Migration of human blood dendritic cells across endothelial cell monolayers: adhesion molecules and chemokines involved in subset-specific transmigration

Aberrant phenotype of circulating antigen presenting cells in giant cell arteritis and polymyalgia rheumatica

Background

Giant Cell Arteritis (GCA) and Polymyalgia Rheumatica (PMR) are overlapping inflammatory diseases. Antigen-presenting cells (APCs), including monocytes and dendritic cells (DCs), are main contributors to the immunopathology of GCA and PMR. However, little is known about APC phenotypes in the peripheral blood at the time of GCA/PMR diagnosis.

Methods

APCs among peripheral blood mononuclear cells (PBMCs) of treatment-naive GCA and PMR patients were compared to those in age- and sex-matched healthy controls (HCs) using flow cytometry (n=15 in each group). We identified three monocyte subsets, and three DC subsets: plasmacytoid DCs (pDCs), CD141+ conventional DCs (cDC1) and CD1c+ conventional DCs (cDC2). Each of these subsets was analyzed for expression of pattern recognition receptors (TLR2, TLR4), immune checkpoints (CD86, PDL1, CD40) and activation markers (HLA-DR, CD11c).

Results

t-SNE plots revealed a differential clustering of APCs between GCA/PMR and HCs. Further analyses showed shifts in monocyte subsets and a lower proportion of the small population of cDC1 cells in GCA/PMR, whereas cDC2 proportions correlated negatively with CRP (r=-0.52). Classical monocytes of GCA/PMR patients show reduced expression of TLR2, HLA-DR, CD11c, which was in contrast to non-classical monocytes that showed higher marker expression. Additionally, single cell RNA sequencing in GCA patients identified a number of differentially expressed genes related to inflammation and metabolism in APCs.

Conclusion

Circulating non-classical monocytes display an activated phenotype in GCA/PMR patients at diagnosis, whereas classical monocytes show reduced expression of activation markers. Whether these findings reflect APC migration patterns or the effects of long-term inflammation remains to be investigated.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

Dendritic Cell-Targeted Therapies to Treat Neurological Disorders

Dendritic cells (DCs) are the immune system's highly specialized antigen-presenting cells. When DCs are sluggish and mature, self-antigen presentation results in tolerance; however, when pathogen-associated molecular patterns stimulate mature DCs, antigen presentation results in the development of antigen-specific immunity. DCs have been identified in various vital organs of mammals (e.g., the skin, heart, lungs, intestines, and spleen), but the brain has long been thought to be devoid of DCs in the absence of neuroinflammation. However, neuroinflammation is becoming more recognized as a factor in a variety of brain illnesses. DCs are present in the brain parenchyma in trace amounts under healthy circumstances, but their numbers rise during neuroinflammation. New therapeutics are being developed that can reduce dendritic cell immunogenicity by inhibiting pro-inflammatory cytokine production and T cell co-stimulatory pathways. Additionally, innovative ways of regulating dendritic cell growth and differentiation and harnessing their tolerogenic capability are being explored. Herein, we described the function of dendritic cells in neurological disorders and discussed the potential for future therapeutic techniques that target dendritic cells and dendritic cell-related targets in the treatment of neurological disorders.

HIF‑1α in cerebral ischemia (Review)

Cerebral ischemic injury may lead to a series of serious brain diseases, death or different degrees of disability. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-sensitive transcription factor, which mediates the adaptive metabolic response to hypoxia and serves a key role in cerebral ischemia. HIF-1α is the main molecule that responds to hypoxia. HIF-1α serves an important role in the development of cerebral ischemia by participating in numerous processes, including metabolism, proliferation and angiogenesis. The present review focuses on the endogenous protective mechanism of cerebral ischemia and elaborates on the role of HIF-1α in cerebral ischemia. In addition, it focuses on cerebral ischemia interventions that act on the HIF-1α target, including biological factors, non-coding RNA, hypoxic-ischemic preconditioning and drugs, and expands upon the measures to strengthen the endogenous compensatory response to support HIF-1α as a therapeutic target, thus providing novel suggestions for the treatment of cerebral ischemia.

Immunotherapy against the radial glia marker GLAST effectively triggers specific antitumor effectors without autoimmunity

The glutamate-aspartate transporter GLAST is a radial glia marker that is highly expressed in GL261 stem-like cells (GSCs). To target GLAST, we treated glioma-bearing mice with three subcutaneous injections of four GLAST peptides emulsified with Montanide ISA-51 in association with granulocyte macrophage colony-stimulating factor (GM-CSF) injections. Vaccination with GLAST peptides significantly prolonged survival, effectively enhanced systemic T-cell and NK-cell responses and promoted robust antitumor cytotoxicity. GLAST expression significantly decreased in gliomas from immunized mice, as evaluated by histological analysis and real-time PCR (RT-PCR). Moreover, the immunization protocol led to the upregulation of interferonγ (IFNγ) and tumor necrosis factorα (TNFα) as well as to the downregulation of transforming growth factor (TGF) β1 and β2 in the tumor. Beyond these changes, gliomas from immunized mice exhibited an increased recruitment of NK cells and antigen-specific CD8+ T cells expressing the tumor homing molecule VLA-4, as well as a local chemotactic gradient featuring expression of CXCL10 (which may be responsible for the recruitment of CTLs), CCL3, CCL4 and CCL5 (which are involved in NK-cell migration), and NKG2D ligand on glioma cells. Importantly, although GLAST is expressed in the central nervous system, autoimmune reactions were not observed in immunized mice. Altogether, these results support the contention that GLAST may constitute a glioma antigen against which immune responses can be efficiently induced without major safety concerns.

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.

To the Brain and Back: Migratory Paths of Dendritic Cells in Multiple Sclerosis

Migration of dendritic cells (DC) to the central nervous system (CNS) is a critical event in the pathogenesis of multiple sclerosis (MS). While up until now, research has mainly focused on the transmigration of DC through the blood-brain barrier, experimental evidence points out that also the choroid plexus and meningeal vessels represent important gateways to the CNS, especially in early disease stages. On the other hand, DC can exit the CNS to maintain immunological tolerance to patterns expressed in the CNS, a process that is perturbed in MS. Targeting trafficking of immune cells, including DC, to the CNS has demonstrated to be a successful strategy to treat MS. However, this approach is known to compromise protective immune surveillance of the brain. Unravelling the migratory paths of regulatory and pathogenic DC within the CNS may ultimately lead to the design of new therapeutic strategies able to selectively interfere with the recruitment of pathogenic DC to the CNS, while leaving host protective mechanisms intact.

