Evaluation of the cell-mediated immune response to reduced doses of Mycobacterium avium ssp. paratuberculosis vaccine in cattle

Vaccination against Johne's disease with an inactivated, oil-adjuvanted Mycobacterium avium ssp. paratuberculosis (MAP) bacterin can reduce clinical signs in infected herds; however, the development of indurated swelling at the injection site limits vaccine acceptability to producers. This study determined whether a reduced dose of vaccine antigen, with a full dose of adjuvant, would produce comparable T cell-mediated immune responses with smaller lesions. T cell responses induced by in vitro stimulation with MAP antigen from calves vaccinated with full, half, and quarter doses of antigen were evaluated 2, 4, and 9 months after vaccination by multi-parameter flow cytometry (FCM) and the whole blood interferon-γ (WB IFN-γ) assay. The WB IFN-γ responses were significantly elevated in vaccinated animals, but did not differ significantly between doses. FCM demonstrated antigen-specific responses for both IFN-γ and IL-4 in the CD4 T cell population from vaccinated animals, while CD8 T cells and γδ T cells mainly responded with increased IFN-γ. Dose may have affected some T cell subset parameters at some time points, but intradermal skin test responses, WB IFN-γ production, IFN-γ responses by T cell subsets in FCM were not significantly different between full, half, or quarter doses of antigen. Injection site lesions were smaller in animals vaccinated with a lower dose of antigen, but reached statistical significance (P < 0.05) in the half dose group only.