Thursday, November 25, 2010

Hot off the presses! Nov 24 Immunity

The Nov 24 issue of the Immunity is now up on Pubget (About Immunity): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

  • Hooked on Hes: A T-ALL of Addiction
    - Immunity 33(5):645-647 (2010)
    Hes1 is a direct Notch1 target; however, its precise function is unclear. In this issue of Immunity, Wendorff et al. (2010) report that Hes1 regulates the number of T cell progenitors and has important functions in both the induction and maintenance of T cell leukemia.
  • Licensing PPARγ to Work in Macrophages
    - Immunity 33(5):647-649 (2010)
    The mechanisms that direct cell-type-specific peroxisome proliferator-activated receptor (PPAR) gene programs are poorly understood. In this issue of Immunity, Szanto et al. (2010) identify signal transducer and activator of transcription 6 as a transcriptional switch that licenses PPARγ-dependent gene expression in macrophages and dendritic cells.
  • The LTi Cell, an Immunologic Chameleon
    - Immunity 33(5):650-652 (2010)
    Lymphoid tissue inducer (LTi) cells are key components of the machinery required for the construction of the lymphoid structures underlying immune responses. In this issue of Immunity, Vonarbourg et. al. (2010) describe how these cells assume several different guises, each associated with different LTi functions.
  • Infected Cell in Trouble: Bystander Cells Ring the Bell
    - Immunity 33(5):652-654 (2010)
    Infection with intracellular pathogens triggers cytokine production in the infected cells. In this issue of Immunity, Kasper et al. (2010) demonstrate that in certain infections, much of the response is mounted by noninfected neighboring cells.
  • Trapped versus Soluble Chemokines: Functions in Leukocyte Adhesion and Motility
    - Immunity 33(5):654-656 (2010)
    In this issue of Immunity, Bao et al. (2010) provide in vivo evidence that heparan sulfate glycosaminoglycans (GAGs) are indispensable for immobilization and function of major chemokines required for leukocyte adhesion to and crossing through blood and lymphatic vessels.
  • Neutrophils, from Marrow to Microbes
    - Immunity 33(5):657-670 (2010)
    Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These contain proteins that enable the neutrophil to deliver lethal hits against microorganisms, but also to cause great tissue damage. Neutrophils circulate in the blood as dormant cells. At sites of infection, endothelial cells capture bypassing neutrophils and guide them through the endothelial cell lining whereby the neutrophils are activated and tuned for the subsequent interaction with microbes. Once in tissues, neutrophils kill microorganisms by microbicidal agents liberated from granules or generated by metabolic activation. As a final act, neutrophils can extrude stands of DNA with bactericidal proteins attached that act as extracellular traps for microorganisms.
  • Hes1 Is a Critical but Context-Dependent Mediator of Canonical Notch Signaling in Lymphocyte Development and Transformation
    - Immunity 33(5):671-684 (2010)
    Although canonical Notch signaling regulates multiple hematopoietic lineage decisions including T cell and marginal zone B cell fate specification, the downstream molecular mediators of Notch function are largely unknown. We showed here that conditional inactivation of Hes1, a well-characterized Notch target gene, in adult murine bone marrow (BM) cells severely impaired T cell development without affecting other Notch-dependent hematopoietic lineages such as marginal zone B cells. Competitive mixed BM chimeras, intrathymic transfer experiments, and in vitro culture of BM progenitors on Delta-like-expressing stromal cells further demonstrated that Hes1 is required for T cell lineage commitment, but dispensable for Notch-dependent thymocyte maturation through and beyond the beta selection checkpoint. Furthermore, our data strongly suggest that Hes1 is essential for the development and maintenance of Notch-induced T cell acute lymphoblastic leukemia. Collectively, our stu! dies identify Hes1 as a critical but context-dependent mediator of canonical Notch signaling in the hematopoietic system.