Inflammation research sails through the sea of immunology to reach immunometabolism

Inflammation occurs as a result of acute trauma, invasion of the host by different pathogens, pathogen-associated molecular patterns (PAMPs) or chronic cellular stress generating damage-associated molecular patterns (DAMPs). Thus inflammation may occur under both sterile inflammatory conditions including certain cancers, autoimmune or autoinflammatory diseases (Rheumatic arthritis (RA)) and infectious diseases including sepsis, pneumonia-associated acute lung inflammation (ALI) or acute respiratory distress syndrome (ARDS). The pathogenesis of inflammation involves dysregulation of an otherwise protective immune response comprising of various innate and adaptive immune cells and humoral (cytokines and chemokines) mediators secreted by these immune cells upon the activation of signaling mechanisms regulated by the activation of different pattern recognition receptors (PRRs). However, the pro-inflammatory and anti-inflammatory action of these immune cells is determined by the metabolic stage of the immune cells. The metabolic process of immune cells is called immunometabolism and its shift determined by inflammatory stimuli is called immunometabolic reprogramming. The article focuses on the involvement of various immune cells generating the inflammation, their interaction, immunometabolic reprogramming, and the therapeutic targeting of the immunometabolism to manage inflammation.

ISG20 promotes local tumor immunity and contributes to poor survival in human glioma

Recent evidence has confirmed that a mutation of the isocitrate dehydrogenase (IDH) gene occurs early in gliomagenesis and contributes to suppressed immunity. The present study aimed to determine the candidate genes associated with IDH mutation status that could serve as biomarkers of immune suppression for improved prognosis prediction. Clinical information and RNA-seq gene expression data were collected for 932 glioma samples from the CGGA and TCGA databases, and differentially expressed genes in both lower-grade glioma (LGG) and glioblastoma (GBM) samples were identified according to IDH mutation status. Only one gene, interferon-stimulated exonuclease gene 20 (ISG20), with reduced expression in IDH mutant tumors, demonstrated significant prognostic value. ISG20 expression level significantly increased with increasing tumor grade, and its high expression was associated with a poor clinical outcome. Moreover, increased ISG20 expression was associated with increased infiltration of monocyte-derived macrophages and neutrophils, and suppressed adaptive immune response. ISG20 expression was also positively correlated with PD-1, PD-L1, and CTLA4 expression, along with the levels of several chemokines. We conclude that ISG20 is a useful biomarker to identify IDH-mediated immune processes in glioma and may serve as a potential therapeutic target.

Junctional adhesion molecules mediate transendothelial migration of dendritic cell vaccine in cancer immunotherapy

In vitro generated dendritic cells (DCs) have been studied in cancer immunotherapy for decades. However, the detailed molecular mechanism underlying transendothelial migration (TEM) of DC vaccine across the endothelial barrier to regional lymph nodes (LNs) remains largely unknown. Here, we found that junctional adhesion molecule (JAM)-Like (JAML) is involved in the TEM of mouse bone marrow-derived DCs (BMDCs). Treatment with an anti-JAML antibody or JAML knock-down significantly reduced the TEM activity of BMDCs, leading to impairment of DC-based cancer immunotherapy. We found that the interaction of JAML of BMDCs with the coxsackie and adenovirus receptor of endothelial cells plays a crucial role in the TEM of BMDCs. On the other hand, human monocyte-derived DCs (MoDCs) did not express the JAML protein but still showed normal TEM activity. We found that MoDCs express only JAM1 and that the homophilic interaction of JAM1 is essential for MoDC TEM across a HUVEC monolayer. Our findings suggest that specific JAM family members play an important role in the TEM of in vitro-generated mouse and human DCs from the inoculation site to regional LNs in DC-based cancer immunotherapy.

Novel Models to Study Stromal Cell-Leukocyte Interactions in Health and Disease

To study human immunology in general and stromal immunology in particular, it is highly motivated to move from monolayers to 3D cultures, such as organotypic models, that better mimic the function of living tissue. These models can potentially contain most if not all cell types present in tissues, in combination with different extracellular matrix components that can critically affect cell phenotype. Besides their well-established use in studies of tissue-specific cells, such as epithelial cells, endothelial cells and stromal fibroblasts in combination with extracellular components, these models have also been shown to be valuable to study how tissue participates in the regulation of leukocyte differentiation and function. Organotypic models with leukocytes represent novel powerful tools to study human stromal immunology and mechanisms involved in the regulation of leukocyte functions and inflammatory processes in human health and disease. In particular, these models are robust, long-lived and reproducible and allow monitoring of disease progression in real time, as well as the mixing of cellular constituents from healthy and pathological tissues. These models are also easy to manipulate, either genetically or by adding external stimulants, such as cytokines and pathogens, to mimic pathological conditions. It is thus not surprising that these models are proposed to be useful in toxicology screening assays, evaluating therapeutic efficacy of drugs and antibiotics, as well as in personalized medicine. Within this chapter, the most recent developments in creating organotypic models for the purpose of study of human leukocyte and stromal cell interactions, in health and disease, will be discussed, in particular focusing on live imaging. Special emphasis will be given on an organotypic model resembling human lung and its usefulness in studying the fine control of physiological and pathological processes in human health and disease. Using these models in studies on human stromal cell and leukocyte interactions will likely help identifying novel disease traits and may point out new potential targets to monitor and treat human diseases.

β2 Integrins As Regulators of Dendritic Cell, Monocyte, and Macrophage Function

Emerging evidence suggests that the β₂ integrin family of adhesion molecules have an important role in suppressing immune activation and inflammation. β₂ integrins are important adhesion and signaling molecules that are exclusively expressed on leukocytes. The four β₂ integrins (CD11a, CD11b, CD11c, and CD11d paired with the β₂ chain CD18) play important roles in regulating three key aspects of immune cell function: recruitment to sites of inflammation; cell-cell contact formation; and downstream effects on cellular signaling. Through these three processes, β₂ integrins both contribute to and regulate immune responses. This review explores the pro- and anti-inflammatory effects of β₂ integrins in monocytes, macrophages, and dendritic cells and how they influence the outcome of immune responses. We furthermore discuss how imbalances in β₂ integrin function can have far-reaching effects on mounting appropriate immune responses, potentially influencing the development and progression of autoimmune and inflammatory diseases. Therapeutic targeting of β₂ integrins, therefore, holds enormous potential in exploring treatment options for a variety of inflammatory conditions.

