• diabetes
• gut microbiota
• intestinal pathogens
• metabolic diseases
• the type III secretion system

• Humans
• Metabolic Diseases/microbiology
• Metabolic Diseases/metabolism
• Type III Secretion Systems/metabolism
• Gastrointestinal Microbiome/physiology
• Animals
• Intestines/microbiology

• host–pathogen interaction
• outer membrane vesicles
• pyroptosis
• virulence factors

• Pyroptosis
• Humans
• Gram-Negative Bacteria/metabolism
• Gram-Negative Bacteria/pathogenicity
• Inflammation/metabolism
• Inflammation/pathology
• Inflammation/microbiology
• Host-Pathogen Interactions
• Animals
• Signal Transduction

• P2022LPT3R European Union - Next Generation EU and Italian Ministry of University and Research. Project PRIN 2022 PNRR

• Eriocheir sinensis
• antioxidant capacity
• chronic heat stress
• dietary methionine level
• immunity
• nutrient metabolism
• oxidative stress

• Antioxidants
• Apoptosis
• Eriocheir sinensis
• Glutathione
• Lipopolysaccharide
• Reactive oxygen species

• Animal Feed/analysis
• Animals
• Antioxidants/metabolism
• Apoptosis
• Aquaculture/methods
• Brachyura/drug effects
• Brachyura/physiology
• China
• Dietary Supplements/analysis
• Glutathione/administration & dosage
• Hepatopancreas/drug effects
• Hepatopancreas/pathology
• Immunity, Innate
• Lipopolysaccharides/adverse effects
• Oxidative Stress
• Protective Agents/administration & dosage
• Seafood

BCG (Bacillus Calmette-Guérin) is the only available vaccine against TB and is also used for the treatment of superficial bladder cancer. BCG-mediated protection against TB and bladder cancer has been shown to rely on its ability to induce superior CD4⁺ and CD8⁺ T cell responses. As the magnitude of T cell responses is defined by dendritic cell (DC) lifespan, we examined the effect of BCG on DC survival and its underlying mechanisms. It was observed that BCG stimulation enhanced DC survival and prolonged DC lifespan in a dose-dependent manner. Live BCG led to a higher DC survival compared with heat-killed BCG. FITC-Annexin V staining showed that BCG promoted DC survival by inhibiting apoptosis. Consistently, higher expressions of anti-apoptotic proteins Bcl-2 and Bcl-x_L were observed in BCG-stimulated DCs. Pharmacological inhibition of Bcl-2 and Bcl-x_L drastically reduced the DC survival efficacy of BCG. Comparable survival of BCG-stimulated wild-type and MyD88^−/− DCs suggested that MyD88 signaling is dispensable for BCG-induced DC survival. NF-κB is one of the key regulators of innate immune responses. We observed that pharmacological inhibition of NF-κB abrogated BCG-mediated increase in DC survival and expression of anti-apoptotic proteins. These findings provide a novel insight into the effect of BCG on DC physiology.

Summary: BCG enhanced the survival of dendritic cells (DCs) and prolonged their lifespan. BCG promoted DC survival by up-regulating Bcl-2 and Bcl-x_L. Increased survival of BCG-stimulated DCs was dependent on NF-κB, but was independent of MyD88 signaling.

• Anti-apoptotic proteins
• Apoptosis
• BCG
• Dendritic cell
• Lifespan
• MyD88
• NF-κB

RIPK1 regulates cytokine signaling and cell death during infection and inflammation. Peterson et al. show that RIPK1 kinase activity triggers apoptosis in response to bacterial pathogen blockade of innate immune signaling and that this pathway of effector-triggered immunity is critical for a successful antibacterial response.

