Effects of respiratory viruses on pulmonary alveolar macrophages

[Treatment of acute bronchiolitis in infants. Role of bronchodilators and steroids]

The management of infant bronchiolitis with bronchodilators and steroids is controversial. A literature review on this topic allows to determine the influence of these medications on the first episode of viral bronchiolitis. The effect of alpha and beta adrenergic drugs is undoubtful but it is not possible to anticipate a positive or negative response based on the age of the child nor on a family history of atopic disease. Systemic steroid therapy has no immediate effect but inhaled steroids may be tried during the recovery period to reduce short term morbidity.

Persistence of respiratory syncytial virus genome and protein after acute bronchiolitis in guinea pigs

Children with acute respiratory syncytial virus (RSV) bronchiolitis often develop sequelae of recurrent wheezing and asthma. To determine whether RSV persists within the lung after resolution of acute bronchiolitis, we examined the lungs of guinea pigs 60 days after intranasal inoculation with either human RSV (n = 10) or uninfected cell culture supernatant (n = 11). Evidence of viral persistence within the lung was determined by viral culture to test for replicating virus, immunohistochemistry to test for viral protein, and the reverse transcriptase-polymerase chain reaction (RT-PCR) to test for viral genomic RNA. Lungs were also examined histologically for evidence of bronchiolar inflammation or increased numbers of mast cells in the airway walls. All viral cultures were negative; however, there was positive immunohistochemical staining of occasional alveolar macrophages in six of ten RSV-inoculated guinea pigs while RT-PCR was positive in seven of ten RSV-inoculated animals. The six guinea pigs with evidence of RSV by immunohistochemistry and RT-PCR showed excess bronchiolar polymorphonuclear cell infiltrates (p < 0.005) but no increase in the number of airway wall mast cells. These results show that RSV protein and genomic RNA can persist in the lungs of experimentally inoculated guinea pigs for at least 60 days after infection and that persistence of the virus within alveolar macrophages might contribute to the pathogenesis of chronic bronchiolar inflammation.