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Ngwe Tun MM, Morita K, Ishikawa T, Urata S. The Antiviral Effect of the Chemical Compounds Targeting DED/EDh Motifs of the Viral Proteins on Lymphocytic Choriomeningitis Virus and SARS-CoV-2. Viruses 2021; 13:1220. [PMID: 34202565 PMCID: PMC8310078 DOI: 10.3390/v13071220] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/14/2021] [Accepted: 06/23/2021] [Indexed: 01/01/2023] Open
Abstract
Arenaviruses and coronaviruses include several human pathogenic viruses, such as Lassa virus, Lymphocytic choriomeningitis virus (LCMV), SARS-CoV, MERS-CoV, and SARS-CoV-2. Although these viruses belong to different virus families, they possess a common motif, the DED/EDh motif, known as an exonuclease (ExoN) motif. In this study, proof-of-concept studies, in which the DED/EDh motif in these viral proteins, NP for arenaviruses, and nsp14 for coronaviruses, could be a drug target, were performed. Docking simulation studies between two structurally different chemical compounds, ATA and PV6R, and the DED/EDh motifs in these viral proteins indicated that these compounds target DED/EDh motifs. The concentration which exhibited modest cell toxicity was used with these compounds to treat LCMV and SARS-CoV-2 infections in two different cell lines, A549 and Vero 76 cells. Both ATA and PV6R inhibited the post-entry step of LCMV and SARS-CoV-2 infection. These studies strongly suggest that DED/EDh motifs in these viral proteins could be a drug target to combat two distinct viral families, arenaviruses and coronaviruses.
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Affiliation(s)
- Mya Myat Ngwe Tun
- Department of Virology, Institute of Tropical Medicine and Leading Program, Graduate School of Biomedical Science, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan; (M.M.N.T.); (K.M.)
| | - Kouichi Morita
- Department of Virology, Institute of Tropical Medicine and Leading Program, Graduate School of Biomedical Science, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan; (M.M.N.T.); (K.M.)
| | - Takeshi Ishikawa
- Department of Chemistry, Biotechnology and Chemical Engineering, Graduate School of Science and Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan
| | - Shuzo Urata
- National Research Center for the Control and Prevention of Infectious Diseases (CCPID), Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan
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2
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Brooks DG, Tishon A, Oldstone MBA, McGavern DB. Prevention of CD8 T Cell Deletion during Chronic Viral Infection. Viruses 2021; 13:v13071189. [PMID: 34206262 PMCID: PMC8310272 DOI: 10.3390/v13071189] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 06/08/2021] [Accepted: 06/18/2021] [Indexed: 01/05/2023] Open
Abstract
During chronic viral infections, CD8 T cells rapidly lose antiviral and immune-stimulatory functions in a sustained program termed exhaustion. In addition to this loss of function, CD8 T cells with the highest affinity for viral antigen can be physically deleted. Consequently, treatments designed to restore function to exhausted cells and control chronic viral replication are limited from the onset by the decreased breadth of the antiviral T cell response. Yet, it remains unclear why certain populations of CD8 T cells are deleted while others are preserved in an exhausted state. We report that CD8 T cell deletion during chronic viral infection can be prevented by therapeutically lowering viral replication early after infection. The initial resistance to deletion enabled long-term maintenance of antiviral cytolytic activity of the otherwise deleted high-affinity CD8 T cells. In combination with decreased virus titers, CD4 T cell help and prolonged interactions with costimulatory molecules B7-1/B7-2 were required to prevent CD8 T cell deletion. Thus, therapeutic strategies to decrease early virus replication could enhance virus-specific CD8 T cell diversity and function during chronic infection.
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Affiliation(s)
- David G. Brooks
- Viral Immunobiology Laboratory, Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 North Torrey Pines Rd., La Jolla, CA 92037, USA; (A.T.); (M.B.A.O.)
- Princess Margaret Cancer Center, University Health Network, Toronto, ON M5G 2M9, Canada
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Correspondence: (D.G.B.); (D.B.M.)
| | - Antoinette Tishon
- Viral Immunobiology Laboratory, Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 North Torrey Pines Rd., La Jolla, CA 92037, USA; (A.T.); (M.B.A.O.)
| | - Michael B. A. Oldstone
- Viral Immunobiology Laboratory, Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 North Torrey Pines Rd., La Jolla, CA 92037, USA; (A.T.); (M.B.A.O.)
| | - Dorian B. McGavern
- Viral Immunology and Intravital Imaging Section, National Institute of Neurological Disorders and Stroke, The National Institutes of Health, 10 Center Drive, Bethesda, MD 20895, USA
- Correspondence: (D.G.B.); (D.B.M.)
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3
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Crow YJ, Lebon P, Casanova JL, Gresser I. A Brief Historical Perspective on the Pathological Consequences of Excessive Type I Interferon Exposure In vivo. J Clin Immunol 2018; 38:694-698. [PMID: 30187308 DOI: 10.1007/s10875-018-0543-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 08/20/2018] [Indexed: 01/04/2023]
Affiliation(s)
- Yanick J Crow
- Centre for Genomic and Experimental Medicine, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, UK.
- INSERM UMR 1163, Laboratory of Neurogenetics and Neuroinflammation, Institute Imagine, Paris, France.
| | - Pierre Lebon
- Hopital Cochin-St Vincent de Paul, Faculté de médecine Paris Descartes, Paris, France
| | - Jean-Laurent Casanova
- St. Giles Laboratory of Human Genetics of Infectious Diseases, The Rockefeller University, New York, NY, USA
- Howard Hughes Medical Institute, New York, NY, USA
- Laboratory of Human Genetics of Infectious Diseases, INSERM UMR 1163, Necker Hospital for Sick Children, Paris, France
- Paris Descartes University, Imagine Institute, Paris, France
- Pediatric Hematology and Immunology Unit, Necker Hospital for Sick Children, Paris, France
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4
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Gangaplara A, Martens C, Dahlstrom E, Metidji A, Gokhale AS, Glass DD, Lopez-Ocasio M, Baur R, Kanakabandi K, Porcella SF, Shevach EM. Type I interferon signaling attenuates regulatory T cell function in viral infection and in the tumor microenvironment. PLoS Pathog 2018; 14:e1006985. [PMID: 29672594 PMCID: PMC5929570 DOI: 10.1371/journal.ppat.1006985] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 05/01/2018] [Accepted: 03/21/2018] [Indexed: 12/11/2022] Open
Abstract
Regulatory T cells (Tregs) play a cardinal role in the immune system by suppressing detrimental autoimmune responses, but their role in acute, chronic infectious diseases and tumor microenvironment remains unclear. We recently demonstrated that IFN-α/β receptor (IFNAR) signaling promotes Treg function in autoimmunity. Here we dissected the functional role of IFNAR-signaling in Tregs using Treg-specific IFNAR deficient (IFNARfl/flxFoxp3YFP-Cre) mice in acute LCMV Armstrong, chronic Clone-13 viral infection, and in tumor models. In both viral infection and tumor models, IFNARfl/flxFoxp3YFP-Cre mice Tregs expressed enhanced Treg associated activation antigens. LCMV-specific CD8+ T cells and tumor infiltrating lymphocytes from IFNARfl/flxFoxp3YFP-Cre mice produced less antiviral and antitumor IFN-γ and TNF-α. In chronic viral model, the numbers of antiviral effector and memory CD8+ T cells were decreased in IFNARfl/flxFoxp3YFP-Cre mice and the effector CD4+ and CD8+ T cells exhibited a phenotype compatible with enhanced exhaustion. IFNARfl/flxFoxp3YFP-Cre mice cleared Armstrong infection normally, but had higher viral titers in sera, kidneys and lungs during chronic infection, and higher tumor burden than the WT controls. The enhanced activated phenotype was evident through transcriptome analysis of IFNARfl/flxFoxp3YFP-Cre mice Tregs during infection demonstrated differential expression of a unique gene signature characterized by elevated levels of genes involved in suppression and decreased levels of genes mediating apoptosis. Thus, IFN signaling in Tregs is beneficial to host resulting in a more effective antiviral response and augmented antitumor immunity. Type I interferons (IFNs) play a predominant role in the immune response to infectious pathogens. The cellular targets of IFNs have been difficult to dissect because of the ubiquitous expression of the type I interferon receptor (IFNAR). The immune response of mice to lymphocytic choriomeningitis virus (LCMV) is one of the major models for analyzing the action of IFNs. Regulatory T cells (Tregs) have been implicated in the control of LCMV and it has been proposed that IFN may influence their function. The major goal of this study was to define the contribution of IFN signaling on Treg function during different stages LCMV infection. Tregs from mice with selective deletion of IFNAR manifested enhanced suppressive activity during acute/chronic LCMV infection resulting in increased CD8 T cell anergy, defective generation of memory T cells and persistence of virus. Similar effects of IFNAR signaling in Tregs were seen in a tumor model. We identified a unique set of genes in Tregs modulated by IFN signaling that may contribute to the enhanced suppressive function of IFNAR deficient Tregs. IFNs play a beneficial role during acute/chronic viral infections not only by contributing to viral clearance but also by attenuating the function of Tregs.
