scholarly journals Hemagglutinin 1-Specific Immunoglobulin G and Fab Molecules Mediate Postattachment Neutralization of Influenza A Virus by Inhibition of an Early Fusion Event

2001 ◽  
Vol 75 (21) ◽  
pp. 10208-10218 ◽  
Author(s):  
M. J. Edwards ◽  
N. J. Dimmock
Keyword(s):  
Immunoglobulin G ◽  
Influenza A ◽  
Contact Point ◽  
Neutralizing Antibody ◽  
Cell Contact ◽  
Target Cells ◽  
Dependent Manner ◽  
Fusion Event ◽  
Virus Attachment ◽  
Early Interaction

ABSTRACT In standard neutralization (STAN), virus and antibody are reacted together before inoculation of target cells, and inhibition of almost any of the processes concerned in the early interaction of virus and cell, including inhibition of virus attachment to cell receptors, can be the cause of neutralization by a particular monoclonal antibody (MAb). To simplify the interpretation of antibody action, we carried out a study of postattachment neutralization (PAN), where virus is allowed to attach to target cells before neutralizing antibody is introduced. We used influenza virus A/PR/8/34 (H1N1) and monoclonal immunoglobulin G (IgG) molecules and their Fabs specific to antigenic sites Sb (tip), Ca2 (loop), and Cb (hinge) of the hemagglutinin 1 (HA1) protein. All IgGs and Fabs gave PAN, although with reduced efficiency compared with STAN. Thus, bivalent binding of antibody was not essential for PAN. By definition, none of these MAbs gave PAN by inhibiting virus attachment, and they did not elute attached virus from the target cell or inhibit endocytosis of virus. However, virus-cell fusion, as demonstrated by R18 fluorescence dequenching or hemolysis of red blood cells, was inhibited in direct proportion to neutralization and in a dose-dependent manner and was thus likely to be responsible for the observed neutralization. However, to get PAN, it was necessary to inhibit the activation of the prefusion intermediate, the earliest known form on the fusion pathway that is created when virus is incubated at pH 5 and 4°C. PAN antibodies may act by binding HA trimers in contact with the cell and/or trimers in the immediate vicinity of the virus-cell contact point and so inhibit the recruitment of additional receptor-HA complexes.

scholarly journals SalmonellaTyphimurium utilizes a T6SS-mediated antibacterial weapon to establish in the host gut

2016 ◽  
Vol 113 (34) ◽  
pp. E5044-E5051 ◽  
Author(s):  
Thibault G. Sana ◽  
Nicolas Flaugnatti ◽  
Kyler A. Lugo ◽  
Lilian H. Lam ◽  
Amanda Jacobson ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Klebsiella Oxytoca ◽  
Specific Interaction ◽  
Commensal Bacteria ◽  
Cell Contact ◽  
Target Cells ◽  
Dependent Manner ◽  
Type Vi Secretion System ◽  
Pathogen Invasion

The mammalian gastrointestinal tract is colonized by a high-density polymicrobial community where bacteria compete for niches and resources. One key competition strategy includes cell contact-dependent mechanisms of interbacterial antagonism, such as the type VI secretion system (T6SS), a multiprotein needle-like apparatus that injects effector proteins into prokaryotic and/or eukaryotic target cells. However, the contribution of T6SS antibacterial activity during pathogen invasion of the gut has not been demonstrated. We report that successful establishment in the gut by the enteropathogenic bacteriumSalmonella entericaserovar Typhimurium requires a T6SS encoded withinSalmonellapathogenicity island-6 (SPI-6). In an in vitro setting, we demonstrate that bile salts increase SPI-6 antibacterial activity and thatS. Typhimurium kills commensal bacteria in a T6SS-dependent manner. Furthermore, we provide evidence that one of the two T6SS nanotube subunits, Hcp1, is required for killingKlebsiella oxytocain vitro and that this activity is mediated by the specific interaction of Hcp1 with the antibacterial amidase Tae4. Finally, we show thatK. oxytocais killed in the host gut in an Hcp1-dependent manner and that the T6SS antibacterial activity is essential forSalmonellato establish infection within the host gut. Our findings provide an example of pathogen T6SS-dependent killing of commensal bacteria as a mechanism to successfully colonize the host gut.