Many pathogens deliver virulence factors or effectors into host cells in order to evade host defenses and establish infection. Although such effector proteins disrupt critical cellular signaling pathways, they also trigger specific antipathogen responses, a process termed “effector-triggered immunity.” The Gram-negative bacterial pathogen Yersinia inactivates critical proteins of the NF-κB and MAPK signaling cascade, thereby blocking inflammatory cytokine production but also inducing apoptosis. Yersinia-induced apoptosis requires the kinase activity of receptor-interacting protein kinase 1 (RIPK1), a key regulator of cell death, NF-κB, and MAPK signaling. Through the targeted disruption of RIPK1 kinase activity, which selectively disrupts RIPK1-dependent cell death, we now reveal that Yersinia-induced apoptosis is critical for host survival, containment of bacteria in granulomas, and control of bacterial burdens in vivo. We demonstrate that this apoptotic response provides a cell-extrinsic signal that promotes optimal innate immune cytokine production and antibacterial defense, demonstrating a novel role for RIPK1 kinase–induced apoptosis in mediating effector-triggered immunity to circumvent pathogen inhibition of immune signaling.

• Caspase-1
• Caspase-8
• Inflammasome
• Yersinia
• YopJ
• Yopk

• Antitumor immunity
• calreticulin
• cancer immunotherapy
• dendritic cells
• heat-shock treatment
• hyperthermia
• immunogenic cell death

Caspases regulate cell death programs in response to environmental stresses, including infection and inflammation, and are therefore critical for the proper operation of the mammalian immune system. Caspase-8 is necessary for optimal production of inflammatory cytokines and host defense against infection by multiple pathogens including Yersinia, but whether this is due to death of infected cells or an intrinsic role of caspase-8 in TLR-induced gene expression is unknown. Caspase-8 activation at death signaling complexes results in its autoprocessing and subsequent cleavage and activation of its downstream apoptotic targets. Whether caspase-8 activity is also important for inflammatory gene expression during bacterial infection has not been investigated. Here, we report that caspase-8 plays an essential cell-intrinsic role in innate inflammatory cytokine production in vivo during Yersinia infection. Unexpectedly, we found that caspase-8 enzymatic activity regulates gene expression in response to bacterial infection as well as TLR signaling independently of apoptosis. Using newly-generated mice in which caspase-8 autoprocessing is ablated (Casp8^DA/DA), we now demonstrate that caspase-8 enzymatic activity, but not autoprocessing, mediates induction of inflammatory cytokines by bacterial infection and a wide variety of TLR stimuli. Because unprocessed caspase-8 functions in an enzymatic complex with its homolog cFLIP, our findings implicate the caspase-8/cFLIP heterodimer in control of inflammatory cytokines during microbial infection, and provide new insight into regulation of antibacterial immune defense.

TLR signaling induces expression of key inflammatory cytokines and pro-survival factors that facilitate control of microbial infection. TLR signaling can also engage cell death pathways through activation of enzymes known as caspases. Caspase-8 activates apoptosis in response to infection by pathogens that interfere with NF-κB signaling, including Yersinia, but has also recently been linked to control of inflammatory gene expression. Pathogenic Yersinia can cause severe disease ranging from gastroenteritis to plague. While caspase-8 mediates cell death in response to Yersinia infection as well as other signals, its precise role in gene expression and host defense during in vivo infection is unknown. Here, we show that caspase-8 activity promotes cell-intrinsic cytokine expression, independent of its role in cell death in response to Yersinia infection. Our studies further demonstrate that caspase-8 enzymatic activity plays a previously undescribed role in ensuring optimal TLR-induced gene expression by innate cells during bacterial infection. This work sheds new light on mechanisms that regulate essential innate anti-bacterial immune defense.

• Animals
• Apoptosis
• Caspase 8/immunology
• Caspase 8/metabolism
• Cytokines/biosynthesis
• Disease Models, Animal
• Enzyme-Linked Immunosorbent Assay
• Flow Cytometry
• Gene Expression Regulation/immunology
• Gene Knockdown Techniques
• Immunity, Innate/immunology
• Mice
• Mice, Inbred C57BL
• Polymerase Chain Reaction
• Signal Transduction/immunology
• Toll-Like Receptors/immunology
• Yersinia Infections/immunology

• R01 AI108685 NIAID NIH HHS
• R01 AI103062 NIAID NIH HHS
• R01 AI083284 NIAID NIH HHS
• T32 AI060516 NIAID NIH HHS
• R21 AI117365 NIAID NIH HHS
• R21 AI109267 NIAID NIH HHS
• K12 GM081259 NIGMS NIH HHS
• R21 CA185681 NCI NIH HHS
• National Institute of Allergy and Infectious Diseases
• National Cancer Institute
• Burroughs Wellcome Fund

