Origin, precursors and differentiation of mouse dendritic cells

Distinct cross talk of IL-17 & TGF-β with the immature CD11c+ TRAF6(-/-) -null myeloid dendritic cell-derived osteoclast precursor (mDDOCp) may engage signaling toward an alternative pathway of osteoclastogenesis for arthritic bone loss in vivo

BACKGROUND

Dendritic cells (DCs), though borne heterogeneous, are the most potent antigen-presenting cells, whose critical functions include triggering antigen-specific naïve T-cell responses and fine-tuning the innate versus adaptive immunity at the osteo-immune and/or mucosal mesenchyme interface. We previously reported that immature myeloid-CD11c+ DCs/mDCs may act like osteoclast (OC) precursors (OCp/mDDOCp) capable of developing into functional OCs via an alternative pathway of inflammation-induced osteoclastogenesis; however, what are their contribution and signaling interactions with key osteotropic cytokines (i.e., interleukin-17 [IL-17] and transforming growth factor-β [TGF-β]) to bearing such inflammatory bone loss in vivo remain unclear to date.

METHODS

Herein, we employed mature adult bone marrow-reconstituted C57BL/6 TRAF6(-/-) -null chimeras without the classical monocyte/macrophage (Mo/Mϕ)-derived OCs to address their potential contribution to OCp/mDDOCp-mediated osteoclastogenesis in the chicken type-II-collagen (CC-II)-induced joint inflammation versus arthritic bone loss and parallel associations with the double-positive CD11c+ TRAP+ TRAF6-null(-/-)  DC-like OCs detected in vivo via the quantitative dual-immunohistochemistry and digital histomorphometry for analyses.

RESULTS

The resulting findings revealed the unrecognized novel insight that (i) immature myeloid-CD11c+ TRAF6(-/-) TRAP+ DC-like OCs were involved, co-localized, and strongly associated with joint inflammation and bone loss, independent of the Mo/Mϕ-derived classical OCs, in CC-II-immunized TRAF6(-/-) -null chimeras, and (ii) the osteotropic IL-17 may engage distinct crosstalk with CD11c+ mDCs/mDDOCp before developing the CD11c+ TRAP+ TRAF6(-/-) OCs via a TGF-β-dependent interaction toward inflammation-induced arthritic bone loss in vivo.

CONCLUSION

These results confirm and substantiate the validity of TRAF6(-/-) -null chimeras to address the significance of immature mCD11c+ TRAP+ DC-like OCs/mDDOCp subset for an alternative pathway of arthritic bone loss in vivo. Such CD11c+ mDCs/mDDOCp-associated osteoclastogenesis through the step-wise twist-in-turns osteo-immune cross talks are thereby theme highlighted to depict a summative re-visitation proposed.

Dendritic cell therapy augments antitumor immunity triggered by CDK4/6 inhibition and immune checkpoint blockade by unleashing systemic CD4 T-cell responses

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy are a mainstay treatment for hormone receptor-positive breast cancer. While their principal mechanism is inhibition of cancer cell proliferation, preclinical and clinical evidence suggests that CDK4/6i can also promote antitumor T-cell responses. However, this pro-immunogenic property is yet to be successfully harnessed in the clinic, as combining CDK4/6i with immune checkpoint blockade (ICB) has not shown a definitive benefit in patients.

METHOD

We performed an in-depth analysis of the changes in the tumor immune microenvironment and systemic immune modulation associated with CDK4/6i treatment in muring breast cancer models and in patients with breast cancer using high dimensional flow cytometry and RNA sequencing. Gain and loss of function in vivo experiments employing cell transfer and depletion antibody were performed to uncover immune cell populations critical for CDK4/6i-mediated stimulation of antitumor immunity.

RESULTS

We found that loss of dendritic cells (DCs) within the tumor microenvironment resulting from CDK4/6 inhibition in bone marrow progenitors is a major factor limiting antitumor immunity after CDK4/6i and ICB. Consequently, restoration of DC compartment by adoptively transferring ex vivo differentiated DCs to mice treated with CDK4/6i and ICB therapy enabled robust tumor inhibition. Mechanistically, the addition of DCs promoted the induction of tumor-localized and systemic CD4 T-cell responses in mice receiving CDK4/6i-ICB-DC combination therapy, as characterized by enrichment of programmed cell death protein-1-negative T helper (Th)1 and Th2 cells with an activated phenotype. CD4 T-cell depletion abrogated the antitumor benefit of CDK4/6i-ICB-DC combination, with outgrowing tumors displaying an increased proportion of terminally exhausted CD8 T cells.

CONCLUSIONS

Our findings suggest that CDK4/6i-mediated DC suppression limits CD4 T-cell responses essential for the sustained activity of CD8 T cells and tumor inhibition. Furthermore, they imply that restoring DC-CD4 T-cell crosstalk via DC transfer enables effective breast cancer immunity in response to CDK4/6i and ICB treatment.

Classical DC2 subsets and monocyte-derived DC: Delineating the developmental and functional relationship

To specifically tailor immune responses to a given pathogenic threat, dendritic cells (DC) are highly heterogeneous and comprise many specialized subtypes, including conventional DC (cDC) and monocyte-derived DC (MoDC), each with distinct developmental and functional characteristics. However, the functional relationship between cDC and MoDC is not fully understood, as the overlapping phenotypes of certain type 2 cDC (cDC2) subsets and MoDC do not allow satisfactory distinction of these cells in the tissue, particularly during inflammation. However, precise cDC2 and MoDC classification is required for studies addressing how these diverse cell types control immune responses and is therefore currently one of the major interests in the field of cDC research. This review will revise murine cDC2 and MoDC biology in the steady state and under inflammatory conditions and discusses the commonalities and differences between ESAM^lo cDC2, inflammatory cDC2, and MoDC and their relative contribution to the initiation, propagation, and regulation of immune responses.

The Experimental Animal Models in Psoriasis Research: A Comprehensive Review

Psoriasis is an autoimmune, chronic, inflammatory skin condition mediated by T cells. It differs from other inflammatory conditions by causing significant alterations in epidermal cell proliferation and differentiation that are both complicated and prominent. The lack of an appropriate animal model has significantly hindered studies into the pathogenic mechanisms of psoriasis since animals other than humans typically do not exhibit the complex phenotypic features of human psoriasis. A variety of methods, including spontaneous mutations, drug-induced mutations, genetically engineered animals, xenotransplantation models, and immunological reconstitution approaches, have all been employed to study specific characteristics in the pathogenesis of psoriasis. Although some of these approaches have been used for more than 50 years and far more models have been introduced recently, they have surprisingly not yet undergone detailed validation. Despite their limitations, these models have shown a connection between keratinocyte hyperplasia, vascular hyperplasia, and a cell-mediated immune response in the skin. The xenotransplantation of diseased or unaffected human skin onto immune-compromised recipients has also significantly aided psoriasis research. This technique has been used in a variety of ways to investigate the function of T lymphocytes and other cells, including preclinical therapeutic studies. The design of pertinent in vivo and in vitro psoriasis models is currently of utmost concern and a crucial step toward its cure. This article outlines the general approach in the development of psoriasis-related animal models, aspects of some specific models, along with their strengths and limitations.

