Immunopathogenesis of respiratory syncytial virus bronchiolitis

BACKGROUND: The objective of this study was to elucidate the relation between respiratory syncytial virus (RSV) infection and cytokine/chemokine concentrations, as well as the impact that these factors have on the severity of bronchiolitis. METHODS: Children <24 months old who presented to the emergency department with clinical symptoms of bronchiolitis were prospectively enrolled in the study. Nasal-wash samples were analyzed to identify viral pathogens and to quantify RSV and cytokine/chemokine concentrations. Severe cases of disease were defined as those requiring hospitalization, and severity was further determined on the basis of the duration of supplemental-oxygen and/or intravenous-fluid therapy. RESULTS: A total of 101 children were enrolled, 63 of whom were infected with RSV and 13 of whom were infected with other respiratory viruses; in 22 children, no virus was detected. RSV bronchiolitis was associated with a greater inflammatory response than was non-RSV bronchiolitis, although RSV infection was not associated with more-severe disease. Levels of interleukin (IL)-6, IL-8, IL-10, interferon (IFN)-gamma, and macrophage inflammatory protein (MIP)-1beta were significantly inversely correlated with the duration of supplemental-oxygen therapy. CONCLUSION: The robust inflammatory response associated with RSV infection does not contribute to the severity of RSV bronchiolitis any more than it contributes to the severity of non-RSV bronchiolitis. Elevated levels of proinflammatory mediators IL-6, IL-8, IFN-gamma, and MIP-1beta, as well as of the regulatory cytokine IL-10, may be protective against hypoxia in bronchiolitis.     

Innate immunity in respiratory syncytial virus bronchiolitis

Respiratory syncytial virus (RSV) bronchiolitis is a serious and distressing illness, which occurs almost exclusively in infants under one year of age. Although the majority of all children will have experienced an infection with RSV by the time they reach their second birthday, only a minority develop bronchiolitis. It is unclear why some otherwise healthy infants develop this severe illness and many studies have investigated whether or not this relates to an over-exuberant immunological response to the infection. It is increasingly being recognized that the innate immune response may play a key role.     

Cytokines in severe respiratory syncytial virus bronchiolitis

Bronchiolitis caused by respiratory syncytial virus (RSV) infection is an important cause of severe lung disease in infants, and increasing evidence suggests that it is immunologically mediated. Experiments in mice suggest that this may be due to differential T-cell activation producing either type 1 or type 2 cytokines. We investigated this hypothesis in man by studying 24 infants ventilated with severe RSV bronchiolitis and by measuring messenger RNA (mRNA) for interleukin-4 (IL-4) and interferon-gamma (IFN-gamma), by polymerase chain reaction, in nasopharyngeal aspirates (NPAs) and bronchoalveolar lavage (BAL) fluids. A semiquantitative assay was used to estimate concentrations of mRNA for these cytokines in comparison to mRNA of the constitutively expressed hypoxanthine guanine phosphoribosyl transferase gene. BAL from 18/24 infants showed polarization of cytokine production: 6 with only IFN-gamma mRNA, and 12 with only IL-4 mRNA. For the 6/24 infants in whom both IL-4 mRNA and IFN-gamma mRNA were detected in BAL fluid, each was present in low amounts, compared with those with mRNA for IL-4 or IFN-gamma alone. IL-4 and IFN-gamma mRNA were not detected in any of the NPAs.These findings provide the first direct evidence in infants that in RSV bronchiolitis there are divergent T-cell responses and suggest that more than one mechanism may be responsible for immune-mediated disease enhancement.     

Relationship between respiratory syncytial virus bronchiolitis and future obstructive airway diseases.

