Construction and immunological assessment of Salmonella typhimurium expressing fox sperm LDH-C4

This study examined immune responses of foxes to oral doses of recombinant Salmonella typhimurium expressing fox sperm-specific lactate dehydrogenase (fLDH). The cDNA for fLDH was cloned into the expression plasmid pKK233.2 (pKKfLDH). Salmonella typhimurium aroA- (SL3261) was transformed with either the pKK233.2 plasmid alone (SpKK) or the pKKfLDH construct (SpKfLDH). The fLDH expressed by SpKfLDH retained enzymatic activity and was recognized by human LDH-C4-specific antibody. Male European red foxes (Vulpes vulpes) were given an initial oral dose of 1 x 10(11) cfu of either SpKK (control, n = 3) or SpKfLDH (test, n = 6), followed four weeks later with a further dose of 1 x 10(11) cfu. Antibodies to Salmonella lipopolysaccharide (LPS-04) and fLDH were measured in plasma and saliva for eight consecutive weeks after the initial doses. Both LPS-04 IgG- and IgA-specific antibodies as well as fLDH-specific IgG antibodies were detected in plasma and saliva. However, there was a marked fLDH-specific IgA response in saliva consistent with induction of the common mucosal immune system. The antibody measurements demonstrated the feasibility of using recombinant Salmonella as an oral vaccine to elicit gamete antigen-specific mucosal immune responses in foxes.