We describe a new B220 ؉ subpopulation of immaturelike dendritic cells (B220 ؉ DCs) with low levels of expression of major histocompatibility complex (MHC) and costimulatory molecules and markedly reduced T-cell stimulatory potential, located in the thymus, bone marrow, spleen, and lymph nodes. B220 ؉ DCs display ultrastructural characteristics resembling those of human plasmacytoid cells and accordingly produce interferon-␣ after virus stimulation. B220 ؉ DCs acquired a strong antigen-presenting cell capacity on incubation with CpG oligodeoxynucleotides, concomitant with a remarkable up-regulation of MHC and costimulatory molecules and the production of interleukin-12 (IL-12) and IL-10. Importantly, our data suggest that nonstimulated B220 ؉ DCs represent a subset of physiological tolerogenic DCs endowed with the capacity to induce a nonanergic state of T-cell unresponsiveness, involving the differentiation of T regulatory cells capable of suppressing antigen-specific T-cell proliferation. In conclusion, our data support the hypothesis that B220 ؉ DCs represent a lymphoid organ subset of immature DCs with a dual role in the immune system-exerting a tolerogenic function in steady state but differentiating on microbial stimulation into potent antigen-presenting cells with type 1 interferon production capacity. IntroductionMaintenance of immunologic self-tolerance is an essential process directed at preventing harmful autoimmune diseases caused by autoreactive T cells capable of responding to self-antigens. Avoidance of pathologic reactivity of self-reactive T cells may occur as a consequence of T-cell deletion, T-cell unresponsiveness, or, in some instances, T helper cell type 2 (TH2) skewing (reviewed in Hackstein et al 1 ). Deletion of autoreactive T-cell clones, resulting in T-cell-negative selection, takes place essentially in the thymus under the control of thymic dendritic cells (DCs) and epithelial cells (reviewed in Ardavín 2 ). In contrast, the molecular mechanisms controlling T-cell unresponsiveness or anergy, which is the basis of peripheral tolerance, are not fully understood. However, increasing evidence supports that T regulatory (T reg ) cells play an essential role in the control of autoreactive T-cell clones and, therefore, in the maintenance of T-cell peripheral tolerance because of their capacity to suppress antigen-specific T-cell responses (reviewed in Roncarolo and Levings 3 ). Interestingly immature DCs have been demonstrated to participate in the differentiation of T reg cells (reviewed in Jonuleit et al 4 ). In this sense, human and mouse interleukin-10 (IL-10)-treated immature DCs have been reported to induce antigen-specific T-cell anergy. [5][6][7][8][9] In addition, in vitrogenerated human immature DCs have been demonstrated to induce the differentiation of T reg cells in vitro and in vivo. 9,10 Therefore, on the basis of these data, the tolerogenic potential of DCs has been proposed to be correlated with an immature DC state. 1 On the other hand, DC-mediated induction of murine T-ce...

