DIFFERENCES IN THE IMMUNE-RESPONSES OF MICE AND SHEEP TO AN AROMATIC-DEPENDENT MUTANT OF SALMONELLA-TYPHIMURIUM

A live mutant aroA Salmonella 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 Salmonella-specific s erum IgM, IgG and IgA were produced in addition to high levels of spec ific intestinal IgA. Moreover, there was also evidence of Salmonella-s pecific cell-mediated immunity in vaccinated mice in the form of stron g delayed-type hypersensitivity and the production of interferon-gamma (IFN-tau) by spleen cells stimulated with Salmonella antigen. The aro A strain was also recovered from the mesenteric lymph nodes and most t issues examined from sheep vaccinated by the oral route. Salmonella-sp ecific IgM was detected in the serum; however, specific IgG responses were very low and there was an absence of specific copro-antibody. Alt hough strong Salmonella-specific lymphocyte proliferative responses we re detected, they did not result in the production of IFN-tau and flow cytometric analysis revealed that the proliferating cells were predom inantly 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 wi ld-type strain S25/1.