Neutrophil and Alveolar Macrophage-Mediated Innate Immune Control of Legionella pneumophila Lung Infection via TNF and ROS

Turning off NADPH oxidase-2 by impeding p67phox activation in infected mouse macrophages reduced viral entry and inflammation

BACKGROUND

Targeting cells of the host immune system is a promising approach to fight against Influenza A virus (IAV) infection. Macrophage cells use the NADPH oxidase-2 (NOX2) enzymatic complex as a first line of defense against pathogens by generating superoxide ions O₂^- and releasing H₂O₂. Herein, we investigated whether targeting membrane -embedded NOX2 decreased IAV entry via raft domains and reduced inflammation in infected macrophages.

METHODS

Confocal microscopy and western blots monitored levels of the viral nucleoprotein NP and p67^phox, NOX2 activator subunit, Elisa assays quantified TNF-α levels in LPS or IAV-activated mouse or porcine alveolar macrophages pretreated with a fluorescent NOX inhibitor, called nanoshutter NS1.

RESULTS

IAV infection in macrophages promoted p67^phox translocation to the membrane, rafts clustering and activation of the NOX2 complex at early times. Disrupting rafts reduced intracellular viral NP. NS1 markedly reduced raft clustering and viral entry by binding to the C-terminal of NOX2 also characterized in vitro. NS1 decrease of TNF-α release depended on the cell type.

CONCLUSION

NOX2 participated in IAV entry and raft-mediated endocytosis. NOX2 inhibition by NS1 reduced viral entry. NS1 competition with p67^phox for NOX2 binding shown by in silico models and cell-free assays was in agreement with NS1 inhibiting p67^phox translocation to membrane-embedded NOX2 in mouse and porcine macrophages.

GENERAL SIGNIFICANCE

We introduce NS1 as a compound targeting NOX2, a critical enzyme controlling viral levels and inflammation in macrophages and discuss the therapeutic relevance of targeting the C-terminal of NADPH oxidases by probes like NS1 in viral infections.

Activation of Porcine Alveolar Macrophages by Actinobacillus pleuropneumoniae Lipopolysaccharide via the Toll-Like Receptor 4/NF-κB-Mediated Pathway

Actinobacillus pleuropneumoniae is the causative agent of porcine contagious pleuropneumonia. Overproduction of proinflammatory cytokines, like interleukin-1β (IL-1β), IL-6, tumor necrosis factor alpha, and resistin, in the lung is an important feature of A. pleuropneumoniae infection. These proinflammatory cytokines enhance inflammatory and immunological responses. However, the mechanism that leads to cytokine production remains unclear. As a major virulence factor of A. pleuropneumoniae, lipopolysaccharide (LPS) may act as a potent stimulator of Toll-like receptor 4 (TLR4), triggering a number of intracellular signaling pathways that lead to the synthesis of proinflammatory cytokines. Porcine alveolar macrophages (PAMs) are the first line of defense against pathogenic microbes during pathogen invasion. The results of the present study demonstrate that A. pleuropneumoniae LPS induces PAMs to produce inflammatory cytokines in time- and dose-dependent manners. Moreover, PAMs were activated by A. pleuropneumoniae LPS, resulting in upregulation of signaling molecules, including TLR4, MyD88, TRIF-related adaptor molecule, and NF-κB. In contrast, the activation effects of A. pleuropneumoniae LPS on PAMs could be suppressed by specific inhibitors, like small interfering RNA and Bay11-7082. Taken together, our data indicate that A. pleuropneumoniae LPS can induce PAMs to produce proinflammatory cytokines via the TLR4/NF-κB-mediated pathway. These findings partially reveal the mechanism of the overproduction of proinflammatory cytokines in the lungs of swine with A. pleuropneumoniae infection and may provide targets for the prevention of A. pleuropneumoniae-induced pneumonia. All the data could be used as a reference for the pathogenesis of respiratory infection.

