Apoptotic cells induce CD103 expression and immunoregulatory function in myeloid dendritic cell precursors through integrin αv and TGF-β activation

International audienceIn the mammalian gut CD103+ve myeloid DCs are known to suppress inflammation threatened by luminal bacteria, but stimuli driving DC precursor maturation towards this beneficial phenotype are incompletely understood. We isolated CD11+ve DCs from mesenteric lymph nodes (MLNs) of healthy mice; CD103+ve DCs were 8-24 fold more likely than CD103-ve DCs to exhibit extensive of prior phagocytosis of apoptotic intestinal epithelial cells. However, CD103+ve and CD103-ve MLN DCs exhibited similar ex vivo capacity to ingest apoptotic cells, indicating that apoptotic cells might drive immature DC maturation towards the CD103+ve phenotype. When cultured with apoptotic cells, myeloid DC precursors isolated from murine bone marrow and characterised as lineage-ve CD103-ve, displayed enhanced expression of CD103 and β8 integrin and acquired increased capacity to induce T regulatory lymphocytes (Tregs) after 7d in vitro. However, DC precursors isolated from αv-tie2 mice lacking αv integrins in the myeloid line exhibited reduced binding of apoptotic cells and complete deficiency in the capacity of apoptotic cells and/or latent TGF-β1 to enhance CD103 expression in culture, whereas active TGF-β1 increased DC precursor CD103 expression irrespective of αv expression. Fluorescence microscopy revealed clustering of αv integrin chains and latent TGF-β1 at points of contact between DC precursors and apoptotic cells. We conclude that myeloid DC precursors can deploy αv integrin to orchestrate binding of apoptotic cells, activation of latent TGF-β1 and acquisition of the immunoregulatory CD103+ve β8+ve DC phenotype. This implies that a hitherto unrecognised consequence of apoptotic cell interaction with myeloid phagocytes is programming that prevents inflammation

EGL-9 Controls C. elegans Host Defense Specificity through Prolyl Hydroxylation-Dependent and -Independent HIF-1 Pathways

Understanding host defense against microbes is key to developing new and more effective therapies for infection and inflammatory disease. However, how animals integrate multiple environmental signals and discriminate between different pathogens to mount specific and tailored responses remains poorly understood. Using the genetically tractable model host Caenorhabditis elegans and pathogenic bacterium Staphylococcus aureus, we describe an important role for hypoxia-inducible factor (HIF) in defining the specificity of the host response in the intestine. We demonstrate that loss of egl-9, a negative regulator of HIF, confers HIF-dependent enhanced susceptibility to S. aureus while increasing resistance to Pseudomonas aeruginosa. In our attempt to understand how HIF could have these apparently dichotomous roles in host defense, we find that distinct pathways separately regulate two opposing functions of HIF: the canonical pathway is important for blocking expression of a set of HIF-induced defense genes, whereas a less well understood noncanonical pathway appears to be important for allowing the expression of another distinct set of HIF-repressed defense genes. Thus, HIF can function either as a gene-specific inducer or repressor of host defense, providing a molecular mechanism by which HIF can have apparently opposing roles in defense and inflammation. Together, our observations show that HIF can set the balance between alternative pathogen-specific host responses, potentially acting as an evolutionarily conserved specificity switch in the host innate immune response

Natural killer cells require selectins for suppression of subcutaneous tumors

Natural killer (NK) cells recognize and destroy cancer cells through a variety of mechanisms. They may also modulate the adaptive immune response to cancer by interacting with DCs and T cells. Although NK cells play an important role in tumor suppression, little is known about the mechanisms of their recruitment to tumors. Previously it has been shown that subcutaneous tumor growth is enhanced in mice lacking selectins, a family of cell adhesion molecules that mediate the first step of immune cell entry into tissue from the blood. Here we demonstrate that NK cell recruitment to tumors is defective in selectin-deficient mice. In vivo NK cell depletion, either pharmacologic or genetic, leads to enhanced subcutaneous tumor growth, similar to the phenotype observed in the selectin-deficient animals. We also show that, although NK cells from selectin-deficient mice appear developmentally normal, and are functional in in vitro assays, their in vivo function is impaired. This study reveals a role for selectins in NK cell recruitment to tumors and in regulation of effective tumor immunity

Activation of caspase-1 by the NLRP3 inflammasome regulates the NADPH oxidase NOX2 to control phagosome function

