RESUMEN
Avian influenza viruses continue to cross the species barrier and infect mammals. In this issue of Cell, Sun and colleagues demonstrate that viruses obtained from humans infected with an emergent avian H3N8 viruses exhibit increasing accumulation of mutations that promote respiratory droplet transmission and disease in mammals.
Asunto(s)
Subtipo H3N8 del Virus de la Influenza A , Virus de la Influenza A , Animales , Humanos , Virus de la Influenza A/genética , Mutación , MamíferosRESUMEN
Germinal centers (GCs) form in lymph nodes after immunization or infection to facilitate antibody affinity maturation and memory and plasma cell (PC) development. PC differentiation is thought to involve stringent selection for GC B cells expressing the highest-affinity antigen receptors, but how this plays out during complex polyclonal responses is unclear. We combine temporal lineage tracing with antibody characterization to gain a snapshot of PCs developing during influenza infection. GCs co-mature B cell clones with antibody affinities spanning multiple orders of magnitude; however, each generates PCs with similar efficiencies, including weak binders. Within lineages, PC selection is not restricted to variants with the highest-affinity antibodies. Differentiation is commonly associated with proliferative expansion to produce "nodes" of identical PCs. Immunization-induced GCs generate fewer PCs but still of low- and high-antibody affinities. We propose that generating low-affinity antibody PCs reflects an evolutionary compromise to facilitate diverse serum antibody responses.
Asunto(s)
Afinidad de Anticuerpos , Linfocitos B , Centro Germinal , Células Plasmáticas , Formación de Anticuerpos , Linfocitos B/citología , Linfocitos B/inmunología , Ganglios Linfáticos , Línea Celular , Humanos , Animales , Ratones , Cricetinae , Virus de la Influenza A/inmunología , Diferenciación CelularRESUMEN
After a century of using the Bacillus Calmette-Guérin (BCG) vaccine, our understanding of its ability to provide protection against homologous (Mycobacterium tuberculosis) or heterologous (for example, influenza virus) infections remains limited. Here we show that systemic (intravenous) BCG vaccination provides significant protection against subsequent influenza A virus infection in mice. We further demonstrate that the BCG-mediated cross-protection against influenza A virus is largely due to the enrichment of conventional CD4+ effector CX3CR1hi memory αß T cells in the circulation and lung parenchyma. Importantly, pulmonary CX3CR1hi T cells limit early viral infection in an antigen-independent manner via potent interferon-γ production, which subsequently enhances long-term antimicrobial activity of alveolar macrophages. These results offer insight into the unknown mechanism by which BCG has persistently displayed broad protection against non-tuberculosis infections via cross-talk between adaptive and innate memory responses.
Asunto(s)
Vacuna BCG , Virus de la Influenza A , Infecciones por Orthomyxoviridae , Animales , Ratones , Administración Intravenosa , Vacuna BCG/inmunología , Células T de Memoria , Inmunidad Entrenada , Vacunación , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/prevención & controlRESUMEN
My coworkers and I have used animal viruses and their interaction with host cells to investigate cellular processes difficult to study by other means. This approach has allowed us to branch out in many directions, including membrane protein characterization, endocytosis, secretion, protein folding, quality control, and glycobiology. At the same time, our aim has been to employ cell biological approaches to expand the fundamental understanding of animal viruses and their pathogenic lifestyles. We have studied mechanisms of host cell entry and the uncoating of incoming viruses as well as the synthesis, folding, maturation, and intracellular movement of viral proteins and molecular assemblies. I have had the privilege to work in institutions in four different countries. The early years in Finland (the University of Helsinki) were followed by 6 years in Germany (European Molecular Biology Laboratory), 16 years in the United States (Yale School of Medicine), and 16 years in Switzerland (ETH Zurich).
