Community study of role of viral infections in exacerbations of asthma in 9-11 year old children

Respiratory infections and asthma

What we know: Respiratory viral infections caused by rhinoviruses, coronaviruses, influenza, parainfluenza and respiratory syncytial viruses (RSVs) are important triggers of asthma attacks. Mycoplasma and Chlamydia infections can also provoke asthma attacks, although less commonly. RSV infections probably do not cause asthma, but are potent triggers of wheezing, with the result that RSV infection often reveals underlying asthma in children. RSV infection does not cause atopy. Bacterial respiratory infections in infancy appear to protect against later atopy. What we need to know: Does RSV infection in infancy alter a child's T(H)1/T(H)2 responses to later infections with other respiratory pathogens? What are the mechanisms (immunological or mechanical) by which respiratory pathogens cause wheezing? What is the role of respiratory infections in exacerbations of asthma? Can epidemiology shed light on this? Do viruses such as RSV cause asthma or uncover underlying asthma? Do children respond differently to RSV than to other viruses? Does atopy affect those responses? Do bacterial respiratory infections truly protect against future atopy?

Effects of glutathione S-transferase P1, M1, and T1 on acute respiratory illness in school children

The relationships between glutathione S-transferase (GST) M1, GSTT1, and GSTP1 genotypes and acute respiratory illness were investigated in a cohort of fourth grade school children aged 9-11 years who resided in 12 southern California communities. We used respiratory illness-related absences as a measure of respiratory illness occurrence. We ascertained respiratory illness-related school absences using an active surveillance system from January 1996 through June 1996. Genotypes for GSTM1 (null versus present), GSTT1 (null versus present), and GSTP1 (Ile105Val) were determined using genomic DNA from buccal cell specimens. The effects of GST genotypes on respiratory illness were assessed using stratified absence incidence rates and Poisson regression models. GSTP1 genotype was associated with risk for respiratory illness severe enough to result in a school absence. Children who were homozygous for the Val105 variant allele had lower incidence rates of upper and lower respiratory illnesses than did children who were homozygous for the Val105 allele. Children inheriting at least one Val105 allele were protected from respiratory illnesses (relative risk, 0.80; 95% confidence interval, 0.65-0.99). GSTM1 and T1 genotypes were not associated with respiratory illness. We conclude that GSTP1 genotype influences the risk or severity of respiratory infections in school-aged children.

Effects of rhinovirus infection on histamine and cytokine production by cell lines from human mast cells and basophils

To understand the biochemical events that occur in the airways after rhinovirus (RV) infection, we developed for the first time a model in which the cell lines from human mast cells (HMC-1) and basophils (KU812) can be infected with RV14, a major group RV. Viral infection was confirmed by demonstrating that viral titers in culture supernatants, and RV RNA increased with time. RV14 infection alone and a combination of PMA plus calcium ionophore A23187, did not increase histamine production by these cells, although IgE plus anti-IgE increased the histamine production. However, histamine content in the supernatants increased in response to PMA plus A23187, or IgE plus anti-IgE after RV14 infection. PMA plus A23187 or IgE plus anti-IgE induced the production of IL-8 and GM-CSF in supernatants of HMC-1 cells and IL-4 and IL-6 in supernatants of KU812 cells. RV14 infection further increased the production of the cytokines, whereas RV14 infection alone did not alter the production of the cytokines by these cells. An Ab to ICAM-1 inhibited RV14 infection of the cells and decreased the production of cytokines and histamine after RV14 infection. RV14 infection enhanced the increases in intracellular calcium concentration and activation of NF-kappaB by PMA plus A23187 in the cells. These findings suggest that RV14 infection may prime the cytokine and histamine production from mast cells and basophils and may cause airway inflammation in asthma.

Review of the molecular and cellular mechanisms of action of glucocorticoids for use in asthma

Asthma is characterized by inflammation in the lung and glucocorticoids (GCs) are the most clinically effective treatment available. The success of chronic GC therapy for asthma stems largely from the ability of the GC-GC receptor (GR) complex to alter transcription of a wide array of molecules involved in the inflammatory process. Many of the adverse effects of elevated systemic GC levels have been reduced through the use of inhalation as a method of administration, as opposed to oral GC. GCs exert their effects by binding to the wild-type GR, GR(alpha). The GR(alpha) complex can directly or indirectly alter gene transcription by binding to specific DNA sites or by activating transcription factors. There is also evidence to support GR(alpha) involvement in post-translational activities. In the management of asthma, the GR(alpha) down-regulates proinflammatory mediators such as interleukin-(IL)-1, 3, and 5, and up-regulates anti-inflammatory mediators such as IkappaB [inhibitory molecule for nuclear factor kappaB1 IL-10, and 12. Newer GCs are being designed to increase potency and topical activity. Mometasone furoate (MF), has recently been developed for the treatment of asthma and inhibits key anti-inflammatory processes with a potency equal to or greater than that of fluticasone propionate. A better understanding of the molecular mechanisms involved might provide strategies for optimizing the effectiveness of GC in the treatment of asthma.

Synergism between rhinovirus infection and oxidant pollutant exposure enhances airway epithelial cell cytokine production

Of the several factors believed to exacerbate asthmatic symptoms, air pollution and viral infections are considered to be particularly important. Although evidence indicates that each of these respiratory insults individually can increase asthma severity in susceptible individuals, we know little about the extent to which exposure to environmental oxidant pollutants can influence the course of respiratory viral infection and its associated inflammation. To investigate the interaction of these two stimuli within their common epithelial cell targets in the upper and lower respiratory tracks, we infected primary human nasal epithelial cells and cells of the BEAS-2B line grown at the air-liquid interface with human rhinovirus type 16 (RV16) and exposed them to NO2 (2.0 ppm) or O3 (0.2 ppm) for 3 hr. Independently, RV16, NO2, and O3 rapidly increased release of the inflammatory cytokine interleukin-8 through oxidant-dependent mechanisms. The combined effect of RV16 and oxidant ranged from 42% to 250% greater than additive for NO2 and from 41% to 67% for O3. We abrogated these effects by treating the cells with the antioxidant N-acetylcysteine. Surface expression of intercellular adhesion molecule 1 (ICAM-1) underwent additive enhancement in response to combined stimulation. These data indicate that oxidant pollutants can amplify the generation of proinflammatory cytokines by RV16-infected cells and suggest that virus-induced inflammation in upper and lower airways may be exacerbated by concurrent exposure to ambient levels of oxidants commonly encountered the indoor and outdoor environments.

Air pollution and asthma among children in Seoul, Korea

BACKGROUND

As information about the health risks associated with air pollution has become available, attention has focused increasingly on susceptible persons such as children and persons with preexisting respiratory diseases, such as asthma.

METHODS

We investigated the association between outdoor air pollution and asthma attacks among children under 15 years of age in Seoul, Korea. We estimated the relative risks of hospitalization associated with an interquartile range (IQR) increase in pollutant concentrations and used time series analysis of the counts by means of the generalized additive Poisson model.