Phagocytosis is a fundamental cellular process that is pivotal for immunity as it coordinates microbial killing, innate immune activation and antigen presentation. An essential step in this process is phagosome acidification, which regulates a number of functions of these organelles that allow them to participate in processes essential to both innate and adaptive immunity. Here we report that acidification of phagosomes containing Gram-positive bacteria is regulated by the NLRP3-inflammasome and caspase-1. Active caspase-1 accumulates on phagosomes and acts locally to control the pH by modulating buffering by the NADPH oxidase NOX2. These data provide insight into a mechanism by which innate immune signals can modify cellular defenses and establish a new function for the NLRP3-inflammasome and caspase-1 in host defense

Persistence of apoptotic cells without autoimmune disease or inflammation in CD14−/− mice

Interaction of macrophages with apoptotic cells involves multiple steps including recognition, tethering, phagocytosis, and anti-inflammatory macrophage responses. Defective apoptotic cell clearance is associated with pathogenesis of autoimmune disease. CD14 is a surface receptor that functions in vitro in the removal of apoptotic cells by human and murine macrophages, but its mechanism of action has not been defined. Here, we demonstrate that CD14 functions as a macrophage tethering receptor for apoptotic cells. Significantly, CD14−/− macrophages in vivo are defective in clearing apoptotic cells in multiple tissues, suggesting a broad role for CD14 in the clearance process. However, the resultant persistence of apoptotic cells does not lead to inflammation or increased autoantibody production, most likely because, as we show, CD14−/− macrophages retain the ability to generate anti-inflammatory signals in response to apoptotic cells. We conclude that CD14 plays a broad tethering role in apoptotic cell clearance in vivo and that apoptotic cells can persist in the absence of proinflammatory consequences

Syrian hamster dermal cell immortalization is not enhanced by power line frequency electromagnetic field exposure

Several epidemiological studies have suggested associations between exposure to residential power line frequency electromagnetic fields and childhood leukaemia, and between occupational exposure and adult leukaemia. A variety of in vitro studies have provided limited supporting evidence for the role of such exposures in cancer induction in the form of acknowledged cellular end points, such as enhanced mutation rate and cell proliferation, though the former is seen only with extremely high flux density exposure or with co-exposure to ionizing radiation. However, in vitro experiments on a scale large enough to detect rare cancer-initiating events, such as primary cell immortalization following residential level exposures, have not thus far been reported. In this study, large cultures of primary Syrian hamster dermal cells were continuously exposed to power line frequency electromagnetic fields of 10 100 and 1000 μT for 60 h, with and without prior exposure to a threshold (1.5 Gy), or sub-threshold (0.5 Gy), immortalizing dose of ionizing radiation. Electromagnetic field exposure alone did not immortalize these cells at a detectable frequency (≥ 1 × 10−7); furthermore, such exposure did not enhance the frequency of ionizing radiation-induced immortalization. © 1999 Cancer Research Campaig

Preferential Expression of Integrin αvβ8 Promotes Generation of Regulatory T Cells by Mouse CD103⁺Dendritic Cells

BACKGROUND and AIMS: Immune responses in the intestine are controlled by regulatory T cells (Tregs), which prevent inflammation in response to commensal bacteria. A specific population of intestinal dendritic cells (DCs), marked by expression of CD103, generate Tregs more efficiently than other DC populations through mechanisms that involve retinoic acid and transforming growth factor (TGF)-β. However, it is not clear how CD103(+) DCs are specialized for this function. We investigated the ability of CD103(+) DCs to promote Treg generation through activation of TGF-β and the role of integrins with the αv subunit in this process. METHODS: Naïve T cells were cultured with purified DCs from mesenteric lymph nodes (MLNs) or intestines of wild-type and αv conditional knockout mice to assess generation of Tregs. Antigens were administered orally to mice, and antigen-specific generation of Tregs was measured in intestinal tissues. Expression of the integrin αv subunit was measured in purified subpopulations of DCs by quantitative polymerase chain reaction and immunoblot analyses. RESULTS: In vitro, CD103(+) DCs generated more Tregs in the presence of latent TGF-β than other MLN DCs. Efficient generation of Tregs required expression of the integrin αv subunit by DCs; mice that lacked αv in immune cells did not convert naïve T cells to intestinal Tregs in response to oral antigen. CD103(+) DCs derived from the MLNs selectively expressed high levels of integrin αvβ8 compared with other populations of DCs. CONCLUSIONS: Expression of αvβ8 is required for CD103(+) DCs to become specialized and activate latent TGF-β and generate Tregs during the induction of tolerance to intestinal antigens in mice