Evidence from a large number of prospective case-control studies shows that respiratory syncytial virus (RSV) bronchiolitis in infancy is often associated with recurrent wheezing and asthma during subsequent years. However, wheezing tends to diminish and most studies show no significant increase in wheezing compared to controls by school age or adolescence. An unresolved question is whether severe RSV infection during infancy causes the respiratory sequelae or inherent abnormalities predispose an infant to develop severe respiratory infection and sequelae, i.e. RSV is associated with the development of pulmonary sequelae. Studies on long-term outcome of RSV bronchiolitis are reviewed from an evidence-based perspective. The majority of prospective placebo-controlled studies do not show any long-term beneficial effects of corticosteroid treatment, i.e. the risk of subsequent wheezing is not diminished by the treatment. The evidence for an increased risk of allergic sensitization after RSV bronchiolitis is not nearly as strong as the evidence for an increased risk of subsequent wheezing. In fact, most studies do not show any significant increase in atopy after RSV bronchiolitis. This suggests that the increased risk of wheezing after RSV is not linked to an increased risk of atopy. There are some indications that infants who develop severe RSV and subsequent wheezing may have aberrations that predate the RSV infection. To decide whether respiratory syncytial virus bronchiolitis causes, or is associated with the respiratory sequelae (or with subsequent allergy), it will be necessary to conduct prospective, randomized studies, where the cytokine profile prior to bronchiolitis onset is known. Such studies should preferably include some form of intervention against respiratory syncytial virus. A more complete understanding of the risk factors for severe respiratory syncytial virus infection and the role of respiratory syncytial virus infection in the initiation of asthma is needed as a basis for large-scale and cost-effective programmes to prevent respiratory syncytial virus-related morbidity.     

Risk factors for hypoxemia and respiratory failure in respiratory syncytial virus bronchiolitis

Respiratory syncytial virus (RSV) bronchiolitis is a common infection in young children and may result in hospitalization. We examined the incidence of, and risk factors associated with, hypoxemia and respiratory failure in 216 children aged < 24 months admitted consecutively for proven RSV bronchiolitis. Hypoxemia was defined as SpO2 < 90% in room air and severe RSV bronchiolitis requiring intubation and ventilation was categorized as respiratory failure. Corrected age at admission was used for premature children (gestation < 37 weeks). Hypoxemia was suffered by 31 (14.3%) children. It was more likely to occur in children who were Malay (OR 2.56, 95%CI 1.05-6.23, p=0.03) or premature (OR 6.72, 95%CI 2.69-16.78, p<0.01). Hypoxemia was also more likely to develop in children with failure to thrive (OR 2.96, 95%CI 1.28-6.82, p<0.01). The seven (3.2%) children who were both premature (OR 11.94, 95%CI 2.50-56.99, p<0.01) and failure to thrive (OR 6.41, 95%CI 1.37-29.87, p=0.02) were more likely to develop respiratory failure. Prematurity was the only significant risk factor for hypoxemia and respiratory failure by logistic regression analysis (OR 1.17, 95%CI 1.06-1.55, p<0.01 and OR 1.14 95%CI 1.02-2.07, p=0.02 respectively). Prematurity was the single most important risk factor for both hypoxemia and respiratory failure in RSV bronchiolitis.     

Pro- and anti-inflammatory responses in respiratory syncytial virus bronchiolitis.

Respiratory syncytial virus (RSV) bronchiolitis is an important cause of severe respiratory disease in infants. This study aimed to characterise changes in pulmonary pro- and anti-inflammatory responses in infants with RSV bronchiolitis over the course of the illness. On the day of intubation (Day 1) and the day of extubation (Day X), nonbronchoscopic bronchoalveolar lavage was performed on term and preterm infants ventilated for RSV bronchiolitis and on control infants on Day 1. Tumour necrosis factor (TNF)-alpha, soluble TNF receptor (sTNFR) and interleukin (IL)-6 messenger ribonucleic acid (mRNA) and protein were measured. Twenty-four infants, born at term and 23 infants born preterm with RSV bronchiolitis and 10 controls were recruited. TNF-alpha and IL-6 mRNA and protein in infants with bronchiolitis were greater than the control group on Day 1. In preterm infants, who were ventilated for longer than term infants, TNF-alpha and IL-6 proteins decreased between Day 1 and Day X. Concentrations of sTNFRs differed between groups on Day 1, but levels did not change between Day 1 and Day X. Large amounts of tumour necrosis factor-alpha and interleukin-6 in the respiratory syncytial virus-infected lung suggest important roles for these cytokines in the pathogenesis of respiratory syncytial virus bronchiolitis. The decrease in tumour necrosis factor-alpha and interleukin-6 protein in preterm infants may reflect the prolonged clinical course seen in these infants.     