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MESH Headings
- Animals
- Antiviral Agents/pharmacology
- Arenaviridae Infections/drug therapy
- Arenaviridae Infections/immunology
- Arenaviridae Infections/metabolism
- Arenaviridae Infections/virology
- CD8-Positive T-Lymphocytes/drug effects
- CD8-Positive T-Lymphocytes/immunology
- CD8-Positive T-Lymphocytes/metabolism
- Cells, Cultured
- Colonic Neoplasms/drug therapy
- Colonic Neoplasms/immunology
- Colonic Neoplasms/metabolism
- Colonic Neoplasms/virology
- Immunity, Innate/drug effects
- Immunity, Innate/immunology
- Interferon Type I/pharmacology
- Interferon-gamma/metabolism
- Lymphocytic Choriomeningitis/drug therapy
- Lymphocytic Choriomeningitis/immunology
- Lymphocytic Choriomeningitis/metabolism
- Lymphocytic Choriomeningitis/virology
- Lymphocytic choriomeningitis virus/drug effects
- Melanoma, Experimental/drug therapy
- Melanoma, Experimental/immunology
- Melanoma, Experimental/metabolism
- Melanoma, Experimental/virology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Receptor, Interferon alpha-beta/physiology
- Signal Transduction/drug effects
- T-Lymphocytes, Regulatory/drug effects
- T-Lymphocytes, Regulatory/immunology
- T-Lymphocytes, Regulatory/metabolism
- T-Lymphocytes, Regulatory/virology
- Tumor Microenvironment/drug effects
- Tumor Microenvironment/immunology
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Affiliation(s)
- Arunakumar Gangaplara
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
| | - Craig Martens
- Genomics Unit, Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, United States of America
| | - Eric Dahlstrom
- Genomics Unit, Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, United States of America
| | - Amina Metidji
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
- The Francis Crick Institute, London, United Kingdom
| | - Ameya S. Gokhale
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
| | - Deborah D. Glass
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
| | - Maria Lopez-Ocasio
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
| | - Rachel Baur
- Genomics Unit, Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, United States of America
| | - Kishore Kanakabandi
- Genomics Unit, Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, United States of America
| | - Stephen F. Porcella
- Genomics Unit, Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, United States of America
| | - Ethan M. Shevach
- Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States of America
- * E-mail:
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Lukacikova L, Oveckova I, Betakova T, Laposova K, Polcicova K, Pastorekova S, Pastorek J, Tomaskova J. Antiviral Effect of Interferon Lambda Against Lymphocytic Choriomeningitis Virus. J Interferon Cytokine Res 2015; 35:540-53. [PMID: 25830339 DOI: 10.1089/jir.2014.0083] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Lambda interferons inhibit replication of many viruses, but their role in the inhibition of lymphocytic choriomeningitis virus (LCMV) infection remains unclear. In this study, we examined the antiviral effects of interferon (IFN)-λ2 and IFN-λ3 against LCMV in A549 cells. We found that IFN-λ2 is a more potent inhibitor of LCMV strain MX compared with IFN-λ3, whereas both cytokines have similar antiviral effects against an immunosuppressive variant of LCMV, clone-13. We also demonstrated that the antiviral activity of IFN-λ2 is more effective if it is delivered early rather than after establishment of a long-term infection, suggesting that virus replication is only partially responsive to the cytokine. In agreement with this observation, we showed that LCMV infection significantly reduces IFNLR1 mRNA expression in infected cells. In addition, LCMV infection, to some extent, compromises the signal transduction pathway of IFN-λ2. This implies that IFN receptors as well as their downstream signaling components could be selectively targeted either directly by LCMV proteins or indirectly by cellular factor(s) that are induced or activated by LCMV infection.
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Affiliation(s)
- Lubomira Lukacikova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Ingrid Oveckova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Tatiana Betakova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Katarina Laposova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Katarina Polcicova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Silvia Pastorekova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Jaromir Pastorek
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - Jana Tomaskova
- Department of Molecular Medicine, Institute of Virology , Slovak Academy of Sciences, Bratislava, Slovak Republic
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6
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Vázquez-Calvo Á, Martín-Acebes MA, Sáiz JC, Ngo N, Sobrino F, de la Torre JC. Inhibition of multiplication of the prototypic arenavirus LCMV by valproic acid. Antiviral Res 2013; 99:172-9. [PMID: 23735299 DOI: 10.1016/j.antiviral.2013.05.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 04/24/2013] [Accepted: 05/24/2013] [Indexed: 11/18/2022]
Abstract
Valproic acid (VPA), a short chain fatty acid commonly used for treatment of neurological disorders, has been shown to inhibit production of infectious progeny of different enveloped viruses including the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV). In this study we have investigated the mechanisms by which VPA inhibits LCMV multiplication in cultured cells. VPA reduced production of infectious LCMV progeny and virus propagation without exerting a major blockage on either viral RNA or protein synthesis, but rather affecting the cell release and specific infectivity of LCMV progeny from infected cells. Our results would support the repurposing of VPA as a candidate antiviral drug to combat arenavirus infections.
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Moreno H, Grande-Pérez A, Domingo E, Martín V. Arenaviruses and lethal mutagenesis. Prospects for new ribavirin-based interventions. Viruses 2012; 4:2786-805. [PMID: 23202505 PMCID: PMC3509673 DOI: 10.3390/v4112786] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 10/17/2012] [Accepted: 10/25/2012] [Indexed: 01/05/2023] Open
Abstract
Lymphocytic choriomeningitis virus (LCMV) has contributed to unveil some of the molecular mechanisms of lethal mutagenesis, or loss of virus infectivity due to increased mutation rates. Here we review these developments, and provide additional evidence that ribavirin displays a dual mutagenic and inhibitory activity on LCMV that can be relevant to treatment designs. Using 5-fluorouracil as mutagenic agent and ribavirin either as inhibitor or mutagen, we document an advantage of a sequential inhibitor-mutagen administration over the corresponding combination treatment to achieve a low LCMV load in cell culture. This advantage is accentuated in the concentration range in which ribavirin acts mainly as an inhibitor, rather than as mutagen. This observation reinforces previous theoretical and experimental studies in supporting a sequential inhibitor-mutagen administration as a possible antiviral design. Given recent progress in the development of new inhibitors of arenavirus replication, our results suggest new options of ribavirin-based anti-arenavirus treatments.
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Affiliation(s)
- Héctor Moreno
- Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Campus de Cantoblanco 28049, Madrid, Spain; (H.M.); (E.D.)
| | - Ana Grande-Pérez
- Área de Genética, Facultad de Ciencias, Campus de Teatinos, Universidad de Málaga, 29071, Málaga, Spain;
| | - Esteban Domingo
- Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Campus de Cantoblanco 28049, Madrid, Spain; (H.M.); (E.D.)
- Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), 08036 Barcelona, Spain
| | - Verónica Martín
- Centro de Investigación en Sanidad Animal (CISA), Carretera de Algete a El Casar s/n, 28130 Valdeolmos, Madrid, Spain;
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8
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Audigé A, Hofer U, Dittmer U, van den Broek M, Speck RF. Evaluation of the immunomodulatory and antiviral effects of the cytokine combination IFN-α and IL-7 in the lymphocytic choriomeningitis virus and Friend retrovirus mouse infection models. Viral Immunol 2011; 24:375-85. [PMID: 21929334 DOI: 10.1089/vim.2011.0006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Existing therapies for chronic viral infections are still suboptimal or have considerable side effects, so new therapeutic strategies need to be developed. One option is to boost the host's immune response with cytokines. We have recently shown in an acute ex vivo HIV infection model that co-administration of interferon (IFN)-α and interleukin (IL)-7 allows us to combine the potent anti-HIV activity of IFN-α with the beneficial effects of IL-7 on T-cell survival and function. Here we evaluated the effect of combining IFN-α and IL-7 on viral replication in vivo in the chronic lymphocytic choriomeningitis virus (LCMV) and acute Friend retrovirus (FV) infection models. In the chronic LCMV model, cytokine treatment was started during the early replication phase (i.e., on day 7 post-infection [pi]). Under the experimental conditions used, exogenous IFN-α inhibited FV replication, but had no effect on viral replication in the LCMV model. There was no therapeutic benefit of IL-7 either alone or in combination with IFN-α in either of the two infection models. In the LCMV model, dose-dependent effects of the cytokine combination on T-cell phenotype/function were observed. It is possible that these effects would translate into antiviral activity in re-challenged mice. It is also possible that another type of IFN-α/β or induction of endogenous IFN-α/β alone or in combination with IL-7 would have antiviral activity in the LCMV model. Furthermore, we cannot exclude that some effect on viral titers would have been seen at later time points not investigated here (i.e., beyond day 34 pi). Finally, IFN-α/IL-7 may inhibit the replication of other viruses. Thus it might be worth testing these cytokines in other in vivo models of chronic viral infections.
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Affiliation(s)
- Annette Audigé
- Division of Infectious Diseases and Hospital Epidemiology, University of Zurich, Zurich, Switzerland.
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9
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Michalek RD, Pellom ST, Holbrook BC, Grayson JM. The requirement of reactive oxygen intermediates for lymphocytic choriomeningitis virus binding and growth. Virology 2008; 379:205-12. [PMID: 18691729 DOI: 10.1016/j.virol.2008.07.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2008] [Revised: 04/07/2008] [Accepted: 07/08/2008] [Indexed: 02/08/2023]
Abstract
Multiple viruses induce reactive oxygen intermediate (ROI) generation during infection that plays an important role in growth. We have examined the importance of ROI during lymphocytic choriomeningitis virus (LCMV) infection of immortalized BHK-21 cells and murine peritoneal macrophages. Within 15 min of virus addition, intracellular ROI levels increased. To examine the contribution of ROI to LCMV infection, cells were pretreated with antioxidant prior to virus addition. Antioxidant treatment inhibited low and high MOI growth of virus. The requirement for ROI was greatest during the initial phase of infection, as antioxidant treatment after 6 h post infection had a weaker inhibitory effect. Furthermore, antioxidant treatment of cells inhibited virus binding, while treatment of virus stocks with N-ethyl malemide, which blocks free thiols, eliminated infectious virus. This illustrates that ROI are critical to the regulation of virus binding and growth and has important implications for understanding the infectivity of related viruses.
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Affiliation(s)
- Ryan D Michalek
- Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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10
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García CC, Djavani M, Topisirovic I, Borden KLB, Salvato MS, Damonte EB. Arenavirus Z protein as an antiviral target: virus inactivation and protein oligomerization by zinc finger-reactive compounds. J Gen Virol 2006; 87:1217-1228. [PMID: 16603524 PMCID: PMC2423342 DOI: 10.1099/vir.0.81667-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Several disulfide-based and azoic compounds have shown antiviral and virucidal properties against arenaviruses in virus yield-inhibition and inactivation assays, respectively. The most effective virucidal agent, the aromatic disulfide NSC20625, was able to inactivate two strains of the prototype arenavirus species Lymphocytic choriomeningitis virus (LCMV). Inactivated viral particles retained the biological functions of the virion envelope glycoproteins in virus binding and uptake, but were unable to perform viral RNA replication. Furthermore, in inactivated virions, the electrophoretic profile of the Z protein was altered when analysed under non-reducing conditions, whereas the patterns of the proteins NP and GP1 remained unaffected. Treatment of a recombinant LCMV Z protein with the virucidal agents induced unfolding and oligomerization of Z to high-molecular-mass aggregates, probably due to metal-ion ejection and the formation of intermolecular disulfide bonds through the cysteine residues of the Z RING finger. NSC20625 also exhibited antiviral properties in LCMV-infected cells without affecting other cellular RING-motif proteins, such as the promyelocytic leukaemia protein PML. Altogether, the investigations described here illustrate the potential of the Z protein as a promising target for therapy and the prospects of the Z-reactive compounds to prevent arenavirus dissemination.
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Affiliation(s)
- Cybele C. García
- Laboratory of Virology, Department of Biological Chemistry, School of Sciences, University of Buenos Aires, Ciudad Universitaria, Pabellón 2, Piso 4, 1428 Buenos Aires, Argentina
| | - Mahmoud Djavani
- Institute of Human Virology, University of Maryland Biotechnology Center, Baltimore, MD 21201, USA
| | - Ivan Topisirovic
- Institute de Recherche en Immunologie et en Cancerologie, Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - Katherine L. B. Borden
- Institute de Recherche en Immunologie et en Cancerologie, Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - María S. Salvato
- Institute of Human Virology, University of Maryland Biotechnology Center, Baltimore, MD 21201, USA
| | - Elsa B. Damonte
- Laboratory of Virology, Department of Biological Chemistry, School of Sciences, University of Buenos Aires, Ciudad Universitaria, Pabellón 2, Piso 4, 1428 Buenos Aires, Argentina
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11
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Abstract
Arenaviruses merit significant attention both as tractable model systems to study acute and persistent viral infections, and as clinically important human pathogens. Evidence indicates that LCMV remains present in the USA and Europe and capable of causing significant morbidity in infected individuals, likely being a neglected human pathogen. Moreover, new arenaviruses are being discovered in the Americas on the average of one every three years, with some of them causing severe hemorrhagic fever. In addition, weaponized forms of these viruses pose a real threat as agents of bioterrorism. Therefore, it is important to develop effective vaccines and better antiviral drugs to combat the dual threats of naturally occurring and intentionally introduced Arenavirus infections. The development of arenavirus reverse genetic systems is allowing investigators to conduct a detailed molecular characterization of the viral cis-acting signals and trans-acting factors that control each of the steps of the Arenavirus life cycle, including RNA synthesis, packaging and budding. We will discuss how this new knowledge is facilitating the establishment of novel assays to identify and characterize compounds capable of interfering with specific steps of the virus life cycle. Likewise, the ability to generate predetermined specific mutations within the arenavirus genome, and analyze their phenotypic expression, would significantly contribute to the elucidation of arenavirus-host interactions, including the bases of their ability to persist, as well as to cause severe HF (hemorrhagic fever) disease in humans. These approaches could also lead to the development of novel potent and safe Arenavirus vaccines.