Asunto(s)
Calnexina/genética , Calreticulina/genética , Interacciones Huésped-Patógeno/genética , Virus de la Influenza A/genética , Picornaviridae/genética , Proteínas Virales/genética , Virología/historia , Animales , Calnexina/química , Calnexina/metabolismo , Calreticulina/química , Calreticulina/metabolismo , Línea Celular , Retículo Endoplásmico/metabolismo , Retículo Endoplásmico/virología , Endosomas/metabolismo , Endosomas/virología , Regulación de la Expresión Génica , Historia del Siglo XX , Historia del Siglo XXI , Humanos , Virus de la Influenza A/metabolismo , Picornaviridae/metabolismo , Pliegue de Proteína , Virus de los Bosques Semliki/genética , Virus de los Bosques Semliki/metabolismo , Vesiculovirus/genética , Vesiculovirus/metabolismo , Proteínas Virales/química , Proteínas Virales/metabolismo , Internalización del VirusRESUMEN
Influenza is one of the best-studied viruses of all time, and as such, it serves as a testbed to extend our biological knowledge to the nanoscale. Many of the key processes underlying influenza infection and our antibody response against the virus have been thoroughly investigated. This SnapShot describes these key numbers for prototypical lab-adapted strains of the human influenza A virus. To view this SnapShot, open or download the PDF.
Asunto(s)
Virus de la Influenza A/metabolismo , Gripe Humana/patología , Formación de Anticuerpos , Eritrocitos/virología , Hemaglutininas/química , Hemaglutininas/metabolismo , Humanos , Virus de la Influenza A/inmunología , Virus de la Influenza A/patogenicidad , Gripe Humana/virología , Neuraminidasa/química , Neuraminidasa/metabolismo , Unión Proteica , Estructura Cuaternaria de Proteína , Ácidos Siálicos/metabolismoRESUMEN
Influenza polymerase uses unique mechanisms to synthesize capped and polyadenylated mRNAs from the genomic viral RNA (vRNA) template, which is packaged inside ribonucleoprotein particles (vRNPs). Here, we visualize by cryoelectron microscopy the conformational dynamics of the polymerase during the complete transcription cycle from pre-initiation to termination, focusing on the template trajectory. After exiting the active site cavity, the template 3' extremity rebinds into a specific site on the polymerase surface. Here, it remains sequestered during all subsequent transcription steps, forcing the template to loop out as it further translocates. At termination, the strained connection between the bound template 5' end and the active site results in polyadenylation by stuttering at uridine 17. Upon product dissociation, further conformational changes release the trapped template, allowing recycling back into the pre-initiation state. Influenza polymerase thus performs transcription while tightly binding to and protecting both template ends, allowing efficient production of multiple mRNAs from a single vRNP.
Asunto(s)
Virus de la Influenza A/genética , Transcripción Genética/genética , Replicación Viral/genética , Dominio Catalítico , Simulación por Computador , Microscopía por Crioelectrón/métodos , Genoma Viral/genética , Humanos , Virus de la Influenza A/metabolismo , Gripe Humana/genética , Gripe Humana/virología , Nucleotidiltransferasas/metabolismo , ARN Mensajero/metabolismo , ARN Viral/metabolismo , ARN Polimerasa Dependiente del ARN/genética , ARN Polimerasa Dependiente del ARN/metabolismo , Relación Estructura-ActividadRESUMEN
Influenza A virus (IAV) is a lytic RNA virus that triggers receptor-interacting serine/threonine-protein kinase 3 (RIPK3)-mediated pathways of apoptosis and mixed lineage kinase domain-like pseudokinase (MLKL)-dependent necroptosis in infected cells. ZBP1 initiates RIPK3-driven cell death by sensing IAV RNA and activating RIPK3. Here, we show that replicating IAV generates Z-RNAs, which activate ZBP1 in the nucleus of infected cells. ZBP1 then initiates RIPK3-mediated MLKL activation in the nucleus, resulting in nuclear envelope disruption, leakage of DNA into the cytosol, and eventual necroptosis. Cell death induced by nuclear MLKL was a potent activator of neutrophils, a cell type known to drive inflammatory pathology in virulent IAV disease. Consequently, MLKL-deficient mice manifest reduced nuclear disruption of lung epithelia, decreased neutrophil recruitment into infected lungs, and increased survival following a lethal dose of IAV. These results implicate Z-RNA as a new pathogen-associated molecular pattern and describe a ZBP1-initiated nucleus-to-plasma membrane "inside-out" death pathway with potentially pathogenic consequences in severe cases of influenza.
