Tissue-resident Dendritic Cells Research Articles

Cross-organ single-cell transcriptome profiling reveals macrophage and dendritic cell heterogeneity in zebrafish

Tissue-resident macrophages (TRMs) and dendritic cells (DCs) are highly heterogeneous and essential for immunity, tissue regeneration, and homeostasis maintenance. Here, we comprehensively profile the heterogeneity of TRMs and DCs across adult zebrafish organs via single-cell RNA sequencing. We identify two macrophage subsets: pro-inflammatory macrophages with potent phagocytosis signatures and pro-remodeling macrophages with tissue regeneration signatures in barrier tissues, liver, and heart. In parallel, one conventional dendritic cell (cDC) population with prominent antigen presentation capacity and plasmacytoid dendritic cells (pDCs) featured by anti-virus properties are also observed in these organs. Remarkably, in addition to a single macrophage/microglia population with potent phagocytosis capacity, a pDC population and two distinct cDC populations are identified in the brain. Finally, we generate specific reporter lines for invivo tracking of macrophage and DC subsets. Our study depicts the landscape of TRMs and DCs and creates valuable tools for in-depth study of these cells in zebrafish.

Extracorporeal Photopheresis Suppresses Transplant Fibrosis by Inducing Decorin Expression in Alveolar Macrophages.

Extracorporeal Photopheresis Suppresses Transplant Fibrosis by Inducing Decorin Expression in Alveolar Macrophages.

Deep tissue infection by an invasive human fungal pathogen requires lipid-based suppression of the IL-17 response

Candida albicans is the most common cause of fungal infection in humans. IL-17 is critical for defense against superficial fungal infections, but the role of this response in invasive disease is less understood. We show that C.albicans secretes a lipase, Lip2, that facilitates invasive disease via lipid-based suppression of the IL-17 response. Lip2 was identified as an essential virulence factor in a forward genetic screen in a mouse model of bloodstream infection. Murine infection with C.albicans strains lacking Lip2 display exaggerated IL-17 responses that lead to fungal clearance from solid organs and host survival. Both IL-17 signaling and lipase activity are required for Lip2-mediated suppression. Lip2 inhibits IL-17 production indirectly by suppressing IL-23 production by tissue-resident dendritic cells. The lipase hydrolysis product, palmitic acid, similarly suppresses dendritic cell activation invitro. Thus, C.albicans suppresses antifungal IL-17 defense in solid organs by altering the tissue lipid milieu.

Upregulated influenza A viral entry factors and enhanced interferon-alpha response in the nasal epithelium of pregnant rats

Despite the increased severity of influenza A infection in pregnancy, knowledge about the expression of cell entry factors for influenza A virus (IAV) and the innate immune response in the nasal epithelium, the primary portal of viral entry, is limited. Here, we compared the expression of IAV cell entry factors and the status of the innate immune response in the nasal epithelium of pregnant vs. non-pregnant female rats. IAV cell entry factors — sialic acid [SA] α-2,3- and α-2,6-linked glycans for avian and human IAV, respectively — were detected and quantified with lectin-based immunoblotting and flow cytometry. Baseline frequencies of innate immune cell phenotypes in single cell suspensions of the nasal epithelium were studied with flow cytometry. Subsequently, the magnitude of interferon and cytokine responses was studied with ELISA and cytokine arrays after intranasal resiquimod, a Toll-like receptor 7/8 agonist that mimics IAV infection. We noted substantially increased expression of cell entry factors for both avian and human IAV in the nasal epithelium during pregnancy. Assessment of the innate immune state of the nasal epithelium during pregnancy revealed two previously unreported features: (i) increased presence of tissue-resident plasmacytoid dendritic cells, and (ii) markedly enhanced release of interferon-α but not of the other interferons or cytokines 2 h after intranasal resiquimod. Collectively, our findings challenge the conventional notion of pregnancy-induced immunosuppression as a cause for severe influenza A disease and suggest the need for focused studies on viral tropism during pregnancy to better understand the proximate cause for the observed immunopathology.

Single-cell RNA sequencing distinguishes dendritic cell subsets in the rat, allowing advanced characterization of the effects of FMS-like tyrosine kinase 3 ligand.