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Affiliation(s)
- Stefan Kunz
- Department of Neuropharmacology, The Scripps Research Institute, IMM-6, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
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Labudová M, Tomásková J, Kaluzová M, Pastorek J, Pastoreková S. Lymphocytic choriomeningitis virus mx strain does not induce the expression of tumor-associated carbonic anhydrase IX in persistently infected HeLa cells. Acta Virol 2006; 50:53-8. [PMID: 16599186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Summary. - Lymphocytic choriomeningitis virus (LCMV) is an arenavirus that readily causes persistent infections, in which it does not interfere with vital functions of the cells, but can affect expression of "luxurious" genes. MX strain of LCMV (MX LCMV) has been identified as an agent transmissible by cell-to-cell contact in the human carcinoma MaTu cells grown in a mixed culture with HeLa cells. When compared to uninfected HeLa, the MaTu-MX-infected HeLa cells, to which the virus was transmitted via co-cultivation with mitomycin C-treated MaTu cells, showed an elevated expression of a protein called MN, suggesting that MN can be induced by MX LCMV. MN protein was later identified as the carbonic anhydrase isoform IX (CA IX), whose expression has been predominantly associated with hypoxic tumors of poor prognosis. Since the proposal that MX LCMV can induce such a cancer-related protein could substantially change our view on the biology of LCMV-host interaction we undertook its verification. Instead of co-cultivation, we used MaTu cell-free extracts to transmit MX LCMV to HeLa cells. These cells were then grown for more than 30 passages, but the level of MN/CA IX did not increase throughout the whole cultivation period as compared to uninfected HeLa cells. Moreover, a treatment of MaTu-MX-infected HeLa cells with ribavirin eliminated the virus, but did not reduce the MN/CA IX expression. Our results clearly showed that MN/CA IX is independent of MX LCMV and that the virus itself does not influence the MN/CA IX level in HeLa cells.
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Affiliation(s)
- M Labudová
- Centre of Molecular Medicine, Institute of Virology, Slovak Academy of Sciences, Díbravská cesta 9, 845 05 Bratislava, Slovak Republic
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13
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Abstract
Viral hemorrhagic fevers represent serious human public health problems causing devastating and often lethal disease. Several hemorrhagic fevers are caused by arenaviruses including Lassa fever virus (LFV) and the South American viral hemorrhagic fevers (SAHF). In recent years, increased air travel between Africa and other areas has led to the importation of LFV into the US, Europe, Japan, and Canada. This has raised awareness about arenaviruses as potential emerging viruses. Moreover, because of its severe morbidity and high mortality, and transmissibility from human to human, weaponized forms of LFV poses a real threat as agent of bioterrorism. No licensed vaccine is available in the US, and currently there is not efficacious therapy to treat these infections. Therefore, the importance of developing novel effective antiviral drugs to combat HF arenaviruses, for which the prototypic Arenavirus lymphocytic choriomeningitis virus (LCMV) provides us with an excellent model system. Recent findings have shown that LCMV multiplication both in cultured cells and in vivo is highly susceptible to the mutagenic agent 5-fluorouracil (FU). FU-mediated extinction of LCMV was associated with only modest increases in virus mutation frequencies, but did not significantly affect virus replication and transcription, or virus particle formation. These findings indicate that, as with other riboviruses, lethal mutagenesis is effective also against LCMV raising the possibility of using this novel antiviral strategy to combat pathogenic arenaviruses.
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Affiliation(s)
- Juan Carlos de la Torre
- Department of Neuropharmacology IMM-6, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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14
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Grande-Pérez A, Lázaro E, Lowenstein P, Domingo E, Manrubia SC. Suppression of viral infectivity through lethal defection. Proc Natl Acad Sci U S A 2005; 102:4448-52. [PMID: 15767582 PMCID: PMC555496 DOI: 10.1073/pnas.0408871102] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Indexed: 11/18/2022] Open
Abstract
RNA viruses replicate with a very high error rate and give rise to heterogeneous, highly plastic populations able to adapt very rapidly to changing environments. Viral diseases are thus difficult to control because of the appearance of drug-resistant mutants, and it becomes essential to seek mechanisms able to force the extinction of the quasispecies before adaptation emerges. An alternative to the use of conventional drugs consists in increasing the replication error rate through the use of mutagens. Here, we report about persistent infections of lymphocytic choriomeningitis virus treated with fluorouracil, where a progressive debilitation of infectivity leading to eventual extinction occurs. The transition to extinction is accompanied by the production of large amounts of RNA, indicating that the replicative ability of the quasispecies is not strongly impaired by the mutagen. By means of experimental and theoretical approaches, we propose that a fraction of the RNA molecules synthesized can behave as a defective subpopulation able to drive the viable class extinct. Our results lead to the identification of two extinction pathways, one at high amounts of mutagen, where the quasispecies completely loses its ability to infect and replicate, and a second one, at lower amounts of mutagen, where replication continues while the infective class gets extinct because of the action of defectors. The results bear on a potential application of increased mutagenesis as an antiviral strategy in that low doses of a mutagenic agent may suffice to drive persistent virus to extinction.
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Affiliation(s)
- Ana Grande-Pérez
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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15
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Uckun FM, Rustamova L, Vassilev AO, Tibbles HE, Petkevich AS. CNS activity of Pokeweed anti-viral protein (PAP) in mice infected with lymphocytic choriomeningitis virus (LCMV). BMC Infect Dis 2005; 5:9. [PMID: 15725345 PMCID: PMC554105 DOI: 10.1186/1471-2334-5-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2004] [Accepted: 02/22/2005] [Indexed: 12/04/2022] Open
Abstract
Background Others and we have previously described the potent in vivo and in vitro activity of the broad-spectrum antiviral agent PAP (Pokeweed antiviral protein) against a wide range of viruses. The purpose of the present study was to further elucidate the anti-viral spectrum of PAP by examining its effects on the survival of mice challenged with lymphocytic choriomeningitis virus (LCMV). Methods We examined the therapeutic effect of PAP in CBA mice inoculated with intracerebral injections of the WE54 strain of LCMV at a 1000 PFU dose level that is lethal to 100% of mice within 7–9 days. Mice were treated either with vehicle or PAP administered intraperitoneally 24 hours prior to, 1 hour prior to and 24 hours, 48 hours 72 hours and 96 hours after virus inoculation. Results PAP exhibits significant in vivo anti- LCMV activity in mice challenged intracerebrally with an otherwise invariably fatal dose of LCMV. At non-toxic dose levels, PAP significantly prolonged survival in the absence of the majority of disease-associated symptoms. The median survival time of PAP-treated mice was >21 days as opposed to 7 days median survival for the control (p = 0.0069). Conclusion Our results presented herein provide unprecedented experimental evidence that PAP exhibits antiviral activity in the CNS of LCMV-infected mice.
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Affiliation(s)
- Fatih M Uckun
- Parker Hughes Center for Clinical Immunology, St. Paul, MN 55113, USA
| | - Larisa Rustamova
- Research Institute for Epidemiology and Microbiology, 220050 MINSK, Belarus
| | - Alexei O Vassilev
- Parker Hughes Center for Clinical Immunology, St. Paul, MN 55113, USA
| | - Heather E Tibbles
- Parker Hughes Center for Clinical Immunology, St. Paul, MN 55113, USA
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16
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Abstract
Arenaviruses include Lassa fever virus (LFV) and the South American hemorrhagic fever viruses. These viruses cause severe human disease, and they pose a threat as agents of bioterrorism. Arenaviruses are enveloped viruses with a bisegmented negative-strand RNA genome whose proteomic capability is limited to four polypeptides: nucleoprotein (NP); surface glycoprotein (GP), which is proteolytically processed into GP1 and GP2; polymerase (L); and a small (11-kDa) RING finger protein (Z). Our investigators have previously shown that Z has a strong inhibitory activity on RNA synthesis mediated by the polymerase of the prototypic arenavirus, lymphocytic choriomeningitis virus (LCMV). In this report we show that cells transduced with a replication-deficient recombinant adenovirus expressing Z (rAd-Z) are resistant to LCMV and LFV infection. Virus cell entry mediated by LCMV or LFV GP was not affected in rAd-Z-transduced cells, but both virus transcription and replication were strongly and specifically inhibited, which resulted in a dramatic reduction in production of infectious virus. These findings open new avenues for developing antiviral strategies to combat the highly pathogenic human arenaviruses, including LFV.