Asunto(s)
Virus de la Influenza A/genética , Necroptosis/genética , Proteínas de Unión al ARN/metabolismo , Animales , Apoptosis/genética , Muerte Celular/genética , Línea Celular Tumoral , Femenino , Virus de la Influenza A/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Necrosis/metabolismo , Fosforilación , Proteínas Quinasas/metabolismo , ARN/metabolismo , ARN Bicatenario/genética , ARN Bicatenario/metabolismo , Proteínas de Unión al ARN/genética , Proteína Serina-Treonina Quinasas de Interacción con Receptores/metabolismo , Proteína Serina-Treonina Quinasas de Interacción con Receptores/fisiologíaRESUMEN
RNA viruses are a major human health threat. The life cycles of many highly pathogenic RNA viruses like influenza A virus (IAV) and Lassa virus depends on host mRNA, because viral polymerases cleave 5'-m7G-capped host transcripts to prime viral mRNA synthesis ("cap-snatching"). We hypothesized that start codons within cap-snatched host transcripts could generate chimeric human-viral mRNAs with coding potential. We report the existence of this mechanism of gene origination, which we named "start-snatching." Depending on the reading frame, start-snatching allows the translation of host and viral "untranslated regions" (UTRs) to create N-terminally extended viral proteins or entirely novel polypeptides by genetic overprinting. We show that both types of chimeric proteins are made in IAV-infected cells, generate T cell responses, and contribute to virulence. Our results indicate that during infection with IAV, and likely a multitude of other human, animal and plant viruses, a host-dependent mechanism allows the genesis of hybrid genes.
Asunto(s)
Caperuzas de ARN/genética , Infecciones por Virus ARN/genética , Proteínas Recombinantes de Fusión/genética , Regiones no Traducidas 5'/genética , Animales , Bovinos , Línea Celular , Cricetinae , Perros , Humanos , Virus de la Influenza A/metabolismo , Ratones , Proteínas Mutantes Quiméricas/genética , Proteínas Mutantes Quiméricas/metabolismo , Sistemas de Lectura Abierta/genética , Caperuzas de ARN/metabolismo , Infecciones por Virus ARN/metabolismo , Virus ARN/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Viral/metabolismo , ARN Polimerasa Dependiente del ARN/genética , ARN Polimerasa Dependiente del ARN/metabolismo , Proteínas Recombinantes de Fusión/metabolismo , Transcripción Genética/genética , Proteínas Virales/metabolismo , Replicación Viral/genéticaRESUMEN
Morphological variation is a common yet poorly understood feature of influenza virus populations. Vahey and Fletcher reveal that the production of physically and phenotypically heterogeneous particles is an inherent feature of the influenza assembly process that may promote virus survival in challenging environments.
Asunto(s)
Virus de la Influenza A , Gripe Humana , HumanosRESUMEN
Influenza viruses inhabit a wide range of host environments using a limited repertoire of protein components. Unlike viruses with stereotyped shapes, influenza produces virions with significant morphological variability even within clonal populations. Whether this tendency to form pleiomorphic virions is coupled to compositional heterogeneity and whether it affects replicative fitness remains unclear. Here, we address these questions by developing a strain of influenza A virus amenable to rapid compositional characterization through quantitative, site-specific labeling of viral proteins. Using this strain, we find that influenza A produces virions with broad variations in size and composition from even single infected cells. This phenotypic variability contributes to virus survival during environmental challenges, including exposure to antivirals. Complementing genetic adaptations that act over larger populations and longer times, this "low-fidelity" assembly of influenza A virus allows small populations to survive environments that fluctuate over individual replication cycles.