RESULTS

The estimated relative risk of hospitalization for asthma was 1.07 (95% confidence interval [CI] = 1.04-1.11) for particulate matters less than or equal to 10 microm in aerodynamic diameter (IQR = 40.4 microg/m3); 1.11 (95% CI = 1.06-1.17) for sulfur dioxide (IQR = 4.4 ppb); 1.15 (95% CI = 1.10-1.20) for nitrogen dioxide (IQR = 14.6 ppb); 1.12 (95% CI = 1.07-1.16) for ozone (IQR = 21.7 ppb); and 1.16 (95% CI = 1.10-1.22) for carbon monoxide (IQR = 1.0 ppm).

CONCLUSIONS

These findings support the hypothesis that air pollution at levels below the current standards of Korea is harmful to sensitive subjects such as asthmatic children.

Management of suspected acute viral upper respiratory tract infection in children with intranasal sodium cromoglicate: a randomised controlled trial

BACKGROUND

Upper respiratory tract infection in children is one of the most frequent reasons for visiting a family doctor, and antibiotics are often prescribed inappropriately. Sodium cromoglicate inhibits the ICAM-1 molecule, which is the receptor for human rhinoviruses. We aimed to investigate whether intranasal cromoglicate shortens duration of infection of the upper respiratory tract.

METHODS

We randomly assigned 290 children diagnosed with suspected acute viral upper respiratory tract infection by their family doctor (137 boys, 153 girls; mean age 5.2 years [SD 3.39]) either intranasal 4% sodium cromoglicate spray or intranasal normal saline spray. Follow-up was by daily symptom diary for 2 weeks and by telephone. Canadian Acute Respiratory Illness and Flu Scale (CARIFS) score was the primary outcome measure.

FINDINGS

195 patients returned symptom diaries, and 20 of these could not be included in the main analysis. 246 patients completed the telephone interview at week 1. There was no difference in recovery rate over the first week between the two groups, with the estimated difference in slope of log (CARIFS) being -0.01 (95% CI -0.05 to 0.03). There were no differences between the two groups in side-effects or re-consultation rates. 43 (17%) of 246 children with suspected acute viral upper respiratory tract infection went back to see their family doctor, and 220 (89%) of 246 were managed without prescription of antibiotics.

INTERPRETATION

Intranasal sodium cromoglicate is not a useful additional treatment for this infection. Our results further clarify the role of prescribed drugs for children with these frequent illnesses.

Protein kinase R regulates double-stranded RNA induction of TNF-alpha but not IL-1 beta mRNA in human epithelial cells

Epithelial cells represent the initial site of respiratory viral entry and the first line of defense against such infections. This early antiviral response is characterized by an increase in the production of proinflammatory cytokines such as TNF-alpha and IL-1 beta. dsRNA, which is a common factor present during the life cycle of both DNA and RNA viruses, is known to induce TNF-alpha and IL-1 beta in a variety of cells. In this work we provide data showing that dsRNA treatment induces TNF-alpha and IL-1 beta in human lung epithelial cells via two different mechanisms. Our data show that dsRNA activation of dsRNA-activated protein kinase (PKR) is associated with induction of TNF-alpha but not IL-1 beta expression. An inhibitor of PKR activation blocked the dsRNA-induced elevations in TNF-alpha but not IL-1 beta mRNA in epithelial cells. Data obtained from infection of epithelial cells with a vaccinia virus lacking the PKR inhibitory polypeptide, E3L, revealed that PKR activation was essential for TNF-alpha but not for IL-1 beta expression. In this report, we provide experimental support for the differential regulation of proinflammatory cytokine expression by dsRNA and viral infections in human airway epithelial cells.

Pathogenesis and management of virus infection-induced exacerbation of senile bronchial asthma and chronic pulmonary emphysema

The number of senile patients with therapy resistant bronchial asthma, chronic pulmonary emphysema increases due to the habit of smoking and increased number of older people, and these inflammatory pulmonary diseases are the leading causes of death worldwide. Rhinoviruses cause the majority of common colds, and provoke exacerbations of bronchial asthma and chronic pulmonary emphysema. Here, I review the pathogenesis and management of rhinovirus infection-induced exacerbation of senile bronchial asthma and chronic pulmonary emphysema.

Infections and asthma in children

The temporal association of acute asthma exacerbations in children with viral infections such as rhinovirus, respiratory syncytial virus, and parainfluenza has been known for many years. Recently, the contributions of infections to the pathophysiology of asthma have been expanded beyond disease exacerbation to include disease inception, chronicity, and even prevention. Respiratory syncytial virus has been implicated in asthma inception, while Chlamydia pneumoniae, Mycoplasma pneumoniae, and latent adenovirus infections have been correlated with asthma chronicity. Measles, hepatitis A, and tuberculosis have been associated with a decreased incidence of asthma, implying a contribution to disease prevention. The following review will briefly highlight the relationships between various microbial infections and the pathophysiology of asthma.

[The epidemiology of COPD and asthma exacerbations in a general hospital]

This retrospective study identified the clinical and epidemiological characteristics of patients coming to the emergency room of our hospital with exacerbated asthma or chronic obstructive pulmonary disease (COPD) in 1993 and 1994. We followed a previously established protocol to review the case histories of patients from both years. The 1,592 exacerbations we identified in 1,209 asthmatics accounted for 0.9% of all emergency visits, with a mean of 2.2 1.6 (0-9) visits daily. The 2,106 exacerbations of COPD in 1,208 patients accounted for 1.2% of all emergencies, with a mean 2.9 (1-12) visits per day. The mean age was 51.2 (14-93) years for asthmatics and 70.3 (29-96) years for COPD patients. Of asthmatics, 69.8% were women and 30.1% were men, whereas 91.4% of COPD patients were men. The readmission rate was 3.4% for asthmatics and 4.8% for COPD patients. The hospitalization rate was 26.7% for asthmatics and 49.4% for COPD exacerbation patients. The hospital saw 22.6% of asthma exacerbations between midnight and 8 a.m. and 41.6% of COPD exacerbations during the same time frame. For both diseases, more emergencies occurred in winter. Correlation between asthma and COPD and declared influenza cases in the community were r = 0.63 (p < 0.001) for asthma and r = 0.83 (p < 0.0001) for COPD. Our findings underline the considerable emergency care burden generated by exacerbations of obstructive airway diseases and suggest that community acquired respiratory infections are usually the underlying cause.

Suppression of airway hyperresponsiveness induced by ovalbumin sensitisation and RSV infection with Y-27632, a Rho kinase inhibitor

BACKGROUND

Smooth muscle contraction is one of the hallmarks of asthma. A recently developed pyridine derivative, Y-27632, a selective Rho kinase inhibitor, has been reported to inhibit the smooth muscle contraction of human and animal trachea in ex vivo systems but its effect in animal models of airway hyperresponsiveness (AHR) has not been examined. The purpose of this study was to evaluate the effect of Y-27632 in a murine model of allergic and virally induced AHR.

METHODS

Baseline lung resistance and methacholine induced AHR were measured in mice sensitised to ovalbumin (OVA) and also in mice infected with respiratory syncytial virus (RSV) following ovalbumin sensitisation (OVA/RSV).