Histone deacetylase 2 (HDAC2) attenuates lipopolysaccharide (LPS)-induced inflammation by regulating PAI-1 expression

Background

Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection, and is primarily characterized by an uncontrolled systemic inflammatory response. In the present study, we developed an effective adjunct therapy mediated by a novel mechanism, to attenuate overt inflammation. LPS-treated macrophages were adopted as an in vitro model of endotoxin-induced inflammation during sepsis. Experiments were carried out using primary mouse peritoneal macrophages and the murine macrophage cell line RAW264.7, to elucidate the mechanisms by which HDAC2 modulates endotoxin-induced inflammation.

Results

Results revealed that PAI-1, TNF, and MIP-2 expression were inhibited by theophylline, an HDAC2 enhancer, in a RAW macrophage cell line, following LPS-induced inflammation. Thus, HDAC2 plays an important role in immune defense by regulating the expression of inflammatory genes via the c-Jun/PAI-1 pathway. During LPS-induced inflammation, overexpression of HDAC2 was found to inhibit PAI-1, TNF, and MIP-2 expression. Following LPS stimulation, HDAC2 knockdown increased nuclear translocation and DNA binding of c-Jun to the PAI-1 gene promoter, thereby activating PAI-1 gene transcription. Furthermore, inhibition of PAI-1 by TM5275 alone or in combination with theophylline notably suppressed TNF and MIP-2 expression.

Conclusion

HDAC2 can attenuate lipopolysaccharide-induced inflammation by regulating c-Jun and PAI-1 expression in macrophages.

Nano Ag/ZnO-Incorporated Hydroxyapatite Composite Coatings: Highly Effective Infection Prevention and Excellent Osteointegration

Interfacial characteristics play an important role in infection prevention and osteointegration of artificial bone implants. In this work, both Ag nanoparticles (AgNPs) and ZnO NPs are incorporated into hydroxyapatite (HA) nanopowders and deposited onto Ti6Al4V (Ti6) implants by laser cladding. The composite coatings possess a hierarchical surface structure with homogeneous distributions of Ag and ZnO. The Ag and ZnO NPs that are immobilized by laser cladding ensure long-term and gradual release of Ag and Zn ions at low cumulative concentrations of 36.2 and 56.4 μg/L after immersion for 21 days. A large concentration of Ag released initially increases the cytotoxicity but the large initial ZnO content enhances the cell viability and osteogenetic ability. The nano Ag/ZnO-embedded HA coating (Ag/ZnO/HA = 7:3:90 wt %, namely Ag7ZnO3HA) exhibits optimal antibacterial efficacy and osteogenetic capability, as exemplified by the broad spectrum antibacterial efficacy of 96.5 and 85.8% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, together with enhanced osteoinductivity with higher alkaline phosphatase (ALP) activity of 134.60 U/g protein compared to 70.79 U/g protein for the untreated implants after culturing for 7 days. The rabbit femoral implant model further confirms that the optimized composite coating accelerates the formation of new bone tissues indicating 87.15% of the newly formed bone area and osteointegration showing 83.75% of the bone-implant contact area even in the presence of injected S. aureus. The laser-cladded Ag7ZnO3HA composite coatings are promising metallic implants with excellent intrinsic antibacterial activity and osteointegration ability.

Innate sensing and cell-autonomous resistance pathways in Legionella pneumophila infection

Legionella pneumophila is a facultative intracellular bacterium which can cause a severe pneumonia called Legionnaires' disease after inhalation of contaminated water droplets and replication in alveolar macrophages. The innate immune system is generally able to sense and -in most cases- control L. pneumophila infection. Comorbidities and genetic risk factors, however, can compromise the immune system and high infection doses might overwhelm its capacity, thereby enabling L. pneumophila to grow and disseminate inside the lung. The innate immune system mediates sensing of L. pneumophila by employing e.g. NOD-like receptors (NLRs), Toll-like receptors (TLRs), as well as the cGAS/STING pathway to stimulate death of infected macrophages as well as production of proinflammatory cytokines and interferons (IFNs). Control of pulmonary L. pneumophila infection is largely mediated by inflammasome-, TNFα- and IFN-dependent macrophage-intrinsic resistance mechanisms. This article summarizes the current knowledge of innate immune responses to L. pneumophila infection in general, and of macrophage-intrinsic defense mechanisms in particular.