High CCL5 expression is associated with osteosarcoma metastasis and poor prognosis of patients with osteosarcoma

Osteosarcoma is the most common primary malignant tumor of the skeletal system and is characterized by an aggressive clinical course and high metastatic potential. Regulated upon Activation Normal T cell Expressed and Secreted, also termed C‑C motif chemokine ligand 5 (CCL5), is associated with metastasis and poor prognosis in various types of cancer. The aim of the current study was to investigate the association between CCL5 expression and clinicopathological features and prognosis in patients with osteosarcoma. Tissue microarrays and reverse transcription‑quantitative polymerase chain reaction and immunohistochemistry were used to examine the expression of CCL5 in human osteosarcoma tissues. The prognostic value of CCL5 expression was evaluated by the Kaplan‑Meier method and Cox proportional hazards regression model. The rate of high CCL5 expression was significantly higher in metastatic osteosarcomas than in osteosarcomas without metastases. The overall survival rates (P=0.001) and the metastasis‑free survival rates (P<0.001) of the low CCL5 expression group were significantly higher than the CCL5 high expression group. Multivariate Cox regression analysis indicated that CCL5 expression had independent predictive value for the prognosis of patients with osteosarcoma. In conclusion, the data of the current study indicated that CCL5 may serve as a biomarker for prognosis of osteosarcoma, and may be a potential molecular target for osteosarcoma therapy.

A Crucial Role of CXCL14 for Promoting Regulatory T Cells Activation in Stroke

Inflammatory processes have a detrimental role in the pathophysiology of ischemic stroke. However, little is known about the endogenous anti-inflammatory mechanisms in ischemic brain. Here, we identify CXCL14 as a critical mediator of these mechanisms. CXCL14 levels were upregulated in the ischemic brains of humans and rodents. Moreover, hypoxia inducible factor-1α (HIF-1α) drives hypoxia- or cerebral ischemia (CI)-dependent CXCL14 expression via directly binding to the CXCL14 promoter. Depletion of CXCL14 inhibited the accumulation of immature dendritic cells (iDC) or regulatory T cells (Treg) and increased the infarct volume, whereas the supplementation of CXCL14 had the opposite effects. CXCL14 promoted the adhesion, migration, and homing of circulating CD11c⁺ iDC to the ischemic tissue via the upregulation of the cellular prion protein (PrP^C), PECAM-1, and MMPs. The accumulation of Treg in ischemic areas of the brain was mediated through a cooperative effect of CXCL14 and iDC-secreted IL-2-induced Treg differentiation. Interestingly, CXCL14 largely promoted IL-2-induced Treg differentiation. These findings indicate that CXCL14 is a critical immunomodulator involved in the stroke-induced inflammatory reaction. Passive CXCL14 supplementation provides a tractable path for clinical translation in the improvement of stroke-induced neuroinflammation.

Challenges in tissue engineering - towards cell control inside artificial scaffolds

Control of living cells is vital for the survival of organisms. Each cell inside an organism is exposed to diverse external mechano-chemical cues, all coordinated in a spatio-temporal pattern triggering individual cell functions. This complex interplay between external chemical cues and mechanical 3D environments is translated into intracellular signaling loops. Here, we describe how external mechano-chemical cues control cell functions, especially cell migration, and influence intracellular information transport. In particular, this work focuses on the quantitative analysis of (1) intracellular vesicle transport to understand intracellular state changes in response to external cues, (2) cellular sensing of external chemotactic cues, and (3) the cells' ability to migrate in 3D structured environments, artificially fabricated to mimic the 3D environment of tissue in the human body.

RUNX2 Mediates Plasmacytoid Dendritic Cell Egress from the Bone Marrow and Controls Viral Immunity

Plasmacytoid dendritic cells (pDCs) represent a unique immune cell type that responds to viral nucleic acids through the rapid production of type I interferons. Within the hematopoietic system, the transcription factor RUNX2 is exclusively expressed in pDCs and is required for their peripheral homeostasis. Here, we show that RUNX2 plays an essential role in promoting pDC localization and function. RUNX2 is required for the appropriate expression of the integrin-mediated adhesion machinery, as well as for the down-modulation of the chemokine receptor CXCR4, which allows pDC egress into the circulation. RUNX2 also facilitates the robust response to viral infection through the control of IRF7, the major regulator of type I interferon production. Mice lacking one copy of Runx2 have reduced numbers of peripheral pDCs and IFN-α expression, which might contribute to the reported difficulties of individuals with cleidocranial dysplasia, who are haploinsufficient for RUNX2, to clear viral infections.

Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina

To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α – CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment.

PACAP38/PAC1 signaling induces bone marrow-derived cells homing to ischemic brain

Understanding stem cell homing, which is governed by environmental signals from the surrounding niche, is important for developing effective stem cell-based repair strategies. The molecular mechanism by which the brain under ischemic stress recruits bone marrow-derived cells (BMDCs) to the vascular niche remains poorly characterized. Here we report that hypoxia-inducible factor-1α (HIF-1α) activation upregulates pituitary adenylate cyclase-activating peptide 38 (PACAP38), which in turn activates PACAP type 1 receptor (PAC1) under hypoxia in vitro and cerebral ischemia in vivo. BMDCs homing to endothelial cells in the ischemic brain are mediated by HIF-1α activation of the PACAP38-PAC1 signaling cascade followed by upregulation of cellular prion protein and α6-integrin to enhance the ability of BMDCs to bind laminin in the vascular niche. Exogenous PACAP38 confers a similar effect in facilitating BMDCs homing into the ischemic brain, resulting in reduction of ischemic brain injury. These findings suggest a novel HIF-1α-activated PACAP38-PAC1 signaling process in initiating BMDCs homing into the ischemic brain for reducing brain injury and enhancing functional recovery after ischemic stroke. Stem Cells2015;33:1153–1172

T cell-extrinsic CD18 attenuates antigen-dependent CD4+ T cell activation in vivo

The β2 integrins (CD11/CD18) are heterodimeric leukocyte adhesion molecules expressed on hematopoietic cells. The role of T cell-intrinsic CD18 in trafficking of naive T cells to secondary lymphoid organs and in Ag-dependent T cell activation in vitro and in vivo has been well defined. However, the T cell-extrinsic role for CD18, including on APC, in contributing to T cell activation in vivo is less well understood. We examined the role for T cell-extrinsic CD18 in the activation of wild-type CD4(+) T cells in vivo through the adoptive transfer of DO11.10 Ag-specific CD4(+) T cells into CD18(-/-) mice. We found that T cell-extrinsic CD18 was required for attenuating OVA-induced T cell proliferation in peripheral lymph nodes (PLN). The increased proliferation of wild-type DO11.10 CD4(+) T cells in CD18(-/-) PLN was associated with a higher percentage of APC, and these APC demonstrated an increased activation profile and increased Ag uptake, in particular in F4/80(+) APC. Depletion of F4/80(+) cells both reduced and equalized Ag-dependent T cell proliferation in CD18(-/-) relative to littermate control PLN, demonstrating that these cells play a critical role in the enhanced T cell proliferation in CD18(-/-) mice. Consistently, CD11b blockade, which is expressed on F4/80(+) macrophages, enhanced the proliferation of DO11.10 CD4(+) T cells in CD18(+/-) PLN. Thus, in contrast to the T cell-intrinsic essential role for CD18 in T cell activation, T cell-extrinsic expression of CD18 attenuates Ag-dependent CD4(+) T cell activation in PLN in vivo.