RESULTS

Time course and dose ranging experiments indicated that 30 mg/kg Y-27632 given by gavage 2 hours before methacholine challenge significantly reduced baseline lung resistance and prevented AHR in OVA sensitised mice. Y-27632 also suppressed AHR induced by the bronchospastic agent serotonin in OVA sensitised mice and prevented methacholine induced AHR in OVA/RSV mice.

CONCLUSIONS

These results suggest that the signalling pathway mediated through Rho kinase may have an important role in bronchial smooth muscle tone in allergen induced and virus induced AHR and should be considered as a novel target for asthma treatment.

Exacerbations: etiology and pathophysiologic mechanisms

Some patients with COPD are prone to frequent exacerbations, which are an important determinant of health status. Such patients have elevated airway cytokine levels, suggesting the presence of increased inflammation that may increase their susceptibility to exacerbation. The inflammatory response during a COPD exacerbation is variable, but increases in interleukin-6 levels during the exacerbation are related to the presence of a common cold. Rhinovirus infection is the most important etiologic factor in COPD exacerbations and is an important target for preventive therapy. The reduction of COPD exacerbations will have an important impact on the considerable morbidity and mortality associated with COPD.

Coronavirus-related nosocomial viral respiratory infections in a neonatal and paediatric intensive care unit: a prospective study

The incidence of nosocomial viral respiratory infections (NVRI) in neonates and children hospitalized in paediatric and neonatal intensive care units (PNICU) is unknown. Human coronaviruses (HCoV) have been implicated in NVRI in hospitalized preterm neonates. The objectives of this study were to determine the incidence of HCoV-related NVRI in neonates and children hospitalized in a PNICU and the prevalence of viral respiratory tract infections in staff. All neonates (age< or =28 days) and children (age>28 days) hospitalized between November 1997 and April 1998 were included. Nasal samples were obtained by cytological brush at admission and weekly thereafter. Nasal samples were taken monthly from staff. Virological studies were performed, using indirect immunofluorescence, for HCoV strains 229E and OC43, respiratory syncytial virus (RSV), influenza virus types A and B, paramyxoviruses types 1, 2 and 3 and adenovirus. A total of 120 patients were enrolled (64 neonates and 56 children). Twenty-two samples from 20 patients were positive (incidence 16.7%). In neonates, seven positive samples, all for HCoV, were detected (incidence 11%). Risk factors for NVRI in neonates were: duration of hospitalization, antibiotic treatment and duration of parenteral nutrition (P<0.01). Monthly prevalence of viral infections in staff was between 0% and 10.5%, mainly with HCoV. In children, 15 samples were positive in 13 children at admission (seven RSV, five influenza and three adenovirus) but no NVRI were observed. In spite of a high rate of community-acquired infection in hospitalized children, the incidence of NVRI with common respiratory viruses appears low in neonates, HCoV being the most important pathogen of NRVI in neonates during this study period. Further research is needed to evaluate the long-term impact on pulmonary function.

Association of rhinovirus infection with increased disease severity in acute bronchiolitis

Respiratory syncytial virus (RSV) is the major pathogen responsible for acute bronchiolitis in infancy. However, evaluation of the relative importance of rhinovirus or multiple viral infections has been hampered by the lack of sensitive diagnostic methodologies. Therefore, in this study we used the reverse transcription-polymerase chain reaction for 11 respiratory pathogens to assess the etiology in infants with acute bronchiolitis and correlate it with clinical characteristics of the disease. Viruses were detected in 73.7% of patients. RSV was identified in 72.4% of virologically confirmed cases, rhinovirus in 29%, whereas multiple infections represented 19.5% of cases, most of which (69%) were combinations of rhinovirus with RSV. In a logistic regression model controlling for age, sex, birth weight, presence of fever, and day of disease on admission, the presence of rhinovirus was found to increase by approximately five-fold, the risk for severe disease. Multiple pathogens had a similar trend in the univariate analysis, which was eliminated in the multivariate model. Multiple virus cases were admitted to the hospital later in the course of their disease than unique pathogen cases, suggesting successive infections. In conclusion, rhinovirus is second only to RSV as a causative agent of bronchiolitis and is associated with more severe disease. The presence of more than one pathogen may influence the natural history of acute bronchiolitis.

Phylogenetic analysis of rhinovirus isolates collected during successive epidemic seasons

Human rhinoviruses (HRV) have been shown to be the major causative agent for mild respiratory infections, but also associated with more serious diseases, such as acute otitis media and pneumonia in children, and asthma. Despite the economical and medical importance of HRV, little is known about the circulation and genetic diversity of HRV during a given season. The aim of this study was to genetically characterize HRV strains causing acute respiratory infections in a cohort of small children during a 2 years follow-up time. Genetic relationships between 61 HRV field isolates were studied using partial genomic sequencing in the VP4/VP2 region (420 nt) and phylogenetic analysis of these sequences. Sequences from the clinical isolates clustered in the two previously known phylogenetic clades, the designated genetic group 2 (including HRV 14) being more predominant. The maximum genetic variation within group 1 was 32.3% and within group 2 it was 32.7%. Several distinct clusters could be observed, some of which were strictly seasonal, whereas some other variants were detected during several seasons. The results of this study show striking genetic diversity of the HRV strains circulating in a given community during a short time.

Rhinovirus respiratory infections and asthma

Viral infections, particularly respiratory illnesses caused by rhinovirus, are the most common cause of asthma exacerbations in children and contribute in large part to asthma morbidity in adults. Epidemiologic studies and increasingly sophisticated viral detection methodologies have helped to define the role of rhinovirus as a potential causative agent in asthma exacerbations. Rhinovirus-induced lung disease is multifaceted and can be characterized in terms of a variety of physiologic, immunologic, and viral processes. The precise direct and indirect mechanisms of viral contribution to exacerbations must still be elucidated. Understanding them will have an impact on the design of future treatment modalities.

Erythromycin inhibits rhinovirus infection in cultured human tracheal epithelial cells

To examine the effects of erythromycin on rhinovirus (RV) infection in airway epithelium, primary cultures of human tracheal epithelial cells were infected with the RV major subgroup, RV14, and the minor subgroup, RV2. Infection was confirmed by increases in viral RNA of the infected cells and viral titers of the supernatants. RV14 upregulated the expression of the mRNA and protein of intercellular adhesion molecule-1 (ICAM-1), the major RV receptor, and it increased the cytokine production. Erythromycin reduced the supernatant RV14 titers, RV14 RNA, the susceptibility to RV14 infection, and the production of ICAM-1 and cytokines. Erythromycin also reduced the supernatant RV2 titers, RV2 RNA, the susceptibility to RV2 infection, and cytokine production, although the inhibitory effects of erythromycin on the expression of the low-density lipoprotein receptor, the minor RV receptor, were small. Erythromycin reduced the nuclear factor-kappaB activation by RV14 and decreased the number of acidic endosomes in the epithelial cells. These results suggest that erythromycin inhibits infection by the major RV subgroup by reducing ICAM-1 and infection by both RV subgroups by blocking the RV RNA entry into the endosomes. Erythromycin may also modulate airway inflammation by reducing the production of proinflammatory cytokines and ICAM-1 induced by RV infection.