Tissue-resident dendritic cells (DCs) are essential for immunological homeostasis and hold promise for a variety of therapeutic interventions. The rare nature of tissue-resident DCs and their suboptimal description in the lab rat model has limited their characterization. To address this limitation, FMS-like tyrosine kinase 3 ligand (FLT3L) has been utilized to expand these population in vitro and in vivo for investigative or therapeutic purposes. However, conflicting reports have suggested that FLT3L can either promote immune tolerance or enhance immunogenicity, necessitating clarification of the effects of FLT3L on DC phenotype and functionality. We first paired single-cell RNA sequencing with multicolour spectral flow cytometry to provide an updated strategy for the identification of tissue-resident classical and plasmacytoid DCs in the rat model. We then administered FLT3L to Lewis rats in vivo to investigate its effect on tissue-resident DC enumeration and phenotype in the liver, spleen, and mesenteric lymph nodes. We found that FLT3L expands classical DCs (cDCs) 1 and 2 in a dose-dependent manner and that cDC1 and cDC2 in secondary lymphoid organs had altered MHC I, MHC II, CD40, CD80, CD86, and PD-L1 cell-surface expression levels following FLT3L administration. These changes were accompanied by an increase in gene expression levels of toll-like receptors 2, 4, 7, and 9 as well as inflammatory cytokines IL-6 and TNF-α. In conclusion, FLT3L administration in vivo increases cDC enumeration in the liver, spleen, and mesenteric lymph nodes accompanied by a tissue-restricted alteration in expression of antigen presentation machinery and inflammatory mediators.

New Therapeutic Tools to Shape Monocyte Functional Phenotypes in Leishmaniasis.

In the innate immunity to Leishmania infection tissue-resident macrophages and inflammatory monocytes accumulate host-cell, effector, and efferocytosis functions. In addition, neutrophils, as host, effector, and apoptotic cells, as well as tissue-resident and monocyte-derived dendritic cells (DCs) imprint innate and adaptive immunity to Leishmania parasites. Macrophages develop phenotypes ranging from antimicrobial M1 to parasite-permissive M2, depending on mouse strain, Leishmania species, and T-cell cytokines. The Th1 (IFN-γ) and Th2 (IL-4) cytokines, which induce classically-activated (M1) or alternatively-activated (M2) macrophages, underlie resistance versus susceptibility to leishmaniasis. While macrophage phenotypes have been well discussed, new developments addressed the monocyte functional phenotypes in Leishmania infection. Here, we will emphasize the role of inflammatory monocytes to access how potential host-directed therapies for leishmaniasis, such as all-trans-retinoic acid (ATRA) and the ligand of Receptor Activator of Nuclear Factor-Kappa B (RANKL) might modulate immunity to Leishmania infection, by directly targeting monocytes to develop M1 or M2 phenotypes.

FMS-like tyrosine kinase 3 ligand (FLT3L) administration alters rat classical and plasmacytoid dendritic cell phenotype in a tissue-specific manner

Abstract Background: Characterization of tissue-resident dendritic cell (DC) subsets, including classical DCs (cDCs) and plasmacytoid DCs (pDCs), is complicated experimentally by their rare nature. Many investigators have artificially increased DC yields through administration of the cytokine FMS-like tyrosine kinase 3 ligand (FLT3L). Despite its previous use experimentally, no study has yet described the effects of in vivo FLT3L administration on rat tissue-resident DCs. This study provides an advanced characterization of rat tissue-resident cDCs and pDCs following FLT3L injection. Methods: Lewis rats were injected once daily for 10 days with PBS vehicle or with 10, 50, or 100μg of FLT3L. Animals were sacrificed on the 11th day and dissected to obtain liver, spleen, and mesenteric lymph nodes. Cells were stained for 13-color flow cytometry and data was acquired on the Cytek Aurora spectral cytometer. Results: cDC and pDC enumeration increased in a dose-dependent manner following FLT3L administration. Expression levels of MHC I, MHC II, CD40, CD80, CD86, and PD-L1 were evaluated on liver, spleen, and mesenteric lymph node-resident cells. MHC II, CD80, and CD86 levels were significantly decreased on liver-resident cDCs but remained unchanged or increased on spleen and lymph node cDCs. Changes in MHC I/II and costimulatory molecule expression levels on pDCs varied by tissue and marker. Conclusions: FLT3L administration in vivo increased cDC and pDC enumeration, generated immature cDCs in the liver, and increased cDC maturation in the spleen and mesenteric lymph nodes. This comprehensive characterization of rat liver, spleen, and lymph node-resident DCs is key to understanding the effects of FLT3L on cDC and pDC phenotype.

