DCs in thymidine uptake and percentage of responder cells producing IFN-γ or TNF-α. However, when DCs were cultured from BM cells with GM-CSF, co-stimulatory molecules such as CD80 and CD86 were expressed much stronger and from earlier time point on IL-17KO DCs compared with WT DCs. This suggested that DCs from IL-17KO tend to be activated much easier, resulting in much severe GVHD. In addition, when recombinant IL-17 was added into MLR mixture (Stimulator: Balb/c IL-17KO mature DCs, Responder: B6 IL-17KO splenocytes), proliferation was significantly decreased, demonstrating that IL-17 has inhibitory effect on alloreaciton. Next, much higher number of infiltrated monocyte/macrophage cluster was observed in spleen and gut in IL-17KO host mice. Residual host-typed peritoneal macrophages in IL-17KO host mice were highly activated with the expression of TNF-α, while activation of donor-typed macrophages was much less with the production of anti-inflammatory cytokine IL-10. Activated monocytes/macrophages in IL-17KO recipients might migrate into inflamed tissue much easier, partially because lack of IL-17 dose not block some macrophage chemotactic factors such as IP-10, RANTES. Finally to explore which host IL-17 producing cells are necessary for protection from acute GVHD, that is, BM-derived IL-17 producing cells or tissue derived IL-17 producing cells such as Paneth cells in the gut, [IL-17KO→WT], [WT→IL-17KO], [WT→WT], and [IL-17KO→IL-17KO] chimeric mice (Balb/c background) were created by reconstituting lethally irradiated WT or IL-17 KO Balb/c (H-2d) with BM cells from WT or IL-17 KO Balb/c mice. Four months later, chimeras were re-irradiated with 8Gy TBI and injected with WT C57BL/6(H-2b) BM plus low dose splenocytes to induce acute GVHD. Although [WT→WT] chimeric recipients were all alive, all [IL-17KO→IL-17KO] chimeric mice died of severe GVHD. In both [WT→IL-17KO] and [IL-17KO→WT] chimeras, half of them died with less GVHD compared to [IL-17KO→IL-17KO] recipients as shown below. This result indicated that as well as tissue derived IL-17, host BM derived IL-17 is necessary for protection from acute GVHD. In conclusion, host-derived IL-17 has a protective effect against acute GVHD due to in part by regulating APCs (monocytes/macrophages/DCs) activation and migration into GVHD target tissues. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Toll-Like Receptors 2 and 4 Regulate the Frequency of IFNγ-Producing CD4+ T-Cells during Pulmonary Infection with Chlamydia pneumoniae

TLR2 and TLR4 are crucial for recognition of Chlamydia pneumoniae in vivo, since infected TLR2/4 double-deficient mice are unable to control the infection as evidenced by severe loss of body weight and progressive lethal pneumonia. Unexpectedly, these mice display higher pulmonary levels of the protective cytokine IFNγ than wild type mice. We show here, that antigen-specific CD4+ T-cells are responsible for the observed IFNγ-secretion in vivo and their frequency is higher in TLR2/4 double-deficient than in wild type mice. The capacity of TLR2/4 double-deficient dendritic cells to re-stimulate CD4+ T-cells did not differ from wild type dendritic cells. However, the frequency of CD4+CD25+Foxp3+ T-cells was considerably higher in wild type compared to TLR2/4 double-deficient mice and was inversely related to the number of IFNγ-secreting CD4+ effector T-cells. Despite increased IFNγ-levels, at least one IFNγ-mediated response, protective NO-secretion, could not be induced in the absence of TLR2 and 4. In summary, CD4+CD25+Foxp3+ regulatory T-cells fail to expand in the absence of TLR2 and TLR4 during pulmonary infection with C. pneumoniae, which in turn enhances the frequency of CD4+IFNγ+ effector T-cells. Failure of IFNγ to induce NO in TLR2/4 double-deficient cells represents one possible mechanism why TLR2/4 double-deficient mice are unable to control pneumonia caused by C. pneumoniae and succumb to the infection.

Targeting the immunoregulator SRA/CD204 potentiates specific dendritic cell vaccine-induced T-cell response and antitumor immunity.