Recombinant human deoxyribonuclease in infants with respiratory syncytial virus bronchiolitis

BACKGROUND: Treatment of hospitalized infants with respiratory syncytial virus (RSV) bronchiolitis is mainly supportive. Bronchodilators and systemic steroids are often used but do not reduce the length of hospital stay. Because hypoxia and airways obstruction develop secondary to viscous mucus in infants with RSV bronchiolitis, and because free DNA is present in RSV mucus, we tested the efficacy of the mucolytic drug recombinant human deoxyribonuclease (rhDNase). METHODS: In a multicenter, randomized, double-blind, controlled clinical trial, 225 oxygen-dependent infants admitted to the hospital for RSV bronchiolitis were randomly assigned to receive 2.5 mg bid of nebulized rhDNase or placebo until discharge. The primary end point was length of hospital stay. Secondary end points were duration of supplemental oxygen, improvement in symptom score, and number of intensive care admissions. RESULTS: There were no significant differences between the groups with regard to the length of hospital stay (p = 0.19) or the duration of supplemental oxygen (p = 0.07). The ratio (rhDNase/placebo) of geometric means of length of stay was 1.12 (95% confidence interval, 0.96 to 1.33); for the duration of supplemental oxygen, the ratio was 1.28 (95% confidence interval, 0.97 to 1.68). There were no significant differences in the rate of improvement of the symptom score or in the number of intensive care admissions. CONCLUSIONS: Administration of rhDNase did not reduce the length of hospital stay or the duration of supplemental oxygen in oxygen-dependent infants with RSV bronchiolitis.     

Whole blood gene expression in infants with respiratory syncytial virus bronchiolitis

Background  

Respiratory syncytial virus (RSV) is a major cause of viral bronchiolitis in infants worldwide, and environmental, viral and host factors are all of importance for disease susceptibility and severity. To study the systemic host response to this disease we used the microarray technology to measure mRNA gene expression levels in whole blood of five male infants hospitalised with acute RSV, subtype B, bronchiolitis versus five one year old male controls exposed to RSV during infancy without bronchiolitis. The gene expression levels were further evaluated in a new experiment using quantitative real-time polymerase chain reaction (QRT-PCR) both in the five infants selected for microarray and in 13 other infants hospitalised with the same disease.     

白介素8、RANTES基因多态性与呼吸道合胞病毒毛细支气管炎

呼吸道合胞病毒(respiratory syncytial virus,RSV)感染2岁以下几乎所有的儿童,但只有少数发展为比较严重的毛细支气管炎及毛细支气管炎后反复喘息.随着对其遗传学研究的不断深入,通过对RSV毛细支气管炎患儿基因型的分析,发现白介素8、RANTES存在基因多态性,且可能与RSV毛细支气管炎及毛细支气管炎后反复喘息的易感性相关.     

Cord blood gene expression in infants hospitalized with respiratory syncytial virus bronchiolitis

BACKGROUND: Only a few infants develop acute bronchiolitis when exposed to respiratory syncytial virus (RSV), and host, environmental, and viral properties are probably all of importance in determining the severity of infection. METHODS: Microarray analysis was used to identify differentially expressed single genes and gene sets in cord blood from 5 infants hospitalized with RSV bronchiolitis versus cord blood from 5 control infants exposed to RSV without bronchiolitis during infancy. Quantitative real-time polymerase chain reaction (QRT-PCR) was performed on single genes in both the 5 infants selected for microarray analysis and 13 more infants hospitalized with the same disease. Gene set enrichment analysis (GSEA) was performed to identify differentially expressed gene sets within the microarray experiments. RESULTS: Microarray analysis identified 15 single genes to be significantly differentially expressed between case and control infants. Eleven of these genes were evaluated with QRT-PCR, and the genes FAM102A, TNFRSF25, and STMN3 were down-regulated in all but 1 of the 18 infants. A pathway involved in regulation of the actin cytoskeleton was found to be clearly down-regulated when analyzed with GSEA. CONCLUSIONS: FAM102A, TNFRSF25, and STMN3 and a pathway involved in regulation of the actin cytoskeleton are down-regulated in cord blood from infants hospitalized with RSV bronchiolitis.     

Impact of human metapneumovirus and respiratory syncytial virus co-infection in severe bronchiolitis

We have previously shown high rates of co-infection with Respiratory Syncytial Virus (RSV) and human Metapneumovirus (hMPV) in infants with severe bronchiolitis at our institution in 2000-2002, and that co-infection was associated with increased disease severity. In this study, we have attempted to identify differences in intubated infants with severe RSV infection with and without hMPV co-infection. Here we show that RSV+/hMPV+ were clinically symptomatic for longer than RSV+/hMPV- infants, but that no differences in airway total cell concentration, differential cell count or cytokine/chemokine concentrations were detectable.     