Expression of programmed cell death-1 on neuroblastoma cells in TH-MYCN transgenic mice

BACKGROUND

Immunotherapy may improve the poor prognosis of high-risk neuroblastoma. Programmed cell death-1 (PD-1) is expressed in several cancers. The tyrosine hydroxylase MYCN (TH-MYCN) transgenic mouse model is widely used in neuroblastoma research, but detailed information on its immunological background is lacking. Therefore, we studied the immunological tumor microenvironment and tumor cell surface antigen expression in homozygote and hemizygote mice and effects of antibody therapy against PD-1.

METHODS

CD4, CD8, CD11b, and CD11c expression in immune cells from retroperitoneal lymph nodes and spleen was analyzed by flow cytometry. Tumor cell surface antigen expression was confirmed, and data from homozygote and hemizygote mice were compared. Effects of anti-PD-1 antibody were evaluated.

RESULTS

CD4-, CD8-, CD11b-, and CD11c-positive cells were not significantly different in homozygote and hemizygote mice, and CD11b- and CD11c-positive cells were identified in the tumor microenvironment in both. Tumor cells expressed PD-1, and anti-PD-1 antibody had anti-tumor effects and significantly reduced the percentage of living tumor cells in cultures after 2 h.

CONCLUSION

The immunological background is similar in homozygote and hemizygote TH-MYCN transgenic mice, and both have PD-1-positive tumor cells. Anti-PD-1 antibody suppresses tumor growth. This mouse model may be a useful for studying immunotherapy of neuroblastoma.

The secretion of sIgA and dendritic cells activation in the intestinal of cyclophosphamide-induced immunosuppressed mice are regulated by Alhagi honey polysaccharides

BACKGROUND

It remains a huge challenge to recover the intestine immune function for the treatment of intestinal mucosal damage from chemotherapy with cyclophosphamide (CY). Alhagi honey polysaccharide (AH) has immunomodulation pharmacological activity, but the effect and mechanism on the intestinal immune system of CY-mice remain unclear.

PURPOSE

In this experiment, the immunomodulatory activity of AH on intestinal immune in CY-mice and its mechanism of regulating the intestinal immune system was investigated.

STUDY DESIGN AND METHODS

The experiment studied the immunomodulatory activity of AH on the intestinal immune system and its mechanism for the first time from in vitro and in vivo experiments. We investigated the immunomodulatory effects of AH on Caco-2 and dendritic cells (DCs) in vitro by using western blot (WB), flow cytometry, quantitative real-time PCR (qPCR), and ELISA methods. In vivo experiment, the immunosuppressive mouse model was established through being given intraperitoneal injection with CY (80 mg/kg) for 3 days. Then, mice oral administration of 800 mg/kg AH and 40 mg/kg levamisole hydrochloride for a week. Immunofluorescence, flow cytometry, ELISA, qPCR and WB were applied to examine the immunomodulatory activity of AH on the intestinal immune function of CY-mice, as well as the function of AH on the concentration of SCFAs in cecum by Gas chromatographic analysis.

RESULTS

In vitro experiments, AH could significantly stimulate the expression of pIgR protein in Caco-2. It could also induce the DCs maturation and release the cytokines to regulate the immune response. In vivo experiments, AH could remarkably stimulate the DCs maturation and secrete more CCL20 to recruit DCs, then induce the T (CD4⁺ and CD8⁺) and B cells proliferation and activation. Moreover, it could further induce T helper cells to differentiate and secrete cytokines to enhance the secretion of sIgA. Furthermore, it also directly activated DCs and released cytokines to increase the content of pIgR, J-chain, and IgA⁺ cells in intestine, thereby enhancing the secretion of sIgA to protect the intestine. In addition, AH could obviously strengthen the SCFAs production in cecum to regulate the intestinal immune dysfunction induced by CY.

CONCLUSION

In summary, oral administrated AH exhibits great benefits for treating CY-induced intestinal immunosuppression, and the mechanism of action mainly involves sIgA, DCs, SCFAs.

Dendritic cells sub-sets are associated with inflammatory cytokine production in progressive vitiligo disease

In autoimmune onset of vitiligo, perilesional area shows inflammatory cells including T cytotoxic, helper cells and macrophages. Dendritic Cells (DCs) regulate immune activities by antigen presentation to T cells or cytokine production. It is evident that pro- and anti-inflammatory DCs are responsible for their respective cytokines release. However, role of DCs in vitiligo is enigmatic. In the present study, we assessed DCs markers (CD11b and CD11c) along with pro- and anti-inflammatory cytokines (IL-17A, IL-10 and IL-12p70) in stable and active vitiligo patients. Our results revealed a significant augmented expression of CD11b⁺CD11c⁺ (pro-inflammatory DC) in peripheral blood mononuclear cells (PBMCs) and skin tissues of active vitiligo patients versus control and stable vitiligo group. Unlikely, CD11b⁺ (anti-inflammatory DC) levels were significantly impeded in active vitiligo group as compared to another two groups. CD11c (T helper 1 stimulating DC) presented no significant alterations in any group. Furthermore, we perceived significantly up-regulated IL-17A (pro-inflammatory cytokine) and down-regulated IL-10 (anti-inflammatory cytokine) expressions in active vitiligo group as compared to control and stable group (in sera, PBMCs and skin tissue). Also, a significant positive correlation was observed between CD11b⁺CD11c⁺ and IL-17A; and CD11b⁺ and IL-10. Contrarily, CD11b⁺CD11c⁺ and CD11b⁺ were negatively correlated with IL-10 and IL-17A, respectively. In conclusion, modulation of pro- and anti-inflammatory DCs in active vitiligo patients may affect cytokines production and thereby, lead to further depigmentation of skin.

Targeting Opposing Immunological Roles of the Junctional Adhesion Molecule-A in Autoimmunity and Cancer

The junctional adhesion molecule-A (JAM-A) is a cell surface adhesion molecule expressed on platelets, epithelial cells, endothelial cells and leukocytes (e. g. monocytes and dendritic cells). JAM-A plays a relevant role in leukocyte trafficking and its therapeutic potential has been studied in several pathological conditions due to its capacity to induce leukocyte migration out of inflamed sites or infiltration into tumor sites. However, disruption of JAM-A pathways may worsen clinical pathology in some cases. As such, the effects of JAM-A manipulation on modulating immune responses in the context of different diseases must be better understood. In this mini-review, we discuss the potential of JAM-A as a therapeutic target, summarizing findings from studies manipulating JAM-A in the context of inflammatory diseases (e.g. autoimmune diseases) and cancer and highlighting described mechanisms.

Recent Advances in Nanotechnology for Dendritic Cell-Based Immunotherapy

Dendritic cells (DCs) are the most important antigen-presenting cells that determine cancer immune responses by regulating immune activation and tolerance, especially in the initiation stage of specific responses. Manipulation of DCs to enhance specific antitumor immune response is considered to be a powerful tool for tumor eradication. Nanotechnology, which can incorporate multifunction components and show spatiotemporal control properties, is of great interest and is widely investigated for its ability to improve immune response activity against cancer and even for prevention and avoiding recurrence. In this mini-review, we aim to provide a general view of DC-based immunotherapy, including that involving the promising nanotechnology. Particularly we discuss: (1) manipulation or engineering of DCs for adoptive vaccination, (2) employing DCs as a combination to more existing therapeutics in tumor treatment, and (3) direct modulation of DCs in vivo to enhance antigen presentation efficacy and priming T cells subsequently. We comprehensively discuss the updates on the application of nanotechnology in DC-based immunotherapy and provide some insights on the challenges and opportunities of DC-based immunotherapeutics, including the potential of nanotechnology, against cancers.