Asunto(s)
Virus de la Influenza A/metabolismo , Ensamble de Virus/fisiología , Línea Celular , Células Cultivadas , Humanos , Virus de la Influenza A/fisiología , Gripe Humana/virología , Proteínas Virales , Virión , Replicación Viral/fisiologíaRESUMEN
Here, we describe the discovery of a naturally occurring human antibody (Ab), FluA-20, that recognizes a new site of vulnerability on the hemagglutinin (HA) head domain and reacts with most influenza A viruses. Structural characterization of FluA-20 with H1 and H3 head domains revealed a novel epitope in the HA trimer interface, suggesting previously unrecognized dynamic features of the trimeric HA protein. The critical HA residues recognized by FluA-20 remain conserved across most subtypes of influenza A viruses, which explains the Ab's extraordinary breadth. The Ab rapidly disrupted the integrity of HA protein trimers, inhibited cell-to-cell spread of virus in culture, and protected mice against challenge with viruses of H1N1, H3N2, H5N1, or H7N9 subtypes when used as prophylaxis or therapy. The FluA-20 Ab has uncovered an exceedingly conserved protective determinant in the influenza HA head domain trimer interface that is an unexpected new target for anti-influenza therapeutics and vaccines.
Asunto(s)
Anticuerpos Monoclonales de Origen Murino/inmunología , Anticuerpos Antivirales/inmunología , Epítopos/inmunología , Glicoproteínas Hemaglutininas del Virus de la Influenza/inmunología , Virus de la Influenza A/inmunología , Vacunas contra la Influenza/inmunología , Infecciones por Orthomyxoviridae , Animales , Perros , Células de Riñón Canino Madin Darby , Ratones , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/patología , Infecciones por Orthomyxoviridae/prevención & controlRESUMEN
Vaccines to generate durable humoral immunity against antigenically evolving pathogens such as the influenza virus must elicit antibodies that recognize conserved epitopes. Analysis of single memory B cells from immunized human donors has led us to characterize a previously unrecognized epitope of influenza hemagglutinin (HA) that is immunogenic in humans and conserved among influenza subtypes. Structures show that an unrelated antibody from a participant in an experimental infection protocol recognized the epitope as well. IgGs specific for this antigenic determinant do not block viral infection in vitro, but passive administration to mice affords robust IgG subtype-dependent protection against influenza infection. The epitope, occluded in the pre-fusion form of HA, is at the contact surface between HA head domains; reversible molecular "breathing" of the HA trimer can expose the interface to antibody and B cells. Antigens that present this broadly immunogenic HA epitope may be good candidates for inclusion in "universal" flu vaccines.
Asunto(s)
Anticuerpos Antivirales/inmunología , Epítopos/inmunología , Glicoproteínas Hemaglutininas del Virus de la Influenza/inmunología , Inmunoglobulina G/inmunología , Virus de la Influenza A/inmunología , Vacunas contra la Influenza/inmunología , Infecciones por Orthomyxoviridae , Adulto , Animales , Perros , Femenino , Humanos , Células de Riñón Canino Madin Darby , Masculino , Ratones , Persona de Mediana Edad , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/patología , Infecciones por Orthomyxoviridae/prevención & controlRESUMEN
Classic major histocompatibility complex class I (MHC-I) presentation relies on shuttling cytosolic peptides into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP). Viruses disable TAP to block MHC-I presentation and evade cytotoxic CD8+ T cells. Priming CD8+ T cells against these viruses is thought to rely solely on cross-presentation by uninfected TAP-functional dendritic cells. We found that protective CD8+ T cells could be mobilized during viral infection even when TAP was absent in all hematopoietic cells. TAP blockade depleted the endosomal recycling compartment of MHC-I molecules and, as such, impaired Toll-like receptor-regulated cross-presentation. Instead, MHC-I molecules accumulated in the ER-Golgi intermediate compartment (ERGIC), sequestered away from Toll-like receptor control, and coopted ER-SNARE Sec22b-mediated vesicular traffic to intersect with internalized antigen and rescue cross-presentation. Thus, when classic MHC-I presentation and endosomal recycling compartment-dependent cross-presentation are impaired in dendritic cells, cell-autonomous noncanonical cross-presentation relying on ERGIC-derived MHC-I counters TAP dysfunction to nevertheless mediate CD8+ T cell priming.
