Hot off the presses! Jul 22 Immunity

The Jul 22 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:

• T Cell Receptor Structures: Three for the Price of One
  - Immunity 35(1):1-3 (2011)
  A T cell receptor (TCR) that binds both major histocompatibility complex (MHC) class I and class II molecules reveals a novel structural variation that can potentially allow a single TCR to have three widely differing binding sites (Yin et al., 2011).
• Love Triangle between Unc93B1, TLR7, and TLR9 Prevents Fatal Attraction
  - Immunity 35(1):3-5 (2011)
  Unc93B1, a multitransmembrane ER-resident protein, controls intracellular trafficking of endosomal Toll-like receptors. In this issue of Immunity, Fukui et al. (2011) revealed that Unc93B1 regulates differential transport of TLR7 and TLR9 into signaling endosomes to prevent autoimmunity.
• It Takes Two to Tango
  - Immunity 35(1):6-8 (2011)
  Regulatory T (Treg) cells are essential for maintaining immune tolerance. In this issue of Immunity, Haribhai et al. (2011) demonstrate that both subsets of Treg cells, natural and induced, are necessary to achieve tolerance, probably because of their nonoverlapping T cell receptor repertoires.
• Sensing Retroviruses
  - Immunity 35(1):8-10 (2011)
  Sensing pathogens is an essential first step in the initiation of a host response to infection. In this issue of Immunity, Kane et al. (2011) used mouse models to demonstrate that Toll-like receptor 7 is required for the generation of an antibody response to infection by retroviruses.
• Beating Atomic Swords into Immunological Ploughshares
  - Immunity 35(1):10-12 (2011)
  Deliberate redirection of T cell responses to human immunodeficiency virus-1 might enhance immunity and thus aid viral containment. Dahirel et al. (2011) identify candidate antigens to achieve this with a theory derived from physics.
• The Role of Retinoic Acid in Tolerance and Immunity
  - Immunity 35(1):13-22 (2011)
  Vitamin A elicits a broad array of immune responses through its metabolite, retinoic acid (RA). Recent evidence indicates that loss of RA leads to impaired immunity, whereas excess RA can potentially promote inflammatory disorders. In this review, we discuss recent advances showcasing the crucial contributions of RA to both immunological tolerance and the elicitation of adaptive immune responses. Further, we provide a comprehensive overview of the cell types and factors that control the production of RA and discuss how host perturbations may affect the ability of this metabolite to control tolerance and immunity or to instigate pathology.
• A Single T Cell Receptor Bound to Major Histocompatibility Complex Class I and Class II Glycoproteins Reveals Switchable TCR Conformers
  - Immunity 35(1):23-33 (2011)
  Major histocompatibility complex class I (MHCI) and MHCII proteins differ in structure and sequence. To understand how T cell receptors (TCRs) can use the same set of variable regions to bind both proteins, we have presented a comparison of a single TCR bound to both MHCI and MHCII ligands. The TCR adopts similar orientations on both ligands with TCR amino acids thought to be evolutionarily conserved for MHC interaction occupying similar positions on the MHCI and MHCII helices. However, the TCR antigen-binding loops use different conformations when interacting with each ligand. Most importantly, we observed alternate TCR core conformations. When bound to MHCI, but not MHCII, Vα disengages from the Jα β strand, switching Vα's position relative to Vβ. In several other structures, either Vα or Vβ undergoes this same modification. Thus, both TCR V-domains can switch among alternate conformations, perhaps extending their ability to react with different MHC-peptide li! gands.
• Anthrax Toxin Induces Macrophage Death by p38 MAPK Inhibition but Leads to Inflammasome Activation via ATP Leakage
  - Immunity 35(1):34-44 (2011)
  Detection of microbial constituents by membrane associated and cytoplasmic pattern recognition receptors is the essence of innate immunity, leading to activation of protective host responses. However, it is still unclear how immune cells specifically respond to pathogenic bacteria. Using virulent and nonvirulent strains of Bacillus anthracis, we have shown that secretion of ATP by infected macrophages and the sequential activation of the P2X7 purinergic receptor and nucleotide binding oligomerization domain (NOD)-like receptors are critical for IL-1-dependent host protection from virulent B. anthracis. Importantly, lethal toxin produced by virulent B. anthracis blocked activation of protein kinases, p38 MAPK and AKT, resulting in opening of a connexin ATP release channel and induction of macrophage death. Prevention of cell death or ATP release through constitutive p38 or AKT activation interfered with inflammasome activation and IL-1β production, thereby compromising! antimicrobial immunity.