Dendritic Cells as Arbiters of Peritoneal Immune Responses

During the past few years, there has been a substantial increase in the understanding of innate immunity. Dendritic cells are emerging as key players in the orchestration of this early phase of immune responses, with a role that will translate into the subsequent type of adaptive immune response against infection. Here we provide an overview of dendritic cell differentiation and function, with particular emphasis on those features unique to the immune defense of the peritoneal cavity and in the context of peritoneal dialysis-associated immune responses. The reader is referred to the primary references included in the accompanying list for specific details in this fascinating field.

MiR-146a Promotes Tolerogenic Properties of Dendritic Cells and through Targeting Notch1 Signaling

BACKGROUND

MiR-146a has been shown to negatively regulate innate immune, inflammatory response and antiviral pathway, however, its role in the tolerogenic responses remains largely unknown. This study aimed to investigate the role of miR-146a in the OVA-induced allergic inflammation of dendritic cells (DCs).

METHODS

Bone marrow-derived DCs (BMDCs) were treated with OVA (100 µg/ml) for 24 h. MiR-146a expressions were assessed by quantitative RT-PCR. BMDCs were transfected with miR-146a mimics or inhibitor. Cell surface markers were analyzed by flow cytometry. Cytokine levels were determined by ELISA assay. Mixed lymphocyte culture assay was adopted to assess CD4 + T-cell differentiation. The 3' UTR luciferase reporter assay was utilized to determine the miRNA target sequence.

RESULTS

OVA treatment significantly up-regulated miR-146a in BMDCs in a dose- and time-dependent manner. In the OVA-treated DCs, overexpression of miR-146a (mimics transfection) down-regulated the surface markers (CD80, CD86) and increased production of anti-inflammatory cytokines TGF-β1 and IL-10 but decreased pro-inflammatory cytokine IL-12. MiR-146a overexpression promoted immature DC to induce regulatory T cells (Treg) differentiation. By contrast, transfection of miR-146a inhibitor into DC exhibited the opposite trends. Notch1 was a direct target of miR-146a, and Notch1 knock-down induced similar effects as miR-146a mimics transfection in BMDCs. Moreover, the effect of miR-146a inhibitor on OVA-induced DC was attenuated by Notch1 knock-down.

CONCLUSION

miRNA-146a promoted tolerogenic properties of DCs, at least partially, through targeting Notch1 signaling.

Psoriasiform skin disease in transgenic pigs with high-copy ectopic expression of human integrins α2 and β1

Psoriasis is a complex human-specific disease characterized by perturbed keratinocyte proliferation and a pro-inflammatory environment in the skin. Porcine skin architecture and immunity are very similar to that in humans, rendering the pig a suitable animal model for studying the biology and treatment of psoriasis. Expression of integrins, which is normally confined to the basal layer of the epidermis, is maintained in suprabasal keratinocytes in psoriatic skin, modulating proliferation and differentiation as well as leukocyte infiltration. Here, we generated minipigs co-expressing integrins α2 and β1 in suprabasal epidermal layers. Integrin-transgenic minipigs born into the project displayed skin phenotypes that correlated with the number of inserted transgenes. Molecular analyses were in good concordance with histological observations of psoriatic hallmarks, including hypogranulosis and T-lymphocyte infiltration. These findings mark the first creation of minipigs with a psoriasiform phenotype resembling human psoriasis and demonstrate that integrin signaling plays a key role in psoriasis pathology.

Summary: A cloned porcine disease model to advance topical treatment in the debilitating skin disorder psoriasis.

The diversity of myeloid immune cells shaping wound repair and fibrosis in the lung

In healthy circumstances the immune system coordinates tissue repair responses in a tight balance that entails efficient inflammation for removal of potential threats, proper wound closure, and regeneration to regain tissue function. Pathological conditions, continuous exposure to noxious agents, and even ageing can dysregulate immune responses after injury. This dysregulation can lead to a chronic repair mechanism known as fibrosis. Alterations in wound healing can occur in many organs, but our focus lies with the lung as it requires highly regulated immune and repair responses with its continuous exposure to airborne threats. Dysregulated repair responses can lead to pulmonary fibrosis but the exact reason for its development is often not known. Here, we review the diversity of innate immune cells of myeloid origin that are involved in tissue repair and we illustrate how these cell types can contribute to the development of pulmonary fibrosis. Moreover, we briefly discuss the effect of age on innate immune responses and therefore on wound healing and we conclude with the implications of current knowledge on the avenues for future research.

Differential Location and Distribution of Hepatic Immune Cells

The liver is one of the main organs in the body, performing several metabolic and immunological functions that are indispensable to the organism. The liver is strategically positioned in the abdominal cavity between the intestine and the systemic circulation. Due to its location, the liver is continually exposed to nutritional insults, microbiota products from the intestinal tract, and to toxic substances. Hepatocytes are the major functional constituents of the hepatic lobes, and perform most of the liver’s secretory and synthesizing functions, although another important cell population sustains the vitality of the organ: the hepatic immune cells. Liver immune cells play a fundamental role in host immune responses and exquisite mechanisms are necessary to govern the density and the location of the different hepatic leukocytes. Here we discuss the location of these pivotal cells within the different liver compartments, and how their frequency and tissular location can dictate the fate of liver immune responses.

miR-181a and miR-150 regulate dendritic cell immune inflammatory responses and cardiomyocyte apoptosis via targeting JAK1-STAT1/c-Fos pathway

The immune inflammatory response plays a crucial role in many cardiac pathophysiological processes, including ischaemic cardiac injury and the post-infarction repair process. MicroRNAs (miRNAs) regulate the development and function of dendritic cells (DCs), which are key players in the initiation and regulation of immune responses; however, the underlying regulatory mechanisms remain unclear. Here, we used the supernatants of necrotic primary cardiomyocytes (Necrotic-S) to mimic the myocardial infarction (MI) microenvironment to investigate the role of miRNAs in the regulation of DC-mediated inflammatory responses. Our results showed that Necrotic-S up-regulated the DC maturation markers CD40, CD83 and CD86 and increased the production of inflammatory cytokines, concomitant with the up-regulation of miR-181a and down-regulation of miR-150. Necrotic-S stimulation activated the JAK/STAT pathway and promoted the nuclear translocation of c-Fos and NF-κB p65, and silencing of STAT1 or c-Fos suppressed Necrotic-S-induced DC maturation and inflammatory cytokine production. The effects of Necrotic-S on DC maturation and inflammatory responses, its activation of the JAK/STAT pathway and the induction of cardiomyocyte apoptosis under conditions of hypoxia were suppressed by miR-181a or miR-150 overexpression. Taken together, these data indicate that miR-181a and miR-150 attenuate DC immune inflammatory responses via JAK1-STAT1/c-Fos signalling and protect cardiomyocytes from cell death under conditions of hypoxia.

Absence of Batf3 results in reduced liver pathology in mice infected with Schistosoma japonicum

Background

The involvement of CD8⁺T cells in schistosomiasis is being increasingly appreciated, but the underlying mechanism is not well defined.