  • Alternative Promoter Usage at the Notch1 Locus Supports Ligand-Independent Signaling in T Cell Development and Leukemogenesis
    - Immunity 33(5):685-698 (2010)
    Loss of the transcription factor Ikaros is correlated with Notch receptor activation in T cell acute lymphoblastic leukemia (T-ALL). However, the mechanism remains unknown. We identified promoters in Notch1 that drove the expression of Notch1 proteins in the absence of a ligand. Ikaros bound to both canonical and alternative Notch1 promoters and its loss increased permissive chromatin, facilitating recruitment of transcription regulators. At early stages of leukemogenesis, increased basal expression from the canonical and 5′-alternative promoters initiated a feedback loop, augmenting Notch1 signaling. Ikaros also repressed intragenic promoters for ligand-independent Notch1 proteins that are cryptic in wild-type cells, poised in preleukemic cells, and active in leukemic cells. Only ligand-independent Notch1 isoforms were required for Ikaros-mediated leukemogenesis. Notch1 alternative-promoter usage was observed during T cell development and T-ALL progression. Thus, a ! network of epigenetic and transcriptional regulators controls conventional and unconventional Notch signaling during normal development and leukemogenesis.
  • STAT6 Transcription Factor Is a Facilitator of the Nuclear Receptor PPARγ-Regulated Gene Expression in Macrophages and Dendritic Cells
    - Immunity 33(5):699-712 (2010)
    Peroxisome proliferator-activated receptor γ (PPARγ) is a lipid-activated transcription factor regulating lipid metabolism and inflammatory response in macrophages and dendritic cells (DCs). These immune cells exposed to distinct inflammatory milieu show cell type specification as a result of altered gene expression. We demonstrate here a mechanism how inflammatory molecules modulate PPARγ signaling in distinct subsets of cells. Proinflammatory molecules inhibited whereas interleukin-4 (IL-4) stimulated PPARγ activity in macrophages and DCs. Furthermore, IL-4 signaling augmented PPARγ activity through an interaction between PPARγ and signal transducer and activators of transcription 6 (STAT6) on promoters of PPARγ target genes, including FABP4. Thus, STAT6 acts as a facilitating factor for PPARγ by promoting DNA binding and consequently increasing the number of regulated genes and the magnitude of responses. This interaction, underpinning cell type-specific res! ponses, represents a unique way of controlling nuclear receptor signaling by inflammatory molecules in immune cells.
  • MicroRNAs Prevent the Generation of Autoreactive Antibodies
    - Immunity 33(5):713-722 (2010)
    MicroRNAs have been shown to be critical for a number of aspects of immune system regulation and function. Here, we have examined the role of microRNAs in terminal B cell differentiation by analyzing Cd19-Creki/+Dicer1fl/fl mice. We found that in the absence of Dicer, the transitional and marginal zone (MZ) B cell compartments were overrepresented and follicular (FO) B cell generation was impaired. microRNA analysis revealed that miR185, a microRNA overexpressed in FO cells, dampened B cell receptor (BCR) signaling through Bruton tyrosine kinase downregulation. Dicer-deficient B cells had a skewed BCR repertoire with hallmarks of autoreactivity, which correlated with high titers of autoreactive antibodies in serum and autoimmune features in females. Together, our results reveal a crucial role for microRNAs in late B cell differentiation and in the establishment of B cell tolerance.
  • Mzb1 Protein Regulates Calcium Homeostasis, Antibody Secretion, and Integrin Activation in Innate-like B Cells
    - Immunity 33(5):723-735 (2010)
    Marginal zone (MZ) B cells of the spleen and B1 cells, termed innate-like B cells, differ from follicular B cells by their attenuated Ca2+ mobilization, fast antibody secretion, and increased cell adhesion. We identified and characterized Mzb1 as an endoplasmic reticulum-localized and B cell-specific protein that was most abundantly expressed in MZ B and B1 cells. Knockdown of Mzb1 in MZ B cells increased Ca2+ mobilization and nuclear NFAT transcription factor localization, but reduced lipopolysaccharide-induced antibody secretion and integrin-mediated cell adhesion. Conversely, ectopic expression of an Lck-Mzb1 transgene in peripheral T cells resulted in attenuated Ca2+ mobilization and augmented integrin-mediated cell adhesion. In addition to its interaction with the substrate-specific chaperone Grp94, Mzb1 augmented the function of the oxidoreductase ERp57 in favoring the expression of integrins in their activated conformation. Thus, Mzb1 helps to diversify peripher! al B cell functions by regulating Ca2+ stores, antibody secretion, and integrin activation.