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2/metabolismo , Transportadoras de Casetes de Unión a ATP/metabolismo , Linfocitos T CD8-positivos/inmunología , Reactividad Cruzada , Células Dendríticas/inmunología , Antígenos de Histocompatibilidad Clase I/inmunología , Virus de la Influenza A/inmunología , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/metabolismo , Infecciones por Orthomyxoviridae/virología , Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2/genética , Transportadoras de Casetes de Unión a ATP/genética , Animales , Linfocitos T CD8-positivos/metabolismo , Linfocitos T CD8-positivos/virología , Proliferación Celular , Células Cultivadas , Técnicas de Cocultivo , Células Dendríticas/metabolismo , Células Dendríticas/virología , Modelos Animales de Enfermedad , Retículo Endoplásmico/inmunología , Retículo Endoplásmico/metabolismo , Retículo Endoplásmico/virología , Femenino , Aparato de Golgi/inmunología , Aparato de Golgi/metabolismo , Aparato de Golgi/virología , Antígenos de Histocompatibilidad Clase I/metabolismo , Interacciones Huésped-Patógeno , Humanos , Virus de la Influenza A/patogenicidad , Activación de Linfocitos , Masculino , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Noqueados , Infecciones por Orthomyxoviridae/genéticaRESUMEN
Ubiquitin-like protein ISG15 (interferon-stimulated gene 15) (ISG15) is a ubiquitin-like modifier induced during infections and involved in host defense mechanisms. Not surprisingly, many viruses encode deISGylating activities to antagonize its effect. Here we show that infection by Zika, SARS-CoV-2 and influenza viruses induce ISG15-modifying enzymes. While influenza and Zika viruses induce ISGylation, SARS-CoV-2 triggers deISGylation instead to generate free ISG15. The ratio of free versus conjugated ISG15 driven by the papain-like protease (PLpro) enzyme of SARS-CoV-2 correlates with macrophage polarization toward a pro-inflammatory phenotype and attenuated antigen presentation. In vitro characterization of purified wild-type and mutant PLpro revealed its strong deISGylating over deubiquitylating activity. Quantitative proteomic analyses of PLpro substrates and secretome from SARS-CoV-2-infected macrophages revealed several glycolytic enzymes previously implicated in the expression of inflammatory genes and pro-inflammatory cytokines, respectively. Collectively, our results indicate that altered free versus conjugated ISG15 dysregulates macrophage responses and probably contributes to the cytokine storms triggered by SARS-CoV-2.
Asunto(s)
COVID-19/inmunología , Citocinas/metabolismo , Inflamación/inmunología , Macrófagos/inmunología , SARS-CoV-2/fisiología , Ubiquitinas/metabolismo , Diferenciación Celular , Proteasas Similares a la Papaína de Coronavirus/metabolismo , Citocinas/genética , Técnicas de Silenciamiento del Gen , Células HeLa , Humanos , Evasión Inmune , Inmunidad Innata , Virus de la Influenza A/fisiología , Gripe Humana/inmunología , Células Madre Pluripotentes/citología , Ubiquitinación , Ubiquitinas/genética , Virus Zika/fisiología , Infección por el Virus Zika/inmunologíaRESUMEN
Broadly neutralizing antibodies (bnAbs) targeting the hemagglutinin (HA) stem of influenza A viruses (IAVs) tend to be effective against either group 1 or group 2 viral diversity. In rarer cases, intergroup protective bnAbs can be generated by human antibody paratopes that accommodate the conserved glycan differences between the group 1 and group 2 stems. We applied germline-engaging nanoparticle immunogens to elicit a class of cross-group bnAbs from physiological precursor frequency within a humanized mouse model. Cross-group protection depended on the presence of the human bnAb precursors within the B cell repertoire, and the vaccine-expanded antibodies enriched for an N55T substitution in the CDRH2 loop, a hallmark of the bnAb class. Structurally, this single mutation introduced a flexible fulcrum to accommodate glycosylation differences and could alone enable cross-group protection. Thus, broad IAV immunity can be expanded from the germline repertoire via minimal antigenic input and an exceptionally simple antibody development pathway.