The Seattle-King County healthy homes project: implementation of a comprehensive approach to improving indoor environmental quality for low-income children with asthma

Pediatric asthma is a growing public health issue, disproportionately affecting low-income people and people of color. Exposure to indoor asthma triggers plays an important role in the development and exacerbation of asthma. We describe the implementation of the Seattle-King County Healthy Homes Project, a randomized, controlled trial of an outreach/education intervention to improve asthma-related health status by reducing exposure to allergens and irritants in the home. We randomly assigned 274 low-income children with asthma ages 4-12 to either a high- or a low-intensity group. In the high-intensity group, community health workers called Community Home Environmental Specialists (CHES) conducted initial home environmental assessments, provided individualized action plans, and made additional visits over a 12-month period to provide education and social support, encouragement of participant actions, provision of materials to reduce exposures (including bedding encasements), assistance with roach and rodent eradication, and advocacy for improved housing conditions. Members of the low-intensity group received the initial assessment, home action plan, limited education during the assessment visit, and bedding encasements. We describe the recruitment and training of CHES and challenges they faced and explain the assessment and exposure reduction protocols addressing dust mites, mold, tobacco smoke, pets, cockroaches, rodents, dust, moisture, and toxic or hazardous chemicals. We also discuss the gap between the practices recommended in the literature and what is feasible in the home. We accomplished home interventions and participants found the project very useful. The project was limited in resolving structural housing quality issues that contributed to exposure to indoor triggers.

Cough, airway inflammation, and mild asthma exacerbation

BACKGROUND

Prospective data on the temporal relation between cough, asthma symptoms, and airway inflammation in childhood asthma is unavailable.

AIMS AND METHODS

Using several clinical (diary, quality of life), lung function (FEV(1), FEV(1) variability, airway hyperresponsiveness), cough (diary, cough receptor sensitivity (CRS)), and inflammatory markers (sputum interleukin 8, eosinophilic cationic protein (ECP), myeloperoxidase; and serum ECP) of asthma severity, we prospectively described the course of these markers in children with asthma during a non-acute, acute, and resolution phase. A total of 21 children with asthma underwent these baseline tests; 11 were retested during days 1, 3, 7, and 28 of an exacerbation.

RESULTS

Asthma exacerbations were characterised by increased asthma and cough symptoms and eosinophilic inflammation. Sputum ECP showed the largest increase and peaked later than clinical scores. Asthma scores consistently related to cough score only early in the exacerbation. Neither CRS nor cough scores related to any inflammatory marker.

CONCLUSION

In mild asthma exacerbations, eosinophilic inflammation is dominant. In asthmatic children who cough as a dominant symptom, cough heralds the onset of an exacerbation and increased eosinophilic inflammation, but cough scores and CRS do not reflect eosinophilic airway inflammation.

A defective type 1 response to rhinovirus in atopic asthma

BACKGROUND

Rhinoviruses (RVs) are the most frequent precipitants of the common cold and asthma exacerbations, but little is known about the immune response to these viruses and its potential implications in the pathogenesis of asthma.

METHODS

Peripheral blood mononuclear cells (PBMC) from patients with atopic asthma and normal subjects were exposed to live or inactivated RV preparations. Levels of interferon (IFN)gamma and interleukins IL-12, IL-10, IL-4, IL-5 and IL-13 were evaluated in the culture supernatants with specific immunoassays.

RESULTS

Exposure of PBMC to RVs induced the production of IFNgamma, IL-12, IL-10, and IL-13. Cells from asthmatic subjects produced significantly lower levels of IFNgamma and IL-12 and higher levels of IL-10 than normal subjects. IL-4 was induced only in the asthmatic group, while the IFNgamma/IL-4 ratio was more than three times lower in the asthmatic group.

CONCLUSIONS

This evidence suggests that the immune response to RVs is not uniquely of a type 1 phenotype, as previously suggested. The type 1 response is defective in atopic asthmatic individuals, with a shift towards a type 2 phenotype in a way similar, but not identical, to their aberrant response to allergens. A defective type 1 immune response to RVs may be implicated in the pathogenesis of virus induced exacerbations of asthma.

Double-stranded RNA causes airway hyperreactivity and neuronal M2 muscarinic receptor dysfunction

Viral infection causes dysfunction of inhibitory M2 muscarinic receptors (M2Rs) on parasympathetic nerves, leading to airway hyperreactivity. The mechanisms of M2R dysfunction are incompletely understood. Double-stranded RNA (dsRNA), a product of viral replication, promotes the expression of interferons. Interferon-gamma decreases M2R gene expression in cultured airway parasympathetic neurons. In this study, guinea pigs were treated with dsRNA (1 mg/kg ip) on 2 consecutive days. Twenty-four hours later, anesthetized guinea pigs had dysfunctional M2Rs and were hyperresponsive to electrical stimulation of the vagus nerves, in the absence of inflammation. DsRNA did not affect either cholinesterase or the function of postjunctional M3 muscarinic receptors on smooth muscle. M2Rs on the nerves supplying the heart were also dysfunctional, but M2Rs on the heart muscle itself functioned normally. Thus dsRNA causes increased bronchoconstriction and bradycardia via increased release of ACh from the vagus nerves because of loss of M2R function on parasympathetic nerves in the lungs and heart. Production of dsRNA may be a mechanism by which viruses cause dysfunction of neuronal M2Rs and airway hyperreactivity.

Rhinovirus-induced alterations on peripheral blood mononuclear cell phenotype and costimulatory molecule expression in normal and atopic asthmatic subjects

BACKGROUND

Rhinovirus (RV) infection is the commonest trigger of acute asthma exacerbations; however, the immune response to these viruses and any potential implications in the mechanisms leading to asthma exacerbations are not well understood.

OBJECTIVE

To assess the effects of in vitro RV infection on the phenotype and expression of costimulatory molecules on peripheral blood mononuclear cells (PBMC) from normal and atopic asthmatic subjects, as a model for RV antigen presentation.

METHODS

PBMC from seven normal and seven asthmatic subjects were exposed to one infectious unit/cell of RV16 for 48 h. Surface expression of CD25, CD28, CD40, CD54, CD80, CD86 and CTLA-4 was evaluated on CD3, CD4, CD8, CD14 and CD19 PBMC subpopulations by three-colour flow cytometry.

RESULTS

No changes in the percentage of CD3, CD4, CD8 or CD19 were observed. CD14 was significantly reduced by the infection and this was more pronounced in normal subjects. On Th cells CTLA-4 was increased after RV infection only in the asthmatic group. Levels of CD80 and CD86 in the control cultures were lower in the asthmatic group. RV infection induced a significant increase of CD80 on monocytes and of CD86 on B cells, which occurred in both groups but were less marked in atopic asthmatic subjects.

CONCLUSION

Exposure of PBMC to RV is able to activate the antigen presentation machinery. Differences between normal and atopic asthmatic individuals are compatible with the hypothesis that an aberrant immune response to RV may be involved in the development of acute exacerbations in atopic asthmatic subjects.

