Antigen-specific systemic and reproductive tract antibodies in foxes immunized with Salmonella typhimurium expressing bacterial and sperm proteins

Attenuated Salmonella typhimurium strains are potential 'safe' delivery vec tors of an oral immunocontraceptive vaccine for the European red fox (Vulpe s vulpes). In the present study, model bacterial (Escherichia coli heat-lab ile enterotoxin B subunit, LTB) and fox sperm (fSP10) antigens were express ed in S. typhimurium SL3261 (Delta aroA) under the control of the trc promo ter. Adult female forts were given three oral immunizations with SL3261 con taining either LTB (SL3261/pLTB), fSP10 (SL3261/pFSP10) or a control plasmi d (pKK233-2 or pTrc99A). All foxes raised serum (IgG) and vaginal (IgG and IgA) antibodies against S. typhimurium lipopolysaccharide (LPS). Each fox t hat received SL3261/pLTB raised high titre LTB-specific serum and vaginal I gG antibodies. However, only one of four foxes immunized with SL3261/pFSP10 raised an anti-fSP10 immune response, in the form of low titre serum and v aginal IgG antibodies, No vaginal IgA antibodies were raised against either LTB or fSP10 in these experiments, The immune responses against recombinan t LTB and fSP10 resulted chiefly from the initial dose of antigen in the in ocula and were minimally influenced by continued in vivo antigen expression , This study demonstrates for the first time in the female red fox that ora l Salmonella can elicit specific systemic and reproductive tract antibodies against heterologous, recombinant proteins.