Although dendritic cell (DC) vaccines offer promise as cancer immunotherapy, further improvements are needed to amplify their clinical therapeutic efficacy. The pattern recognition scavenger receptor SRA/CD204 attenuates the ability of DCs to activate CD8(+) T-cell responses. Therefore, we examined the impact of SRA/CD204 on antitumor responses generated by DC vaccines and we also evaluated the feasibility of enhancing DC vaccine potency by SRA/CD204 blockade. DCs from SRA/CD204-deficient mice were more immunogenic in generating antitumor responses to B16 melanoma, compared with DCs from wild-type mice. Similarly, siRNA-mediated knockdown of SRA/CD204 by lentiviral vectors improved the ability of wild-type DCs to stimulate the expansion and activation of CD8(+) T cells specific for idealized or established melanoma antigens in mice. Using SRA/CD204-silenced DCs to generate antigen-targeted vaccines, we documented a marked increase in the level of antitumor immunity achieved against established B16 tumors and metastases. This increase was associated with enhanced activation of antigen specific CTLs, greater tumor infiltration by CD8(+) T cells and NK cells, and increased intratumoral ratios of both CD4(+) and CD8(+) T-effector cells to CD4(+)CD25(+) T-regulatory cells. Our studies establish that downregulating SRA/CD204 strongly enhances DC-mediated antitumor immunity. In addition, they provide a rationale to enhance DC vaccine potency through SRA/CD204-targeting approaches that can improve clinical outcomes in cancer treatment.

Immunotherapy with Costimulatory Dendritic Cells To Control Autoimmune Inflammation

Costimulation-deficient dendritic cells (DCs) prevent autoimmune disease in mouse models. However, autoimmune-prone mice and humans fail to control expansion of peripheral autoreactive effector memory T cells (T(EMs)), which resist immunoregulation by costimulation-deficient DCs. In contrast, activation of DC costimulation may be coupled with regulatory capacity. To test whether costimulatory DCs control T(EMs) and attenuate established autoimmune disease, we used RelB-deficient mice, which have multiorgan inflammation, expanded peripheral autoreactive T(EMs), and dysfunctional Foxp3(+) regulatory T cells (Tregs) cells and conventional DCs. T(EMs) were regulated by Foxp3(+) Tregs when costimulated by CD3/CD28-coated beads or wild-type DCs but not DCs deficient in RelB or CD80/CD86. After transfer, RelB and CD80/CD86-sufficient DCs restored tolerance and achieved a long-term cure of autoimmune disease through costimulation of T(EM) and Foxp3(+) Treg IFN-γ production, as well as induction of IDO by host APCs. IDO was required for regulation of T(EMs) and suppression of organ inflammation. Our data challenge the paradigm that costimulation-deficient DCs are required to regulate established autoimmune disease to avoid T(EM) activation and demonstrate cooperative cross-talk between costimulatory DCs, IFN-γ, and IDO-dependent immune regulation. IFN-γ and IDO activity may be good surrogate biomarkers measured against clinical efficacy in trials of autoimmune disease immunoregulation.

Involvement of aquaporin‐7 in the cutaneous primary immune response through modulation of antigen uptake and migration in dendritic cells

Dendritic cells (DCs) have the ability to present antigen and play a critical role in the induction of the acquired immune response. Skin DCs uptake antigen and subsequently migrate to regional draining lymph nodes (LNs), where they activate naive T cells. Here we show that the water/glycerol channel protein aquaporin 7 (AQP7) is expressed on epidermal and dermal DCs and involved in the initiation of primary immune responses. AQP7-deficient DCs showed a decreased cellular uptake of low-molecular-mass compounds (fluorescein isothiocyanate and Lucifer yellow) and high-molecular-mass substances (ovalbumin and dextran), suggesting that AQP7 is involved in antigen uptake. AQP7-deficient DCs also exhibited reduced chemokine-dependent cell migration in comparison to wild-type DCs. Consistent with these in vitro results, AQP7-deficient mice demonstrated a reduced accumulation of antigen-retaining DCs in the LNs after antigen application to the skin, which could be attributed to decreased antigen uptake and migration. Coincidentally, AQP7-deficient mice had impaired antigen-induced sensitization in a contact hypersensitivity model. These observations suggested that AQP7 in skin DCs is primarily involved in antigen uptake and in the subsequent migration of DCs and is responsible for antigen presentation and the promotion of downstream immune responses.

DC mobilization from the skin requires docking to immobilized CCL21 on lymphatic endothelium and intralymphatic crawling

Dendritic cells (DCs) must travel through lymphatics to carry skin antigens into lymph nodes. The processes controlling their mobilization and migration have not been completely delineated. We studied how DCs in live mice respond to skin inflammation, transmigrate through lymphatic endothelium, and propagate in initial lymphatics. At steady state, dermal DCs remain sessile along blood vessels. Inflammation mobilizes them, accelerating their interstitial motility 2.5-fold. CCR7-deficient BMDCs crawl as fast as wild-type DCs but less persistently. We observed discrete depositions of CCL21 complexed with collagen-IV on the basement membrane of initial lymphatics. Activated DCs move directionally toward lymphatics, contact CCL21 puncta, and migrate through portals into the lumen. CCR7-deficient DCs arrive at lymphatics through random migration but fail to dock and transmigrate. Once inside vessels, wild-type DCs use lamellipodia to crawl along lymphatic endothelium and, sensing lymph flow, proceed downstream. DCs start drifting freely only in collecting lymphatics. These results demonstrate in vivo that the CCL21-CCR7 axis plays a dual role in DC mobilization: promoting both chemotaxis and arrest of DCs on lymphatic endothelium. Intralymphatic crawling, in which DCs combine active adhesion-based migration and directional cues from lymph flow, represents a new step in DC mobilization which may be amenable to regulation.