Synergism between allergens and viruses and risk of hospital admission with asthma: case-control study

OBJECTIVE

To investigate the importance of sensitisation and exposure to allergens and viral infection in precipitating acute asthma in adults resulting in admission to hospital.

DESIGN

Case-control study.

SETTING

Large district general hospital.

PARTICIPANTS

60 patients aged 17-50 admitted to hospital over a year with acute asthma, matched with two controls: patients with stable asthma recruited from the outpatient department and patients admitted to hospital with non-respiratory conditions (inpatient controls).

MAIN OUTCOME MEASURES

Atopic status (skin testing and total and specific IgE), presence of common respiratory viruses and atypical bacteria (polymerase chain reaction), dust samples from homes, and exposure to allergens (enzyme linked immunosorbent assay (ELISA): Der p 1, Fel d 1, Can f 1, and Bla g 2).

RESULTS

Viruses were detected in 31 of 177 patients. The difference in the frequency of viruses detected between the groups was significant (admitted with asthma 26%, stable asthma 18%, inpatient controls 9%; P=0.04). A significantly higher proportion of patients admitted with asthma (66%) were sensitised and exposed to either mite, cat, or dog allergen than patients with stable asthma (37%) and inpatient controls (15%; P<0.001). Being sensitised and exposed to allergens was an independent associate of the group admitted to hospital (odds ratio 2.3, 95% confidence interval 1.0 to 5.4; P=0.05), whereas the combination of sensitisation, high exposure to one or more allergens, and viral detection considerably increased the risk of being admitted with asthma (8.4, 2.1 to 32.8; P=0.002).

CONCLUSIONS

Allergens and viruses may act together to exacerbate asthma.

The failure of interleukin-10-deficient mice to develop airway hyperresponsiveness is overcome by respiratory syncytial virus infection in allergen-sensitized/challenged mice

Interleukin-10-deficient mice develop a robust pulmonary inflammatory response but no airway hyperresponsiveness (AHR) to inhaled methacholine (MCh) following allergen sensitization and challenge. In the present study, we investigated the effect of respiratory syncytial virus (RSV) infection on AHR and pulmonary inflammation in allergic IL-10-/- mice. Unlike littermate control mice, RSV-infected or ovalbumin (OVA)-sensitized/challenged IL-10-/- mice failed to develop significant AHR. In contrast, sensitized/challenged IL-10-/- mice infected with RSV did develop AHR accompanied by increased eosinophil numbers, both in bronchoalveolar lavage (BAL) and pulmonary tissue, and mucin production in airway epithelium. The cytokine profile in OVA-sensitized/challenged IL-10-/- mice was skewed toward a Th1 response but after RSV infection, this response was more of a Th2 type, with increased IL-5 levels in the BAL. Studies with an RSV mutant that lacks the G and SH genes showed equal enhancement of the AHR response as the parental wild-type strain, indicating that G protein is not essential to this response. These data suggest that RSV infection can overcome the failure of development of AHR in allergic IL-10-/- mice.

Frequency, severity, and duration of rhinovirus infections in asthmatic and non-asthmatic individuals: a longitudinal cohort study

BACKGROUND

Rhinovirus infections cause exacerbations of asthma. We postulated that people with asthma are more susceptible to rhinovirus infection than people without the disease and compared the susceptibility of these groups.

METHODS

We recruited 76 cohabiting couples. One person in every couple had atopic asthma and one was healthy. Participants completed daily diary cards of upper-respiratory-tract (URT) and lower-respiratory-tract (LRT) symptoms and measured peak expiratory flow twice daily. Every 2 weeks nasal aspirates were taken and examined for rhinovirus. Mixed models were used to compare risks of infection between groups. We also compared the severity and duration of infections.

FINDINGS

We analysed 753 samples. Rhinovirus was detected in 10.1% (38/378) of samples from participants with asthma and 8.5% (32/375) of samples from healthy participants. After adjustment for confounding factors, asthma did not significantly increase risk of infection (odds ratio 1.15, 95% CI 0.71-1.87). Groups did not differ in frequency, severity, or duration of URT infections or symptoms associated with rhinovirus infection. First rhinovirus infection was associated more frequently with LRT infection in participants with asthma than in healthy individuals (12 of 28 infections vs four of 23, respectively, p=0.051). Symptoms of LRT associated with rhinovirus infection were significantly more severe (p=0.001) and longer-lasting in participants with asthma than in healthy participants (p=0.005).

INTERPRETATION

People with atopic asthma are not at greater risk of rhinovirus infection than healthy individuals but suffer from more frequent LRT infections and have more severe and longer-lasting LRT symptoms.

Comparison of three methods for respiratory virus detection between induced sputum and nasopharyngeal aspirate specimens in acute asthma

Viral respiratory tract infections are associated frequently with acute exacerbations of asthma. Nasopharyngeal aspirates and bronchoalveolar lavage specimens are used extensively for detecting viral respiratory tract infections, but not sputum. The aim of the study was to determine the efficiency of viral detection in induced sputum versus nasopharyngeal aspirate obtained during acute exacerbations of asthma, comparing three laboratory methods of viral diagnosis. Paired samples of induced sputum and nasopharyngeal aspirate obtained from 32 adults admitted to hospital with acute asthma were subjected to reverse transcription-polymerase chain reaction (RT-PCR), viral culture, and immunofluorescence assay. The results show that RT-PCR was associated with significantly higher rates of viral detection than culture (P=0.005) or immunofluorescence (P=0.001), without significant differences in the rates of viral detection between induced sputum and nasopharyngeal aspirate. It is concluded that induced sputum specimens are feasible for detection of viral respiratory tract infections by RT-PCR during acute exacerbations of asthma.

Altered eosinophil levels as a result of viral infection in asthma exacerbation in childhood

Respiratory viral infection is known to be a significant cause of asthma exacerbation. Eosinophils have been considered to play an important role in the pathogenesis of virus-induced asthma exacerbations. To determine how often asthma exacerbation is caused by virus infections and to examine the relationship between eosinophilia and asthma episode, we investigated 64 children who experienced asthma attacks between October 1999 and March 2000. We used rapid enzyme immunoassays to detect antigens of respiratory syncytial virus (RSV), influenza A virus, and adenovirus in nasopharyngeal secretions (NPS) of these children, and enumerated eosinophils in the blood and NPS. We detected RSV in 27% and influenza A virus in 17% of the patients. No adenovirus infection or RSV/influenza A co-infection was detected. RSV-infected children were younger (3.85 +/- 0.83 years old) than influenza A virus-infected patients (5.23 +/- 1.34 years old). Eighty-two per cent of patients in the RSV group and 36% of patients in the influenza A virus group had moderate-to-severe asthma episodes (p < 0.05). In RSV-infected children, the eosinophil counts in NPS were higher in the 'severe' group, and younger patients had a greater number of eosinophils in their NPS than older patients (p < 0.05). These trends were not found in influenza A virus patients. In conclusion, our results indicate that, compared with influenza A virus-induced asthma attacks, RSV infection had a higher probability of being associated with asthma exacerbation in infants and younger children and induced attacks of greater severity. The increase in the number of eosinophils in the NPS of RSV-infected children may be responsible, in part, for these differences.

