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See detailTumor microenvironment converts plasmacytoid dendritic cells into immunosuppressive/tolerogenic cells: insight into the molecular mechanisms
Demoulin, Stéphanie ULg; Herfs, Michael ULg; Delvenne, Philippe ULg et al

in Journal of Leukocyte Biology (2013), 93(3), 343-352

Human pDCs represent a rare population of circulating cells characterized by a rapid and massive TLR-dependent secretion of type I IFN in response to pathogenic agents or danger signals. Through their ... [more ▼]

Human pDCs represent a rare population of circulating cells characterized by a rapid and massive TLR-dependent secretion of type I IFN in response to pathogenic agents or danger signals. Through their capacity to bring together innate and adaptive immunity and to secrete soluble factors controlling cancer development, these cells could represent important actors in antitumor immunity. However, accumulating evidence suggests that pDCs recruited to the tumor microenvironment often display a nonactivated state and are associated with the development and maintenance of immunosuppression. Here, we present an overview of neoplastic lesions associated with an infiltration of immunosuppressive/ tolerogenic pDC. Moreover, as the proper response of pDC against cancer depends on a critical balance between immune-activating and immune-suppressing mechanisms, we summarize current knowledge about the molecular pathways developed by tumors to prevent antitumoral pDC immune responses. A better understanding of the mechanisms regulating pDC function in tumors could aid in the development of new therapies. Indeed, effective cancer vaccines or therapies could combine immunoactivating strategies (i.e., TLR agonists) with elimination of immune-suppressing mechanisms, leading to pDC reprogramming and thus, allowing tumor rejection in a clinical setting. [less ▲]

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See detailHIV-1 regulation of latency in the monocyte-macrophage lineage and in CD4+ T lymphocytes.
Redel, Laetitia; Le Douce, Valentin; Cherrier, Thomas ULg et al

in Journal of Leukocyte Biology (2010), 87(4), 575-88

The introduction in 1996 of the HAART raised hopes for the eradication of HIV-1. Unfortunately, the discovery of latent HIV-1 reservoirs in CD4+ T cells and in the monocyte-macrophage lineage proved the ... [more ▼]

The introduction in 1996 of the HAART raised hopes for the eradication of HIV-1. Unfortunately, the discovery of latent HIV-1 reservoirs in CD4+ T cells and in the monocyte-macrophage lineage proved the optimism to be premature. The long-lived HIV-1 reservoirs constitute a major obstacle to the eradication of HIV-1. In this review, we focus on the establishment and maintenance of HIV-1 latency in the two major targets for HIV-1: the CD4+ T cells and the monocyte-macrophage lineage. Understanding the cell-type molecular mechanisms of establishment, maintenance, and reactivation of HIV-1 latency in these reservoirs is crucial for efficient therapeutic intervention. A complete viral eradication, the holy graal for clinicians, might be achieved by strategic interventions targeting latently and productively infected cells. We suggest that new approaches, such as the combination of different kinds of proviral activators, may help to reduce dramatically the size of latent HIV-1 reservoirs in patients on HAART. [less ▲]

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See detailThe cross-talk between dendritic and regulatory T cells: good or evil?
Hubert, Pascale ULg; Jacobs, Nathalie ULg; Caberg, Jean-Hubert ULg et al

in Journal of Leukocyte Biology (2007), 82(4), 781-94

Immune responses against pathogens require fine regulation in order to avoid excessive inflammation, which could be harmful to the host. Moreover, the immune system must be tolerant to non-pathogenic ... [more ▼]

Immune responses against pathogens require fine regulation in order to avoid excessive inflammation, which could be harmful to the host. Moreover, the immune system must be tolerant to non-pathogenic antigens in order to prevent allergy, autoimmunity and transplant rejection. There is accumulating evidence that interactions between dendritic cells (DC) and regulatory T (Treg) cells play a crucial role in the balance between immune response and tolerance. Communications between these cells are complex, bi-directional and mediated by soluble or cell surface molecules. The maturation status of DC, which may be influenced by different microenvironmental factors, is considered as an important checkpoint for the induction of peripheral tolerance through modifications of the activation status of T cells. Moreover, several lines of experimental evidence suggest that different subsets or the functional status of DC are also involved in the promotion of Treg cell differentiation. A better knowledge of the regulatory mechanisms of the immune response induced or inhibited by DC via their interactions with Treg cells could be relevant for the development of new immunotherapeutic approaches. [less ▲]

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See detailDe novo C16- and C24-ceramide generation contributes to spontaneous neutrophil apoptosis.
Seumois, Gregory; Fillet, Marianne ULg; Gillet, Laurent ULg et al

in Journal of Leukocyte Biology (2007), 81(6), 1477-1486

Neutrophils rapidly undergo spontaneous apoptosis following their release from the bone marrow. Although central to leukocyte homeostasis, the mechanisms that regulate neutrophil apoptosis remain poorly ... [more ▼]

Neutrophils rapidly undergo spontaneous apoptosis following their release from the bone marrow. Although central to leukocyte homeostasis, the mechanisms that regulate neutrophil apoptosis remain poorly understood. We show here that apoptosis of cultured neutrophils is preceded by a substantial increase in the intracellular levels of 16 and 24 carbon atom (C(16)- and C(24))-ceramides, which are lipid second messengers of apoptosis and stress signaling. Treatment of neutrophils with fumonisin B(2), a selective inhibitor of the de novo pathway of ceramide synthesis, prevented accumulation of C(16)- and C(24)-ceramides. Moreover, fumonisin B(2) significantly reduced caspase-3, -8, and -9 activation and apoptosis in these cells. Conversely, 3-O-methylsphingomyelin and fantofarone, which are specific inhibitors of neutral and acid sphingomyelinases, respectively, neither inhibited C(16)- and C(24)-ceramide production nor decreased the apoptosis rate in neutrophils, indicating that in these cells, ceramides are not generated from membrane sphingomyelin. Further experiments showed that increasing endogenous C(16)- and C(24)-ceramide levels by using DL-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol and (1S,2R)-D-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol, two inhibitors of ceramide metabolism, enhances caspase-3, -8, and -9 activity and increases neutrophil apoptosis. Similarly, apoptosis was induced rapidly when synthetic C(16)- and/or C(24)-ceramides were added to neutrophil cultures. Finally, GM-CSF, a cytokine that delays neutrophil apoptosis, abrogated C(16)- and C(24)-ceramide accumulation totally in cultured neutrophils, whereas Fas ligation accelerated apoptosis in these cells without affecting de novo ceramide production. We conclude that de novo generation of C(16)- and C(24)-ceramides contributes to spontaneous neutrophil apoptosis via caspase activation and that GM-CSF exerts its antiapoptotic effects on neutrophils, at least partly through inhibition of ceramide accumulation. [less ▲]

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