The innate immune system is the first line of defense against invading pathogens. Innate immune cells recognize molecular patterns from the pathogen and mount a response to resolve the infection. The production of proinflammatory cytokines and reactive oxygen species, phagocytosis, and induced programmed cell death are processes initiated by innate immune cells in order to combat invading pathogens. However, pathogens have evolved various virulence mechanisms to subvert these responses. One strategy utilized by Gram-negative bacterial pathogens is the deployment of a complex machine termed the type III secretion system (T3SS). The T3SS is composed of a syringe-like needle structure and the effector proteins that are injected directly into a target host cell to disrupt a cellular response. The three human pathogenic Yersinia spp. (Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis) are Gram-negative bacteria that share in common a 70 kb virulence plasmid which encodes the T3SS. Translocation of the Yersinia effector proteins (YopE, YopH, YopT, YopM, YpkA/YopO, and YopP/J) into the target host cell results in disruption of the actin cytoskeleton to inhibit phagocytosis, downregulation of proinflammatory cytokine/chemokine production, and induction of cellular apoptosis of the target cell. Over the past 25 years, studies on the Yersinia effector proteins have unveiled tremendous knowledge of how the effectors enhance Yersinia virulence. Recently, the long awaited crystal structure of YpkA has been solved providing further insights into the activation of the YpkA kinase domain. Multisite autophosphorylation by YpkA to activate its kinase domain was also shown and postulated to serve as a mechanism to bypass regulation by host phosphatases. In addition, novel Yersinia effector protein targets, such as caspase-1, and signaling pathways including activation of the inflammasome were identified. In this review, we summarize the recent discoveries made on Yersinia effector proteins and their contribution to Yersinia pathogenesis.

• Type III secretion
• Yersinia
• Effectors
• Innate
• Virulence

• apoptosis
• bacteria
• dendritic cells
• viruses

• apoptosis
• innate immunity
• macrophage
• programmed necrosis
• pyroptosis

Activation of the inflammasome occurs in response to a notably high number of pathogenic microbes and is a broad innate immune response that effectively contributes to restriction of pathogen replication and generation of adaptive immunity. Activation of these platforms leads to caspase-1- and/or caspase-11-dependent secretion of proteins, including cytokines, and induction of a specific form of cell death called pyroptosis, which directly or indirectly contribute for restriction of pathogen replication. Not surprisingly, bona fide intracellular pathogens developed strategies for manipulation of cell death to guarantee intracellular replication. In this sense, the remarkable advances in the knowledge of the inflammasome field have been accompanied by several reports characterizing the inhibition of this platform by several pathogenic bacteria. Herein, we review some processes used by pathogenic bacteria, including Yersinia spp., Pseudomonas aeruginosa, Vibrio parahaemolyticus, Chlamydia trachomatis, Francisella tularensis, Shigella flexneri, Legionella pneumophila, and Coxiella burnetii to evade the activation of the inflammasome and the induction of pyroptosis.

• infection control
• inflammasome inhibition
• pyroptosis
• subversion strategies

Yersinia pestis causes pneumonic plague, a disease characterized by inflammation, necrosis and rapid bacterial growth which together cause acute lung congestion and lethality. The bacterial type III secretion system (T3SS) injects 7 effector proteins into host cells and their combined activities are necessary to establish infection. Y. pestis infection of the lungs proceeds as a biphasic inflammatory response believed to be regulated through the control of apoptosis and pyroptosis by a single, well-conserved T3SS effector protein YopJ. Recently, YopJ-mediated pyroptosis, which proceeds via the NLRP3-inflammasome, was shown to be regulated by a second T3SS effector protein YopK in the related strain Y. pseudotuberculosis. In this work, we show that for Y. pestis, YopK appears to regulate YopJ-mediated apoptosis, rather than pyroptosis, of macrophages. Inhibition of caspase-8 blocked YopK-dependent apoptosis, suggesting the involvement of the extrinsic pathway, and appeared cell-type specific. However, in contrast to yopJ, deletion of yopK caused a large decrease in virulence in a mouse pneumonic plague model. YopK-dependent modulation of macrophage apoptosis was observed at 6 and 24 hours post-infection (HPI). When YopK was absent, decreased populations of macrophages and dendritic cells were seen in the lungs at 24 HPI and correlated with resolution rather than progression of inflammation. Together the data suggest that Y. pestis YopK may coordinate the inflammatory response during pneumonic plague through the regulation of apoptosis of immune cells.

