Assessment of interferon-γ response profiles after vaccination against bovine viral diarrhea virus (BVDV) as correlates of protection.

Identifying immune responses and/or profiles that correlate to protection can be used to assess vaccine efficacy. In this study, we utilized vaccination against bovine viral diarrhea virus (BVDV) as a model to assess the level of protection against challenge in cattle with immune responses that vary in the magnitude of cell mediated responses. Based on the variability in the frequency of interferon-γ (IFN-γ) positive CD4+ cells, vaccinated cattle were categorized as responders or non-responders; unvaccinated animals served as controls. Cattle were administered an intranasal BVDV challenge. Humoral and cell mediated responses were assessed pre- and post-challenge and complete blood counts and virus isolation from white blood cells were assessed during the 2-week period after challenge for prevention of disease and protection against BVDV challenge. Virus was only isolated from cattle characterized as non-responders and controls, but not from cattle in the responder category. Humoral responses did not differ from responders and non-responders only control cattle. An increased frequency of IFN-γ positive CD4+ cells was observed for responder and non-responder groups after challenge as compared to controls. Data from this study suggests CD4+ specific IFN-γ responses are important for prevention of viremia and protection. Cell mediated response profiles associated with immunization and protection need to be further evaluated.