A holobiont birth narrative: the epigenetic transmission of the human microbiome

This essay plans to explore, expand, and re-tell the human birth narrative. Usually, human birth narratives focus on the origins of a new individual, focusing on the mother and fetus. This essay discusses birth as the origin of a new community. For not only is the eukaryotic body being reproduced, but so also are the bodies of its symbiotic microbes and so is the set of relationships between these organic components. Several parts of the new narrative are surprising: (1) bacterial symbionts might cause some of the characteristics of pregnancy and prepare a symbiotic community for transfer; (2) the first bacterial colonizers of the mammalian organism my enter the fetus prior to the lysing of the amniotic membrane and birth; (3) the same signals that often cause immunological attack against a microbe may serve under these conditions to signal homeostatic stability between symbiont and host; and (4) the mother may actively provide substances that promote the growth and settlement of helpful bacteria. The birth of the holobiont exemplifies principles of co-evolution, co-development, niche construction, and scaffolding. Birth is nothing less than the passage from one set of symbiotic relationships to another.

Effect of natalizumab treatment on circulating plasmacytoid dendritic cells: a cross-sectional observational study in patients with multiple sclerosis

Objectives

Dendritic cells (DCs) serve a critical role both in promoting and inhibiting adaptive immunity. The goal of this study was to investigate the effect of natalizumab (NTZ) treatment on DC numbers, phenotype, and function in patients with multiple sclerosis (MS).

Methods

Frequency and phenotype of myeloid and plasmacytoid DCs (MDCs and PDCs, respectively) were analyzed in blood from two separate cohorts of untreated, interferon-treated, or NTZ-treated MS patients. In addition, PDCs were stimulated with CpG-containing oligonucleotides or co-cultured with homologous T cells in the presence or absence of NTZ in vitro to determine functional effects of NTZ treatment.

Results

We observed that NTZ treatment was associated with a 25–50% reduction in PDC frequency in peripheral blood as compared to untreated MS patients, while the frequency of MDCs was unchanged. PDCs in NTZ-treated patients displayed a mature, activated phenotype with increased expression of HLA-DR, TLR9, CCR7, IL-6 and IL-12. In contrast, in vitro treatment with NTZ did not increase markers of PDC activation or their ability to induce T cell differentiation.

Conclusion

Our study shows that NTZ treatment is associated with a reduced frequency of PDCs in the peripheral circulation, but that PDCs in NTZ-treated individuals display an activated phenotype. Taken together the data suggests that transmigration of activated PDCs is preferentially affected by blockade of integrin α4 leading to an increased frequency of activated PDCs in blood.

Plasmacytoid dendritic cells: development, functions, and role in atherosclerotic inflammation

Plasmacytoid dendritic cells (pDCs) are a specialized subset of DCs that links innate and adaptive immunity. They sense viral and bacterial pathogens and release high levels of Type I interferons (IFN-I) in response to infection. pDCs were shown to contribute to inflammatory responses in the steady state and in pathology. In atherosclerosis, pDCs are involved in priming vascular inflammation and atherogenesis through production of IFN-I and chemokines that attract inflammatory cells to inflamed sites. pDCs also contribute to the proinflammatory activation of effector T cells, cytotoxic T cells, and conventional DCs. However, tolerogenic populations of pDCs are found that suppress atherosclerosis-associated inflammation through down-regulation of function and proliferation of proinflammatory T cell subsets and induction of regulatory T cells with potent immunomodulatory properties. Notably, atheroprotective tolerogenic DCs could be induced by certain self-antigens or bacterial antigens that suggests for great therapeutic potential of these DCs for development of DC-based anti-atherogenic vaccines.

Technical advance: live-imaging analysis of human dendritic cell migrating behavior under the influence of immune-stimulating reagents in an organotypic model of lung

This manuscript describes technical advances allowing manipulation and quantitative analyses of human DC migratory behavior in lung epithelial tissue. DCs are hematopoietic cells essential for the maintenance of tissue homeostasis and the induction of tissue-specific immune responses. Important functions include cytokine production and migration in response to infection for the induction of proper immune responses. To design appropriate strategies to exploit human DC functional properties in lung tissue for the purpose of clinical evaluation, e.g., candidate vaccination and immunotherapy strategies, we have developed a live-imaging assay based on our previously described organotypic model of the human lung. This assay allows provocations and subsequent quantitative investigations of DC functional properties under conditions mimicking morphological and functional features of the in vivo parental tissue. We present protocols to set up and prepare tissue models for 4D (x, y, z, time) fluorescence-imaging analysis that allow spatial and temporal studies of human DCs in live epithelial tissue, followed by flow cytometry analysis of DCs retrieved from digested tissue models. This model system can be useful for elucidating incompletely defined pathways controlling DC functional responses to infection and inflammation in lung epithelial tissue, as well as the efficacy of locally administered candidate interventions.

The two main forms of histiocytic sarcoma in the predisposed Flatcoated retriever dog display variation in gene expression

Examination of gene functions in specific tumor types improves insight in tumorigenesis and helps design better treatments. Due to the rarity of histiocytic/dendritic cell sarcoma in humans, it is difficult to accrue such knowledge. Therefore, comparative research of these cancers in predisposed dog breeds, such as the Flatcoated retriever, can be of value. Histiocytic sarcoma in the dog can be grouped into a soft tissue- and visceral form. The soft tissue form at first is localized, while the visceral form progresses more quickly to a terminal state, which might be related to variations in gene expression. Microarray analyses were performed on fresh-frozen tissue from Flatcoated retrievers with either soft tissue- or visceral histiocytic sarcoma. Expression differences of ten most significantly differentially expressed genes were validated with quantitative real-time PCR (q PCR) analyses. Q PCR analyses confirmed the significantly aberrant expression of three of the selected genes: C6 was up-regulated; CLEC12A and CCL5 were down-regulated in the visceral histiocytic sarcoma compared to the soft tissue form. The findings of our study indicate that these two forms of histiocytic sarcoma in the dog display a variation in gene expression and warrant analysis of functional changes in the expression of those genes in these rare sarcomas in man.