Genetic clustering of all 102 human rhinovirus prototype strains: serotype 87 is close to human enterovirus 70

Human rhinoviruses (HRV), common agents of respiratory infections, comprise 102 designated serotypes. The genetic relationships of HRV prototype strains and the possibility of using genetic identification of a given HRV field strain were studied. Genomic sequences in the VP4/VP2 region were obtained from all 102 prototype strains. Phylogenetic analysis included 61 recently isolated Finnish field strains. Seventy-six out of the 102 prototype strains clustered in the HRV genetic group A and 25 in group B. Serotype 87 clustered separately and together with human enterovirus 70. The 'percentage' interserotypic differences were generally similar to those between different enterovirus serotypes, but for six pairs of HRV serotypes they were less than 10%. The maximum variation in genetic group A was 41% at the nucleotide level and 28% at the amino acid level, and in genetic group B 34% and 20%, respectively. Judging from the observed interserotypic differences, the 61 Finnish field isolates might represent as many as 19 different serotypes. One cluster of the field strains did not directly associate with any of the prototype strains and might represent a new serotype. However, larger numbers of field isolates of known serotype need to be characterized, possibly also in the VP1 region, to evaluate the feasibility of genetic typing of HRV strains.

Role of picornaviruses in flu-like illnesses of adults enrolled in an oseltamivir treatment study who had no evidence of influenza virus infection

The primary objective of this study was to determine the role of picornavirus in flu-like episodes (temperature of > or =38.0 degrees C plus one respiratory and one constitutional symptom) among otherwise healthy adults enrolled in a placebo-controlled, double-blind, randomized oseltamivir treatment study. Combined nasal and pharyngeal swabs were collected at baseline for influenza cultures and picornavirus reverse transcription (RT)-PCR. In addition, acute- and convalescent-serum samples were obtained for serological studies of common respiratory pathogens. From a total of 719 subjects enrolled in the clinical trial within 36 h of the onset of symptoms, 475 (66%) had evidence of recent influenza A or B virus infections by means of culture and/or serological testing. Of the 244 remaining patients, 36 (15%) presented a seroconversion for at least one of the common respiratory viruses or atypical pathogens. An RT-PCR assay for the picornavirus 5" noncoding region (NCR) was positive in a subset of 15 (19%) of 78 patients with flu-like illnesses of undetermined etiology. Sequence analysis of the picornavirus 5" NCR amplicons revealed that 14 (93%) of them had greater homology to rhinoviruses, whereas 1 (7%) was related to enteroviruses. Interestingly, median total symptom scores and oral temperatures of picornavirus-positive patients (n = 15) and placebo-treated influenza virus-positive patients (n = 161) were similar over a 3-week period. We conclude that, among the influenza virus-negative preselected cases of this study, rhinoviruses were relatively frequent pathogens associated with important respiratory and systemic symptoms.

Treatment of picornavirus infections

The picornaviruses are a diverse group of viral pathogens that together comprise the most common causes of infections of humans in the developed world. Within the picornavirus family are three well-known groups of human pathogens-the enteroviruses (including polioviruses, coxsackieviruses, and echoviruses), the rhinoviruses, and the hepatoviruses (including hepatitis A). Recently, the parechoviruses (formerly, echoviruses 22 and 23) have been classified as a fourth genus of human picornaviruses. This article will focus on the enteroviruses and rhinoviruses agents, for which substantial effort has been expended and recent successes reported towards the development of safe and effective antiviral therapy.

Pneumonia due to viral and atypical organisms and their sequelae

Most children presenting with pneumonia in the industrialised world will have a viral or 'atypical' organism. The clinical features of these 'atypical' pneumonias may be indistinguishable from bacterial pneumonia. New diagnostic techniques such as the polymerase chain reaction may help in diagnosis and choice of treatment, where appropriate. The pathological and clinical features of infection with each agent are discussed, together with their sequelae.

Relationship of viral infections to wheezing illnesses and asthma

Viral infections can influence both the development and the severity of asthma. In early life, viral infections can either increase or, remarkably, decrease the risk of subsequent asthma. In children and adults with existing asthma, viral respiratory infections frequently cause acute airway obstruction and wheezing. This article discusses the influence of viral infections on mechanisms of virus-induced airway inflammation in relationship to the development, persistence and severity of asthma.

The childhood origins of asthma (COAST) study

Although asthma is probably a heterogeneous disease or syndrome, three factors and/or events consistently emerge for their ability to significantly influence asthma inception in the first decade of life: immune response aberrations, which appear to be defined best by the concept of cytokine dysregulation; lower respiratory tract infections, in particular respiratory syncytial virus (RSV); and some form of gene-environment interaction that needs to occur at a critical time-period in the development of the immune system or the lung. It remains to be firmly established, however, how any one or all of these factors, either independently or interactively, influence the development of childhood asthma. For example, cytokine dysregulation (T helper 1/T helper 2 imbalance) appears to track best epidemiologically with allergic diseases. As not everyone who undergoes allergic sensitization develops asthma, some other host-environment interaction must need to occur to target this chronic allergic inflammatory response to the lower airway. Some evidence suggests that this event might be an environmental insult in the form of a virus infection, particularly with RSV, which has a predilection for infecting, destroying, and/or in some way biologically altering lower airway epithelium. However, only a fraction of children develop recurrent wheezing following RSV infections, despite the fact that nearly all children have been infected at least once by 2 years of age. Thus, although RSV infections may have the potential of targeting the inflammatory response to the lower airway, they may only be able to do so during a vulnerable time-period during development of the immune system or lung. This developmental component may further reflect important gene-environment interactions that regulate both short- and long-term airway physiological alterations that manifest themselves clinically as childhood asthma. Efforts to determine and define the importance of these three factors to asthma pathogenesis are the focus and goal of the COAST (Childhood Origins of Asthma) project.

Infections

Infection, in particular by respiratory viruses, plays an important role in triggering exacerbations and has also been implicated in the etiology of asthma and chronic obstructive pulmonary disease (COPD). This chapter reviews the epidemiological evidence that implicates infectious pathogens as triggers. The chapter also discusses the mechanisms of interaction between the host-pathogen response and preexisting airway pathology resulting in an exacerbation. Much of the treatment of infective exacerbations for both asthma and COPD is symptomatic, consisting of bronchodilators or supportive in the form of oxygen, and in severe cases it includes noninvasive or invasive ventilatory measures. The current therapy for virus-induced exacerbations of asthma and COPD relies on increased treatment of preexisting disease. Antibiotics are indicated for bacterial infections. The effective use of antiviral agents, particularly for influenza viruses, requires viral diagnosis, commencement of treatment early in the course of an exacerbation, or the targeting of high-risk groups for prophylaxis. Alternative strategies for drug development involve the identification of key factors common to exacerbations induced by a range of different viruses. Increased knowledge of the host–virus interaction can help in designing treatments that can increase virus clearance and minimize immunopathology.

