RESUMEN
Herpes simplex virus type 1 (HSV-1) infection can manifest locally as mucocutaneous lesions or keratitis and can also spread to the central nervous system to cause encephalitis. HSV-1 establishes a lifelong latent infection and neither cure nor vaccine is currently available. The innate immune response is the first line of defense against infection. Caspases and gasdermins are important components of innate immunity. Caspases are a family of cysteine proteases, most of which mediate regulated cell death. Gasdermins are a family of pore-forming proteins that trigger lytic cell death. To determine whether caspases or gasdermins contribute to innate immune defenses against HSV-1, we screened mice deficient in specific cell death genes. Our results indicate a modest role for caspase-6 in defense against HSV-1. Further, Asc-/-Casp1/11-/- mice also had a modest increased susceptibility to HSV-1 infection. Caspase-7, -8, and -14 did not have a notable role in controlling HSV-1 infection. We generated Gsdma1-Gsdma2-Gsdma3 triple knockout mice, which also had normal susceptibility to HSV-1. We confirmed that the previously published importance of RIPK3 during systemic HSV-1 infection also holds true during skin infection. Overall, our data highlight that as a successful pathogen, HSV-1 has multiple ways to evade host innate immune responses.
Asunto(s)
Herpes Simple , Herpesvirus Humano 1 , Animales , Caspasa 6 , Caspasa 7 , Caspasas/genética , Herpesvirus Humano 1/fisiología , Inmunidad Innata , Ratones , Ratones Noqueados , Proteínas Citotóxicas Formadoras de Poros , ProteínasRESUMEN
Eukaryotic cells can die from physical trauma, which results in necrosis. Alternatively, they can die through programmed cell death upon the stimulation of specific signalling pathways. In this Review, we discuss the role of different cell death pathways in innate immune defence against bacterial and viral infection: apoptosis, necroptosis, pyroptosis and NETosis. We describe the interactions that interweave different programmed cell death pathways, which create complex signalling networks that cross-guard each other in the evolutionary 'arms race' with pathogens. Finally, we describe how the resulting cell corpses - apoptotic bodies, pore-induced intracellular traps (PITs) and neutrophil extracellular traps (NETs) - promote the clearance of infection.
Asunto(s)
Muerte Celular/inmunología , Inmunidad Innata/inmunología , Infecciones/inmunología , Animales , HumanosRESUMEN
Inflammasomes activate caspase-1, initiating a lytic form of programmed cell death termed pyroptosis, which is an important innate immune defense mechanism against intracellular infections. We recently demonstrated in a mouse infection model of pyroptosis that instead of releasing bacteria into the extracellular space, bacteria remain trapped within the pyroptotic cell corpse, termed the pore-induced intracellular trap (PIT). This trapping mediates efferocytosis of the PIT and associated bacteria by neutrophils; bacteria are subsequently killed via neutrophil ROS. Using this pyroptosis model, we now show that the pro-inflammatory cytokines IL-1ß and IL-18 and inflammatory lipid mediators termed eicosanoids are required for effective clearance of bacteria downstream of pyroptosis. We further show that IL-1ß, IL-18, and eicosanoids affect this in part by mediating neutrophil recruitment to the PIT. This is in addition to our prior findings that complement is also important to attract neutrophils. Thus, the PIT initiates a robust and coordinated innate immune response involving multiple mediators that attract neutrophils to efferocytose the PIT and its entrapped bacteria.