Effect of immunoglobin-like transcript 7 cross-linking on plasmacytoid dendritic cells differentiation into antigen-presenting cells

Plasmacytoid dendritic cells (pDC) are innate immunity effector cells which play a critical role in the transition from innate to adaptive immune response. Circulating blood pDC present an immature phenotype and can differentiate into either antigen-presenting cells (APC) or type I interferon (IFN-I)-producing cells (IPC). The immunoglobulin-like transcript (ILT)7 is a surface receptor expressed by immature pDC, and ILT7 cross-linking (XL-ILT7) inhibits IFN-I production by pDC in response to toll-like receptor (TLR)7 and 9 stimulation. We used peripheral blood mononuclear cells (PBMC) from healthy donors to test the effect of XL-ILT7 on 1) TLR7/9-mediated regulation of gut mucosal (α4β7 integrin) and lymph node (CCR7) migration markers; and 2) the maturation of pDC into APC. We found that XL-ILT7 mitigated the upregulation of CCR7 and enhanced that of β7 on TLR7/9-stimulated pDC. TLR7/9 stimulation induced upregulation of CD40, CD80 and CD86. CD40 expression was partially reduced by XL-ILT7, whereas CD86 was further enhanced. Plasmacytoid DC stimulated with TLR9 ligand in presence of XL-ILT7 retained the ability to induce T cell proliferation and activation in response to staphylococcal enterotoxin B (SEB) in pDC-T cell co-cultures. Our results suggest that XL-ILT7 favours the differentiation of immature pDC into APC rather than IPC.

IL-27 improves migrational and antiviral potential of CB dendritic cells

Interleukin (IL)-27 is known to be increased considerably in cord blood (CB) dendritic cells (DCs) after TLR ligation. Previously, we demonstrated that also basal IL-27 levels are higher in CB DCs. Here, we examined effects of IL-27 on monocyte derived dendritic cells (moDCs) to approach its particular role in the specialized immune system of the human neonate. Exogenous IL-27 promotes IL-27 transcription in CB and adult blood (AB) moDCs. IL-27 acts on CB moDCs primarily by significantly augmenting IL-27 protein, secondarily by increasing transcription of CXCL10 among other chemokines, chemokine receptor CCR1, interferon stimulated genes, transcription factor IRF8 and genes involved in antigen presentation. Furthermore, CB moDCs respond to IL-27 with augmented IL-8 and Tumor necrosis factor (TNF)-α. The results suggest that IL-27 enhances migrational and antiviral properties of CB dendritic cells.

Mycobacterium tuberculosis infection of human dendritic cells decreases integrin expression, adhesion and migration to chemokines

Tuberculosis (TB) remains a major global health problem accounting for millions of deaths annually. Approximately one-third of the world's population is infected with the causative agent Mycobacterium tuberculosis. The onset of an adaptive immune response to M. tuberculosis is delayed compared with other microbial infections. This delay permits bacterial growth and dissemination. The precise mechanism(s) responsible for this delay have remained obscure. T-cell activation is preceded by dendritic cell (DC) migration from infected lungs to local lymph nodes and synapsis with T cells. We hypothesized that M. tuberculosis may impede the ability of DCs to reach lymph nodes and initiate an adaptive immune response. We used primary human DCs to determine the effect of M. tuberculosis on expression of heterodimeric integrins involved in cellular adhesion and migration. We also evaluated the ability of infected DCs to adhere to and migrate through lung endothelial cells, which is necessary to reach lymph nodes. We show by flow cytometry and confocal microscopy that M. tuberculosis-infected DCs exhibit a significant reduction in surface expression of the β(2) (CD18) integrin. Distribution of integrin β(2) is also markedly altered in M. tuberculosis-infected DCs. A corresponding reduction in the αL (CD11a) and αM (CD11b) subunits that associate with integrin β(2) was also observed. Consistent with reduced integrin surface expression, we show a significant reduction in adherence to lung endothelial cell monolayers and migration towards lymphatic chemokines when DCs are infected with M. tuberculosis. These findings suggest that M. tuberculosis modulates DC adhesion and migration to increase the time required to initiate an adaptive immune response.

Human plasmacytoid dendritic cells: from molecules to intercellular communication network

Plasmacytoid dendritic cells (pDCs) are a specific subset of naturally occurring dendritic cells, that secrete large amounts of Type I interferon and play an important role in the immune response against viral infection. Several studies have highlighted that they are also effective antigen presenting cells, making them an interesting target for immunotherapy against cancer. However, the modes of action of pDCs are not restricted to antigen presentation and IFN secretion alone. In this review we will highlight a selection of cell surface proteins expressed by human pDCs that may facilitate communication with other immune cells, and we will discuss the implications of these molecules for pDC-driven immune responses.

Apoptosis and dysfunction of blood dendritic cells in patients with falciparum and vivax malaria

Acute Plasmodium infections in humans result in dendritic cell dysfunction and apoptosis caused in part by elevated levels of IL-10.

Malaria causes significant morbidity worldwide and a vaccine is urgently required. Plasmodium infection causes considerable immune dysregulation, and elicitation of vaccine immunity remains challenging. Given the central role of dendritic cells (DCs) in initiating immunity, understanding their biology during malaria will improve vaccination outcomes. Circulating DCs are particularly important, as they shape immune responses in vivo and reflect the functional status of other subpopulations. We performed cross-sectional and longitudinal assessments of the frequency, phenotype, and function of circulating DC in 67 Papuan adults during acute uncomplicated P. falciparum, P. vivax, and convalescent P. falciparum infections. We demonstrate that malaria patients display a significant reduction in circulating DC numbers and the concurrent accumulation of immature cells. Such alteration is associated with marked levels of spontaneous apoptosis and impairment in the ability of DC to mature, capture, and present antigens to T cells. Interestingly, sustained levels of plasma IL-10 were observed in patients with acute infection and were implicated in the induction of DC apoptosis. DC apoptosis was reversed upon IL-10 blockade, and DC function recovered when IL-10 levels returned to baseline by convalescence. Our data provide key information on the mechanisms behind DC suppression during malaria and will assist in developing strategies to better harness DC’s immunotherapeutic potential.