Asunto(s)
Anticuerpos Neutralizantes , Anticuerpos Antivirales , Virus de la Influenza A , Vacunas contra la Influenza , Infecciones por Orthomyxoviridae , Vacunación , Animales , Ratones , Humanos , Anticuerpos Antivirales/inmunología , Vacunas contra la Influenza/inmunología , Virus de la Influenza A/inmunología , Anticuerpos Neutralizantes/inmunología , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/prevención & control , Glicoproteínas Hemaglutininas del Virus de la Influenza/inmunología , Sustitución de Aminoácidos , Linfocitos B/inmunología , Gripe Humana/inmunología , Gripe Humana/prevención & control , Anticuerpos ampliamente neutralizantes/inmunologíaRESUMEN
Lung-tissue-resident memory (TRM) CD8+ T cells are critical for heterosubtypic immunity against influenza virus (IAV) reinfection. How TRM cells surveil the lung, respond to infection, and interact with other cells remains unresolved. Here, we used IAV infection of mice in combination with intravital and static imaging to define the spatiotemporal dynamics of lung TRM cells before and after recall infection. CD69+CD103+ TRM cells preferentially localized to lung sites of prior IAV infection, where they exhibited patrolling behavior. After rechallenge, lung TRM cells formed tight clusters in an antigen-dependent manner. Transcriptomic analysis of IAV-specific TRM cells revealed the expression of several factors that regulate myeloid cell biology. In vivo rechallenge experiments demonstrated that protection elicited by TRM cells is orchestrated in part by interferon (IFN)-γ-mediated recruitment of inflammatory monocytes into the lungs. Overall, these data illustrate the dynamic landscapes of CD103+ lung TRM cells that mediate early protective immunity against IAV infection.
Asunto(s)
Antígenos CD , Linfocitos T CD8-positivos , Memoria Inmunológica , Virus de la Influenza A , Cadenas alfa de Integrinas , Pulmón , Células T de Memoria , Infecciones por Orthomyxoviridae , Animales , Pulmón/inmunología , Pulmón/virología , Infecciones por Orthomyxoviridae/inmunología , Linfocitos T CD8-positivos/inmunología , Ratones , Memoria Inmunológica/inmunología , Cadenas alfa de Integrinas/metabolismo , Virus de la Influenza A/inmunología , Antígenos CD/metabolismo , Células T de Memoria/inmunología , Ratones Endogámicos C57BL , Interferón gamma/metabolismo , Interferón gamma/inmunología , Microscopía Intravital , Monocitos/inmunologíaRESUMEN
The nasal mucosa is often the initial site of respiratory viral infection, replication, and transmission. Understanding how infection shapes tissue-scale primary and memory responses is critical for designing mucosal therapeutics and vaccines. We generated a single-cell RNA-sequencing atlas of the murine nasal mucosa, sampling three regions during primary influenza infection and rechallenge. Compositional analysis revealed restricted infection to the respiratory mucosa with stepwise changes in immune and epithelial cell subsets and states. We identified and characterized a rare subset of Krt13+ nasal immune-interacting floor epithelial (KNIIFE) cells, which concurrently increased with tissue-resident memory T (TRM)-like cells. Proportionality analysis, cell-cell communication inference, and microscopy underscored the CXCL16-CXCR6 axis between KNIIFE and TRM cells. Secondary influenza challenge induced accelerated and coordinated myeloid and lymphoid responses without epithelial proliferation. Together, this atlas serves as a reference for viral infection in the upper respiratory tract and highlights the efficacy of local coordinated memory responses.