Asunto(s)
Infecciones por Bacterias Grampositivas/inmunología , Neutrófilos/inmunología , Salmonella enterica/inmunología , Animales , Caspasa 1/metabolismo , Movimiento Celular , Células Cultivadas , Eicosanoides/metabolismo , Trampas Extracelulares/inmunología , Inmunidad Innata , Inflamasomas/metabolismo , Interleucina-18/metabolismo , Interleucina-1beta/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Porinas/metabolismo , Piroptosis , Especies Reactivas de Oxígeno/metabolismoRESUMEN
Inflammasomes activate caspase-1 in response to cytosolic contamination or perturbation. This inflammatory caspase triggers the opening of the GSDMD pore in the plasma membrane, resulting in lytic cell death called pyroptosis. We had previously assumed that pyroptosis releases intracellular bacteria to the extracellular space. Here, we find that viable bacteria instead remain trapped within the cellular debris of pyroptotic macrophages. This trapping appears to be an inevitable consequence of how osmotic lysis ruptures the plasma membrane, and may also apply to necroptosis and some forms of nonprogrammed necrosis. Although membrane tears release soluble cytosolic contents, they are small enough to retain organelles and bacteria. We call this structure the pore-induced intracellular trap (PIT), which is conceptually parallel to the neutrophil extracellular trap (NET). The PIT coordinates innate immune responses via complement and scavenger receptors to drive recruitment of and efferocytosis by neutrophils. Ultimately, this secondary phagocyte kills the bacteria. Hence, caspase-1-driven pore-induced cell death triggers a multifaceted defense against intracellular bacteria facilitated by trapping the pathogen within the cellular debris. Bona fide intracellular bacterial pathogens, such as Salmonella, must prevent or delay pyroptosis to avoid being trapped in the PIT and subsequently killed by neutrophils.
Asunto(s)
Espacio Intracelular/metabolismo , Fagocitosis , Piroptosis , Salmonella typhimurium/fisiología , Animales , Proteínas del Sistema Complemento/metabolismo , Proteínas Fluorescentes Verdes/metabolismo , Macrófagos/metabolismo , Macrófagos/microbiología , Macrófagos/ultraestructura , Ratones , Ratones Endogámicos C57BL , Viabilidad Microbiana , Necrosis , Neutrófilos/metabolismo , Receptores Depuradores/metabolismo , Salmonella typhimurium/ultraestructura , SolubilidadRESUMEN
Interferon (IFN)-inducible guanylate binding proteins (GBPs) mediate cell-autonomous host resistance to bacterial pathogens and promote inflammasome activation. The prevailing model postulates that these two GBP-controlled activities are directly linked through GBP-dependent vacuolar lysis. It was proposed that the rupture of pathogen-containing vacuoles (PVs) by GBPs destroyed the microbial refuge and simultaneously contaminated the host cell cytosol with microbial activators of inflammasomes. Here, we demonstrate that GBP-mediated host resistance and GBP-mediated inflammatory responses can be uncoupled. We show that PVs formed by the rodent pathogen Chlamydia muridarum, so-called inclusions, remain free of GBPs and that C. muridarum is impervious to GBP-mediated restrictions on bacterial growth. Although GBPs neither bind to C. muridarum inclusions nor restrict C. muridarum growth, we find that GBPs promote inflammasome activation in C. muridarum-infected macrophages. We demonstrate that C. muridarum infections induce GBP-dependent pyroptosis through both caspase-11-dependent noncanonical and caspase-1-dependent canonical inflammasomes. Among canonical inflammasomes, we find that C. muridarum and the human pathogen Chlamydia trachomatis activate not only NLRP3 but also AIM2. Our data show that GBPs support fast-kinetics processing and secretion of interleukin-1ß (IL-1ß) and IL-18 by the NLRP3 inflammasome but are dispensable for the secretion of the same cytokines at later times postinfection. Because IFN-γ fails to induce IL-1ß transcription, GBP-dependent fast-kinetics inflammasome activation can drive the preferential processing of constitutively expressed IL-18 in IFN-γ-primed macrophages in the absence of prior Toll-like receptor stimulation. Together, our results reveal that GBPs control the kinetics of inflammasome activation and thereby shape macrophage responses to Chlamydia infections.