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Affiliation(s)
- Tatjana I Cornu
- Division of Virology, Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA
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17
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Asper M, Sternsdorf T, Hass M, Drosten C, Rhode A, Schmitz H, Günther S. Inhibition of different Lassa virus strains by alpha and gamma interferons and comparison with a less pathogenic arenavirus. J Virol 2004; 78:3162-9. [PMID: 14990737 PMCID: PMC353741 DOI: 10.1128/jvi.78.6.3162-3169.2004] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2003] [Accepted: 11/10/2003] [Indexed: 11/20/2022] Open
Abstract
The high pathogenicity of Lassa virus is assumed to involve resistance to the effects of interferon (IFN). We have analyzed the effects of alpha IFN (IFN-alpha), IFN-gamma, and tumor necrosis factor alpha (TNF-alpha) on replication of Lassa virus compared to the related, but less pathogenic, lymphocytic choriomeningitis virus (LCMV). Three low-passage Lassa virus strains (AV, NL, and CSF), isolated from humans with mild to fulminant Lassa fever, were tested. Lassa virus replication was inhibited by IFN-alpha and IFN-gamma, but not TNF-alpha, in Huh7 and Vero cells. The degree of IFN sensitivity of a Lassa virus isolate did not correlate with disease severity in human patients. Furthermore, cytokine effects observed for Lassa virus and LCMV (strains CH-5692, Armstrong, and WE) were similar. To address the mechanisms involved in the IFN effect, we used cell lines in which overexpression of IFN-stimulated proteins promyelocytic leukemia protein (PML) and Sp100 could be induced. Both proteins reside in PML bodies, a cellular target of the LCMV and Lassa virus Z proteins. Overexpression of PML or Sp100 did not affect replication of either virus. This, together with the previous finding that PML knockout facilitates LCMV replication in vitro and in vivo (M. Djavani, J. Rodas, I. S. Lukashevich, D. Horejsh, P. P. Pandolfi, K. L. Borden, and M. S. Salvato, J. Virol. 75:6204-6208, 2001; W. V. Bonilla, D. D. Pinschewer, P. Klenerman, V. Rousson, M. Gaboli, P. P. Pandolfi, R. M. Zinkernagel, M. S. Salvato, and H. Hengartner, J. Virol. 76:3810-3818, 2002), describes PML as a mediator within the antiviral pathway rather than as a direct effector protein. In conclusion, the high pathogenicity of Lassa virus compared to LCMV is probably not due to increased resistance to the effects of IFN-alpha or IFN-gamma. Both cytokines inhibit replication which is relevant for the design of antiviral strategies against Lassa fever with the aim of enhancing the IFN response.
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Affiliation(s)
- Marcel Asper
- Department of Virology, Bernhard-Nocht-Institute of Tropical Medicine, 20359 Hamburg, Germany
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18
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Affiliation(s)
- Tara L Greenhow
- Department of Pediatrics, University of California, San Francisco, USA
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19
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Abstract
Passage of the prototypic arenavirus lymphocytic choriomenigitis virus (LCMV) in cultured cells in the presence of the mutagenic agent 5-fluorouracil (FU) resulted in efficient and systematic virus extinction under conditions that did not significantly affect cell survival. FU-mediated extinction of LCMV was associated with 3.6- to 10-fold increases in the mutation frequencies for the three viral genes examined, but with only very modest effects on virus replication and transcription during a single round of infection. Likewise, FU did not affect expression of a LCMV minigenome. In contrast, the well documented antiviral effect of ribavirin against LCMV was not associated with significant increases in virus mutation frequencies, but rather with a dramatic inhibition of both viral RNA synthesis and LCMV minigenome expression. Mutagen induced viral extinction has been recently reported for positive strand RNA viruses polio and foot-and-mouth disease, and the lentivirus HIV-1. Our findings indicate that lethal mutagenesis can be effective also against LCMV, a negative strand RNA virus. Moreover, FU treatment prevented the establishment of LCMV persistent infection in mice deficient in B and T cells, suggesting the feasibility in vivo of lethal mutagenesis as a novel antiviral strategy.
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Affiliation(s)
- Carmen M Ruiz-Jarabo
- Centro de Biologia Molecular Severo Ochoa (CSIC, UAM), Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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20
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Djavani M, Rodas J, Lukashevich IS, Horejsh D, Pandolfi PP, Borden KL, Salvato MS. Role of the promyelocytic leukemia protein PML in the interferon sensitivity of lymphocytic choriomeningitis virus. J Virol 2001; 75:6204-8. [PMID: 11390623 PMCID: PMC114337 DOI: 10.1128/jvi.75.13.6204-6208.2001] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Lymphocytic choriomeningitis virus (LCMV) induces type I interferon (alpha and beta interferon [IFN-alpha and IFN-beta]) upon infection and yet is sensitive to the addition of type II interferon (gamma interferon [IFN-gamma]) to the culture media. This sensitivity is biologically important because it correlates inversely with the ability of certain LCMV strains to persist in mice (D. Moskophidis, M. Battegay, M. A. Bruendler, E. Laine, I. Gresser, and R. M. Zinkernagel, J. Virol. 68:1951-1955, 1994). The cellular oncoprotein PML is induced by both IFN-alpha/beta and IFN-gamma, and PML binds the LCMV Z protein and becomes redistributed within cells from nucleus to cytoplasm upon LCMV infection. In the present study, increased PML expression results in diminished LCMV replication, implicating PML in the IFN sensitivity of LCMV. Virus production in PML -/- murine embryonic fibroblasts (MEF) exceeds virus production in PML +/+ MEF, and this difference is exacerbated by IFN treatment that upregulates PML expression. IFN-gamma also diminishes LCMV production in PML -/- cells; therefore, viral IFN sensitivity is not entirely due to PML. Both viral mRNA production and viral protein production decrease as PML expression increases. Here we propose that PML reduces LCMV transcription through its interaction with the Z protein.
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Affiliation(s)
- M Djavani
- Institute of Human Virology, University of Maryland Biotechnology Center, 725 W. Lombard St., Baltimore, MD 21201, USA
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21
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Schwarz K, Giuli RD, Schmidtke G, Kostka S, van den Broek M, Bo Kim K, Crews CM, Kraft R, Groettrup M. The selective proteasome inhibitors lactacystin and epoxomicin can be used to either up- or down-regulate antigen presentation at nontoxic doses. J Immunol 2000; 164:6147-57. [PMID: 10843664 PMCID: PMC2507740 DOI: 10.4049/jimmunol.164.12.6147] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The complete inhibition of proteasome activities interferes with the production of most MHC class I peptide ligands as well as with cellular proliferation and survival. In this study we have investigated how partial and selective inhibition of the chymotrypsin-like activity of the proteasome by the proteasome inhibitors lactacystin or epoxomicin would affect Ag presentation. At 0.5-1 microM lactacystin, the presentation of the lymphocytic choriomeningitis virus-derived epitopes NP118 and GP33 and the mouse CMV epitope pp89-168 were reduced and were further diminished in a dose-dependent manner with increasing concentrations. Presentation of the lymphocytic choriomeningitis virus-derived epitope GP276, in contrast, was markedly enhanced at low, but abrogated at higher, concentrations of either lactacystin or epoxomicin. The inhibitor-mediated effects were thus epitope specific and did not correlate with the degradation rates of the involved viral proteins. Although neither apoptosis induction nor interference with cellular proliferation was observed at 0.5-1 microM lactacystin in vivo, this concentration was sufficient to alter the fragmentation of polypeptides by the 20S proteasome in vitro. Our results indicate that partial and selective inhibition of proteasome activity in vivo is a valid approach to modulate Ag presentation, with potential applications for the treatment of autoimmune diseases and the prevention of transplant rejection.