Viruses in asthma

Current evidence suggests that the overall load of infectious agents, including respiratory viruses, encountered early in life is an important factor influencing maturation of the immune system from a type 2 bias at birth towards predominantly type 1 responses, thus avoiding atopic diseases. The 'hygiene hypothesis' proposes that the relatively sterile environment present in industrialised Western countries has contributed to the recent epidemic of asthma and atopy. Whether specific infections are of greater or lesser protective value is an important question if strategies are to be derived to mimic the beneficial effects of childhood infection whilst avoiding morbidity and potential mortality of the natural pathogens. Infection by respiratory viruses is a major trigger of wheezing in infants and of exacerbations of asthma in older children. Viruses are detected in up to 85% of such episodes. Rhinovirus is common in all age groups; respiratory syncytial virus (RSV) is most important in infants and young children. Knowledge of the immunopathogenetic mechanisms of virus infection in the asthmatic airway will lead to the development of new treatments for virus-induced asthma.

Safety and tolerability of cold-adapted influenza virus vaccine in children and adolescents with asthma

BACKGROUND

Influenza infections can cause severe respiratory disease in high risk persons such as those with asthma, but immunization rates for high risk groups remain suboptimal. An investigational influenza virus vaccine, trivalent, types A and B, live, cold-adapted (CAIV-T) administered by intranasal spray was shown previously to be effective in healthy adults and healthy children.

PURPOSE

To assess the safety and tolerability of CAIV-T in subjects 9 years of age and older with moderate to severe asthma.

METHODS

In this randomized, double blind, placebo-controlled study, spirometry was performed twice before vaccination to establish a baseline forced expiratory volume at 1 s (FEV1) and once 2 to 5 days thereafter. The primary outcome index was the percent change in percent predicted FEV1 before and after vaccination. Peak flows, clinical asthma symptom scores and nighttime awakening scores were measured daily from 7 days pre- to 28 days postvaccination.

RESULTS

The primary outcome index (percentage change in percent predicted FEV1) was not different between the two groups (0.2% vs. 0.4% for the treatment and placebo groups, respectively; P = 0.78). Secondary outcomes did not differ between the two groups; these included the number of subjects with a decrease in FEV1 > or =15% from baseline, reductions in peak flows > or =15%, > or =30% or > or =2 sd below baseline, use of beta-adrenergic rescue medications, asthma exacerbations and clinical asthma symptom scores before and after vaccination. The same proportion of subjects in each group experienced postvaccination symptoms within 10 days (92% and 91%, respectively; P = 1.0). No serious adverse event occurred.

CONCLUSION

CAIV-T was generally safe and well-tolerated in children and adolescents with moderate to severe asthma.

Acute Exacerbations of COPD

This chapter explains the exacerbations of chronic obstructive pulmonary disease (COPD) and its causes, mechanisms, and treatment approaches. COPD exacerbations are an important cause of the significant morbidity and mortality related to COPD. These COPD exacerbations increase with severity of the disease, and frequent exacerbations impact the patient's quality of life and activities of daily living. These exacerbations are also associated with considerable physiological deterioration and increased airway inflammatory changes caused by a variety of factors such as viruses, bacteria, and some common pollutants. Exacerbation of COPD results in an increase in airflow obstruction, which further increases the load on the respiratory muscles and increases the effort in breathing, thereby leading to respiratory failure in severe cases. Treatment approaches include the use of corticosteroids, antibiotics, inhaled bronchodilator therapy in certain cases, and ventilatory support. Increased patient education about detecting and treating exacerbations early in the natural history of COPD can be significantly beneficial. Following an exacerbation, the patient's condition should be constantly reviewed, giving attention to risk factors and compliance with therapy.

[Viral identification, and during asthma exacerbation: comparative epidemiology between infants and children.]

Objectifs. – L’utilisation des nouvelles techniques d’identification par les méthodes moléculaires apporte de nouvelles données épidémiologiques.

Patients et méthodes. – Cent dix-huit aspirations nasales pratiquées chez des enfants hospitalisés pour une exacerbation aiguë d’asthme ont été colligées. Les techniques conventionnelles ont associé la culture virale et l’immunofluorescence et les techniques moléculaires une polymerase chain reaction (PCR).

Résultats. – L’utilisation des techniques conventionnelles a mis en évidence un virus dans 34 % des prélèvements respiratoires (40 cas sur 118), tandis que l’étude par PCR permet une identification positive sur 68 % des prélèvements (80 cas sur 118) et l’association des deux méthodes amène la positivité à 77 % (91 cas sur 118). Les co-infections ont concerné 23 % des prélèvements positifs. L’identification virale par les outils traditionnels est significativement plus fréquente chez les jeunes asthmatiques, ainsi que lors de l’utilisation des outils de biologie moléculaire de façon non significative. L’épidémiologie comparative retrouve la prépondérance dans les deux groupes d’âge du rhinovirus (45 %), puis du virus respiratoire syncytial (28 %) et de l’entérovirus (8,5 %). Chez les enfants âgés de moins de deux ans, rhinovirus et virus respiratoire syncytial ont une prévalence proche (42 et 36 % respectivement) sensiblement différente de celle des enfants âgés de plus de deux ans (66 et 27 % respectivement). L’identification par PCR de Chlamydia pneumoniae et de Mycoplasma pneumoniae reste rare (six cas sur 118 prélèvements).

Conclusion. – La prééminence du rhinovirus et du virus respiratoire syncytial est retrouvée lors des exacerbations d’asthme chez le nourrisson tandis que C. pneumoniae et M. pneumoniae ne semblent pas particulièrement impliqués. L’identification est plus forte chez les jeunes asthmatiques avec probablement une charge virale plus importante, car la positivité de la culture virale est plus fréquente chez les enfants âgés de moins de deux ans.

Management of influenza in patients with asthma or chronic obstructive pulmonary disease

OBJECTIVE

To review the prevention and treatment of influenza in patients with asthma and/or chronic obstructive pulmonary disease (COPD).

DATA SOURCES

Computer-assisted MEDLINE searches for article and manual searches of conference proceedings on influenza, influenza vaccination, rimantadine, amantadine, oseltamivir, zanamivir, asthma, and/or COPD.

STUDY SELECTION

Published articles and pertinent conference abstracts in the areas mentioned in Data sources were selected. Articles included for review were studies conducted on humans.

RESULTS

Annual vaccination against influenza is the currently accepted practice for influenza management in patients with asthma and/or COPD. However, despite the availability and use of vaccination, influenza continues to cause serious morbidity and increased mortality. The management of influenza in at-risk patients with the older antivirals such as amantadine or rimantadine has not been widely accepted because of the rapid emergence of resistant variants, their lack of effect against influenza B, and poor adverse event profile. A new class of influenza antivirals, the neuraminidase inhibitors, has recently become available for the management of influenza. The currently marketed neuraminidase inhibitors are zanamivir and oseltamivir. Clinical studies have shown that these neuraminidase inhibitors are effective for the treatment and chemoprophylaxis of influenza A and B.

