The B subunits of cholera and Escherichia coli heat-labile toxins enhance the immune responses in mice orally immunised with a recombinant live P-fimbrial vaccine for avian pathogenic E. coli

This study aimed to investigate the adjuvant effect of recombinant attenuated Salmonella expressing cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin B subunit (LTB) for the P-fimbriae subunit-based vaccine of avian pathogenic E. coli (APEC) in a murine model. The PapA-specific sIgA and IgG responses were significantly enhanced after immunisation with the Salmonella-PapA vaccine in the presence of CTB or LTB. The group immunised with the Salmonella-LTB strain promoted Th1-type immunity, whereas that immunised with the Salmonella-CTB strain produced Th2-type immunity. We concluded that both Salmonella-CTB and -LTB strains can enhance the immune response to PapA, and that the LTB strain may be a more effective adjuvant for APEC vaccination, which requires higher Th1-type immunity for protection. Thus, our findings provide evidence that immunisation with an adjuvant, LTB, is one of the strategies of developing effective vaccines against P-fimbriated APEC

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Multivalent salmonella-based vaccines : consequences of prior exposure to the vector strain / Christofer John Vindurampulle.

"April 2002"Bibliography: leaves 143-173.[12], 173 leaves : ill. ; 30 cm.Research into methods of vaccination against enteric diseases has demonstrated the advantages of using live attenuated Salmonella as carriers of foreign antigen. However, recent data have shown that prior exposure of mice to Salmonella can dramatically reduce serum antibody responses to foreign antigen subsequently delivered by the same strain. Since these findings contradict earlier reports, the aim of this thesis was to further assess the significance of pre-existing anti-vector immunity as an impediment to the Salmonella-based vaccine strategy. The results of experiments conducted strengthen concerns that pre-existing anti-vector immunity represents a serious threat to the Salmonella-based vaccine strategy.Thesis (Ph.D.)--University of Adelaide, Dept. of Molecular Biosciences, 200

Impact of Vector Priming on the Immunogenicity of Recombinant Salmonella Vaccines

There are conflicting reports concerning the impact of prior vector priming on the immunogenicity of recombinant-Salmonella-based vaccines. A comparison of experimental protocols identified two variables which might account for this inconsistency: the potential of the vector strain to colonize the murine gut-associated lymphoid tissue (GALT) and the nature of the foreign antigen subsequently delivered by the recombinant Salmonella construct. The former was investigated by constructing an aroA mutant of the Salmonella enterica serovar Stanley vector previously used in our laboratory. Although the introduction of an aroA mutation had surprisingly little effect on GALT colonization, it did reduce the strength of antilipopolysaccharide (anti-LPS) antibody responses and the impact of vector priming. Studies were also performed to ascertain the extent to which any observed hyporesponsiveness consequent upon vector priming might be determined by the characteristics of the foreign antigen. S. enterica serovar Stanley was used to deliver either of two Escherichia coli antigens, K88 pilus protein or the LT-B toxin subunit, to vector-primed mice. Both serum immunoglobulin G (IgG) and intestinal IgA responses to K88 were completely abolished, and those to LT-B were significantly reduced, as a consequence of vector priming. When similar experiments were performed with an aroA S. enterica serovar Dublin vector, responses to K88 were significantly reduced but those to LT-B were unaffected by vector priming. Paradoxically, a priming infection with this vector induced stronger anti-LPS antibody responses but was less likely to elicit a state of hyporesponsiveness to subsequently presented foreign antigen. The impact of vector priming thus depends on both the Salmonella strain used and the nature of the foreign antigen, but our present data strengthen concerns that preexisting antivector immunity represents a serious threat to the Salmonella-based vaccine strategy

Vector Priming Reduces the Immunogenicity of Salmonella-Based Vaccines in Nramp1(+/+) Mice

The present studies in Nramp1(−/−) BALB/c and Nramp1(+/+) CBA mice question the significance of this genotype as a determinant of the level of gut colonization following oral administration of naturally attenuated or highly virulent Salmonella strains. In line with previous results in BALB/c hosts, vector priming of CBA mice with Salmonella enterica serovar Stanley was found to significantly compromise the immunogenicity of a recombinant construct expressing a foreign pilus protein

Vector-primed mice display hypo-responsiveness to foreign antigen presented by recombinant Salmonella regardless of the route of delivery

C1 - Journal Articles RefereedOur previous studies have shown that mice which have been orally primed with an attenuated Salmonella vector [S. enterica serovar Stanley] are hypo-responsive to foreign antigens later delivered orally by the same vector strain, responding with significantly impaired serum and intestinal antibody responses compared with those seen in unprimed controls. Initial vector priming of the gut-associated lymphoid tissue (GALT) is likely to result in impaired persistence of recombinant Salmonella later administered orally. Delivery of recombinant bacteria by the intra-peritoneal or intra-nasal route, to avoid exposure to a primed GALT, did not allow vector-primed recipients to mount normal antibody responses to the foreign pilus protein K88. The negative impact of vector priming could be largely overcome, however, if mice were exposed to the foreign protein just prior to priming with the vector strain. Using this strategy, vector-primed mice displayed normal gut IgA and intermediate serum IgG responses to K88 following oral administration of recombinant Salmonella. Our findings are compatible with the concept of epitopic suppression, in which failure to respond to the foreign vaccine antigen reflects the clonal dominance of B cells specific for epitopes associated with the vector strain

Molecular and genetic characterization of the capsule biosynthesis locus of Streptococcus pneumoniae type 23F

The authors have previously reported the nucleotide sequence of the 5' and 3' portions of the Streptococcus pneumoniae type 23F capsular polysaccharide biosynthesis locus (cps23f) (from dexB to cps23fB and from cps23fL to aliA). These regions of cps23f were very similar to the sequence reported for cps19f, the capsule locus of S. pneumoniae type 19F. However, Southern hybridization analysis indicated that no other genes closely related to cps19f are present in the cps23f locus. In this study long-range PCR was used to amplify and clone the section of the S. pneumoniae type 23F capsule locus between cps23fB and cps23fL. This region is 13 kb in size and contains 12 new ORFs, designated cps23fC-E, I, J, and T-Z. Functions are proposed for all of the protein products, including functional homologues of Cps19fC-E, Cps19fI and Cps19fJ. A biosynthetic pathway for type 23F capsular polysaccharide is also proposed

Reactive oxygen species are the major antibacterials against Salmonella Typhimurium purine auxotrophs in the phagosome of RAW 264.7 cells

Intramacrophage survival appears to be a pathogenic trait common to Salmonellae and definition of the metabolic requirements of Salmonella within macrophages might provide opportunities for novel therapeutic interventions. We show that loss of PurG function in Salmonella enterica serovar Typhimurium SL1344 leads to death of the bacterium in RAW264.7 cells, which was due to unavailability of purine nucleotides but not thiamine in the phagosome of RAW264.7 cells. Phagosomal escape of purG mutant restored growth, suggesting that the phagosomal environment, but not the cytosol, is toxic to Salmonella purine auxotrophs. NADPH oxidase inhibition restored the growth of purG mutant in RAW264.7 cells, implying that the Salmonella-containing vacuole acquires reactive oxygen species (ROS) that are lethal to purine auxotrophs. Under purine limiting conditions, purG mutant was unable to repair the damage caused by hydrogen peroxide or UV irradiation, suggesting that ROS-mediated DNA damage may have been responsible for the attenuated phenotype of purG mutant in RAW264.7 cells and in mice