Mesenchymal contribution to recruitment, infiltration, and positioning of leukocytes in human melanoma tissues

To understand factors that regulate leukocyte entry and positioning within human melanoma tissues, we performed a multiparametric quantitative analysis of two separated regions: the intratumoral area and the peritumoral stroma. Using two mesenchymal markers, fibroblast activation protein (FAP) and CD90, we identified three subsets of mesenchymal cells (MCs): (i) intratumoral FAP(+)CD90(low/-) MC, (ii) peritumoral FAP(+)CD90(+) MC, and (iii) FAP(-)CD90(+) perivascular MC. We characterized CD90(+) MCs, which showed a stable CCL2-secretory phenotype when long-term expanded ex vivo, and heavily surrounded peritumoral Duffy antigen receptor for chemokine(+) (DARC) postcapillary venules, supporting a role for these vessels in peritumoral inflammatory leukocyte recruitment. Conversely, the intratumoral area was variably invaded by FAP(+)CD90(low/-) MCs that colocalized with a distinct extracellular matrix (ECM) network. A positive correlation was observed between intratumoral stromal cell/ECM networks and leukocyte infiltration among tumor cells (TCs), as well as in a stroma-dependent xenograft tumor model. Adoptively transferred T lymphocytes preferentially infiltrated tumors composed of TC+MC, compared with TCs only. Altogether, our results suggest that a variety of MCs contribute to regulate different steps of leukocyte tumor infiltration, that is, CD90(+) cells surrounding peritumoral vessels secrete CCL2 to recruit CCR2(+) leukocytes at the tumor periphery, whereas intratumoral FAP(+) cells organize a stromal scaffold that contact guide further invasion among densely packed tumor cells.

ALCAM/CD166 adhesive function is regulated by the tetraspanin CD9

ALCAM/CD166 is a member of the immunoglobulin superfamily of cell adhesion molecules (Ig-CAMs) which mediates intercellular adhesion through either homophilic (ALCAM-ALCAM) or heterophilic (ALCAM-CD6) interactions. ALCAM-mediated adhesion is crucial in different physiological and pathological phenomena, with particular relevance in leukocyte extravasation, stabilization of the immunological synapse, T cell activation and proliferation and tumor growth and metastasis. Although the functional implications of ALCAM in these processes is well established, the mechanisms regulating its adhesive capacity remain obscure. Using confocal microscopy colocalization, and biochemical and functional analyses, we found that ALCAM directly associates with the tetraspanin CD9 on the leukocyte surface in protein complexes that also include the metalloproteinase ADAM17/TACE. The functional relevance of these interactions is evidenced by the CD9-induced upregulation of both homophilic and heterophilic ALCAM interactions, as reflected by increased ALCAM-mediated cell adhesion and T cell migration, activation and proliferation. The enhancement of ALCAM function induced by CD9 is mediated by a dual mechanism involving (1) augmented clustering of ALCAM molecules, and (2) upregulation of ALCAM surface expression due to inhibition of ADAM17 sheddase activity.

CCL5 and CCR5 interaction promotes cell motility in human osteosarcoma

BACKGROUND

Osteosarcoma is characterized by a high malignant and metastatic potential. CCL5 (previously called RANTES) was originally recognized as a product of activated T cells, and plays a crucial role in the migration and metastasis of human cancer cells. It has been reported that the effect of CCL5 is mediated via CCR receptors. However, the effect of CCL5 on migration activity and integrin expression in human osteosarcoma cells is mostly unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Here we found that CCL5 increased the migration and expression of αvβ3 integrin in human osteosarcoma cells. Stimulation of cells with CCL5 increased CCR5 but not CCR1 and CCR3 expression. CCR5 mAb, inhibitor, and siRNA reduced the CCL5-enhanced the migration and integrin up-regulation of osteosarcoma cells. Activations of MEK, ERK, and NF-κB pathways after CCL5 treatment were demonstrated, and CCL5-induced expression of integrin and migration activity was inhibited by the specific inhibitor and mutant of MEK, ERK, and NF-κB cascades. In addition, over-expression of CCL5 shRNA inhibited the migratory ability and integrin expression in osteosarcoma cells.

CONCLUSIONS/SIGNIFICANCE

CCL5 and CCR5 interaction acts through MEK, ERK, which in turn activates NF-κB, resulting in the activations of αvβ3 integrin and contributing the migration of human osteosarcoma cells.

Tumor metabolism as modulator of immune response and tumor progression

About a century ago Otto Warburg observed that tumor cells exhibited increased glycolysis despite the presence of oxygen and stated this metabolic shift to glycolysis as the origin of cancer cell. In the meantime it has become clear, that the altered glucose metabolism is only one piece of the tumor metabolome puzzle. In addition, amino acid, lipid and adenosine metabolism are adapted to fulfill the tumors needs for energy and generation of building blocks such as lipids and nucleotides for new cell structures. The altered tumor metabolism leads to accumulation of specific metabolites in the tumor environment and creates a favorable milieu for tumor growth, progression and metastasis. These tumor-derived metabolites are important players in immune escape mechanisms beside other known factors such as cytokines, chemokines and growth factors. A variety of metabolites re-educate immune cells and prevent an effective immune response against tumor cells. Furthermore, tumor infiltrating immune cells support tumor growth by the secretion of cytokines, growth factors and other metabolic determinants. Hence, a complex interplay of tumor metabolites, cytokines and stromal factors is active in tumors and facilitates their establishment and growth. Pharmacological blockade of tumor metabolites could overcome some limitations of cancer treatment and rescue the endogenous immune response against tumor cells.

Tumour tissue microenvironment can inhibit dendritic cell maturation in colorectal cancer

Inflammatory mediators in the tumour microenvironment promote tumour growth, vascular development and enable evasion of anti-tumour immune responses, by disabling infiltrating dendritic cells. However, the constituents of the tumour microenvironment that directly influence dendritic cell maturation and function are not well characterised. Our aim was to identify tumour-associated inflammatory mediators which influence the function of dendritic cells. Tumour conditioned media obtained from cultured colorectal tumour explant tissue contained high levels of the chemokines CCL2, CXCL1, CXCL5 in addition to VEGF. Pre-treatment of monocyte derived dendritic cells with this tumour conditioned media inhibited the up-regulation of CD86, CD83, CD54 and HLA-DR in response to LPS, enhancing IL-10 while reducing IL-12p70 secretion. We examined if specific individual components of the tumour conditioned media (CCL2, CXCL1, CXCL5) could modulate dendritic cell maturation or cytokine secretion in response to LPS. VEGF was also assessed as it has a suppressive effect on dendritic cell maturation. Pre-treatment of immature dendritic cells with VEGF inhibited LPS induced upregulation of CD80 and CD54, while CXCL1 inhibited HLA-DR. Interestingly, treatment of dendritic cells with CCL2, CXCL1, CXCL5 or VEGF significantly suppressed their ability to secrete IL-12p70 in response to LPS. In addition, dendritic cells treated with a combination of CXCL1 and VEGF secreted less IL-12p70 in response to LPS compared to pre-treatment with either cytokine alone. In conclusion, tumour conditioned media strongly influences dendritic cell maturation and function.