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Affiliation(s)
- Katrin Schwarz
- Research Department, Cantonal Hospital St. Gall, St. Gallen, Switzerland
| | - Rita de Giuli
- Research Department, Cantonal Hospital St. Gall, St. Gallen, Switzerland
| | - Gunter Schmidtke
- Research Department, Cantonal Hospital St. Gall, St. Gallen, Switzerland
| | - Susanne Kostka
- Max Delbrück Center for Molecular Medicine, Berlin-Buch, Germany
| | - Maries van den Broek
- Institute of Experimental Immunology, Department of Pathology, University Hospital Zurich, Zurich, Switzerland
| | - Kyung Bo Kim
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520
| | - Craig M. Crews
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520
| | - Regine Kraft
- Max Delbrück Center for Molecular Medicine, Berlin-Buch, Germany
| | - Marcus Groettrup
- Research Department, Cantonal Hospital St. Gall, St. Gallen, Switzerland
- Address correspondence and reprint requests to Dr. Marcus Groettrup, Kantonsspital St. Gallen, Laborforschungsabteilung, Haus 09, CH-9007 St. Gallen, Switzerland. E-mail address:
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22
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Abstract
Persistent infections caused by such agents as the human immunodeficiency virus, hepatitis B virus, Epstein-Barr virus, etc., present formidable medical problems. A defining characteristic of these infections is that anti-viral cytotoxic T lymphocytes (CTL) may be lost or, if present, fail to clear the infection. Here we report a vaccination strategy which was successful in generating lytic CTL in persistently infected mice. Vaccination with an immunodominant CTL epitope derived from the nucleoprotein of lymphocytic choriomeningitis virus (LCMV) delivered in the form of a lipopeptide incorporating a universal CD4 helper epitope successfully induced lytic MHC-restricted CTL in mice persistently infected with LCMV since birth. However, induction of such CTL did not eliminate the virus, most likely because the CTL were generated at low frequencies and had 2 to 3 logs lower affinity than CTL generated in uninfected mice inoculated with the vaccine. Both CTL populations from either uninfected or persistently infected mice produced significant and similar amounts of interferon-gamma and IL-6. Vaccine-induced low-affinity CTL were still inadequate at complete removal of the virus when combined with LCMV-specific CD4 helper T lymphocytes. Thus, our results establish that CTL can be generated in persistently infected mice and that a crucial factor for clearing viral infection is the affinity of the CTL.
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Affiliation(s)
- M G von Herrath
- Division of Virology, Department of Neuropharmacology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, California, 92037, USA.
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23
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Gebhard JR, Perry CM, Mahadeviah S, Whitton JL. Use of a nonviral vector to express a chimeric tRNA-ribozyme against lymphocytic choriomeningitis virus: cytoplasmic accumulation of a catalytically competent transcript but minimal antiviral effect. Antisense Nucleic Acid Drug Dev 1997; 7:3-11. [PMID: 9055033 DOI: 10.1089/oli.1.1997.7.3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
RNA polymerase III promoters direct the ubiquitous, high-level, expression of small, stable RNAs such as tRNAs, and thus are attractive candidates for achieving stable expression of small therapeutic (e.g., antiviral) molecules, such as ribozymes or antisense RNAs. In this article, we describe the use of a nonviral vector containing a tRNA promoter to express an antilymphocytic choriomeningitis virus (LCMV) ribozyme (tRNA-Rib5). The chimeric tRNA-ribozyme is specifically and efficiently transcribed by pol III in cell-free extracts, and the resulting transcript has appropriate ribozyme activity. In tissue culture studies, high levels of chimeric transcripts were readily detectable and were transported to the cytoplasm, the site of LCMV replication. Despite accumulation of tRNA-Rib5 in the cytoplasm of stably transformed cell clones, antiviral effects were minimal or absent. The implications of these findings and the potential use of this vector system for in vivo studies requiring the delivery of small molecules are discussed.
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MESH Headings
- 3T3 Cells
- Animals
- Antiviral Agents/pharmacology
- Antiviral Agents/therapeutic use
- Chimera
- Chlorocebus aethiops
- Clone Cells
- Cytoplasm/metabolism
- Gene Expression/drug effects
- Gene Expression/genetics
- Genetic Vectors/metabolism
- Genetic Vectors/pharmacology
- Genetic Vectors/therapeutic use
- Lymphocytic choriomeningitis virus/drug effects
- Lymphocytic choriomeningitis virus/genetics
- Mice
- Mice, Inbred BALB C
- Oligonucleotides, Antisense/genetics
- Oligonucleotides, Antisense/pharmacology
- Oligonucleotides, Antisense/therapeutic use
- Plasmids/genetics
- Plasmids/metabolism
- Plasmids/therapeutic use
- Promoter Regions, Genetic/genetics
- RNA Polymerase III/drug effects
- RNA, Catalytic/biosynthesis
- RNA, Catalytic/genetics
- RNA, Catalytic/pharmacology
- RNA, Catalytic/therapeutic use
- RNA, Transfer, Met/biosynthesis
- RNA, Transfer, Met/genetics
- RNA, Transfer, Met/therapeutic use
- Transcription, Genetic/drug effects
- Transcription, Genetic/genetics
- Vero Cells
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Affiliation(s)
- J R Gebhard
- Department of Neuropharmacology, Scripps Research Institute, La Jolla, CA 92037, USA
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24
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Xing Z, Mahadeviah S, Whitton JL. Antiviral activity of RNA molecules containing self-releasing ribozymes targeted to lymphocytic choriomeningitis virus. Antisense Res Dev 1995; 5:203-12. [PMID: 8785476 DOI: 10.1089/ard.1995.5.203] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Ribozymes catalytically cleave substrate RNA molecules in a sequence-specific manner. Engineered ribozymes can be developed and introduced into tissue culture cells to regulate gene expression and to inhibit viral replication. We have previously reported on the construction of cell lines that constitutively express a single antiviral ribozyme embedded in a lengthy RNA transcript. These cells exhibited a marked reduction in their ability to support viral infection. Here we report the construction of RNA molecules that contain one or two antiviral ribozymes, each specific for a different cleavage site on the genome of the target virus, lymphocytic choriomeningitis virus (LCMV), and each contained in a self-cleavage cassette comprising cis-acting ribozymes designed to release the antiviral molecules from the transcript. In vitro studies showed that both antiviral ribozymes were released properly from the RNAs following cleavage by the flanking ribozymes and that these released ribozymes functioned as expected in cleaving the target virus RNA. These self-cleaving cassettes have been clones into a retroviral vector downstream of, but in the same transcript as, the chloramphenicol acetyltransferase (CAT) gene. Thus, we hoped to employ CAT as a surrogate marker of ribozyme transcription. Stably transformed cell lines were established. Cleavage by the cis-acting ribozymes was incomplete, as assessed by Northern blot analysis and by the ability of transformed cells to produce infectious retroviral particles. Nevertheless, the antiviral ribozyme sequences exerted effects in tissue culture. LCMV RNA levels in ribozyme-expressing cells were suppressed, and infectious virus yields were decreased by up to 95% compared with normal cells and with cells expressing inverted ribozymes. The antiviral effects correlated with CAT levels, but there was no significant difference between cell lines expressing a single ribozymes and those expressing two.
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Affiliation(s)
- Z Xing
- Department of Neuropharmacology, Scripps Research Institute, La Jolla, CA 92037, USA
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25
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Welsh RM, O'Donnell CL, Shultz LD. Antiviral activity of NK 1.1+ natural killer cells in C57BL/6 scid mice infected with murine cytomegalovirus. Nat Immun 1994; 13:239-245. [PMID: 7833623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The activation, proliferation, and antiviral effects of natural killer (NK) cells were examined in a newly developed stock of mice, C57BL/6JSz mice homozygous for the severe combined immunodeficiency (scid) mutation. These mice lack functional T and B cells and express the NK 1.1 alloantigen. Such NK 1.1 expression facilitates the analysis of NK cells and their depletion in vivo with a monoclonal anti-NK 1.1 antibody. These mice, therefore, provide an excellent model to examine unambiguously the interactions between viral infections and NK cells in a system devoid of adaptive immune response mechanisms. Here we show that murine cytomegalovirus (MCMV) and lymphocytic choriomeningitis virus (LCMV) infections resulted in profound levels of NK cell activation. NK cells also proliferated greatly in response to LCMV but generally to a lesser degree in response to MCMV. Depletion of the NK cell activity in vivo caused substantial increases in MCMV synthesis and MCMV-induced pathology. These results further support the concept that NK cells are major regulators of MCMV pathogenesis.