Results

In this study, we showed that the absence of Batf3 alleviated liver damage in Batf3^−/− mice infected with S. japonicum. We found alleviated liver granulomatous inflammation in Batf3^−/− mice with schistosomiasis japonica could not be attributed to the difference in schistosome egg or worm burden. The stronger Tc1 cell responses observed in Batf3^−/− mice suggested that the deletion of Batf3 resulted in more activation of CD8⁺T cells unexpectedly during the natural infection of schistosomes. We detected a small amount of CD8α⁺ DCs in the spleen of Batf3^−/− mice at 9w post-infection. This small amount of newly generated CD8α⁺ DCs might contribute to enhanced activation of CD8⁺T cells via cross-presentation and activation which then attenuate hepatic pathological damage found in Batf3^−/− mice.

Conclusions

Our study provides evidence that Batf3 is associated with the immunoregulation of the liver granuloma formation, which may confer a new options for schistosomiasis treatment.

Radiation-induced decrease of CD8+ dendritic cells contributes to Th1/Th2 shift

Exposure to ionizing radiation (IR) often reduce the helper T (Th) 1 like function, resulting in a Th1/Th2 imbalance, which could affect the efficacy of cancer radiotherapy. As the most potent antigen presenting cells, dendritic cells (DC) can be divided into several subsets with specialized function. However, there is no literature covering the changes of DC subsets and their roles in immune regulation in response to IR. In the present study, we were aimed to investigate the changes of DC subsets after IR and its relationship with Th1/Th2 immunity. We found a significant decrease of BDCA3+DC in the blood of patients treated with radiotherapy. CD8+DC, a mouse equivalent of human BDCA3+DC, was also found decreased in mice spleen, peripheral blood and lymph node tissues after irradiation. As CD8+DC mainly induce Th1 immunity, we tested the changes of Th1/Th2 response and found that IR caused a repression of Th1 immunity, indicating a possible role of CD8+DC in radiation-induced Th1/Th2 imbalance. We also found that a CD8+DC-inducing cytokine, Fms-like tyrosine kinase 3 ligand (FLT3 ligand), restored CD8+DC and reversed Th1/Th2 shift. And then we found that bone marrow cells from irradiated mice differentiated into less CD8+DC, which was also protected by FLT3 ligand. In conclusion, our data showed that IR induced a decrease of CD8+DC and Th1/Th2 shift, which was reversed by Flt3 ligand treatment, suggesting a novel mechanism for radiation-induced immunosuppression.

CD1- and CD1+ porcine blood dendritic cells are enriched for the orthologues of the two major mammalian conventional subsets

Conventional dendritic cells (cDC) are professional antigen-presenting cells that induce immune activation or tolerance. Two functionally specialised populations, termed cDC1 and cDC2, have been described in humans, mice, ruminants and recently in pigs. Pigs are an important biomedical model species and a key source of animal protein; therefore further understanding of their immune system will help underpin the development of disease prevention strategies. To characterise cDC populations in porcine blood, DC were enriched from PBMC by CD14 depletion and CD172a enrichment then stained with lineage mAbs (Lin; CD3, CD8α, CD14 and CD21) and mAbs specific for CD172a, CD1 and CD4. Two distinct porcine cDC subpopulations were FACSorted CD1^- cDC (Lin^-CD172⁺ CD1^-CD4^-) and CD1⁺ cDC (Lin^-CD172a⁺ CD1⁺ CD4^-), and characterised by phenotypic and functional analyses. CD1⁺ cDC were distinct from CD1^- cDC, expressing higher levels of CD172a, MHC class II and CD11b. Following TLR stimulation, CD1⁺ cDC produced IL-8 and IL-10 while CD1^- cDC secreted IFN-α, IL-12 and TNF-α. CD1^- cDC were superior in stimulating allogeneic T cell responses and in cross-presenting viral antigens to CD8 T cells. Comparison of transcriptional profiles further suggested that the CD1^- and CD1⁺ populations were enriched for the orthologues of cDC1 and cDC2 subsets respectively.

Direct Delivery of Antigens to Dendritic Cells via Antibodies Specific for Endocytic Receptors as a Promising Strategy for Future Therapies

Dendritic cells (DCs) are the most potent professional antigen presenting cells and are therefore indispensable for the control of immunity. The technique of antibody mediated antigen targeting to DC subsets has been the basis of intense research for more than a decade. Many murine studies have utilized this approach of antigen delivery to various kinds of endocytic receptors of DCs both in vitro and in vivo. Today, it is widely accepted that different DC subsets are important for the induction of select immune responses. Nevertheless, many questions still remain to be answered, such as the actual influence of the targeted receptor on the initiation of the immune response to the delivered antigen. Further efforts to better understand the induction of antigen-specific immune responses will support the transfer of this knowledge into novel treatment strategies for human diseases. In this review, we will discuss the state-of-the-art aspects of the basic principles of antibody mediated antigen targeting approaches. A table will also provide a broad overview of the latest studies using antigen targeting including addressed DC subset, targeted receptors, outcome, and applied coupling techniques.

Culture and Identification of Mouse Bone Marrow-Derived Dendritic Cells and Their Capability to Induce T Lymphocyte Proliferation

Background

The aim of this study was to establish a culture method for mouse dendritic cells (DCs) in vitro and observe their morphology at different growth stages and their ability to induce the proliferation of T lymphocytes.

Material/Methods

Granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) were used in combination to induce differentiation of mouse bone marrow (BM) mononucleocytes into DCs. The derived DCs were then assessed for morphology, phenotype, and function.

Results

The mouse BM-derived mononucleocytes had altered cell morphology 3 days after induction by GM-CSF and IL-4 and grew into colonies. Typical dendrites appeared 8 days after induction. Many mature DCs were generated, with typical dendritic morphology observed under scanning electron microscopy. Expression levels of CD11c, a specific marker of BM-derived DCs, and of co-stimulatory molecules such as CD40, CD80, CD86, and MHC-II were elevated in the mature DCs. Furthermore, the mature DCs displayed a strong potency in stimulating the proliferation of syngenic or allogenic T lymphocytes.

Conclusions

Mouse BM-derived mononucleocytes cultured in vitro can produce a large number of DCs, as well as immature DCs, in high purity. The described in vitro culture method lays a foundation for further investigations of anti-tumor vaccines.

In vivo and in vitro analyses of α-galactosylceramide uptake by conventional dendritic cell subsets using its fluorescence-labeled derivative

Conventional dendritic cells (cDCs) present α-galactosylceramide (αGC) to invariant natural killer T (iNKT) cells through CD1d. Among cDC subsets, CD8(+) DCs efficiently induce IFN-γ production in iNKT cells. Using fluorescence-labeled αGC, we showed that CD8(+) DCs incorporated larger amounts of αGC and kept it intact longer than CD8(-) DCs. Histological analyses revealed that Langerin(+)CD8(+) DCs in the splenic marginal zone, which was the unique equipment to capture blood-borne antigens, preferably incorporated αGC, and the depletion of Langerin(+) cells decreased IFN-γ and IL-12 production in response to αGC. Furthermore, splenic Langerin(+)CD8(+) DCs expressed more membrane-bound CXCL16, which possibly anchored iNKT cells in the marginal zone, than CD8(-) DCs. Collectively, it is suggested that the cellular properties and localization of CD8(+) DCs are important for stimulation of iNKT cells by αGC.

