Lymphocyte transformation response of calves to respiratory syncytial virus.

Virus-specific cell-mediated immunity, as determined by in vitro lymphocyte transformation (LT), was demonstrated in calves following infection and vaccination with respiratory syncytial virus (RSV). After experimental infection, 4 of 6 gnotobiotic calves and 6 of 21 conventional calves developed a significant LT response to RSV. By means of a whole blood assay, the LT responses of calves were examined after vaccination with an inactivated vaccine, which consisted of glutaraldehyde-fixed bovine nasal mucosa cells persistently infected with a bovine strain of RSV (GC), a live modified bovine strain of RSV (MV), or a live temperature-sensitive mutant of a human strain of RSV (ts-l). Three weeks after vaccination, a virus-specific LT response was detected in 6 of 6 calves given the GC vaccine, 0 of 4 calves given the MV vaccine, and 2 of 4 calves given the ts-l vaccine. The magnitude of the response was greatest in those animals given the GC vaccine. There was no significant correlation between the magnitude of the LT response and levels of serum neutralising antibody. However, the LT response did correlate with serum antibody measured by the single radial haemolysis test 3 weeks after the first vaccination. LT activity to RSV was associated with T and not B lymphocytes. The development of a virus-specific LT response in calves given an inactivated RSV vaccine was not associated with an increase in respiratory disease following challenge with live virus, but rather was related to increased resistance to RSV infection.