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Affiliation(s)
- R M Welsh
- Department of Pathology, University of Massachusetts Medical Center, Worcester 01655
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26
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Moskophidis D, Battegay M, Bruendler MA, Laine E, Gresser I, Zinkernagel RM. Resistance of lymphocytic choriomeningitis virus to alpha/beta interferon and to gamma interferon. J Virol 1994; 68:1951-5. [PMID: 8107255 PMCID: PMC236657 DOI: 10.1128/jvi.68.3.1951-1955.1994] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The susceptibility to alpha/beta interferon (IFN-alpha/beta) or to gamma interferon (IFN-gamma) of various lymphocytic choriomeningitis virus (LCMV) strains was evaluated in C57BL/6 mice and in various cell lines. Anti-IFN-gamma treatment in vivo revealed that the LCMV strains Armstrong, Aggressive, and WE were most susceptible to IFN-gamma whereas Traub, Cl 13-Armstrong, and Docile were resistant. The same pattern of susceptibility to recombinant IFN-gamma was observed in vitro. In vivo treatment with anti-IFN-alpha/beta showed a sizeable increase in replication of Aggressive, Armstrong, and WE; effects were less pronounced for Docile, Cl 13-Armstrong, or Traub. Correspondingly, WE, Armstrong, and Aggressive were all relatively sensitive to purified IFN-alpha/beta in vitro, and Cl 13-Armstrong, Docile, and Traub were more resistant. Overall, there was a good correlation between the capacity of LCMV strains to establish a persistent infection in adult immunocompetent mice and their relative resistance to IFN-gamma and IFN-alpha/beta.
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Affiliation(s)
- D Moskophidis
- Institute of Experimental Immunology, University of Zurich, Switzerland
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27
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Abstract
The path that the arenavirus lymphocytic choriomeningitis virus (LCMV) uses to enter rodent fibroblastic cell lines was dissected by infectivity and inhibition studies and immunoelectron microscopy. Lysosomotropic weak bases (chloroquine and ammonium chloride) and carboxylic ionophores (monensin and nigericin) inhibited virus entry, assessed as virus nucleoprotein expression at early times post-infection, indicating that the entry process involved a pH-dependent fusion step in intracellular vesicles. That entry occurred in vesicles rather than by direct fusion of virions with the plasma membrane was confirmed by immunoelectron microscopy. The vesicles involved were large (150-300 nm diameter), smooth-walled, and not associated with clathrin. Unlike classical phagocytosis, virus uptake in these vesicles was a microfilament-independent process, as it was not blocked by cytochalasins. LCMV entry into rodent fibroblast cell lines thus involves viropexis in large smooth-walled vesicles, followed by a pH-dependent fusion event inside the cell.
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Affiliation(s)
- P Borrow
- Department of Neuropharmacology, Scripps Research Institute, La Jolla, California 92037
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28
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Abstract
The human monocytic cell line THP-1 was used as a model to study the mechanism of infection in the monocyte/macrophage, a natural target of lymphocytic choriomeningitis virus (LCMV) infection in vivo. Both the virulent strain, LCMV.WE, and the avirulent strain, LCMV.ARM, infected THP-1 cells, but did not stimulate THP-1 cells to secrete interleukin 1 (IL-1) or tumour necrosis factor (TNF-alpha). When lipopolysaccharide (LPS) was added to THP-1 cells together with LCMV, an 80 to 90% reduction in the number of infected cells (measured by immunofluorescence) and a 90% reduction in viral plaques was observed 5 to 6 days post-infection. Neither interferon alpha (IFN-alpha) nor IFN-beta were detected in supernatants from THP-1 cells after the addition of LCMV, LPS, or LPS plus LCMV. In contrast, the same levels of IL-1 and TNF-alpha were observed in the presence of LPS and LCMV, or LPS alone. However, antibodies to IL-1, TNF-alpha, interleukin 6 and IFN-alpha did not block the antiviral effect of LPS. In kinetic studies, LPS added 1 day after adding LCMV to THP-1 cells was still effective in reducing the number of infected cells. Our findings suggest that LPS alters cellular metabolism, possibly through the induction of IFN-alpha, and that IFN-alpha in the absence of LPS suppresses virus production.
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Affiliation(s)
- T Krakauer
- Disease Assessment Division, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland 21702-5011
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29
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Abstract
Intracellular events in the synthesis, glycosylation, and transport of the lymphocytic choriomeningitis virus (LCMV) glycoproteins have been examined. We have shown by N-glycanase digestion that LCMV strain Arm-4 bears five oligosaccharides on GP-1 and two on GP-2. By pulse-chase labeling experiments in the presence of drugs which inhibit N-linked oligosaccharide addition and processing we demonstrate that addition of high mannose precursor oligosaccharides is necessary for transport and cleavage of the viral GP-C glycoprotein. Moreover, in the presence of tunicamycin which inhibits en bloc addition of these mannose-rich side chains, virus budding was substantially decreased and infectious virions were reduced by more than 1000-fold in the supernatant medium. Incubation in the presence of castantospermine, which permits addition of oligomannosyl-rich chains but blocks further processing, restored transport and cleavage of GP-C and maturation of virions. Finally, by temperature block experiments we have determined that maturation of GP-C oligosaccharides to an endoglycosidase H resistant form precedes cleavage to GP-1 and GP-2. The latter process is most likely to occur in the Golgi or post-Golgi compartment.
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Affiliation(s)
- K E Wright
- Department of Neuropharmacology, Research Institute of Scripps Clinic, La Jolla, California 92037
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30
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Podoplekina LE, Shutova NA. Influence of several chemical reagents on lymphocytic choriomeningitis and Tacaribe viruses. Virologie (Montrouge) 1986; 37:43-8. [PMID: 3962180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The sensitivity of lymphocytic choriomeningitis virus (LCMV) and Tacaribe virus to several chemical reagents was investigated. The viruses were sensitive to lipid solvents (ether, chloroform) and to detergents (sodium desoxycholate and Triton X-100); they were rapidly inactivated by formalin, beta-propiolactone, hydrogen peroxide and chloramine B. The results obtained contribute to a more complete characterization of the biological features of the arenavirus group and may be useful for scientific research and manufacturing of viral preparations.
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31
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Bruns M, Lehmann-Grube F. Lymphocytic choriomeningitis virus. VII. Structural alterations of the virion by treatment with proteolytic enzymes without loss of infectivity. J Gen Virol 1984; 65 ( Pt 8):1431-5. [PMID: 6379102 DOI: 10.1099/0022-1317-65-8-1431] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Treatment of lymphocytic choriomeningitis virus with proteolytic enzymes, hyaluronidase, and phospholipase C increased infectious titres. Biochemical analysis of bromelain- and trypsin-treated virus revealed that infectivity was high in spite of the decrease to low or undetectable levels of all viral glycoproteins as well as partial degradation of the nucleoprotein.