Tolerogenic Dendritic Cells on Transplantation: Immunotherapy Based on Second Signal Blockage

Dendritic cells (DCs), the most important professional antigen-presenting cells (APC), play crucial role in both immunity and tolerance. It is well known that DCs are able to mount immune responses against foreign antigens and simultaneously tolerate self-antigens. Since DCs can be modulated depending on the surrounding microenvironment, they can act as a bridge between innate and adaptive immunity. However, the mechanisms that support this dual role are not entirely clear. Recent studies have shown that DCs can be manipulated ex vivo in order to trigger their tolerogenic profile, what can be a tool to be used in clinical trials aiming the treatment of various diseases and the prevention of transplant rejection. In this sense, the blockage of costimulatory molecules on DC, in the attempt of inhibiting the second signal in the immunological synapse, can be considered as one of the main strategies under development. This review brings an update on current therapies using tolerogenic dendritic cells modulated with costimulatory blockers with the aim of reducing transplant rejection. However, although there are current clinical trials using tolerogenic DC to treat allograft rejection, the actual challenge is to modulate these cells in order to maintain a permanent tolerogenic profile.

Plant components for immune modulation targeting dendritic cells: implication for therapy

Medicinal plant utilization is as old as human life. There are thousands of herbs consumed for medicinal purposes all over the world, especially in east. Their value has not decreased over time and many modern pharmaceuticals have originated from traditional medicinal plants. Studying the reason for their influence is an attractive field of medicine. Among various types of herbs, some function via their immunomodulatory effects. Experiments have shown the regulatory influences of several plants on each type of immune cell, including T cells, B cells, dendritic cells (DCs), macrophages and NK cells. Because of the prominent role of DCs in antigen presentation as the major APC, this review summarizes the immunomodulatory effects of some plants performed through DC effects.

An immunology primer for computational modelers

The immune system is designed to protect an organism from infection and damage caused by a pathogen. A successful immune response requires the coordinated function of multiple cell types and molecules in the innate and adaptive immune systems. Given the complexity of the immune system, it would be advantageous to build computational models to better understand immune responses and develop models to better guide the design of immunotherapies. Often, researchers with strong quantitative backgrounds do not have formal training in immunology. Therefore, the goal of this review article is to provide a brief primer on cellular immunology that is geared for computational modelers.

Aging impairs peritoneal but not bone marrow-derived macrophage phagocytosis

Aging results in deterioration of the immune system, which is associated with increased susceptibility to infection and impaired wound healing in the elderly. Phagocytosis is an essential process in both wound healing and immune defence. As such, age-related impairments in phagocytosis impact on the health of the elderly population. Phagocytic efficiency in peritoneal macrophages, bone marrow-derived macrophages and bone marrow monocytes from young and old mice was investigated. Aging significantly impaired phagocytosis by peritoneal macrophages, both in vitro and in vivo. However, bone marrow-derived macrophages and bone marrow monocytes did not exhibit age-related impairments in phagocytosis, suggesting no intrinsic defect in these cells. We sought to investigate underlying mechanisms in age-related impairments in phagocytosis by peritoneal macrophages. We hypothesized that microenvironmental factors in the peritoneum of old mice impaired macrophage phagocytosis. Indeed, macrophages from young mice injected into the peritoneum of old mice exhibited impaired phagocytosis. Proportions of peritoneal immune cells were characterized, and striking increases in numbers of T cells, B1 and B2 cells were observed in the peritoneum of old mice compared with young mice. In addition, B cell-derived IL-10 was increased in resting and LPS-activated peritoneal cell cultures from old mice. These data demonstrate that aging impairs phagocytosis by tissue-resident peritoneal macrophages, but not by bone marrow-derived macrophages/monocytes, and suggest that age-related defects in macrophage phagocytosis may be due to extrinsic factors in the tissue microenvironment. As such, defects may be reversible and macrophages could be targeted therapeutically in order to boost immune function in the elderly.

CXCL17 is a major chemotactic factor for lung macrophages

Chemokines are a superfamily of chemotactic cytokines that direct the movement of cells throughout the body under homeostatic and inflammatory conditions. The mucosal chemokine CXCL17 was the last ligand of this superfamily to be characterized. Several recent studies have provided greater insight into the basic biology of this chemokine and have implicated CXCL17 in several human diseases. We sought to better characterize CXCL17's activity in vivo. To this end, we analyzed its chemoattractant properties in vivo and characterized a Cxcl17 (-/-) mouse. This mouse has a significantly reduced number of macrophages in its lungs compared with wild-type mice. In addition, we observed a concurrent increase in a new population of macrophage-like cells that are F4/80(+)CDllc(mid). These results indicate that CXCL17 is a novel macrophage chemoattractant that operates in mucosal tissues. Given the importance of macrophages in inflammation, these observations strongly suggest that CXCL17 is a major regulator of mucosal inflammatory responses.

Effects of virulent and attenuated transmissible gastroenteritis virus on the ability of porcine dendritic cells to sample and present antigen

Virulent transmissible gastroenteritis virus (TGEV) results in an acute, severe pathology and high mortality in piglets, while attenuated TGEV only causes moderate clinical reactions. Dendritic cells (DCs), through uptake and presentation of antigens to T cells, initiate distinct immune responses to different infections. In this study, an attenuated TGEV (STC3) and a virulent TGEV (SHXB) were used to determine whether porcine DCs play an important role in pathogenetic differences between these two TGEVs. Our results showed that immature and mature monocyte-derived dendritic cells (Mo-DCs) were susceptible to infection with SHXB and STC3. However, only SHXB inhibited Mo-DCs to activate T-cell proliferation by down-regulating the expression of cell–surface markers and the secretion of cytokines in vitro. In addition, after 48 h of SHXB infection, there was the impairment in the ability of porcine intestinal DCs to sample the antigen, to migrate from the villi to the lamina propria and to activate T-cell proliferation in vivo. In contrast, these abilities of intestinal DCs were enhanced in STC3-infected piglets. In conclusion, our results show that SHXB significantly impaired the functions of Mo-DCs and intestinal DCs in vitro and in vivo, while STC3 had the opposite effect. These differences may underlie the pathogenesis of virulent and attenuated TGEV in piglets, and could help us to develop a better strategy to prevent virulent TGEV infection.

Continuous retinoic acid induces the differentiation of mature regulatory monocytes but fails to induce regulatory dendritic cells

BACKGROUND

Myeloid cells (MC) have potent immunoregulatory abilities that can be therapeutically useful to treat inflammatory disease. However, the factors which promote regulatory myeloid cell differentiation remain poorly understood. We have previously shown that estriol (E3) induces mature regulatory dendritic cells in vivo. To determine whether additional steroid hormones could induce mature regulatory myeloid cells, we investigated the effects of retinoic acid (RA) on MCs. Retinoic acid is a steroid hormone important in regulating mucosal immunity in the gut and promoting myeloid differentiation. We hypothesized that the presence of RA during differentiation would promote the formation of mature regulatory myeloid cells (MCregs).

METHODS

To determine RA's ability to induce regulatory myeloid cells, we differentiated bone marrow progenitor cells with granulocytic-macrophage colony-stimulating factor (GM-CSF) under the influence of RA. We found that day 7 MCs differentiated in the presence of RA had an increase in the percent positive and relative expression levels of both maturation (CD80, CD86, and MHCII) and inhibitory (PD-L1 and PD-L2) markers compared to control cells. Functionally, these day 7 RA MCs expressed increased intracellular IL-10, induced regulatory T cells in vitro compared to controls and suppressed the proliferation of responder immune cells even after inflammatory challenge with LPS.