scholarly journals Differential natural killer cell–mediated inhibition of HIV-1 replication based on distinct KIR/HLA subtypes

2007 ◽  
Vol 204 (12) ◽  
pp. 3027-3036 ◽  
Author(s):  
Galit Alter ◽  
Maureen P. Martin ◽  
Nickolas Teigen ◽  
William H. Carr ◽  
Todd J. Suscovich ◽  
...  
Keyword(s):  
Nk Cells ◽  
Natural Killer ◽  
Nk Cell ◽  
Killer Cell ◽  
Cell Activity ◽  
Cell Contact ◽  
Target Cells ◽  
Dependent Manner ◽  
Hiv 1

Decline of peak viremia during acute HIV-1 infection occurs before the development of vigorous adaptive immunity, and the level of decline correlates inversely with the rate of AIDS progression, implicating a potential role for the innate immune response in determining disease outcome. The combined expression of an activating natural killer (NK) cell receptor, the killer immunoglobulin-like receptor (KIR) 3DS1, and its presumed ligand, human leukocyte antigen (HLA)–B Bw4-80I, has been associated in epidemiological studies with a slow progression to AIDS. We examined the functional ability of NK cells to differentially control HIV-1 replication in vitro based on their KIR and HLA types. NK cells expressing KIR3DS1 showed strong, significant dose- and cell contact–dependent inhibition of HIV-1 replication in target cells expressing HLA-B Bw4-80I compared with NK cells that did not express KIR3DS1. Furthermore, KIR3DS1+ NK cells and NKLs were preferentially activated, and lysed HIV-1 infected target cells in an HLA-B Bw4-80I–dependent manner. These data provide the first functional evidence that variation at the KIR locus influences the effectiveness of NK cell activity in the containment of viral replication.

scholarly journals Clathrin-Dependent Entry of Severe Acute Respiratory Syndrome Coronavirus into Target Cells Expressing ACE2 with the Cytoplasmic Tail Deleted

2007 ◽  
Vol 81 (16) ◽  
pp. 8722-8729 ◽  
Author(s):  
Yuuki Inoue ◽  
Nobuyuki Tanaka ◽  
Yoshinori Tanaka ◽  
Shingo Inoue ◽  
Kouichi Morita ◽  
...  
Keyword(s):  
Severe Acute Respiratory Syndrome ◽  
Viral Entry ◽  
Cytoplasmic Tail ◽  
Host Cells ◽  
Target Cells ◽  
Dependent Manner ◽  
Virus Attachment ◽  
Caveolin 1 ◽  
Early Endosomes ◽  
Interfering Rna

ABSTRACT The penetration of various viruses into host cells is accomplished by hijacking the host endocytosis machinery. In the case of severe acute respiratory syndrome coronavirus (SARS-CoV) infection, viral entry is reported to require a low pH in intracytoplasmic vesicles; however, little is known about how SARS-CoV invades such compartments. Here we demonstrate that SARS-CoV mainly utilizes the clathrin-mediated endocytosis pathway for its entry to target cells by using infectious SARS-CoV, as well as a SARS-CoV pseudovirus packaged in the SARS-CoV envelope. The SARS-CoV entered caveolin-1-negative HepG2 cells, and the entry was significantly inhibited by treatment with chlorpromazine, an inhibitor for clathrin-dependent endocytosis, and by small interfering RNA-mediated gene silencing for the clathrin heavy chain. Furthermore, the SARS-CoV entered COS7 cells transfected with the mutant of ACE2 with the cytoplasmic tail deleted, SARS-CoV receptor, as well as the wild-type ACE2, and their entries were significantly inhibited by treatment with chlorpromazine. In addition, ACE2 translocated into EEA1-positive early endosomes immediately after the virus attachment to ACE2. These results suggest that when SARS-CoV binds ACE2 it is internalized and penetrates early endosomes in a clathrin-dependent manner and that the cytoplasmic tail of ACE2 is not required for the penetration of SARS-CoV.

scholarly journals Cancer cell elimination by cytotoxic T cell cooperation and additive damage

