The mechanisms by which respiratory syncytial virus (RSV) infection induces bronchiolitis and airway disease are unclear. The presence of large numbers of polymorphonuclear leukocytes (PMN) in the airways of infants with RSV infection suggests a potential role of PMN in airway injury associated with RSV infection. To investigate the potential role of neutrophils in RSV bronchiolitis, human alveolar type II cells (A549 cells) were infected with different doses of RSV for 6-48 h. A 51Cr-releasing assay was used to measure PMN-induced damage and image analysis was used to determine PMN adhesion and detachment of epithelial cells. The results showed that RSV infection of epithelial cells enhanced PMN adherence in a dose- and time-dependent pattern, RSV infection alone could damage and detach epithelial cells to a limited extent and PMN significantly augmented RSV infection-induced damage and detachment of epithelial cells. These data suggest that respiratory syncytial virus infection of respiratory epithelial cells enhances neutrophil adhesion to the epithelium and that activated neutrophils augment the damage and detachment of epithelium infected with the virus. Polymorphonuclear leukocytes may contribute to the pathogenesis of respiratory syncytial virus airway disease by inducing epithelial damage and cell loss.

Respiratory epithelium is both a target and an effector of airway inflammation. Adhesion molecules on epithelium play an important role in a variety of airway diseases. Respiratory syncytial virus (RSV) is the most important pathogen for airway diseases in infants. The expression of adhesion molecules on epithelium in RSV infection, however, is unclear.The expression of selected adhesion molecules and major histocompatibility complex (MHC) class I and II antigens on a human alveolar type II epithelial cell line (A549) infected with RSV was investigated by means of flow cytometry and immunocytochemistry.The results showed that intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were expressed on A549 cells at a low level. Ecadherin and MHC class I antigen were constitutively expressed on the cells. RSV infection of A549 cells significantly upregulated the expression of ICAM-1, VCAM-1 and MHC class I and II antigens on these cells. RSV infection also altered the expression of E-cadherin on A549 cells. Immunostaining showed that E-cadherin was mainly upregulated around or in RSV-induced giant cells.These data suggest that respiratory syncytial virus infection of respiratory epithelial cells enhances the expression of adhesion molecules and major histocompatiblity complex antigens. These changes may play an important role in the pathophysiology of respiratory syncytial virus disease. The respiratory epithelium is not only a physical barrier between environmental noxious agents and the internal body milieu but also a metabolically active physiochemical structure [1]. Respiratory epithelial cells are both "target" and "effector" cells in airway inflammation [2]. As target cells, epithelial cells can be infected and damaged by various pathogens, such as respiratory syncytial virus (RSV) [3]. As effector cells, epithelial cells can express adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1) [4±6], and can produce a wide array of cytokines [2,7], and thereby be involved in inflammation and immune responses.RSV is the most frequent cause of bronchiolitis and pneumonia in infants requiring hospitalization [8]. Moreover, $50% of infants who have acute viral bronchiolitis due to RSV have subsequent episodes of wheezing consistent with asthma [9] and it seems that there is a strong link between RSV bronchiolitis and asthma in epidemiology and immunology, reviewed by WANG and FOR-SYTH [10]. It has previously been reported that RSV infection can damage epithelial cells to a certain extent and neutrophils can augment the epithelial damage and detachment induced by RSV [3]. However, the pathophysiology of RSV disease, especially the role of respiratory epithelial cells in RSV infection, is unclear. Although the cytokine production profile of respiratory epithelial cells in RSV infection has been well studied [7, 11±14], the expression of adhesion molecules on epithelial cells in RSV infection is poorly understood [3,5].It has been demonstrated that both primary cu...

SUMMARYNeutrophils are the predominant inflammatory cell in the lung tissues and airways in RSV infection, and can augment the epithelial cell damage induced by RSV. Neutrophil apoptosis has been suggested to be a mechanism to reduce the potential for tissue injury. The apoptosis of neutrophils from nasopharyngeal aspirates (NPA) (n ¼ 19) and peripheral blood (PB) of infants with RSV bronchiolitis (n ¼ 11) and PB from healthy controls (n ¼ 9) was investigated. Monoclonal antibody against CD95 (Fas) and a binding protein Annexin V were used to determine the apoptosis of neutrophils. The expression of CD11b and CD18 on neutrophils was also detected with flow cytometry. The mean fluorescence intensity (MFI) of CD95 on neutrophils from RSV þ NPA was increased compared with cells from control PB (73·6 Ϯ 7·6 versus 31·5 Ϯ 4·3); the MFI of Annexin V, CD11b and CD18 on neutrophils from RSV þ NPA was upregulated compared with cells from both control PB (105·3 Ϯ 18·1 versus 11·8 Ϯ 1·5; 1683 Ϯ 153·3 versus 841·1 Ϯ 72·3; 517 Ϯ 50·5 versus 147 Ϯ 8·7, respectively) and RSV þ PB (105·3 Ϯ 18·1 versus 35·8 Ϯ 4·1; 1683 Ϯ 153·3 versus 818 Ϯ 141·2; 517 Ϯ 50·5 versus 260 Ϯ 25·8, respectively). Furthermore, the percentage of neutrophils expressing Annexin V and the MFI of CD18 on neutrophils from RSV þ PB were increased compared with neutrophils from control PB. In addition, both CD11b (MFI) and CD18 (MFI) correlated with Annexin V (MFI) on neutrophils. We conclude that neutrophil apoptosis in RSV bronchiolitis is accelerated; and CD11b/CD18 may play an important role in RSV infection by influencing neutrophil apoptosis.