Insights Into the Role of the Lung Virome During Respiratory Viral Infections

The virome constitutes the viral component of the microbiome and it consists of the genomes of all the viruses that inhabit a particular region of the human body, including those that cause acute, persistent or latent infection, and retroviral elements integrated to host chromosomes. The human virome is composed by eukaryotic viruses, bacteriophages and archaeal viruses. The understanding of the virome composition and role on human health has been delayed by the absence of specific tools and techniques to accurately characterize viruses. However, more recently, advanced methods for viral diagnostics, such as deep sequencing and metagenomics, have allowed a better understanding of the diverse viral species present in the human body. Previous studies have shown that the respiratory virome modulates the host immunity and that, since childhood, the human lung is populated by viruses for whom there is no disease association. Whether these viruses are potentially pathogenic and the reason for their persistence remain elusive. Increased respiratory viral load can cause exacerbation of chronic pulmonary diseases, including COPD, cystic fibrosis, and asthma. Moreover, the presence of resident viral populations may contribute to the pathogenesis of community-acquired respiratory virus infections. In this mini review, I will discuss the recent progress on our understanding of the human lung virome and summarize the up-to-date knowledge on the relationships among community-acquired respiratory viruses, the lung virome and the immune response to better understand disease pathophysiology and the factors that may lead to viral persistence.

New Insights on the Early Interaction Between Typhoid and Non-typhoid Salmonella Serovars and the Host Cells

Salmonella enterica is a common source of food and water-borne infections, causing a wide range of clinical ailments in both human and animal hosts. Immunity to Salmonella involves an interplay between different immune responses, which are rapidly initiated to control bacterial burden. However, Salmonella has developed several strategies to evade and modulate the host immune responses. In this sense, the main knowledge about the pathogenicity of this bacterium has been obtained by the study of mouse models with non-typhoidal serovars. However, this knowledge is not representative of all the pathologies caused by non-typhoidal serovars in the human. Here we review the most important features of typhoidal and non-typhoidal serovars and the diseases they cause in the human host, describing the virulence mechanisms used by these pathogens that have been identified in different models of infection.

The triad: respiratory microbiome - virus - immune response in the pathophysiology of pulmonary viral infections

INTRODUCTION

The longstanding dogma that the healthy lung is sterile has been refuted by recent advances in culture-independent analyses of airway samples. The respiratory microbiome comprises all airway and lung tissue-associated microbes. These micro-organisms occur throughout the upper and lower respiratory tracts, with different populations and distinct burdens at specific sites and can be classified as pathogenic or commensal.

AREAS COVERED

The majority of studies investigating the respiratory microbiome have focused on bacteria; however, emerging evidence has revealed the composition of the lung virome, the global viral communities present in the lung tissue. In this review, we searched PubMed and used keywords such as airway microbiome. We restricted outputs to English language and did not limit by any dates. We summarize the up-to-date knowledge on how the microbiome interacts with the host immune system and influences the pathogenesis of pulmonary viral infections.

EXPERT OPINION

The relationship between colonizing microbes and the host is complex and various factors need to be considered in order to appreciate its pathophysiological consequences. Understanding these intricate mechanisms of interaction among the respiratory microbiome, viruses and the immune response may lead to the development of better therapies to treat or prevent respiratory viral infections.

The role of extracellular nucleic acids in the immune system modulation of Rhodnius prolixus (Hemiptera: Reduviidae)

Extracellular traps (ETs) are extracellular nucleic acids associated with cytoplasmic proteins that may aid in the capture and killing of pathogens. To date, only a few insects were shown to display this kind of immune response. Jaburetox, a peptide derived from jack bean urease, showed toxic effects in Rhodnius prolixus, affecting its immune response. The present study aims to evaluate the role of extracellular nucleic acids in R. prolixus' immune response, using Jaburetox as a model entomotoxin. The insects were treated with extracellular nucleic acids and/or Jaburetox, and the cellular and humoral responses were assessed. We also evaluated the release of extracellular nucleic acids induced by toxins, and performed immunocompetence assays using pathogenic bacteria. Our results demonstrated that extracellular nucleic acids can modulate the insect immune responses, either alone or associated with the toxin. Although RNA and DNA induced a cellular immune response, only DNA was able to neutralize the Jaburetox-induced aggregation of hemocytes. Likewise, the activation of the humoral response was different for RNA and DNA. Nevertheless, it was observed that both, extracellular DNA and RNA, immunocompensated the Jaburetox effects on insect defenses upon the challenge of a pathogenic bacterium. The toxin was not able to alter cellular viability, in spite of inducing an increase in the reactive species of oxygen formation. In conclusion, we have demonstrated a protective role for extracellular nucleic acids in R. prolixus´ immune response to toxins and pathogenic bacteria.

