A live mutant serotype Typhimurium ovine strain (S25/1) could be cultured from tissues of mice for up to 90 days after oral infection. Following vaccination, high levels of -specific serum IgM, IgG and IgA were produced in addition to high levels of specific intestinal IgA. Moreover, there was also evidence of -specific cell-mediated immunity in vaccinated mice in the form of strong delayed-type hypersensitivity and the production of interferon-gamma (IFN-t) by spleen cells stimulated with antigen. The strain was also recovered from the mesenteric lymph nodes and most tissues examined from sheep vaccinated by the oral route. -specific IgM was detected in the serum; however, specific IgG responses were very low and there was an absence of specific copro-antibody. Although strong -specific lymphocyte proliferative responses were detected, they did not result in the production of IFN- and flow cytometric analysis revealed that the proliferating cells were predominantly B lymphocytes. Despite the absence of strong vaccine-specific immune responses in vaccinated sheep compared with those seen in mice, both mice and sheep were protected against challenge with virulent wild-type strain S25/1.


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