Hot off the presses! Jul 17 Immunity

The Jul 17 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:

• Does Def6 Deficiency Cause Autoimmunity?
  - Immunity 31(1):1-2 (2009)
  
• Response to Letter from Altman and Bécart
  - Immunity 31(1):2-3 (2009)
  
• A Nonself RNA Pattern: Tri-p to Panhandle
  - Immunity 31(1):4-5 (2009)
  In this issue of Immunity, Schlee et al. (2009) defines key RNA structures recognized by a cellular viral sensor, RIG-I. This and another recent report by Schmidt et al. (2009) provide new insights into the mechanism of antiviral innate immunity.
• IL-33 Raises Alarm
  - Immunity 31(1):5-7 (2009)
  The interleukin-1 (IL-1)-like cytokine IL-33 is widely assumed to undergo proteolytic maturation by caspase-1. In this issue of Immunity, Lüthi et al. (2009) show that IL-33 is not a caspase-1 substrate. IL-33 is inactivated by caspase-3 and -7 to prevent an inappropriate immune response during apoptosis, but not in necrosis.
• Integr-ating IL-1α in Antiviral Host Defenses
  - Immunity 31(1):7-9 (2009)
  Adenoviral vectors used in gene therapy induce inflammation, although the underlying mechanisms are currently unknown. In this issue of Immunity, Di Paolo et al. (2009) implicate interleukin-1α (IL-1α) in virus-induced inflammation and identify the β3 integrin as the key receptor regulating IL-1α activity.
• How to be Naive
  - Immunity 31(1):9-11 (2009)
  The transcription factor KLF2 directs expression of receptors involved in trafficking of naive T cells. In this issue of Immunity, Weinreich et al. (2009) demonstrate that KLF2 additionally represses IL-4 production, which otherwise induces CXCR3 expression.
• Helping the Helpers!
  - Immunity 31(1):12-14 (2009)
  T follicular helper (Tfh) cells are crucial for generating humoral immune responses. In this issue of Immunity, Schmitt et al. (2009) reveal the differentiation of human Tfh cells is dependent on dendritic cell-derived interleukin-12.
• Interleukin-22-Producing Natural Killer Cells and Lymphoid Tissue Inducer-like Cells in Mucosal Immunity
  - Immunity 31(1):15-23 (2009)
  Blood, lymphoid tissues, and placenta contain diverse subpopulations of natural killer (NK) cells that possess distinct immune functions. Recent studies have shown that human and mouse gut-associated lymphoid tissues harbor a unique NK cell subset that specializes in production of interleukin (IL)-22. This cytokine plays a role in host defense of mucosal barriers, although dysregulated secretion may cause autoimmune disease. In parallel, human fetal lymphoid tissue inducer (LTi) cells and mouse adult LTi-like cells in secondary lymphoid tissues were found to release IL-22, as well as IL-17, a proinflammatory cytokine that mediates host defense against extracellular pathogens. Here, we compare these recently identified immune cells, reviewing what is known about their anatomical location, differentiation requirements, function, and potential involvement in host defense and autoimmunity. Finally, we discuss the challenges faced in furthering our understanding of the deve! lopmental relationships and role of NK and LTi-like cells in mucosal immune responses.
• Recognition of 5′ Triphosphate by RIG-I Helicase Requires Short Blunt Double-Stranded RNA as Contained in Panhandle of Negative-Strand Virus
  - Immunity 31(1):25-34 (2009)
  Antiviral immunity is triggered by immunorecognition of viral nucleic acids. The cytosolic helicase RIG-I is a key sensor of viral infections and is activated by RNA containing a triphosphate at the 5′ end. The exact structure of RNA activating RIG-I remains controversial. Here, we established a chemical approach for 5′ triphosphate oligoribonucleotide synthesis and found that synthetic single-stranded 5′ triphosphate oligoribonucleotides were unable to bind and activate RIG-I. Conversely, the addition of the synthetic complementary strand resulted in optimal binding and activation of RIG-I. Short double-strand conformation with base pairing of the nucleoside carrying the 5′ triphosphate was required. RIG-I activation was impaired by a 3′ overhang at the 5′ triphosphate end. These results define the structure of RNA for full RIG-I activation and explain how RIG-I detects negative-strand RNA viruses that lack long double-stranded RNA but do contain blunt sho! rt double-stranded 5′ triphosphate RNA in the panhandle region of their single-stranded genome.