Role of dendritic cell-mediated immune response in oral homeostasis: A new mechanism of osteonecrosis of the jaw.

Dendritic cells are an important link between innate and adaptive immune response. The role of dendritic cells in bone homeostasis, however, is not understood. Osteoporosis medications that inhibit osteoclasts have been associated with osteonecrosis, a condition limited to the jawbone, thus called medication-related osteonecrosis of the jaw. We propose that disruption of the local immune response renders the oral microenvironment conducive to osteonecrosis. We tested whether zoledronate (Zol) treatment impaired dendritic cell (DC) functions and increased bacterial load in alveolar bone in vivo and whether DC inhibition alone predisposed the animals to osteonecrosis. We also analyzed the role of Zol in impairment of differentiation and function of migratory and tissue-resident DCs, promoting disruption of T-cell activation in vitro. Results demonstrated a Zol induced impairment in DC functions and an increased bacterial load in the oral cavity. DC-deficient mice were predisposed to osteonecrosis following dental extraction. Zol treatment of DCs in vitro caused an impairment in immune functions including differentiation, maturation, migration, antigen presentation, and T-cell activation. We conclude that the mechanism of Zol-induced osteonecrosis of the jaw involves disruption of DC immune functions required to clear bacterial infection and activate T cell effector response.

Murine cytomegalovirus disseminates independently of CX3CR1, CCL2 or its m131/m129 chemokine homologue.

Cytomegaloviruses (CMVs) use myeloid cells to move within their hosts. Murine CMV (MCMV) colonizes the salivary glands for long-term shedding, and reaches them via CD11c+ infected cells. A need to recruit patrolling monocytes for systemic spread has been proposed, based on poor salivary gland infection in fractalkine receptor (CX3CR1)-deficient mice. We found no significant CX3CR1 dependence of salivary gland infection. CCL2 and the viral m131/m129 chemokine homologue were also redundant for acute MCMV spread, arguing against a need for inflammation or infection to recruit additional monocytes to the entry site. M131/m129 promoted salivary gland infection, but only after the initial seeding of infected cells to this site. Our data support the idea that MCMV disseminates by infecting and mobilizing tissue-resident dendritic cells.

Keratinocytes Share Gene Expression Fingerprint with Epidermal Langerhans Cells via mRNA Transfer

The immune functions of epithelia-resident dendritic cells are influenced by epithelial-derived cytokines. Here we identified a communication form between tissue-resident dendritic cells and niche cells that allows direct intracellular material exchange between the parties. We show that many keratinocyte (KC)-specific molecules such as keratins and adhesion molecules could be detected in the epidermal-resident Langerhans cells (LCs) as mRNA and protein. Furthermore, KC-derived Cre led to genetic recombination in the LCs. We also found that LCs containing KC-derived material were more prone to migration. The KC-specific signatures were transferred from KCs to LCs through an exosome-independent mechanism that likely involved nanotubes/dendrites. The transfer of material between epithelial cells and epithelia-associated dendritic cells was not limited to mice or to KC-to-LC transfer. Taken together, these data suggest that the epithelial environment might have a long-term effect on dendritic cell biology and that genetic tools that specifically target epithelial cells also affect tissue-resident immune cells.