Asunto(s)
Infecciones por Chlamydia/inmunología , Chlamydia muridarum/inmunología , Proteínas de Unión al GTP/inmunología , Inflamasomas/inmunología , Macrófagos/inmunología , Animales , Proteínas Portadoras/genética , Proteínas Portadoras/inmunología , Caspasas/genética , Caspasas/inmunología , Caspasas Iniciadoras , Infecciones por Chlamydia/genética , Infecciones por Chlamydia/microbiología , Infecciones por Chlamydia/patología , Chlamydia muridarum/genética , Chlamydia muridarum/patogenicidad , Chlamydia trachomatis/genética , Chlamydia trachomatis/inmunología , Chlamydia trachomatis/patogenicidad , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/inmunología , Fibroblastos/inmunología , Fibroblastos/microbiología , Proteínas de Unión al GTP/genética , Regulación de la Expresión Génica , Interacciones Huésped-Patógeno , Cuerpos de Inclusión/inmunología , Cuerpos de Inclusión/microbiología , Inflamasomas/genética , Interferón gamma/genética , Interferón gamma/inmunología , Interleucina-18/genética , Interleucina-18/inmunología , Interleucina-1beta/genética , Interleucina-1beta/inmunología , Macrófagos/microbiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína con Dominio Pirina 3 de la Familia NLR , Cultivo Primario de Células , Transducción de Señal , Vacuolas/inmunología , Vacuolas/microbiologíaRESUMEN
Inflammatory caspases play a central role in innate immunity by responding to cytosolic signals and initiating a twofold response. First, caspase-1 induces the activation and secretion of the two prominent pro-inflammatory cytokines, interleukin-1ß (IL-1ß) and IL-18. Second, either caspase-1 or caspase-11 can trigger a form of lytic, programmed cell death called pyroptosis. Pyroptosis operates to remove the replication niche of intracellular pathogens, making them susceptible to phagocytosis and killing by a secondary phagocyte. However, aberrant, systemic activation of pyroptosis in vivo may contribute to sepsis. Emphasizing the efficiency of inflammasome detection of microbial infections, many pathogens have evolved to avoid or subvert pyroptosis. This review focuses on molecular and morphological characteristics of pyroptosis and the individual inflammasomes and their contribution to defense against infection in mice and humans.
Asunto(s)
Infecciones/inmunología , Inflamasomas/metabolismo , Animales , Caspasa 1/metabolismo , Caspasas/metabolismo , Caspasas Iniciadoras/metabolismo , Replicación del ADN , Humanos , Evasión Inmune , Inmunidad Innata , Inflamasomas/inmunología , Interleucina-1/metabolismo , Interleucina-18/metabolismo , Espacio Intracelular , Ratones , PiroptosisRESUMEN
Caspase-1-mediated detection of pathogens is a potent arm of the innate immune system. LaRock and Cookson (2012) show that the Yersinia type III secretion effector, YopM, directly inhibits caspase-1.
Asunto(s)
Proteínas de la Membrana Bacteriana Externa/metabolismo , Caspasa 1/metabolismo , Inflamasomas/antagonistas & inhibidores , Factores de Virulencia/metabolismo , Yersinia pestis/inmunología , Animales , Hielo , YersiniaAsunto(s)
Infecciones por Escherichia coli/inmunología , Infecciones por Escherichia coli/microbiología , Escherichia coli/patogenicidad , Infecciones Urinarias/inmunología , Infecciones Urinarias/microbiología , Animales , Escherichia coli/inmunología , Femenino , Interacciones Huésped-Patógeno , Humanos , Ratones , Receptor Toll-Like 4/inmunología , Sistema Urinario/microbiologíaRESUMEN
During infection of epithelial cells, the obligate intracellular pathogen Chlamydia trachomatis secretes the serine protease Chlamydia protease-like activity factor (CPAF) into the host cytosol to regulate a range of host cellular processes through targeted proteolysis. Here we report the development of an in vitro assay for the enzyme and the discovery of a cell-permeable CPAF zymogen-based peptide inhibitor with nanomolar inhibitory affinity. Treating C. trachomatis-infected HeLa cells with this inhibitor prevented CPAF cleavage of the intermediate filament vimentin and led to the loss of vimentin cage surrounding the intracellular vacuole. Because Chlamydia is a genetically intractable organism, this inhibitor may serve as a tool for understanding the role of CPAF in pathogenesis.
