Chronic changes in the lung after RSV infection. Lungs were collected 28 d after viral challenge and examined microscopically. (A–F) Chronic changes included persistent peribronchiolar inflammatory infiltrates, (B, C) mucosal and goblet cell hyperplasia, (C) the continuing presence of eosinophils (*) in the bronchiolar mucosa and submucosa, and (E) the presence of mast cells (*) in the smooth muscle layer. (F) Mucus was present in terminal airways. Images were taken at a magnification of 100× (A, D, E) or 400× (B, C, F)). Panels B and C show high-power images of fields outlined in panel A. Panel E is a high-power image of the field outlined in panel D.