Activation of NF-kB-Mediated TNF-Induced Antimicrobial Immunity Is Required for the Efficient Brucella abortus Clearance in RAW 264.7 Cells

In this study, we explore the regulatory roles of pro-inflammatory cytokine tumor necrosis factor alpha (TNF) in the innate immunity of macrophages against B. abortus infection. We show that infection of macrophage with B. abortus induces marked expression and secretion of TNF which subsequently binds to TNF receptor 1 (TNFR-1) and activates a downstream signaling cascade of the innate immunity. Blocking of TNF signaling resulted in a notable increase of B. abortus survival which was associated with an increase of anti-inflammatory cytokine interleukin 10 (IL-10), a beneficial effector of Brucella survival, as well as remarkable decrease of reactive oxygen species (ROS) and nitric oxide (NO), antibrucella molecules. However, surprisingly, the interference of TNF did not show any influence on phagolysosome and cell death events. Furthermore, the transcriptional factor NF-kB was found to be a main mediator of TNF signaling when blocking of NF-kB pathway drastically suppressed the TNF-induced brucellacidal effect. Taken together, these findings clearly indicate that the immune cascade activated by TNF/TNFR-1 is required for the sufficient resistance to B. abortus survival in macrophages.

Targeting calpains: A novel immunomodulatory approach for microbial infections

Calpains are a family of Ca²⁺ dependent cytosolic non-lysosomal proteases with well conserved cysteine-rich domains for enzymatic activity. Due to their functional dependency on Ca²⁺ concentrations, they are involved in various cellular processes that are regulated by intracellular ca²⁺ concentration (i.e. embryo development, cell development and migration, maintenance of cellular architecture and structure etc.). Calpains are widely studied proteases in mammalian (i.e. mouse and human) physiology and pathophysiology due to their ubiquitous presence. For example, these proteases have been found to be involved in various inflammatory disorders such as neurodegeneration, cancer, brain and myocardial ischemia and infarction, cataract and muscular dystrophies etc. Besides their role in these sterile inflammatory conditions, calpains have also been shown to regulate a wide range of infectious diseases (i.e. sepsis, tuberculosis, gonorrhoea and bacillary dysentery etc.). One of these regulatory mechanisms mediated by calpains (i.e. calpain 1 and 2) during microbial infections involves the regulation of innate immune response, inflammation and cell death. Thus, the major emphasis of this review is to highlight the importance of calpains in the pathogenesis of various microbial (i.e. bacterial, fungal and viral) diseases and the use of calpain modulators as potential immunomodulators in microbial infections.

Neutrophils and Ly6Chi monocytes collaborate in generating an optimal cytokine response that protects against pulmonary Legionella pneumophila infection

Early responses mounted by both tissue-resident and recruited innate immune cells are essential for host defense against bacterial pathogens. In particular, both neutrophils and Ly6Chi monocytes are rapidly recruited to sites of infection. While neutrophils and monocytes produce bactericidal molecules, such as reactive nitrogen and oxygen species, both cell types are also capable of synthesizing overlapping sets of cytokines important for host defense. Whether neutrophils and monocytes perform redundant or non-redundant functions in the generation of anti-microbial cytokine responses remains elusive. Here, we sought to define the contributions of neutrophils and Ly6Chi monocytes to cytokine production and host defense during pulmonary infection with Legionella pneumophila, responsible for the severe pneumonia Legionnaires' disease. We found that both neutrophils and monocytes are critical for host defense against L. pneumophila. Both monocytes and neutrophils contribute to maximal IL-12 and IFNγ responses, and monocytes are also required for TNF production. Moreover, natural killer (NK) cells, NKT cells, and γδ T cells are sources of IFNγ, and monocytes direct IFNγ production by these cell types. Thus, neutrophils and monocytes cooperate in eliciting an optimal cytokine response that promotes effective control of bacterial infection.