Dendritic cells in human atherosclerosis: from circulation to atherosclerotic plaques

Background. Atherosclerosis is a chronic inflammatory disease with atherosclerotic plaques containing inflammatory infiltrates predominantly consisting of monocytes/macrophages and activated T cells. More recent is the implication of dendritic cells (DCs) in the disease. Since DCs were demonstrated in human arteries in 1995, numerous studies in humans suggest a role for these professional antigen-presenting cells in atherosclerosis. Aim. This paper focuses on the observations made in blood and arteries of patients with atherosclerosis. In principal, flow cytometric analyses show that circulating myeloid (m) and plasmacytoid (p) DCs are diminished in coronary artery disease, while immunohistochemical studies describe increased intimal DC counts with evolving plaque stages. Moreover, mDCs and pDCs appear to behave differently in atherosclerosis. Yet, the origin of plaque DCs and their relationship with blood DCs are unknown. Therefore, several explanations for the observed changes are postulated. In addition, the technical challenges and discrepancies in the research field are discussed. Future. Future studies in humans, in combination with experimental animal studies will unravel mechanisms leading to altered blood and plaque DCs in atherosclerosis. As DCs are crucial for inducing but also dampening immune responses, understanding their life cycle, trafficking and function in atherosclerosis will determine potential use of DCs in antiatherogenic therapies.

NFκB and JNK/MAPK activation mediates the production of major macrophage- or dendritic cell-recruiting chemokine in human first trimester decidual cells in response to proinflammatory stimuli

CONTEXT

Preeclampsia is associated with elevated levels of proinflammatory cytokines, excess decidual macrophages, and dendritic cells. IL-1β- or TNF-α-stimulated leukocyte-free first trimester decidual cells produced abundant macrophage- and dendritic cell-recruiting chemokines identified in preeclamptic decidua.

OBJECTIVE

The relative potency of IL-1β- or TNF-α-induced first trimester decidual cell-secreted chemokines in chemoattracting macrophages or dendritic cells and the signaling pathways involved in the expression of these chemokines were evaluated.

INTERVENTIONS AND MAIN OUTCOME MEASURES

First trimester decidual cells were treated with estradiol + medroxyprogesterone acetate ± IL-1β or TNF-α. The chemotaxis assay was performed by incubating conditioned medium from first trimester decidual cells with neutralizing antibody for six chemokines. The activation of each signaling pathway was examined by Western blotting, flow cytometry, confocal microscopy, and ELISA with or without kinase and nuclear factor κB (NFκB) inhibitors.

RESULTS

Neutralization of CCL2 and CCL5 significantly reduced chemotaxis of monocyte and dendritic cells up to 50 and 36%, respectively. NFκB and MAPK (MAPK kinase, JUN NH₂-terminal kinase, p38 kinase) pathways were activated by IL-1β or TNF-α in first trimester decidual cells. In IL-1β- or TNF-α-stimulated first trimester decidual cells, NFκB inhibitor suppressed production of all six chemokines; JUN NH₂-terminal kinase inhibitor inhibited secretion of CCL2, CCL4, and CCL5; and MAPK kinase and p38 inhibitor decreased production of CXCL8.

CONCLUSIONS

Up-regulation of CCL2 and CCL5 by first trimester decidual cells in response to proinflammatory stimuli may account for the accumulation of macrophages and dendritic cells in preeclamptic decidua. These chemokines and underlying IL-1β- or TNF-α-induced signaling molecules are potential diagnostic and therapeutic targets for preeclampsia.

Immunohistochemical characterisation of dendritic cells in human atherosclerotic lesions: possible pitfalls

BACKGROUND

Previously we demonstrated decreased blood myeloid (m) and plasmacytoid (p) dendritic cell (DC) counts in atherosclerotic patients. Therefore, we examined whether DCs, in particular DC precursors, accumulate in human plaques.

METHODS

Blood DC antigen (BDCA)-1, CD11c (mDCs), BDCA-2, CD123 (pDCs), langerin, fascin, S-100 (immature/mature DCs), and CD1a and CD83 (mature DCs) were investigated by immunohistochemistry of carotid arteries obtained by endarterectomy (EAS, frozen n = 11, fixed n = 11) or autopsy (fixed, n = 87).

RESULTS

Fascin and S-100 required formaldehyde fixation, other markers needed cryo-preservation. BDCA-1, BDCA-2, langerin, and S-100 appeared specific for intimal DCs, unlike CD123 and fascin (staining endothelial cells), CD11c and CD1a (staining monocytes, foam cells) or CD83 (staining lymphocytes). BDCA-1 and BDCA-2 cells were detected in EAS, preferentially near microvessels. S-100 cells increased successively from intimal thickening, via pathological intimal thickening, fibrous cap atheroma and finally complicated plaques. Fascin cells followed the same pattern, but were more abundant. However, in lesions containing microvessels (complicated plaques, plaque shoulders and most EAS) this was partly explained by fascin positive endothelial cells. Even complicated plaques contained relatively few mature CD83 DCs.

CONCLUSIONS

Accumulation of BDCA-1 and BDCA-2 around neovessels showed that mDCs and pDCs are recruited to advanced plaques, which is in line with the previously described decline of circulating blood DCs in patients with coronary artery disease. Unexpectedly, several DC markers yielded false positive signals. Hence, some accounts on numbers, trafficking and activation of DCs in atherosclerotic plaques may require re-evaluation.

Multiparametric luminescence method for quantitative cell surface protein expression analysis and imaging

A luminometric method for quantitative cell surface protein expression analysis has been developed in a microtiter plate format. The method is based on immunocytochemistry, the use of long-lived europium(III) and terbium(III) chelates and platinum(II) porphyrin luminescence labels in addition to short-lived syto13 DNA stain, and detection of photoluminescence emission from adhered cells by both time-resolved luminescence and conventional fluorescence. After the immunoreactions, the wells were evaporated to dryness, allowing repeated and postponed luminescence analysis even after months and cellular protein localization studies by microscopy imaging. The multiparametric method assayed the cell surface expression of ß1-integrin, E-selectin and intercellular adhesion molecule 1 (ICAM-1) in HUVE cells (human umbilical vein endothelial cells). The expression of E-selectin and ICAM-1 was enhanced by treating HUVECs with tumor necrosis factor α (TNF-α), while the expression level of ß1-integrin remained unchanged. The sensitivity limit of TNF-α detection by the method was ca. 1 pg/ml and the Z'-factors for the quantification of E-selectin and ICAM-1 were >0.7 suggesting a highly robust method. The novel approach proposed in this paper can be potentially applied to cell surface protein expression analysis in screening applications combined with localization studies of the target proteins by fluorescence microscopy imaging.