PLD-dependent phosphatidic acid microdomains are signaling platforms for podosome formation

Local membrane phospholipid enrichment serves as docking platform for signaling proteins involved in many processes including cell adhesion and migration. Tissue-resident dendritic cells (DCs) assemble actomyosin-based structures called podosomes, which mediate adhesion and degradation of extracellular matrix for migration and antigen sampling. Recent evidence suggested the involvement of phospholipase D (PLD) and its product phosphatidic acid (PA) in podosome formation, but the spatiotemporal control of this process is poorly characterized. Here we determined the role of PLD1 and PLD2 isoforms in regulating podosome formation and dynamics in human primary DCs by combining PLD pharmacological inhibition with a fluorescent PA sensor and fluorescence microscopy. We found that ongoing PLD2 activity is required for the maintenance of podosomes, whereas both PLD1 and PLD2 control the early stages of podosome assembly. Furthermore, we captured the formation of PA microdomains accumulating at the membrane cytoplasmic leaflet of living DCs, in dynamic coordination with nascent podosome actin cores. Finally, we show that both PLD1 and PLD2 activity are important for podosome-mediated matrix degradation. Our results provide novel insight into the isoform-specific spatiotemporal regulation of PLD activity and further our understanding of the role of cell membrane phospholipids in controlling localized actin polymerization and cell protrusion.

Abstract B75: Loss of cross-presentation by tissue resident DC1 in lung adenocarcinomas is an early event that correlates to exhaustion of endogenous antitumor CD8+ T cell responses

Abstract Recent studies highlighted the essential role of tissue-resident dendritic cells (DCs) for T cells priming and immune checkpoint therapy, however the mechanism leading to DCs suppression during tumor growth are still poorly understood. Here we have isolated CD103 (DC1) and Cd11b (DC2) from orthotopic Kras/Trp53 adenocarcinomas to study their function and gene expression profiles. At early stages of tumor progression (day 14-21) DC1 effectively cross-presented tumor antigens acquired in vivo and this was paralleled by the presence of IFN-γ; secreting tumor specific CD8+ T cells in the lung. Starting from day 28 post tumor inoculation, despite minor changes in tumor burden, DC1 were no longer able to cross present tumor associated antigens and CD8+ T cell responses were concomitantly shut-off. DC1 isolated from tumor bearing lungs and fed with antigen ex-vivo confirmed a selective loss in cross-presentation. In parallel, DC2 skewed their cytokine profile and acquired a Th17 promoting phenotype mediated by high production of IL-23. In order to identify factors causing the sudden loss in DC1 activity we analyzed gene expression profiles in total lung tissues. At day 21 we observed a peak in T cell attracting chemokines together with expression of inhibitory pathways. This signature was dramatically modified at day 28, with a decrease in T cell associated genes and an increase in neutrophils related transcripts. Gene expression profiles in de-activated DC1 showed modulation of transcripts related to innate activation and antigen processing. In summary, this study identifies a narrow temporal window during which tissue resident DCs lose the ability to cross-present tumor associated antigens. Loss of DC1 function is accompanied by cell-intrinsic changes in gene expression, cell extrinsic changes in the tumor microenvironment and loss of activity in endogenous CD8+ T antitumor responses. Citation Format: Nicoletta Caronni, Francesca Simoncello, Karla Cervantes-Luevano, Licio Collavin, Federica Benvenuti. Loss of cross-presentation by tissue resident DC1 in lung adenocarcinomas is an early event that correlates to exhaustion of endogenous antitumor CD8+ T cell responses [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B75.

Super-Resolution Correlative Light and Electron Microscopy (SR-CLEM) Reveals Novel Ultrastructural Insights Into Dendritic Cell Podosomes.

Podosomes are multimolecular cytoskeletal structures that coordinate the migration of tissue-resident dendritic cells (DCs). They consist of a protrusive actin-rich core and an adhesive integrin-rich ring that contains adaptor proteins such as vinculin and zyxin. Individual podosomes are typically interconnected by a dense network of actin filaments giving rise to large podosome clusters. The actin density in podosome clusters complicates the analysis of podosomes by light microscopy alone. Here, we present an optimized procedure for performing super-resolution correlative light and electron microscopy (SR-CLEM) to study the organization of multiple proteins with respect to actin in podosome clusters at the ventral plasma membrane of DCs. We demonstrate that our procedure is suited to correlate at least three colors in super-resolution Airyscan microscopy with scanning electron microscopy (SEM). Using this procedure, we first reveal an intriguing complexity in the organization of ventral and radiating actin filaments in clusters formed by DCs which was not properly detected before by light microscopy alone. Next, we demonstrate a differential organization of vinculin and zyxin with respect to the actin filaments at podosomes. While vinculin mostly resides at sites where the actin filaments connect to the cell membrane, zyxin is primarily associated with filaments close to and on top of the core. Finally, we reveal a novel actin-based structure with SEM that connects closely associated podosome cores and which may be important for podosome topography sensing. Interestingly, these interpodosomal connections, in contrast to the radiating and ventral actin filaments appear to be insensitive to inhibition of actin polymerization suggesting that these pools of actin are not dynamically coupled. Together, our work demonstrates the power of correlating different imaging modalities for studying multimolecular cellular structures and could potentially be further exploited to study processes at the ventral plasma membrane of immune cells such as clathrin-mediated endocytosis or immune synapse formation.

