Abstract
To describe immune responses following administration of experimental Salmonella Dublin siderophore receptor protein (SRP) vaccines in Holstein heifer calves with adequate passive antibody transfer. Calves were randomly assigned to receive placebo, vaccination with S Dublin SRP in adjuvant A, or vaccination with S Dublin SRP in adjuvant B at 7 ± 3 days of age and 3 weeks later. Before each vaccination, 4 and 8 days after the second vaccination (postvaccination), and 61 to 91 days postvaccination, S Dublin antibody titers were measured. Blood mononuclear cells isolated from blood collected 4 and 8 days postvaccination were stimulated with S Dublin SRP antigen (1 or 5 µg/mL) or positive or negative controls, then analyzed to quantify S Dublin SRP-responsive cells. Cultures of blood mononuclear cells were similarly stimulated to quantify interferon-γ (IFN-γ)-producing and IL-17-producing cells. The trial spanned September 4, 2022, through January 15, 2023. 78 calves were enrolled. Vaccinates had significantly higher IFN-γ-producing cells and IFN-γ and IL-17 concentrations at 4 and 8 days postvaccination, except IFN-γ concentration at day 4 after stimulation with 1 µg/mL. Vaccinates also had higher S Dublin titers at 8 and 61 to 90 days postvaccination. No differences in health events were noted. Vaccination can induce S Dublin SRP-specific humoral and cellular immune responses in Holstein heifer calves. Vaccination with SRP vaccines resulted in immune responses that may help mitigate S Dublin infection. Further research is needed to determine whether vaccination will be protective against S Dublin challenge.
Published Version
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