The Role of Plasmacytoid Dendritic Cells in Innate and Adaptive Immune Responses against Alpha Herpes Virus Infections

In 1999, two independent groups identified plasmacytoid dendritic cells (PDC) as major type I interferon- (IFN-) producing cells in the blood. Since then, evidence is accumulating that PDC are a multifunctional cell population effectively coordinating innate and adaptive immune responses. This paper focuses on the role of different immune cells and their interactions in the surveillance of alpha herpes virus infections, summarizes current knowledge on PDC surface receptors and their role in direct cell-cell contacts, and develops a risk factor model for the clinical implications of herpes simplex and varicella zoster virus reactivation. Data from studies involving knockout mice and cell-depletion experiments as well as human studies converge into a "spider web", in which the direct and indirect crosstalk between many cell populations tightly controls acute, latent, and recurrent alpha herpes virus infections. Notably, cells involved in innate immune regulations appear to shape adaptive immune responses more extensively than previously thought.

Control of TNF-induced dendritic cell maturation by hybrid-type N-glycans

The activity of α-1,2-mannosidase I is required for the conversion of high-mannose to hybrid-type (ConA reactive) and complex-type N-glycans (Phaseolus vulgaris-leukoagglutinin [PHA-L] reactive) during posttranslational protein N-glycosylation. We recently demonstrated that α-1,2-mannosidase I mRNA decreases in graft-infiltrating CD11c(+) dendritic cells (DCs) prior to allograft rejection. Although highly expressed in immature DCs, little is known about its role in DC functions. In this study, analysis of surface complex-type N-glycan expression by lectin staining revealed the existence of PHA-L(low) and PHA-L(high) subpopulations in murine splenic conventional DCs, as well as in bone marrow-derived DC (BMDCs), whereas plasmacytoid DCs are nearly exclusively PHA-L(high). Interestingly, all PHA-L(high) DCs displayed a strongly reduced responsiveness to TNF-α-induced p38-MAPK activation compared with PHA-L(low) DCs, indicating differences in PHA-L-binding capacities between DCs with different inflammatory properties. However, p38 phosphorylation levels were increased in BMDCs overexpressing α-1,2-mannosidase I mRNA. Moreover, hybrid-type, but not complex-type, N-glycans are required for TNF-α-induced p38-MAPK activation and subsequent phenotypic maturation of BMDCs (MHC-II, CD86, CCR7 upregulation). α-1,2-mannosidase I inhibitor-treated DCs displayed diminished transendothelial migration in response to CCL19, homing to regional lymph nodes, and priming of IFN-γ-producing T cells in vivo. In contrast, the activity of α-1,2-mannosidase I is dispensable for LPS-induced signaling, as well as the DCs' general capability for phenotypic and functional maturation. Systemic application of an α-1,2-mannosidase I inhibitor was able to significantly prolong allograft survival in a murine high-responder corneal transplantation model, further highlighting the importance of N-glycan processing by α-1,2-mannosidase I for alloantigen presentation and T cell priming.

CCR7 essentially contributes to the homing of plasmacytoid dendritic cells to lymph nodes under steady-state as well as inflammatory conditions

The chemokine receptor CCR7 represents an important determinant for circulating lymphocytes to enter lymph nodes (LN) via high endothelial venules. High endothelial venules also represent the major site of entry for plasmacytoid dendritic cells (pDC). In the steady-state, murine pDC have been suggested to home to LN engaging the chemokine receptors CXCR3, CXCR4, and CCR5, whereas responsiveness to CCR7 ligands is thought to be acquired only upon activation. In this study, we show that already resting pDC express minute amounts of CCR7 that suffice to trigger migration to CCL19/CCL21 in vitro. Upon activation with TLR ligands, CCR7 levels on pDC are strongly increased. Notably, CCR7-deficient mice display substantially reduced pDC counts in LN but not in bone marrow and spleen. Adoptive cell transfer experiments revealed that under both steady-state as well as inflammatory conditions, the homing of CCR7-deficient pDC is severely impaired, indicating that the reduced cell counts of naive pDC observed in CCR7(-/-) mice reflect an intrinsic homing defect of pDC. Together, these observations provide strong evidence that similar to naive lymphocytes, nonstimulated pDC exploit CCR7 to gain entry into LN. This adds to the repertoire of chemokine receptors permitting them to enter diverse tissues.

The chemokine CXCL12 regulates monocyte-macrophage differentiation and RUNX3 expression

Monocytes are versatile cells that can express different functional programs in response to microenvironmental signals. We show that primary blood monocytes secrete the CXCL12 chemokine, and express the CXCR4 and CXCR7 receptors, leading to an autocrine/paracrine loop that contribute to shape monocyte differentiation to a distinct type of macrophages, with an enhanced expression of CD4, CD14, and CD163, or dendritic cells, with a reduced functional ability to stimulate antigen-specific T-lymphocyte responses. The in vivo relevance of CXCL12 production by mononuclear phagocytes was studied in metastatic melanoma tissues by a thoroughly immunofluorescence phenotyping of CXCL12(high) expressing cells, which were CD45(+), coexpressed the macrophage antigens CD68, CD163, and CD209 and constituted the 60%-90% of tumor-associated macrophages. Microarray analysis of primary monocytes revealed that the vascular endothelial growth factor and the angiogenic chemokine CCL1 mRNA levels were up-regulated in response to CXCL12, leading to enhanced expression of both proteins. In addition, we found that CXCL12 autocrine/paracrine signaling down-regulates the expression of the transcription factor RUNX3 and contributes to maintain the long-term CD4 and CD14 expression in monocytes/macrophages. Together, these results suggest that autocrine CXCL12 production modulates differentiation of monocytes toward a distinct program with proangiogenic and immunosuppressive functions.

Plasmacytoid dendritic cells accumulate and secrete interferon alpha in lymph nodes of HIV-1 patients

Circulating plasmacytoid dendritic cells (pDC) decline during HIV-1 infection, but at the same time they express markedly higher levels of interferon alpha (IFNalpha), which is associated with HIV-1 disease progression. Here we show an accumulation of pDC in lymph nodes (LN) of treatment-naïve HIV-1 patients. This phenomenon was associated with elevated expression of the LN homing marker, CCR7, on pDC in peripheral blood of HIV-1 patients, which conferred increased migratory capacity in response to CCR7 ligands in ex vivo functional assays. LN-homed pDC of HIV-1 patients presented higher CD40 and lower BDCA2 levels, but unchanged CD83 and CD86 expression. In addition, these cells expressed markedly higher amounts of IFNalpha compared to uninfected individuals, and were undergoing faster rates of cell death. These results demonstrate for the first time that in asymptomatic, untreated HIV-1 patients circulating pDC up-regulate CCR7 expression, accumulate in lymph nodes, and express high amounts of IFNalpha before undergoing cell death. Since IFNalpha inhibits cell proliferation and modulates immune responses, chronically high levels of this cytokine in LN of HIV-1 patients may impair differentiation and immune function of bystander CD4(+) T cells, thus playing into the mechanisms of AIDS immunopathogenesis.