CONCLUSION

RA induced mature regulatory myeloid cells that were suppressive and had a CD11b+ CD11c-Ly6C low/intermediate monocyte phenotype. Surprisingly, RA CD11c+ dendritic cells were not suppressive and could contribute to enhanced proliferation. These results suggest that continuous RA has unique effects on different myeloid populations during monopoeisis and dendropoiesis and promotes a population of regulatory monocytes.

Quantitative immunophenotypic analysis of antigen-presenting cells involved in ectromelia virus antigen presentation in BALB/c and C57BL/6 mice

During mousepox in resistant (C57BL/6) or susceptible (BALB/c) strains of mice, stimulation of Th1 or Th2 cytokine immune response, respectively, is observed. Because mechanisms of different polarization of T cells remain elusive, in this study, we quantitatively assessed the phenotype of antigen-presenting cells (APCs) involved in ectromelia virus (ECTV) antigen presentation and cluster formation with effector cells in secondary lymphoid organs of BALB/c and C57BL/6 mice. We showed that both strains of mice display similar dynamics and kinetics of viral antigen presentation by CD11c(+) , CD11b(+) , and CD19(+) cells. CD11c(+) and CD11b(+) cells highly participated in viral antigen presentation during all stages of mousepox, whereas CD19(+) cells presented viral peptides later in infection. The main population of dendritic cells (DCs) engaged in ECTV antigen presentation and cell junction formation with effector cells was a population of myeloid CD11b(+) DCs (mDCs). We suggest that, on the one hand, ECTV may differentially affect the functions of APCs depending on the strain of mice. On the other hand, we suggest that some types of APCs, such as mDCs or other DCs subsets, have different abilities to direct the shape of immune response depending on the host resistance to mousepox.

Innate immunity modulation by the IL-33/ST2 system in intestinal mucosa

Innate immunity prevents pathogens from entering and spreading within the body. This function is especially important in the gastrointestinal tract and skin, as these organs have a large surface contact area with the outside environment. In the intestine, luminal commensal bacteria are necessary for adequate food digestion and play a crucial role in tolerance to benign antigens. Immune system damage can create an intestinal inflammatory response, leading to chronic disease including inflammatory bowel diseases (IBD). Ulcerative colitis (UC) is an IBD of unknown etiology with increasing worldwide prevalence. In the intestinal mucosa of UC patients, there is an imbalance in the IL-33/ST2 axis, an important modulator of the innate immune response. This paper reviews the role of the IL-33/ST2 system in innate immunity of the intestinal mucosa and its importance in inflammatory bowel diseases, especially ulcerative colitis.

Assessment of an imiquimod-induced psoriatic mouse model in relation to oxidative stress

Psoriasis is a chronic inflammatory skin disease that is thought to be related to oxidative stress. Much progress has been made in understanding the pathophysiology of psoriasis in relation to the immunologic and antioxidant systems. However, this progress has been hindered by the lack of an appropriate animal model for psoriasis. Recently, imiquimod (IQM)-induced psoriasis-like cutaneous inflammation has been reported in mice and humans. We verified the usefulness of an IQM-induced mouse model in relation to the antioxidant system. BALB/C female mice at 8-10 weeks of age were treated with IQM cream in this study. We analyzed clinical and histopathological changes. Increased reactive oxygen species production was measured by glutathione assay. Levels of myeloperoxidase (MPO) and superoxide dismutase-1 (SOD1) were determined by western blotting and immunohistochemical analyses. The activity of SOD was measured by a SOD activity assay kit. Application of IQM-induced skin inflammation similar to psoriasis in clinical and histopathological aspects. Accumulation of immune cells was confirmed. Oxidative stress was increased, the antioxidant enzyme MPO levels were increased, and both SOD levels and activity were decreased. In conclusion, the IQM-induced mouse model showed an aberrant antioxidant system. Levels of MPO and oxidative stress were increased, and the level and activity of SOD were decreased. Since this model seemed to be an appropriate model for psoriasis, it can be used to further study the pathogenic role of redox imbalance in psoriasis.

Acellular vaccines for ovine brucellosis: a safer alternative against a worldwide disease

Ovine brucellosis is a very contagious zoonotic disease distributed worldwide and constitutes a very important zoosanitary and economic problem. The control of the disease includes animal vaccination and slaughter of infected flocks. However, the commercially available vaccine in most countries is based on the attenuated strain Brucella melitensis Rev 1, which presents important safety drawbacks. This review is focused on the most recent and promising acellular vaccine proposals.

Tumor antigen-pulsed CD8α(+) dendritic cells induce T cell-mediated graft-versus-tumor effect in vitro

The graft-versus-tumor (GVT) effect of T cells induced by tumor antigen-pulsed CD8α(+) dendritic cells (DCs) in vitro was investigated in this study. Immature CD8α(+) DCs were prepared from C57BL/6 (H-2(b)) bone marrow cells by using a cytokine cocktail. On the 3rd day of culture, CD8α(+) DCs were pulsed by allogeneic (Balb/c, H-2(d)) EL9611 leukemia antigen, or RM-1 syngeneic prostate cancer antigen, with the concentration series of 0, 2.5, 5.0, 10.0, 20.0 μg/mL, respectively, then antigen-loaded immature CD8α(+) DCs were co-cultured with syngeneic T cells according to the DC/T ratio of 1:1, 2:1 and 4:1. T cell proliferation was measured by MTT assay. Cytokines including interferon gamma (IFN-γ) and interleukin-10 (IL-10) in CD8α(+) DCs and T co-culture supernatant were detected by using ELISA. Cytotoxic effect of antigen-specific T cells was tested by LDH release assay. Conventional mature DCs (mDCs) induced from C57BL/6 (H-2(b)) bone marrow cells by using granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) served as a control. The results showed that the proliferative activity of T cells stimulated by CD8α(+) DCs loaded with allogeneic or syngeneic tumor antigen was augmented with the CD8α(+) DC/T ratio increased (P<0.05). When antigen concentration ≤ 5 μg/mL and CD8α(+) DC/T ratio ≤ 2:1, the ability of CD8α(+) DCs to stimulate T cell proliferation was higher than mDC control in allogeneic tumor antigen-pulsed groups (P<0.05), but not in syngeneic tumor antigen-pulsed groups (P>0.05). The level of IFN-γ and IL-10 in CD8α(+) DCs and T cell co-culture supernatant were increased in both allogeneic and syngeneic antigen-pulsed groups (P<0.05), and the cytokine level was higher in allogeneic antigen-pulsed groups than in syngeneic antigen groups when the CD8α(+) DC/T was 1:1 or 2:1 (P<0.05). There existed a negative correlation between the level of IL-10 and T cell proliferation. T cell cytotoxicity assay showed that when CD8α(+) DCs were pulsed with allogeneic tumor antigen, the maximal T cell killing efficiency could reach (100±7.7)%, whereas syngeneic tumor antigen-pulsed group had only (65.0±3.4)%. It was concluded that syngeneic and allogeneic tumor antigen-pulsed immature CD8α(+) DCs could stimulate T cells to exert the GVT effect in vitro, and the GVT effect was more obvious with allogeneic tumor antigen than with syngeneic tumor antigen. The optimal condition was low allogeneic tumor antigen pulsation (≤ 5 μg/mL) and low CD8α(+) DC/T ratio (1:1 and 2:1).