Asunto(s)
Chlamydia trachomatis/enzimología , Endopeptidasas/química , Precursores Enzimáticos/antagonistas & inhibidores , Precursores Enzimáticos/química , Péptidos/antagonistas & inhibidores , Inhibidores de Proteasas/química , Secuencia de Aminoácidos , Chlamydia trachomatis/efectos de los fármacos , Endopeptidasas/metabolismo , Precursores Enzimáticos/fisiología , Células HeLa , Humanos , Líquido Intracelular/enzimología , Datos de Secuencia Molecular , Péptido Hidrolasas/química , Péptido Hidrolasas/fisiología , Unión Proteica , Vacuolas/enzimología , Vimentina/antagonistas & inhibidores , Vimentina/químicaRESUMEN
The obligate intracellular bacterial pathogen Chlamydia trachomatis injects numerous effector proteins into the epithelial cell cytoplasm to manipulate host functions important for bacterial survival. In addition, the bacterium secretes a serine protease, chlamydial protease-like activity factor (CPAF). Although several CPAF targets are reported, the significance of CPAF-mediated proteolysis is unclear due to the lack of specific CPAF inhibitors and the diversity of host targets. We report that CPAF also targets chlamydial effectors secreted early during the establishment of the pathogen-containing vacuole ("inclusion"). We designed a cell-permeable CPAF-specific inhibitory peptide and used it to determine that CPAF prevents superinfection by degrading early Chlamydia effectors translocated during entry into a preinfected cell. Prolonged CPAF inhibition leads to loss of inclusion integrity and caspase-1-dependent death of infected epithelial cells. Thus, CPAF functions in niche protection, inclusion integrity and pathogen survival, making the development of CPAF-specific protease inhibitors an attractive antichlamydial therapeutic strategy.
Asunto(s)
Chlamydia trachomatis/patogenicidad , Endopeptidasas/metabolismo , Interacciones Huésped-Patógeno , Clorometilcetonas de Aminoácidos/farmacología , Secuencia de Aminoácidos , Animales , Antígenos Bacterianos/metabolismo , Proteínas Bacterianas/metabolismo , Sistemas de Secreción Bacterianos , Caspasa 1/metabolismo , Muerte Celular/fisiología , Permeabilidad de la Membrana Celular , Chlamydia trachomatis/metabolismo , Células Epiteliales/microbiología , Ratones , Datos de Secuencia Molecular , Péptidos/metabolismo , Inhibidores de Proteasas/farmacología , Transporte de Proteínas , Factores de Virulencia/metabolismoRESUMEN
The obligate intracellular pathogen Chlamydia trachomatis secretes effector proteins across the membrane of the pathogen-containing vacuole (inclusion) to modulate host cellular functions. In an immunological screen for secreted chlamydial proteins, we identified CT049 and CT050 as potential inclusion membrane-associated proteins. These acidic, nonglobular proteins are paralogously related to the passenger domain of the polymorphic membrane protein PmpC and, like other Pmp proteins, are highly polymorphic among C. trachomatis ocular and urogenital strains. We generated antibodies to these Pmp-like secreted (Pls) proteins and determined by immunofluorescence microscopy that Pls1 (CT049) and Pls2 (CT050) localized to globular structures within the inclusion lumen and at the inclusion membrane. Fractionation of membranes and cytoplasmic components from infected cells by differential and density gradient centrifugation further indicated that Pls1 and Pls2 associated with membranes distinct from the bulk of bacterial and inclusion membranes. The accumulation of Pls1 and, to a lesser extent, Pls2 in the inclusion lumen was insensitive to the type III secretion inhibitor C1, suggesting that this translocation system is not essential for Pls protein secretion. In contrast, Pls secretion and stability were sensitive to low levels of beta-lactam antibiotics, suggesting that a functional cell wall is required for Pls secretion from the bacterial cell. Finally, we tested the requirement for these proteins in Chlamydia infection by microinjecting anti-Pls1 and anti-Pls2 antibodies into infected cells. Coinjection of anti-Pls1 and -Pls2 antibodies partially inhibited expansion of the inclusion. Because Pls proteins lack classical sec-dependent secretion signals, we propose that Pls proteins are secreted into the inclusion lumen by a novel mechanism to regulate events important for chlamydial replication and inclusion expansion.