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32
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Abstract
Previous work by M.J. Buchmeier and his colleagues and by our group has led to the conclusion that the lymphocytic choriomeningitis (LCM) virus contains seven distinct structural proteins, which we have named p200, gp85, p77, p63, gp60, gp44, and gp35. Their arrangement in the virion has now been analysed by establishing nearest-neighbour relationships with a homobifunctional crosslinker, by performing polyacrylamide gel electrophoresis in parallel under reducing and non-reducing conditions, and by determining the proteins that are covalently bound to viral lipids. A hypothetical model of the virion of LCM virus is proposed. Its envelope is assumed to consist of a membranous layer composed of gp60 and lipids and two types of spikes with either gp85 or gp44 as tips and gp35 as bases. The last-mentioned glycoprotein also appears to be complexed with p63, the main protein component of the nucleocapsid, and this in turn was found to be spatially associated with p200. Probably p77 is also an internal component, but a more exact position cannot yet be assigned to this protein.
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33
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Gaidamovich SY, Cherednichenko YN, Zhdanov VM. On the mechanism of the persistence of lymphocytic choriomeningitis virus in the continuous cell line Detroit-6. Intervirology 1978; 9:156-61. [PMID: 338548 DOI: 10.1159/000148932] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
A persistent lymphocytic choriomeningitis virus, noninfectious for mice, was revealed in the continuous human cell line, Detroit-6. The virus was detected in the cell monolayer by an indirect immunofluorescence test and in the cell homogenate by a complement-fixation test. Between 30 and 80% of the cells produced viral antigen in subsequent passages of the culture. Thymidine analogues (BrDU and IDU) stimulated the synthesis of antigen. DNA of the persistently infected cell line was transfected to the mouse lymphoid cell line, L1210, which became persistently infected with the virus.
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34
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Logan JC, Fox MP, Morgan JH, Makohon AM, Pfau CJ. Arenavirus inactivation on contact with N-substituted isatin beta-thiosemicarbazones and certain cations. J Gen Virol 1975; 28:271-83. [PMID: 809544 DOI: 10.1099/0022-1317-28-3-271] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
N-methyl and N-ethyl isatin beta-thiosemicarbazones inactivate cell-free Parana and Pichinde viruses as well as three strains of lymphocytic choriomeningitis virus. This antiviral activity is abolished in the presence of the chelating agent EDTA. The rate of virus inactivation by N-methyl isatin beta-thiosemicarbazone is greatly enhanced and controlled by the addition of cupric sulphate. Divalent cations of other first transition series metals are less effective. A difference exists in the copper requirement for fast inactivation of the prototype arenavirus (lymphocytic choriomeningitis) and the Tacaribe Complex of viruses (Parana and Pichinde). In the presence of 20 muM-N-methyl isatin beta-thiosemicarbazone, LCM and Pichinde viruses can be inactivated at about the same rate if 20 muM-CuSO4 is added to the former and 160 muM-CuSO4 is added to the latter. Using 20 muM-N-methyl isatin beta-semicarbazone and CuSO4 the inactivation of LCM is reduced, but not eliminated, in the presence of an equal amount of infectious Pichinde virus. Crude and highly purified Pichinde virus are inactivated at the same rate when exposed to identical concentrations of N-methyl isatin beta-thiosemicarbazone and cupric sulphate. There is little detectable change in the inactivation rates when Pichinde or LCM viruses are grown in a variety of different cell lines.
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35
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Abstract
Mycoplasmas are totally inactivated by a 20-min treatment with 1% phenethyl alcohol, whereas suspensions of enveloped viruses resist the same treatment. This treatment has proved successful in eliminating mycoplasma contamination of a virus suspension.
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Gilden DH, Cole GA, Monjan AA, Nathanson N. Immunopathogenesis of acute central nervous system disease produced by lymphocytic choriomeningitis virus. I. Cyclophosphamide-mediated induction by the virus-carrier state in adult mice. J Exp Med 1972; 135:860-73. [PMID: 4622912 PMCID: PMC2139156 DOI: 10.1084/jem.135.4.860] [Citation(s) in RCA: 97] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
A single dose of 150 mg/g of cyclophosphamide (CY), given 3 days after intracerebral (i.c.) inoculation of lymphocytic choriomeningitis (LCM) virus, protected over 90% of adult BALB/c mice against acutely fatal choriomeningitis. Surviving mice became persistently infected carriers, with high virus titers in blood and brain. Immunofluorescent examination of the brain showed that in CY-induced carriers infection was initially confined to the choroid plexus, ependyma, and leptomeninges, but over the next 30 days gradually spread to the neural parenchyma, most notably to the molecular layer of the cerebellum. By contrast, LCM virus-carrier mice produced by neonatal virus injection and examined as adults, showed a much less marked infection of choroid plexus and much more widespread infection of parenchyma, with a different distribution among brain nuclei, including heavy infection of the Purkinje cells of the cerebellum.
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37
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38
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Furusawa E, Ramanathan S, Furusawa S, Cutting W. Antiviral activity of tobacco leaf on encephalomyocarditis (EMC) virus infection. Exp Biol Med (Maywood) 1971; 138:790-5. [PMID: 4331947 DOI: 10.3181/00379727-138-35990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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39
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Abstract
Depending on the concentration of actinomycin D, the yield of lymphocytic choriomeningitis virus in baby hamster kidney cells was either enhanced or inhibited.
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40
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Abstract
The yields of the Armstrong and WE strains of lymphocytic choriomeningitis virus in baby hamster kidney (BHK) cells cultivated in either bovine, calf, fetal bovine, or horse serum were investigated. Lines of BHK cells were established in these sera. When the infected cell lines were observed by immunofluorescence, the per cent fluorescing cells for a given virus strain did not vary. However, for both strains, the extracellular virus yields per cell were significantly greater in the fetal bovine-cell line than in the other serum-cell lines.
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Welsh RM, Trowbridge RS, Kowalski JB, O'Connell CM, Peau CJ. Amantadine hydrochloride inhibition of early and late stages of lymphocytic choriomenigitis virus-cell interactions. Virology 1971; 45:679-86. [PMID: 5001514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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42
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Abstract
All of the ten strains of lymphocytic choriomeningitis virus assayed on BHK 21/13S cells showed various degrees of plaque size heterogeneity. The amount of virus released from these plaques was usually very small because of rapid photodynamic inactivation by neutral red. When virus from large and small plaques of a specific strain was plated, the same distribution of plaque size was obtained from each clone. Although it was shown that surface virus could possibly be randomly distributed at the time of addition of neutral red overlays, no virus could be isolated from nonplaque areas. Two different strains of virus (CA1371 and WE) with markedly different plaque size ranges were separated by plaque excision from plates infected with a mixture of both viruses.
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43
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Abstract
Lymphocytic choriomeningitis (LCM) virus was observed by electron microscopy in thin sections of infected tissue cultures. The particles were pleomorphic and varied greatly in size. The smaller particles (50 to 200 nm) appeared to be spherical, whereas the largest (over 200 nm) were often cup-shaped. All particles contained one to eight or more electron-dense granules which were removed by ribonuclease. The particles were formed by budding from the plasma membrane and appeared to have spikes. The morphological evidence suggests that LCM should be considered as belonging to the presently unclassified group of lipoprotein-enveloped ribonucleic acid viruses.
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44
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45
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46
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Furusawa E, Ramanathan S, Furusawa S, Woo YK, Cutting W. Antiviral activity of higher plants and propionin on lymphocytic choriomeningitis infection. Proc Soc Exp Biol Med 1967; 125:234-9. [PMID: 4961253 DOI: 10.3181/00379727-125-32057] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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47
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48
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Abstract
Chemotherapy experiments carried out in vitro demonstrated that 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) was active against lymphocytic choriomeningitis virus and had an equivocal antiviral effect on Semliki Forest, herpes simplex, and vaccinia viruses. No antiviral effect was observed with BCNU against western equine encephalomyelitis, polio, and parainfluenza (HA-1) viruses. Activity of the drug was determined by inhibition of viral-induced cytopathogenic effect in KB or chick embryo cells and by reduction of virus titer in cell culture supernatant fluid. Maximal activity against the viruses was observed when drug and virus were incubated together for 30 min prior to addition to cells; essentially no activity could be demonstrated if BCNU and virus were added to cells with no prior incubation.
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