Inflammatory responses induce an identity crisis of alveolar macrophages, leading to pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a severe respiratory disease characterized by dyspnea caused by accumulation of surfactant protein. Dysfunction of alveolar macrophages (AMs), which regulate the homeostasis of surfactant protein, leads to the development of PAP; for example, in mice lacking BTB and CNC homology 2 (Bach2). However, how Bach2 helps prevent PAP is unknown, and the cell-specific effects of Bach2 are undefined. Using mice lacking Bach2 in specific cell types, we found that the PAP phenotype of Bach2-deficient mice is due to Bach2 deficiency in more than two types of immune cells. Depletion of hyperactivated T cells in Bach2-deficient mice restored normal function of AMs and ameliorated PAP. We also found that, in Bach2-deficient mice, hyperactivated T cells induced gene expression patterns that are specific to other tissue-resident macrophages and dendritic cells. Moreover, Bach2-deficient AMs exhibited a reduction in cell cycle progression. IFN-γ released from T cells induced Bach2 expression in AMs, in which Bach2 then bound to regulatory regions of inflammation-associated genes in myeloid cells. Of note, in AMs, Bach2 restricted aberrant responses to excessive T cell-induced inflammation, whereas, in T cells, Bach2 puts a brake on T cell activation. Moreover, Bach2 stimulated the expression of multiple histone genes in AMs, suggesting a role of Bach2 in proper histone expression. We conclude that Bach2 is critical for the maintenance of AM identity and self-renewal in inflammatory environments. Treatments targeting T cells may offer new therapeutic strategies for managing secondary PAP.

Human Herpesvirus 8 Infects and Replicates in Langerhans Cells and Interstitial Dermal Dendritic Cells and Impairs Their Function.

ABSTRACTThe predominant types of dendritic cells (DC) in the skin and mucosa are Langerhans cells (LC) and interstitial dermal DC (iDDC). LC and iDDC process cutaneous antigens and migrate out of the skin and mucosa to the draining lymph nodes to present antigens to T and B cells. Because of the strategic location of LC and iDDC and the ability of these cells to capture and process pathogens, we hypothesized that they could be infected with human herpesvirus 8 (HHV-8) (Kaposi's sarcoma [KS]-associated herpesvirus) and have an important role in the development of KS. We have previously shown that HHV-8 enters monocyte-derived dendritic cells (MDDC) through DC-SIGN, resulting in nonproductive infection. Here we show that LC and iDDC generated from pluripotent cord blood CD34+ cell precursors support productive infection with HHV-8. Anti-DC-SIGN monoclonal antibody (MAb) inhibited HHV-8 infection of iDDC, as shown by low expression levels of viral proteins and DNA. In contrast, blocking of both langerin and the receptor protein tyrosine kinase ephrin A2 was required to inhibit HHV-8 infection of LC. Infection with HHV-8 did not alter the cell surface expression of langerin on LC but downregulated the expression of DC-SIGN on iDDC, as we previously reported for MDDC. HHV-8-infected LC and iDDC had a reduced ability to stimulate allogeneic CD4+ T cells in the mixed-lymphocyte reaction. These results indicate that HHV-8 can target both LC and iDDC for productive infection via different receptors and alter their function, supporting their potential role in HHV-8 pathogenesis and KS.IMPORTANCE Here we show that HHV-8, a DNA tumor virus that causes Kaposi's sarcoma, infects three types of dendritic cells: monocyte-derived dendritic cells, Langerhans cells, and interstitial dermal dendritic cells. We show that different receptors are used by this virus to infect these cells. DC-SIGN is a major receptor for infection of both monocyte-derived dendritic cells and interstitial dermal dendritic cells, yet the virus fully replicates only in the latter. HHV-8 uses langerin and the ephrin A2 receptor to infect Langerhans cells, which support full HHV-8 lytic replication. This infection of Langerhans cells and interstitial dermal dendritic cells results in an impaired ability to stimulate CD4+ helper T cell responses. Taken together, our data show that HHV-8 utilizes alternate receptors to differentially infect and replicate in these tissue-resident DC and support the hypothesis that these cells play an important role in HHV-8 infection and pathogenesis.

