Cellular immune responses of pigs induced by vaccination with either a whole cell sonicate or pepsin-digested Brachyspira (Serpulina) hyodysenteriae bacterin

Brachyspira (Serpulina) hyodysenteriae infection of pigs (swine dysentery) causes a mucohemorrhagic diarrhea resulting in significant economic losses for producers. A commercial vaccine consisting of a proteinase-digested bacterin has shown efficacy in the reduction of disease due to B. hyodysenteriae. Vaccines consisting of whole cell bacterins, however, generally fail to protect pigs from disease. In the present study, cellular immune responses induced by a proteinase-digested bacterin were compared to responses induced by a whole cell sonicate antigen preparation. In addition, usage of either squalene or Freund's incomplete adjuvants in combination with each antigen preparation was also compared. Both antigen preparations induced significant cellular immune responses as measured by in vitro (IFN-γ production and T cell proliferation) and in vivo methods (DTH responses). No significant differences were detected in proliferative, interferon-γ (IFN-γ), or delayed type hypersensitivity (DTH) responses by pigs receiving either adjuvant or antigen preparation. T cells (CD3⁺) but not B cells from vaccinated animals proliferated in response to in vitro stimulation with B. hyodysenteriae antigen. CD8⁺ (single positive and CD4/CD8 double positive) and γδ⁺ T cells were particularly responsive. In addition, high percentages of both CD8 single positive and CD4/CD8 double positive cells were detected in antigen-stimulated cultures. These findings demonstrate the unique sensitivity of porcine CD8⁺ T cells to priming for recall response by vaccination with a proteinase-digested B. hyodysenteriae bacterin.