Severe infantile RSV and influenza virus LRTI is characterized by inadequate (rather than excessive) adaptive immune responses, robust viral replication, and apoptotic crisis.

Respiratory syncytial virus (RSV) is

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A new respiratory virus, human metapneumovirus, was recently identified. We detected this virus by PCR in ten (8%) of 132 consecutive children admitted to Turku Hospital, Finland, for acute expiratory wheezing (median age 7 months, range 4-25). The mean duration of hospital stay was 2.5 days (SD 1.6) and mean duration of respiratory symptoms was 19 days (8). The white blood cell count, C-reactive protein, and regulated upon activation, normal T-cell-expressed and T-cell-secreted (RANTES) concentrations in nasal secretion remained low, whereas interleukin 8 concentrations in nasal secretion were high. Human metapneumovirus is a clinically important causative agent of acute wheezing in young children.

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.

The chemokine CXCL1/MGSA plays a pivotal role in the host immune response by recruiting and activating neutrophils for microbial killing at the tissue site. CXCL1 exists reversibly as monomers and dimers, and mediates its function by binding glycosaminoglycans (GAG) and CXCR2 receptor. We recently showed that both monomers and dimers are potent CXCR2 agonists, the dimer is the high-affinity GAG ligand, lysine and arginine residues located in two non-overlapping domains mediate GAG interactions, and there is extensive overlap between GAG and receptor-binding domains. To understand how these structural properties influence in vivo function, we characterized peritoneal neutrophil recruitment of a trapped monomer and trapped dimer and a panel of WT lysine/arginine to alanine mutants. Monomers and dimers were active, but WT was more active indicating synergistic interactions promote recruitment. Mutants from both domains showed reduced GAG heparin binding affinities and reduced neutrophil recruitment, providing compelling evidence that both GAG-binding domains mediate in vivo trafficking. Further, mutant of a residue that is involved in both GAG binding and receptor signaling showed the highest reduction in recruitment. We conclude that GAG interactions and receptor activity of CXCL1 monomers and dimers are fine-tuned to regulate neutrophil trafficking for successful resolution of tissue injury.

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)-