IFN regulatory factors 4 and 8 expression in the NOD mouse

Dendritic cells (DCs) contribute to islet inflammation and its progression to diabetes in NOD mouse model and human. DCs play a crucial role in the presentation of autoantigen and activation of diabetogenic T cells, and IRF4 and IRF8 are crucial genes involved in the development of DCs. We have therefore investigated the expression of these genes in splenic DCs during diabetes progression in NOD mice. We found that IRF4 expression was upregulated in splenocytes and in splenic CD11c⁺ DCs of NOD mice as compared to BALB/c mice. In contrast, IRF8 gene expression was higher in splenocytes of NOD mice whereas its expression was similar in splenic CD11c⁺ DCs of NOD and BALB/c mice. Importantly, levels of IRF4 and IRF8 expression were lower in tolerogenic bone marrow derived DCs (BMDCs) generated with GM-CSF as compared to immunogenic BMDCs generated with GM-CSF and IL-4. Analysis of splenic DCs subsets indicated that high expression of IRF4 was associated with increased levels of CD4⁺CD8α⁻IRF4⁺CD11c⁺ DCs but not CD4⁻CD8α⁺IRF8⁺CD11c⁺ DCs in NOD mice. Our results showed that IRF4 expression was up-regulated in NOD mice and correlated with the increased levels of CD4⁺CD8α⁻ DCs, suggesting that IRF4 may be involved in abnormal DC functions in type 1 diabetes in NOD mice.

Genome-wide expression profiling of five mouse models identifies similarities and differences with human psoriasis

Development of a suitable mouse model would facilitate the investigation of pathomechanisms underlying human psoriasis and would also assist in development of therapeutic treatments.

However, while many psoriasis mouse models have been proposed, no single model recapitulates all features of the human disease, and standardized validation criteria for psoriasis mouse models have not been widely applied. In this study, whole-genome transcriptional profiling is used to compare gene expression patterns manifested by human psoriatic skin lesions with those that occur in five psoriasis mouse models (K5-Tie2, imiquimod, K14-AREG, K5-Stat3C and K5-TGFbeta1). While the cutaneous gene expression profiles associated with each mouse phenotype exhibited statistically significant similarity to the expression profile of psoriasis in humans, each model displayed distinctive sets of similarities and differences in comparison to human psoriasis. For all five models, correspondence to the human disease was strong with respect to genes involved in epidermal development and keratinization. Immune and inflammation-associated gene expression, in contrast, was more variable between models as compared to the human disease. These findings support the value of all five models as research tools, each with identifiable areas of convergence to and divergence from the human disease. Additionally, the approach used in this paper provides an objective and quantitative method for evaluation of proposed mouse models of psoriasis, which can be strategically applied in future studies to score strengths of mouse phenotypes relative to specific aspects of human psoriasis.

Distinct responses of splenic dendritic cell subsets to infection with Listeria monocytogenes: maturation phenotype, level of infection, and T cell priming capacity ex vivo

To determine the relative contributions of DC subsets in the development of protective immunity to Listeria monocytogenes we examined the relationship between maturation, bacterial burden, and T cell priming capacity of four well characterized subsets of splenic DC following infection with Lm. CD8α(+), CD4(+), and CD8α(-)CD4(-) DC and the B220(+) plasmacytoid DC (pDC) were compared for abundance and costimulatory molecule expression at 24, 48, and 72h post i.v. infection. We further determined the bacterial burden associated with each DC subset and their relative capacities to prime CD8(+) T cells at 24hpi. The CD8α(+) DC displayed the highest level of maturation, association with live bacteria, and T cell activation potential. Second, the CD4(+) DC were also mature, yet were associated with fewer bacteria, and stimulated T cell proliferation, but not IFN-γ production. The CD8α(-)CD4(-) DC showed a modest maturation response and were associated with a high number of bacteria, but failed to induce T cell proliferation ex vivo. pDC displayed a strong maturation response, but were not associated with detectable bacteria and also failed to stimulate T cell activation. Finally, we measured the cytokine responses in these subsets and determined that IL-12 was produced predominantly by the CD8(+) DC, correlating with the ability of this subset DC to induce IFN-γ production in T cells. We conclude that Listeria-specific CD8(+) T cell activation in the spleen is most effectively achieved by infection-induced maturation of the CD8α(+) DC subset.

Limited transplantation of antigen-expressing hematopoietic stem cells induces long-lasting cytotoxic T cell responses

Harnessing the ability of cytotoxic T lymphocytes (CTLs) to recognize and eradicate tumor or pathogen-infected cells is a critical goal of modern immune-based therapies. Although multiple immunization strategies efficiently induce high levels of antigen-specific CTLs, the initial increase is typically followed by a rapid contraction phase resulting in a sharp decline in the frequency of functional CTLs. We describe a novel approach to immunotherapy based on a transplantation of low numbers of antigen-expressing hematopoietic stem cells (HSCs) following nonmyeloablative or partially myeloablative conditioning. Continuous antigen presentation by a limited number of differentiated transgenic hematopoietic cells results in an induction and prolonged maintenance of fully functional effector T cell responses in a mouse model. Recipient animals display high levels of antigen-specific CTLs four months following transplantation in contrast to dendritic cell-immunized animals in which the response typically declines at 4–6 weeks post-immunization. Majority of HSC-induced antigen-specific CD8⁺ T cells display central memory phenotype, efficiently kill target cells in vivo, and protect recipients against tumor growth in a preventive setting. Furthermore, we confirm previously published observation that high level engraftment of antigen-expressing HSCs following myeloablative conditioning results in tolerance and an absence of specific cytotoxic activity in vivo. In conclusion, the data presented here supports potential application of immunization by limited transplantation of antigen-expressing HSCs for the prevention and treatment of cancer and therapeutic immunization of chronic infectious diseases such as HIV-1/AIDS.

Innate immune responses to human rotavirus in the neonatal gnotobiotic piglet disease model

Intestinal and systemic dendritic cell (DC) frequencies, serum and small intestinal content cytokines and uptake/binding of human rotavirus (HRV) virus-like particles (VLP) were studied in HRV acutely infected or mock-inoculated neonatal gnotobiotic piglets. Intestinal, mesenteric lymph node (MLN) and splenic plasmacytoid DCs (pDCs), conventional DCs (cDCs) and macrophages/monocytes were assessed by flow cytometry. In infected pigs, serum and small intestinal content interferon-α (IFN-α) were highest, interleukin-12 (IL-12) was lower and IL-10, tumour necrosis factor-α and IL-6 were minimal. Compared with mock-inoculated piglets, frequencies of total intestinal DCs were higher; splenic and MLN DC frequencies were lower. Most intestinal pDCs, but few cDCs, were IFN-α(+) and intestinal macrophages/monocytes were negative for IFN-α. Serum IFN-α levels and IFN-α(+) intestinal pDCs were highly correlated, suggesting IFN-α production in vivo by intestinal pDCs (r=0·8; P<0·01). The intestinal pDCs and cDCs, but not intestinal macrophages/monocytes, of HRV-infected piglets showed significantly lower VLP uptake/binding compared with mock-inoculated piglets, suggesting higher activation of pDCs and cDCs in infected piglets. Both intestinal pDCs and cDCs were activated (IFN-α(+) and lower VLP binding) after HRV infection, suggesting their role in induction of HRV-specific immunity. Dose-effects of HRV on serum IFN-α and IFN-α(+) DCs were studied by infecting piglets with 100-fold higher HRV dose. A high dose increased parameters associated with inflammation (diarrhoea, intestinal pathology) but serum IFN-α and IFN-α(+) DCs were similar between both groups. The pDCs have both anti- and pro-inflammatory functions. Stimulation of the anti-inflammatory effects of pDCs after the high dose, without increasing their pro-inflammatory impacts, may be critical to reduce further immunopathology during HRV infection.