Genomic Characterization of Murine Monocytes Reveals C/EBPβ Transcription Factor Dependence of Ly6C− Cells

Monocytes are circulating, short-lived mononuclear phagocytes, which in mice and man comprise two main subpopulations. Murine Ly6C+ monocytes display developmental plasticity and are recruited to complement tissue-resident macrophages and dendritic cells on demand. Murine vascular Ly6C- monocytes patrol the endothelium, act as scavengers, and support vessel wall repair. Here we characterized population and single cell transcriptomes, aswell as enhancer and promoter landscapes ofthe murine monocyte compartment. Single cell RNA-seq and transplantation experiments confirmed homeostatic default differentiation of Ly6C+ into Ly6C- monocytes. The main two subsets were homogeneous, but linked by a more heterogeneous differentiation intermediate. We show that monocyte differentiation occurred through denovo enhancer establishment and activation of pre-established (poised) enhancers. Generation of Ly6C- monocytes involved induction of the transcription factor C/EBPβ and C/EBPβ-deficient mice lacked Ly6C- monocytes. Mechanistically, C/EBPβ bound the Nr4a1 promoter and controlled expression of this established monocyte survival factor.

Factors controlling the tolerogenic phenotype of lymphatic endothelial cells.

Abstract The prevailing model of peripheral tolerance necessitates tissue-resident dendritic cells migrating to lymph nodes and cross presenting self-antigen to T cells, resulting in their deletion or anergy. Our lab has identified a novel mechanism of peripheral tolerance involving a subset of lymph node stromal cells called lymphatic endothelial cells (LEC). LEC in the lymph node induce peripheral tolerance by presenting epitopes derived from peripheral tissue antigens (PTAs) in conjunction with expression of PD-L1, leading to CD8 T cell deletion. However, PTAs and PD-L1 are not expressed on LEC in the colon or diaphragm. We performed RNAseq analysis on LEC from lymph node and diaphragm to identify differences in expression of transcription factors that might control expression of PD-L1 and PTA. We found that Spi-B is the most differentially expressed transcription factor in the lymph node compared to the diaphragm, with a fold change of over 500. Spi-B has been implicated in the development and function of medullary thymic epithelial cells, a key cell type in central tolerance. Lymph node LEC harvested from Spi-B deficient mice have a significant shift in markers associated with LEC tolerogenicity. Expression levels of PD-L1, ICAM-1, MAdCAM-1, and LTbR delineate different lymph node LEC subpopulations that vary in their ability to express PTAs and tolerize CD8 T cells. LEC from Spi-B deficient mice have decreased MAdCAM-1 expression and increased LTbR and ICAM-1 expression suggesting a population shift of non-tolerogenic lymph node LEC to tolerogenic lymph node LEC. This data suggests Spi-B may be involved in a negative feedback mechanism to limit the number of tolerogenic LEC during development.