CD204 Suppresses Large Heat Shock Protein-Facilitated Priming of Tumor Antigen gp100-Specific T Cells and Chaperone Vaccine Activity against Mouse Melanoma

We previously reported that scavenger receptor A (SRA/CD204), a binding structure on dendritic cells (DCs) for large stress/heat shock proteins (HSPs; e.g., hsp110 and grp170), attenuated an antitumor response elicited by large HSP-based vaccines. In this study, we show that SRA/CD204 interacts directly with exogenous hsp110, and lack of SRA/CD204 results in a reduction in the hsp110 binding and internalization by DCs. However, SRA(-/-) DCs pulsed with hsp110 or grp170-reconstituted gp100 chaperone complexes exhibit a profoundly increased capability of stimulating melanoma Ag gp100-specific naive T cells compared with wild-type (WT) DCs. Similar results were obtained when SRA/CD204 was silenced in DCs using short hairpin RNA-encoding lentiviruses. In addition, hsp110-stimulated SRA(-/-) DCs produced more inflammatory cytokines associated with increased NF-κB activation, implicating an immunosuppressive role for SRA/CD204. Immunization with the hsp110-gp100 vaccine resulted in a more robust gp100-specific CD8(+) T cell response in SRA(-/-) mice than in WT mice. Lastly, SRA/CD204 absence markedly improved the therapeutic efficacy of the hsp110-gp100 vaccine in mice established with B16 melanoma, which was accompanied by enhanced activation and tumor infiltration of CD8(+) T cells. Given the presence of multiple HSP-binding scavenger receptors on APCs, we propose that selective scavenger receptor interactions with HSPs may lead to highly distinct immunological consequences. Our findings provide new insights into the immune regulatory functions of SRA/CD204 and have important implications in the rational design of protein Ag-targeted recombinant chaperone vaccines for the treatment of cancer.

The Signaling Adaptor Eps8 Is an Essential Actin Capping Protein for Dendritic Cell Migration

Dendritic cells (DCs) flexibly adapt to different microenvironments by using diverse migration strategies that are ultimately dependent on the dynamics and structural organization of the actin cytoskeleton. Here, we have shown that DCs require the actin capping activity of the signaling adaptor Eps8 to polarize and to form elongated migratory protrusions. DCs from Eps8-deficient mice are impaired in directional and chemotactic migration in 3D invitro and are delayed in reaching the draining lymph node (DLN) invivo after inflammatory challenge. Hence, Eps8-deficient mice are unable to mount a contact hypersensitivity response. We have also shown that the DC migratory defect is cell autonomous and that Eps8 is required for the proper architectural organization of the actin meshwork and dynamics of cell protrusions. Yet, Eps8 is not necessary for antigen uptake, processing, and presentation. Thus, we have identified Eps8 as a unique actin capping protein specifically required for DC migration.

CD69 Modulates Sphingosine-1-Phosphate-Induced Migration of Skin Dendritic Cells

In this study, we have investigated the role of CD69, an early inducible leukocyte activation receptor, in murine dendritic cell (DC) differentiation, maturation, and migration. Skin DCs and DC subsets present in mouse lymphoid organs express CD69 in response to maturation stimuli. Using a contact sensitization model, we show that skin DCs migrated more efficiently to draining lymph nodes (LNs) in the absence of CD69. This was confirmed by subcutaneous transfer of CD69-/- DCs, which presented an increased migration to peripheral LNs. Two-photon microscopy analysis showed that once DCs reached the LNs, CD69 deficiency did not alter DC interstitial motility in the LNs. Chemotaxis to sphingosine-1-phosphate (S1P) was enhanced in CD69-/- DCs compared with wild-type DCs. Accordingly, we detected a higher expression of S1P receptor type-1 (S1P(1)) by CD69-/- DCs, whereas S1P(3) expression levels were similar in wild-type and CD69-/- DCs. Moreover, in vivo treatment with S1P analogs SEW2871 and FTY720 during skin sensitization reduced skin DC migration to peripheral LNs. These results suggest that CD69 regulates S1P-induced skin DC migration by modulating S1P(1) function. Together, our findings increase our knowledge on DC trafficking patterns in the skin, enabling the development of new directed therapies using DCs for antigen (Ag) delivery.