Innate immunity against Legionella pneumophila during pulmonary infections in mice

Legionella pneumophila is an etiological agent of the severe pneumonia known as Legionnaires' disease (LD). This gram-negative bacterium is thought to replicate naturally in various freshwater amoebae, but also replicates in human alveolar macrophages. Inside host cells, legionella induce the production of non-endosomal replicative phagosomes by injecting effector proteins into the cytosol. Innate immune responses are first line defenses against legionella during early phases of infection, and distinguish between legionella and host cells using germline-encoded pattern recognition receptors such as Toll-like receptors , NOD-like receptors, and RIG-I-like receptors, which sense pathogen-associated molecular patterns that are absent in host cells. During pulmonary legionella infections, various inflammatory cells such as macrophages, neutrophils, natural killer (NK) cells, large mononuclear cells, B cells, and CD4+ and CD8+ T cells are recruited into infected lungs, and predominantly occupy interstitial areas to control legionella. During pulmonary legionella infections, the interplay between distinct cytokines and chemokines also modulates innate host responses to clear legionella from the lungs. Recognition by NK cell receptors triggers effector functions including secretion of cytokines and chemokines, and leads to lysis of target cells. Crosstalk between NK cells and dendritic cells, monocytes, and macrophages provides a major first-line defense against legionella infection, whereas activation of T and B cells resolves the infection and mounts legionella-specific memory in the host.

Pseudomonas aeruginosa Enolase Influences Bacterial Tolerance to Oxidative Stresses and Virulence

Pseudomonas aeruginosa is a Gram negative opportunistic pathogenic bacterium, which causes acute and chronic infections. Upon entering the host, bacteria alter global gene expression to adapt to host environment and avoid clearance by the host. Enolase is a glycolytic enzyme involved in carbon metabolism. It is also a component of RNA degradosome, which is involved in RNA processing and gene regulation. Here, we report that enolase is required for the virulence of P. aeruginosa in a murine acute pneumonia model. Mutation of enolase coding gene (eno) increased bacterial susceptibility to neutrophil mediated killing, which is due to reduced tolerance to oxidative stress. Catalases and alkyl hydroperoxide reductases play a major role in protecting the cell from oxidative damages. In the eno mutant, the expression levels of catalases (KatA and KatB) were similar as those in the wild type strain in the presence of H₂O₂, however, the expression levels of alkyl hydroperoxide reductases (AhpB and AhpC) were significantly reduced. Overexpression of ahpB but not ahpC in the eno mutant fully restored the bacterial resistance to H₂O₂ as well as neutrophil mediated killing, and partially restored bacterial virulence in the murine acute pneumonia model. Therefore, we have identified a novel role of enolase in the virulence of P. aeruginosa.

Impact of micro-environmental changes on respiratory tract infections with intracellular bacteria

Community-acquired pneumonia is caused by intra- and extracellular bacteria, with some of these bacteria also being linked to the pathogenesis of chronic lung diseases, including asthma and chronic obstructive pulmonary disease. Chlamydia pneumoniae is an obligate intracellular pathogen that is highly sensitive to micro-environmental conditions controlling both pathogen growth and host immune responses. The availability of nutrients, as well as changes in oxygen, pH and interferon-γ levels, have been shown to directly influence the chlamydial life cycle and clearance. Although the lung has been traditionally regarded as a sterile environment, sequencing approaches have enabled the identification of a large number of bacteria in healthy and diseased lungs. The influence of the lung microbiota on respiratory infections has not been extensively studied so far and data on chlamydial infections are currently unavailable. In the present study, we speculate on how lung microbiota might interfere with acute and chronic infections by focusing exemplarily on the obligate intracellular C. pneumoniae. Furthermore, we consider changes in the gut microbiota as an additional player in the control of lung infections, especially in view the increasing evidence suggesting the involvement of the gut microbiota in various immunological processes throughout the human body.