IMMUNE-RESPONSES IN CALVES IMMUNIZED ORALLY OR SUBCUTANEOUSLY WITH A LIVE SALMONELLA-TYPHIMURIUM ARO VACCINE

Salmonella aro vaccines ar-e able to confer solid protection against h omologous virulent challenge in several animal species. Calves were pr otected against virulent S. typhimurium challenge following administra tion of a single oral dose of live BRD562 vaccine. Immune responses el icited by the S, typhimurium aro vaccine strain BRD562 were studied fo llowing administration to calves by either the oral or subcutaneous ro ute, Serum antibodies to Salmonella polypeptides, following or-al or s ubcutaneous vaccination, were detected by immunoblotting and the route of inoculation found to affect both the antibody isotype and the anti gens defected Oral, but not subcutaneous, immunisation induced bovine serum IgA antibodies against Salmonella antigens of 30 kDa and 65 kDa and bovine IgG2 antibodies against a 35 kDa antigen. Subcutaneous vacc ination triggered responses against antigens of 52 kDa, 54 kDa and 57k Da which were not detected by immune plasma of animals immunised orall y Antibody responses to LPS were poor in animals inoculated by either route. Subcutaneous vaccination elicited T-cell responses against Salm onella antigens as measured by in vitro peripheral blood cell thymidin e incorporation These studies show that the S, typhimurium vaccine str ain BRD562 is capable of inducing both humoral and cellular immune res ponses. Further studies are necessary to identity the nature of the an tigens responsible for protection. Oral or subcutaneous inoculation of BRD562(pTETnir15) failed to induce serum antibodies against the fragm ent C of tetanus toxin (TetC) but was effective in mice. Oral vaccinat ion with this recombinant vaccine induced mucosal IgA against TetC, Th is is the first time that Salmonella recombinant vaccines have been sh own to successfully elicit antibodies against a guest antigen in cattl e after one single oral inoculation, (C) 1997 Elsevier-Science Ltd.