Bovine respiratory syncytial virus-specific immune responses in calves after inoculation with commercially available vaccines.

A study was designed to determine if inactivated bovine respiratory syncytial virus (BRSV) vaccines induce the same types of antibody and cellular responses as does a modified-live BRSV vaccine. Ninety mixed-breed, 5- to 6-month-old beef calves were randomly assigned to 1 of 6 groups with 15 animals/group. Calves in 5 of the groups were inoculated on days 0 and 14 with 1 of 4 inactivated virus vaccines or with a modified-live virus vaccine. The remaining 15 calves were maintained as unvaccinated controls. Immune responses were measured on days 0 and 24, by means of ELISA, virus neutralization assay, blocking ELISA for the BRSV fusion (F) protein, immunoblotting, and lymphocyte blastogenesis assay. All vaccines induced production of antibodies that recognized the F protein; however, the ratio of neutralizing antibody titer to change in BRSV-specific IgG antibody concentration (as determined by use of ELISA) was lower for calves that received an inactivated virus vaccine than for calves that received the modified-live virus vaccine. All of the vaccines induced lymphocyte proliferative responses to BRSV. Results suggest that commercially employed inactivation processes can alter functionally important epitopes on BRSV envelope glycoproteins, leading to production of predominantly nonneutralizing antibodies in immunized cattle.