• Structure of Natural Killer Cell Receptor KLRG1 Bound to E-Cadherin Reveals Basis for MHC-Independent Missing Self Recognition
  - Immunity 31(1):35-46 (2009)
  The cytolytic activity of natural killer (NK) cells is regulated by inhibitory receptors that detect the absence of self molecules on target cells. Structural studies of missing self recognition have focused on NK receptors that bind MHC. However, NK cells also possess inhibitory receptors specific for non-MHC ligands, notably cadherins, which are downregulated in metastatic tumors. We determined the structure of killer cell lectin-like receptor G1 (KLRG1) in complex with E-cadherin. KLRG1 mediates missing self recognition by binding to a highly conserved site on classical cadherins, enabling it to monitor expression of several cadherins (E-, N-, and R-) on target cells. This site overlaps the site responsible for cell-cell adhesion but is distinct from the integrin αEβ7 binding site. We propose that E-cadherin may coengage KLRG1 and αEβ7 and that KLRG1 overcomes its exceptionally weak affinity for cadherins through multipoint attachment to target cells, resulting ! in inhibitory signaling.
• Differential Recognition of CD1d-α-Galactosyl Ceramide by the Vβ8.2 and Vβ7 Semi-invariant NKT T Cell Receptors
  - Immunity 31(1):47-59 (2009)
  The semi-invariant natural killer T cell receptor (NKT TCR) recognizes CD1d-lipid antigens. Although the TCRα chain is typically invariant, the β chain expression is more diverse, where three Vβ chains are commonly expressed in mice. We report the structures of Vα14-Vβ8.2 and Vα14-Vβ7 NKT TCRs in complex with CD1d-α-galactosylceramide (α-GalCer) and the 2.5 Å structure of the human NKT TCR-CD1d-α-GalCer complex. Both Vβ8.2 and Vβ7 NKT TCRs and the human NKT TCR ligated CD1d-α-GalCer in a similar manner, highlighting the evolutionarily conserved interaction. However, differences within the Vβ domains of the Vβ8.2 and Vβ7 NKT TCR-CD1d complexes resulted in altered TCRβ-CD1d-mediated contacts and modulated recognition mediated by the invariant α chain. Mutagenesis studies revealed the differing contributions of Vβ8.2 and Vβ7 residues within the CDR2β loop in mediating contacts with CD1d. Collectively we provide a structural basis for the differential! NKT TCR Vβ usage in NKT cells.
• T Cell Receptor CDR2β and CDR3β Loops Collaborate Functionally to Shape the iNKT Cell Repertoire
  - Immunity 31(1):60-71 (2009)
  Mouse type I natural killer T cell receptors (iNKT TCRs) use a single Vα14-Jα18 sequence and Vβs that are almost always Vβ8.2, Vβ7, or Vβ2, although the basis of this differential usage is unclear. We showed that the Vβ bias occurred as a consequence of the CDR2β loops determining the affinity of the iNKT TCR for CD1d-glycolipids, thus controlling positive selection. Within a conserved iNKT-TCR-CD1d docking framework, these inherent Vβ-CD1d affinities are further modulated by the hypervariable CDR3β loop, thereby defining a functional interplay between the two iNKT TCR CDRβ loops. These Vβ biases revealed a broadly hierarchical response in which Vβ8.2 > Vβ7 > Vβ2 in the recognition of diverse CD1d ligands. This restriction of the iNKT TCR repertoire during thymic selection paradoxically ensures that each peripheral iNKT cell recognizes a similar spectrum of antigens.
• Deltex1 Is a Target of the Transcription Factor NFAT that Promotes T Cell Anergy
  - Immunity 31(1):72-83 (2009)
  The molecular process underlying T cell anergy is incompletely understood. Deltex1 (DTX1) is a Notch target with unknown physiological function. Here we show that Dtx1 was a transcription target of nuclear factor of activated T cells (NFAT) and participated in T cell anergy. DTX1 protein was upregulated during T cell anergy, and transgenic expression of Dtx1 attenuated T cell activation. DTX1 inhibited T cell activation by both E3-dependent and E3-independent mechanisms. In addition, DTX1 suppressed T cell activation in the absence of its Notch-binding domain. Importantly, DTX1 regulated the expression of two anergy-associated molecules, growth arrest and DNA-damage-inducible 45 β (Gadd45β) and Cbl-b. DTX1 interacted with early growth response 2 (Egr-2) for optimum expression of Cbl-b. Furthermore, deficiency of DTX1 augmented T cell activation, conferred resistance to anergy induction, enhanced autoantibody generation, and increased inflammation. DTX1 therefore repr! esents a component downstream of calcium-NFAT signaling that regulates T cell anergy.