Macrophage migration inhibitory factor (MIF) controls cytokine release during respiratory syncytial virus infection in macrophages

OBJECTIVE AND DESIGN

Respiratory syncytial virus (RSV) is the major cause of infection in children up to 2 years old and reinfection is very common among patients. Tissue damage in the lung caused by RSV leads to an immune response and infected cells activate multiple signaling pathways and massive production of inflammatory mediators like macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine. Therefore, we sought to investigate the role of MIF during RSV infection in macrophages.

METHODS

We evaluated MIF expression in BALB/c mice-derived macrophages stimulated with different concentrations of RSV by Western blot and real-time PCR. Additionally, different inhibitors of signaling pathways and ROS were used to evaluate their importance for MIF expression. Furthermore, we used a specific MIF inhibitor, ISO-1, to evaluate the role of MIF in viral clearance and in RSV-induced TNF-α, MCP-1 and IL-10 release from macrophages.

RESULTS

We showed that RSV induces MIF expression dependently of ROS, 5-LOX, COX and PI3K activation. Moreover, viral replication is necessary for RSV-triggered MIF expression. Differently, p38 MAPK in only partially needed for RSV-induced MIF expression. In addition, MIF is important for the release of TNF-α, MCP-1 and IL-10 triggered by RSV in macrophages.

CONCLUSIONS

In conclusion, we demonstrate that MIF is expressed during RSV infection and controls the release of pro-inflammatory cytokines from macrophages in an in vitro model.

Respiratory Syncytial Virus induces the classical ROS-dependent NETosis through PAD-4 and necroptosis pathways activation

Respiratory syncytial virus (RSV) is a major cause of diseases of the respiratory tract in young children and babies, being mainly associated with bronchiolitis. RSV infection occurs primarily in pulmonary epithelial cells and, once infection is established, an immune response is triggered and neutrophils are recruited. In this study, we investigated the mechanisms underlying NET production induced by RSV. We show that RSV induced the classical ROS-dependent NETosis in human neutrophils and that RSV was trapped in DNA lattices coated with NE and MPO. NETosis induction by RSV was dependent on signaling by PI3K/AKT, ERK and p38 MAPK and required histone citrullination by PAD-4. In addition, RIPK1, RIPK3 and MLKL were essential to RSV-induced NETosis. MLKL was also necessary to neutrophil necrosis triggered by the virus, likely promoting membrane-disrupting pores, leading to neutrophil lysis and NET extrusion. Finally, we found that RSV infection of alveolar epithelial cells or lung fibroblasts triggers NET-DNA release by neutrophils, indicating that neutrophils can identify RSV-infected cells and respond to them by releasing NETs. The identification of the mechanisms responsible to mediate RSV-induced NETosis may prove valuable to the design of new therapeutic approaches to treat the inflammatory consequences of RSV bronchiolitis in young children.

The Impact of Helicobacter pylori Urease upon Platelets and Consequent Contributions to Inflammation

