Respiratory syncytial virus (RSV) is

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Respiratory syncytial virus (RSV), named by its ability to induce fusion of infected epithelial cells (49), is a leading cause of epidemic respiratory tract illness in children (28). Spread primarily by contact with contaminated secretions, RSV replicates in the nasopharyngeal epithelium and spreads to the lower respiratory tract via epithelial cell-to-cell transfer along intracytoplasmic bridges (27). Although only two RSV serotypes, A and B, circulate in RSV epidemics (29), immunity to naturally acquired infection is incomplete, resulting in repeated infections through adulthood (24; reviewed in reference 28). In humans, RSV infection produces a spectrum of airway involvement ranging from otitis media to lower tract infection.Clinically severe RSV infections involving the lower respiratory tract are primarily seen in young children with naïve immune systems and/or genetic predispositions (32), patients with suppressed T-cell immunity (such as heart transplant recipients [41]), and the elderly (48). In autopsy studies of fatal disease, RSV infection is characterized by the presence of cytoplasmic eosinophilic inclusion bodies, characteristic of viral replication, in airway epithelial cells; sloughing and necrosis of the epithelial surface; and concomitant mucous plugging of the airways with trapping of air (1,18,19). In addition to these manifestations of direct epithelial involvement, RSV infection produces a pronounced perivascular infiltrate of mononuclear cells and lymphocytes (1, 18) and a neutrophil-rich exudate detected by bronchoalveolar lavage (16). Finally, the presence of eosinophil cationic protein (20,30) and histamine (64) in nasal secretions at concentrations that correlate with disease severity suggests the participation of eosinophils and basophils in the pathology of RSV infection.The mechanisms responsible for recruitment of circulating leukocytes, mononuclear cells, and lymphocytes into the lung as a consequence of RSV infection are largely unknown. Cellular recruitment into inflamed tissues is a multistep process in which circulating leukocytes first demarginate, adhere to stimulated endothelial cells, and subsequently become activated. Activated leukocytes then migrate through the vascular endothelium toward chemical gradients of chemoattractant peptides or antigens (reviewed in reference 58). Recent attention has focused on the important role of chemokines in mediat-* Corresponding author. Mailing address: Division of Endocrinology, MRB 8.138, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1060.

Oxidative stress plays an important role in the pathogenesis of lung inflammation. Respiratory syncytial virus (RSV) infection induces reactive oxygen species (ROS) production in vitro and oxidative injury in lungs in vivo; however, the mechanism of RSV-induced cellular oxidative stress has not been investigated. Therefore, we determined whether RSV infection of airway epithelial cells modified the expression and/or activities of antioxidant enzymes (AOE). A549 cells, a human alveolar type II-like epithelial cell line, and small airway epithelial (SAE) cells, normal human cells derived from terminal bronchioli, were infected with RSV and harvested at various time points to measure F(2)-8 isoprostanes by enzyme-linked immunosorbent assay and total and reduced glutathione (GSH and GSSG) by colorimetric assay. Superoxide dismutase (SOD) 1, 2, and 3, catalase, glutathione peroxidase (GPx), and glutathione S-transferase (GST) expression was determined by quantitative real-time PCR and Western blot, and their activity was measured by colorimetric assays. RSV infection induced a significant increase of lipid peroxidation products as well as a significant decrease in the GSH/GSSG ratio. There was a significant decrease in SOD 1, SOD 3, catalase, and GST expression with a concomitant increase of SOD 2 in RSV-infected cells, compared with uninfected cells. Total SOD activity was increased, but catalase, GPx, and GST activities were decreased, after RSV infection. Our findings suggest that RSV-induced cellular oxidative damage is the result of an imbalance between ROS production and antioxidant cellular defenses. Modulation of oxidative stress represents a potential novel pharmacologic approach to ameliorate RSV-induced acute lung inflammation.

Exosomes are membrane-enclosed vesicles actively released into the extracellular space, whose content reflect the physiological/pathological state of the cells they originate from. These vesicles participate in cell-to-cell communication and transfer of biologically active proteins, lipids, and RNAs. Their role in viral infections is just beginning to be appreciated. RNA viruses are an important class of pathogens and affect millions of people worldwide. Recent studies on Human Immunodeficiency Virus (HIV), Hepatitis C Virus (HCV), human T-cell lymphotropic virus (HTLV), and Dengue Virus (DENV) have demonstrated that exosomes released from infected cells harbor and deliver many regulatory factors including viral RNA and proteins, viral and cellular miRNA, and other host functional genetic elements to neighboring cells, helping to establish productive infections and modulating cellular responses. Exosomes can either spread or limit an infection depending on the type of pathogen and target cells, and can be exploited as candidates for development of antiviral or vaccine treatments. This review summarizes recent progress made in understanding the role of exosomes in RNA virus infections with an emphasis on their potential contribution to pathogenesis.