Asunto(s)
Memoria Inmunológica , Células T de Memoria , Mucosa Nasal , Infecciones por Orthomyxoviridae , Animales , Memoria Inmunológica/inmunología , Ratones , Mucosa Nasal/virología , Mucosa Nasal/inmunología , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/virología , Células T de Memoria/inmunología , Células Epiteliales/inmunología , Células Epiteliales/virología , Ratones Endogámicos C57BL , Humanos , Análisis de la Célula Individual , Gripe Humana/inmunología , Gripe Humana/virología , Femenino , Receptores CXCR6/metabolismo , Receptores CXCR6/inmunología , Virus de la Influenza A/inmunología , Virus de la Influenza A/fisiologíaRESUMEN
100 years after the infamous "Spanish flu" pandemic, the 2017-2018 flu season has been severe, with numerous infections worldwide. In between, there have been continuous, relentless attacks from (re-)emerging viruses. To fully understand viral pathogenesis and develop effective medical countermeasures, we must strengthen current surveillance and basic research efforts.
Asunto(s)
Subtipo H5N2 del Virus de la Influenza A/patogenicidad , Gripe Aviar/virología , Infección por el Virus Zika/virología , Virus Zika/patogenicidad , Animales , Aves , Enfermedades Transmisibles Emergentes/epidemiología , Enfermedades Transmisibles Emergentes/virología , Humanos , Virus de la Influenza A/clasificación , Virus de la Influenza A/patogenicidad , Gripe Aviar/epidemiología , Gripe Humana/epidemiología , Gripe Humana/virología , Pandemias , Filogeografía , Infección por el Virus Zika/epidemiologíaRESUMEN
Influenza hemagglutinin (HA) is the canonical type I viral envelope glycoprotein and provides a template for the membrane-fusion mechanisms of numerous viruses. The current model of HA-mediated membrane fusion describes a static "spring-loaded" fusion domain (HA2) at neutral pH. Acidic pH triggers a singular irreversible conformational rearrangement in HA2 that fuses viral and cellular membranes. Here, using single-molecule Förster resonance energy transfer (smFRET)-imaging, we directly visualized pH-triggered conformational changes of HA trimers on the viral surface. Our analyses reveal reversible exchange between the pre-fusion and two intermediate conformations of HA2. Acidification of pH and receptor binding shifts the dynamic equilibrium of HA2 in favor of forward progression along the membrane-fusion reaction coordinate. Interaction with the target membrane promotes irreversible transition of HA2 to the post-fusion state. The reversibility of HA2 conformation may protect against transition to the post-fusion state prior to arrival at the target membrane.
Asunto(s)
Membrana Celular/metabolismo , Glicoproteínas Hemaglutininas del Virus de la Influenza/química , Virus de la Influenza A/fisiología , Gripe Humana/metabolismo , Imagen Individual de Molécula/métodos , Células A549 , Transferencia Resonante de Energía de Fluorescencia/métodos , Células HEK293 , Glicoproteínas Hemaglutininas del Virus de la Influenza/metabolismo , Hemaglutininas/metabolismo , Humanos , Concentración de Iones de Hidrógeno , Gripe Humana/virología , Unión Proteica , Conformación Proteica , Internalización del VirusRESUMEN
Early recruitment of neutrophils from the blood to sites of tissue infection is a hallmark of innate immune responses. However, little is known about the mechanisms by which apoptotic neutrophils are cleared in infected tissues during resolution and the immunological consequences of in situ efferocytosis. Using intravital multiphoton microscopy, we show previously unrecognized motility patterns of interactions between neutrophils and tissue-resident phagocytes within the influenza-infected mouse airway. Newly infiltrated inflammatory monocytes become a chief pool of phagocytes and play a key role in the clearance of highly motile apoptotic neutrophils during the resolution phase. Apoptotic neutrophils further release epidermal growth factor and promote the differentiation of monocytes into tissue-resident antigen-presenting cells for activation of antiviral T cell effector functions. Collectively, these results suggest that the presence of in situ neutrophil resolution at the infected tissue is critical for optimal CD8+ T cell-mediated immune protection.