Respiratory syncytial virus and parainfluenza virus

Respiratory syncytial virus infection of human airway epithelial cells is polarized, specific to ciliated cells, and without obvious cytopathology

Gene therapy for cystic fibrosis (CF) lung disease requires efficient gene transfer to airway epithelial cells after intralumenal delivery. Most gene transfer vectors so far tested have not provided the efficiency required. Although human respiratory syncytial virus (RSV), a common respiratory virus, is known to infect the respiratory epithelium, the mechanism of infection and the epithelial cell type targeted by RSV have not been determined. We have utilized human primary airway epithelial cell cultures that generate a well-differentiated pseudostratified mucociliary epithelium to investigate whether RSV infects airway epithelium via the lumenal (apical) surface. A recombinant RSV expressing green fluorescent protein (rgRSV) infected epithelial cell cultures with high gene transfer efficiency when applied to the apical surface but not after basolateral inoculation. Analyses of the cell types infected by RSV revealed that lumenal columnar cells, specifically ciliated epithelial cells, were targeted by RSV and that cultures became susceptible to infection as they differentiated into a ciliated phenotype. In addition to infection of ciliated cells via the apical membrane, RSV was shed exclusively from the apical surface and spread to neighboring ciliated cells by the motion of the cilial beat. Gross histological examination of cultures infected with RSV revealed no evidence of obvious cytopathology, suggesting that RSV infection in the absence of an immune response can be tolerated for >3 months. Therefore, rgRSV efficiently transduced the airway epithelium via the lumenal surface and specifically targeted ciliated airway epithelial cells. Since rgRSV appears to breach the lumenal barriers encountered by other gene transfer vectors in the airway, this virus may be a good candidate for the development of a gene transfer vector for CF lung disease.

Perflubron reduces lung inflammation in respiratory syncytial virus infection by inhibiting chemokine expression and nuclear factor-kappa B activation

Airway mucosa inflammation plays a critical role in the pathogenesis of lower respiratory tract infections caused by respiratory syncytial virus (RSV), the major etiologic agent of bronchiolitis in infancy. Type and intensity of cellular infiltration are dictated by inflammatory chemokines, which are rapidly and abundantly induced in lung tissue by RSV. This process is, to a large extent, transcriptionally regulated by RSV-mediated activation of the nuclear factor-kappa B. The administration of a perfluorocarbon (PFC) liquid, such as perflubron, during partial liquid ventilation improves lung function and also reduces inflammation. In this study we demonstrate that treatment of BALB/c mice with perflubron intranasally 6 hours after RSV infection significantly inhibited lung cellular inflammation as well as the expression of the chemokines RANTES, MIP-1 alpha, MIP-1 beta, and MIP-2, compared with phosphate-buffered saline-treated control mice. However, perflubron treatment did not affect RSV replication. Strikingly, treatment with perflubron abrogated nuclear factor-kappa B activation in lung of RSV-infected mice. These results demonstrate a novel mechanism by which PFC may exert antiinflammatory activity and suggest that partial liquid ventilation with PFC may be considered in future clinical trials for infants with severe RSV infections requiring mechanical ventilation.

Diagnosis of respiratory syncytial virus infection: comparison of reverse transcription-PCR to viral culture and serology in adults with respiratory illness

Diagnosis of respiratory syncytial virus (RSV) during acute infection in adults is difficult because of the poor sensitivity of viral culture and antigen detection. A recently developed single-tube nested reverse transcription-PCR (RT-PCR) was compared to viral culture and serology by enzyme immunoassay for the diagnosis of RSV in adults with respiratory illness. Nasal swab samples were collected during respiratory illnesses from five groups of subjects: healthy young adults, healthy elderly adults, adults with chronic heart and lung disease, nursing home residents, and adults admitted to the hospital during the winter with cardiopulmonary illnesses. Of 1,112 samples for which all three tests were available, 117 were positive by at least one method and 995 were negative by all methods. One hundred ten were considered true positives because culture and/or serology was positive. Of these, 80 (73%) were PCR positive compared to 43 (39%) that were culture positive. Seven PCR results were considered false positives due to negative culture and serology. The overall RT-PCR sensitivity was 73%, and specificity was 99%. These data indicate that RT-PCR is an excellent method for the diagnosis of acute RSV infection in adults.