Gastric infection by Helicobacter pylori is considered a risk factor for gastric and duodenal cancer, and extragastric diseases. Previous data have shown that, in a non-enzymatic way, H. pylori urease (HPU) activates neutrophils to produce ROS and also induces platelet aggregation, requiring ADP secretion modulated by the 12-lipoxygenase pathway, a signaling cascade also triggered by the physiological agonist collagen. Here we investigated further the effects on platelets of recombinant versions of the holoenzyme HPU, and of its two subunits (HpUreA and HpUreB). Although HpUreA had no aggregating activity on platelets, it partially inhibited collagen-induced aggregation. HpUreB induced platelet aggregation in the nanomolar range, and also interfered dose-dependently on both collagen- and ADP-induced platelet aggregation. HPU-induced platelet aggregation was inhibited by antibodies against glycoprotein VI (GPVI), the main collagen receptor in platelets. Flow cytometry analysis revealed exposure of P-selectin in HPU-activated platelets. Anti-glycoprotein IIbIIIa (GPIIbIIIa) antibodies increased the binding of FITC-labeled HPU to activated platelets, whereas anti-GPVI did not. Evaluation of post-transcriptional events in HPU-activated platelets revealed modifications in the pre-mRNA processing of pro-inflammatory proteins, with increased levels of mRNAs encoding IL-1β and CD14. We concluded that HPU activates platelets probably through its HpUreB subunit. Activation of platelets by HPU turns these cells into a pro-inflammatory phenotype. Altogether, our data suggest that H. pylori urease, besides allowing bacterial survival within the gastric mucosa, may have an important, and so far overlooked, role in gastric inflammation mediated by urease-activated neutrophils and platelets.

Neuropeptide gastrin-releasing peptide induces PI3K/reactive oxygen species-dependent migration in lung adenocarcinoma cells

Nerve fibers and neurotransmitters have increasingly been shown to have a role in tumor progression. Gastrin-releasing peptide is a neuropeptide linked to tumor aggressiveness, acting as an autocrine tumor growth factor by binding to its receptor, gastrin-releasing peptide receptor, expressed by many tumors. Although neuropeptides have been previously linked to tumor cell proliferation, more recent studies have uncovered roles for neuropeptides in chemotaxis and metastasis. Understanding the precise roles of such peptides in cancer is crucial to optimizing targeted therapy design. We have previously described that gastrin-releasing peptide acts directly as a chemotactic factor for neutrophils, dependent on PI3K, ERK, and p38. In this study, we investigated roles for gastrin-releasing peptide in lung adenocarcinoma. We asked if gastrin-releasing peptide would act as a proliferative and/or chemotactic stimulus for gastrin-releasing peptide receptor-expressing tumor cells. In A549 cells, a non-small cell lung carcinoma line, the treatment with gastrin-releasing peptide leads to activation of AKT and ERK1/2, and production of reactive oxygen species. Gastrin-releasing peptide induced migration of A549 cells, dependent on gastrin-releasing peptide receptor and PI3K, but not ERK. However, no proliferation was observed in these cells in response to gastrin-releasing peptide, and gastrin-releasing peptide did not promote resistance to treatment with a chemotherapy drug. Our results suggest that, similar to what happens in neutrophils, gastrin-releasing peptide is a migratory, rather than a proliferative, stimulus, for non-small cell lung carcinoma cells, indicating a putative role for gastrin-releasing peptide and gastrin-releasing peptide receptor in metastasis.

LPS-induced neonatal stress in mice affects the response profile to an inflammatory stimulus in an age and sex-dependent manner

The aim of this study is to evaluate the response to an inflammatory stimulus in mice exposed to LPS-induced neonatal stress at different ages and sexes. Balb/c mice were submitted to intraperitoneal injections on postnatal days 3 and 10 with lipopolysaccharide (nLPS) or saline solution (nSal). At 21 or 60 days, either saline solution was injected or an inflammatory stimulus was induced by the injection of 1% carrageenan. Inflammatory cytokines, reactive oxygen species, and neutrophil extracellular traps (NETs) production were measured in peritoneal fluid. LPS-induced neonatal stress can reduce inflammatory cytokines in males and females. An increase in NETs production was observed when 60 day nLPS animals were compared to 21 day mice in both sexes. The ROS production was not affected by neonatal stress. The results shown here indicate that LPS-induced neonatal stress can alter cytokine production in response to inflammatory stimuli at different ages, in a sex-dependent effect. © 2016 Wiley Periodicals, Inc. Dev Psychobiol 58: 600-613, 2016.