• Signaling by the Phosphatase MKP-1 in Dendritic Cells Imprints Distinct Effector and Regulatory T Cell Fates
  - Immunity 35(1):45-58 (2011)
  Naive T cells respond to antigens by differentiating into effector and regulatory lineages. Whereas the roles of T cell-intrinsic pathways have been extensively studied, how T cell lineage choices are controlled by innate immune signals remains elusive. Here we report that dendritic cell (DC)-expressed phosphatase MKP-1, a negative regulator of the MAP kinases, programmed reciprocal T helper 1 (Th1) and Th17 cell differentiation by modulating IL-12-STAT4 and IL-6-STAT3 axes and cytokine receptor expression at the DC-T cell interface. MKP-1 was regulated by innate recognition signals and its deficiency disrupted antimicrobial responses and promoted T cell-mediated inflammation. Moreover, MKP-1 inhibited induction of regulatory T cells by downregulating TGF-β2 production from DCs. Our findings identify a regulatory circuit linking MKP-1 signaling in DCs, production of polarizing cytokines, and integration of DC-derived signals in responding T cells, that bridges innate ! and adaptive immunity to coordinate protective immunity and immunopathology.
• Skint-1 Identifies a Common Molecular Mechanism for the Development of Interferon-γ-Secreting versus Interleukin-17-Secreting γδ T Cells
  - Immunity 35(1):59-68 (2011)
  Murine T cell development begins with the generation of a unique Vγ5+Vδ1+ epidermal γδ T cell compartment and a unique, more broadly distributed Vγ6+Vδ1+ subset that is an important source of interleukin-17 (IL-17). This study showed that these respective functional programs were determined by Skint-1, a thymic epithelial cell determinant. By engaging Skint-1+ cells, Vγ5+Vδ1+ thymocytes induced an Egr3-mediated pathway, provoking differentiation and the potential to produce IFN-γ while suppressing the γδ T cell lineage factor, Sox13, and a RORγt transcription factor-associated IL-17-producing capacity. Hence, the functions of the earliest T cells are substantially preprogrammed in the thymus. Additionally, the phenotype of Skint-1-selected fetal thymocytes permitted identification in the adult thymus of an analogous gene regulatory network regulated by the γδ T cell receptor. Hence, these observations describe a molecular pathway by which distinct stress-! responsive lymphocyte repertoires may emerge throughout ontogeny and offer parallels with emerging perspectives on the functional selection of other lymphoid cells.
• Unc93B1 Restricts Systemic Lethal Inflammation by Orchestrating Toll-like Receptor 7 and 9 Trafficking
  - Immunity 35(1):69-81 (2011)
  Toll-like receptor-7 (TLR7) and 9, innate immune sensors for microbial RNA or DNA, have been implicated in autoimmunity. Upon activation, TLR7 and 9 are transported from the endoplasmic reticulum (ER) to endolysosomes for nucleic acid sensing by an ER-resident protein, Unc93B1. Little is known, however, about a role for sensor transportation in controlling autoimmunity. TLR9 competes with TLR7 for Unc93B1-dependent trafficking and predominates over TLR7. TLR9 skewing is actively maintained by Unc93B1 and reversed to TLR7 if Unc93B1 loses preferential binding via a D34A mutation. We here demonstrate that mice harboring a D34A mutation showed TLR7-dependent, systemic lethal inflammation. CD4+ T cells showed marked differentiation toward T helper 1 (Th1) or Th17 cell subsets. B cell depletion abolished T cell differentiation and systemic inflammation. Thus, Unc93B1 controls homeostatic TLR7 activation by balancing TLR9 to TLR7 trafficking.
• The Ubiquitin-Editing Protein A20 Prevents Dendritic Cell Activation, Recognition of Apoptotic Cells, and Systemic Autoimmunity
  - Immunity 35(1):82-96 (2011)
  Dendritic cells (DCs) regulate both immunity and tolerance. Here we have shown that the ubiquitin editing enzyme A20 (Tnfaip3) determines the activation threshold of DCs, via control of canonical NF-κB activation. Tnfaip3fl/flCd11c-cre+ mice lacking A20 in DCs demonstrated spontaneous proliferation of conventional and double-negative T cells, their conversion to interferon-γ (IFN-γ)-producing effector cells, and expansion of plasma cells. They developed ds-DNA antibodies, nephritis, the antiphospholipid syndrome, and lymphosplenomegaly—features of systemic lupus erythematosus—and extramedullary hematopoiesis. A20-deficient DCs were resistant to apoptosis, caused by increased sensitivity to CD40L and RANKL prosurvival signals and upregulation of antiapoptotic proteins Bcl-2 and Bcl-x. They captured injected apoptotic cells more efficiently, resisted the inhibitory effects of apoptotic cells, and induced self-reactive effector lymphocytes. Because genetic polymorp! hisms in TNFAIP3 are associated with human autoimmune disorders, these findings identify A20-mediated control of DC activation as a crucial checkpoint in the development of systemic autoimmunity.