In this work, we studied the mechanism whereby bacteria manipulate innate immune responses by controlling host cell death. Yersinia pestis, the causative agent of plague, requires effector Yops of the Type III Secretion System (T3SS) to evade the innate immune system during infection. We show that Yersinia induces apoptosis of macrophages through two distinct mechanisms, each through the activity of the well-characterized T3SS effector YopJ, yet regulated in an opposing manner through the activity of a second effector protein YopK. In a murine pneumonic plague model, we found evidence that YopK regulates apoptosis of macrophages during the early stage of infection, leading to uncontrolled inflammation and disease. In contrast, the absence of YopK-regulated apoptosis allowed recruitment of lymphocytes and CCR2⁺ immune cells which led to bacterial clearance and resolution of inflammation. Together the data suggest that Yersinia YopK modulates apoptosis of immune cells to control the inflammatory response during plague.

• Animals
• Apoptosis
• Apoptosis Regulatory Proteins/genetics
• Apoptosis Regulatory Proteins/metabolism
• Bacterial Proteins/genetics
• Bacterial Proteins/metabolism
• Bacterial Secretion Systems
• Caspase 3/metabolism
• Caspase 8/metabolism
• Dendritic Cells/metabolism
• Enzyme Activation
• Female
• Macrophages/immunology
• Macrophages/physiology
• Male
• Mice
• Mice, Inbred BALB C
• Mice, Inbred C57BL
• Plague/immunology
• Promoter Regions, Genetic
• Yersinia pestis/immunology
• Yersinia pestis/metabolism
• Yersinia pestis/pathogenicity

• R56 AI064703 NIAID NIH HHS
• R21AI064703 NIAID NIH HHS
• U54157160 PHS HHS

Cell death plays a central role in host-pathogen interactions, as it can eliminate the pathogen's replicative niche and provide pro-inflammatory signals necessary for an effective immune response; conversely, cell death can allow pathogens to eliminate immune cells and evade anti-microbial effector mechanisms. In response to developmental signals or cell-intrinsic stresses, the executioner caspases-3 and -7 mediate apoptotic cell death, which is generally viewed as immunologically silent or immunosuppressive. A proinflammatory form of cell death that requires caspase-1, termed pyroptosis, is activated in response to microbial products within the host cytosol or disruption of cellular membranes by microbial pathogens. Infection by the bacterial pathogen Yersinia has features of both apoptosis and pyroptosis. Cell death and caspase-1 processing in Yersinia-infected cells occur in response to inhibition of NF-κB and MAPK signaling by the Yersinia virulence factor YopJ. However, the molecular basis of YopJ-induced cell death, and the role of different death pathways in anti-Yersinia immune responses remain enigmatic. Here, we discuss the role that cell death may play in inducing specific pro-inflammatory signals that shape innate and adaptive immune responses against Yersinia infection.

• Yersinia
• YopJ
• apoptosis
• caspase-1
• cell death
• inflammasome
• pyroptosis

• Adhesins, Bacterial/metabolism
• Animals
• Aorta/metabolism
• Aorta/microbiology
• Bacteroidaceae Infections/metabolism
• Cysteine Endopeptidases/metabolism
• Endothelial Cells/metabolism
• Endothelial Cells/microbiology
• Gingipain Cysteine Endopeptidases
• Humans
• Mice
• Mice, Knockout
• Porphyromonas gingivalis/metabolism
• Porphyromonas gingivalis/pathogenicity
• Proteolysis
• Receptor-Interacting Protein Serine-Threonine Kinase 2/metabolism
• Receptor-Interacting Protein Serine-Threonine Kinases/metabolism