Respiratory syncytial virus fusion protein promotes TLR-4-dependent neutrophil extracellular trap formation by human neutrophils

Acute viral bronchiolitis by Respiratory Syncytial Virus (RSV) is the most common respiratory illness in children in the first year of life. RSV bronchiolitis generates large numbers of hospitalizations and an important burden to health systems. Neutrophils and their products are present in the airways of RSV-infected patients who developed increased lung disease. Neutrophil Extracellular Traps (NETs) are formed by the release of granular and nuclear contents of neutrophils in the extracellular space in response to different stimuli and recent studies have proposed a role for NETs in viral infections. In this study, we show that RSV particles and RSV Fusion protein were both capable of inducing NET formation by human neutrophils. Moreover, we analyzed the mechanisms involved in RSV Fusion protein-induced NET formation. RSV F protein was able to induce NET release in a concentration-dependent fashion with both neutrophil elastase and myeloperoxidase expressed on DNA fibers and F protein-induced NETs was dismantled by DNase treatment, confirming that their backbone is chromatin. This viral protein caused the release of extracellular DNA dependent on TLR-4 activation, NADPH Oxidase-derived ROS production and ERK and p38 MAPK phosphorylation. Together, these results demonstrate a coordinated signaling pathway activated by F protein that led to NET production. The massive production of NETs in RSV infection could aggravate the inflammatory symptoms of the infection in young children and babies. We propose that targeting the binding of TLR-4 by F protein could potentially lead to novel therapeutic approaches to help control RSV-induced inflammatory consequences and pathology of viral bronchiolitis.

Prolonged survival of allografts induced by mycobacterial Hsp70 is dependent on CD4+CD25+ regulatory T cells

Background

Heat shock proteins (Hsps) are stress induced proteins with immunomodulatory properties. The Hsp70 of Mycobacterium tuberculosis (TBHsp70) has been shown to have an anti-inflammatory role on rodent autoimmune arthritis models, and the protective effects were demonstrated to be dependent on interleukin-10 (IL-10). We have previously observed that TBHsp70 inhibited maturation of dendritic cells (DCs) and induced IL-10 production by these cells, as well as in synovial fluid cells.

Methodology/Principal Findings

We investigated if TBHsp70 could inhibit allograft rejection in two murine allograft systems, a transplanted allogeneic melanoma and a regular skin allograft. In both systems, treatment with TBHsp70 significantly inhibited rejection of the graft, and correlated with regulatory T cells (Tregs) recruitment. This effect was not tumor mediated because injection of TBHsp70 in tumor-free mice induced an increase of Tregs in the draining lymph nodes as well as inhibition of proliferation of lymph node T cells and an increase in IL-10 production. Finally, TBHsp70 inhibited skin allograft acute rejection, and depletion of Tregs using a monoclonal antibody completely abolished this effect.

Conclusions/Significance

We present the first evidence for an immunosuppressive role for this protein in a graft rejection system, using an innovative approach – immersion of the graft tissue in TBHsp70 solution instead of protein injection. Also, this is the first study that demonstrates dependence on Treg cells for the immunosuppressive role of TBHsp70. This finding is relevant for the elucidation of the immunomodulatory mechanism of TBHsp70. We propose that this protein can be used not only for chronic inflammatory diseases, but is also useful for organ transplantation management.

Trypanosoma cruzi infection is enhanced by vector saliva through immunosuppressant mechanisms mediated by lysophosphatidylcholine

Trypanosoma cruzi, the etiological agent of Chagas disease, is transmitted by bug feces deposited on human skin during a blood meal. However, parasite infection occurs through the wound produced by insect mouthparts. Saliva of the Triatominae bug Rhodnius prolixus is a source of lysophosphatidylcholine (LPC). Here, we tested the role of both triatomine saliva and LPC on parasite transmission. We show that vector saliva is a powerful inducer of cell chemotaxis. A massive number of inflammatory cells were found at the sites where LPC or saliva was inoculated into the skin of mice. LPC is a known chemoattractant for monocytes, but neutrophil recruitment induced by saliva is LPC independent. The preincubation of peritoneal macrophages with saliva or LPC increased fivefold the association of T. cruzi with these cells. Moreover, saliva and LPC block nitric oxide production by T. cruzi-exposed macrophages. The injection of saliva or LPC into mouse skin in the presence of the parasite induces an up-to-sixfold increase in blood parasitemia. Together, our data suggest that saliva of the Triatominae enhances T. cruzi transmission and that some of its biological effects are attributed to LPC. This is a demonstration that a vector-derived lysophospholipid may act as an enhancing factor of Chagas disease.

