Lung dendritic cells in respiratory syncytial virus bronchiolitis

Respiratory syncytial virus (RSV) bronchiolitis, an important respiratory disease in infancy, is thought to be caused by severe inflammation of the small peripheral airways and has been associated with the development of recurrent wheeze, childhood asthma, and early allergen sensitization. Both innate and adaptive immune responses are thought to contribute to the development of bronchiolitis in RSV infection. If vaccination and specific therapy for bronchiolitis, which are currently lacking, are to be developed, detailed understanding of the immune responses involved is essential. Dendritic cells (DCs) are uniquely positioned to link innate to adaptive immune responses and may therefore be central to the development of bronchiolitis. In murine models, plasmacytoid DCs are recruited to the lung early in infection, presumably from the bone marrow, whereas lung myeloid DCs increase in numbers later in infection, with the advent of inflammation, and are derived from local lung precursors. Plasmacytoid DCs limit viral replication and they may have additional regulatory properties controlling pulmonary inflammation and lung function changes during bronchiolitis. In contrast, lung myeloid DCs are likely to contribute to inflammation during and after bronchiolitis and they may also facilitate sensitization to allergens. Myeloid DCs mature upon RSV infection and become potent activators of naive T cells, whereas in healthy lungs they are mostly immature and unable to stimulate naive T cells. As central players in the induction of adaptive immune responses, lung DCs need to be considered as targets for novel therapies and vaccination approaches.