Effects of dual vaccination for bovine respiratory syncytial virus and Haemophilus somnus on immune responses.

Bovine respiratory syncytial virus (BRSV) and Haemophilus somnus (H. somnus) co-infect to form a polymicrobial respiratory disease in calves. Both BRSV and H. somnus vaccinations have independently been shown to sometimes induce adverse IgE mediated responses. We hypothesized that combining these disease agents in vaccination would induce cytokine shifts resulting in greater IgE production and enhanced disease. Concurrent vaccination with subsequent infection with one or both pathogens in calves was conducted to evaluate the isotypic antibody responses, disease severity and cytokine response. BRSV-specific serum IgE levels were elevated for the most clinically diseased calves, while no difference was detected in the IgE levels to H. somnus among groups. The IFN-gamma message and H. somnus-specific IgG2 antibodies were significantly elevated in calves with the lowest clinical scores. Vaccination preferentially stimulated higher levels of IgG1 antibodies to BRSV, but in contrast higher levels of IgG2 antibodies to H. somnus. Concurrent vaccination induced IgE antibodies to BRSV, which were directly correlated with disease severity whereas vaccine induced IgG2 antibodies to H. somnus were inversely correlated with disease severity.