  • Regulated Expression of Nuclear Receptor RORγt Confers Distinct Functional Fates to NK Cell Receptor-Expressing RORγt+ Innate Lymphocytes
    - Immunity 33(5):736-751 (2010)
    Whether the recently identified innate lymphocyte population coexpressing natural killer cell receptors (NKRs) and the nuclear receptor RORγt is part of the NK or lymphoid tissue inducer (LTi) cell lineage remains unclear. By using adoptive transfer of genetically tagged LTi-like cells, we demonstrate that NKR−RORγt+ innate lymphocytes but not NK cells were direct progenitors to NKR+RORγt+ cells in vivo. Genetic lineage tracing revealed that the differentiation of LTi-like cells was characterized by the stable upregulation of NKRs and a progressive loss of RORγt expression. Whereas interleukin-7 (IL-7) and intestinal microbiota stabilized RORγt expression within such NKR-LTi cells, IL-12 and IL-15 accelerated RORγt loss. RORγt+ NKR-LTi cells produced IL-22, whereas RORγt− NKR-LTi cells released IFN-γ and were potent inducers of colitis. Thus, the RORγt gradient in NKR-LTi cells serves as a tunable rheostat for their functional program. Our data also defin! e a previously unappreciated role of RORγt− NKR-LTi cells for the onset or maintenance of inflammatory bowel diseases.
  • Regulation of Cytokine Secretion in Human CD127+ LTi-like Innate Lymphoid Cells by Toll-like Receptor 2
    - Immunity 33(5):752-764 (2010)
    Lymphoid tissue inducer cells are members of an emerging family of innate lymphoid cells (ILC). Although these cells were originally reported to produce cytokines such as interleukin-17 (IL-17) and IL-22, we demonstrate here that human CD127+RORC+ and CD56+CD127+ LTi-like ILC also express IL-2, IL-5, and IL-13 after activation with physiologic stimuli such as common γ-chain cytokines, Toll-like receptor (TLR) 2 ligands, or IL-23. Whereas TLR2 signaling induced IL-5, IL-13, and IL-22 expression in a nuclear factor κB (NF-κB)-dependent manner, IL-23 costimulation induced only IL-22 production. CD127+ LTi-like ILC displayed clonal heterogeneity for IL-13 and IL-5 production, suggesting in vivo polarization. Finally, we identified a role for autocrine IL-2 signaling in mediating the effects of TLR2 stimulation on CD56+CD127+ and CD127+ LTi-like ILC. These results indicate that human LTi-like ILC can directly sense bacterial components and unravel a previously unrecogniz! ed functional heterogeneity among this important population of innate lymphoid cells.
  • The Ubiquitin Ligase TRIM56 Regulates Innate Immune Responses to Intracellular Double-Stranded DNA
    - Immunity 33(5):765-776 (2010)
    The innate immune system detects pathogen- and host-derived double-stranded DNA exposed to the cytosol and induces type I interferon (IFN) and other cytokines. Here, we identified interferon-inducible tripartite-motif (TRIM) 56 as a regulator of double-stranded DNA-mediated type I interferon induction. TRIM56 overexpression enhanced IFN-β promoter activation after double-stranded DNA stimulation whereas TRIM56 knockdown abrogated it. TRIM56 interacted with STING and targeted it for lysine 63-linked ubiquitination. This modification induced STING dimerization, which was a prerequisite for recruitment of the antiviral kinase TBK1 and subsequent induction of IFN-β. Taken together, these results indicate that TRIM56 is an interferon-inducible E3 ubiquitin ligase that modulates STING to confer double-stranded DNA-mediated innate immune responses.
  • Signaling via the MyD88 Adaptor Protein in B Cells Suppresses Protective Immunity during Salmonella typhimurium Infection
    - Immunity 33(5):777-790 (2010)
    The myeloid differentiation primary response gene 88 (Myd88) is critical for protection against pathogens. However, we demonstrate here that MyD88 expression in B cells inhibits resistance of mice to Salmonella typhimurium infection. Selective deficiency of Myd88 in B cells improved control of bacterial replication and prolonged survival of the infected mice. The B cell-mediated suppressive pathway was even more striking after secondary challenge. Upon vaccination, mice lacking Myd88 in B cells became completely resistant against this otherwise lethal infection, whereas control mice were only partially protected. Analysis of immune defenses revealed that MyD88 signaling in B cells suppressed three crucial arms of protective immunity: neutrophils, natural killer cells, and inflammatory T cells. We further show that interleukin-10 is an essential mediator of these inhibitory functions of B cells. Collectively, our data identify a role for MyD88 and B cells in regulation ! of cellular mechanisms of protective immunity during infection.