The transcription factor nuclear factor (NF)-kB controls the expression of numerous respiratory syncytial virus (RSV)-inducible inflammatory and immunomodulatory genes. Using a BALB/c mouse model, the present article shows that RSV potently and specifically activates NF-kB in vivo, a process that involves nuclear translocation of the subunits RelA, p50, and c-Rel in the lung. By depletion of alveolar macrophages (AMs) in BALB/c mice and use of C3H/HeJ mice lacking a functional Toll-like receptor (TLR)-4 signaling pathway, we demonstrate the existence of distinct but sequentially integrated RSV-inducible early NF-kB responses in the lung. The first response occurs early after RSV inoculation, is AM and TLR4 dependent, and is viral replication independent, whereas the second response involves epithelial cells and/or inflammatory cells, is TLR4 independent, and requires viral replication. NF-kB may be considered a central activator of not only inflammatory but also innate immune responses to RSV.Respiratory syncytial virus (RSV), the major cause of serious lower respiratory tract infections in infancy and early childhood [1], can be considered among the most potent biological stimuli inducing the expression and/or secretion of proinflammatory and immunomodulatory mediators [2-4]. These events have been extensively demonstrated in airway epithelial cells, the primary site of RSV replication, and in other cell types that are targets of abortive viral replication or viral attachment only (such as monocytes/macrophages, eosinophils, and neutrophils). In vitro, RSV has been shown to induce expression of a number of genes in epithelial cells and macrophages, including the cytokines interleukin (IL)-1 [5], tumor necrosis factor (TNF)-a, IL-6 [6], and IL-10 [7]; the CXC chemokines IL-8, growth-related oncogene (GRO)-a, epithelial-derived neutrophil-activating protein(ENA)-

Human metapneumovirus (hMPV) is a leading cause of acute respiratory tract infection in infants, as well as in the elderly and immunocompromised patients. No effective treatment or vaccine for hMPV is currently available. A recombinant hMPV lacking the G protein (rhMPV-ΔG) was recently developed as a potential vaccine candidate and shown to be attenuated in the respiratory tract of a rodent model of infection. The mechanism of its attenuation, as well as the role of G protein in modulation of hMPV-induced cellular responses in vitro, as well as in vivo, is currently unknown. In this study, we found that rhMPV-ΔG-infected airway epithelial cells produced higher levels of chemokines and type I interferon (IFN) compared to cells infected with rhMPV-WT. Infection of airway epithelial cells with rhMPV-ΔG enhanced activation of transcription factors belonging to the nuclear factor (NF)-κB and interferon regulatory factor (IRF) families, as revealed by increased nuclear translocation and/or phosphorylation of these transcription factors. Compared to rhMPV-WT, rhMPV-ΔG also increased IRF- and NF-κB-dependent gene transcription, which was reversely inhibited by G protein expression. Since RNA helicases have been shown to play a fundamental role in initiating viral-induced cellular signaling, we investigated whether retinoic induced gene (RIG)-I was the target of G protein inhibitory activity. We found that indeed G protein associated with RIG-I and inhibited RIG-I-dependent gene transcription, identifying an important mechanism by which hMPV affects innate immune responses. This is the first study investigating the role of hMPV G protein in cellular signaling and identifies G as an important virulence factor, as it inhibits the production of important immune and antiviral mediators by targeting RIG-I, a major intracellular viral RNA sensor.

Lower respiratory tract disease caused by respiratory syncytial virus (RSV) is characterized by profound airway mucosa inflammation, both in infants with naturally acquired infection and in experimentally inocuRespiratory syncytial virus (RSV) is the major cause of serious lower respiratory disease in infancy and early childhood (5). Bronchiolitis, the more severe clinical manifestation of RSV infection, is characterized by necrosis and sloughing of the respiratory epithelium and plugging of the small bronchioles with fibrin and mucus. An intense peribronchial infiltration of mononuclear cells (lymphocytes and monocytes) occurs, with considerable edema (1, 8, 10). In addition, presence of the granule-associate cytotoxic proteins histamine, eosinophil cationic protein, and major basic protein in nasopharyngeal secretions and tracheobronchial aspirates suggests that RSV infection triggers the migration to the airways and activation of basophils and eosinophils (12,17,37,46). The evidence of an inverse correlation between the levels of these cytotoxic mediators and the degree of oxygen saturation in RSV-infected infants further underscores the critical role played by mucosal inflammation in the pathogenesis of RSV airway disease (12,45,46).The mouse model shows close similarity to the pathogenesis of RSV-induced lower airway disease in humans. In BALB/c mice, RSV rapidly replicates in the lungs after intranasal inoculation, and induces mononuclear cell infiltration around peribronchial and perivascular tissues (41) and objective plethysmographic signs of pulmonary dysfunction (i.e., increased respiratory rates and airway hyperresponsiveness) (29, 44).These pathophysiologic changes correlate with the amount of viral inoculum (44), consistent with the observation that more severe disease occurs in infected children who have higher concentrations of RSV in their secretions (4, 16).The mechanisms that regulate selective recruitment of inflammatory cells to the airways and their activation following RSV infection are still largely unknown. Similarly, virus-or host-specific factors that may influence these events have not been yet identified. Much of the cellular response at sites of tissue inflammation is controlled by gradients of chemotactic factors that direct leukocyte transendothelial migration and movement through the extracellular matrix. The composition of this cellular response is dependent upon the discrete target cell selectivity of these chemotactic molecules. Chemokines, a superfamily of small chemotactic cytokines, have emerged as central regulatory molecules in inflammatory, immune, and infectious processes of the lung (28). Chemokines have been primarily divided into two main subfamilies, CXC (␣) and CC (␤), upon their sequence homology and the position of the first two cysteine residues. In general, this subdivision is mirrored by the activity of these two chemokine groups on neutrophils (CXC) or monocytes, eosinophils, and basophils (CC). However, within the CXC subfamily, chemokines such as gamma inte...