Systemic and mucosal intestinal antibody response of sheep immunized with aromatic-dependent live or killed Salmonella typhimurium

Abstract

Following the development of a suitable formulation capable of inhibiting intestinal proteolytic activity, the total anti-lipopolysaccharide (LPS) and anti-flagellin (Fla) antibody response and isotype in the sera and intestinal washings of sheep, immunized with live aromatic-dependent (aro-) Salmonella typhimurium strain CS332 by the intramuscular (live i.m.) or oral (live oral) route or acetone-killed virulent S. typhimurium by the intramuscular route (killed i.m.), were determined at various intervals post-immunization. The serum or intestinal anti-lipopolysaccharide (LPS) or anti-flagellin (Fla) antibody titres of immunized sheep, regardless of the route of immunization, were significantly greater (P < 0.01) than those of non-immune control sheep. Although significant differences between the serum anti-LPS or anti-Fla antibody titres of sheep in various immunization regimes were observed, they were not consistent for different periods post-immunization. The predominant isotype contributing to serum anti-LPS antibody activity was IgM whereas the serum antiflagellar antibody activity was confined to IgM, IgG1 and IgG2. In either case, the contribution of the IgA antibody isotype was minimal. Antibody activity in the intestinal washings of immunized sheep, regardless of the route of immunization was significantly greater (P < 0.01) than that in non-immune control sheep. However, the titres in sheep immunized with the live S. typhimurium vaccines were significantly greater than those immunized with the killed vaccine. The major anti-LPS or anti-flagellin antibody isotype in the intestinal washings of sheep in the live i.m. or live oral groups was IgM at day 7 post-immunization followed by IgG1 and IgG2 at days 14 and 21 post-immunization, with only a minimal contribution by the IgA antibody isotype. On the other hand, the major antibody isotype in the intestinal washings of sheep immunized with the killed S. typhimurium was IgG1.