  • T Regulatory Cells Maintain Intestinal Homeostasis by Suppressing γδ T Cells
    - Immunity 33(5):791-803 (2010)
    Immune tolerance against enteric commensal bacteria is important for preventing intestinal inflammation. Deletion of phosphoinositide-dependent protein kinase 1 (Pdk1) in T cells via Cd4-Cre induced chronic inflammation of the intestine despite the importance of PDK1 in T cell activation. Analysis of colonic intraepithelial lymphocytes of PDK1-deficient mice revealed markedly increased CD8α+ T cell receptor (TCR)γδ+ T cells, including an interleukin-17 (IL-17)-expressing population. TCRγδ+ T cells were responsible for the inflammatory colitis as shown by the fact that deletion of Tcrd abolished spontaneous colitis in the PDK1-deficient mice. This dysregulation of intestinal TCRγδ+ T cells was attributable to a reduction in the number and functional capacity of PDK1-deficient T regulatory (Treg) cells. Adoptive transfer of wild-type Treg cells abrogated the spontaneous activation and proliferation of intestinal TCRγδ+ T cells observed in PDK1-deficient mice and! prevented the development of colitis. Therefore, suppression of intestinal TCRγδ+ T cells by Treg cells maintains enteric immune tolerance.
  • Cell-Cell Propagation of NF-κB Transcription Factor and MAP Kinase Activation Amplifies Innate Immunity against Bacterial Infection
    - Immunity 33(5):804-816 (2010)
    The enteroinvasive bacterium Shigella flexneri uses multiple secreted effector proteins to downregulate interleukin-8 (IL-8) expression in infected epithelial cells. Yet, massive IL-8 secretion is observed in Shigellosis. Here we report a host mechanism of cell-cell communication that circumvents the effector proteins and strongly amplifies IL-8 expression during bacterial infection. By monitoring proinflammatory signals at the single-cell level, we found that the activation of the transcription factor NF-κB and the MAP kinases JNK, ERK, and p38 rapidly propagated from infected to uninfected adjacent cells, leading to IL-8 production by uninfected bystander cells. Bystander IL-8 production was also observed during Listeria monocytogenes and Salmonella typhimurium infection. This response could be triggered by recognition of peptidoglycan and is mediated by gap junctions. Thus, we have identified a mechanism of cell-cell communication that amplifies innate immunity aga! inst bacterial infection by rapidly spreading proinflammatory signals via gap junctions to yet uninfected cells.
  • Endothelial Heparan Sulfate Controls Chemokine Presentation in Recruitment of Lymphocytes and Dendritic Cells to Lymph Nodes
    - Immunity 33(5):817-829 (2010)
    Heparan sulfate can bind several adhesion molecules involved in lymphocyte trafficking. However, the in vivo function of endothelial heparan sulfate in lymphocyte homing and stimulation of the immune response has not been elucidated. Here, we generated mutant mice deficient in the enzyme Ext1, which is required for heparan sulfate synthesis, in a Tek-dependent and inducible manner. Chemokine presentation was diminished in the mutant mice, causing the lack of appropriate integrin-mediated adhesion, and resulted in a marked decrease in lymphocyte sticking to high endothelial venules and in recruitment of resident dendritic cells through lymphatic vessels to the lymph nodes. As a consequence, mutant mice displayed a severe impairment in lymphocyte homing and a compromised contact hypersensitivity response. By contrast, lymphocyte rolling was increased because of loss of electrostatic repulsion by heparan sulfate. These results demonstrate critical roles of endothelial hep! aran sulfate in immune surveillance and immune response generation.
  • K33-Linked Polyubiquitination of T Cell Receptor-ζ Regulates Proteolysis-Independent T Cell Signaling
    - Immunity 33(5):830 (2010)

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