A number of live attenuated and killed vaccines are widely used to protect against bovine respiratory disease complex as it is one of the major economic losses in the beef industry. To determine which vaccination protocol induces the highest immune response, here we investigated humoral and CMI responses by different vaccination protocols.
A live attenuated vaccine (L) used in this study contains BHV-1, BVDV1a, BVDV2, PI3V, BRSV, and ADV7, whereas a killed vaccine (K) contains BVDV1b, in addition to all the components of L. Twenty three cows were divided into 5 groups and assigned to the following vaccination protocols; (1) KK, (2) KL, (3) LK, (4) LL, and (5) control. The cows in immunized groups were vaccinated twice, 3 weeks apart. Blood samples were collected from all cows from day 0 to 70 post-vaccination. Neutralizing antibodies against each virus were measured by serum virus neutralization (SVN) tests. After PBMCs were cultured with each virus, IFN-γ and IL-4 production were measured in the supernatants, and the activation of each T cell subset (CD4, CD8, γδTCR, WC1, WC1.1, and WC1.2) was evaluated by CD25 expression.
After second vaccination, SVN titers against BHV-1 in KK and LK groups were higher than those in the other groups whereas SVN titers against all BVDV strains in KL group were the highest in all groups. IL-4 production was detected in response to BHV-1, PI3V, and BRSV stimulation in LK and LL groups. IFN-γ production was higher in LK group than the other groups in the cells stimulated with all viruses. In addition, all T cell subsets in response to all viral stimulation in LK group were most strongly activated.
These observations indicate that LK protocol induces high CMI response as well as humoral response. A vaccine challenge study will be performed to evaluate the protective efficacy.