Respiratory syncytial virus infection following hematopoietic stem cell transplantation

Respiratory syncytial virus, one of the most common causes of respiratory infections in immunocompetent individuals, is frequently spread to recipients of HSCT by family members, other patients, and health care workers. In immunosuppressed individuals, progression from upper respiratory tract disease to pneumonia is common, and usually fatal if left untreated. We performed a retrospective analysis of RSV infections in recipients of autologous or allogeneic transplants. The incidence of RSV following allogeneic or autologous HSCT was 5.7% and 1.5%, respectively. Of the 58 patients with an RSV infection, 16 of 21 patients identified within the first post-transplant month, developed pneumonia. Seventy-two percent of patients received aerosolized ribavirin and/or RSV-IGIV, including 23 of 25 patients diagnosed with RSV pneumonia. In this aggressively treated patient population, three patients died of RSV disease, each following an unrelated HSCT.

Aerosols in bronchiolitis

Bronchiolitis is a common illness of the lower respiratory tract affecting infants that has considerable short and long-term morbidity and occasional mortality. It is the commonest cause of hospitalization for respiratory infection in early childhood, and the seasonal nature of the illness places considerable strain on health care resources during the bronchiolitis season. The youngest infants and those with preexisting cardiorespiratory disease are particularly at risk of severe illness. The treatment of infants with bronchiolitis is largely supportive. There are no therapies that have been proven to reduce the length of the hospitalization or intensive care stay. This paper will review the clinical course of bronchiolitis and discuss the aerosolized therapies that have been proposed for its treatment.

Prevention and treatment of respiratory syncytial virus bronchiolitis and postbronchiolitic wheezing

Respiratory syncytial virus (RSV) is the primary cause of hospitalization for acute respiratory tract illness in general and specifically for bronchiolitis in young children. The link between RSV bronchiolitis and reactive airway disease is not completely understood, even though RSV bronchiolitis is frequently followed by recurrent episodes of wheezing. Therapy with ribavirin does not appear to significantly reduce long-term respiratory outcome of RSV lower respiratory tract infection, and corticosteroid or bronchodilator therapy may possibly improve outcomes only on a short-term basis. No vaccine against RSV is yet available. It is not known whether prophylaxis with RSV intravenous immune globulin or palivizumab can reduce postbronchiolitic wheezing.

[Immunization: leaps into the future. The vaccinology at the beginning of the 21th century (II)]

The second part of the article is a review of the perspectives on orphan vaccines, therapeutic immunization and strategies to improve the compliance to the vaccination programmes.

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.

Primary prevention of asthma

There has been a dramatic increase in the prevalence of asthma over the last quarter century, particularly in the industrialized world. Although our understanding of asthma continues to improve, there is no cure for the disease. Primary prevention of asthma is the focus of this review. Asthma is a disease with multiple gene-environment interactions. Candidate genes for asthma are considered, and potential interaction between one of those genes, CD14, and an environmental factor, endotoxin, is reviewed as it relates to the hygiene hypothesis. Environmental risk factors for asthma including allergens, pollutants, infectious factors, and dietary modifications are considered, particularly their potential for primary prevention of asthma. Ongoing cohort studies including the Canadian Allergy and Asthma Prevention Study, the Manchester Allergy and Asthma Study, the Children's Asthma Prevention Study from Australia, and the Prevention and Incidence of Asthma and Mite Allergy Study from the Netherlands are briefly reviewed. A more definitive understanding of genetic background and environmental triggers and their interactions is required before any specific approach to the primary prevention of asthma can be championed aggressively.

Immunostimulatory DNA sequences inhibit respiratory syncytial viral load, airway inflammation, and mucus secretion

BACKGROUND

Immunostimulatory DNA sequences (ISS) activate the innate immune system to generate antiviral cytokines, such as IFN-gamma.

OBJECTIVE

This study investigated whether ISS could reduce viral load, mucus secretion, airway inflammation, and airway hyperreactivity to methacholine in a mouse model of respiratory syncytial virus (RSV) infection.

METHODS

Mice were pretreated with ISS 6 days before RSV infection, and lung indices of RSV viral load (viral titer and PCR), bronchoalveolar lavage fluid cytokines (IFN-gamma), airway inflammation (peribronchial inflammation and periodic acid-Schiff-positive mucus cells), and airway hyperreactivity (methacholine responsiveness) were assessed 4 to 6 days after RSV infection.

RESULTS

ISS induced the expression of the antiviral cytokine IFN-gamma in the lung, and this was associated with significantly reduced RSV viral titers, mucus secretion, and peribronchial inflammation. ISS reduced, but did not significantly inhibit, RSV-induced airway hyperreactivity to methacholine.

CONCLUSION

Because ISS induced significant levels of lung IFN-gamma, an immunization strategy based solely on the administration of IFN-gamma may be insufficient to inhibit RSV-induced airway hyperreactivity to methacholine, an endpoint important in the subset of RSV-infected subjects with asthma.