The growth of respiratory syncytial virus in organ cultures of bovine foetal trachea.

Respiratory syncytial (RS) virus grown in organ cultures of bovine foetal trachea at 37 degrees C and pH 7.2 reached maximum titres of up to 1 X 10(5) PFU/ml between 11 and 21 days after inoculation. Virus yield was increased three fold by incubation at 33 degrees C, but depressed by the addition of RS virus antiserum, with or without bovine complement, or by the addition of alveolar macrophages. Variation in pH or the concentration of foetal calf serum and magnesium chloride did not affect the virus yield. Virus growth did not affect ciliary activity of the cultures. Histological changes involved slight flattening of the epithelium and the appearance of phloxinophilic inclusion bodies. Fluorescent antibody staining showed more virus antigen in the peri-tracheal connective tissue than in the ciliated epithelium. The presence of non-cytopathic mucosal disease (MD) virus in RS virus infected organ cultures slightly depressed RS virus growth but did not influence ciliary activity. These in vitro experiments suggest that the tracheal epithelium may not be an important target in the pathogenesis of RS virus infection in vivo.