Hematopoietic-to-mesenchymal transition of adipose tissue macrophages is regulated by integrin β1 and fabricated fibrin matrices

ABSTRACTSome bona fide adult adipocytes arise de novo from a bone marrow-derived myeloid lineage. These studies further demonstrate that adipose tissue stroma contains a resident population of myeloid cells capable of adipocyte and multilineage mesenchymal differentiation. These resident myeloid cells lack hematopoietic markers and express mesenchymal and progenitor cell markers. Because bone marrow mesenchymal progenitor cells have not been shown to enter the circulation, we hypothesized that myeloid cells acquire mesenchymal differentiation capacity in adipose tissue. We fabricated a 3-dimensional fibrin matrix culture system to define the adipose differentiation potential of adipose tissue-resident myeloid subpopulations, including macrophages, granulocytes and dendritic cells. Our data show that multilineage mesenchymal potential was limited to adipose tissue macrophages, characterized by the acquisition of adipocyte, osteoblast, chondrocyte and skeletal muscle myocyte phenotypes. Fibrin hydrogel matrices stimulated macrophage loss of hematopoietic cell lineage determinants and the expression of mesenchymal and progenitor cell markers, including integrin β1. Ablation of integrin β1 in macrophages inhibited adipocyte specification. Therefore, some bona fide adipocytes are specifically derived from adipose tissue-resident macrophages via an integrin β1-dependent hematopoietic-to-mesenchymal transition, whereby they become capable of multipotent mesenchymal differentiation. The requirement for integrin β1 highlights this molecule as a potential target for controlling the production of marrow-derived adipocytes and their contribution to adipose tissue development and function.

Batf3 selectively determines acquisition of CD8+ dendritic cell phenotype and function.

Batf3 is a transcription factor that impacts the development of CD103+ tissue-resident dendritic cells (DCs). However, whether Batf3 is absolutely required for the development of CD8+ DCs remains controversial. Id2 is required for CD8+ DC development. Here we show that bone marrow chimeric mice with a deletion of Id2 in the CD11c compartment lose the ability to reject a skin graft expressing a non-self protein antigen or mount a delayed hypersensitivity response. In contrast, Batf3−/− mice remained competent for skin graft rejection and delayed hypersensitivity, and retained a CD8+ DC population with markers characteristic of the CD11b+ DC lineage including CD11b, CD4 and CD172α as well as the key regulator transcription factor IRF4, but lacked IRF8 expression. CD8+ DCs in Batf3−/− mice took up and cleaved protein antigen and larger particles but were unable to phagocytose dying cells, a characteristic feature to the CD8+ DC lineage. These data clarify a requirement for CD8+ lineage DCs for inducing effectors of neo-antigen driven skin graft rejection, and improve our understanding of DC subtype commitment by demonstrating that in the absence of Batf3, CD8+ DCs can change their fate and become CD11b+ DCs.

The transcriptome of lung tumor-infiltrating dendritic cells reveals a tumor-supporting phenotype and a microRNA signature with negative impact on clinical outcome

ABSTRACTTargeting immunomodulatory pathways has ushered a new era in lung cancer therapy. Further progress requires deeper insights into the biology of immune cells in the lung cancer micro-environment.Dendritic cells (DCs) represent a heterogeneous and highly plastic immune cell system with a central role in controlling immune responses. The intratumoral infiltration and activation status of DCs are emerging as clinically relevant parameters in lung cancer.In this study, we used an orthotopic preclinical model of lung cancer to dissect how the lung tumor micro-environment affects tissue-resident DCs and extract novel biologically and clinically relevant information.Lung tumor-infiltrating leukocytes expressing generic DC markers were found to predominantly consist of CD11b+ cells that, compare with peritumoral lung DC counterparts, strongly overexpress the T-cell inhibitory molecule PD-L1 and acquire classical surface markers of tumor-associated macrophages (TAMs). Transcriptome analysis of these CD11b+ tumor-infiltrating DCs (TIDCs) indicates impaired antitumoral immunogenicity, confirms the skewing toward TAM-related features, and indicates exposure to a hypoxic environment. In parallel, TIDCs display a specific microRNA (miRNA) signature dominated by the prototypical lung cancer oncomir miR-31. In vitro, hypoxia drives intrinsic miR-31 expression in CD11b+ DCs. Conditioned medium of miR-31 overexpressing CD11b+ DCs induces pro-invasive lung cancer cell shape changes and is enriched with pro-metastatic soluble factors. Finally, analysis of TCGA datasets reveals that the TIDC-associated miRNA signature has a negative prognostic impact in non-small cell lung cancer.Together, these data suggest a novel mechanism through which the lung cancer micro-environment exploits the plasticity of the DC system to support tumoral progression.