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 vectors of an oral immunocontraceptive vaccine for the European red fox (Vulpes vulpes). In the present study, model bacterial (Escherichia coli heat-labile enterotoxin B subunit, LTB) and fox sperm (fSP10) antigens were expressed in S. typhimurium SL3261 (delta aroA) under the control of the trc promoter. Adult female foxes were given three oral immunizations with SL3261 containing either LTB (SL3261/pLTB), fSP10 (SL3261/pFSP10) or a control plasmid (pKK233-2 or pTrc99A). All foxes raised serum (IgG) and vaginal (IgG and IgA) antibodies against S. typhimurium lipopolysaccharide (LPS). Each fox that received SL3261/pLTB raised high titre LTB-specific serum and vaginal IgG 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 vaginal IgG antibodies. No vaginal IgA antibodies were raised against either LTB or fSP10 in these experiments. The immune responses against recombinant LTB and fSP10 resulted chiefly from the initial dose of antigen in the inocula and were minimally influenced by continued in vivo antigen expression. This study demonstrates for the first time in the female red fox that oral Salmonella can elicit specific systemic and reproductive tract antibodies against heterologous, recombinant proteins.