• P01 AI078894 NIAID NIH HHS
• R01 HL080387 NHLBI NIH HHS
• T32 HL007224 NHLBI NIH HHS
• R01 HL80387 NHLBI NIH HHS

Yersinia outer protein J (YopJ) is a type III secretion system (T3SS) effector of pathogenic Yersinia (Yersinia pestis, Yersinia enterocolitica and Yersinia pseudotuberculosis) that is secreted into host cells. YopJ inhibits survival response pathways in macrophages, causing cell death. Allelic variation of YopJ is responsible for differential cytotoxicity in Yersinia strains. YopJ isoforms in Y. enterocolitica O:8 (YopP) and Y. pestis KIM (YopJ^KIM) strains have high cytotoxic activity. In addition, YopJ^KIM-induced macrophage death is associated with caspase-1 activation and interleukin-1β (IL-1β secretion. Here, the mechanism of YopJ^KIM-induced cell death, caspase-1 activation, and IL-1β secretion in primary murine macrophages was examined. Caspase-3/7 activity was low and the caspase-3 substrate poly (ADP-ribose) polymerase (PARP) was not cleaved in Y. pestis KIM5-infected macrophages. In addition, cytotoxicity and IL-1β secretion were not reduced in the presence of a caspase-8 inhibitor, or in B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 homologous antagonist/killer (Bak) knockout macrophages, showing that YopJ^KIM-mediated cell death and caspase-1 activation occur independent of mitochondrial-directed apoptosis. KIM5-infected macrophages released high mobility group protein B1 (HMGB1), a marker of necrosis, and microscopic analysis revealed that necrotic cells contained active caspase-1, indicating that caspase-1 activation is associated with necrosis. Inhibitor studies showed that receptor interacting protein 1 (RIP1) kinase and reactive oxygen species (ROS) were not required for cytotoxicity or IL-β release in KIM5-infected macrophages. IL-1β secretion was reduced in the presence of cathepsin B inhibitors, suggesting that activation of caspase-1 requires cathepsin B activity. Ectopically-expressed YopP caused higher cytotoxicity and secretion of IL-1β in Y. pseudotuberculosis-infected macrophages than YopJ^KIM. Wild-type and congenic caspase 1 knockout C57BL/6 mice were equally susceptible to lethal infection with Y. pseudotuberculosis ectopically expressing YopP. These data suggest that YopJ-induced caspase-1 activation in Yersinia-infected macrophages is a downstream consequence of necrotic cell death and is dispensable for innate host resistance to a strain with enhanced cytotoxicity.

• Animals
• Apoptosis/drug effects
• Bacterial Proteins/genetics
• Bacterial Proteins/metabolism
• Caspase 1/deficiency
• Caspase 1/genetics
• Caspase 1/metabolism
• Caspase 3/metabolism
• Caspase 7/metabolism
• Caspase 8/metabolism
• Caspase Inhibitors
• Cathepsin B/antagonists & inhibitors
• Cathepsin B/metabolism
• Cells, Cultured
• Enzyme Activation
• Female
• GTPase-Activating Proteins/antagonists & inhibitors
• GTPase-Activating Proteins/metabolism
• HMGB1 Protein/metabolism
• Immunity, Innate
• Interleukin-1beta/metabolism
• Macrophages/metabolism
• Macrophages/microbiology
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Mitochondria/metabolism
• Necrosis/metabolism
• Necrosis/pathology
• Protease Inhibitors/pharmacology
• Protein Binding
• Protein Isoforms/genetics
• Protein Isoforms/metabolism
• Reactive Oxygen Species/metabolism
• Yersinia/metabolism
• Yersinia/pathogenicity
• Yersinia Infections/metabolism
• Yersinia Infections/microbiology
• Yersinia Infections/pathology
• Yersinia enterocolitica/metabolism
• Yersinia enterocolitica/pathogenicity
• Yersinia pestis/metabolism
• Yersinia pestis/pathogenicity
• Yersinia pseudotuberculosis/metabolism
• Yersinia pseudotuberculosis/pathogenicity
• bcl-2 Homologous Antagonist-Killer Protein/deficiency
• bcl-2 Homologous Antagonist-Killer Protein/genetics
• bcl-2 Homologous Antagonist-Killer Protein/metabolism
• bcl-2-Associated X Protein/deficiency
• bcl-2-Associated X Protein/genetics
• bcl-2-Associated X Protein/metabolism