CONCLUSIONS

Vaccination against influenza remains the gold standard for the prevention of influenza in patients with asthma and/or COPD. The neuraminidase inhibitors zanamivir and oseltamivir are useful adjuncts to influenza vaccines for the management of influenza in these patients who are at high-risk of developing influenza related complications.

Analysis of sputum taken from wheezy and asthmatic infants and children, with special reference to respiratory infections

Children who are destined to develop asthma are considered to be susceptible to a variety of respiratory pathogens. To elucidate respiratory inflammation among these children, we measured the levels of eosinophil cationic protein (ECP) and tryptase in sputum taken from three different groups of wheezy infants and young children: those with a first wheeze (n = 15); those with recurrent wheeze (n = 27); and those with recurrent wheeze with respiratory distress, namely asthma (n = 56). The numbers of eosinophils or metachromatic cells determined by microscopic analysis of sputum samples were also evaluated in combination with the ECP and tryptase levels. Although neither sputum ECP nor tryptase was a clear discriminative marker that differentiated the three different types of wheezy disease, ECP levels in sputum from the asthma group were significantly higher (2,269.2 +/- 6,216.8 ng/g) than those in the recurrent wheezy group (440.3 +/- 1,199.8 ng/g) or in the first-wheeze group (209.0 +/- 172.9 ng/g). A similar trend was observed with tryptase levels in sputum, but there were no significant differences among the three groups. Sputum taken from asthmatic children showed a marked accumulation of eosinophils. However, an accumulation of eosinophils in sputum (even in the presence of an elevated level of sputum ECP) was not identified in the asthmatic infants < 1 year of age. An accumlation of eosinophils in sputum was not evident until children became > 1 year old and thereafter the eosinophils rapidly increased in number until the children reached 5 years of age. It was noteworthy that sputa positive for pathogenic bacteria, taken from the 1- and 2-year-old asthmatic infants, had a tendency to show high levels of ECP but a reduced number of eosinophils. Along with the wheezy episodes induced by viral infection, primarily and occasionally in combination with secondary bacterial infection, eosinophil activation and infiltration may develop. These predestined immune reactions to various pathogens might be associated with triggering the onset of asthma.

February asthma outbreaks in NSW: a case control study

OBJECTIVES

To investigate individual factors associated with an asthma outbreak among children aged one to 14 years in Sydney in February 1999.

METHODS

A case control study was undertaken with cases (n=92) defined as all children admitted to Sydney Children's Hospital for asthma in February 1999. Unmatched controls (n=76) were all children admitted for asthma in the previous three months. We obtained information by a structured telephone survey of parents. Logistic regression analyses were used to determine odds ratios for risk factors for hospital admission.

RESULTS

Mean age for hospital admission of 4.7 years for cases and 4.4 years for controls. The presence of one or more siblings reduced the risk of admission during an asthma outbreak (OR=0.59, 95% CI 0.37 to 0.93). Children with older siblings aged 10 to 14 years were also less likely to be admitted (OR=0.3, 95% CI 0.12 to 0.74). An age effect was observed. Other demographic, clinical and environmental characteristics, including smoking, were not associated with admission during the outbreak.

CONCLUSIONS

The main findings of this study are the protective effect of siblings and an age-dependent effect in risk of hospital admission during an asthma outbreak. These findings are consistent with an infective cause of the outbreak.

IMPLICATIONS

Children without siblings, particularly older siblings, appear to be at highest risk of hospital admission during an asthma outbreak. Environmental and other factors need to be examined to further explain the episodicity of such outbreaks and to determine means of predicting and preventing future episodes.

Autocrine regulation of asthmatic airway inflammation: role of airway smooth muscle

Chronic airway inflammation is one of the main features of asthma. Release of mediators from infiltrating inflammatory cells in the airway mucosa has been proposed to contribute directly or indirectly to changes in airway structure and function. The airway smooth muscle, which has been regarded as a contractile component of the airways responding to various mediators and neurotransmitters, has recently been recognised as a rich source of pro-inflammatory cytokines, chemokines and growth factors. In this review, we discuss the role of airway smooth muscle cells in the regulation and perpetuation of airway inflammation that contribute to the pathogenesis of asthma.

Role of latent viral infections in chronic obstructive pulmonary disease and asthma

Acute viral respiratory tract infections are well known to precipitate asthma attacks and acute exacerbations of chronic obstructive pulmonary disease, but their role in the pathogenesis of chronic disease is poorly defined. Double-stranded DNA viruses have the ability to persist in airway epithelial cells long after the acute infection has cleared. During these latent infections, viral genes are expressed at the protein level without replication of a complete virus. The expression of the adenoviral trans-activating protein has been demonstrated in the airway epithelium of both human and animal lungs and is associated with an amplification of the cigarette smoke-induced inflammatory response. Studies of cultured human airway epithelial cells have also shown that transfection with this viral gene upregulates the expression of intercellular adhesion molecule 1 and interleukin 8 by these cells when they are challenged with endotoxin. In guinea pigs, cigarette smoke-induced emphysema is amplified by latent adenoviral infection. Furthermore, this infection independently increased the number of CD-8 cells, whereas the cigarette smoke independently increased the number of CD-4 cells in the inflammatory infiltrate. On the other hand, allergen-induced lung inflammation was uninfluenced by latent adenoviral infection in the guinea pig, but the latent infection caused the eosinophilic component of this response to become steroid resistant. These studies suggest that latent adenoviral infections may have a role in the pathogenesis of obstructive airway disease by amplifying the response to cigarette smoke and inducing steroid resistance.

Rhinovirus-induced airway inflammation in asthma: effect of treatment with inhaled corticosteroids before and during experimental infection

Asthma exacerbations are frequently linked to rhinovirus infections. However, the associated inflammatory pathways are poorly understood, and treatment of exacerbations is often unsatisfactory. In the present study we investigated whether antiinflammatory treatment with inhaled corticosteroids prevents any rhinovirus-induced worsening of lower airway inflammation. To that end, we selected 25 atopic patients with mild asthma who underwent experimental rhinovirus 16 (RV16) infection, while receiving double-blind, placebo-controlled treatment with the inhaled corticosteroid budesonide (800 microg twice a day) throughout the study period, starting 2 wk before infection. We assessed inflammatory cell numbers in the bronchial mucosa as obtained by bronchial biopsies 2 d before and 6 d after RV16 infection, and analyzed those in relation to cold symptoms, changes in blood leukocyte counts, airway obstruction, and airway hyperresponsiveness. RV16 colds induced an increase in CD3(+) cells in the lamina propria (p = 0.03) and tended to decrease the numbers of epithelial eosinophils (p = 0.06) in both groups analyzed as a whole. The T cell accumulation was positively associated with cold symptoms. Budesonide pretreatment improved airway hyperresponsiveness (p = 0.02) and eosinophilic airways inflammation (p = 0.04). Yet it did not significantly affect the RV16-associated changes in the numbers of any of the inflammatory cell types. We conclude that RV16 infection by itself induces only subtle worsening of airway inflammation in asthma, which is not improved (or worsened) by inhaled corticosteroids. The latter finding is in keeping with the limited protection of inhaled corticosteroids against acute asthma exacerbations.