• Suppression of Interleukin-33 Bioactivity through Proteolysis by Apoptotic Caspases
  - Immunity 31(1):84-98 (2009)
  Interleukin-33 (IL-33) is a member of the IL-1 family and is involved in polarization of T cells toward a T helper 2 (Th2) cell phenotype. IL-33 is thought to be activated via caspase-1-dependent proteolysis, similar to the proinflammatory cytokines IL-1β and IL-18, but this remains unproven. Here we showed that IL-33 was processed by caspases activated during apoptosis (caspase-3 and -7) but was not a physiological substrate for caspases associated with inflammation (caspase-1, -4, and -5). Furthermore, caspase-dependent processing of IL-33 was not required for ST2 receptor binding or ST2-dependent activation of the NF-κB transcription factor. Indeed, caspase-dependent proteolysis of IL-33 dramatically attenuated IL-33 bioactivity in vitro and in vivo. These data suggest that IL-33 does not require proteolysis for activation, but rather, that IL-33 bioactivity is diminished through caspase-dependent proteolysis within apoptotic cells. Thus, caspase-mediated proteoly! sis acts as a switch to dampen the proinflammatory properties of IL-33.
• Integrin-Dependent Organization and Bidirectional Vesicular Traffic at Cytotoxic Immune Synapses
  - Immunity 31(1):99-109 (2009)
  Cytotoxic lymphocytes kill target cells by releasing the content of secretory lysosomes at the immune synapse. To understand the dynamics and control of cytotoxic immune synapses, we imaged human primary, live natural killer cells on lipid bilayers carrying ligands of activation receptors. Formation of an organized synapse was dependent on the presence of the β2 integrin ligand ICAM-1. Ligands of coactivation receptors 2B4 and NKG2D segregated into central and peripheral regions, respectively. Lysosomal protein LAMP-1 that was exocytosed during degranulation accumulated in a large and spatially stable cluster, which overlapped with a site of membrane internalization. Lysosomal compartments reached the plasma membrane at focal points adjacent to centrally accumulated LAMP-1. Imaging of fixed cells revealed that perforin-containing granules were juxtaposed to an intracellular compartment where exocytosed LAMP-1 was retrieved. Thus, cytotoxic immune synapses include a ce! ntral region of bidirectional vesicular traffic, which is controlled by integrin signaling.
• Virus Binding to a Plasma Membrane Receptor Triggers Interleukin-1α-Mediated Proinflammatory Macrophage Response In Vivo
  - Immunity 31(1):110-121 (2009)
  The recognition of viral components by host pattern-recognition receptors triggers the induction of the antiviral innate immune response. Toll-like receptor 9 (TLR9) and NLRP3 inflammasome were shown to be the principal specific sensors of viral double-stranded DNA. Here we present evidence that macrophages in vivo activated an innate immune response to a double-stranded DNA virus, adenovirus (Ad), independently of TLR9 or NLRP3 inflammasome. In response to Ad, macrophage-derived IL-1α triggered IL-1RI-dependent production of a defined set of proinflammatory cytokines and chemokines. The IL-1α-mediated response required a selective interaction of virus arginine-glycine-aspartic acid (RGD) motifs with macrophage β3 integrins. Thus, these data identify IL-1α-IL-1RI as a key pathway allowing for the activation of proinflammatory responses to the virus, independently of its genomic nucleic acid recognition.
• KLF2 Transcription-Factor Deficiency in T Cells Results in Unrestrained Cytokine Production and Upregulation of Bystander Chemokine Receptors
  - Immunity 31(1):122-130 (2009)
  The transcription factor KLF2 regulates T cell trafficking by promoting expression of the lipid-binding receptor S1P1 and the selectin CD62L. Recently, it was proposed that KLF2 also represses the expression of chemokine receptors. We confirmed the upregulation of the chemokine receptor CXCR3 on KLF2-deficient T cells. However, we showed that this was a cell-nonautonomous effect, as revealed by CXCR3 upregulation on wild-type bystander cells in mixed bone-marrow chimeras with KLF2-deficient cells. Furthermore, KLF2-deficient T cells overproduced IL-4, leading to the upregulation of CXCR3 through an IL-4-receptor- and eomesodermin-dependent pathway. Consistent with the increased IL-4 production, we found high concentrations of serum IgE in mice with T cell-specific KLF2 deficiency. Our findings support a model where KLF2 regulates T cell trafficking by direct regulation of S1P1 and CD62L and restrains spontaneous cytokine production in naive T cells.
