In vitro cell-dependent lysis of respiratory syncytial virus-infected cells mediated by antibody from local respiratory secretions.

Respiratory syncytial (RS) virus causes a local infection of the respiratory tract which is frequently severe in infants. We report the development in infected infants of antibodies in respiratory secretions capable of mediating in vitro destruction of RS virus-infected tissue culture cells in conjunction with non-immune lymphoid cells. The cytotoxic antibody activity was not detectable in nasal secretions from infants hospitalized with respiratory infections where RS virus was not identified. The rise in activity occurred concurrently with recovery from infection and the rise in specific IgG, IgM and IgA antibody levels measured by membrane immunofluorescence assay, but was dissociated from the development of plaque-neutralizing activity. In serum it appears that the cytotoxic antibody belongs to the IgG class as shown by its ability to cross the placenta and by neutralization with specific antiserum. These findings are discussed in relationship to secretory antibody responses in RS virus infection with respect to pathogenesis and recovery.