2020 ◽  
Author(s):  
Bettina Weigelin ◽  
Annemieke Th. den Boer ◽  
Esther Wagena ◽  
Kelly Broen ◽  
Harry Dolstra ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Nuclear Lamina ◽  
Time Lapse ◽  
Cytotoxic T Cell ◽  
Cell Contact ◽  
Target Cells ◽  
Dependent Manner ◽  
Membrane Pore ◽  
Induced Apoptosis

SummaryCytotoxic T lymphocytes (CTL) eliminate tumor target cells in an antigen and cell-contact dependent manner. Lethal hit delivery occurs as a rapid and binary, “yes/no” process when immunogenicity is very high1–3, however in vivo CTL often fail to kill solid tumor cells during 1:1 conjugations4–6. Using long-term time-lapse microscopy in three distinct tumor cytotoxicity models and statistical modeling, we here show that migrating CTL transit between target cells and initiate apoptosis by a series of sublethal interactions (‘additive cytotoxicity’), while individual conjugations rarely induced apoptosis. Sublethal damage included perforin-dependent membrane pore formation, nuclear lamina rupture and DNA damage, and these events resolved within minutes to hours. In immunogenic B16F10 melanoma tumors in vivo, frequent serial engagements and sublethal hit delivery of CTL was largely confined to interstitial niches in the invasion front, resulting in eradication of invading tumor cells. Thus, additive cytotoxicity is a probabilistic process achieved by a series of CTL-target cell engagements and sublethal events. The need for additive “hits” has implications for the topographic mechanisms of elimination or immune evasion of tumor cells and microenvironmental regulation of CTL accumulation and cooperation by targeted therapy.

scholarly journals A haemagglutinin (HA1)-specific FAb neutralizes influenza A virus by inhibiting fusion activity

2001 ◽  
Vol 82 (6) ◽  
pp. 1387-1395 ◽  
Author(s):  
M. J. Edwards ◽  
N. J. Dimmock
Keyword(s):  
Influenza Virus ◽  
Influenza A Virus ◽  
Influenza A ◽  
Antigenic Site ◽  
Detectable Effect ◽  
Target Cells ◽  
Fusion Activity ◽  
Influenza Virus A ◽  
Virus Attachment ◽  
Virus Fusion

H9-D3-4R2 (referred to as H9), a murine monoclonal HA1-specific IgG3, recognizes an epitope within antigenic site Cb of influenza virus A/PR/8/34 (H1N1). At 50% neutralization, inhibition of virus-mediated fusion was responsible for the majority of neutralization but, at higher antibody concentrations, the attachment of virus to target cells was also inhibited and may have contributed to neutralization. H9 FAb was also neutralizing, although the concentration needed was two orders of magnitude greater than for the IgG. Functional affinity of the IgG and affinity of the FAb were almost identical, and it is not clear why the neutralization efficiency of the FAb was so low. Unlike its IgG, H9 FAb had no detectable effect on virus attachment but inhibited virus fusion activity. It thus appears that monovalent binding by this antibody is sufficient to inhibit fusion activity and that this was directly responsible for neutralization of infectivity.

scholarly journals Shaping of T Cell Functions by Trogocytosis

Cells ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 1155
Author(s):  
Masafumi Nakayama ◽  
Arisa Hori ◽  
Saori Toyoura ◽  
Shin-Ichiro Yamaguchi
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Antigen Processing ◽  
Cell Contact ◽  
Target Cells ◽  
Dependent Manner ◽  
Mhc Molecules ◽  
Cell Functions ◽  
Cell Cell

Trogocytosis is an active process whereby plasma membrane proteins are transferred from one cell to the other cell in a cell-cell contact-dependent manner. Since the discovery of the intercellular transfer of major histocompatibility complex (MHC) molecules in the 1970s, trogocytosis of MHC molecules between various immune cells has been frequently observed. For instance, antigen-presenting cells (APCs) acquire MHC class I (MHCI) from allografts, tumors, and virally infected cells, and these APCs are subsequently able to prime CD8+ T cells without antigen processing via the preformed antigen-MHCI complexes, in a process called cross-dressing. T cells also acquire MHC molecules from APCs or other target cells via the immunological synapse formed at the cell-cell contact area, and this phenomenon impacts T cell activation. Compared with naïve and effector T cells, T regulatory cells have increased trogocytosis activity in order to remove MHC class II and costimulatory molecules from APCs, resulting in the induction of tolerance. Accumulating evidence suggests that trogocytosis shapes T cell functions in cancer, transplantation, and during microbial infections. In this review, we focus on T cell trogocytosis and the related inflammatory diseases.