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The CXCR4 chemokine receptor and the delta opioid receptor (DOR) are pertussis toxinsensitive G protein-coupled receptors (GPCR). Both are widely distributed in brain tissues and immune cells, and have key roles in inflammation processes and in pain sensation on proximal nerve endings. We show that in immune cells expressing CXCR4 and DOR, simultaneous addition of their ligands CXCL12 and [D-Pen2, DPen5]enkephalin does not trigger receptor function. This treatment does not affect ligand binding or receptor expression, nor does it promote heterologous desensitization. Our data indicate that CXCR4 and DOR form heterodimeric complexes that are dynamically regulated by the ligands. This is compatible with a model in which GPCR oligomerization leads to suppression of signaling, promoting a dominant negative effect. Knockdown of CXCR4 and DOR signaling by heterodimerization might have repercussions on physiological and pathological processes such as inflammation, pain sensation and HIV-1 infection.Supporting Information for this article is available at http://www.wiley-vch.de/contents/jc_2040/2008/37630_s.pdf See accompanying article: http://dx.doi.org/10.1002/eji200738101 IntroductionThe G protein-coupled receptors (GPCR) represent the largest, most diverse family of transmembrane receptors expressed in the body. They act through G proteins to regulate intracellular processes including cell adhesion, migration and proliferation [1]. Studies show that the GPCR can function as oligomers [2,3]. Perhaps their most striking feature is that GPCR form not only functional homo-oligomers, but can also associate with other GPCR to form hetero-oligomers. Homo-and hetero-oligomers differ in their pharmacological pro- files, ligand binding affinity, and/or internalization pathways [4][5][6]. GPCR hetero-oligomerization would thus enable generation of new types of signaling units. Opioid and chemokine receptors are members of the Ga i protein-linked GPCR. These receptors and their ligands are expressed in neurons and glial cells, and in immune system cells such as lymphocytes, monocytes and neutrophils [7]. They share the same microenvironment in many physiological situations and are essential for inflammation processes. Chemokine receptors promote immune cell migration to and adhesion at the inflammation site, whereas opioid receptors reduce pain sensation on proximal nerve endings. Opioid receptors can also regulate the immune response, as they alter antibody responses, cell-mediated immunity, phagocytic activity, adhesion and chemotaxis [8][9][10][11]. Opioids also prevent leukocyte movement toward chemokine gradients [12], and cross-desensitization is described between opioid and chemokine receptors [8,10]. The CCR5 chemokine receptor can form heterodimers with each of the three opioid receptor subtypes (l, d, and j) [8,10].CXCR4, the most widely expressed chemokine receptor [13], is crucial for correct lymphocyte trafficking [14], hematopoiesis, and development [15][16][17]. It is also a coreceptor for T-tropic HIV strains [1...

The monocyte capacity to differentiate into dendritic cells (DCs) was originally demonstrated by human in vitro DC differentiation assays that have subsequently become the essential methodologic approach for the production of DCs to be used in DC-mediated cancer immunotherapy protocols. In addition, in vitro DC generation from monocytes is a powerful tool to study DC differentiation and maturation. However, whether DC differentiation from monocytes occurs in vivo remains controversial, and the physiologic counterparts of in vitro monocyte-derived DCs are unknown. In addition, information on murine monocytes and monocyte-derived DCs is scarce. Here we show that mouse bone marrow monocytes can be differentiated in vitro into DCs using similar conditions as those defined in humans, including in vitro cultures with granulocyte-macrophage colony-stimulating factor and interleukin 4 and reverse transendothelial migration assays. Importantly, we demonstrate that after in vivo transfer monocytes generate CD8 ؊ and CD8 ؉ DCs in the spleen, but differentiate into macrophages on migration to the thoracic cavity. In conclusion, we support the hypothesis that monocytes generate DCs not only on entry into the lymph and migration to the lymph nodes as proposed, but also on extravasation from blood and homing to the spleen, suggesting that monocytes represent immediate precursors of lymphoid organ DCs.

Hypermethylation of SOCS genes is associated with many human cancers, suggesting a role as tumor suppressors. As adaptor molecules for ubiquitin ligases, SOCS proteins modulate turnover of numerous target proteins. Few SOCS targets identified so far have a direct role in cell cycle progression; the mechanism by which SOCS regulate the cell cycle thus remains largely unknown. Here we show that SOCS1 overexpression inhibits in vitro and in vivo expansion of human melanoma cells, and that SOCS1 associates specifically with Cdh1, triggering its degradation by the proteasome. Cells therefore show a G1/S transition defect, as well as a secondary blockade in mitosis and accumulation of cells in metaphase. SOCS1 expression correlated with a reduction in cyclin D/E levels and an increase in the tumor suppressor p19, as well as the CDK inhibitor p53, explaining the G1/S transition defect. As a result of Cdh1 degradation, SOCS1-expressing cells accumulated cyclin B1 and securin, as well as apparently inactive Cdc20, in mitosis. Levels of the late mitotic Cdh1 substrate Aurora A did not change. These observations comprise a hitherto unreported mechanism of SOCS1 tumor suppression, suggesting this molecule as a candidate for the design of new therapeutic strategies for human melanoma.