• U54-AI057158 NIAID NIH HHS
• R56-AI043389 NIAID NIH HHS
• U54 AI057158 NIAID NIH HHS
• P01 AI055621 NIAID NIH HHS
• R56 AI043389 NIAID NIH HHS
• P01-AI055621 NIAID NIH HHS

Yersiniosis is a food-borne illness that has become more prevalent in recent years due to human transmission via the fecal-oral route and prevalence in farm animals. Yersiniosis is primarily caused by Yersinia enterocolitica and less frequently by Yersinia pseudotuberculosis. Infection is usually characterized by a self-limiting acute infection beginning in the intestine and spreading to the mesenteric lymph nodes. However, more serious infections and chronic conditions can also occur, particularly in immunocompromised individuals. Y. enterocolitica and Y. pseudotuberculosis are both heterogeneous organisms that vary considerably in their degrees of pathogenicity, although some generalizations can be ascribed to pathogenic variants. Adhesion molecules and a type III secretion system are critical for the establishment and progression of infection. Additionally, host innate and adaptive immune responses are both required for yersiniae clearance. Despite the ubiquity of enteric Yersinia species and their association as important causes of food poisoning world-wide, few national enteric pathogen surveillance programs include the yersiniae as notifiable pathogens. Moreover, no standard exists whereby identification and reporting systems can be effectively compared and global trends developed. This review discusses yersinial virulence factors, mechanisms of infection, and host responses in addition to the current state of surveillance, detection, and prevention of yersiniosis.

• Adaptor Proteins, Vesicular Transport/physiology
• Animals
• Antigen Presentation
• Blotting, Western
• CD4-Positive T-Lymphocytes/immunology
• CD4-Positive T-Lymphocytes/microbiology
• Cytokines/metabolism
• Dendritic Cells/immunology
• Dendritic Cells/metabolism
• Dendritic Cells/microbiology
• Female
• Flow Cytometry
• Fluorescent Antibody Technique
• Immune Evasion/immunology
• Immunoenzyme Techniques
• Lymphocyte Activation
• Mice
• Mice, Inbred C57BL
• Spleen/cytology
• Spleen/immunology
• Spleen/microbiology
• Toll-Like Receptor 4/physiology
• Virulence Factors/genetics
• Virulence Factors/metabolism
• Yersinia Infections/immunology
• Yersinia Infections/metabolism
• Yersinia Infections/microbiology
• Yersinia enterocolitica/immunology

The human innate immune system relies on the coordinated activity of macrophages and polymorphonuclear leukocytes (neutrophils or PMNs) for defense against bacterial pathogens. Yersinia spp. subvert the innate immune response to cause disease in humans. In particular, the Yersinia outer protein YopJ (Y. pestis and Y. pseudotuberculosis) and YopP (Y. enterocolitica) rapidly induce apoptosis in murine macrophages and dendritic cells. However, the effects of Yersinia Yop J/P on neutrophil fate are not clearly defined.

In this study, we utilized wild-type and mutant strains of Yersinia to test the contribution of YopJ and YopP on induction of apoptosis in human monocyte-derived macrophages (HMDM) and neutrophils. Whereas YopJ and YopP similarly induced apoptosis in HMDMs, interaction of human neutrophils with virulence plasmid-containing Yersinia did not result in PMN caspase activation, release of LDH, or loss of membrane integrity greater than PMN controls. In contrast, interaction of human PMNs with the virulence plasmid-deficient Y. pestis strain KIM6 resulted in increased surface exposure of phosphatidylserine (PS) and cell death. PMN reactive oxygen species (ROS) production was inhibited in a virulence plasmid-dependent but YopJ/YopP-independent manner. Following phagocytic interaction with Y. pestis strain KIM6, inhibition of PMN ROS production with diphenyleneiodonium chloride resulted in a reduction of PMN cell death similar to that induced by the virulence plasmid-containing strain Y. pestis KIM5.

Our findings showed that Yersinia YopJ and/or YopP did not induce pronounced apoptosis in human neutrophils. Furthermore, robust PMN ROS production in response to virulence plasmid-deficient Yersinia was associated with increased PMN cell death, suggesting that Yersinia inhibition of PMN ROS production plays a role in evasion of the human innate immune response in part by limiting PMN apoptosis.