• Opposing Effects of TGF-β and IL-15 Cytokines Control the Number of Short-Lived Effector CD8+ T Cells
  - Immunity 31(1):131-144 (2009)
  An effective immune response against infectious agents involves massive expansion of CD8+ T cells. Once the infection is cleared, the majority of these effector cells die through unknown mechanisms. How is expansion controlled to maximize pathogen clearance and minimize immunopathology? We found, after Listeria infection, plasma transforming growth factor β (TGF-β) titers increased concomitant with the expansion of effector CD8+ T cells. Blocking TGF-β signaling did not affect effector function of CD8+ T cells. However, TGF-β controlled effector cell number by lowering Bcl-2 amounts and selectively promoting the apoptosis of short-lived effector cells. TGF-β-mediated apoptosis of this effector subpopulation occurred during clonal expansion and contraction, whereas interleukin-15 (IL-15) promoted their survival only during contraction. We demonstrate that the number of effector CD8+ T cells is tightly controlled by multiple extrinsic signals throughout effector dif! ferentiation; this plasticity should be exploited during vaccine design and immunotherapy against tumors and autoimmune diseases.
• Cell-Intrinsic Transforming Growth Factor-β Signaling Mediates Virus-Specific CD8+ T Cell Deletion and Viral Persistence In Vivo
  - Immunity 31(1):145-157 (2009)
  Although deficient CD8+ T cell responses have long been associated with chronic viral infections, the underlying mechanisms are still unclear. Here we report that sustained transforming growth factor-β (TGF-β) expression and phosphorylation of its signaling mediator, Smad-2, were distinctive features of virus-specific CD8+ T cells during chronic versus acute viral infections in vivo. The result was TGF-β-dependent apoptosis of virus-specific CD8+ T cells that related to upregulation of the proapoptotic protein Bim during chronic infection. Moreover, selective attenuation of TGF-β signaling in T cells increased the numbers and multiple functions of antiviral CD8+ T cells and enabled rapid eradication of the persistence-prone virus and memory generation. Finally, we found that cell-intrinsic TGF-β signaling was responsible for virus-specific-CD8+ T cell apoptosis and decreased numbers but was not necessary for their functional exhaustion. Our findings reveal persist! ing TGF-β-Smad signaling as a hallmark and key regulator of CD8+ T cell responses during chronic viral infections in vivo.
• Human Dendritic Cells Induce the Differentiation of Interleukin-21-Producing T Follicular Helper-like Cells through Interleukin-12
  - Immunity 31(1):158-169 (2009)
  T follicular helper (Tfh) cells help development of antibody responses via interleukin-21 (IL-21). Here we show that activated human dendritic cells (DCs) induced naive CD4+ T cells to become IL-21-producing Tfh-like cells through IL-12. CD4+ T cells primed with IL-12 induced B cells to produce immunoglobulins in a fashion dependent on IL-21 and inducible costimulator (ICOS), thus sharing fundamental characteristics with Tfh cells. The induction of Tfh-like cells by activated DCs was inhibited by neutralizing IL-12. IL-12 induced two different IL-21-producers: IL-21+IFN-γ+T-bet+ Th1 cells and IL-21+IFN-γ−T-bet− non-Th1 cells, in a manner dependent on signal transducer and activator of transcription 4 (STAT4). IL-12 also regulated IL-21 secretion by memory CD4+ T cells. Thus, IL-12 produced by activated DCs regulates antibody responses via developing IL-21-producing Tfh-like cells and inducing IL-21 secretion from memory CD4+ T cells. These data suggest that the d! evelopmental pathway of Tfh cells differs between mice and humans, which have considerable implications for vaccine development.
• Cyclic Adenosine Monophosphate Suppresses the Transcription of Proinflammatory Cytokines via the Phosphorylated c-Fos Protein
  - Immunity 31(1):170 (2009)