Peripheral blood cytokine responses and disease severity in respiratory syncytial virus bronchiolitis.

The role of cellular immunity in disease severity in respiratory syncytial virus (RSV) bronchiolitis is largely unknown. This study investigated the association between disease severity and systemic cytokine responses in hospitalized ventilated and nonventilated RSV bronchiolitis patients. In whole blood cultures stimulated with phytohaemagglutinin (PHA), lymphoproliferative responses and interferon (IFN)-gamma and interleukin (IL)-4 production during acute illness were measured. In addition, plasma cytokines were measured. Measurements were repeated in the convalescent phase, 3-4 weeks after admission. Fifty patients were included. The median age in ventilaled patients was significantly lower than in nonventilated patients (1 versus 4 months, p<0.05). In comparison with nonventilated patients, the ventilated patients had significantly lower lymphoproliferative responses and a lower production of IFN-gamma and IL-4. In fact, IFN-gamma and IL-4 production in ventilated patients was almost completely undetectable. Plasma IL-8 levels in ventilated patients were significantly higher than in nonventilated patients. In the convalescent phase, lymphoproliferative and cytokine responses as well as plasma IL-8 levels were normal in both patient groups. Since RSV bronchiolitis is associated with the subsequent development of asthma, the possible skewing of the T-helper (Th1/Th2) cytokine balance was investigated. This was found neither in the acute nor in the convalescent phase. In conclusion, the data indicate that depressed lymphocyte function and elevated plasma interleukin-8 levels are markers of severe disease. It is suggested that age and maturation related immune mechanisms could explain the occurrence of severe respiratory syncytial virus bronchiolitis requiring mechanical ventilation in young infants.     

Diaphragmatic flutter in three babies with bronchopulmonary dysplasia and respiratory syncytial virus bronchiolitis

Abnormalities of respiratory control, especially apnea, have been reported previously in infants with respiratory syncytial virus (RSV) infections. This is the first report of yet another abnormality of respiratory control, diaphragmatic flutter (DF), in infants with RSV infection. The presentation of these infants did not differ from the usual clinical presentation of RSV infection. While being monitored with respiratory inductive plethysmography for occurrences of apnea known to be common in RSV infection, DF was detected. This abnormality consisted of high frequency, diaphragmatic contractions which were intermittent in nature. They lasted no more than 4 days and were not associated with change in arterial oxygen saturation or heart rate. These infants were discharged free of DF and no further episodes have been observed over a 12-month period. © 1995 Wiley-Liss, Inc.     

Type 1 and type 2 cytokine imbalance in acute respiratory syncytial virus bronchiolitis

We examined the in vivo immune response of infants to natural respiratory syncytial virus (RSV) infection through analysis of cytokine levels in nasal lavage fluid and stimulated peripheral blood mononuclear cells. Eighty-eight babies with at least one parent with atopy and asthma were prospectively studied through their first winter. Twenty-eight infants had an upper respiratory tract infection where RSV was detected, of whom nine developed signs of acute bronchiolitis. Nasal lavage specimens were assayed for interferon-gamma, interleukin (IL)-4, IL-10, and IL-12 and the RSV load determined by quantitative polymerase chain reaction. Messenger RNA (mRNA) was extracted from stimulated peripheral blood mononuclear cells and interferon-gamma, IL-4, IL-12, and IL-18 mRNA levels determined by polymerase chain reaction. Cytokine profiles were analyzed in relation to clinical outcome. The IL-4/interferon-gamma ratio for infants with acute bronchiolitis was elevated in nasal lavage fluid on both Days 1-2 (p = 0.014) and Days 5-7 (p = 0.001) of the illness compared with infants with upper respiratory tract infection alone. Those with acute bronchiolitis demonstrated a higher IL-10/IL-12 ratio (p = 0.0015) on Days 1-2. IL-18 mRNA levels were reduced (p = 0.019) and the IL-4/interferon-gamma ratio elevated (p = 0.01) in stimulated peripheral blood mononuclear cells from infants with acute bronchiolitis. There was no difference in initial RSV load. These data strongly implicate excess type 2 and/or deficient type 1 immune responses in the pathogenesis of RSV bronchiolitis.