• The Costimulatory Molecule CD27 Maintains Clonally Diverse CD8+ T Cell Responses of Low Antigen Affinity to Protect against Viral Variants
  - Immunity 35(1):97-108 (2011)
  CD70 and CD27 are costimulatory molecules that provide essential signals for the expansion and differentiation of CD8+ T cells. Here, we show that CD27-driven costimulation lowered the threshold of T cell receptor activation on CD8+ T cells and enabled responses against low-affinity antigens. Using influenza infection to study in vivo consequences, we found that CD27-driven costimulation promoted a CD8+ T cell response of overall low affinity. These qualitative effects of CD27 on T cell responses were maintained into the memory phase. On a clonal level, CD27-driven costimulation established a higher degree of variety in memory CD8+ T cells. The benefit became apparent when mice were reinfected, given that CD27 improved CD8+ T cell responses against reinfection with viral variants, but not with identical virus. We propose that CD27-driven costimulation is a strategy to generate memory clones that have potential reactivity to a wide array of mutable pathogens.
• A Requisite Role for Induced Regulatory T Cells in Tolerance Based on Expanding Antigen Receptor Diversity
  - Immunity 35(1):109-122 (2011)
  Although both natural and induced regulatory T (nTreg and iTreg) cells can enforce tolerance, the mechanisms underlying their synergistic actions have not been established. We examined the functions of nTreg and iTreg cells by adoptive transfer immunotherapy of newborn Foxp3-deficient mice. As monotherapy, only nTreg cells prevented disease lethality, but did not suppress chronic inflammation and autoimmunity. Provision of Foxp3-sufficient conventional T cells with nTreg cells reconstituted the iTreg pool and established tolerance. In turn, acute depletion of iTreg cells in rescued mice resulted in weight loss and inflammation. Whereas the transcriptional signatures of nTreg and in vivo-derived iTreg cells were closely matched, there was minimal overlap in their T cell receptor (TCR) repertoires. Thus, iTreg cells are an essential nonredundant regulatory subset that supplements nTreg cells, in part by expanding TCR diversity within regulatory responses.
• T Cell Surveillance of Oncogene-Induced Prostate Cancer Is Impeded by T Cell-Derived TGF-β1 Cytokine
  - Immunity 35(1):123-134 (2011)
  Tolerance induction in T cells takes place in most tumors and is thought to account for tumor evasion from immune eradication. Production of the cytokine TGF-β is implicated in immunosuppression, but the cellular mechanism by which TGF-β induces T cell dysfunction remains unclear. With a transgenic model of prostate cancer, we showed that tumor development was not suppressed by the adaptive immune system, which was associated with heightened TGF-β signaling in T cells from the tumor-draining lymph nodes. Blockade of TGF-β signaling in T cells enhanced tumor antigen-specific T cell responses and inhibited tumor development. Surprisingly, T cell- but not Treg cell-specific ablation of TGF-β1 was sufficient to augment T cell cytotoxic activity and blocked tumor growth and metastases. These findings reveal that T cell production of TGF-β1 is an essential requirement for tumors to evade immunosurveillance independent of TGF-β produced by tumors.
• Innate Immune Sensing of Retroviral Infection via Toll-like Receptor 7 Occurs upon Viral Entry
  - Immunity 35(1):135-145 (2011)
  Innate immune sensors are required for induction of pathogen-specific immune responses. Retroviruses are notorious for their ability to evade immune defenses and establish long-term persistence in susceptible hosts. However, some infected animals are able to develop efficient virus-specific immune responses, and thus can be employed for identification of critical innate virus-sensing mechanisms. With mice from two inbred strains that control retroviruses via adaptive immune mechanisms, we found that of all steps in viral replication, the ability to enter the host cell was sufficient to induce antivirus humoral immune responses. Virus sensing occurred in endosomes via a MyD88-Toll-like receptor 7-dependent mechanism and stimulated virus-neutralizing immunity independently of type I interferons. Thus, efficient adaptive immunity to retroviruses is induced in vivo by innate sensing of the early stages of retroviral infection.
• The Myeloid Transcription Factor KLF2 Regulates the Host Response to Polymicrobial Infection and Endotoxic Shock
  - Immunity 35(1):146 (2011)