Bovine respiratory syncytial virus-specific immune responses in cattle following immunization with modified-live and inactivated vaccines. Analysis of proliferation and secretion of lymphokines by leukocytes in vitro.

Cattle were immunized with vaccines containing modified-live or inactivated bovine respiratory syncytial virus (BRSV) and lymphocyte proliferative responses and cytokine secretion were monitored sequentially. Compared to pre-inoculated values, significant increases in proliferative responses to modified-live BRSV were detectable by Day 7 after the primary immunization with the vaccine containing inactivated BRSV, and by 7 days after the second immunization with modified-live virus. After a third immunization with the respective vaccines, proliferative responses to live BRSV were significantly higher in the group that received modified-live vaccine compared to the group that received inactivated vaccine. Proliferative responses to live BRSV corresponded with the presence of interleukin-2 (IL-2) in the supernatants from BRSV-stimulated leukocyte cultures and there were significantly higher levels of IL-2 in cultures from the group that received modified-live BRSV. An interferon species with the characteristics of interferon-alpha was also present in the supernatants from leukocyte cultures and there were no significant differences between the groups of vaccines. The predominant phenotype of proliferating cells in BRSV-stimulated leukocyte cultures derived from both groups of bovine vaccines was a BoCD4+ T-lymphocyte. These in vitro data suggest that both types of vaccines are capable of stimulating cell-mediated immune responses to BRSV in cattle.