scholarly journals Role of MDA5 in regulating CXCL10 expression induced by TLR3 signaling in human rheumatoid fibroblast-like synoviocytes

2021 ◽  
Author(s):  
Tatsuro Saruga ◽  
Tadaatsu Imaizumi ◽  
Shogo Kawaguchi ◽  
Kazuhiko Seya ◽  
Tomoh Matsumiya ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Neutralizing Antibody ◽  
Poly I:C ◽  
Enzyme Linked Immunosorbent Assay ◽  
Dependent Manner ◽  
Inflammatory Reactions ◽  
Polyinosinic:Polycytidylic Acid ◽  
Tlr3 Signaling ◽  
Fibroblast Like Synoviocytes

AbstractC-X-C motif chemokine 10 (CXCL10) is an inflammatory chemokine and a key molecule in the pathogenesis of rheumatoid arthritis (RA). Melanoma differentiation-associated gene 5 (MDA5) is an RNA helicase that plays a role in innate immune and inflammatory reactions. The details of the regulatory mechanisms of CXCL10 production and the precise role of MDA5 in RA synovitis have not been fully elucidated. The aim of this study was to examine the role of MDA5 in regulating CXCL10 expression in cultured human rheumatoid fibroblast-like synoviocytes (RFLS). RFLS was stimulated with Toll-like receptor 3 (TLR3) ligand polyinosinic:polycytidylic acid (poly I:C), a synthetic double-stranded RNA mimetic. Expression of interferon beta (IFN-β), MDA5, and CXCL10 was measured by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting, and enzyme-linked immunosorbent assay. A neutralizing antibody of IFN-β and siRNA-mediated MDA5 knockdown were used to determine the role of these molecules in regulating CXCL10 expression downstream of TLR3 signaling in RFLS. Poly I:C induced IFN-β, MDA5, and CXCL10 expression in a concentration- and time-dependent manner. IFN-β neutralizing antibody suppressed the expression of MDA5 and CXCL10, and knockdown of MDA5 decreased a part of CXCL10 expression (p < 0.001). The TLR3/IFN-β/CXCL10 axis may play a crucial role in the inflammatory responses in RA synovium, and MDA5 may be partially involved in this axis.

scholarly journals Influenza A Virus Hemagglutinin and Other Pathogen Glycoprotein Interactions with NK Cell Natural Cytotoxicity Receptors NKp46, NKp44, and NKp30

Viruses ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 156
Author(s):  
Jasmina M. Luczo ◽  
Sydney L. Ronzulli ◽  
Stephen M. Tompkins
Keyword(s):  
Influenza Virus ◽  
Nk Cells ◽  
Influenza A Virus ◽  
Influenza A ◽  
Nk Cell ◽  
Influenza Virus Infection ◽  
Target Cells ◽  
Natural Cytotoxicity ◽  
Activating Receptors ◽  
Natural Cytotoxicity Receptors

Natural killer (NK) cells are part of the innate immunity repertoire, and function in the recognition and destruction of tumorigenic and pathogen-infected cells. Engagement of NK cell activating receptors can lead to functional activation of NK cells, resulting in lysis of target cells. NK cell activating receptors specific for non-major histocompatibility complex ligands are NKp46, NKp44, NKp30, NKG2D, and CD16 (also known as FcγRIII). The natural cytotoxicity receptors (NCRs), NKp46, NKp44, and NKp30, have been implicated in functional activation of NK cells following influenza virus infection via binding with influenza virus hemagglutinin (HA). In this review we describe NK cell and influenza A virus biology, and the interactions of influenza A virus HA and other pathogen lectins with NK cell natural cytotoxicity receptors (NCRs). We review concepts which intersect viral immunology, traditional virology and glycobiology to provide insights into the interactions between influenza virus HA and the NCRs. Furthermore, we provide expert opinion on future directions that would provide insights into currently unanswered questions.

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