Biochemical and biological characterization of the venoms of Bothriopsis bilineata and Bothriopsis taeniata (Serpentes: Viperidae)

Snake venom is a complex mixture containing diverse protein components with different structures and functions that are used for prey immobilization and death. Snake venoms from the family Viperidae cause pronounced local and systemic effects, such as pain, edema, hemorrhage and necrosis. Here, we investigated the enzymatic and biological activities of venoms from two Amazonian snakes, Bothriopsis bilineata and Bothriopsis taeniata. Both venoms presented high enzymatic activities for proteases kallikrein, thrombin and plasmin, low levels of trypsin, cathepsin C and leucine aminopeptidase activities, while lacked acetylcholinesterase activity. B. taeniata and B. bilineata crude venoms caused inflammation inducing neutrophil recruitment into peritoneal cavity of mice 4h after injection. Neutrophil recruitment induced by B. taeniata venom was accompanied by hemorrhage. EDTA treatment profoundly impaired neutrophil recruitment, suggesting the involvement of a metalloproteinase on venoms-induced neutrophil recruitment. Pretreatment with dexamethasone and zileuton, a 5-lipoxygenase inhibitor, significantly reduced neutrophil migration, but indomethacin and montelukast, a cysteinyl leukotriene receptor antagonist, had no effect, suggesting the involvement of lipoxygenase-derived metabolites, probably LTB(4). Together, these results show that B. bilineata and B. taeniata venoms induce a marked inflammatory reaction, with leukocyte recruitment, and hemorrhage, which parallels to a high proteolytic activity found in these venoms.

Heme induces neutrophil migration and reactive oxygen species generation through signaling pathways characteristic of chemotactic receptors

Hemolysis or extensive cell damage can lead to high concentrations of free heme, causing oxidative stress and inflammation. Considering that heme induces neutrophil chemotaxis, we hypothesize that heme activates a G protein-coupled receptor. Here we show that similar to heme, several heme analogs were able to induce neutrophil migration in vitro and in vivo. Mesoporphyrins, molecules lacking the vinyl groups in their rings, were not chemotactic for neutrophils and selectively inhibited heme-induced migration. Moreover, migration of neutrophils induced by heme was abolished by pretreatment with pertussis toxin, an inhibitor of Galpha inhibitory protein, and with inhibitors of phosphoinositide 3-kinase, phospholipase Cbeta, mitogen-activated protein kinases, or Rho kinase. The induction of reactive oxygen species by heme was dependent of Galpha inhibitory protein and phosphoinositide 3-kinase and partially dependent of phospholipase Cbeta, protein kinase C, mitogen-activated protein kinases, and Rho kinase. Together, our results indicate that heme activates neutrophils through signaling pathways that are characteristic of chemoattractant molecules and suggest that mesoporphyrins might prove valuable in the treatment of the inflammatory consequences of hemorrhagic and hemolytic disorders.

Characterization of heme as activator of Toll-like receptor 4

Heme is an ancient and ubiquitous molecule present in organisms of all kingdoms, composed of an atom of iron linked to four ligand groups of porphyrin. A high amount of free heme, a potential amplifier of the inflammatory response, is a characteristic feature of diseases with increased hemolysis or extensive cell damage. Here we demonstrate that heme, but not its analogs/precursors, induced tumor necrosis factor-alpha (TNF-alpha) secretion by macrophages dependently on MyD88, TLR4, and CD14. The activation of TLR4 by heme is exquisitely strict, requiring its coordinated iron and the vinyl groups of the porphyrin ring. Signaling of heme through TLR4 depended on an interaction distinct from the one established between TLR4 and lipopolysaccharide (LPS) since anti-TLR4/MD2 antibody or a lipid A antagonist inhibited LPS-induced TNF-alpha secretion but not heme activity. Conversely, protoporphyrin IX antagonized heme without affecting LPS-induced activation. Moreover, heme induced TNF-alpha and keratinocyte chemokine but was ineffective to induce interleukin-6, interleukin-12, and interferon-inducible protein-10 secretion or co-stimulatory molecule expression. These findings support the concept that the broad ligand specificity of TLR4 and the different activation profiles might in part reside in its ability to recognize different ligands in different binding sites. Finally, heme induced oxidative burst, neutrophil recruitment, and heme oxygenase-1 expression independently of TLR4. Thus, our results presented here reveal a previous unrecognized role of heme as an extracellular signaling molecule that affects the innate immune response through a receptor-mediated mechanism.