Bcl6 is required for the development of mouse CD4+ and CD8α+ dendritic cells

Th2-type inflammation spontaneously shown in Bcl6-knockout (KO) mice is mainly caused by bone marrow (BM)-derived nonlymphoid cells. However, the function of dendritic cells (DCs) in Bcl6-KO mice has not been reported. We show in this article that the numbers of CD4(+) conventional DCs (cDCs) and CD8α(+) cDCs, but not of plasmacytoid DCs, were markedly reduced in the spleen of Bcl6-KO mice. Generation of cDCs from DC progenitors in BM cells was perturbed in the spleen of irradiated wild-type (WT) mice transferred with Bcl6-KO BM cells, indicating an intrinsic effect of Bcl6 in cDC precursors. Although cDC precursors were developed in a Bcl6-KO BM culture with Fms-like tyrosine kinase 3 ligand, the cDC precursors were more apoptotic than WT ones. Also p53, one of the molecular targets of Bcl6, was overexpressed in the precursors. The addition of a p53 inhibitor to Bcl6-KO BM culture protected apoptosis, suggesting that Bcl6 is required by cDC precursors for survival by controlling p53 expression. Furthermore, large numbers of T1/ST2(+) Th2 cells were naturally developed in the spleen of Bcl6-KO mice. Th2 skewing was accelerated in the culture of WT CD4 T cells stimulated with Ags and LPS-activated Bcl6-KO BM-derived DCs, which produced more IL-6 and less IL-12 than did WT DCs; the addition of anti-IL-6 Abs to the culture partially abrogated the Th2 skewing. These results suggest that Bcl6 is required in cDC precursors for survival and in activated DCs for modulating the cytokine profile.

MicroRNA-148/152 impair innate response and antigen presentation of TLR-triggered dendritic cells by targeting CaMKIIα

MicroRNAs (miRNAs) are involved in the regulation of immunity, including the lymphocyte development and differentiation, and inflammatory cytokine production. Dendritic cells (DCs) play important roles in linking innate and adaptive immune responses. However, few miRNAs have been found to regulate the innate response and APC function of DCs to date. Calcium/calmodulin-dependent protein kinase II (CaMKII), a major downstream effector of calcium (Ca(2+)), has been shown to be an important regulator of the maturation and function of DCs. Our previous study showed that CaMKIIα could promote TLR-triggered production of proinflammatory cytokines and type I IFN. Inspired by the observations that dicer mutant Drosophila display defect in endogenous miRNA generation and higher CaMKII expression, we wondered whether miRNAs can regulate the innate response and APC function of DCs by targeting CaMKIIα. By predicting with software and confirming with functional experiments, we demonstrate that three members of the miRNA (miR)-148 family, miR-148a, miR-148b, and miR-152, are negative regulators of the innate response and Ag-presenting capacity of DCs. miR-148/152 expression was upregulated, whereas CaMKIIα expression was downregulated in DCs on maturation and activation induced by TLR3, TLR4, and TLR9 agonists. We showed that miR-148/152 in turn inhibited the production of cytokines including IL-12, IL-6, TNF-α, and IFN-β upregulation of MHC class II expression and DC-initiated Ag-specific T cell proliferation by targeting CaMKIIα. Therefore, miRNA-148/152 can act as fine-tuner in regulating the innate response and Ag-presenting capacity of DCs, which may contribute to the immune homeostasis and immune regulation.

Vitamin A deficiency alters splenic dendritic cell subsets and increases CD8(+)Gr-1(+) memory T lymphocytes in C57BL/6J mice

Vitamin A-deficient populations have impaired T cell-dependent antibody responses. Dendritic cells (DCs) are the most proficient antigen-presenting cells to naïve T cells. In the mouse, CD11b(+) myeloid DCs stimulate T helper (Th) 2 antibody immune responses, while CD8α(+) lymphoid DCs stimulate Th1 cell-mediated immune responses. Therefore, we hypothesized that vitamin A-deficient animals would have decreased numbers of myeloid DCs and unaffected numbers of lymphoid DCs. We performed dietary depletion of vitamin A in C57BL/6J male and female mice and used multicolor flow cytometry to quantify immune cell populations of the spleen, with particular focus on DC subpopulations. We show that vitamin A-depleted animals have increased polymorphonuclear neutrophils, lymphoid DCs, and memory CD8(+) T cells and decreased CD4(+) T lymphocytes. Therefore, vitamin A deficiency alters splenic DC subpopulations, which may contribute to skewed immune responses of vitamin A-deficient populations.

Directly transfected langerin+ dermal dendritic cells potentiate CD8+ T cell responses following intradermal plasmid DNA immunization

Dendritic cells (DCs) play a critical role in CD8(+) T cell priming following DNA vaccination. In contrast to other DNA injection routes or immunization with viral vectors, Ag presentation is delayed following needle injection of plasmid DNA into the skin. The contribution of various skin DC subsets to this process is not known. In this study, we show that dermal CD11c(+) cells are the most important transgene-expressing cells following immunization. Using langerin- diphtheria toxin receptor mice we demonstrated that langerin(+) dermal DCs (Ln(+) dDCs) were crucial for generating an optimal CD8(+) T cell response. Blocking migration of skin cells to the lymph node (LN) ablated immunogenicity, suggesting that migration of dDC subsets to the LN is essential for generating immunity. This migration generated a weak Ag-presenting activity in vivo until day 5 postimmunization, which then increased dramatically. We further found that Ln(+) dDCs and dDCs were the only DC populations directly presenting Ag to CD8(+) T cells ex vivo during the initial 8-d period postimmunization. This activity changed on the following days, when both skin DCs and LN-resident DCs were able to present Ag to CD8(+) T cells. Taken together, our in vivo and ex vivo results suggest that activation of CD8(+) T cells following intradermal plasmid DNA immunization depends on directly transfected Ln(+)dDCs and dDCs. Moreover, the type of DCs presenting Ag changed over time, with Ln(+)dDCs playing the major role in potentiating the initial CD8(+) T cell response.

Dendritic cell apoptosis: regulation of tolerance versus immunity

Dendritic cell (DC) apoptosis is an important event that regulates the balance between tolerance and immunity through multiple pathways, and defects in DC apoptosis can trigger autoimmunity. DC apoptosis is also associated with immunosuppression and has been observed under several pathologies and infections. Recent studies indicate that apoptotic DCs can also play an active role in induction of tolerance. This review discusses the regulatory pathways of DC apoptosis, stimuli inducing DC apoptosis, and the implications of DC apoptosis in the induction of immunosuppression and/or tolerance.

The regulatory role of dendritic cells in the induction and maintenance of T-cell tolerance

The induction and maintenance of T-cell tolerance to tissue antigens is essential to prevent autoimmunity. Combinations of central and peripheral mechanisms act in parallel to inactivated, eliminated or control autoreactive T cells. Both centrally and peripherally, a key requirement for self-tolerance is the presentation of self-antigens in a correct context. There is now evidence to suggest that dendritic cells (DCs) play a fundamental role in the development of central and peripheral tolerance. In this review, we summarize recent progress toward the definition of the multiple roles of DCs in these processes. We will also discuss the association between defects in the DC compartment and the development of autoimmune responses, with particular reference to DC deregulation in the context of type I diabetes.