Swine immunity to an attenuated Salmonella typhimurium mutant containing a recombinant plasmid which codes for production of a 31-kilodalton protein of Brucella abortus.

Salmonella typhimurium chi 4064, an attenuated delta cya delta crp mutant of S. typhimurium SR-11, was shown to be avirulent in swine. S. typhimurium chi 4064 was used as a carrier for plasmid pBA31-R7, which codes for the expression of a 31-kDa protein from Brucella abortus (BCSP31). Given orally, S. typhimurium chi 4064(pBA31-R7) colonized the intestine and mesenteric lymph nodes of 5- to 6-week-old crossbred swine. Orally immunized animals developed serum and intestinal antibody responses to the B. abortus 31-kDa protein and to salmonella endotoxin as measured by enzyme-linked immunosorbent assay. Similarly immunized swine did not develop delayed-type hypersensitivity following a subcutaneous injection of recombinant BCSP31. However, swine parenterally immunized with recombinant BCSP31 incorporated in Freund incomplete adjuvant did develop a delayed-type hypersensitivity response to the homologous antigen. The data indicated that oral presentation of antigen to swine in the context of recombinant S. typhimurium effective stimulated mucosal and systemic antibody-mediated immunity but failed to sensitize swine for either an antigen-specific delayed-type hypersensitivity or a blastogenic response to the cloned BCSP31.